Chelating N-heterocyclic carbene–carboranes offer flexible ligand coordination to IrIII, RhIII and RuII: effect of ligand cyclometallation in catalytic transfer hydrogenation. Issue 40 (21st July 2016)

• Record Type: Journal Article
• Authors: Holmes, Jordan; Pask, Christopher M.; Willans, Charlotte E.
• Is Part Of: Dalton transactions. Volume 45:Issue 40(2016)
• Page Start: 15818
• Page End: 15827
• Publication Date: 2016-07-21
• Subjects: Chemistry, Inorganic -- Periodicals; Chemistry, Physical and theoretical -- Periodicals; Chemistry, Inorganic -- Periodicals; 546.05
• DOI: 10.1039/c6dt02079h
• Languages: English
• ISSNs: 1477-9226

Abstract

Abstract : NHC–carborane ligands, with flexible coordination through either the carbon or the boron atom of the carborane, provide effective transfer hydrogenation catalysts. 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 Ag2 O 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- t Bu substituent, C–H activation of the t Bu 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.