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) 2 (M = Sn, Pb; OTf = CF 3 SO 3 ) with soft phosphine and arsine ligands, L, where L = o -C 6 H 4 (ER 2 ) 2 (E = P, R = Me or Ph; E = As, R = Me), MeC(CH 2 ER 2 ) 3 (E = P, R = Ph; E = As, R = Me), PhP(CH 2 CH 2 PPh 2 ) 2 or P(CH 2 CH 2 PPh 2 ) 3 , affords complexes of stoichiometry M(L)(OTf) 2 as white powders, which have been characterised via elemental analysis, 1 H, 19 F{ 1 H}, 31 P{ 1 H} and 119 Sn NMR spectroscopy, with the expected 31 P- 119 Sn and 31 P- 207 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. 19 F{ 1 H} NMR spectra indicate that the OTf is essentially anionic (dissociated) in solution. Anion metathesis of [M(OTf) 2 {MeC(CH 2 PPh 2 ) 3 }] with Na[BAr F ] (BAr F = B{3,5-(CF 3 ) 2 C 6 H 3 } 4 ) yields the corresponding [M{MeC(CH 2 PPh 2 ) 3 }][BAr F ] 2 salts, the crystal structures of all three (M = Ge, Sn, Pb) reveal pyramidal dications with discrete [BAr F ] - anions providing charge balance. Density functional theory (DFT) calculations on these [M{MeC(CH 2 PPh 2 ) 3 }] 2+ (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 z 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.