Geometry and Electronic Structure of (CO)3NiCH2. A Model Transition-Metal Carbene

The first application of nonempirical molecular electronic structure theory to a realistic transition-metal carbene complex is reported. The system chosen was (CO)3NiCH2, methylene(tricarbonyl)nickel(0). All studies were carried out at the self-consistent-field (SCF) level. A large and flexibly contracted basis set was chosen, labeled Ni(15s lip 6d/l Is 8p 3d), C,0(9s 5p/4s 2p), H(5s/3s). The critical predicted equilibrium geometrical parameters were R[Ni-C(methylene)] = 1.83 Å, 0(HCH) = 108°. The sixfold barrier to rotation about the Ni-C(methylene) axis is small, ~0.2 kcal. The electronic structure of (CO)3NiCH2 is discussed and compared with those of the “naked” complex NiCH2 and the stable Ni(CO)4 molecule.