Syntheses and crystal structures of 4-benzyl-1-ethyl-1,2,4-triazolium bromide and its corresponding NHC complexes of rhodium and iridium.

The syntheses and crystal structures of a triazolium salt, 4-benzyl-1-ethyl-1,2,4-triazolium bromide, C(11)H(14)N(3) (+)·Br(-) (2), and the corresponding N-heterocyclic carbene complexes, (4-benzyl-1-ethyl-1,2,4-triazol-5-yl-idene)chlorido-[(1,2,5,6-η)-cyclo-octa-1,5-diene]rhodium(I), [RhCl(C(8)H(12))(C(11)H(13)N(3))] (3), (4-benzyl-1-ethyl-1,2,4-triazol-5-yl-idene)[(1,2,5,6-η)-cyclo-octa-1,5-diene](tri-phenyl-phosphane)iridium(I) tetra-fluorido-borate, [Ir(C(8)H(12))(C(11)H(13)N(3))(C(18)H(15)P)]BF(4) (5), and (4-benzyl-1-ethyl-1,2,4-triazol-5-yl-idene)[(1,2,5,6-η)-cyclo-octa-1,5-diene](tri-cyclo-hexyl-phosphane)iridium(I) tetra-fluorido-borate dicholoro-methane sesquisolvate, [Ir(C(8)H(12))(C(11)H(13)N(3))(C(18)H(33)P)]BF(4)·1.5CH(2)Cl(2) (6), are presented. Complexes 2 and 6 crystallize in the monoclinic space group P2(1)/c, complex 3 in the triclinic space group P1 and complex 5 in the triclinic space group P1 with two mol-ecules in the asymmetric unit. The three metal complexes 3, 5, and 6 have a distorted square-planar geometry around the metal ions. The N1-C1-N3 bond angle in the triazolium salt 2 is 107.1†(2)° and is observed in the range of 102.2†(3) to 103.8†(5)° in the NHC ligands in complexes 3, 5, and 6. The two substituent 'wing tips' in the NHC ligand (N-ethyl and N-benz-yl) are oriented in an anti-arrangement in compounds 2 and 3, a syn-arrangement in compound 6, and both syn and anti-arrangements in the two independent ion pairs in compound 5. All structures exhibit non-classical hydrogen-bonding inter-actions with the most acidic hydrogen atoms in complexes 2 and 3 playing critical roles in the orientations of structural units.