title: Chelating N-heterocyclic carbene-carboranes offer flexible ligand coordination to IrIII, RhIIIand 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]2or [Ru(p-cymene)Cl2]2in 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 thetBu 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.
authors.affiliation: School of Chemistry, University of Leeds, Woodhouse Lane, Leeds, LS2 9JT, UK. c.e.willans@leeds.ac.uk.
authors.forename: Jordan
authors.initials: J
authors.lastname: Holmes
authors.affiliation: School of Chemistry, University of Leeds, Woodhouse Lane, Leeds, LS2 9JT, UK. c.e.willans@leeds.ac.uk.
authors.forename: Christopher M
authors.initials: CM
authors.lastname: Pask
authors.affiliation: School of Chemistry, University of Leeds, Woodhouse Lane, Leeds, LS2 9JT, UK. c.e.willans@leeds.ac.uk.
authors.forename: Charlotte E
authors.initials: CE
authors.lastname: Willans