INTRAMOLECULAR HYDRIDE MIGRATION FROM FORMYL TO CARBONYL AND NITRENE LIGANDS

Reaction of [Tp'W(CO)2(NPh)][PF6] [Tp' = hydrotris(3,5-dimethylpyrazolyl)borate] with lithium borohydride at -40-degrees-C generates Tp'W(CO)(NPh)(CHO) (1), which undergoes hydride migration from carbon to nitrogen (at -70-degrees-C, k(obs) = 7.2 x 10(-6) s-1 DELTA-G double-ended dagger = 16.5 kcal/mol, t 1/2 = 27 h) to form Tp'W(CO)2(NHPh). Crossover experiments indicate that the hydride migration is intramolecular. The metal formyl intermediate is fluxional; hydride migration interconverts the formyl and carbonyl ligands. The rate constant for this degenerate migration is 40 s-1 at -41-degrees-C with DELTA-G double-ended dagger = 11.7 kcal/mol. The analogous acyl complex Tp'W(CO)(NPh)[C(O)Ph] (3) has been synthesized from the reaction of [Tp'W(CO)2-(NPh)][PF6] with PhMgBr.