The rate and mechanism of oxidative addition of H_2 to the centre dot Cr(CO)_3C_5Me_5 radical-generation of a model for reaction of H_2 with the centre dot Co(CO)_4 radical

摘要

The rate of reaction of hydrogen with the 17 e~- metal centered radical centre dot Cr(CO)_3C_5Me_5 obeys the third-order rate law d[P]/dt = k_(obs)[centre dot Cr]~2[H_2] in toluene solution. In the temperature range 20-60 deg K, k_(obs) = 330 +- 30 M~(-2) s~(-2), #DELTA#H~(not=) = 0 +- 1 kcal mol~(-1), #DELTA#S~not= = -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)_3C_5Me_5]_2 + H_2 -> 2H-Cr(CO)_3C_5Me_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 centre dot Co(CO)_4 radical with hydrogen.