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π-Extended DPCB for Activation-Free Homogeneous Gold Catalysis

Authors

  • Prof. Shigekazu Ito,

    Corresponding author
    1. Department of Applied Chemistry, Graduate School of Science and Engineering, Tokyo Institute of Technology, 2-12-1 Ookayama, Meguro, Tokyo 152-8552 (Japan), Fax: (+81) 3-5734-2143
    • Department of Applied Chemistry, Graduate School of Science and Engineering, Tokyo Institute of Technology, 2-12-1 Ookayama, Meguro, Tokyo 152-8552 (Japan), Fax: (+81) 3-5734-2143

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  • Masaki Nanko,

    1. Department of Applied Chemistry, Graduate School of Science and Engineering, Tokyo Institute of Technology, 2-12-1 Ookayama, Meguro, Tokyo 152-8552 (Japan), Fax: (+81) 3-5734-2143
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  • Prof. Koichi Mikami

    1. Department of Applied Chemistry, Graduate School of Science and Engineering, Tokyo Institute of Technology, 2-12-1 Ookayama, Meguro, Tokyo 152-8552 (Japan), Fax: (+81) 3-5734-2143
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  • DCPB=3,4-bis(2,4,6-tri-tert-butylphenyl)-3,4-diphosphinidenecyclobutene

Abstract

The catalytic properties of bis[chlorogold(I)] complexes that bear the 3,4-bis(2,4,6-tri-tert-butylphenyl)-3,4-diphosphinidenecyclobutene (DPCB) ligand could be improved by suitable extension of the π-conjugation. If the 1-naphthyl substituent was employed in the 1,2-positions in the kinetically stabilized DPCB skeleton, high catalytic activity of the DPCB-bis(chlorogold) complex was induced in the intermolecular alkoxycyclization of 1,6-enyne without activation by a Ag cocatalyst. DFT calculations of the 1,2-diaryl-substituted DPCB derivatives indicated that both suitable energetic reduction of the LUMO level and steric characteristics of the ligand structure are important for the high catalytic activity. The optimized 1-naphthyl-substituted DPCB-chlorogold(I) complex was further employed for catalytic intramolecular cyclizations to afford heterocyclic structures by the activation of terminal acetylene and allene moieties and the hydration of terminal acetylene under the mild conditions.

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