Highly Active Ruthenium CNC Pincer Photocatalysts for Visible-Light-Driven Carbon Dioxide Reduction

Abstract

Five ruthenium catalysts described herein facilitate self-sensitized carbon dioxide reduction to form carbon monoxide with a ruthenium catalytic center. These catalysts include four new and one previously reported CNC pincer complexes featuring a pyridinol derived N-donor and N-heterocyclic carbene (NHC) C-donors derived from imidazole or benzimidazole. The complexes have been characterized fully by spectroscopic and analytic methods, including X-ray crystallography. Introduction of a 2,2′-bipyridine (bipy) coligand and phenyl groups on the NHC ligand was necessary for rapid catalysis. [(CNC)­Ru­(bipy)­(CH3CN)]­(OTf)2 is among the most active and durable photocatalysts in the literature for CO2 reduction without an external photosensitizer. The role of the structure of this complex in catalysis is discussed, including the importance of the pincer’s phenyl wingtips, the bipyridyl ligand, and a weakly coordinating monodentate ligand.

Transition Metal Complexes Supported by N‐Heterocyclic Carbene‐Based Pincer Platforms: Synthesis, Reactivity and Applications

“…A series of structurally similar Ru pincers 22 – 24 have also been reported (Scheme 10). [21] Complex 22 , which can be viewed as a homolog of 19 , was accessed via metalation with Ru II precursors. In contrast, 23 can only be synthesized by treating 21 with a Ru IV precursor followed by reducing with zinc.…”

The Stronger the Better: Donor Substituents Push Catalytic Activity of Molecular Chromium Olefin Polymerization Catalysts

“…Para-substituted pyridines with increased basicity are used as ligands or as part of a more complex ligand structure in catalytically active metal complexes. [25][26][27][28][29][30][31][32][33][34] Depending on the catalysed reaction the increased donor ability of the pyridine can have a significant influence on the catalytic behaviour of these complexes and in some cases catalytic activity is increased. [25][26]31,34] The effect of the basicity of aromatic N-donors on the catalytic behaviour of corresponding chromium polymerisation catalysts has not yet been investigated systematically.…”

“…Para ‐substituted pyridines with increased basicity are used as ligands or as part of a more complex ligand structure in catalytically active metal complexes. [ 25 , 26 , 27 , 28 , 29 , 30 , 31 , 32 , 33 , 34 ] Depending on the catalysed reaction the increased donor ability of the pyridine can have a significant influence on the catalytic behaviour of these complexes and in some cases catalytic activity is increased. [ 25 , 26 , 31 , 34 ]…”

Photocatalytic CO2 Reduction under Visible‐Light Irradiation by Ruthenium CNC Pincer Complexes

“…The use of this complex for the photocatalytic CO 2 reduction in CH 3 CN with photosensitizer [Ir(ppy) 3 ] resulted in selective production of CO (TON CO =227; selectivity 97 %), but in DMF with photosensitizer [Ru(bpy) 3 ] 2+ production of formate was dominant (TON HCOOH =143; selectivity 90 %). More recently, replacing the imidazole with a benzimidazole moiety and coordination of a bpy ligand led to formation of CO (TON CO =55) without photosensitizer . Interestingly, the low loading of the catalyst (1.0 n m ) afforded TON CO =33 000.…”