Phosphine free diamino-diol based palladium catalysts and their application in Suzuki–Miyaura cross-coupling reactions

Abstract

Inexpensive air and moisture stable diamino-diol ligands [(2-OH-C10H6)CH2(μ-NC4H8N)CH2(C10H6-2-OH)] (1) and [(5-tBuC6H3-2-OH)CH2(μ-NC4H8N)CH2(5-tBuC6H3-2-OH)] (2) were synthesized by reacting corresponding alcohols with formaldehyde and piperazine. Treatment of ligands 1 and 2 with Pd(OAc)2 in 1:1 molar ratio afforded neutral palladium complexes [Pd{(OC10H6)CH2(μ-NC4H8N)CH2(C10H6O)}] (3) and [Pd{(5-tBuC6H3-2-O)CH2(μ-NC4H8N)CH2(5-tBuC6H3-2-O)}] (4) in good yield. The palladium complexes 3 and 4 are employed in Suzuki–Miyaura cross-coupling reactions between phenylboronic acid and several aryl chlorides or bromides. They are found to be competent homogeneous catalysts for a variety of substrates to afford the coupled products in good to excellent yields. The crystal structures of compounds 2 and 4 are also reported.