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Phosphine-free ruthenium NCN-ligand complexes and their use in catalytic CO2 hydrogenation

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Abstract

This work investigates the hydrogenation of carbon dioxide to formate catalysed by the phosphine-free Ru complexes Ru(OtBu)(κ3-NCN)(tBubpy) and RuH(OtBu)(κ2-NCN)(tBubpy) (OtBu = tert-butoxide, κ2-NCN = 1,3-di(2-methylpyridyl)-4,5-diphenyl-1H-imidazol-2-ylidene, where one pyridyl moiety is not coordinated to Ru, tBubpy = 4,4′-di-tert-butyl-2,2′-dipyridyl). A catalytic cycle is proposed for this reaction, supported by computational studies and the characterization of the hydride and the formate intermediates proposed to be involved. Modest catalytic turnovers are demonstrated at relatively low pressures and temperatures. The proposed rate determining step is heterolytic H2 splitting to regenerate the Ru–H complex, which has an estimated hydricity of approx. 27 kcal mol−1. The κ2-NCN ligand in the hydride complex undergoes a variety of dynamic processes as detected by EXSY spectroscopy including a pyridyl “roll-over” carbon–hydrogen – ruthenium hydride exchange, possibly occuring via a Perutz–Sabo-Etienne CAM mechanism.

Graphical abstract: Phosphine-free ruthenium NCN-ligand complexes and their use in catalytic CO2 hydrogenation

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Publication details

The article was received on 02 Aug 2019, accepted on 20 Sep 2019 and first published on 20 Sep 2019


Article type: Paper
DOI: 10.1039/C9DT03143J
Dalton Trans., 2019, Advance Article

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    Phosphine-free ruthenium NCN-ligand complexes and their use in catalytic CO2 hydrogenation

    M. M. H. Sung, D. E. Prokopchuk and R. H. Morris, Dalton Trans., 2019, Advance Article , DOI: 10.1039/C9DT03143J

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