Structural Effect of Pincer Pd(II)-ONO Complexes Modified with Acylthiourea on Sizes of the In Situ Generated Pd Nanoparticles During Heck Coupling Reaction

The Pd nanoparticles generated in situ from Pd-pincer complexes catalyzed Heck coupling reaction. For this purpose, new Pd(II)-ONO pincer complexes (1-4) containing acylthiourea ancillary ligand were obtained by treating [Pd(ONO)(CH3CN)] with the respective N-substituted carbamothioyl benzamide ligand (L1-L4). Formation of these complexes was confirmed by UV-Visible, FT-IR, NMR and mass spectroscopic techniques. The sizes of in situ formed Pd nanoparticles were greatly affected by the substituent in ancillary ligand, which in turn influenced their catalytic activity towards Heck coupling reaction. The in situ formed Pd nanoparticles during Heck reaction were removed from the reaction medium and analyzed using HR-TEM to estimate the sizes of the Pd nanoparticles. Complex [Pd(ONO)((N-benzylcarbamothioyl)benzamide)] (1)which does not possess any substituent on the benzyl moiety of acylthiourea produced the smallest Pd nanoparticles with the average particle size of 3.7 nm. Hence, complex1showed the utmost catalytic activity. With complex1, 51-99% of conversion was observed during Heck coupling reaction of styrene with various aryl halides. XPS results confirmed that the recovered black particles were Pd(0). A reasonable recyclability results were achieved by these in situ generated Pd nanoparticles. [GRAPHICS] .

Automated summary

In this study, Pd nanoparticles generated in situ from Pd-pincer complexes catalyzed the Heck coupling reaction, and the size and catalytic activity of the nanoparticles were found to be influenced by the substituent in the ancillary ligand.