Synthetic and Structural Peculiarities in Molybdenum(VI) Nitrido N-Heterocyclic Carbene Complexes

Abstract

The synthesis of molybdenum(VI) nitrido N-heterocyclic carbene (NHC) complexes bearing alkoxide and siloxide ligands, respectively, is reported. The molybdenum nitrido trisalkoxide precursor Mo(≡N)(OC(CF₃)₂(CH₃))₃ is reacted with the NHCs 1,3-diisopropylimidazol-2-ylidene (IiPr), 1,3-dimethylimidazol-2-ylidene (IMe), and 1,3-dicyclohexylimidazol-2-ylidene (ICy), respectively, to yield the corresponding molybdenum nitrido trisalkoxide NHC complexes. Further salt metathesis allows to replace the alkoxide ligands by the thermally more robust siloxide ligands. In case an asymmetric NHC, i.e., 1-butyl-3-methylimidazol-2-ylidene, is reacted with the trisalkoxide precursor, a mixture of two isomers of the corresponding product is observed; these two isomers interconvert to some extent at elevated temperature. Selected complexes are subjected to single-crystal X-ray analysis. The molybdenum nitrido NHC complexes show moderate activity in alkyne cross-metathesis.