Ir−Sn Tetrazole Complexes with Proton‐Responsive P−OH Groups and an Ir−Ir Tetrazole Complex for CO₂ Hydrogenation

Abstract

We dedicate this work to the memory of Novisi K. Oklu.Bimetallic catalytic systems, especially heterogeneous bimetallic catalytic systems, have been shown to be effective catalysts for CO 2 hydrogenation as a result of synergistic effects. Here-in we report the synthesis of bimetallic IrÀ Ir, IrÀ Sn and a novel fivemembered heteroatomic IrÀ Sn tetrazole complex. These complexes were obtained as a result of the heterolysis of PÀ S bond in the ligands during complexation. These complexes were evaluated for catalytic activity in homogeneous CO 2 hydrogenation where they displayed excellent catalytic activity generating formate selectively. The mechanism of action for the IrÀ Sn catalysts for CO 2 hydrogenation indicates metalÀ metal bond breakage prior to formation of catalytically active species. However, this metalÀ metal bond breakage did not result in the decomposition of the catalysts. In addition, these bimetallic complexes were observed to effectively hydrogenate CO 2 directly, or hydrogenate bicarbonate ions formed in solution during the catalytic cycle. For IrÀ Ir catalyst, only one metal center was found to be directly involved in CO 2 hydrogenation with the second iridium center primarily responsible as an electron source [a

Metal–Ligand Cooperation in Cp*Ir-Pyridylpyrrole Complexes: Rational Design and Catalytic Activity in Formic Acid Dehydrogenation and CO2 Hydrogenation under Ambient Conditions

“…Obviously, the hydrogenation of CO 2 in basic aqueous solution is more feasible thermodynamically. However, in most cases of CO 2 hydrogenation, harsh conditions including high temperature, high pressure, and the use of organic solvents as well as catalyst are still required. , Although homogeneous catalysts based on Ru, − Ir, − Co, − Fe, − and so on , have been extensively investigated, reports of metal complexes under ambient conditions are still quite rare. For example, for Cp*Ir complexes (Scheme ), [Cp*Ir­(4-(1 H -pyrazol-1-yl-κN 2 )­benzoic acid-κC 3 )­(H 2 O)] 2 ­SO 4 reported by Fukuzumi and [Cp*Ir­(dhbp)­(H 2 O)]­SO 4 (dhbp = 4,4′-di­hydroxy-2,2′-bipyridine) reported by Fujita achieved respective 6.8 and 70 h –1 TOFs for CO 2 hydrogenation to produce formate under atmospheric pressure (CO 2 /H 2 = 0.05 MPa/0.05 MPa) at 25 °C.…”