MECHANISM AND ENERGETICS OF THE LIGAND-INDUCED REDUCTIVE ELIMINATION OF HYDROGEN FROM A BINUCLEAR PLATINUM HYDRIDE.

Article abstract of DOI:10.1021/ja00356a017

The mechanism of reaction of tertiary phosphine ligands, L, with left bracket Pt//2H//2( mu -H)( mu -dppm)//2 right bracket ** plus (I) to give left bracket Pt//2HL( mu -dppm)//2 left bracket left bracket Pt//2HL( mu -dppm)//2 right bracket ** plus (II) and H//2 has been studied. It is shown that an intermediate, left bracket Pt//2H//2( mu -H)L( mu -dppm)//2 right bracket ** plus (III), is formed and the equilibrium constants associated with formation of III at low temperature have been determined. Hydrogen loss from intermediate III is intramolecular, and there is a primary isotope effect k//H/k//D of 3. 5 for the reductive elimination step. Kinetic studies of the reductive elimination have demonstrated a correlation between equilibrium constants for formation of III and the overall rate of reaction to give II and H//2 and have yielded activation parameters needed to construct a reaction coordinate energy level diagram for the reductive elimination reaction. The probability of the reductive elimination occuring at a single platinum center or across the two platinum centers is discussed.