ON THE STABILITY OF HYDRIDOALKYL COMPLEXES OF CO+

The triplet and quintet potential energy surfaces for the reaction of Co+ with methane have been investigated by ab initio calculations. The CASSCF equilibrium structures on the triplet surface do not persist a t the CASPT2 level of approximation; and therefore, no sufficiently st able insertion product can be expected for the triplet surface. The qu intet surface has been studied and a linear H-Co-CH3+ conformation wit h sufficient stability was detected. Due to a large energy barrier in the entrance channel this conformation is not accessible at thermal en ergies. Its computed relative energy makes it however, a likely candid ate as an intermediate in the reverse reaction of CoCH2++D-2, that mig ht be responsible for the recently observed isotope scrambling. Also f or the reactions of the higher alkanes ethane and propane, the CASSCF equilibrium structures are not maintained at the CASPT2 level; no nota ble stability for any triplet structure could be located. In the case of the hydridopropyl complex, for which no theoretical calculations ha ve been reported so far, it is hue that an extra stabilization effect was found to be associated with the internal adduct formation, but thi s is not sufficient to produce a true intermediate.