Neutral and Cationic Methyl Complexes of Platinum(II) with 6-Substituted 2,2′-Bipyridines: Synthesis, Characterisation and Reactivity with Carbon Monoxide − Molecular Structures of [PtCl(methyl)(6-ethyl-2,2′-bipyridine)] and of [Pt(methyl)(acetonitrile)(6-ethyl-2,2′-bipyridine)][BF4

Abstract

The complex trans-[PtCl(Me)(SMe2)2] reacts with 6-R-substituted 2,2′-bipyridine, HLn (n = 1, R = H; n = 2, R = Me; n = 3, R = Et; n = 4, R = iPr; n = 5, R = CH2Ph; n = 7, R = Ph), to afford the neutral complexes [PtCl(Me)(HLn)]. Only one isomer is formed (R cis to Cl) with all the ligands, but one (R = Ph). When R = C(Me)2Ph (HL6), only an (N−N−C) cyclometallated species is formed. The stereoselectivity observed is interpreted in terms of the nature of the substituent R, and of the hydrogen bond formed between H−C(α) of the R substituent and the chloride ion bound to the platinum center. The molecular structure of [PtCl(Me)(HL3)] has been resolved by an X-ray analysis and shows that the above-mentioned hydrogen bond length is 2.28 Å. The reactivity of three representative complexes (R = H, Et, CH2Ph) with carbon monoxide has been studied. The reaction affords the ionic species [Pt(Me)(CO)(HLn)]+[PtCl2(Me)(CO)]− and the free ligand. There is evidence of the formation of an acyl species, which does not contain the bipyridine ligand, only when working at high pressures of CO. The above cations are also obtained by direct carbonylation of the solvent species, [Pt(Me)(MeCN)(HLn)][BF4], achieve by halide abstraction from the neutral complexes. The molecular structure of [Pt(Me)(MeCN)(HL3)][BF4] has been resolved by an X-ray analysis.