Issue 44, 2019

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

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

Supplementary files

Article information

Article type
Paper
Submitted
02 août 2019
Accepted
20 sept. 2019
First published
20 sept. 2019

Dalton Trans., 2019,48, 16569-16577

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, 48, 16569 DOI: 10.1039/C9DT03143J

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