Synthesis and spectroscopic studies of phenyllead halide and thiocyanate adducts with hexamethylphosphoramide

Abstract

Hexamethylphosphoramide (HMPA) adducts of the type Ph 3PbX·HMPA (XCl, Br, I, and NCS), Ph 2PbX 2·2HMPA (XCl, Br, and I), and Ph 2PbX 2·HMPA (XBr and I), have been prepared and characterized by infrared, Raman, mass, and 31P nmr spectroscopy. Molecular weight and infrared solution data show that Ph 3PbX·HMPA adducts dissociate in benzene, the degree of dissociation being NCS«Cl<Br<I. The thiocyanate adducts Ph 3PbNCS·HMPA and Ph 2Pb(NCS) 2·2HMPA have v(CN) and v(CS) frequencies in the solid state, and v(CN) frequencies and absorptivities in benzene solution consistent with N-bonded thiocyanate in the solid state and in benzene solution. Vibrational frequencies are reported in the range 260 to 80 cm −1 and assignments are made for v(Pb-X), v(Pb-O0, and v(Pb-NCS) modes. The 1:1 adducts Ph 3PbX·HMPA are monomeric and trigonal bipyramidal, whereas the 1:2 adducts Ph 2PbX 2·2HMPA are monomeric and cis-octahedral and the Ph 2PbX 2·HMPA appear to be halogen bridged polymers with lead six-coordinate. Coordination of HMPA causes a small upfield change in 31P chemnical shift values, and 2J(Pb-P) values vary with X in the order: NCS>I-Br>Cl for Ph 3PbX·HMPA adducts. Corresponding tin and lead adducts are compared with respect to mode of adduct formation.