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 at the CASPT2 level of approximation; and therefore, no sufficiently stable insertion product can be expected for the triplet surface. The quintet surface has been studied and a linear HCoCH3+ conformation with sufficient stability was detected. Due to a large energy barrier in the entrance channel this conformation is not accessible at thermal energies. Its computed relative energy makes it, however, a likely candidate as an intermediate in the reverse reaction of CoCH2++D2, that might be responsible for the recently observed isotope scrambling. Also for the reactions of the higher alkanes ethane and propane, the CASSCF equilibrium structures are not maintained at the CASPT2 level; no notable stability for any triplet structure could be located. In the case of the hydridopropyl complex, for which no theoretical calculations have been reported so far, it is true that an extra stabilization effect was found to be associated with the internal adduct formation, but this is not sufficient to produce a true intermediate.