The rate and mechanism of oxidative addition of H-2 to the Cr-center dot(CO)(3)C5Me5 radical - generation of a model for reaction of H-2 with the Co-center dot(CO)(4) radical

The rate of reaction of hydrogen with the 17 e(-) metal centered radical Cr -.(CO)(3)C5Me5 obeys the third-order rate law d[P]/dt = k(obs)[Cr-.](2)[H-2 ] in toluene solution. In the temperature range 20-60 degrees C, k(obs) = 3 30 +/- 30 M-2 s(-1), Delta H-not equal = 0 +/- 1 kcal mol(-1), Delta S-not equal = -47 +/- 3 cal mol(-1) deg(-1). The rate of oxidative addition is no t inhibited by added pressure of CO. The rate of binding of D-2 is slower t han that of H-2: k(H-2)/k(D-2) = 1.18. These results are combined with earl ier work to generate a complete reaction profile for hydrogenation of the m etal-metal bonded dimer [Cr(CO)(3)C5Me5](2) + H-2 --> 2H-Cr(CO)(3)C5Me5. 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 activ ation parameters for reaction of the Co-.(CO)(4) radical with hydrogen. (C) 1999 Elsevier Science S.A. All rights reserved.