(κ³-N∩N∩N)-Palladium Pincer Complex-Catalyzed Synthesis of Quinazolin-4(3H)-Ones Through the Acceptorless Dehydrogenation Process: Experimental Results and Computational Insights

In this work, the synthesis of the palladium complexes coordinated with thiazoline-derived N∩NH∩N pincer ligands and their application in the synthesis of quinazolin-4(3H)-ones through the acceptorless dehydrogenation (ADH) process along with the sequential C–C coupling reaction is presented. Initially, treatment of chloroacetyl chloride with thiazoline amine produced compound N∩NH∩CH2Cl (2), which on subsequent reaction with morpholine or piperidine afforded the corresponding N∩NH∩N pincer ligands 3 and 4. Reactions of ligands with PdCl2 or Pd(OAc)2 in a 1:1 molar ratio at room temperature afforded the mononuclear palladium(II) complexes [(κ3-N∩N∩N)PdX] (X = Cl, OAc) 5–8, while treatment of ligands with Pd(OAc)2 in the presence of trifluoroacetic acid afforded the complexes [(κ3-N∩N∩N)Pd(TFA)] 9 and 10. 1H, 13C{1H} NMR spectroscopic techniques and HR-MS data confirm the proposed structures and chemical compositions. Further, molecular structures of 3, 4, 6, 8, and 10 were established through single-crystal X-ray diffraction studies. The catalytic activity of palladium(II) complexes 5–10 was evaluated for the synthesis of quinazolinone derivatives from 2-aminobenzamide and substituted benzyl alcohols via ADH coupling reactions along with sequential C–C coupling reactions. The thermodynamics associated with this transformation have been established using DFT calculations.