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

Abstract

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 (1H, 19F{1H}, 31P{1H} and 119Sn) 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(PiPr3)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(PiPr3)2(OTf)] and [SnF2(PiPr3)2(OTf)2], again with axial phosphines, although some OTf dissociation from the former to give [SnF3(PiPr3)2]+ may occur in solution at room temperature. The new phosphine complexes of SnF4, trans-[SnF4(PiPr3)2] and (cis) [SnF4(κ2-triphos)] (triphos = CH3C(CH2PPh2)3) have also been fully characterised, including the crystal structure of [SnF4(κ2-triphos)]. Attempts to promote P3-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 (1H, 19F{1H}, 119Sn). 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.