KINETICS AND MECHANISM OF REDUCTIVE ELIMINATION OF HYDROCARBONS FROM (MU-H)3RU3(MU-3CPH)(CO)9, (MU-H)3RUE(MU-3CET)(CO)9, (MU-H)3RUE(MU-3-CCL)(CO)9, (MU-H)3RU3(MU-3CCO2ME)(CO)9, (MU-H)3RU3(MU-3-CSET)(CO)9, (MU-H)3RU3(MU-3CCHPHCH2PH)(CO)9

The reaction of CO with (μ-H)3Ru3(μ3-CX)(CO)9 forms the corresponding CH3X (X = CO2Me, Ph, Et, CHPhCH2Ph) and Ru3(CO)12/Ru(CO)5; if β-hydrogens are present, alkenes and H4Ru4(CO)12 are also products. The rate law (X = Ph, Cl, and Et) is of the following form: rate = [kakcPco/(kb + kcPco)}[H3Ru3(CX)(CO)9] (X = Ph, ka = (6.4 ± 0.6) X 10-6 s-1, kb/kc = 0.49 ± 0.14 atm, 100 °C; X = Cl, kA = (7.5 ± 0.7) X 10-5 s-1 and kb/kc = 3.5 ± 0.9 atm, 100 °C; X = Et, ka = (7.6 ± 2.5) X 10-5 s-1, kb/kc = 14 ± 7 atm, 125 °C). For X = CO2Me the rate law is zero order in Pco. Activation parameters for the limiting rate constant ka were determined (Ph, 35 atm, ΔH = 131 ± 3 kJ/mol, ΔS* = 6 ± 8 J/(K mol); Cl, 35 atm, ΔH* = 125 ± 9 kJ/mol, ΔS* = 9 ± 25 J/(K mol); Et, 34 atm, ΔH* = 140 ± 19 kJ/mol, ΔS* = 22 ± 49 J/(K mol); CO2Me, 1 atm, ΔH* = 111.2 ± 1.3 kJ/mol, ΔS* = -0.8 ± 4 J/(K mol)). For X = Ph, Cl, and Et inverse deuterium isotope effects were measured (Ph, 86% d, kH/kD = 0.64 ± 0.08,100 °C, 35 atm; Cl, 85% d, kH/kD = 0.56 ± 0.06,100 °C, 6.8 atm; Et, 80% d, kH/kD = 0.46 ± 0.03,100 °C, 35 atm), but kH/kD = 1.01 ± 0.03 (95% d, 70 °C, 1 atm) for X = CO2Me. The proposed mechanism involves a sequence of C–H reductive eliminations, each of which is preceded by reversible migration of hydrogen from Ru–H–Ru bridging to Ru–H–C bridging. The rate-determining step at high CO pressures is cleavage of the first Ru–H–C bond. For X = CO2R or SEt anchimeric assistance of the reductive elimination, perhaps through a species containing a (μ3-H)Ru2C interaction, is proposed. © 1990, American Chemical Society. All rights reserved.