We describe rhenium(I) triscarbonyl compounds (3 and 4) decorated with simple-to-use 2-iminomethyl-pyridine (1, impy) and 2-aminomethyl-pyridine (2, ampy) ligands, respectively, which can serve as cooperative ligand scaffolds enabling CO 2 binding via a formal [1,3] addition under Re−O and C−C bond formation. fac-[Re(impy)-(CO) 3 Br] (3) is readily prepared by stirring (1-(pyridin-2yl)-N-(p-tolyl)methanimine (impy, 1) and [Re(CO ) 5 Br] in refluxing THF. Alternatively, complex 3 can be readily obtained when a mixture of [Re(CO) 5 Br], p-toluidine, and picolinaldehyde is refluxed in ethanol. Complex 3 is reduced with excess potassium metal in THF (two-electron reduction) to give the anionic amido complex K[Re(amidopy*)(CO) 3 ] (5b, the asterisk indicates the dearomatized ligand). Analysis of the 1 H and 13 C{ 1 H} NMR spectra of 5b suggest the dearomatization of the pyridine unit. Complex 5b is highly reactive and gives rise to the facile [1,3] addition of CO 2 . The addition of the CO 2 and thus the formation of K[Re(amidopy-COO)(CO) 3 ] ( 6) is characterized by the concomitant formation of a Re−O and a C−C bond. The addition is triggered by the rearomatization of the pyridine unit in 6. Remarkably, isotopic labeling experiments involving 13 CO 2 suggest a reversible binding of CO 2 to the complex. The related amine complex fac-[Re(ampy)(CO) 3 Br] (4) is similarly prepared by stirring (4-methyl-N-(pyridin-2ylmethyl)aniline ( 2) and [Re(CO) 5 Br] in THF at 60 °C. Upon addition of excess base (LiHMDS), complex 3 is readily deprotonated twice to give likewise the anionic amido complex Li[Re(amidopy*)(CO) 3 ] (5a). The latter reaction gives rise to a facile access to the reactive dearomatized anionic fragment [Re(amidopy*)(CO) 3 ] − with no need for the application of strong reducing agents. The ion pair M + /[Re(amidopy*)(CO) 3 ] − is highly reactive and combines MLC (metal−ligand cooperation) via a dearomatization/rearomatization scheme and bifunctional reactivity enabled by the nucleophilic nature of the Re complex and the Lewis acidic counter alkali cation.

Metal−ligand cooperative activation of C=O and CN multiple bonds in transition metal complexes with pyridine-based ligands is a currently active field of research. We herein expand the substrate scope to S=O bonds. The anionic complex K [Re(amidopy)(CO) 3 ] readily reacts with a SO 2 source to give the sulfinate fac-K[Re(amidopy-OSO)-(CO) 3 ] under Re−O and C−S bond formation as a diastereomeric mixture, which shows mutual dynamic interconversion even at ambient temperature. The chemical exchange was studied by 2D 1 H 1 H EXSY NMR spectroscopy. Activation parameters are obtained via VT 1 H NMR and spectral line shape analysis.

We synthesized and characterized the novel olefinic multidentate actor ligand dbap-py. The ligand consists of a 2-methyl pyridine unit and an azepine component fused by an N-alkylation. The coordination chemistry to Rh­(I) centers was explored and dbap-py revealed interesting tridentate chelation (pyridine–amine–olefin), which can suit square planar as well as distorted trigonal bipyramidal coordination spheres in Rh­(I) complexes. Most notably, dbap-py in [Rh­(dbap-py)­(PPh3)­Cl] (3) entails an acidic benzylic methylene moiety, which is readily deprotonated allowing for the formation of the neutral square planar complex [Rh­(dbap-py*)­(PPh3)] (4, the asterisk indicates the deprotonated ligand). As a result, the deprotonation disrupts the aromatic π-system of the pyridine unit in 4 and a C-nucleophilic methine moiety is formed. Complex 4 reacts in tetrahydrofuran solution at ambient temperature rapidly with CO bonds present in CO2 or the NC bond of phenyl isocyanate (Ph-NCO) to give the penta-coordinated rhodium κ1-O carboxylate [Rh­(dbap-COO)­(PPh3)] (5) and the rhodium κ1-N amidate [Rh­(dbap-NCO)­(PPh3)] (6), respectively. Both reactions are characterized by a C–C and Rh–E (E = O (5); N (6)) bond formation under concomitant redistribution of the ligand’s π-system of the pyridine unit (“rearomatization”). To the best of our knowledge, compound 6 gives precedence to Rh­(I) complexes with a κ1-N amidate ligand. Remarkably, metal–ligand cooperation is key to the uptake of Ph-NCO and allows for a convenient access to an amidate ligand motif.

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") πelectron 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, CO 2 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 13 CO 2 indicate reversible C−C and Mn−O bond formation at ambient temperature. Likewise, bonded benzaldehyde is exchanged from the complex under a CO 2 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.