A density functional study on the Pt(0)-catalysed hydrosilylation of ethylene

A theoretical investigation has been performed on the reaction pathways involved in the Pt(PH3)(2)-catalysed ethylene hydrosilylation by SiH4. We have analysed both mechanisms proposed to explain the formation of the vinyl-silane product, i.e. (i) the Chalk-Harrod mechanism, which consists of Si-H oxidative addition of SiH4 to Pt(PH3)(2), ethylene insertion into the Pt-H bond followed by Si-C reductive elimination; and (ii) the modified Chalk-Harrod mechanism, which consists of the same oxidative addition of SiH4 to Pt(PH3)(2) followed by ethylene insertion into the Pt-Si bond and by C-H reductive elimination. We characterised all the elementary steps involved in both mechanisms by gradient-corrected DFr methods, and performed ab initio molecular dynamics simulations on the initial oxidative addition step. We compute a maximum energy barrier of 25.1 and 38.2 kcal/mol for the Chalk-Harrod and modified Chalk-Harrod mechanisms, respectively, both in correspondence of the ethylene insertion-isomerisation step. Our DFT approach is found to provide comparable results to those obtained at the MP4SDQ level on the Hartree-Fock optimised geometries, except for the ethylene insertion and isomerisation steps in the modified Chalk-Harrod mechanism, for which we compute lower energy barriers at the DFT level. Our results confirm that the Chalk-Harrod mechanism is kinetically favored over its modified version. (C) 2003 Elsevier Science B.V. All rights reserved.