Heteroleptic Palladium(II) Complexes of Thiazolinyl‐picolinamide Derived N∩N∩N Pincer Ligand: An Efficient Catalyst for Acylative Suzuki Coupling Reactions

Abstract

AbstractSynthesis, reactivity, characterization, and catalytic activities of a series of palladium(II) complexes containing the thiazolinyl‐picolinamide derived pincer ligand is reported. Treatment of 2‐aminobenzonitrile with cysteamine and subsequent treatment with 2‐picolinic acid afforded the thiazolinyl‐picolinamide derived tridentate pincer ligand N∩N∩N (2). Treatment of 2 either with (COD)PdCl2 or PdCl2 in 1 : 1 ratio afforded the palladium(II) complex [(κ3‐N∩N∩N)PdCl] (3). A reaction between Pd(OAc)2 and 2 in equimolar ratio in dichloromethane gave [(κ3‐N∩N∩N)Pd(η1‐OAc)] (4) which on further treatment with triflic acid in acetonitrile produced the [(κ3‐N∩N∩N)Pd(N≡C−CH3)]OTf (5). The complex 5 was further treated with auxiliary ligands to produce the cationic heteroleptic palladium complexes, [(κ3‐N∩N∩N)Pd(NC5H5)]OTf (6), [(κ3‐N∩N∩N)Pd(NC5H4CN)]OTf (7), and [(κ3‐N∩N∩N)Pd(NC5H4NMe2)]OTf (8), respectively. The newly synthesized compounds were characterized by 1H and 13C{1H} NMR spectroscopic techniques and the molecular structures of 2–4, 6 and 8 were established. The catalytic activity of palladium(II) complexes (3–8) were evaluated for the acylative Suzuki coupling reaction between aryl carboxylic acids and arylboronic acids to yield unsymmetrically substituted biaryl ketones. The effect of reaction conditions viz., solvent, base, temperature, catalyst loading were evaluated, and complex 4 was found to be an excellent catalyst with a maximum TOF of 19.8 min−1.