Utilization of supercritical carbon dioxide as green solvent for the Suzuki-Miyaura reaction

Newly designed alkylated acetyl acetone ligands which are 3-n-butyl-2,4-pentanedione and 3-perfluorobutyl-2,4pentanedione were prepared by alkylation of active methylene group of 2,4-pentanedione and then used as ligands for preparation of palladium (II) (Pd) complexes soluble in supercritical carbon dioxide deposition. The solubility of prepared palladium complexes was inclusively measured in supercritical carbon dioxide at varying pressures and temperatures. The results showed that solubility of the fluorinated complex is higher than the nonfluorinated complex. The solubility of Pd complex of 3-perfluorobutyl-2,4-pentandione [Pd(FBACAC)2] ranged between 4.51 g & BULL;L-1 and 8.66 g & BULL;L-1 while the solubility of Pd complex of 3-n-butyl-2,4-pentandione Pd(BACAC)2 varied from 0.21 g & BULL;L-1 to 1.1 g & BULL;L-1 at different temperature and pressures. Efficient Suzuki-Miyaura crosscoupling reaction catalytic system for novel catalysts was carried out at various temperatures and pressures. To the best of our knowledge, it is the first study without using co-solvent, ionic liquid and phase transfer catalyst for Suzuki-Miyaura C-C coupling reaction in supercritical carbon dioxide catalyst system. The results demonstrated a successful application of novel alkylated acetylacetone for palladium-catalyzed Suzuki-Miyaura coupling reaction between a phenylboronic acid and bromobenzene in scCO2.