Synthesis, Characterization and Theoretical Investigation on Thiazoline‐Derived Palladium‐Complexes‐Catalyzed Denitrogenative Cross‐Coupling of Aryl Halides with Arylhydrazines

Abstract

AbstractHomo‐ and heteroleptic palladium(II) complexes of thiazoline derived ligand were synthesized and their catalytic application was reported. The reactions of [1‐(C3H4NS)‐2‐OH‐C6H4] (2) with PdCl2 and [(1‐(CH3)2NCH2C6H4)PdCl]2 in 2:1 molar ratios afforded the homoleptic palladium complex, [Pd{κ12, κ12‐N,O‐(1‐(C3H4NS)‐2‐O‐C6H4)2}] (3) and the heteroleptic palladium complex [{κ12‐N,O‐(1‐(C3H4NS)‐2‐O‐C6H4)}Pd{(κ22‐N,C‐(1‐(CH3)2NCH2C6H4)}] (4) respectively. Equimolar reactions of 2 with PdCl2 and 8‐quinolinol or 2‐methyl‐8‐quinolinol under reflux condition produced the heteroleptic palladium complexes [{κ12‐N,O‐(1‐(C3H4NS)‐2‐O‐C6H4)}Pd{(κ22‐N,O‐(8‐O‐C9H6‐1‐N)}] (5) or [{κ12‐N,O‐(1‐(C3H4NS)‐2‐O‐C6H4)}Pd{(κ22‐N,O‐(8‐O‐2‐CH3‐C9H5‐1‐N)}] (6) in good yields. The molecular structures of ligand 2 and palladium complexes 3–6 were confirmed through multinuclear NMR spectroscopic techniques and further the crystal structure for palladium complexes 3 and 4 were established. Under the optimized reaction condition, the heteroleptic palladium complex 4 display an excellent catalytic activity with a maximum turn over frequency of 49.5 h−1 for the conversion of bi‐aryls from aryl halides and unactivated phenylhydrazine. The energies, activation barriers and transition state structures of reaction involved in the catalytic cycle were assessed by utilizing quantum chemical method to confirm Csp2‐Csp2 bond formation reaction catalyzed by heteroleptic palladium complex 4.