Johnson Jeffrey B, Bercot Eric A, Rowley John M, Coates Geoffrey W, Rovis Tomislav
Colorado State University, Fort Collins, CO 80523, USA.
J Am Chem Soc. 2007 Mar 7;129(9):2718-25. doi: 10.1021/ja067845g. Epub 2007 Feb 13.
Results from a mechanistic study on the Ni(COD)2-bipy-catalyzed alkylation of anhydrides are consistent with turnover-limiting reductive elimination at high Et2Zn concentrations. While the presence of styrene does not affect the initial rate of alkylation, it appears to inhibit catalyst decomposition and provides higher product yield at long reaction times. In contrast, Ni(COD)2-iPrPHOX-catalyzed anhydride alkylation proceeds through two competing catalytic cycles differentiated by the presence of styrene. The presence of styrene in this system appears to accelerate rate-limiting oxidative addition and promotes the cycle which proceeds 4 times more rapidly and with much higher enantioselectivity than its styrene-lacking counterpart.
关于Ni(COD)₂-联吡啶催化酸酐烷基化的机理研究结果与在高浓度二乙基锌条件下的周转限制还原消除相一致。虽然苯乙烯的存在不影响烷基化的初始速率，但它似乎能抑制催化剂分解，并在较长反应时间下提供更高的产物产率。相比之下，Ni(COD)₂-iPrPHOX催化的酸酐烷基化通过两个相互竞争的催化循环进行，这两个循环因苯乙烯的存在而有所不同。该体系中苯乙烯的存在似乎加速了限速氧化加成，并促进了比无苯乙烯对应循环快4倍且对映选择性高得多的循环。
