| Some progress has been made in developing catalytic systems of cheap metals such as iron,cobalt,and nickel in recent years.Due to their low price,abundant reserve and excellent catalytic effect,they have received extensive attention from the chemists.Cobalt contains 9d electrons and has+2 and+3 oxidation states.Compared with other transition metals,cobalt is more prone to one-electron redox reactions,making cobalt complexes have novel reactivity and unique reaction mechanisms.In this study,the catalytic performance of Co(OAc)2·4H2O and eight new cobalt complexes in the acceptorless dehydrogenative coupling(ADC)of alcohols and in wacker oxidation reaction was explored.The details are as follows:(1)The ADC reaction of alcohols to synthesize quinoline and quinazoline derivatives was studied under ligand-free conditions using Co(OAc)2·4H2O as the catalyst and KOtBu as the base.It was found that the ADC reactions of 2-aminobenzyl alcohols with various substituents afforded quinolines in yields of 44-83%;and those of ketones produced quinolines in yields of 15-97%.Catalyzed by Co(OAc)2·4H2O,the ADC reactions of2-aminobenzyl alcohols with different substituents gave quinazolines in yields of 17-97%and those of nitrile provided quinazolines in yields of 17-97%.(2)Based on the above-mentioned results,we conducted a series of controlled experiments to investigate the reaction mechanism and proposed a possible mechanism.(3)Eight Co(?)complexes 8a-8h were prepared by through the reactions of ligands1,10-Phenanthroline(L1),2,9-Dimethyl-1,10-phenanthroline(L2),2,2'-Bipyridyl(L3),TMEDA(L4),6,6'-dimethyl-2,2'-Bipyridine(L5),4,4'-dimethoxy-2,2'-Bipyridine(L6),6,6'-dibromo-2,2'-Bipyridine(L7)and 6,6'-bis(trifluoromethyl)-2,2'-Bipyridine(L8)with anhydrous Co Cl2.They were characterized by IR and HR-MS.(4)Complexes 8a-8h applied as catalysts in the Wacker oxidation reaction.Complexes8a,8b,8f and 8g exhibit good catalytic activity,while complexes 8c,8d,8e and 8h are less activity.With 8g as the selected catalyst and phenylsilane as the additive,the oxidative reactions of a range of styrenes with different substituent groups were carried out to give the corresponding ketones selectively in 48-97% yields. |
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