The rate and mechanism of oxidative addition of H2 to the Cr(CO)3C5Me5 radical—generation of a model for reaction of H2 with the Co(CO)4 radical

Abstract

Abstract The rate of reaction of hydrogen with the 17 e − metal centered radical Cr(CO) 3 C 5 Me 5 obeys the third-order rate law d[P]/d t = k obs [ Cr] 2 [H 2 ] in toluene solution. In the temperature range 20–60°C, k obs =330±30 M −2 s −1 , Δ H ≠ =0±1 kcal mol −1 , Δ S ≠ =−47±3 cal mol −1 deg −1 . The rate of oxidative addition is not inhibited by added pressure of CO. The rate of binding of D 2 is slower than that of H 2 : k (H 2 )/ k (D 2 )=1.18. These results are combined with earlier work to generate a complete reaction profile for hydrogenation of the metal–metal bonded dimer [Cr(CO) 3 C 5 Me 5 ] 2 +H 2 →2H–Cr(CO) 3 C 5 Me 5 . A similar reaction profile for Co 2 (CO) 8 +H 2 →2H–Co(CO) 4 under high pressures of CO is constructed based on literature data and estimated activation parameters for reaction of the Co(CO) 4 radical with hydrogen.