(κ<sup>3</sup>-N∩N∩N)-Palladium Pincer Complex-Catalyzed Synthesis of Quinazolin-4(3H)-Ones Through the Acceptorless Dehydrogenation Process: Experimental Results and Computational Insights
Selvam Sivaprakash, Srilata Goswami, Hemalatha Maricherla, Mahesh Kumar Ravva, Dinesh Harijan, Ganesan Prabusankar, Arlin Jose Amali, D. Suresh
Abstract
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 ∩ CH 2 Cl ( 2 ), which on subsequent reaction with morpholine or piperidine afforded the corresponding N ∩ NH ∩ N pincer ligands 3 and 4 . Reactions of ligands with PdCl 2 or Pd(OAc) 2 in a 1:1 molar ratio at room temperature afforded the mononuclear palladium(II) complexes [(κ 3 -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 [(κ 3 -N ∩ N ∩ N)Pd(TFA)] 9 and 10 . 1 H, 13 C{ 1 H} 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.