Selective Reduction of CO₂ to a Tantalum Formate Complex and Release of Methyl Formate from the Tantalum(V) Center

Abstract

A cyclometalated NHC-coordinated hydrido tantalum alkoxide was found to selectively react with CO 2 to afford the genuine tantalum formate (NHC)(HCOO)Ta(OR F ) 3 with OR F = OC-(CF 3 ) 2 CH 3 . In the solid state, the presence of a κ 2 -O,O-formate moiety was established by single-crystal X-ray diffraction and ATR-IR spectroscopy, while NMR experiments and DFT modeling studies suggest that the κ 1 -O-coordination mode is preferred in solution. Despite the accessibility of the latter κ 1 -O-formate in solution, no overreduction to a dinuclear methylene diolate was observed. Upon treatment with MeOTf, the κ 1 -O-formate was methylated selectively, which led to the formation of a tantalum triflate complex along with methyl formate. This is a rare example in which a value-added oxygencontaining organic product (here HCOOMe) is released from an oxophilic early transition metal (here Ta V ).

CO2 cleavage by tantalum/M (M = iridium, osmium) heterobimetallic complexes

“…Complex 2 , along with its Ta–Ir analogue, 1 , exhibit clean CO 2 cleavage reactivity, driven by the formation of a tantalum oxo species in conjunction with late metal carbonyls. Given the propensity of related transition metal alkyls and hydrides for CO 2 insertion, 55–59 the selective, divergent bimetallic reactivity observed herein is notable. These results clearly further demonstrate how the synergistic action of early/late metal assemblies – particularly those based on tantalum – can facilitate the deoxygenation of CO 2 .…”

Research Progress on Carbon Dioxide Reduction Coupled with the Formation of C−O Bonds to Oxygenated Compounds

“…[41][42][43][44][45][46] At present, the hydrogenation of carbon dioxide to alkyl formate is highly desirable, which can combine with molecular hydrogen to convert CO 2 into highvalue chemicals. [47][48][49] The initial idea of the reaction is to hydrogenate carbon dioxide to formic acid, but it is necessary to add base (1) and esterify with alcohol or directly esterify (2) to form alkyl formate due to the reaction is thermodynamically challenging, as shown in Figure 2. [50][51][52][53]…”