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\DOI{10.5802/crchim.260}
\datereceived{2023-04-28}
\daterevised{2023-07-19}
\dateaccepted{2023-09-04}
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\begin{document}

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%\makeatletter
%\def\TITREspecial{\relax}
%\def\cdr@specialtitle@english{French/Nordic Special Issue on Materials and Coordination Chemistry}
%%\def\cdr@specialtitle@french{Num\'ero sp\'ecial franco-nordique sur les mat\'eriaux et la chimie de coordination}
%\makeatother

\title{Organotin(IV) trifluoromethanesulfonate chemistry: isolation and
characterization of novel 1,10-phenanthroline-based derivatives}

\alttitle{Chimie des trifluorom\'{e}thanesulfonates
d'organo\'{e}tain(IV) : Synth\`{e}se et caract\'{e}risation de
nouveaux d\'{e}riv\'{e}s \`{a} base de 1,10-ph\'{e}nanthroline}

\author{\firstname{H\'{e}l\`{e}ne} \lastname{Cattey}\CDRorcid{0000-0002-4416-7510}}
\address{Institut de Chimie Mol\'eculaire de l'Universit\'e de Bourgogne, UMR-CNRS 6302, Universit\'e de Bourgogne, 9 avenue A. Savary, F-21078 Dijon, France}
\email[H. Cattey]{helene.cattey@u-bourgogne.fr}

\author{\firstname{Laurent} \lastname{Plasseraud}\CDRorcid{0000-0002-7870-1881}\IsCorresp}
\address[1]{Institut de Chimie Mol\'eculaire de l'Universit\'e de Bourgogne, UMR-CNRS 6302, Universit\'e de Bourgogne, 9 avenue A. Savary, F-21078 Dijon, France}
\email[L. Plasseraud]{laurent.plasseraud@u-bourgogne.fr}

\keywords{\kwd{Di-\textit{n}-butyltin(IV) complexes}
\kwd{Trifluoromethanesulfonate anion}
\kwd{Nitrogen-containing heterocyclic compounds}
\kwd{1,10-Phenanthroline derivatives}
\kwd{\textsuperscript{119}Sn\{\textsuperscript{1}H\} NMR monitoring}
\kwd{Single crystal X-ray diffraction}}

\altkeywords{\kwd{Complexes de Di-\textit{n}-butyl\'{e}tain(IV)}
\kwd{Anion trifluorom\'{e}thanesulfonate}
\kwd{Compos\'{e}s h\'{e}t\'{e}rocycliques azot\'{e}s}
\kwd{D\'{e}riv\'{e}s de la 1,10-ph\'{e}nanthroline}
\kwd{Spectroscopie RMN \textsuperscript{119}Sn\{\textsuperscript{1}H\}}
\kwd{Diffraction des rayons X sur monocristaux}}

\begin{abstract}
The reactivity of the hydroxo di-\textit{n}-butyltin trifluoromethanesulfonato
dimer complex
[\textit{n}-Bu\textsubscript{2}Sn(\text{µ}-OH)(H\textsubscript{2}O)(CF\textsubscript{3}SO\textsubscript{3})]\textsubscript{2}
(\textbf{1}) toward 1,10-phenanthroline (phen) has been investigated,
leading to the formation of two novel di-\textit{n}-butyltin(IV)
trifluoromethanesulfonate complexes
[\textit{n}-Bu\textsubscript{2}Sn(\text{µ}-OH)(phen)]\textsubscript{2}[CF\textsubscript{3}SO\textsubscript{3}]\textsubscript{2} 
(\textbf{5}) and [\textit{n}-Bu\textsubscript{2}Sn(phen)\textsubscript{2}][CF\textsubscript{3}SO\textsubscript{3}]\textsubscript{2}
(\textbf{6}), in which the tin atoms are bis-chelated by one and two
bidentate phen ligands, respectively. Salts \textbf{5} and \textbf{6}
were characterized by single crystal X-ray diffraction analysis,
elemental analysis, mass spectrometry, and infrared spectroscopy as
well as \textsuperscript{1}H, \textsuperscript{19}F, \textsuperscript{13}C\{\textsuperscript{1}H\}, and
\textsuperscript{119}Sn\{\textsuperscript{1}H\} NMR spectroscopy.~Monitoring by
\textsuperscript{119}Sn\{\textsuperscript{1}H\} NMR spectroscopy in CD\textsubscript{3}CN solution of the
reaction proceeding with successive addition of phen revealed the
\textit{in situ} formation of three organotin(IV)
trifluoromethanesulfonate intermediate species. Two of these, namely
\{[\textit{n}-Bu\textsubscript{2}Sn(H\textsubscript{2}O)]\textsubscript{2}O\textperiodcentered\textit{n}-Bu\textsubscript{2}Sn(OH)\textsubscript{2}\}[CF\textsubscript{3}SO\textsubscript{3}]\textsubscript{2}  (\textbf{2}) and
[\textit{n}-Bu\textsubscript{2}Sn\textsubscript{2}(OH)(CF\textsubscript{3}SO\textsubscript{3})]\textsubscript{2}O (\textbf{4}), were
already known and could be clearly identified on the basis of their
\textsuperscript{119}Sn\{\textsuperscript{119}H\} NMR chemical shifts. The composition of the third
intermediate, \textbf{3}, with an unknown chemical shift value, was
investigated. A possible structure, especially suggested by
electrospray-ionization mass spectrometry, is proposed as
[\{\textit{n}-Bu\textsubscript{2}Sn(phen)(CF\textsubscript{3}SO\textsubscript{3})\}\textsubscript{2}(\text{µ}-CF\textsubscript{3}SO\textsubscript{3})][CF\textsubscript{3}SO\textsubscript{3}]. 
Furthermore, from a mixture of \textbf{1} and phen in equimolar ratio,
in dichloromethane solvent and at --20~\textdegree C,
temperature-sensitive crystals of a new hydrated di-\textit{n}-butyltin
cation, [\textit{n}-Bu\textsubscript{2}Sn(phen)(OH)(H\textsubscript{2}O)][CF\textsubscript{3}SO\textsubscript{3}]
(\textbf{7}), were isolated. Crystals of the organic salt
1,10-phenanthrolinium trifluoromethanesulfonate (phenHOTf) were also
obtained from the filtrate of the mother-liquor. The reactivity of
\textbf{1} toward~2,9-dimethyl-1,10-phenanthroline was also explored
(dmphen), leading to the detection of characteristic fingerprints of
distannoxanes \textbf{2} and \textbf{4} by \textsuperscript{119}Sn\{\textsuperscript{119}H\} NMR,
and to the crystallization of phenanthrolinium triflate salts, which
were characterized by X-ray diffraction analysis as \textbf{dmphenHOTf}
and \textbf{dmphenHOTf\textperiodcentered\textbf{dmphen}}.
\end{abstract}

\begin{altabstract}
La r\'{e}activit\'{e} du complexe dim\'{e}rique
[\textit{n}-Bu\textsubscript{2}Sn(\textit{m}-OH)(H\textsubscript{2}O)(CF\textsubscript{3}SO\textsubscript{3})]\textsubscript{2} 
(\textbf{1}) vis-\`{a}-vis de la 1,10-ph\'{e}nanthroline (phen) 
a \'{e}t\'{e} \'{e}tudi\'{e}e et a conduit \`{a} la formation de
[\textit{n}-Bu\textsubscript{2}Sn(\textit{m}-OH)(phen)]\textsubscript{2}[CF\textsubscript{3}SO\textsubscript{3}]\textsubscript{2}
(\textbf{5}) et [\textit{n}-Bu\textsubscript{2}Sn(phen)\textsubscript{2}][CF\textsubscript{3}SO\textsubscript{3}]\textsubscript{2}
(\textbf{6}), dans lesquels les atomes d'\'{e}tain sont respectivement
ch\'{e}lat\'{e}s par un et deux ligands phen. Les sels \textbf{5} et
\textbf{6} ont \'{e}t\'{e} caract\'{e}ris\'{e}s \`{a} l'\'{e}tat solide
et en solution. Le suivi de la r\'{e}action par RMN
\textsuperscript{119}Sn\{\textsuperscript{1}H\}, dans CD\textsubscript{3}CN et en fonction d'additions
successives de phen, a r\'{e}v\'{e}l\'{e} la formation \textit{in situ}
de trois esp\`{e}ces interm\'{e}diaires d'organo\'{e}tain(IV). Deux
d'entre elles,
\{[\textit{n}-Bu\textsubscript{2}Sn(H\textsubscript{2}O)]\textsubscript{2}C\textperiodcentered\textit{n}-Bu\textsubscript{2}Sn(OH)\textsubscript{2}\}[CF\textsubscript{3}SO\textsubscript{3}]\textsubscript{2} 
(\textbf{2}) et [\textit{n}-Bu\textsubscript{2}Sn\textsubscript{2}(OH)(CF\textsubscript{3}SO\textsubscript{3})]\textsubscript{2}O
(\textbf{4}), \'{e}taient d\'{e}j\`{a} r\'{e}pertori\'{e}es et ont pu
\^{e}tre clairement identifi\'{e}es sur la base de leur d\'{e}placement
chimique RMN \textsuperscript{119}Sn\{\textsuperscript{1}H\}. La composition du troisi\`{e}me
interm\'{e}diaire, \textbf{3}, dont le d\'{e}placement chimique
\'{e}tait inhabituel, a \'{e}t\'{e} investigu\'{e}e. Une possible
structure, sugg\'{e}r\'{e}e notamment par spectrom\'{e}trie de masse
par ionisation (Electrospray), est propos\'{e}e comme \'{e}tant
[\{\textit{n}-Bu\textsubscript{2}Sn(phen)(CF\textsubscript{3}SO\textsubscript{3})\}\textsubscript{2}(\textit{m}-CF\textsubscript{3}SO\textsubscript{3})][CF\textsubscript{3}SO\textsubscript{3}]. 
Par ailleurs, \`{a} partir d'un m\'{e}lange de \textbf{1} et de phen,
pr\'{e}sents dans un rapport \'{e}quimolaire, dans une solution de
dichlorom\'{e}thane plac\'{e}e \`{a} --20~\textdegree C, des
monocristaux d'un nouveau cation di-\textit{n}-butyl\'{e}tain hydrat\'{e}
[\textit{n}-Bu\textsubscript{2}Sn(phen)(OH)(H\textsubscript{2}O)][CF\textsubscript{3}SO\textsubscript{3}] (\textbf{7}),
sensibles \`{a} la temp\'{e}rature, ont pu \^{e}tre isol\'{e}s. Des
cristaux du sel organique trifluorom\'{e}thanesulfonate de
1,10-ph\'{e}nanthrolinium (\textbf{phenHOTf}) ont \'{e}galement
\'{e}t\'{e} obtenus \`{a} partir du filtrat de la solution m\`{e}re. La
r\'{e}activit\'{e} de \textbf{1} vis-\`{a}-vis de la
2,9-dim\'{e}thyl-1,10-ph\'{e}nanthroline a \'{e}galement \'{e}t\'{e}
explor\'{e}e (dmphen), conduisant \`{a} la d\'{e}tection par RMN
\textsuperscript{119}Sn\{\textsuperscript{1}H\} aux empreintes caract\'{e}ristiques des
distannoxanes \textbf{2} et \textbf{4} et \`{a} la cristallisation de
nouveaux sels de triflate de ph\'{e}nanthrolinium, caract\'{e}ris\'{e}s
comme \'{e}tant \textbf{dmphenHOTf} et \textbf{dmphenHOTf-dmphen}.
\end{altabstract}

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\def\boldcdot{${{\bm{\cdot}}}$}
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\section{Introduction}\label{sec1}

To the best of our knowledge, the first study describing the synthesis
of organotin trifluoromethanesulfonates dates back to the 1970s, led
by Schmei{\ss}er's group~\cite{1}. Since
then, this class of compounds has attracted much interest in
homogeneous catalysis and synthesis. These compounds are indeed
reported to be efficient for specific metal-assisted organic reactions,
acting as appropriate \textit{Lewis} acid catalysts. Beneficial
effects have been particularly described for the aldol reaction of
\textit{Mukaiyama}~\cite{2}, \textit{Robinson}
annulation~\cite{3}, acetylation of alcohols~\cite{4},
transesterification of dimethyl carbonate with phenol~\cite{5}, and
direct synthesis of dimethyl carbonate (DMC) from methanol and carbon
dioxide~\cite{6,7}. From a synthetic point of view, organotin
trifluoromethanesulfonates are generally prepared by reacting an
organotin oxide with trifluoromethanesulfonic acid
(CF$_{3}$SO$_{3}$H, TfOH)~\cite{8,9}, or alternatively, from an
organotin chloride (R$_{(4-x)}$SnCl$_{x}$
with R ${=}$ alkyl) in the presence of silver trifluoromethanesulfonate
(AgCF$_{3}$SO$_{3}$)~\cite{8,10}. Several organotin(IV) complexes
have been characterized in the solid state by single crystal X-ray
analysis. The CF$_{3}$SO$_{3}$ group can be ionic and behave as a
counter anion, or be a ligand directly bound to tin. In the latter
case, it can adopt various coordination modes. Examples of mono-, bi-,
and tridentate as well as terminal, \textit{pseudo}-terminal, and
bridging CF$_{3}$SO$_{3}$ groups have already been reported in the
literature for ${p}$-block metals and are shown in 
Scheme~\ref{sch1}~\cite{11,12}.\looseness=-1

\begin{scheme*}
\vspace*{-2pt}
\includegraphics{sc01}
\vspace*{4pt}
\caption{\label{sch1}Molecular representations of known coordination
modes involving the trifluoromethanesulfonate ligand and
${p}$-block metals (M).}
\vspace*{-6pt}
\end{scheme*}

\begin{scheme*}
\includegraphics{sc02}
\vspace*{-2pt}
\caption{\label{sch2}Synthetic pathway leading to \textbf{5} and
\textbf{6}.}
\vspace*{-15pt}
\end{scheme*}

{\advance\baselineskip-.6pt
The chemistry and structural aspects of organotin
trifluoromethanesulfonates were first reviewed by {Beckmann} in
2005~\cite{13}. Since 2006, our group has also contributed to this
field by characterizing several new specimens by X-ray crystallographic
analysis: (i) ionic monobenzyltin(IV) trifluoromethanesulfonate
clusters exhibiting unprecedented Sn$_6$, Sn$_{11}$, and Sn$_{12}$
frameworks~\cite{14,15}, (ii)~a two-dimensional organostannoxane
coordination network
$^{2}_{\infty}$\{[${n}$-Bu$_{2}$($\upmu$-OH)SnOSn(${\upmu}$-${\eta}^{2}$--O$_{3}$SCF$_{3}$)$n$-Bu$_{2}$]$_{2}$[$n$-Bu$_{2}$(${\eta}^{1}$-O$_{3}$SCF$_{3}$)SnOSn(${\upmu}$-OH)${n}$-Bu$_{2}$]$_{2}$\}~\cite{12},
which was found to be a polymorph of the tetra-${n}$-butyldistannoxane
trifluoromethanesulfonate cluster,
[${n}$-Bu$_{2}$Sn$_{2}$(OH)(CF$_{3}$SO$_{3}$)]$_{2}$O (\textbf{4}),
described initially by Otera~\cite{16,17}, (iii) a polymeric
chain of dimeric hydroxo di-${n}$-butyltin(IV) units bridged by
trifluoromethanesulfonate ligands,
[Sn$_{2}$(CF$_{3}$O$_{3}$S)$_{2}${(C$_4$H}$_{9}$)$_{4}$(OH)$_{2}$]$_{n}$~\cite{10}. 
More\unskip\break recently, we reported the isolation and characterization of the
dihydrated di-${n}$-butyltin(IV) trifluoromethanesulfonate salt
\{[${n}$-Bu$_{2}$Sn(H$_{2}$O)]$_{2}$O${\cdot}{n}${-Bu$_{2}$Sn(OH)}$_{2}$\}[CF$_{3}$SO$_{3}$]$_{2}$ 
(\textbf{2}), 
which is characterized by a Sn$_{3}$O$_{3}$ {core~\cite{18}.}
\textbf{2} was obtained by reacting at room temperature with~the
dimeric hydroxo di-${n}$-butyl trifluoromethanesulfonate
[${n}$-Bu$_{2}$Sn(${\upmu}$-OH)(H$_{2}$O)(CF$_{3}$SO$_{3}$)]$_{2}$
(\textbf{1}) with a mixture of anthracene and phenazine.\looseness=-1

Continuing to explore the reactivity of \textbf{1} toward
nitrogen-containing heterocyclic compounds, we report herein the
synthesis and characterization of two novel diorganotin
trifluoromethanesulfonate derivatives,
[${n}$-Bu$_{2}${Sn(${\upmu}$-OH)(phen)}]$_{2}$[CF$_{3}$SO$_{3}$]$_{2}$
(\textbf{5}) and
[${n}$-Bu$_{2}${Sn(phen)}$_{2}$]{[CF$_{3}$SO$_{3}$]$_{2}$ (\textbf{6}),
resulting from the reaction of} \textbf{1} {with 1,10-phenanthroline
(phen), with the latter acting as bidentate ligand. Monitoring of the
reaction by} $^{119}${Sn\{}$^{1}${H\} NMR spectroscopy in solution
(CD}$_{3}$CN) and as a function of the amount of phen added revealed
successive {\textit{in situ}} formation of species \textbf{2},
\textbf{3}{, and} \textbf{4}. From the three molar equivalents of phen,
only the resonance of \textbf{5} is visible in the spectrum. Species
\textbf{2} {and} \textbf{4} have already been reported in the
literature; however, to the best of our knowledge, \textbf{3} {is a new
species. Complexes} \textbf{5} {and} \textbf{6} {were fully
characterized by IR, $^{1}$H, $^{11}${F}, $^{13}$C, and
$^{119}$Sn\{$^{1}$H\} NMR spectroscopy, mass spectrometry, elemental
analysis, and X-ray diffraction analysis. Further investigations were
conducted to isolate and identify species} \textbf{3}. By changing the
solvent conditions from acetonitrile to dichloromethane and in a 1:1
molar ratio of \textbf{1} and phen, the unprecedented mononuclear
hydrated di-${n}$-butyltin cation,
[${n}$-Bu$_{2}${Sn(phen)(OH)(H}$_{2}${O)][CF$_{3}$SO$_{3}$]
(\textbf{7}), was isolated, with the tin center}
\textit{N},\textit{N}-chelated by a bidentate phen ligand and bearing a
terminal hydroxyl group. Moreover, the reactivity of \textbf{1} was
also tested in the presence of 2,9-dimethyl-1,10-phenanthroline
(dmphen). From this reaction, only the phenanthrolinium triflates
(\textbf{dmphenHOTf} and \textbf{dmphen{\boldcdot}dmphenHOTf}), resulting from
the mono-protonation of dmphen, were obtained.\looseness=-1
}
\vspace*{-3pt}
\section{Results and discussion}\label{sec2}
\vspace*{-3pt}

\subsection{Synthesis and isolation of
[$n$-Bu$_{2}$Sn($\upmu$-OH)\ubreak(Phen)]$_{2}$[CF$_{3}$SO$_{3}$]$_{2}$
(\textbf{5}) and  [$n$-Bu$_{2}$Sn(Phen)$_{2}$]\ubreak[CF$_{3}$SO$_{3}$]$_{2}$
(\textbf{6})}\label{sec21}
\vspace*{-2pt}

The air-stable dinuclear di-${n}$-butyltin(IV)
trifluoromethanesulfonate salts
[${n}$-Bu$_{2}$Sn(${\upmu}$-OH)(phen)]$_{2}$\ubreak[CF$_{3}$SO$_{3}$]$_{2}$
(\textbf{5}) and
[${n}$-Bu$_{2}$Sn(phen)$_{2}$]{[CF$_{3}$SO$_{3}$]$_{2}$ (\textbf{6})
were obtained at room temperature, under air atmosphere, from a mixture
of dichloromethane/toluene by reacting dimeric
trifluoromethanesulfonato hydroxo organotin(IV)}
[${n}$-Bu$_{2}${Sn(OH)(H}$_{2}$O)(CF$_{3}$SO$_{3}$)]$_{2}$ (\textbf{1})
with two molar equivalents of 1,10-phenenthroline
(C$_{12}$H$_{8}$N$_{2}$, phen) (Scheme~\ref{sch2}). A pinkish
precipitate is first formed, leading, after recrystallization in
dichloromethane/toluene, to the formation of single crystals later
characterized as \textbf{6}. Colorless single crystals of \textbf{5}
were obtained from the filtrate of the mother liquor by slow
evaporation at room temperature.

\begin{figure*}
\vspace*{-3pt}
\includegraphics{fig01}
\vspace*{-2pt}
\caption{\label{fig1}FT-IR (ATR) spectra of (a)
[${n}$-Bu$_{2}${Sn(OH)(H}$_{2}$O)(CF$_{3}$SO$_{3}$)]$_{2}$
(\textbf{1}), (b)
[${n}$-Bu$_{2}${Sn(${\upmu}$-OH)(phen)}]$_{2}$\ubreak[CF$_{3}$SO$_{3}$]$_{2}$
(\textbf{5}), (c)
[${n}$-Bu$_{2}${Sn(phen)}$_{2}$][CF$_{3}$SO$_{3}$]$_{2}$ (\textbf{6}),
and (d) [${n}$-Bu$_{2}$Sn(phen)(OH)(H$_{2}$O)][CF$_{3}$SO$_{3}$]
(\textbf{7}).\vspace*{-5pt}}
\end{figure*}

The two new organotin compounds which are ionic were characterized by
elemental analysis, ESI-MS, IR and NMR spectroscopy, and single-crystal
X-ray diffraction analysis. Compound \textbf{5} exhibits good
solubility in organic solvents such as dichloromethane, acetone, and
acetonitrile. In CD$_{3}$CN, the $^{119}$Sn\{$^{1}$H\} NMR
spectrum of \textbf{5} exhibits one single resonance at ${\delta}\,{-}226$~ppm 
(Figure~S1). Such a chemical shift is in agreement with a
six-coordinate tin atom substituted by two ${n}$-butyl moieties. It is
interesting to note that in acetone-$d_6$, the signal moves
significantly, shifting to $-$150~ppm, suggesting that the tin center is
pentacoordinated in this solvent environment. For comparison, the tin
atoms of [${n}$-Bu$_{2}$Sn$_{2}$(OH)(CF$_{3}$SO$_{3}$)]$_{2}$O
(\textbf{4}), which is characterized as a distannoxane, exhibit two
resonances in acetone-$d_{6}$ {at $-$146 and $-$151~ppm~\cite{9,12}.
The} $^{1}${H and} $^{13}${C\{}$^{1}${H\} NMR spectra of} \textbf{5}
depicted in Figures~S2 and~S3,
respectively, corroborate the structure
depicted in Scheme~\ref{sch2}, showing two sets of signals
characteristic of phenanthroline {ligands and} ${n}$-butyl
substituents. The CF$_{3}$ moieties of the
$\mathrm{CF}_{3}\mathrm{SO}_{3}^{-}$ {anions are also clearly
identified in the} $^{13}${C\{}$^{1}${H\} NMR spectrum, giving a
typical quartet at} ${\delta}${119.9~ppm, with a distinctive}
$^{1}J_{\text{C}\ndash\text{F}}$ {coupling constant of 318~Hz.
The} $^{19}${F NMR spectrum exhibits one singlet at} ${\delta}\,{-}78.2$~ppm 
(Figure~S4). The infrared spectrum of \textbf{5} highlights a
distinctive broad absorption centered at 3321~cm$^{-1}$ 
(Figure~\ref{fig1}b), which is quite different from the fingerprint
of \textbf{1} (Figure~\ref{fig1}a), but can be assigned to the
presence of OH groups (Figure~\ref{fig1}b). Characteristic\unskip\break vibration
bands of trifluoromethasulfonate ligands, in particular
${\nu}${(CF$_{3}$) and} ${\nu}$(SO$_{3}$), are also observed for
\textbf{3} in the stretching region between 1000 and 1300~cm$^{-1}$
(outlined by a blue banner in Figure~\ref{fig1})~\cite{19a,19b,19c}. The additional
intense bands at 1518, 1427 and 854~cm$^{-1}$ arise from the
${\nu}${(C${=}$C),} ${\nu}$(C${=}$N) and ${\gamma}${(C--H aromatic rings)
absorptions of the phen ligands, respectively. The coordination of
these ligands to tin is supported by the shift of the two bands at 
1518~cm$^{-1}$, and 1427~cm$^{-1}$ relative to the free ligand 
(1503~cm$^{-1}$ and 1420~cm$^{-1}$)~\cite{20a,20b}. An electrospray mass
spectrum (positive mode) of} \textbf{5} in a mixture of
dichloromethane/methanol displays major mass clusters centered at 
$m/z= 431.11333$~Da (100\%), which fits closely with the
[${n}$-Bu$_{2}$Sn(OH)(phen)]$^{+}$ fragment
(C$_{20}$H$_{27}$N$_{2}$OSn, calc.: 431.11453~Da) (Figure~S5). Finally,
the micro-analytical (C, H, N, S) data also support the composition of
\textbf{5} (see\break Section~\ref{sec4}).

{Compound} \textbf{6} {was collected as a precipitate from the starting
reaction. However, it was found to be well soluble in acetone and
dichloromethane. Suitable single-crystals for X-ray diffraction
analysis were grown from a dichloromethane/toluene mixture. Compared
with} \textbf{1} {and} \textbf{5}, the infrared spectrum of \textbf{6}
shows no absorption bands above 3100~cm$^{-1}$ excluding the presence of
OH or H$_{2}$O ligands. Otherwise, the characteristic absorption bands
of ${n}$-butyl chain [${\nu}$(C--H)], CF$_{3}$SO$_{3}$, and phen are
present and support the coordination of the phen ligand to the tin
center (Figure~\ref{fig1}c). In the aceton-$d_{6}$ solution, the
$^{119}$Sn\{$^{1}$H\} NMR of \textbf{6} reveals a broad resonance at
${\delta}\,{-}231$~ppm (Figure~S6) [for comparison, in the same deuterated
solvent, \textbf{5} {exhibits a weak resonance at} 
${\delta}\,{-}150$~ppm (Figure~S7)], and the $^{1}${H NMR spectrum shows a 1:1
integration ratio between the protons of the} ${n}$-butyl chains and
the phen ligands (Figure~S8). The $^{13}${C\{}$^{1}${H\} NMR spectrum
exclusively reveals phen and} ${n}$-butyl resonances and highlights the
presence of $\mathrm{CF}_{3}\mathrm{SO}_{3}^{-}$ anions by giving a quartet centered
at ${\delta}$121.9~ppm, which is attributable to CF$_{3}$ moieties
($^{1}J_{\text{C}\ndash\text{F}}= 321$~Hz) (Figure~S9). A single resonance at
${\delta}\,{-}78.8$~ppm is also observed in the $^{19}$F NMR spectrum
(Figure~S10). The electrospray mass spectrum (positive mode) of
\textbf{6} in a mixture of dichloromethane/methanol displays two
predominant mass clusters centred at ${m/z} = 445.13055$~Da
(100\%) and 431.11559~Da (80\%), which can be assigned to
[${n}$-Bu$_{2}$Sn(phen)(OCH$_{3}$)]$^{+}$
(C$_{21}$H$_{29}$N$_{2}$OSn, calc.: 445.13019~Da) and
[${n}$-Bu$_{2}${\ubreak}Sn(phen)(OH)]$^{+}$(C$_{20}$H$_{27}$N$_{2}$OSn,
calc.: 431.11454~Da) fragments, respectively (Figure~S11).

\subsection{Single-crystal X-ray diffraction analysis of \textbf{5}}\label{sec22}

The solid-state structure of \textbf{5} consists of a
[${n}$-Bu$_{2}${Sn(OH)(phen)}]$_{2}^{2+}$ dication
surrounded by two non-coordinated $\mathrm{CF}_{3}\mathrm{SO}_{3}^{-}$ anions. An
O{\textsc{RTEP}} {view of} \textbf{5} {is shown in Figure~\ref{fig2} together
with the selected bond distances and angles. The inorganic core of the
cation is based on a planar four-membered distannoxane
[Sn}$_{2}$(${\upmu}${-OH)}$_{2}${] unit, where the tin atoms are bridged
by two hydroxide ligands. The two tin atoms are bound to two}
${n}$-butyl ligands [Sn--C13 ${=}$ 2.131(2){, Sn--C17 ${=}$ 2.128(2)~\AA{}], to two oxygen atoms of bridging hydroxide ligands [Sn--O1 ${=}$}
2.0828(13), {Sn--O1}$^{i}$ {${=}$} 2.2334(14)~\AA{}], and
are chelated by a bidentate 1,10-phenanthroline molecule forming
five-membered rings. However, the Sn--N distances show significant
differences [Sn--N1 ${=}$ 2.4171(17), Sn--N2 ${=}$ 2.6330(18)~{\AA{}].
Thus, the tin centers can be considered to be hexacoordinated, adopting
a markedly distorted octahedral geometry [C17--Sn--C13 ${=}$
156.93(9)\textdegree, N1--Sn--O1}$^{i}$ {${=}$
156.85(5)\textdegree, N2--Sn--O1 ${=}$ 150.33(6)\textdegree].
Furthermore, the phen ligands are parallel to each other and exhibit a
twist angle of 25.55(4)\textdegree~to the plane containing the
Sn$_{2}$O}$_{2}$ {ring. Two trifluoromethanesulfonate anions complete
the structure of} \textbf{5}. For both $\mathrm{CF}_{3}\mathrm{SO}_{3}^{-}$, one of
their oxygen atoms is involved in hydrogen interaction with a hydroxide
group of the cation [$\mathrm{O}_3\cdots \mathrm{HO} = 2.791(2)$~\AA].  Moreover,
we can also suspect for each $\mathrm{CF}_{3}\mathrm{SO}_{3}^{-}$ {a possible weak
interaction involving another oxygen atom of sulfonate functions and
one tin atom of the cation  [O4$\cdots$Sn ${=}$ 3.342(2)~\AA{}], which
could explain the different Sn--N distances. The existence of such
long-distance  Sn$\cdots$O interactions in the solid state has already
been underlined for previous diorganotin compounds~\cite{10,21}. In the
past,} {\textit{Blaschette}} {and} {\textit{Jones}} {reported the
isolation of
[Me}$_{2}$\{(MeSO$_{2}$)$_{2}${N\}(phen)Sn(${\upmu}$-OH)]}$_{2}${, a
compound structurally analogous to} \textbf{5} {and prepared from
Me}$_{2}${Sn[N(SO$_{2}${Me)}$_{2}$]$_{2}$ and 1,10-phenanthroline by
adventitious hydrolysis~\cite{22}. Interestingly, in this compound, the
(MeSO$_{2}$)$_{2}${N}$^{-}$ {anions operate in the same
manner as the triflate anions of} \textbf{5}{. They are non-coordinated
and are involved in hydrogen bonding and long Sn$\cdots$O
interactions. The authors then described the tin atoms as being
heptacoordinated in a pentagonal bipyramidal arrangement. With regard
to compound} \textbf{5} {and based on the} $^{119}${Sn\{}$^{1}${H\} NMR
chemical shift value (}${\delta}\,{-}226$~ppm in CD}$_{3}$CN), we argue
in this case for the hexacoordination of the tin atoms. 

\begin{figure}
\includegraphics{fig02}
\caption{\label{fig2}\textsc{Ortep} {drawing of} \textbf{5} {using
a~partial atom labeling scheme (30\% probability thermal ellipsoids).
Hydrogen atoms of phenanthroline ligands and} ${n}$-butyl chains are
omitted for clarity. Hydrogen bonds involving CF$_{3}$SO$_{3}$--
and ${\upmu}$--OH groups are represented by red dotted lines. Selected
bond lengths (\AA{}) and angles (\textdegree): Sn--C17 2.128(2), Sn--C13
2.131(2), Sn--O1 2.0820(13), Sn--O1$^{i}$ 2.2343(14), Sn--N1
2.4171(17), C21--F3 1.315(3), C21--F1 1.329(3), C21--F2 1.334(3),
C21--S1 1.816(3), S1--O2 1.4239(19), S1--O4 1.4331(18), S1--O3
1.4406(15); O1--Sn--C17 100.02(7), O1--Sn--C13 102.51(8), C17--Sn--C13
156.93(9), O1--Sn--O1$^{i}$ 72.08(6), C17--Sn--O1$^{i}$ 90.38(8),
C13--Sn--O1$^{i}$ 91.85(8), O1--Sn--N1 84.98(6), C17--Sn--N1
90.58(8), C13--Sn--N1 96.24(8), O1$^{i}${--Sn--N1 156.85(5),
Sn--O1--Sn}$^{i}$ 107.92(6), F3--C21--F1 107.0(2), F3--C21--F2
108.8(3), F1--C21--F2 106.7(2), F3--C21--S1 112.27(19), F1--C21--S1
110.9(2), F2--C21--S1 110.95(18), O2--S1--O4 116.03(13), O2--S1--O3
114.98(13), O4--S1--O3 113.25(10), O2--S1--C21 103.25(13), O4--S1--C21
104.76(13), O3--S1--C21 102.36(10) (symmetry transformations used to
generate equivalent atoms: ($^{i}$) : 3/2--${x}$,
$1/2-y, -z$).}
\end{figure}

\begin{figure}
\includegraphics{fig03}
\caption{\label{fig3}\textsc{Ortep} drawing of \textbf{6} using a
partial atom labeling scheme (30\% probability thermal ellipsoids).
Hydrogen atoms and one molecule of toluene (solvent) are omitted for
clarity. Selected bond lengths (\AA{}) and angles (\textdegree):
Sn1--C29 2.162(9), Sn1--C25 2.158(9), Sn--N1 2.273(8), Sn--N2 2.369(8),
Sn--N3 2.309(7), Sn--N4 2.275(8), S1--O2 1.415(8), S1--O1 1.427(8),
S1--O3 1.431(9), S1--C33 1.823(11), C33--F1 1.299(12), C33--F2
1.328(14), C33--F3 1.312(13), C25--Sn1--C29 116.9(4), N1--Sn1--N2
71.9(3), N1--Sn1--N3 87.7(3), N1--Sn1--N4 154.5(3), C29--Sn1--N1
98.0(3), C25--Sn1--N1 97.0(4), N3--Sn1--N2 76.3(3), N4--Sn1--N2
87.5(3), C29--Sn1--N2 84.12(3), C25--Sn1--N2 157.9(3), N4--Sn1--N3
72.6(3), C29--Sn1--N3 156.9(3), C25--Sn1--N3 84.3(3), C29--Sn1--N4
94.6(3), C25--Sn1--N4 96.9(4).}
\end{figure}

\subsection{Single-crystal X-ray structural analysis of \textbf{6}}\label{sec23}

The structure of salt 6 in the solid state consists of a
[${n}$-Bu$_{2}$Sn(Phen)$_{2}$]$^{2+}$ dication
surrounded by two non-coordinating $\mathrm{CF}_{3}\mathrm{SO}_{3}^{-}$ anions. One
toluene molecule (crystallization solvent) co-crystallizes with
\textbf{6}. Figure~\ref{fig3} shows an O{\textsc{rtep}} {view of} \textbf{6}
with the atom numbering scheme, and Figure~\ref{fig4} shows a perspective view
of the crystal packing in the unit cell. The molecular structure of the
title compound consists of a central six-coordinated tin atom that
exhibits an octahedral coordination environment comprising four
nitrogen atoms from two distinct chelating phen ligands and two carbon
atoms of the two ${n}$-butyl chains. The ligands are positioned in a
\textit{cis}-arrangement. The N1--Sn--N4, N2--Sn--C25,\unskip\break N3--Sn--C29
bond angles measure 154.5(3), 157.9(3), and 156.9(3)\textdegree,
respectively, indicating a distortion from an ideal octahedral
geometry. The two phen ligands are bidentate to tin, forming
five-membered chelate rings that are nearly planar. The Sn--N distances
are in the range of 2.273(8) and 2.368~\AA{}. They are comparable to
that found in [MeSn(phen)2]$^{2+}$~\cite{23}, which is, to
the best of our knowledge, the only example reported to date for a
diorganotin complex bis-\textit{N},\textit{N}-chelated by two
1,10-phenanthroline ligands.

\begin{figure}
\includegraphics{fig04}
\caption{\label{fig4} Projection of the crystal structure approximately
along the \textit{b} axis, showing the orientation of the phen ligands
between two neighboring cations of \textbf{6}. The solvent toluene
molecules co-crystallizing with \textbf{6} and hydrogen protons are
omitted (\textsc{Mercury} representation~\cite{25}, color code: Sn ${=}$
violet, N ${=}$ blue, C ${=}$ gray, O ${=}$ red, S ${=}$ yellow, 
F ${=}$ green).\vspace*{-10pt}}
\end{figure}

\begin{figure*}
\includegraphics{fig05}
\vspace*{4pt}
\caption{\label{fig5}$^{119}$Sn\{$^{1}$H\} NMR monitoring of the
evolution of a solution of \textbf{1} in CD$_{3}$CN ([0.08 M], 298~K)
as a function of successive additions of 1,10-phenanthroline (phen):
(a) starting solution of \textbf{1}, (b) after addition of 0.5 molar
equivalent, (c) of 0.75 molar equivalent, (d) of 1 molar equivalent,
(e) of 2 molar equivalent, and~(f) of 3 molar equivalent.\vspace*{8pt}}
\end{figure*}


From a supramolecular point of view, the molecules of \textbf{6} are
organized in pairs \textit{via} offset ${\uppi}$--${\uppi}$ interactions
involving the aromatic rings of each phen ligand (Figure~\ref{fig4}).
The interplanar and centroid-to-centroid distances between the two
parallel phen molecules are 3.393 and 4.732~\AA{}, respectively. In
general, for such interactions, the interplanar distance is assumed to
be in the range of 3.3--3.8~\AA{}~\cite{24}. In the arrangement of
\textbf{6}, the rings are severely offset with a slippage angle (angle
between the normal to the planes and the centroid vector centroid
vector) of 44.19\textdegree, which corresponds to a slip distance of
3.298~\AA{}.

\begin{scheme*}
\includegraphics{sc03}
\caption{\label{sch3}Molecular representations of \textbf{2} (a) and
\textbf{4} (b).\vspace*{5pt}}
\end{scheme*}

\subsection{Solution $^{119}$Sn\{$^{1}$H\} NMR monitoring}\label{sec24}  

\begin{table*} %tab1
\caption{\label{tab1}$^{119}$\{$^{1}$H] NMR chemical shift~data of
di-${n}$-butyltin(IV) trifluoromethanesulfonates}
\begin{tabular}{cccc}
\thead
\xmorerows{1}{Compounds} &  \multicolumn{3}{c}{${\delta}$ {(ppm)}$^{a}$}\\\cline{2-4}
& In CD$_{2}${Cl}$_{2}$ & In acetone-$d_{6}$ & in CD$_{3}$CN\\
\endthead
\textbf{1} & ${-}$145 &&  ${-}$209\\
\textbf{2} & ${-}$127, ${-}$149~\cite{18} && ${-}$133,  ${-}$161\\
\textbf{3} & ${-}$288 && ${-}$267\\
\textbf{4} & ${-}$135,  ${-}$144~\cite{18} & ${-}$146,  ${-}$151~\cite{12} & ${-}$139, ${-}$143\\
\textbf{5} & Not visible & ${-}$150 & ${-}$226\\
\textbf{6} & Not visible & ${-}$231  & Insoluble\\
\textbf{7} & && ${-}$260
\botline
\end{tabular}
\tabnote{$^a$ At $T= 298$~K.\vspace*{2pt}}
\end{table*}

The reactivity of \textbf{1} toward successive additions 
of~1,10-phenanthroline was followed by $^{119}$Sn\{$^{1}$H\}
spectroscopy in CD$_{3}$CN directly in an NMR tube, as shown in 
Figure~\ref{fig5}. In CD$_{3}$CN, compound \textbf{1}  shows a broad
signal at ${\delta}\,{-}209$~ppm in agreement with the value reported
previously in the literature~\cite{8} (Figure~\ref{fig5}a). The
addition of 0.5  molar equivalents of phen leads to the appearance of
three new signals at ${\delta}\,{-}133$, ${-}161$, and ${-}267$~ppm in addition
to the signal of \textbf{1}, which is still present at
${\delta}\,{-}209$~ppm  (Figure~\ref{fig5}b). The two de-shielded chemical
shifts \mbox{exhibiting} a 1:2 intensity ratio correspond to the signature of
the ionic complex \textbf{2}, already known and characterized by us as
the unusual trinuclear complex
\{[${n}$-Bu$_{2}${Sn(H}$_{2}${O)]}$_{2}$O${\cdot}n$-Bu$_{2}$Sn(OH)$_{2}$\}
[CF$_{3}$SO$_{3}$]$_{2}$ (\textbf{2}) (Scheme~\ref{sch3}a)~\cite{16}, 
while the signal at ${\delta}\,{-}267$~ppm can be attributed to a new
species \textbf{3} whose composition and structure will be discussed
later. Further addition of phen (up to 1 molar equivalent) lead to a
progressive disappearance of the previously described resonances in
favor of the emergence, and then the predominance, of a new pair of
signals \mbox{located} at ${-}$139 and ${-}$143~ppm (Figure~\ref{fig5}b and~c). 
They reflect the formation of
3-hydroxy-1-(triflato)tetra-${n}$-butyldistannoxane,
[${n}$-Bu$_{2}$Sn$_{2}$(OH)(CF$_{3}$SO$_{3}$)]$_{2}$O (\textbf{4}),
whose solid-state structure was initially established by  Otera
\etal~(Scheme~\ref{sch3}b)~\cite{9}. For our part, we had previously
shown the possible transformation of \textbf{2} to \textbf{4} in the
presence of phenazine~\cite{16}. It is likely that a similar reaction
can occur in the presence of 1,10-phenanthroline. When the addition of
phen reaches two molar equivalents, the residual signals of \textbf{4}
are still visible, but a broad resonance, prevailing, appears at
${\delta}\,{-}226$~ppm (Figure~\ref{fig5}e). This corresponds to the
formation of complex \textbf{5}. In the presence of three molar
equivalents, this compound is~the only species detected in solution
(Figure~\ref{fig5}f). However, a white precipitate is also observed at
the bottom of the NMR tube, which corresponds to complex \textbf{6}
insoluble in CD$_{3}$CN. The values of the $^{119}$Sn\{$^{1}$H\} NMR
chemical shifts of the different organotin species implicated in this
study are summarized in Table~\ref{tab1}.

\subsection{Isolation and characterization of species \textbf{3}}\label{sec25}

During the monitoring of the reaction by $^{119}$Sn\{$^{1}$H\} NMR,
all signals were attributed to identified organotin species, except for
the single broad resonance at ${\delta}\,{-}267$~ppm in CD$_{3}$CN
(Figure~S12), which was assigned to compound \textbf{3}. We did not
find any bibliographic data associated with this species; therefore, it
appeared to be new and its composition remains to be clarified. We
first sought to isolate it by reproducing the experimental conditions
of the NMR measurement depicted in Figure~\ref{fig5}d in glassware conditions,
i.e., by adding 1 molar equivalent of phen to a solution
of \textbf{1} in a mixture of acetonitrile/toluene (15~mL/10~mL). After
three successive separations by crystallization at 4~\textdegree C
(\textbf{2} and \textbf{4} were collected as crystalline products)
in a CH$_{3}$CN/toluene mixture, it was possible to isolate only
\textbf{3}. After complete evaporation of the solvents, \textbf{3}
consists of a colorless pasty solid. Infrared analysis, shown in
Figure~S13, reveals several characteristic bands: (i)~${\nu}$(C--H)
absorption bands between 2800 and 3000~cm$^{-1}$, (ii)
${\nu}$(C${=}$C), ${\nu}$(C${=}$N) and $\delta$(C--H) fingerprints of
the phen ligand~\cite{20a,20b}, and (iii) stretching vibration bands of
trifluoromethasulfonate ligands [${\nu}$(CF$_{3}$) and
${\nu}$(SO$_{3}$)] between 1000 and 1300~cm$^{-1}$~\cite{19a,19b,19c}. A
$^{119}$Sn\{$^{1}$H\} NMR spectrum of a solution of \textbf{3} in
CD$_{2}$Cl$_{2}$  shows a singlet resonance at
${\delta}\,{-}288$~ppm. The $^{13}$C\{$^{1}$H\} NMR spectrum of
\textbf{3} in CD$_{2}$Cl$_{2}$ (Figure~S14) highlights two sets of
signals attributed to the presence of ${n}$-butyl and phenanthroline
ligands. A quartet at ${\delta}$ 121.2~ppm ($^{1}J_{\text{C}\ndash\text{F}}=
320$~Hz) reveals the presence of CF$_{3}$ moieties, which is
corroborated by the $^{19}$F NMR spectrum, which exhibits one singlet
at ${\delta}\,{-}78.4$~ppm (Figure~S15). The $^{1}$H spectrum
establishes a phen/${n}$-butyl ligand ratio of 1:2 (Figure~S16). The
electrospray mass spectrum (positive mode) of \textbf{3} in
dichloromethane/acetonitrile solution displays three intense mass
clusters (Figure~S17). The first one centered at ${m/z}=563.0613$ 
Da ($z=1$, 67\%) matches with high accuracy to a
mononuclear di-${n}$-butyltin fragment bearing a positive charge that
can be assigned to [${n}$-Bu$_{2}$Sn(phen)(CF$_{3}$SO$_{3}$)]$^{+}$
(C$_{21}$H$_{26}${O}$_{3}$N$_{2}${F}$_{3}$SSn), calc.
${=}$ 563.0628~Da), whereas the cluster centered at $m/z= 1275.07507$~Da 
($z=1$, 100\%) is consistent with the monocationic
dinuclear framework of the empirical formula
C$_{43}$H$_{52}$O$_{9}$N$_4$F$_{9}$S$_{3}$Sn$_{2}$ (calc. ${=}$ 
1275.07912~Da). The intermediate cluster at $m/z=893.0887$~Da 
(67\%) is compatible with
[M$+$H--{phen}--${n}$-Bu$_{2}$Sn]$^{+}$
(C$_{34}$H$_{35}$O$_6$N$_4$F$_6$S$_{2}$Sn, calc. ${=}$
893.0819~Da). Simulations of these ESI-MS mass clusters are depicted in
Figures~S18--S20. On the basis of these data, we suggest that for
species \textbf{3}, the structure reproduced on Figure~\ref{fig6} could
correspond to two [${n}$-Bu$_{2}$Sn(phen)(CF$_{3}$SO$_{3}$)] entities
bounded by a bridging trifluoromethanesulfonate ligand,
[\{${n}$-Bu$_{2}${Sn(phen)(CF$_{3}$SO$_{3}$)\}$_{2}$(${\upmu}$-CF$_{3}$SO$_{3}$)][CF$_{3}$SO$_{3}$]. 
The overall positive charge of} \textbf{3} {is compensated by an
$\mathrm{CF}_{3}\mathrm{SO}_{3}^{-}$ {anion. To the best of our knowledge, such a
structure has not yet been described in the literature. However, there
are some reports confirming in the solid-state the existence of}
\unskip\break --CF$_{3}$SO$_{3}$ groups bridging di-${n}$-butyltin derivatives. In
general, this results in the propagation of polymeric networks:
[Sn$_{2}$(CF$_{3}$O$_{3}$S)$_{2}$(C$_4$H}$_{9}$)$_{4}${(OH)}$_{2}$]$_{n}$~\cite{10}, 
${}^{2}_{\infty}\{[{n}\hyphen\mathrm{Bu}_{2}({\upmu}\hyphen\mathrm{OH})
\mathrm{SnOSn}({\upmu}\ndash {\eta}^{2}\ndash\mathrm{OSO}_{2}\mathrm{CF}
_{3}){n}\hyphen \mathrm{Bu}_{2}]\}$~\cite{9}, 
${}^{2}_{\infty}\{[{n}\hyphen\mathrm{Bu}_{2}({\upmu}\hyphen\mathrm{OH})
\mathrm{SnOSn}({\upmu}\ndash{\eta}^{2}\ndash\mathrm{O}_{3}\mathrm{SCF}_{3}
){n}\hyphen\mathrm{Bu}_{2}]_{2}[{n}\hyphen\break\mathrm{Bu}_{2}({\eta}^{1}
\hyphen\mathrm{O}_{3}\mathrm{SCF}_{3})\mathrm{SnOSn}({\upmu}\hyphen
\mathrm{OH}){n}\hyphen\mathrm{Bu}_{2}]_{2}\}$~\cite{12}. 
In \textbf{3}, the presence of phen ligands occupying two \mbox{coordination}
sites on each tin atom probably prevents polymerization. In the context
of the related chemistry of organotin(IV) alkanesulphonates,
Shankar \etal~recently reported the solid-state structures
of di-${n}$-butyltin complexes with bridging and terminal 
--OSO$_{2}$R ligands (R ${=}$ Me, Et), quite comparable to the
structure suspected for\break \textbf{3}~\cite{26}.

\begin{figure}
\includegraphics{fig06}
\caption{\label{fig6}Possible molecular representation of \textbf{3}
(OTf ${=}$ CF$_{3}$SO$_{3}$).}
\end{figure}

The elemental analysis calculated for
[\{${n}$-Bu$_{2}$Sn\ubreak(phen)(CF$_{3}$SO$_{3}$)\}$_{2}$(${\upmu}$-CF$_{3}$SO$_{3}$)][CF$_{3}$SO$_{3}$] 
(C$_{44}$H$_{52}$F$_{12}${\ubreak}N$_4$O$_{12}${S$_4$Sn$_{2}$, 
1422.57~g$\cdot$mol$^{-1}$) is also in accordance with the formula
suggested for \textbf{3}: Calculated: C, 37.17; H, 3.68; N, 3.94; S,
9.02 Found: C, 36.43; H, 3.74; N, 4.13; S, 8.16\%. Furthermore, as
highlighted by the NMR measurements reported in Figures~\ref{fig5}d 
and~\ref{fig5}e, we
verified that the addition of phen to a solution of \textbf{3} in CDCN
does indeed result in the appearance of the characteristic signal of
\textbf{5} {at} $\delta\,{-}227$~ppm. However, to date, it was not possible
to confirm the proposed structure by single crystal X-ray diffraction
analysis because the compound does not crystallize properly in
acetonitrile.

\subsection{Reactivity in dichloromethane}\label{sec26}

\begin{scheme*}
\includegraphics{sc04}
\vspace*{-4pt}
\caption{\label{sch4}Plausible mechanism leading to the formation of
\textbf{5} from \textbf{7}.\vspace*{-12pt}}
\end{scheme*}

In contrast, when the reaction between \textbf{1} {and phen (in 1:1
molar ratio) is conducted in dichloromethane instead of acetonitrile,
colourless single crystals are grown at~${-}20$~\textdegree C from the
filtrate of the reaction. They are unstable and melt very quickly as
the temperature increases. This is recurrent and was observed in
several batches. The crystallographic analysis could be performed
despite the poor quality of crystals. However, several difficulties
were encountered during the treatment of the crystallographic data: 
(i)~the determination of the space group was delicate and finally defined
as C2/c, (ii) several ligands were affected by disorders, (iii) a
solvent-accessible voids remained. The resolution of the structure
remains imperfect, but we believe that the structural data provided are
informative in relation to the intermediate species leading to
\textbf{5} and \textbf{6}. Thus, the structure of compound
\textbf{7} (Figure~\ref{fig7}) established the presence of a cationic
mononuclear compound based on a tin atom carrying two ${n}$-butyl
chains [Sn--C13 ${=}$ 2.136(7), Sn--C17 ${=}$ 2.123(7)~\AA{}] in
\textit{trans}-position with respect to each other and chelated by a
bidentate phenanthroline ligand [Sn--N1 ${=}$ 2.208(11), Sn--N2 ${=}$
2.342(8)~\AA{}]. The Sn--N bond lengths are comparable with those
measured for \textbf{6}. Two oxygen atoms, O1 and O2, complete the
coordination sphere of the tin atom, which describes a distorted
octahedral geometry [N1--Sn--O1 ${=}$ 157.1(3), N2--Sn--O2 ${=}$ 162.2(3),
C17--Sn--C13 ${=}$ 156.89(9)]. The O1 and O2 atoms are assigned to
OH}$_{2}$ and OH ligands, respectively, but unfortunately, their
hydrogen atoms could not be located. Their assignments were
nevertheless possible based on the Sn--O interatomic distances, which
are significantly different: Sn1--O1 ${=}$ 2.512(8), as opposed to~Sn--O2
${=}$ 2.142(5)~\AA{}. Distances greater than 2.3~\AA{} have already been
observed for several di-${n}$-butyltin derivatives with Sn--OH$_{2}$
bonds: 2.365~\AA{} in
[${n}$-Bu$_{2}$Sn(H}$_{2}$O)(${\upmu}$-OH)]$_{2}${[CF$_{3}$SO$_{3}$]~\cite{5}, 
2.409~\AA{} in [${n}$-Bu$_{2}${Sn(${\upmu}$-OH)(H}$_{2}$O)(CF$_{3}$SO$_{3}$)]$_{2}$~\cite{4}, 
2.511~\AA{} in \{[${n}$-Bu$_{2}${Sn(H}$_{2}${O)]}$_{2}$O${\cdot}{n}$-Bu$_{2}${Sn(OH)}$_{2}$\}[CF$_{3}$SO$_{3}$]$_{2}$ 
\cite{16}. Sn--OH bonds are generally shorter: between 2.062 and 2.150
\AA{} in
[${n}$-Bu$_{2}${Sn(H}$_{2}${O)(${\upmu}$-OH)]}$_{2}$[CF$_{3}$SO$_{3}$]~\cite{5}, 
2.120~\AA{} in
\{[${n}$-Bu$_{2}${Sn(H}$_{2}$O)]$_{2}$O${\cdot}{n}$--Bu$_{2}${Sn(OH)}$_{2}$\}[CF$_{3}$SO$_{3}$]$_{2}$
\cite{16}. These examples support the attribution of O1 and O2. The
positive charge of [${n}$-Bu$_{2}$Sn(phen)(OH)(H$_{2}$O)]$^{+}$ is
compensated by one non-coordinated $\mathrm{CF}_{3}\mathrm{SO}_{3}^{-}$ anion. To the
best of our knowledge, such a structure describing a monomeric complex
is unprecedented. Diorganotin hydroxides are difficult to purify and
characterize~\cite{27}. In the solid state, they are mainly described
as dimers, hydroxyl groups acting as bridging ligands between two tin
atoms, and also as polymers. Thus, the \mbox{number} of complexes with an OH
group singly coordinated to tin is very limited~\cite{28,29,30}. In the
case of \textbf{7}, although the resolution of its structure is not
optimal, we assume that the coordination of the phen ligand favours the
existence of a monomeric form. To the best of our knowledge, another
example of tin-hydroxide stabilized by a phen ligand was previously
reported by Aghabozorg \etal, characterized by
X-ray crystallographic structure as being
[Sn(pydc)(phen)(OH)$_{2}$]$\cdot$3H$_{2}$O (pydc ${=}$
pyridine-2,6-dicarboxyate)~\cite{31}. The two terminal OH groups occupy
the apical positions of a pentagonal bipyramid. The IR spectrum
recorded from the crystals of \textbf{7} corroborates the presence of
H$_{2}$O and OH ligands by showing two shoulders centered at 3407 and
3213~cm$^{-1}$ and a sharp band at 1628~cm$^{-1}$ assigned to
${\delta}$(H$_{2}$O) elongation. The characteristic absorption bands
of CF$_{3}$SO$_{3}$ and phen are also well visible (Figure~\ref{fig1}d).
Globally, the IR fingerprint of \textbf{7} shows strong similarities
to that of \textbf{5}.

\begin{figure}
\includegraphics{fig07}
\caption{\label{fig7}O\textsc{rtep} drawing of \textbf{7} using the
atom labeling scheme (30\% probability thermal ellipsoids). The
hydrogen atoms of O1 and O2 could not be precisely located. Selected
bond lengths (\AA{}) and angles (\textdegree): Sn--N1 2.208(11), Sn--N2
2.342(8), Sn--O1 2.512(8), Sn--O2 2.142(5), Sn--C13 2.136(17), Sn--C17
2.123(7), S--O3 1.466(7), S--O4 1.403(8), S--O5 1.408(6), C21--F1
1.311(13), C21--F2 1.309(12), C21--F3 1.330(11), C21--S 1.794(11);
O1--Sn--O2 113.8(3), O2--Sn--O1 89.1(3), O2--Sn--N2 162.2(3),
N1--Sn--O1 157.1(3), N1--Sn--N2 73.1(4), N2--Sn--O1 84.1(3),
C13--Sn--C17 161.9(3), C13--Sn--O1 79.9(3), C13--Sn--O2 91.9(2),
C13--Sn--N1 100.1(4), C13--Sn--N2 90.7(3), C17--Sn--O1 82.2(3),
C17--Sn--O2 97.4(2), C17--Sn--N1 95.6(4), C17--Sn--N2 85.2(3),
O3--S--C21 103.7(5), O4--S--C21 104.5(5), O4--S--O3 113.9(5), O4--S--O5
117.0(5), O5--S--C21 104.2(4), O5--S--O3 111.7(4). F1--C21--F3
109.1(11), F1--C21--S 110.5(7), F2--C21--F1 106.5(9), F2--C21--F3
106.6(9), F2--C21--S 113.1(9), F3--C21--S 110.8(7).}
\end{figure}

Compound \textbf{7} can be viewed as a reaction intermediate
resulting from the reactivity of \textbf{1} {toward
1,10-phenanthroline under sub-stoichiometric phen conditions 
(Equation~(\ref{eq1})).
This can then lead to the formation of \textbf{5} by dimerization,
driven by the nucleophilicity of the OH group, resulting in the
expulsion of aqua ligands (Scheme~\ref{sch4}). This mechanism is similar
to that proposed earlier by Chandrasekhar \etal~for the
dimerization of
\{[${n}$-Bu$_{2}${Sn(OH}$_{2}$)$_{4}$]$^{2+}
${[2,5-Me}$_{2}${C$_6$H}$_{3}$SO$_{3}^{-}$]$_{2}$ 
into \{[${n}$-Bu$_{2}${Sn(${\upmu}$-OH)(O}$_{3}
$SC$_6$H}$_{3}$-2,5-Me}$_{2}$)]$_{2}$\}$_{n}$~\cite{32}.
\begin{equation}\label{eq1}
\begin{gathered}
\begin{matrix} 
\;  1/2 [n-{\text{Bu}}_{2}\text{Sn}
(\mu-\text{OH})({\mathrm{H}}_{2}\mathrm{O})({\text{CF}}_{3}{\text{SO}}_{3})]_2 + \mathrm{phen}\\
\mathbf{(1)}
\end{matrix}
\\
\longrightarrow
 \begin{matrix}
[n-\text{Bu}_{2}\text{Sn}(\text{phen})(\text{OH})({\mathrm{H}}_2\mathrm{O})]
[{\text{CF}}_{3}{\text{SO}}_{3}]
\\ \mathbf{(7)}
\end{matrix}
\end{gathered}
\end{equation}
\noindent From a structural point of view, \textbf{7} can be related to the salt
\{[${n}$-Bu$_{2}$Sn(OH$_{2}$)(phen)(O$_{3}$SC$_{6}$H$_{3}$-2,5-Me$_{2}$)]$+$[2,5-Me$_{2}$C$_{6}$H$_{3}$SO$_{3}$]$^{-}$\} 
also described by Chandrasekhar \etal, and isolated by reacting
\{[${n}$-Bu$_{2}$Sn(OH$_{2}$)$_{4}$]$^{2+}$[2,5-Me$_{2}$C$_{6}$H$_{3}$SO$_{3}^{-}$]$_{2}$ 
with 1,10-phen~\cite{32}. The two compounds exhibit strong
similarities. They consist of mononuclear hydrated diorganotin cations
chelated by a phen ligand. In the \textit{Chandrasekhar} cation, the
coordination of the tin atom is completed by a sulfonate ligand,
whereas for \textbf{7}, we claim the presence of a terminal OH group.
It is interesting to note that in solution in CD$_{3}$CN, the
$^{119}$Sn\{$^{1}$H\} NMR spectroscopic analysis of the crystals of
\textbf{7} shows the presence of a mixture of four species
(Figure~S21), which highlights the instability of the mononuclear
cation \textbf{7} also in solution. It is nevertheless possible to
identify the characteristic resonances of compounds \textbf{2} (${-}$133,
${-}$161~ppm), \textbf{4} (${-}$139, ${-}$143~ppm), and \textbf{5}
(${-}$226~ppm). The most shielded signal at ${-}$260~ppm is thus attributed
to \textbf{7}. Based on the relative integration, the two main species
are \textbf{5} and \textbf{7}, which is consistent with the
dimerization reaction suggested in Scheme~\ref{sch4}. However, the
presence of species \textbf{2} and \textbf{4}, which are in the
minority according to a $^{119}$Sn\{$^{1}$H\} NMR spectrum and do not
bear phen ligands, from \textbf{7}, is still\break unexplained.

Thus, the solid-state structure of \textbf{7} resulting from the
reaction in dichloromethane differs markedly from the results obtained
in acetonitrile, leading to the hypothesis of compound \textbf{3}. This
implies a determining role of the solvent used on the nature of the
trifluoromethanesulfonate intermediate species formed. This has already
been demonstrated experimentally in the past by Otera \etal,
who showed that when ${n}$-Bu$_{2}$SnO reacts with triflic acid in
CH$_{2}$Cl$_{2}$ conditions, the compound \textbf{1}, characterized as
a dimeric cation is preferentially formed~\cite{8}, whereas in
acetonitrile, a polymeric structure prevails, alternating anhydrous and
hydrated moieties of [${n}$-Bu$_{2}$Sn(OH)(OTf)]$_{2}$ and
[${n}$-Bu$_{2}$Sn(OH)(OTf)(H$_{2}$O)]$_{2}$, respectively~\cite{5}. In
the future, we plan to use this modularity to explore the performance
of the compounds described in this study for tin-assisted organic
reactions, especially since 1,10-phenanthroline derivatives are known
to be efficient and stable ligands in homogeneous catalysis~\cite{33}.
%\vspace*{42pt}

%\break
\subsection{Isolation and solid-state structure of
[C$_{12}$H$_{9}${N}$_{2}$][CF$_{3}$SO$_{3}$]  (\textbf{phenHOTf})}\label{sec27}


In addition to \textbf{7}, single crystals of 1,10-phenanthrolinium
trifluoromethanesulfonate,
[C$_{12}${H}$_{9}$N$_{2}${][CF$_{3}$SO$_{3}$] (\textbf{phenHOTf}), were
obtained after a few days from the filtrate of the mother-liquor. The
\textbf{phenHOTf} salt consists of a monoprotonated
1,10-phenanthrolinium cation interacting with a surrounding
trifluoromethanesulfonate anion through N--H$\cdots$O hydrogen bonding
[N1$\cdots$O3 ${=}$ 2.804(2)~\AA, N1}--H$\cdots$O3 ${=}$
147.61(11)\textdegree]. An \textsc{Ortep}~representation is shown in
Figure~\ref{fig8}. To date, a large number of structures of
1,10-phenanthrolinium salts [C$_{12}${H}$_{9}$N$_{2}${][X]} have been
resolved by X-ray crystallography, such as X ${=}$ Cl$^{-}$~\cite{34},
$\mathrm{BPh}_{4}^{-}$~\cite{35}, $\mathrm{I}_{3}^{-}$~\cite{36}, 
$\mathrm{PF}_{6}^{-}$~\cite{37}.
The structure of \textbf{phenHOTf} is a new example. The crystal
stacking of \textbf{phenHOTf} (Figure~\ref{fig9}) shows that the
phenanthrolinium cations are grouped in pairs {\textit{via}} {offset}
${\uppi}$--${\uppi}$ interactions characterized by an interplanar distance
of 3.398~\AA{}, a centroid--centroid distance of 4.878~\AA{}, and a
slippage distance of 3.50~\AA{}~(slippage angle ${=}$ 45.85\textdegree).


\begin{figure}
{\vspace*{4pt}}
\includegraphics{fig08}
{\vspace*{4pt}}
\caption{\label{fig8}\textsc{Ortep} drawing of \textbf{phenHOTf} using
the atom labeling scheme (30\% probability thermal ellipsoids). The
N--H$\cdots$O interaction is indicated by a red dotted line. Selected
bond lengths (\AA{}) and angles (\textdegree): C1--N1 1.333(2), C5--N1
1.358(2), C5--C6 1.438(3), C6--N2 1.359(2), C12--N2 1.326(3), O1--S
1.4367(14), O2--S 1.4417(14), O3--S 1.4505(14), C13--S 1.825(2),
C13--F1 1.336(2), C13--F2 1.335(2), C13--F3 1.335(2); C1--N1--C5
123.04(17), C12--N2--C6 116.54(18), O1--S--C13 103.50(9), O1--S--O2
115.68(8), O1--S--O3 114.80(8), O2--S--C13 103.31(9), O2--S--O3
114.88(8), O3--S--C13 102.07(9), F1--C13--F3 107.57(16), F1--C13--S
111.34(13), F2--C13--F1 107.49(16), F2--C13--F3 107.62(15), F2--C13--S
111.31(14), F3 C13 S 111.31(14).}
\end{figure}

\begin{figure}
\includegraphics{fig09}
\caption{\label{fig9}Crystal packing of \textbf{phenHOTf} along the
${a}$-axis. (\textsc{Mercury} representation~\cite{25}, color
code: N ${=}$ blue, C ${=}$ gray, H ${=}$ white, O ${=}$ red, S ${=}$ yellow, F
${=}$ green.)}
\end{figure}

\subsection{Reactivity of 1 to 2,9-dimethyl-1,10-phenanthroline}\label{2.8}

Subsequently, the reactivity of \textbf{1} {was extended to the
disubstituted 1,10-phenanthrolines. Under the reaction conditions (room
temperature, dichloromethane/toluene mixture), we found that
4,7-diphenyl-1,10-phenanthroline (bathophenanthroline) did not react,
fully recovering the starting compounds. However, in the presence of
2,9-dimethyl-1,10-phenanthroline (}{\textbf{dmphen}}), two types of
colorless crystals were successively obtained from the mother liquor.
Monitoring of the reaction by $^{119}${Sn\{}$^{1}${H\} NMR in
CD}$_{2}${Cl}$_{2}$ {revealed the transformation of} \textbf{1} {into
distannoxanes} \textbf{2} {and} \textbf{4}. {However, we did not detect
the formation of organotin species coordinated by dmphen ligands, as in
the case of compounds} \textbf{5}, \textbf{6} {and} \textbf{7}. This
is probably due to steric hindrance caused by the presence of methyl
substituents. The first type of crystals collected as long needles was
characterized by X-ray diffraction analysis as being the organic salt
[C$_{14}$H$_{13}${N}$_{2}${][CF$_{3}$SO$_{3}$]
({\textbf{dmphenHOTf}}). An O}{\textsc{rtep}} representation is shown
in Figure~\ref{fig10}. The monoprotonation of dmphen led to the formation of the
cation [C$_{14}$H$_{13}${N}$_{2}$]$^{+}${. The
positive charge is balanced by a triflate anion, which is also involved
in hydrogen bonding to the cation} {\textit{via}} {an N--H$\cdots$O
interaction [N1$\cdots$O1 ${=}$ 2.910} {\AA{}, N1}{--H1$\cdots$O1 ${=}$
157.63(14)\textdegree]. The crystal packing view of}
{\textbf{dmphenHOTf}} {shows a folded sheet organization
(Figure~\ref{fig11}), stacked along the} {\textit{a}}{-axis via}
${\uppi}$--${\uppi}$ {interactions between the aryl rings of
[C$_{14}$H$_{13}${N}$_{2}$]$^{+}$ {with an interplanar distance of
3.449~\AA{}, a centroid--centroid distance of 3.626~\AA{}, and a
slippage distance of 1.119~\AA{} (slip angle of 17.98\textdegree).
Recently,} {\textit{Assefa}} {and} {\textit{Gore}} 
{unintentionally
obtained the same compound by adding 2,9-dimethyl-1,10-phenanthroline
drop wise to a Eu(CF$_{3}$O}$_{3}$S)}$_{3}$ solution~\cite{38}. In
addition, several structures of 2,9-dimethyl-1,10-phenanthrolinium
salts [C$_{14}$H$_{13}${N}$_{2}$][X] have already been solved. This is
the case for $\mathrm{X} = \mathrm{ClO}_{4}^-$~\cite{39},  Cl$^-$~\cite{40},
$\mathrm{NO}_{3}^{-}$~\cite{41}, $\mathrm{PF}_{6}^{-}$~\cite{42}.

\begin{figure}
\includegraphics{fig10}
\caption{\label{fig10}O\textsc{rtep} drawing of \textbf{dmphenHOTf}
using the atom labeling scheme (30\% probability thermal ellipsoids).
The N--H$\cdots$O interaction is indicated by a red dotted line.
Selected bond lengths (\AA{}) and angles (\textdegree): N1--C5
1.371(3), N1--C1 1.336(3), N2--C6 1.355(3), N2--C12 1.327(3), S--O1
1.4472(17), S--O2 1.4306(19), S--O3 1.4359(17), S--C15 1.832(3),
F1--C15 1.329(3), F2--C15 1.334(3), F3--C15 1.336(3); O1--S--C15
102.31(11), O3--S--O1 115.26(11), O3--S--C15 103.14(12), O2--S--O1
115.68(12), O2--S--O3 114.96(11), O2--S--C15 102.71(14), F2--C15--S
111.2(2), F2--C15--F3 107.5(2), F3--C15--S 111.46(18), F1--C15--S
111.25(18), F1--C15--F2 108.1(2), F1--C15--F3 107.2(2).}
\end{figure}

\begin{figure}
\vspace*{-2pt}
\includegraphics{fig11}
\vspace*{-2pt}
\caption{\label{fig11}Organization of \textbf{dmphenHOTf} in the
crystal lattice along the ${a}$-axis. Hydrogen atoms are omitted for
clarity (\textsc{Mercury} representation~\cite{25}, color code: N ${=}$
blue, C ${=}$ gray, O ${=}$ red, S ${=}$ yellow, F ${=}$ green).}
\vspace*{-2pt}
\end{figure}

A second type of colorless crystals, exhibiting a different shape
(prism), was collected from the filtrate of the solution from which
{\textbf{dmphenHOTf}} crystals were initially obtained. Their
composition consists of a monoprotonated dmphen molecule
({\textbf{dmphenH}}) co-crystallizing with a free dmphen molecule to
form {\textbf{dmphenHOTf{\boldcdot}dmphen}}{. The two components interact
through an N--H$\cdots$N hydrogen bond [N1$\cdots$N3 ${=}$ 2.927(3)}
{\AA{}]}. In fact, the hydrogen atom is split between the two nitrogen
atoms [{N1}--H$\cdots$N3 ${=}$ 152.78(14)\textdegree,
{N3}{--H$\cdots$N1 ${=}$ 159.92(14)\textdegree]. Interestingly, the
steric hindrance of the methyl substituents leads to a positioning
close to orthogonality between the two heterocycles. Their arrangement
can be described as a head--tail assembly. A dihedral angle of
77.74(3)\textdegree~was determined between the two planes containing
dmphenH and dmphe. The overall positive charge is compensated by the
presence of a triflate anion. An O}{\textsc{rtep}} {view of}
{\textbf{dmphenHOTf{\boldcdot}dmphen}} is shown in Figure~\ref{fig12}. The crystal
packing view, depicted in Figure~\ref{fig13}, also shows that the dmphen rings
are in ${\uppi}$--${\uppi}$ {aromatic interaction and are organized in
pairs. However, two distinctive stacking patterns can be observed for}
{\textbf{dmphen}} {and} {\textbf{dmphenH}}{, respectively,
characterized by interplanar distances of 3.631 and 3.353} {\AA{}}{,
centroid--centroid distances of 3.762} {\AA{}} {and 4.445} {\AA{}}{, and
slip distances of 0.984} {\AA{}} {(slip angle of 15.16\textdegree)}
{and 2.918} {\AA{}} {(slip angle of 41.03\textdegree)}, \mbox{respectively}.

\begin{figure}
\includegraphics{fig12}
\caption{\label{fig12}\textsc{Ortep} drawing of
\textbf{dmphenHOTf{\boldcdot}dmphen} using the atom labeling scheme (30\%
probability thermal ellipsoids). The N--H$\cdots$N interaction is
indicated by a blue dotted line. Selected bond lengths (\AA{}) and
angles (\textdegree): C1--N1 1.336(3), C5--N1 1.366(3), C6--N2
1.366(3), C12--N2 1.324(3), C15--N3 1.335(3), C19--N3 1.367(3), C20--N4
1.357(3), C26--N4 1.330(3), C29--F1 1.334(3), C29--F2 1.333(3), C29--F3
1.340(3), C29--S 1.832(3), O1--S 1.4364(18), O2--S 1.4423(19), O3--S
1.4426(18); F2--C29--F3 107.3(2), F2--C29--F1 107.4(2), F2--C29--S
111.80(18), F3--C29--S 110.85(17), F1--C29--F3 107.1(2), F1--C29--S
112.11(17), O2--S--C29 102.19(12), O2--S--O3 114.84(11), O3--S--C29
103.17(11), O1--S--C29 103.78(11), O1--S--O2 115.20(12), O1--S--O3
115.13(12).}
\end{figure}

\begin{figure*}
\includegraphics{fig13}
\caption{\label{fig13}Crystal packing of \textbf{dmphenHOTf{\boldcdot}dmphen}
along the \textit{b}-axis. Hydrogen atoms are omitted for clarity
(\textsc{Mercury} representation~\cite{25}, color code: N ${=}$ blue, C
${=}$ gray, O ${=}$ red, S ${=}$ yellow, F ${=}$ green).}
\end{figure*}


{In the past, we have shown the possibility of accessing phenazinium
and acridinium trifluoromethanesulfonate salts by reacting compound}
\textbf{1}, at room temperature, in the presence of phenazine
(phz)~\cite{12} and acridine (acr)~\cite{43}, respectively. The
isolation of original architectures based on molecular stacks driven by
hydrogen and ${\uppi}$--${\uppi}$ {interactions, has underlined the
predisposition of} {\textit{N}}{-heterocyclic molecules as suitable
building-blocks. In our opinion, this approach,} {\textit{via}} {the
assistance of an organotin compound, could be seen as an innovative
method of crystal engineering. It is successfully applied here to
1,10-phenanthroline and 2,9-dimethyl-1,10-phenanthroline, leading to
new phenanthrolinium trifluoromethanesulfonate salts.}

\section{Conclusion and perspectives}\label{sec3}

In conclusion, the study of the reactivity between 1,10-phenanthroline
(phen) and the complex
[${n}$-Bu$_{2}${Sn(${\upmu}$-OH)(H}$_{2}${O)(CF$_{3}$SO$_{3}$)]$_{2}$
(\textbf{1}) led to the complete characterization of two new
di-}${n}$-butyltin(IV) trifluoromethanesulfonates, \textbf{5} {and}
\textbf{6}, {\textit{N}},{\textit{N}}{-bis-chelated with phen ligands.
Furthermore, using} $^{119}${Sn(}$^{1}${H) NMR spectroscopy as an
investigation probe under deuterated acetonitrile conditions, we were
also able to highlight the formation of \mbox{additional} tin
trifluoromethanesulfonate intermediates. Two,} \textbf{2} {and}
\textbf{4}{, exhibiting distannoxane-like frameworks but without
phen-coordinated ligands, were clearly identified by comparison with
previous work while investigations were conducted to clarify the
unknown} $^{119}${Sn(}$^{1}${H) NMR fingerprint attributed to}
\textbf{3}{. Crystallization attempts are underway to corroborate the
suggested dinuclear structure.} We also observed that the identity of
the solvent used for the reaction had a notable impact on the
intermediates formed. In the presence of dichloromethane, the
solid-state structure of a mononuclear hydrated di-${n}$-butyltin
hydroxide, stabilized by a phen ligand and assigned to \textbf{7},
was revealed. To the best of our knowledge, there are few comparable
examples to date. Thus, new structural and spectroscopic insights into
organotin(IV) trifluoromethanesulfonates have been obtained, thereby
opening the way for further investigations. In the future, we plan to
explore the catalytic properties of these compounds.

\section{Experimental section}\label{sec4}

\subsection{Materials and instrumentation} \label{sec41}

Organic solvents, dichloromethane (Carlo Erba, 99.5\% purity), toluene
(Acros, 99.99\%), acetonitrile (99.9\% purity), were refluxed over
appropriate dessicants, distilled, and saturated with argon prior to
use. Chemicals were purchased from Aldrich, Acros Organics, and Fluka
and used without further purification. The starting compound
[${n}$-Bu$_{2}${Sn(OH)(H}$_{2}${O)(CF$_{3}$SO$_{3}$)]$_{2}$
(\textbf{1}) was synthesized from} ${n}$-Bu$_{2}${SnO (Acros, 98\%
purity) and trifluoromethanesulfonic acid (Fluka, 98\% purity) in
acetonitrile, according to a published method~\cite{8}. The} $^{1}${H,}
$^{19}${F,} $^{119}${Sn\{}$^{1}${H\}, and} $^{13}${C\{}$^{1}${H\} NMR
experiments were recorded on Bruker Avance 300 and 500~MHz
spectrometers and calibrated with Me$_4$Si, trifluoromethylbenzene, or
Me$_4$Sn as an internal standard. Chemical shift} ${\delta}$ {values
are given in~ppm. FT-IR spectra were recorded on a Bruker Alfa
spectrometer equipped with a Specac Golden Gate{\texttrademark} ATR
device. ESI-MS spectra were obtained on a Bruker micro Q-TOF instrument
using acetonitrile, dichloromethane and methanol mobile phases.}
Elemental analyses (C, H, N, S) were performed at the Institut de
Chimie Mol\'{e}culaire de l'Universit\'{e} de Bourgogne, Dijon.

\subsection{Preparation of
[n-Bu$_{2}$Sn(OH)(phen)]$_{2}$[CF$_{3}${\ubreak}SO$_{3}$]$_{2}$ 
(\textbf{5}) and [n-Bu$_{2}$Sn(Phen)$_{2}$][CF$_{3}$SO$_{3}$] 
(\textbf{6}) from [n-Bu$_{2}$Sn(OH)(H$_{2}$O)(CF$_{3}$SO$_{3}$)]$_{2}$ 
(\textbf{1}) and 1,10-phenanthroline}\label{sec42}

Two molar equivalents of 1,10-phenanthroline (C$_{8}$H$_{8}$N$_{2}$,
Sigma-Aldrich, 99\% purity) (0.130~g, 0.72~mmol) were added to a
colourless solution of{\break}
[${n}$-Bu$_{2}$Sn(OH)(H$_{2}$O)(CF$_{3}$SO$_{3}$)]$_{2}$ (\textbf{1})
(0.300~g, 0.360 mmol) in a mixture of dichloromethane/toluene
(15~mL/10~mL). The reaction medium is stirred for 3 h at room
temperature leading to a clear pinkish solution. A precipitate 
(0.160~g) was collected after one week of evaporation at room
temperature. This corresponds to the formation of compound \textbf{6},
which was then recrystallized as fine needles in
dichloromethane/toluene. Compound \textbf{5} was obtained a few days
later from the reaction filtrate as colorless, parallelepipedal
crystals (0.050~g). The use of four equivalents of 1,10-phenanthroline
gave exclusive access to compound \textbf{6}.\looseness=-1

\textbf{5}: $^{1}${H NMR (300~MHz, CD}$_{2}${Cl}$_{2}$, 301~K):
${\delta}$0.5--2.1\unskip\break (m, 36H, Ant), 3.78 (br, 2H), 
8.02 (m, 4H), 8.11
(s, 4H),\unskip\break 8.66 (m, 4H), 9.37 (m, 4H); $^{13}${C\{}$^{1}$H\} NMR
(75~MHz, CD$_{2}${Cl}$_{2}$, 300~K): ${\delta}$13.4, 26.5, 27.6,
120.8 (q, $^{1}{J}_{\text{CF}}= 320$~Hz), 125.7, 127.8,
130.1, 139.9, 141.7, 149.9; $^{19}$F NMR (282~MHz,
CD$_{2}$C1$_{2}$, 301~K): ${\delta}\,{-}78.5$ (s,
$\mathrm{CF}_{3}\mathrm{SO}_{3}^{-}$); $^{119}$Sn\{$^{1}$H\} (186~MHz,
CD$_{3}$CN, 298~K): ${\delta} \,{-}226$; $^{119}${Sn\{}$^{1}$H\}
(186~MHz, acetone-$d_6$, 298~K): ${\delta}\,{-}150$; ESI-HRMS
(+): ${m}/z$ 431.1133~Da (100\%)
[M--OH--phen--${n}$-Bu$_{2}${Sn]}$^{+}$
(C$_{20}${H}$_{27}$N$_{2}$OSn, calc.: 431.1145~Da); FT-IR
(ATR,~cm$^{-1}$): 3321, 3081, 3066, 2956, 2929, 2871, 1626, 1575, 1589,
1543, 1518, 1427, 1379, 1282, 1237, 1223, 1155, 1027, 854, 731, 717,
683, 633, 573, 515. Anal. Calc. For
C$_{42}${H}$_{54}${F$_6$N$_4$O}$_{8}${S}$_{2}${Sn}$_{2}$ (1158.44): C,
43.55; H, 4.70; N, 4.84; S, 5.54. Found: C, 43.42; H, 5.45; N, 4.90; S,
4.32\%.

\textbf{6}: $^{1}$H NMR (500~MHz, acetone-$d_6$, 298~K):
0.65 (t, $J$ {${=}$ 7.3~Hz, 6H), 1.20 (m, 4H), 1.34 (m, 4H),
2.10 (m, 4H), 8.26 (m, 4H), 8.50 (s, 4H), 9.18 (m, 8H);}
$^{13}${C\{}$^{1}$H\} NMR (125~MHz, acetone-$d_6$, 298~K):
${\delta}$13.1, 26.5, 27.8, 27.81, 121.9 (q,
$^{1}J_{\text{CF}}=321$~Hz), 127.20, 128.7, 131.0,
138.5, 142.9, 149.0; $^{19}$F NMR (470~MHz, acetone-$d_6$,
298~K): ${\delta}\,{-}78.8$ (s, $\mathrm{CF}_{3}\mathrm{SO}_{3}^{-}$);
$^{119}${Sn\{}$^{1}$H\} (186~MHz, acetone-$d_6$, 298~K):
${\delta}\,{-}231$; ESI-HRMS (+): m/z 445.1305~Da (100\%)
[M--phen+OCH$_{3}$]$^{+}$ (C$_{21}$H$_{29}$N$_{2}$OSn, calc.:
445.1301~Da), $m/z$ 431.11559~Da (80\%) [M--phen+OH]$^{+}$
(C$_{20}${H}$_{27}$N$_{2}$OSn, calc.: 431.11454~Da); FT-IR
(ATR,~cm$^{-1}$): 3104, 3070, 2960, 2925, 2870, 2860, 1630, 1589, 1543,
1523, 1431, 1259, 1223, 1153, 1027, 868, 720, 633, 573, 516. Anal.
Calc. For C$_{34}${H}$_{34}${F$_6$N$_4$O$_6$S}$_{2}$Sn (891.49): C,
45.81; H, 3.84; N, 6.28; S, 7.19 Found: C, 45.56; H, 3.38; N, 6.30; S,
7.29\%.\looseness=-1

\vspace*{-5pt}
\subsection{Isolation and characterization of \textbf{3}}\label{sec43}

The protocol used the same conditions as those used in the
$^{119}$Sn\{$^{1}$H\} NMR experiment shown in Figure~\ref{fig5}d. One
molar equivalent of 1,10-phenanthroline (0.065~g, 0.360~mmol) was added
to a colourless solution of
[${n}$-Bu$_{2}$Sn(OH)(H$_{2}$O)(CF$_{3}$SO$_{3}$)]$_{2}$ (\textbf{1})
(0.300~g, 0.360~mmol) in a mixture of acetonitrile/toluene
(15~mL/10~mL). The solution was progressively enriched in compound
\textbf{3} by eliminating species \textbf{2}, \textbf{3}, and
\textbf{4} by successive crystallizations, and the filtrate was stored
each time at ${-}20$~\textdegree C. \textbf{3} was finally obtained
after three cycles ($^{119}$Sn\{$^{1}$H\} NMR monitoring) and after the
total evaporation of the solvents leading to a colorless pasty solid.

\textbf{3}: $^{1}${H NMR (499~MHz, CD}$_{3}$CN, 298~K): 0.61 (t, 
$J = 7.0$~Hz, 6H), 1.09 (m, 4H), 1.17 (m, 4H), 2.08 (m, 4H), 8.36 (m,
2H), 8.41 (s, 2H), 9.13 (m, 2H), 9.53 (m, 2H); $^{13}$C\{$^{1}$H\}
NMR (125~MHz, CD$_{3}$Cl$_{2}$, 298~K): 13.1, 25.9, 27.3, 33.9,
120.55 ($^{1}J_{\text{CF}}= 319$~Hz), 127.2, 128.6, 130.9, 139.4,
143.0, 150.3; $^{19}$F NMR (470~MHz, CH$_{2}${Cl}$_{2}$, 298~K):
${\delta}\,{-}78.4$ (s, C{F}SO$_{3}$);
$^{119}$Sn\{$^{1}$H\} (149~MHz, CD$_{3}$CN, 298~K): ${\delta}\,{-}266$, 
$^{119}$Sn\{$^{1}$H\} (186~MHz, CD$_{2}${Cl}$_{2}$,
298~K): ${\delta}\,{-}288$; ESI~MS (+): ${m/z}$ 1275.07507~Da
(100\%) [M]$^{+}$
{(C}$_{43}${H}$_{52}$O$_{9}$N$_4$F$_{9}${S}$_{3}$Sn$_{2}$, calc.:
1275.07912~Da), ${m/z}$ 893.0887~Da (67\%)
[M$+$H--phen--${n}$-Bu$_{2}$Sn]$^{+}$
(C$_{34}${H}$_{35}${O$_6$N$_4$F$_6$S}$_{2}$Sn, calc.: 893.09201
Da), ${m/z}$ 563.06134~Da ($z$ {${=}$ 1, 67\%)
[${n}$-Bu$_{2}$Sn(phen)(CF$_{3}$SO$_{3}$)]$^{+}$
(C$_{21}${H}$_{26}${O}$_{3}$N$_{2}${F}$_{3}$SSn, calc.: 563.06328~Da); 
FT-IR (ATR,~cm$^{-1}$): 3091, 3071, 2960, 2931, 2871, 1631, 1607,
1586, 1525, 1264, 1200, 1162, 1016, 866, 723, 691, 631, 573, 513, 426.
Anal. Calc. For C$_{44}${H}$_{52}$F$_{12}$N$_4$O$_{12}${S$_4$Sn}$_{2}$
(1422.57): C, 37.15; H, 3.68; N, 3.94; S, 9.02 Found: C, 36.43; H,
3.74; N, 4.13;\break S,~8.16\%.

\subsection{Isolation and characterization of \textbf{phenHOTf}}\label{sec44}

Small crystals of \textbf{phenHOTf} were obtained from the filtrate of
the mother-liquor from which compound \textbf{7} had been isolated.

{\textbf{\textit{phenHOTf}}}: $^{1}$H NMR (500~MHz,
CD$_{2}${Cl}$_{2}$, 298~K): ${\delta}$8.03 (dd, 1H, $J=8.17$, 
5.02~Hz), 8.08 (s, 1H), 8.16 (brs, 2H), 8.71 (d, 1H, $J=8.12$~Hz), 
8.79 (d, 1H, $J=7.30$~Hz), 9.36 (d, 1H, $J=4.35$~Hz), 
9.64 (brs, 1H); $^{19}$F NMR (470~MHz,
CD$_{2}${Cl}$_{2}$, 298~K): ${\delta}\,{-}78.57$ (s,
C{F}SO$_{3}$); $^{13}$C\{$^{1}$H\} NMR (125~MHz,
CD$_{2}${Cl}$_{2}$, 298~K): 120.4 ($^{1}J_{\text{CF}}= 320$~Hz),
125.6, 126.6, 127.5, 129.8, 130.3, 137.8, 141.4, 147.8, 150.5; FT-IR
(ATR,~cm$^{-1}$): 3100, 3070, 3043, 2960, 2930, 2872, 1598, 1542, 1525,
1497, 1471, 1438, 1283, 1223, 1152, 10256, 847, 719, 632, 571, 514,
463.

\subsection{Isolation and characterization of
\textbf{{dmphenHOTf}} {and} 
\textbf{dmphenHOTf\raisebox{2pt}{.}dmphen}}\label{sec45}

Four molar equivalents of 2,9-dimethyl-1,10-phenanthroline
(C$_{10}$H$_{12}$N$_{2}$, Sigma-Aldrich, 99\% purity) (0.200~g, 0.96
mmol) were added to a colourless solution of
[${n}$-Bu$_{2}$Sn(OH)(H$_{2}$O)(CF$_{3}$SO$_{3}$)]$_{2}$ (\textbf{1})
(0.200~g, 0.24~mmol) in a dichloromethane/toluene mixture (10~mL/5~mL).
The reaction medium is stirred for 3 h at room temperature in ambient
air. In the following days, \textbf{\textit{dmphenHOTf}} crystals first
grew and then, after filtration of the mother-liquor, new crystals
characterized as \textbf{\textit{dmphenHOTf{\boldcdot}dmphen}} were collected.

{\textbf{\textit{dmphenHOTf}}}: $^{1}${H NMR (300~MHz,
CD}$_{2}${Cl}$_{2}$, {299~K):} ${\delta}${8.65 (d, 2H,} $J=8.4$~Hz), 
8.08 (s, 2H), 7.90 (d, 2H,} $J=8.4$~Hz), 7.66 (br, 1H),
3.18 (s, 6H, CH$_{3}$); $^{19}$F NMR (470~MHz, CD$_{2}${Cl}$_{2}$,
298~K): ${\delta}\,{-}78.93$ (s, C{{F}}{SO$_{3}$);
$^{13}${C\{}$^{1}${H\} NMR (125~MHz, CD}$_{2}${Cl}$_{2}$, 298~K):
23.3, 121.2 ($^{1}J_{\text{CF}}= 320$~Hz), 126.8, 126.9, 128.2,
137.4, 141.5, 159.9; FT-IR (ATR, cm$^{-1}$): 3174, 3111, 3046, 3016,
2980, 1635, 1604, 1533, 1503, 1463, 1278, 1253, 1246, 1222, 1142, 1032,
813, 719, 691, 677, 631, 573, 542, 513; Anal. Calc. For
C$_{15}${H$_{13}${F}$_{3}$N}$_{2}${O}$_{3}$S (358.34): C, 50.28; H,
3.66; N, 7.829; S, 8.95. Found: C, 49.96; H, 4.05; N, 7.82; S, 6.29\%.}

{\textbf{\textit{dmphenHOTf{\boldcdot}dmphen}}}: $^{1}${H NMR (500~MHz,
CD}$_{2}${Cl}$_{2}${, 298~K):} ${\delta}${8.33 (d, 4H,} $J=8.30$~Hz), 
7.84 (s, 4H), 7.57 (d, 4H, $J$ {${=}$ 8.38~Hz), 7.41 (br, 1H),
2.59 (s, 12H, CH}$_{3}$); $^{19}${F NMR (470~MHz, CD}$_{2}${Cl}$_{2}${,
298~K):} ${\delta}${--78.92 (s, C}{{F}}{SO$_{3}$);
$^{13}${C\{}$^{1}${H\} NMR (125~MHz, CD}$_{2}${Cl}$_{2}$, {298~K):
23.6, 121.3 (}$^{1}J_{\text{CF}}$ {${=}$ 321~Hz), 125.4, 126.4, 127.96,
139.08, 141.7, 159.1; FT-IR (ATR, cm$^{-1}$): 2958, 2929, 2858, 1636,
1626, 1605, 1595, 1541, 1499, 1466, 1353, 1257, 1221, 1152, 1027, 853,
754, 735, 724, 634, 570, 546, 515, 441; Anal. Calc. For
C$_{29}${H}$_{25}${F}$_{3}$N$_4$O}$_{3}$S (566.59): C, 61.47; H, 4.45;
N, 9.89; S, 5.66. Found: C, 60.93; H, 4.80; N, 10.08; S, 5.09\%.}

\subsection{X-ray diffraction analysis and refinement}\label{sec46}

Crystallographic data and structure refinement details for \textbf{5},
\textbf{6}, \textbf{7}, \textbf{phenHOTf}, 
\textbf{dmphenHOTf}{\boldcdot} and
\textbf{dmphenHOTf{\boldcdot}dmphen} are reported and detailled in
\textit{Supporting information -- Crystallographic Data}.

\section*{Declaration of interests}
The authors do not work for, advise, own shares in, or receive funds
from any organization that could benefit from this article, and have
declared no affiliations other than their research organizations.

\section*{Funding}
The authors are grateful to the University of Burgundy-Dijon and the
CNRS for their constant financial support.

\section*{Acknowledgements}
The authors would particularly like
to thank Dr. Q. Bonin, Ms M.-J. Penouilh (ESI-HRMS) and Ms T.
R\'{e}gnier (elemental analysis), as well as the Professor~Klaus
Jurkschat and the second anonymous reviewer for their corrections and
suggestions, which significantly improved the initial manuscript. 

\section*{Supplementary data}

Supporting information for this article is available on the journal's
website under \printDOI\ or from the author.   

Additional spectroscopic data ($^{1}${H}, $^{19}$F,
$^{13}${C\{}$^{1}${H\},} $^{119}${Sn\{}$^{1}${H\}, FT-IR, and ESI-MS
spectra; Figures~S1}--{S21) related to complexes} \textbf{5}, 
\textbf{6}, \textbf{7} are
given in \textit{Supporting Information---Spectroscopic Data}.
Crystallographic data regarding the X-ray structures reported in this
study (compounds \textbf{5}, \textbf{6}, \textbf{7}, \textbf{phenHOTf},
\textbf{dmphenHOTf}, and \textbf{dmphenHOTf{\boldcdot}dmphen}) are available in
\textit{Supporting Information---Crystallographic Data}. 

\CDRsupplementaryTwotypes{supplementary-material}{\cdrattach{crchim-260-suppl.pdf}}

CCDC 2254272 (\textbf{5}), 2254273 (\textbf{6}), 2254274 (\textbf{7}),
2254275 (\textbf{phenHOTf}), 2254276 (\textbf{dmphenHOTf}), and 2254277
(\textbf{dmphenHOTf{\boldcdot}dmphen}) contain the supplementary crystallographic
data for this paper. These data can be obtained free of charge from the
Cambridge Crystallographic Data Centre via
\url{www.ccdc.cam.ac.uk/data\_request/cif}.

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