Reactivity of Mn(I) Picolyl-NHC Complexes Toward H2 and CO2 Activation and the Catalytic Dehydrogenation of Formic Acid

We report the synthesis and reactivity of [MnBr(HL)(CO) 3 ], 1 (where HL = 3,4,5-trimethyl-1-(2-picolyl)-imidazol-2-ylidene). The reaction of 1 with a base leads to the deprotonation of the methylene group of the ligand backbone and the formation of two isomeric dimers [MnL(CO) 3 ] 2, 2 and 2’ . The deprotonation of 1 under an H 2 atmosphere gives the hydrido complex [Mn(HL)(CO) 3 H], 3 . Alternatively, 3 can be obtained as the major product from the reaction of 1 with KHBEt 3 or the reaction of 2 and 2’ with H 2 . The reaction of 3 with carbon dioxide yields the O -bound formate complex [Mn(HL)(CO) 3 (OOCH)], 4, which can be converted back to 3 upon deprotonation under an H 2 atmosphere or heating under vacuum. Complexes 1, 3, and 4 show catalytic activity toward the dehydrogenation of formic acid.