Kinetics of the combination of methyl ligands with carbonyl or isonitrile ligands in ruthenium(II) complexes

Abstract

Methyl complexes [Ru(CO)₂MeR(PMe₂Ph)₂][(1a), R = Ph; (1b), R = COMe; (1c), R = Me] react with Me₃CNC to form acetyl complexes [Ru(CO)(CNCMe₃)(COMe)R(PMe₂Ph)₂], (2a)–(2c). The reaction rate is independent of isonitrile concentration, and the rate-determining step is believed to involve combination of methyl and carbonyl ligands. The reactions of complexes (1b) and (1c) are similar both in rate and in activation parameters, but for (1a)ΔH‡ is appreciably lower and S‡ more negative: this may be due to increasing Ru–Ph π bonding in the approach to the transition state. Complex (2c) reacts with more Me₃CNC to form [Ru(CO)(CNCMe₃)(COMe){C(NCMe₃)Me}-(PMe₂Ph)₂], (3c). Here the rate-determining step appears to involve combination of methyl and isonitrile ligands; this is much slower than combination of methyl and carbonyl ligands owing to a more negative ΔS‡. In the absence of added Me₃CNC, complex (2c) slowly disproportionates into (1c) and (3c).