Binuclear Fused 5-membered Palladacycle and Palladium Complex of Amido-Functionalized N-heterocyclic Carbene Precatalysts for the One-Pot Tandem Hiyama Alkynylation/Cyclization Reactions

Abstract

A binuclear fused 5-membered palladacycle (2) and a palladium complex of amido-functionalized N-heterocyclic carbene (6) successfully performed the Csp2−Csp type Hiyama coupling followed by cyclization giving the biologically important benzofuran compounds in a convenient time economic method involving one-pot tandem reaction between 2-iodophenol and triethoxysilylalkynes. The aromatic triethoxysilylalkyne substrates exhibited higher yields than the aliphatic triethoxysilylalkyne substrates for both of the palladium complexes 2 (ca. 19−48%) and 6 (ca. 11−34%). The binuclear fused 5-membered palladacycle (2) was readily synthesized by the nucleophilic addition of 2-amino-pyridine on the cis-{(2,4,6-(CH3)3C6H2)NC}2PdCl2 in good yield (ca. 74%) and the palladium complex of amido-functionalized N-heterocyclic carbene (6) was synthesized by transmetallation route from the silver complex (5) with (COD)PdCl2 in CH3CN under reflux condition in ca. 38% of yield.