Department of Chemistry and Biochemistry, University of California, Los Angeles , 607 Charles E. Young Drive East, Los Angeles, California 90095, United States.
Department of Chemistry and Biochemistry, University of California, San Diego , 9500 Gilman Drive, La Jolla, California 92093, United States.
J Am Chem Soc. 2017 Jun 14;139(23):7729-7732. doi: 10.1021/jacs.7b04080. Epub 2017 Jun 1.
We report the first observed Pd-catalyzed isomerization ("cage-walking") of B(9)-bromo-meta-carborane during Pd-catalyzed cross-coupling, which enables the formation of B-O and B-N bonds at all boron vertices (B(2), B(4), B(5), and B(9)) of meta-carborane. Experimental and theoretical studies suggest this isomerization mechanism is strongly influenced by the steric crowding at the Pd catalyst by either a biaryl phosphine ligand and/or substrate. Ultimately, this "cage-walking" process provides a unique pathway to preferentially introduce functional groups at the B(2) vertex using B(9)-bromo-meta-carborane as the sole starting material through substrate control.
我们报告了首例观察到的钯催化 B(9)-溴代间卡硼烷异构化（“笼式迁移”），该异构化发生于钯催化交叉偶联过程中，使间卡硼烷所有硼原子顶点（B(2)、B(4)、B(5)和 B(9)）均能够形成 B-O 和 B-N 键。实验和理论研究表明，这种异构化机制强烈受到钯催化剂上的位阻的影响，这种位阻由双芳基膦配体和/或底物引起。最终，这种“笼式迁移”过程提供了一种独特的途径，通过底物控制，仅使用 B(9)-溴代间卡硼烷作为唯一起始原料，优先在 B(2)顶点上引入官能团。
