Chemistry of metal hydrides. Part XX. The nature of the insertion rearrangement of acetylenes with platinum(II) hydrides

Abstract

The reactions of platinum(II) hydrides, trans-PtHXL₂, where X = NO₃, Cl or CH₃OH, and L = PEt₃ or tricyclohexylphosphine, with disubstituted acetylenes, R₁C≡CR₂ have been examined under a variety of conditions. From spectroscopic parameters, the gross geometry at platinum as well as the geometry of the resulting alkenyl groups in the products have been determined. The observation that all alkenyl groups have a cis geometry is consistent with a migratory insertion step involving a four-centred transition state, in which the disposition of the acetylene relative to the Pt—H bond appears to be dependent on the Pt—H bond polarity. Evidence is presented to demonstrate that this polarity depends on several factors including solvent, and ligands on Pt(II). For L = tricyclohexylphosphine, the occurrence of a side reaction which competes with insertion and which leads to a Pt(0) acetylene complex is also demonstrated, and other interesting reactions are described.