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, C₁₁H₁₄N₃ ⁺·Br^- (<b>2</b>), 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(C₈H₁₂)(C₁₁H₁₃N₃)] (<b>3</b>), (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(C₈H₁₂)(C₁₁H₁₃N₃)(C₁₈H₁₅P)]BF₄ (<b>5</b>), 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(C₈H₁₂)(C₁₁H₁₃N₃)(C₁₈H₃₃P)]BF₄·1.5CH₂Cl₂ (<b>6</b>), are presented. Complexes <b>2</b> and <b>6</b> crystallize in the monoclinic space group <i>P</i>2₁/<i>c</i>, complex <b>3</b> in the triclinic space group <i>P</i>1 and complex <b>5</b> in the triclinic space group <i>P</i>1 with two mol-ecules in the asymmetric unit. The three metal complexes <b>3</b>, <b>5</b>, and <b>6</b> have a distorted square-planar geometry around the metal ions. The N1-C1-N3 bond angle in the triazolium salt <b>2</b> is 107.1 (2)° and is observed in the range of 102.2 (3) to 103.8 (5)° in the NHC ligands in complexes <b>3</b>, <b>5</b>, and <b>6</b>. The two substituent 'wing tips' in the NHC ligand (N-ethyl and N-benz-yl) are oriented in an <i>anti</i>-arrangement in compounds <b>2</b> and <b>3</b>, a <i>syn</i>-arrangement in compound <b>6</b>, and both <i>syn</i> and <i>anti</i>-arrangements in the two independent ion pairs in compound <b>5</b>. All structures exhibit non-classical hydrogen-bonding inter-actions with the most acidic hydrogen atoms in complexes <b>2</b> and <b>3</b> playing critical roles in the orientations of structural units.