Reductions of metal carbonyls by quaternary ammonium borohydrides

Abstract

Quaternary ammonium borohydrides, used directly or generated in phase transfer reactions, are highly effective reagents for preparing metal carbonyl anions from metal carbonyls [Mo(CO) 6, Mn 2(CO) 10, Re 2(CO) 10, CO 2(CO) 8, Fe 3(CO) 12, Ru 3(CO) 12 and (η 5-C 5H 5) 2Mo 2(CO) 6] and from some metal carbonyl halides [BrMn(CO) 5 and η 5-C 5H 5Mo(CO) 3Cl]. Where strongly basic anions would be formed from a halide [BrMn(CO) 4PPh 3 and η 5-C 5H 5Ru(CO) 2Br], the reactions provide efficient syntheses of the corresponding hydrides instead. The anion η 5-C 5H 5Fe(CO) 2 − is not accessible by these techniques; reaction of η 5-C 5H 5Fe(CO) 2Br yields the iron dimer (via the highly nucleophilic anion) and the dimer is unreactive toward Q +BH 4 −. Reductions of Re 2(CO) 10 conducted in CH 2Cl 2 provide Re 2(CO) 9Cl − in high yield.