Crystal structures of [l₂-(R_a,S_a,3aR,7aR)-1,3bis(2,7-dicyclohexylnaphthalen-1-yl)octahydro-1Hbenzo[d]imidazolidin-2-ylidene]chlorido(g⁴-1,5-cyclooctadiene)iridium dichloromethane monosolvate and [l₂-(S_a,S_a,3aR,7aR)-1,3-bis(2,7-dicyclohexylnaphthalen-1-yl)octahydro-1H-benzo[d]imidazolidin-2-ylidene]chlorido(g⁴-1,5-cyclooctadiene)iridium

The title compounds, [Ir(C₅₁H₆₄N₂)Cl(C₈H₁₂)].CH₂Cl₂, (I), and [Ir(C₅₁H₆₄N₂)Cl(C₈H₁₂)], (II), represent the first two examples of hexahydrobenzoimidazolebased N-heterocyclic carbene (NHC) iridium complexes. The diastereomeric complexes differing only in their axial chirality, which could be separated via column chromatography, show noticeable differences in their ¹H NMR spectra. Compound (I) crystallizes in the monoclinic system (P2₁) with two independent complexes and two half-occupied dichloromethane molecules in the asymmetric unit, while compound (II) crystallizes in the orthorhombic system (P2₁2₁2₁) with one complex in the asymmetric unit. The fused five-membered N-heterocycles of NHCs show unusually high backbone torsion angles of -34.1 (5) and -30.9 (5)◦ for (I) and -31.5 (7)◦ for (II), but the Ir-C_carbene bond lengths of 2.046 (6) and 2.021 (6) Å for (I) and 2.045 (8) Å for (II) present typical NHC-Ir bond lengths. The solvent molecule in the crystal of (I) was found to be highly disordered and its contribution to the scattering was masked using the solvent-masking routine smtbx.mask in OLEX2 [Dolomanov et al. (2009). J. Appl. Cryst. 42, 339-341]. The solvent contribution is not included in the reported chemical formula and other crystal data.