Manganese(I) Tricarbonyl Complexes with Bidentate Pyridine-Based Actor Ligands: Reversible Binding of CO2 and Benzaldehyde via Cooperative C–C and Mn–O Bond Formation at Ambient Temperature

We report manganese(I) tricarbonyl complexes decorated with imino- and amino-pyridine ligands [Mn(impy)(CO)3Br] and [Mn(ampy)(CO)3Br], respectively. Both compounds can be transformed either via two-electron reduction for the former or double deprotonation for the latter into anionic species with a disturbed (“dearomatized”) π-electron system of the pyridine ring M[Mn(amidopy*)(CO)3] (M = alkali metal). The newly formed five-coordinated complex is anionic and encompasses a nucleophilic carbon center within its metalla cycle. This leads to noteworthy reactivity: [Mn(amidopy*)(CO)3]− readily reacts with CO double bonds. Specifically, CO2 and benzaldehyde can bind to the complex via a metal–ligand cooperative [1,3]-addition under C–C and Mn–O bond formation and concomitant rearomatization of the pyridine ring. Remarkably, we found that this addition is reversible. Exchange reactions using isotopically labeled 13CO2 indicate reversible C–C and Mn–O bond formation at ambient temperature. Likewise, bonded benzaldehyde is exchanged from the complex under a CO2 atmosphere. Density functional theory calculations suggest a significant role for the cationic counter ion in the bond activation reactions that can make this bond activation feasible.