Cationic Rh and Ir complexes containing bidentate imidazolylidene– 1,2,3-triazole donor ligands : synthesis and preliminary catalytic studies

Khuong Q. Vuong, Marina G. Timerbulatova, Matthew B. Peterson, Mohan Bhadbhade, Barbara A. Messerle

A series of new cationic Rh(I), Rh(III) and Ir(III) complexes containing hybrid bidentate N-heterocyclic carbene–1,2,3-triazolyl donor of general formulae [Rh(CaT)(COD)]BPh4 (2a–d), [Rh(CaT)(CO)2]BPh4 (3a–d) and [M(CaT)(Cp*)Cl]BPh4 (M = Rh, 4a–d; M = Ir, 5a–c), where CaT = bidentate N-heterocyclic carbene–triazolyl ligands, COD = 1,5-cyclooctadiene and Cp* = 1,2,3,4,5-pentamethylcyclopentadienyl, were synthesised. The imidazolium–1,2,3-triazolyl pre-ligands (1a–c and 1e–i) were readily prepared using the Cu(I) catalysed ‘click reaction’ between phenyl azide or benzyl azides with propargyl functionalised imidazolium salts. The single crystal solid state structures of complexes 2a–d; 3a–b; 4a–d and 5a–b confirm the bidentate coordination of the NHC–1,2,3-triazolyl ligand with the NHC coordinating via the ‘normal’ C2-carbon and the 1,2,3-triazolyl donor coordinating via the N3′ atom to form six membered metallocycles. These complexes are the first examples of Rh and Ir complexes containing the hybrid NHC–1,2,3-triazolyl ligands which exhibit a bidentate coordination mode. A number of these complexes showed limited efficiency as catalysts for the intramolecular hydroamination of 4-pentyn-1-amine to 2-methylpyrroline.