Addition-elimination equilibria involving 16e(-) platinum(O) and 18e(-) platinum(II) complexes

The addition-elimination equilibrium involving a platinum(0) nucleophile [Pt(N,N'-chelate)(olefin)] (1), an organometal electrophile R(m)MX(n) (M = Hg, Sn; X = Cl, Br, I; R = hydrocarbyl group), and the corresponding five-coordinate adduct [PtX(MR(m)X(n-1))(N,N'-chelate)(olefin)] (2) has been investigated. The influence on the equilibrium of the groups bonded to the electrophilic center and of the ligands bonded to platinum has been evaluated. It has been found that the adduct is stabilized by the presence of electron-donor olefins on platinum and of electron-withdrawing groups on the electrophilic metal. It has also been found that the influence of the halide moving onto platinum can be rationalized in terms of the relative softness of the two metals involved in the equilibrium. The X-ray molecular structures of [Pt(dmphen)(E-MeO(2)CCH=CHCO(2)Me)] (1k, dmphen = 2,9-Me(2)-1,10-phenanthroline) and of the related addition product [PtCl(SnMe(2)Cl)(dmphen)(E-MeO(2)CCH=CHCO(2)Me)] (2i) have been determined for a better understanding of the influence of steric and bonding features.