LIGAND DEPENDENCE OF MOLYBDENUM-CATALYZED ALKYLATIONS - MOLYBDENUM ISONITRILE COMPLEXES AS A NEW CLASS OF HIGHLY REACTIVE ALKYLATION CATALYSTS

A series of molybdenum complexes bearing alpha-diimine, N,N'-diarylideneethylenediamine, and isonitrile ligands have been prepared and evaluated for their ability to catalyze alkylations by using allyl acetates and especially allyl sulfones. (bpy)Mo(CH3CN)(CO)3 proved to be a very effective catalyst in contrast to bypMo(CO)4. The addition of isonitrile ligands to molybdenum hexacarbonyl generates the most effective molybdenum catalysts known to date. The reactive catalyst proved to be Mo(RNC)4(CO)2. With this new catalyst, a much broader range of substrates can be employed including many that failed or reacted very poorly by using molybdenum hexacarbonyl. The regioselectivity also differs from that obtained with molybdenum hexacarbonyl. The stereochemistry of the reaction proceeds with very clean net retention of configuration even under conditions that produced diastereomeric mixtures with molybdenum hexacarbonyl. A mechanistic rationale that accounts for the seemingly disparate complexes that are catalysts is presented.