Synthesis of novel Pd-NCN pincer complexes having additional nitrogen coordination sites and their application as catalysts for the Heck reaction

A novel Pd-NCN pincer complex, 7, bearing two additional nitrogen atoms has been synthesized and characterized. The dynamic NMR study of 7 shows the two-site exchange reaction in the NCN pincer ligand with a relatively low DeltaG(double dagger) value, suggesting easy interconversion in the pincer complex. The use of 7 as a catalyst in the Heck reaction was studied. Catalyst 7 is quite effective for all aryl iodides. A turnover number (TON) value of 4.3 x 10(6) was observed with 4-tolyl iodide. However, 7 is not an effective catalyst for nonactivated bromobenzene and chlorobenzene substrates. According to the study of the Heck reaction, the facile interconversion of the pincer ligand positively affects the catalytic activity.