Coordination chemistry and properties of unusually π-basic molybdenum fragments

A series of complexes of the form TpMo(NO)(L)(eta(2)-L-pi) were synthesized, where Tp = hydridotris(pyrazolyl)borate, L = 1-methylimidazole or ammonia, and L-pi is an alkene, alkyne, ketone, polyaromatic hydrocarbon, or aromatic heterocycle. The thermal stability of the dihapto-coordinated aromatic complexes is indicative of a strong pi back-bonding interaction similar to that found in the heavy metal analogues [Os(NH3)(5) (eta(2)-arene)](2+), TpRe(CO)(L)(eta(2)-arene), and TpW(NO)(L)(eta(2)-arene). Several synthetic routes to these molybdenum complexes are outlined.