Ligand assisted cleavage of H2 across a Ru−N Bond within a four-membered metallacycle and the catalytic hydrogenation of CO2 to formate

Abstract

The catalytic hydrogenation of CO₂ to formate was achieved using the previously reported dichloro(η⁶-p-cymene){diphenyl(3-methyl-2-indolyl)phosphine}ruthenium (1) as a catalyst under mild conditions. In this complex, the phosphorus-based ligand adopts a κ¹-P coordination mode. The catalytic activity was achieved in the presence of DBU as a base providing a TON_max value of 3,800. In order to explore potential transformations occurring within the catalytic reactions, a series of stoichiometric tests were performed. Complex 1 was reacted with DBU to form chloro(η⁶-p-cymene){diphenyl(3-methyl-2-indolide)phosphine}ruthenium (2). Structural characterization of complex 2 confirmed a κ²-P,N coordination mode for the ligand resulting in a four membered metallacycle. Reaction of 2 with H₂ led to the formation of hydrochloro(η⁶-p-cymene){diphenyl(3-methyl-indolyl)phosphine}ruthenium (3), albeit not with a clean conversion. This is the product resulting from the formal addition of hydrogen across the Ru−N bond of the metallacycle. Complex 3 was also synthesized via an alternative route involving the reaction of complex 1 with Me₂NH • BH₃ as a means of converting Ru−Cl to Ru−H

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Identifiers

ORCID for Graham J. Tizzard: orcid.org/0000-0002-1577-5779

ORCID for Simon J. Coles: orcid.org/0000-0001-8414-9272

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