Reductive functionalization of CO2 under mild reaction conditions for the catalytic synthesis of N-formamides by Mannich base based Cobalt (III) complex

Abstract

Reductive functionalization of carbon dioxide is an important approach which not only reduces CO2 concentration but also functionalized it for the formation of value added chemicals. In this perspective, a hexadentate mononuclear cobalt (III) complex [CoIIIL] of Mannich base ligand (H4L) was synthesized and structurally characterized by single crystal X-ray diffraction. The electronic spectra of the complex showed two bands at 448 and 561 nm corresponds to the LMCT and d-d transitions respectively. The derived inexpensive [CoIIIL] complex was very much effective as catalyst in carbon dioxide functionalization reaction. The catalytic synthesis of mono selective N-formamide product from amines was produced through diagonal transformation of carbon dioxide in presence of polymethylhydrosiloxane (PMHS) as reducing agent and [CoIIIL] complex as catalyst. The effects of various reaction parameters were examined. Broad range of substrates (aromatic as well as aliphatic amines) smoothly produced good percentage of respective N-formamides product (72–94%) under mild reaction condition utilizing 1 atmospheric CO2. The high TON (1540–2000) and TOF value (192.5–400.0 h−1) for the catalytic reactions strongly depicted the productive nature of the [CoIII(L)] catalyst. The probable mechanestics studies clearly reveals that the [CoIIIL] complex activated the Si−H bond of PMHS to react with carbon dioxide in order to form the silyl formates intermediate for activation of N–H bonds in amines, thus leading to the excellent performance of the catalytic reaction.