Dioxomolybdenum(VI) complexes containing N-heterocyclic carbenes

Compound MoO2Cl2(THF)2 reacts with two equivalents of 1,3-dialkyl substituted 4,5-dimethylimidazol-2-ylidenes to give the dioxomolybdenum(VI) complexes MoO2Cl2(LR)2 [R = Me (1), i-Pr (2)]. Treatment of MoO2Cl2(THF)2 with one equivalent of the N-heterocyclic carbenes LMe, Li-Pr and C1Ln-Bu (LMe = 1,3,4,5-tetramethylimidazol-2-ylidene, Li-Pr = 1,3-diisopropyl-4,5-dimethylimidazol-2-ylidene, and C1Ln-Bu = 1,3-dibutyl-4,5-dichloroimidazol-2-ylidene) affords the monocarbene adducts MoO2Cl2(LR) [R = Me (3), i-Pr (4)] and MoO2Cl2(C1Ln-Bu) (5), respectively. Decomposition of complexes 1–5 affords a molybdenum oxychloride anion [Mo2O5Cl4]2− as an imidazolium salt.