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

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Abstract
Bimetallic catalytic systems, especially heterogeneous bimetallic catalytic systems, have been shown to be effective catalysts for CO2 hydrogenation as a result of synergistic effects. Here‐in we report the synthesis of bimetallic Ir−Ir, Ir−Sn and a novel five‐membered heteroatomic Ir−Sn tetrazole complex. These complexes were obtained as a result of the heterolysis of P−S bond in the ligands during complexation. These complexes were evaluated for catalytic activity in homogeneous CO2 hydrogenation where they displayed excellent catalytic activity generating formate selectively. The mechanism of action for the Ir−Sn catalysts for CO2 hydrogenation indicates metal−metal bond breakage prior to formation of catalytically active species. However, this metal−metal bond breakage did not result in the decomposition of the catalysts. In addition, these bimetallic complexes were observed to effectively hydrogenate CO2 directly, or hydrogenate bicarbonate ions formed in solution during the catalytic cycle. For Ir−Ir catalyst, only one metal center was found to be directly involved in CO2 hydrogenation with the second iridium center primarily responsible as an electron source
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  • University of Johannesburg

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