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

摘要

The reaction of triethylborane adduct of N-heterocyclic carbene, NHC (.) BEt3, (NHC = I'Pr = 1,3-diisopropylimidazol-2-ylidene (I'Pr (.) 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(eta(3)-allyl) {eta(2)- (NPh)(2)CH}(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(eta(3)-allyl){eta(2)-(NPh)(2)CH}(CO)(2)(NHC)] (M=Mo, NHC = I'Pr; 3a-Mo, M = Mo, NHC = IMes; 3b-Mo, M = W, NHC = I'Pr; 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 1,2dimethoxyethane (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 degrees 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. (c) 2005 Elsevier B.V. All rights reserved.