Site‐Selective C−H Alkenylation of N‐Heteroarenes by Ligand‐Directed Co/Al and Co/Mg Cooperative Catalysis**

Abstract

AbstractWe report herein the design and development of Co/Al and Co/Mg bimetallic catalysts, supported by a phosphine/secondary phosphine oxide (PSPO) bifunctional ligand, for the site‐selective C−H alkenylation of nitrogen‐containing heteroarenes with alkynes. These catalysts enable the alkenylation of pyridine, pyridone, and imidazo[1,2‐a]pyridine derivatives at the C−H site proximal to the Lewis basic nitrogen or oxygen atom, which represents a selectivity profile distinct from that of the previously developed cobalt‐diphosphine/aluminum catalyst. The alkenylated products were obtained in moderate to good yields using various heterocycles and differently substituted internal alkynes. Kinetic isotope effect experiments suggest the irreversibility of the C−H activation step, the relevance of which to the rate‐limiting step depends on the reaction conditions. Density functional theory calculations indicate that ligand‐to‐ligand hydrogen transfer is the common mechanism of C−H activation.