Isomers of Molybdenum Imido Alkylidene N‑Heterocyclic Carbene Complexes

The library of molybdenum imido alkylidene N-heterocyclic carbene (NHC) complexes Mo­(N-G)­(CHCMe₂R¹)­(OTf)₂(NHC) (G = 2,6-Me₂-C₆H₃, 2,6-Cl₂-C₆H₃, 2-CF₃-C₆H₄, 2-tBu-C₆H₄, 2,6-iPr₂-C₆H₃, tBu, adamantyl, 1-phenylcyclohexyl, 1-phenyl-3-methylcyclohexyl) was extended to complexes with unsymmetrical (4i) and chiral (4j) imido ligands. New 1,3-bis­(2,4,6-trimethylphenyl)­imidazol-2-ylidene (IMes, 4b−d, 4f,g, 4i–k), 1,3-biscyclohexylimidazol-2-ylidene (ICy, 4h, 4l−n), and 1,3,4-triphenyl-4,5-dihydro-1H-1,2,4-triazol-5-ylidene (TPT, 4a, 4e, 4o) complexes were synthesized. Substitution of one triflate in the molybdenum imido alkylidene NHC bistriflate compounds with an alkoxide or a phenoxide afforded complexes Mo­(N-G)­(CHCMe₂R¹)­(OTf)­(OR²)­(NHC) (5a–i) and was confirmed to proceed via a selective replacement of one specific triflate. The careful analysis of NMR and single-crystal X-ray data allowed for the determination of solution and solid-state structures. Cis- and trans-OTf isomers of IMes complexes with alkyl-substituted imido ligands, rotamers of TPT-ligated complexes, and syn-/anti-isomers and diastereomers were identified.