Molybdenum and tungsten monoalkoxide pyrrolide (MAP) alkylidene complexes that contain a 2,6-dimesitylphenylimido ligand

Article abstract of DOI:10.1021/om4000693

Molybdenum and tungsten bispyrrolide alkylidene complexes that contain a 2,6-dimesitylphenylimido (NAr) ligand have been prepared, in which the pyrrolide is the parent pyrrolide or 2,5-dimethylpyrrolide. Monoalkoxide pyrrolide (MAP) complexes were prepared through addition of 1 equiv of an alcohol to the bispyrrolide complexes. MAP compounds that contain the parent pyrrolide (NC ₄H₄^-) are pyridine adducts, while those that contain 2,5-dimethylpyrrolide are pyridine free. Molybdenum and tungsten MAP 2,5-dimethylpyrrolide complexes that contain O-t-Bu, OCMe(CF₃) ₂, or O-2,6-Me₂C₆H₃ ligands were found to have approximately equal amounts of syn and anti alkylidene isomers, which allowed a study of the interconversion of the two employing ¹H-¹H EXSY methods. The K_eq values ([syn]/[anti]) are all 2-3 orders of magnitude smaller than those observed for a large number of Mo bisalkoxide imido alkylidene complexes, as a consequence of the destabilization of the syn isomer by the sterically demanding NAr* ligand. The rates of interconversion of syn and anti isomers were found to be 1-2 orders of magnitude faster for W MAP complexes than for Mo MAP complexes.