Issue 40, 2016

Chelating N-heterocyclic carbene–carboranes offer flexible ligand coordination to IrIII, RhIII and RuII: effect of ligand cyclometallation in catalytic transfer hydrogenation

Abstract

Imidazolium salts linked by an ethyl tether to closo-dicarbadodecaboranes were reacted with [IrCp*Cl2]2, [RhCp*Cl2]2 or [Ru(p-cymene)Cl2]2 in the presence of Ag2O to prepare complexes of the type [MCp*(NHC)Cl2] (M = Ir, Rh; NHC = N-heterocyclic carbene) or [Ru(p-cymene)(NHC)Cl2]. When the NHC contained an N-tBu substituent, C–H activation of the tBu and subsequent alkyl coordination was observed at Ir. Coordination of the closo-dicarbadodecaborane moiety to Ir was possible to give 7-membered metallacycles, coordinated through the carbenic carbon of the NHC and either a carbon atom or a boron atom of the carborane. Examination of the Ir complexes in the transfer hydrogenation of acetophenone to 1-phenylethanol reveals that cyclometallation of the carborane moiety is important for catalytic efficacy, indicating a bifunctional mechanism and involvement of the dicarbadodecaborane anion.

Graphical abstract: Chelating N-heterocyclic carbene–carboranes offer flexible ligand coordination to IrIII, RhIII and RuII: effect of ligand cyclometallation in catalytic transfer hydrogenation

Supplementary files

Article information

Article type
Paper
Submitted
24 may. 2016
Accepted
09 jul. 2016
First published
21 jul. 2016

Dalton Trans., 2016,45, 15818-15827

Author version available

Chelating N-heterocyclic carbene–carboranes offer flexible ligand coordination to IrIII, RhIII and RuII: effect of ligand cyclometallation in catalytic transfer hydrogenation

J. Holmes, C. M. Pask and C. E. Willans, Dalton Trans., 2016, 45, 15818 DOI: 10.1039/C6DT02079H

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