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

The complexes of type [Pt(eta(2)-ol(1))(L-L')] (ol(1) = dimethylfumarate (dmf), naphthoquinone (nq); L- L' = pyridylmethanimine (N-N'R'; R' = Bu-t, 4-MeOC6H4), pyridyl-thioether (N-SR; R = Bu-t, 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(o) olefin substrates occurs via inversion at sp(3) sulfur only (L-L' = N-SR). Moreover, the exchange olefin reactions between [Pt(eta(2)-ol(1))(L- L')] complexes and the entering olefin ol(2) [ol(2) = 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(eta(2)-ol)(L- L')] (ol = fn, ma, dmf) were also determined and compared with those of analogous platinum(o) and palladium(o) species.