Rational Design of Sterically Hindered and Unsymmetrical NpyNimOph Pincer‐Type Ligands and Their Palladium(II) Complexes: Catalytic Applications in Suzuki–Miyaura Reaction and Allylation of Aldehydes

Abstract

AbstractPalladium(II) complexes 1–4 [Pd(L1 to L4)Cl] derived from pincer‐type tridentate ligands having NpyNimOph donors were synthesized from ligands L1H to L4H (where L1H=(2‐phenyl‐2‐(pyridin‐2‐ylmethyl)hydrazono)methyl)phenol, L2H =[2‐((2‐phenyl‐2‐(pyridinyl‐2‐ylmethyl) hydrazono) methyl) phenol], L3H=[2‐((2‐benzyl‐2‐phenylhydrazono) methyl)‐4,6‐di‐tert‐butylphenol], and L4H=[2‐((2‐benzyl‐2‐phenylhydrazono)methyl)‐6‐(tert‐butyl)‐4‐methoxy phenol where H stands for dissociable proton)in quantitative yields. Synthesized ligands L1H to L4H and corresponding palladium(II) complexes 1–4 were characterized by NMR, IR and HR‐MS spectroscopic studies. Molecular structures of ligand L4H and complexes 1 and 3 were determined by X‐ray crystallography. Complexes 1–4 were utilized as catalysts to investigate Suzuki–Miyaura cross‐coupling reaction upon catalyst loading 0.01 mol%. These catalysts also catalysed allylation of aldehydes upto 95% yield upon catalyst loading 0.5 mol% with broad substrate scopes. Theoretical and experimental investigation was performed to speculate reaction pathway of Suzuki–Miyaura cross‐coupling reaction. A reaction model has also proposed for allylation of aldehydes the presence of allyltributylstannane.