Zerovalent Triphosphine Ruthenium Complexes for Coupling Carbon Dioxide and Ethylene

The coupling of carbon dioxide and ethylene to generate value-added chemicals has been part of recent fundamental advances to improve sustainability in commercial chemical synthons. A formal zerovalent triphosphine-ligated ruthenium complex, (tBuP­(CH2CH2PEt2)2)­Ru­(κ-S-DMSO)­(C2H4), was found to promote CO2 functionalization, affording products derived from both a 1:1 and 1:2 ethylene to CO2 coupling stoichiometry. The equimolecular coupling reaction selectively afforded a five-membered ruthenium lactone species, (tBuP­(CH2CH2PEt2)2)­Ru­(κ-S-DMSO)­(κ-C,κ-O-CH2CH2CO2), under low CO2 pressure. At higher CO2 pressure, the ruthenium lactone complex activated a second equivalent of CO2, yielding a dimeric methylmalonate ruthenium compound, [(tBuP­(CH2CH2PEt2)2)­Ru­(μ2, κ1-O, κ2-O,O-O2CCHCH3CO2)]2. Both carbon dioxide activation products were characterized by X-ray diffraction. Preliminary mechanistic studies suggest that reversible β-H elimination is a key process in the conversion between the two ruthenium carboxylate species. A rare, formally zerovalent ruthenium coordination compound stabilized only by ethylene and DMSO ligands was also isolated and characterized.