Heterocyclic Tridentate Ligands for Effective Alkyne Metathesis

A library of 29 structurally diverse tripodal ligands sharing a tris(biphenyl)methane scaffold was constructed by Suzuki reactions of the common intermediate 1 and commercial halogenated phenols. Rapid screening was conducted for the ligands using the homometathesis of 4-nitrophenylpropylene as a model reaction, and pyridine ligand CP227 emerged as the optimal ligand. The in situ generated catalyst of CP227 and precatalyst cat-III was highly effective in CHCl3, eliminating the need for toxic CCl4 for 2-component alkyne metathesis catalysts. The catalyst was compatible with substrates bearing aniline, phenol, aldehyde, nitro, pyridine, quinoline, azide, and amide moieties. Various macrocycles were also successfully prepared via ring-closing alkyne metathesis. This study demonstrates the potential of tridentate ligands for alkyne metathesis catalysts with a tailored catalytic performance.