Coordination Chemistry and Properties of Unusually π-Basic Molybdenum Fragments

A series of complexes of the form TpMo(NO)(L)(η2-Lπ) were synthesized, where Tp = hydridotris(pyrazolyl)borate, L = 1-methylimidazole or ammonia, and Lπ is an alkene, alkyne, ketone, polyaromatic hydrocarbon, or aromatic heterocycle. The thermal stability of the dihapto-coordinated aromatic complexes is indicative of a strong π back-bonding interaction similar to that found in the heavy metal analogues [Os(NH3)5(η2-arene)]2+, TpRe(CO)(L)(η2-arene), and TpW(NO)(L)(η2-arene). Several synthetic routes to these molybdenum complexes are outlined.