title: Synthesis and structures of gold and copper carbene intermediates in catalytic amination of alkynes.
abstract: Metal carbenes are often proposed as reactive intermediates in the late transition metal-catalysed transformations of alkynes. Owing to their high reactivity, however, isolation and structural characterization of metal carbene intermediates in these transformations has remained unknown. Herein, we report the isolation of two acyclic gold and copper carbene intermediates in either Au(I)- or Cu(I)-catalysed cyclization of N-alkynyl formamidines through five-exo-dig cyclization. X-ray diffraction,13C NMR spectra data and computational analyses provide evidence for the formation of a gold carbene intermediate with a carbocation-like electronic character. Using the intrinsic bond orbital (IBO) approach, we also evaluate the π-stabilizing effects of organic substituents at the carbene carbon atom in the gold carbene intermediate. Another rare six-membered copper carbene complex is also obtained through 6-endo-dig cyclization. These metal carbenes have proven reactive toward oxidation. The metal-promoted cyclization of N-alkynyl formamidine provides a facile approach to synthesize metal carbene species.
authors.affiliation: Key Laboratory for Advanced Materials and Institute of Fine Chemicals, School of Chemistry &Molecular Engineering, East China University of Science and Technology, 130 Mei Long Road, Shanghai 200237, China.
authors.forename: Jiwei
authors.initials: J
authors.lastname: Wang
authors.affiliation: Center for Computational Chemistry and Research Institute of Industrial Catalysis, School of Chemistry &Molecular Engineering, East China University of Science and Technology, 130 Mei Long Road, Shanghai 200237, China.
authors.forename: Xiaoming
authors.initials: X
authors.lastname: Cao
authors.affiliation: Key Laboratory for Advanced Materials and Institute of Fine Chemicals, School of Chemistry &Molecular Engineering, East China University of Science and Technology, 130 Mei Long Road, Shanghai 200237, China.
authors.forename: Shichang
authors.initials: S
authors.lastname: Lv
authors.affiliation: Key Laboratory for Advanced Materials and Institute of Fine Chemicals, School of Chemistry &Molecular Engineering, East China University of Science and Technology, 130 Mei Long Road, Shanghai 200237, China.
authors.forename: Caiyun
authors.initials: C
authors.lastname: Zhang
authors.affiliation: Key Laboratory for Advanced Materials and Institute of Fine Chemicals, School of Chemistry &Molecular Engineering, East China University of Science and Technology, 130 Mei Long Road, Shanghai 200237, China.
authors.forename: Sheng
authors.initials: S
authors.lastname: Xu
authors.affiliation: Key Laboratory for Advanced Materials and Institute of Fine Chemicals, School of Chemistry &Molecular Engineering, East China University of Science and Technology, 130 Mei Long Road, Shanghai 200237, China.|State Key Laboratory of Organometallic Chemistry, Shanghai Institute of Organic Chemistry, Chinese Academy of Sciences, 354 Fenglin Road, Shanghai 200032, China.
authors.forename: Min
authors.initials: M
authors.lastname: Shi
authors.affiliation: Key Laboratory for Advanced Materials and Institute of Fine Chemicals, School of Chemistry &Molecular Engineering, East China University of Science and Technology, 130 Mei Long Road, Shanghai 200237, China.
authors.forename: Jun
authors.initials: J
authors.lastname: Zhang