title: Selective Double Carbomagnesiation of Internal Alkynes Catalyzed by Iron-N-Heterocyclic Carbene Complexes: A Convenient Method to Highly Substituted 1,3-Dienyl Magnesium Reagents.
abstract: Controlled multicarbometalation of alkynes has been envisaged as an efficient synthetic method for dienyl and polyenyl metal reagents, but an effective catalyst enabling the transformation has remained elusive. Herein, we report that an iron(II)-N-heterocyclic carbene (NHC) complex (IEt2Me2)2FeCl2 (IEt2Me2 = 1,3-diethyl-4,5-dimethylimidazol-2-ylidene) can serve as a precatalyst for the double carbometalation of internal unsymmetrical alkynes with alkyl Grignard reagents, producing highly substituted 1,3-dienyl magnesium reagents with high regio- and stereoselectivity. Mechanistic studies suggest the involvement of low-coordinate organoiron(II)-NHC species as the in-cycle intermediates. The strong σ-donating nature of IEt2Me2 and its appropriate steric property are thought the key factors endowing the iron-NHC catalyst fine performance.
authors.affiliation: State Key Laboratory of Organometallic Chemistry, Shanghai Institute of Organic Chemistry, Chinese Academy of Sciences , 345 Lingling Road, Shanghai 200032, P. R. China.
authors.forename: Yuesheng
authors.initials: Y
authors.lastname: Liu
authors.affiliation: State Key Laboratory of Organometallic Chemistry, Shanghai Institute of Organic Chemistry, Chinese Academy of Sciences , 345 Lingling Road, Shanghai 200032, P. R. China.
authors.forename: Lijun
authors.initials: L
authors.lastname: Wang
authors.affiliation: State Key Laboratory of Organometallic Chemistry, Shanghai Institute of Organic Chemistry, Chinese Academy of Sciences , 345 Lingling Road, Shanghai 200032, P. R. China.
authors.forename: Liang
authors.initials: L
authors.lastname: Deng