Direct synthesis of oxalic acid via oxidative CO coupling mediated by a dinuclear hydroxycarbonylcobalt(III) complex

Abstract

Oxidative coupling of CO is a straightforward and economic benign synthetic route for value-added α-diketone moiety containing C2 or higher carbon compounds in both laboratory and industry, but is still undeveloped to date. In this work, a rare coplanar dinuclear hydroxycarbonylcobalt(III) complex, bearing a Schiff-base macrocyclic equatorial ligand and a μ-κ1(O):κ1(O’)-acetate bridging axial ligand, is synthesized and characterized. The Co(III)-COOH bonds in this complex can be feasibly photocleaved, leading to the formation of oxalic acid. Moreover, the light-promoted catalytic direct production of oxalic acid from CO and H2O using O2 as the oxidant with good selectivity (> 95%) and atom economy at ambient temperature and gas pressure based on this dicobalt(III) complex have been achieved, with a turnover number of 38.5. The 13C-labelling and 18O-labelling experiments confirm that CO and H2O act as the sources of the -COOH groups in the dinuclear hydroxycarbonylcobalt(III) complex and the oxalic acid product.

Redox-Inactive Cation Assisted Direct Productions of Oxalic Acid and Dimethyl Oxalate via Oxidative CO Coupling Catalyzed by Coplanar Dicobalt Complexes

“…Exposure of the previously reported dicobalt(III) complex 1 to 1 atm of CO at 50 °C for 24 h in ethanol yielded an orange paramagnetic complex 2 in 32% isolated yield (Scheme a). The solid-state structure of 2 revealed a coplanar dicobalt complex bearing two axial −COOH ligands on the same side (Figure a).…”

“…Previously, the dinuclear hydroxycarbonylcobalt complex 3 exhibited good photocatalytic performance for the production of oxalic acid via oxidative CO coupling . Herein, the same catalytic reactivity of 2 , which was isostructural to 3 , was tested.…”

“…Previously, the dinuclear hydroxycarbonylcobalt complex 3 exhibited good photocatalytic performance for the production of oxalic acid via oxidative CO coupling. 10 Herein, the same catalytic reactivity of 2, which was isostructural to 3, was tested. Irradiation of 2 in ethanol under N 2 at room temperature using a Xe lamp as the light source resulted in the formation of oxalic acid in moderate yield (41%) in 10 h. When the reaction was conducted under a CO/O 2 (1:1 v/v, 2 atm) atmosphere instead of N 2 at room temperature, the catalytic oxalic acid production was achieved with a turnover number (TON) of 10.5 and 40.3 in a reaction time of 10 and 28 h (Table 2, entries 1 and 2), which were very comparable to the performances of the reaction using 3 as the catalyst (Table 2, entries 3 and 4).…”

“…The complexes 1, 3, and H 2 L were synthesized by literature procedures. 10 Physical Measurements. 1 H NMR spectra were recorded on a Bruker Ascend 400 spectrometer at 298 K, and the chemical shifts were reported in parts per million relative to residual solvent resonances.…”

“…Following this mechanism, recently, we showed the light-induced direct production of oxalic acid via oxidative CO coupling catalyzed by a dinuclear hydroxycarbonylcobalt complex. 10 The hydroxycarbonyl radical, which was formed via photolysis of the Co−COOH bonds, was proposed to be the key intermediate in this catalysis. In the presented research, we report the catalytic production of oxalic acid with significantly enhanced performance by introducing redox-inactive cations (such as Li + , Na + , K + , Mg 2+ , and Ca 2+ ), which are considered to bridge the two axial hydroxycarbonyl groups in the dicobalt complex, into the catalytic system (Scheme 1, pathway c).…”