Synthesis, spectroscopic and structural properties of Sn(II) and Pb(II) triflate complexes with soft phosphine and arsine coordination.

Reaction of the divalent M(OTf) (M = Sn, Pb; OTf = CFSO) with soft phosphine and arsine ligands, L, where L = -CH(ER) (E = P, R = Me or Ph; E = As, R = Me), MeC(CHER) (E = P, R = Ph; E = As, R = Me), PhP(CHCHPPh) or P(CHCHPPh), affords complexes of stoichiometry M(L)(OTf) as white powders, which have been characterised elemental analysis, H, F{H}, P{H} and Sn NMR spectroscopy, with the expected P-Sn and P-Pb couplings clearly evident. The crystal structures of nine of these pnictine complexes are reported, in each case revealing retention of one or both OTf anions, which gives rise to a diverse range of coordination environments including monomers, as well as varying degrees of oligomerisation to form weakly associated (OTf-bridged) dimers, trimers and polymers. F{H} NMR spectra indicate that the OTf is essentially anionic (dissociated) in solution. Anion metathesis of [M(OTf){MeC(CHPPh)}] with Na[BAr] (BAr = B{3,5-(CF)CH}) yields the corresponding [M{MeC(CHPPh)}][BAr] salts, the crystal structures of all three (M = Ge, Sn, Pb) reveal pyramidal dications with discrete [BAr] anions providing charge balance. Density functional theory (DFT) calculations on these [M{MeC(CHPPh)}] (M = Ge, Sn, Pb) dications using the B3LYP-D3 functional show the presence of a directional lone pair, which is a mixture of valence s and p character, with the valence p-orbital character decreasing down group 14. Natural bond orbital (NBO) analysis also shows that the natural charge at the metal centre increases and the charge on the P centre decreases upon going down group 14.