Tin(iv) fluoride complexes with neutral phosphine coordination and comparisons with hard N- and O-donor ligands

The reactions of trans-[SnF4(PMe3)(2)] with one, two or three equivalents of Me3SiO3SCF3 (TMSOTF), respectively, in anhydrous CH2Cl2 form six-coordinate [SnF4-n(PMe3)(2)(OTf)(n)] (n = 1-3), which have been characterised by microanalysis, IR and multinuclear NMR (H-1, F-19{H-1}, P-31{H-1} and Sn-119) spectroscopy. The crystal structure of [SnF3(PMe3)(2)(OTf)] reveals the three fluorines are in a mer-arrangement with mutually trans PMe3 ligands. The multinuclear NMR spectra confirm this structure is retained in solution, and show that [SnF2(PMe3)(2)(OTf)(2)] has trans-phosphines, while [SnF(PMe3)(2)(OTf)(3)] has trans PMe3 groups and hence mer-triflate ligands. The [SnF4-n(PMe3)(2)(OTf)(n)] are unstable in solution and the decomposition products include [Me3PF](+) and the tin(ii) complexes [Sn(PMe3)(2)(OTf)(2)] and [Sn3F5(OTf)], both of the latter identified by their crystal structures. The reaction of trans-[SnF4((PPr3)-Pr-i)(2)] containing the bulkier phosphine, with one and two equivalents of TMSOTf produced unstable mono- and bis-triflates, which the NMR data also suggest contain weakly coordinated triflate, [SnF3((PPr3)-Pr-i)(2)(OTf)] and [SnF2((PPr3)-Pr-i)(2)(OTf)(2)], again with axial phosphines, although some OTf dissociation from the former to give [SnF3((PPr3)-Pr-i)(2)](+) may occur in solution at room temperature. The new phosphine complexes of SnF4, trans-[SnF4((PPr3)-Pr-i)(2)] and (cis) [SnF4(kappa(2)-triphos)] (triphos = CH3C(CH2PPh2)(3)) have also been fully characterised, including the crystal structure of [SnF4(kappa(2)-triphos)]. Attempts to promote P-3-coordination by further treatment of this complex with TMSOTf were unsuccessful. The [SnF4(L)(2)] (L = dmso, py, pyNO, DMF, OPPh3) complexes, which exist as mixtures of cis and trans isomers, react with one equivalent of TMSOTf, followed by addition of one equivalent of L, to form the ionic [SnF3(L)(3)][OTf] complexes, which were characterised by microanalysis, IR and multinuclear NMR spectroscopy. In nitromethane solution they are a mixture of mer and fac isomers based upon multinuclear NMR data (H-1, F-19{H-1}, Sn-119). Reaction of [SnF4(OPPh3)(2)] with two equivalents of TMSOTf and further OPPh3 produced [SnF2(OPPh3)(4)][OTf](2), which is a mixture of cis and trans isomers in solution. The crystal structure of [SnF2(OPPh3)(4)][OTf](2) confirms the trans isomer in the solid state, with the triflate ionic. These complexes are rare examples of fluorotin(iv) cations with neutral monodentate ligands.

Automated summary

The study characterized various Sn-F organometallic complexes through multiple analytical techniques, showing specific structural features in both solution and solid state, including unstable compounds and the presence of coordinated impurities.