Lead(IV) complexes with phosphinoyldithioformates, R2P(O)CS2− (R = Ph or PhCH2). Syntheses and characterization. Crystal structures of [PPh4][S2CP(O)Ph2]·0.5H2O, [PbPh2{S2CP(O)Ph2}2] and [PbPh2Cl{S2CP(O)Ph2}]

Abstract

Lead(IV) complexes with phosphinoyl substituted dithioformate, L = R₂P(O)CS₂⁻ (R = Ph or PhCH₂), have been synthesized and characterized by UV/vis, IR and NMR (¹H, ¹³C and ³¹P). The following types of compounds are described: (PPh₄)L, PbPh₂L₂, PbPh₂X(L) (X = Cl, Br or I) and PbPh₃L. Among these compounds the structure has been determined from single crystal X-ray diffraction data (122 K) of [PPh₄][Ph₂P(O)CS₂]·0.5 H₂O, [PbPh₂{S₂CP(O)Ph₂}₂] and [PbPh₂Cl{S₂CP(O)Ph₂}]. The preferred co-ordination mode for L is bidentate through S and O. The crystal structures of the two complexes show them both to be mononuclear, one octahedral with the phenyl ligands trans to each other and the other five-co-ordinated. The complexes are buckled to form nearly planar five-membered chelate rings. The magnitude of the NMR coupling constants between lead and atoms in the phenyl ligands close to lead, especially the ipso carbon atom, reflects the co-ordination number in a remarkable way. On that basis the PbPh₃L complex with R = PhCH₂ is found to be four-co-ordinated in non-co-ordinating organic solvents. Variable-temperature NMR measurements reveal a fluxional behaviour of the six- and five-co-ordinated complexes, and different molecular symmetries are observed at low temperature.