Cleavage of CO by Mo[N(R)Ar]3 Complexes

The reaction of MoL3 [L = NH2 and N(tBu)Ar] with CO was explored using DFT in order to rationalize why CO cleavage is not observed experimentally for this system in contrast to the corresponding N2 reaction which results in spontaneous cleavage of the N-N bond. The binding of CO to MoL3 was found to be both kinetically and thermodynamically favored over the binding of N2, with the formation of the encounter complex, L3Mo-CO, calculated to be without barrier and exothermic. While the overall reaction to form the C-MoL3 and O-MoL3 products was calculated to be energetically favorable, both the encounter complex and intermediate dimer, L3Mo-CO-MoL3, were found to be lower in energy than the products, with the final C-O cleavage step calculated to be endothermic by 169 kJ mol-1 and 163 kJ mol -1 for L = NH2 and N(tBu)Ar, respectively. The unfavorable CO cleavage step can be attributed to the fact that Mo does not possess the optimum d-electron configuration to sufficiently stabilise the carbide and oxide products relative to the CO-bridged intermediate dimer. © Wiley-VCH Verlag GmbH & Co. KGaA, 2007.