Cyclometallation, steric and electronic tendencies in a series of Pd(II) complex pre-catalysts bearing imidazole–phenol ligands and effects on Suzuki–Miyaura catalytic efficiencies

摘要: Abstract A series of new structurally and electronically diversified palladium complexes derived from seven less sterically crowded 2-(4,5-dimethyl-1H-imidazol-2-yl) phenol/2-(4,5-diethyl-1H-imidazol-2-yl) phenol ligands fourteen 2-(4,5-diphenyl-1H-imidazol-2-yl) phenols/2-(1H-phenanthro[9,10-d]imidazol-2-yl) phenols bearing varying degrees higher steric bulk have been prepared characterized. While single crystals grown precipitated products complexation reactions confirmed the bis-ligand Pd(N^O)2 coordination, few obtained reaction filtrates involving provided evidence for formation N^O^C chelation species achieved by cyclometallation. Results structural analyses catalytic outcomes generally indicate that desirable variables on ligand frameworks obtaining superior catalyst activities either provides hemilabile or strained characters, which would both favour generation monodentate coordination at catalysis temperature. In particular, correlation was observed between tendency cyclometallation in poor Suzuki–Miyaura prospects. Based hopeful activity complex 4-bromo-2-(4,5-dimethyl-1H-imidazol-2-yl) phenol, it also concluded bulky is not a necessity high coupling efficiency, while presence potentially cyclometallating substituent moieties vicinity centre may fact destroy