RATIONAL DESIGN OF CATALYSTS FOR C-C BOND FORMATION

我的研究小组最近发现了一类新的C-C键形成反应：钯配合物催化的酮的直接α-芳基化反应。 我们现在已经将该反应扩展到包括羧酸衍生物如酰胺和丙二酸酯的α-芳基化，同时发现了在室温下使用芳基溴和仅在70 ℃下使用芳基氯提供酮的α-芳基化的显著催化剂。 在美国国立卫生研究院的支持下，我的小组将1）研究新的烷基膦配体的催化过程的基础上，我们的假设，空间位阻，螯合烷基膦加速反应速率，2）扩大这一新的过程的范围，以其他类型的羰基化合物，烷基氰化物，硝基烷烃和3）发展一个详细的，定量的机理理解的反应，包括催化循环。更具体地说，我们将制备烷基膦配体，其在磷上含有大的和小的取代基，并且具有提供大的和小的咬角的主链。 这些配体将用于进一步提高产率、速率和底物范围，同时揭示我们目前提供如此快速率的配体的特征。 这些配体也将用于将亲电体的范围扩展到乙烯基和杂芳族卤化物和磺酸盐的研究中，以及亲核伙伴，例如α-二酮，α-甲硅烷氧基酮，α，β-不饱和酮，β-二羰基化合物，酯，腈，硝基烷烃和吖内酯的阴离子。基于公司的定量数据的催化化学的详细机理描述是拟议的研究的一个重要目标。 在一般情况下，我们将进行仔细的研究，以确定配体的空间和电子性质如何影响催化循环的每一步，包括氧化加成的芳基卤化物，这可能是反应的速率决定步骤，从所得的芳基钯卤化物络合物形成的芳基钯烯醇络合物，和C-C键形成还原消除，这是催化循环中的关键耦合步骤。 我们已经对这种还原消除进行了第一次直接观察。 将研究与还原消除竞争的烯醇化钯络合物的β-氢消除，以确定如何防止该过程。 最后，我们将开始一个详细的机理研究的酮芳基化过程的初始不对称版本结合Buchwald的合成努力，作为一种手段，为我们的两个小组，以创建改进的对映选择性催化剂。

My group recently discovered a new class of C-C bond-forming reaction: the direct alpha-arylation of ketones catalyzed by palladium complexes. We have now extended this reaction to include the alpha-arylation of carboxylic acid derivatives such as amides and malonates, while finding remarkable catalysts that provide alpha-arylation of ketones at room temperature using aryl bromides and at only 70 C using aryl chlorides. Under NIH support my group would 1) study new alkylphosphine ligands for the catalytic process based on our hypothesis that sterically hindered, chelating alkyl phosphines accelerate reaction rates, 2) expand the scope of this new process to other types of carbonyl compounds, alkyl cyanides, and nitroalkanes and 3) develop a detailed, quantitative mechanistic understanding of the reactions comprising the catalytic cycle. More specifically, we will prepare alkylphosphine ligands containing large and small substituents at phosphorus and with backbones that provide large and small bite angles. These ligands will be used to further improve yields, rates, and substrate scope, while uncovering the features of our current ligands that provide such fast rates. These ligands will also be used in studies toward extending the scope of electrophiles to vinyl and heteroaromatic halides and sulfonates, and to nucleophilic partners such as the anions of alpha-diketones, alpha-siloxy ketones, alpha, beta-unsaturated ketones, beta-dicarbonyl compounds, esters, nitriles, nitroalkanes, and azlactones. A detailed mechanistic description of the catalytic chemistry based on firm quantitative data is an important goal of the proposed research. In general, we will conduct a careful study to determine how ligands steric and electronic properties affect each step of the catalytic cycle, including oxidative addition of aryl halide that is likely to be the rate determining step of the reaction, formation of an arylpalladium enolate complex from the resulting arylpalladium halide complex, and C-C bond-forming reductive elimination that is the crucial coupling step in the catalytic cycle. We have conducted the first direct observation of this type of reductive elimination. Beta-Hydrogen elimination from the palladium enolate complexes, which competes with reductive elimination, will be investigated to determine how this process can be prevented. Finally, we will begin a detailed mechanistic study of the initial asymmetric version of the ketone arylation process in conjunction with Buchwald's synthetic effort as a means for our two groups to create improved enantioselective catalysts.