Reactivity of CO₂ Activated on Transition Metals and Sulfur Ligands

Abstract

Dicationic dicarbonyl [Ru(bpy)2(CO)2](2+) (bpy = 2,2'- bipyridyl) exists as equilibrium mixtures with [Ru(bpy)2(CO)(COOH)](+) and [Ru(bpy)2(CO)(CO2)](0) depending on the pH in H2O. Those three complexes work as the precursors to CO, HCOOH production, and CO2 carrier, respectively, in electro- and photochemical CO2 reduction in aqueous solutions. However, [Ru(bpy)2(CO)2](2+) loses the catalytic activity toward CO2 reduction under aprotic conditions because [Ru(bpy)2(CO)2](2+) is not regenerated from [Ru(bpy)2(CO)(CO2)](0) in the absence of proton sources. Analogous monocarbonylruthenium complexes such as [Ru(tpy)(bpy)(CO)](2+) and [Ru(bpy)2(qu)(CO)](2+) catalyze CO2 reduction in the absence and presence of proton sources. Both complexes are reproduced through oxide transfer from the corresponding Ru-CO2 to CO2 in CO2 reduction and produce the same amount of CO and CO3(2-) in the absence of proton donors. The reduction of CO2 catalyzed by polypyridylrhenium complexes in the presence of proton sources takes place via essentially the similar mechanism as that in the case of ruthenium complexes. On the other hand, CO evolution in CO2 reduction under aprotic conditions is ascribed to the dissociation of CO from a dimeric Re-C(O)OC(O)O-Re scaffold. Visible-light irradiation to a catalytic system composed of [Ru(bpy)2(CO)2](2+)/[Ru(bpy)3](2+)/Me2NH2(+)/Me2NH as the catalyst, photosensitizer, proton donor, and nucleophile in addition to the electron donor, respectively, in CO2-saturated CH3CN selectively produces N,N-dimethylformamide without concomitant CO and HCOOH formation. Structurally robust μ3-S of reduced metal-sulfur clusters provides a suitable site for reductive activation of CO2 with retention of the framework. Indeed, CO2 activated on μ3-S of [Fe6Mo2S8(SEt)3](5-) is fixed at the carbonyl carbon of thioesters trapped on a neighboring iron of the cluster, and α-keto acids are produced catalytically. Furthermore, two-electron reduction of [(CpMen)3M3S3](2+) (n = 1, M = Co; n = 5, M = Rh, Ir) creates the catalytic ability to produce oxalate through the coupling of two CO2 molecules possibly activated on μ3-S and a metal ion.

Reaction of CO2 with Atomic Transition Metal M+/0/– Ions: A Theoretical Study

“…Transition-metal atom, ion, metal clusters as well as metallic oxides that could convert this gas into valuable chemicals have attracted much attention. − In particular, metal ions, serving as a prototypical model of heterogeneous catalysis, with CO 2 have been studied extensively. − Bohme and co-workers reported detailed results of the transition-metal ions react with CO 2 in the gas-phase. They found that only nine transition-metal ions can get O from CO 2 at room temperature, with lots of heat released, but others can only form M + (CO 2 ) complexes.…”

Cis-Bis(2,2′-Azopyridinido)dicarbonylruthenium(II)

“…Meanwhile, two carbonyl stretching frequencies in the newly prepared dicarbonyl complex were observed at 2060 and 1995 cm −1 in the IR spectra (Figure S1). These values are 30-40 cm −1 lower than those of similar Ru complexes ([Ru(N-N) 2 (CO) 2 ] 2+ ; N-N = bidentate pyridyl ligands) [11][12][13]. The reason is that the reduction of the azo moiety increases the electron density of the complex, resulting in a red shift of the CO bands [5].…”

Coordination Chemistry of Ru(II) Complexes of an Asymmetric Bipyridine Analogue: Synergistic Effects of Supporting Ligand and Coordination Geometry on Reactivities

“…Bipyridine analogues function not only as supporting ligands for stabilizing metal complexes, but also as electron pool sites. For example, in addition to catalysts for the production of useful resources, such as in multi-electron reductions of carbon dioxide and water-gas shift reactions [4][5][6][7][8][9][10][11], bipyridine analogues are also utilized as photosensitizers [12] and phosphorescence materials [13]. A variety of studies that imparted selectivity to various reactions by strictly controlling the coordination sphere have been reported for many ruthenium complexes.…”