Oxime Palladacycle Catalyzed Carbonylative Sonogashira Cross-Coupling with High Turnovers in PEG as a Benign and Recyclable Solvent System

Oxime palladacycles-di-m-chlorobis [5-chloro-2-[(4-chlorophenyl)(hydroxyimino-kN) methyl] phenyl-kC] palladium (II) dimer (1) and di-m-chlorobis[5-hydroxy-2-[1-(hydroxyimino-kN) ethyl] phenyl-kC] palladium (II) dimer (2) provide a phosphine free approach for the synthesis of ynones at low palladium loadings (10(-5) mol%) thus resulting in catalytic turnover numbers (TONs) and turnover frequencies (TOFs) of the order of 10(6). Oxime palladacycle 1 shows TON 587 times and TOF 331 times higher than the best palladium catalyst reported in the literature for the carbonylative cross-coupling between 4-iodoanisole and phenylacetylene as a model reaction. The use of poly (ethylene glycol) as an environmentally benign solvent system allows the recyclability of the oxime palladacycle at low palladium loading up to four times. Further, the oxime palladacycles are advantageous in effecting higher conversion and selectivity at low palladium loadings as compared to conventional palladium precursors-Pd (OAc)(2) and PdCl2(PPh3)(2).