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

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]BPh ₄ (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.