Herein, we present the synthesis of a thiazoline-derived N∩NH∩CH pincer ligand and a series of orthometalated N∩N∩C palladium (II) complexes as catalysts in solvent-free quinoline synthesis via the acceptorless dehydrogenation (ADH) process and subsequent C (sp2) –C (sp2) bond-forming reactions. The N∩NH∩CH (2) pincer ligand was produced by the equimolar reaction of thiazoline amine (N∩NH2, 1) and benzoyl chloride, which upon further treatment with Pd (OAc) 2 in acetonitrile, afforded the orthometalated palladium (II) complex (κ3–N∩N∩C) Pd (NCCH3) (3). A series of heteroleptic palladium (II) complexes of (κ3–N∩N∩C) Pd (L) 4–12 was explored by reacting complex 3 with various substituted pyridine derivatives. Proposed structures and chemical compositions were confirmed using 1H, 13C1H NMR, and HR–MS spectroscopic techniques. Additionally, the molecular structures of complexes 3, 4, 6, 10, and 12 were established through single-crystal X-ray diffraction studies. The catalytic activity of palladium (II) complexes 3–12 was evaluated for the synthesis of quinoline derivatives from 2-aminobenzyl alcohol and substituted acetophenones via ADH reactions. The further utility of the complexes in C (sp2) –C (sp2) coupling reactions was also explored using 2- (4-bromophenyl) quinoline with phenylboronic acid derivatives. A tenable reaction mechanism has been suggested through several control experiments and spectroscopic investigations. DFT calculations have been employed to prove the thermodynamics associated with this conversion.
Sivaprakash et al. (Fri,) studied this question.