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

Abstract

The complexes of type [Pt(η²-ol₁)(L–L′)] (ol₁ = dimethylfumarate (dmf), naphthoquinone (nq); L–L′ = pyridyl–methanimine (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(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.