Platinum metal complexes of potentially chelating alkene–sulphur and alkene–selenium ligands. The synthesis by chalcogen dealkylation and X-ray structures of the dimeric complexes [{PtI(SCH2CH2CMeCH2)}2] and [{PtI(PPh3)(SCH2CH2CMeCH2)}2], and a dynamic nuclear magnetic resonance study of [{PtI(L)(SCH2CH2CMeCH2)}2][L = PPh3, PPh2Me, or As(CH2SiMe3)3]

Abstract

The chelating ligands 2,8-dimethyl- 5-thianona-1,8-diene and 2,8-dimethyl-5-selenanona-1,8-diene have been found to undergo unusually facile chalcogen dealkylation on treatment with halide when co-ordinated to platinum(II). The resulting dimeric complexes contain chelating bridging alkenyl thiolato and alkenyl selenato ligands and have been fully characterised. An X-ray diffraction study of [{PtI(SCH₂CH₂CMeCH₂)}₂] is reported: the crystals are orthorhombic, space group Pbca with Z= 1 in a unit cell of dimensions a= 12.733(3), b= 15.288(2), and c= 16.904(3)Å. The molecular structure involves a non-planar Pt₂S₂ ring, with square-planar co-ordination at each platinum being completed by the chelating alkene and iodide ligands. The principal internuclear distances are Pt(1)–I(1) 2.624(2), Pt(2)–I(2) 2.621(2), Pt(1)–S(1) 2.295(6), Pt(1)–S(2) 2.330(6), Pt(2)–S(1) 2.334(6), Pt(2)–S(2) 2.304(6), Pt(1)–C 2.216(25) and 2.21 (3), Pt(2)–C 2.207(24) and 2.155(23)Å. The co-ordinated alkene functions are displaced by ligands containing Group 5A donor atoms yielding dimeric complexes which contain non-chelating bridging alkenyl thiolato and alkenyl selenato ligands and which have been fully characterised. Inversion of configuration at the bridging chalcogen atom is observed at moderate temperatures and has been studied by dynamic n.m.r. spectroscopy. An X-ray diffraction study of [{PtI(PPh₃)-(SCH₂CH₂CMeCH₂)}₂] is reported: the crystals are triclinic, of space group P, with Z = 1 in a unit cell of dimensions a= 10.396(1), b= 11.250(5), and c= 13.348(2)Å with α= 91.63(3)β= 94.53(1), and γ= 116.02(3)°. The molecular structure involves a planar Pt₂S₂ ring, with square-planar co-ordination at each platinum being completed by triphenylphosphine and iodide ligands. The molecule has a centre of inversion. The principal internuclear distances are Pt–I 2.621 (1), Pt–S 2.367(3), and Pt–P 2.267(3)Å.