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 <b>1</b> and commercial halogenated phenols. Rapid screening was conducted for the ligands using the homometathesis of 4-nitrophenylpropylene as a model reaction, and pyridine ligand <b>CP227</b> emerged as the optimal ligand. The <i>in situ</i> generated catalyst of <b>CP227</b> and precatalyst <b>cat-III</b> 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.