The mechanism of olefin exchange in platinum(0) pyridyl–methanimine and pyridyl–thioether complexes. A kinetic study

The complexes of type [Pt(η2-ol1)(L–L′)] (ol1 = dimethylfumarate (dmf), naphthoquinone (nq); L–L′ = pyridyl–methanimine (N-N′R′; R′ = But, 4-MeOC6H4), pyridyl–thioether (N-SR; R = But, Ph) ligands) were synthesised and fully characterised by means of spectrometric and spectroscopic techniques and elemental analysis. At variance with analogous palladium complexes which display a more complicated solution behaviour, the fluxional rearrangement of pyridyl–thioether platinum(0) olefin substrates occurs via inversion at sp3 sulfur only (L–L′ = N-SR). Moreover, the exchange olefin reactions between [Pt(η2-ol1)(L–L′)] complexes and the entering olefin ol2 [ol2 = maleic anhydride (ma), fumaronitrile (fn), naphthoquinone (nq) and tetramethylethylenetetracarboxylate (tmetc)] were studied in CHCl3 either under pseudo-first order or second order conditions. On the basis of the ensuing results and of the activation parameters, an associative reaction mechanism is proposed and a novel reactivity scale for the electron poor olefins acting as entering species is determined. The crystal structures of the complexes [Pt(η2-ol)(L–L′)] (ol = fn, ma, dmf) were also determined and compared with those of analogous platinum(0) and palladium(0) species.