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)(3)Br] and [Mn(ampy)(CO)(3)Br], 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") pi-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 (CO2)-C-13 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.