The reaction of amidinato(pyridine) complexes of molybdenum and tungsten with triethylborane adduct of N-heterocyclic carbene (NHC · BEt3): Investigation on the reactivity of NHC · BEt3 as carbene precursor toward transition metal complexes

The reaction of triethylborane adduct of N-heterocyclic carbene, NHC · BEt3, (NHC = IiPr = 1,3-diisopropylimidazol-2-ylidene (IiPr · BEt3; 1a), NHC = IMes = 1,3-dimesitylimidazol-2-ylidene (IMes · BEt3; 1b)), which was prepared by the reaction of the corresponding imidazolium salt with one equivalent of LiBEt3H, with amidinato(pyridine) complex, [M(η3-allyl){η2-(NPh)2CH}(CO)2(NC5H5)] (M = Mo; 2-Mo M = W; 2-W), was investigated. The reaction of compound 1 with complex 2 under toluene-reflux conditions resulted in the formation of carbene complex [M(η3-allyl){η2-(NPh)2CH}(CO)2(NHC)] (M = Mo, NHC = IiPr; 3a-Mo, M = Mo, NHC = IMes; 3b-Mo, M = W, NHC = IiPr; 3a-W, M = W, NHC = IMes; 3b-W). These complexes were characterized spectroscopically as well as by X-ray analyses. Complex 3a-Mo was formed in various solvents such as 1,2-dimethoxyethane (DME), 1,2-dichloroethane, and acetonitrile under refluxing conditions for 3 h. In toluene, 3a-Mo was obtained in a good yield by heating at 70 °C for only 20 min. Employment of NHC · BEt3 (1) was found to afford convenient route for the introduction of the carbene ligand to the transition metal complexes.