| Carbon-carbon bond formation is one of the most important methods of modern organic synthesis. Among various cross-coupling reactions, the palladium-catalyzed Suzuki cross-coupling is an extremely efficient tool for preparation of unsymmetrical biaryls, which provides the key steps in the construction of more complex molecules of natural products, pharmaceutical intermediates, and functional materials.Green chemistry is a major issue of modern chemistry currently. The use of environmentally benign solvent instead of traditional organic solvents is the important and efficient strategy in green chemistry. Water is a promising green solvent for use in chemistry because it is cheap, readily available, and nontoxic. This dissertation studied mainly the phosphine-free palladium-catalyzed Suzuki and Suzuki-Type cross-coupling reaction in aqueous media. The main contents of research are as follows:1. Pd(OAc)2-H2O-IL system as a catalytic medium for the Suzuki cross-coupling reaction was developedWe studied Suzuki cross-coupling reaction using Pd(OAc)2 as catalyst in H2O-IL (Ionic Liquids) system. Water was found to have a remarkable rate accelerating effect on the Suzuki reaction in ionic liquids. The ratio of water and ILs was pivotal to the Suzuki reaction. Pd(OAc)2-H2O-IL system could tolerate a broad range functional groups, such as NO2, NH2, OMe, OH, COMe and CN. The eletron-withdrawing aryl bromides and aryl iodides showed excellent reactivity and gave the desired products with high yields in short times, while the eletron-rich aryl bromides need longer times in order to obtain the high yields. Sterical effect influenced slightly yields and the ortho-substituted afforded the desired product with lower yields. The use of expensive and environmentally unfavorable phosphine ligand was avoided. The Pd(OAc)2-[bmim][PF6] could be recycled seven times with only a small decrease in activity. Compared with the previous aqueous or pure ionic liquid systems, This system was active, air stable, recyclable, and the products could be separated easily.2. Pd(OAc)2-H2O-[bmim][PF6] system as a catalytic medium for the Suzuki-Type cross-coupling reaction was developedWe investigated palladium acetate-catalyzed Suzuki-Type cross-coupling of aryl boronic acid with carboxylic anhydride or acyl chlorides in H2O-[bmim][PF6] system. It is clear that H2O dramatically improved the reactivity of the Suzuki-Type reaction in [bmim][PF6]. The reactivity was strongly influenced by the ratio of H2O and [bmim][PF6]. Pd(OAc)2-H2O-[bmim][PF6] system could tolerate a broad range functional groups, such as NO2, Cl, OMe, Me and CN. The aromatic carboxylic anhydride and aryl acyl chlorides with both electron-releasing and electron-withdrawing substituents showed excellent reactivity and gave the desired products with high yields, while the heteroaryl carboxylic anhydrides and acyl chlorides obtained analogous results. The ortho-substituted afforded the desired product with lower yields due to sterical effect. The activity of aryl acyl chloride was superior to that of aromatic carboxylic anhydrides. Either aryl boronic acid or heteroarylboronic acids gave the ketone in excellent yields. The use of phosphine ligand is avoided. This system could be recycled eight times with only a small decrease in activity. This method is superior to the previous methods in organic systems in terms of reaction conditions, efficiency, and recycle of catalyst.3. Pd(OAc)2-H2O-PEG system as a catalytic medium for the Suzuki-Type cross-coupling reaction was developedWe described Suzuki-Type cross-coupling reaction using Pd(OAc)2 as catalyst in H2O-PEG system. Water was found to have a remarkable rate accelerating effect on the Suzuki-Type reaction in PEG., which the ratio of H2O and PEG was crucial to the Suzuki-type reaction. Pd(OAc)2-H2O-PEG system could tolerate a broad range functional groups. All of the aromatic carboxylic anhydride and aryl acyl chlorides, showed excellent reactivity. Sterical effect influences slightly yields and the ortho-substituted afforded the desired product with lower yields. Both aryl boronic acid and heteroarylboronic acids gave the ketone in excellent yields. Phosphine ligand is avoided using. Catalytic efficiency in Pd(OAc)2-PEG system was higher than that in Pd(OAc)2-[bmim][PF6] system and TONs (turnover numbers) were up to 2.5×104. Compared with the previous methods in organic systems, Pd(OAc)2-H2O-PEG system was active, air stable, recyclable, and the products could be separated easily. In addition, the formation of the by-product of biphenyl generated from the self-coupling of phenylboronic acid was impressed obviously.4. PdCl2-H2O-SDS system as a catalytic medium for the Suzuki-Type crosscoupling reaction was developedWestudied SDS-improved Suzuki-Type cross-coupling reaction using PdCl2 as catalyst in H2O. It is clear that SDS dramatically improves the reactivity of the Suzuki-Type reaction in H2O, and the concentration of the SDS was pivotal to the Suzuki-Type reaction. When the concentration of the SDS was lower than its critical micelle concentration (CMC), the effect of SDS on the coupling reaction was poor. But the isolation of the products is more difficult in the presence of high concentration of SDS. PdCl2-H2O-SDS system could tolerate a broad range functional groups. The reactions were unaffected by the presence of electron-releasing and electron-withdrawing substituents in both the arylboronic acids and carboxylic derivatives. The ortho-substituted afforded the desired product with lower yields due to the sterical effect. The use of phosphine ligand was avoided. The green character of water and easy isolation of the product made the present method attractive.
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