Introducing A Podand Motif to Alkyne Metathesis Catalyst Design: A Highly Active Multidentate Molybdenum(VI) Catalyst that Resists Alkyne Polymerization

摘要

Compared to alkyne metathesis catalysts with monodentate ligands, the high catalytic activity and robustness of 1 can be attributed to two major factors: 1) stronger complexation offered by the multidentate ligand (entropyfavored) in comparison to a monodentate ligand, making the catalyst more robust and elongating its life time; and 2) spatial blocking of one substrate-binding site of the molybdenum alkylidyne complex, completely inhibiting undesired alkyne polymerization, and also greatly minimizing non-productive substrate binding, thus enabling the efficient metathesis of heterocycles that contain donor moieties. The high functional group tolerance, fast reaction rate, and high stability are three great advantages of catalyst 1. More importantly, the strategy of utilizing multidentate ligands opens many new possibilities for the design of highly efficient, robust alkyne metathesis catalysts. Currently, the structure-activity relationship of this novel class of catalysts and their synthetic applications toward well-defined molecular architectures are being investigated in our laboratories and will be reported in due course.