Probing the influence of steric bulk on anion binding by triarylboranes: comparative studies of FcB(o-Tol)2, FcB(o-Xyl)2 and FcBMes2.
Probing the influence of steric bulk on anion binding by triarylboranes: comparative studies of FcB(o-Tol)2, FcB(o-Xyl)2 and FcBMes2.
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DOI：
10.1039/c1dt10185d
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发表时间：
2011-10
影响因子：
4
通讯作者：
Inke Siewert;P. Fitzpatrick;Alexander E. J. Broomsgrove;M. Kelly;D. Vidović;S. Aldridge
中科院分区：
文献类型：
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作者：
Inke Siewert;P. Fitzpatrick;Alexander E. J. Broomsgrove;M. Kelly;D. Vidović;S. Aldridge
在硼的金字塔化过程中产生的空间拥挤已经被计算预测为对三芳基硼烷阴离子结合的强度和选择性至关重要。本研究通过比较FcB(o-Tol)(2) (1, o-Tol = C（6)H(4)Me-2）、FcB(o-Xyl)(2, o-Xyl = C（6)H(3) -2,6）和FcBMes(2) (3, Mes = C（6)H(2)Me(3)-2,4,6)）在溶液和固态中的F(-)/CN（-）结合特性，系统地探讨了位阻因子在含有二茂铁基报告单元的体系中的作用。有些令人惊讶的是，额外的邻甲基芳基取代基（例如2/3vs）的包含。1)对这些硼烷的结合亲和力的影响相对较小(例如，log(10)K（CN）分别为5.94(0.02),4.73（0.01),5.56(0.02)，分别为1,2和3）。与这一观察结果相一致的是，固体状态下氰化物加合物[1·CN]（-）、[2·CN]（-）和[3·CN]（-）在硼上的锥体化程度也基本不变（∠C（芳基）-B-C（芳基）分别= 338、337、337°），B-CN和B-C（芳基）的平均距离也基本不变。至少在固态中，很明显，增加邻位取代可能带来的不利空间效应被更大程度的芳基取代基围绕B-C（芳基）键的同步旋转所减轻。因此，[1·CN]（-）的平均面间角为71°，而[2·CN]（-）和[3·CN]（-）的对应值分别为78°和79°。
Steric crowding brought about on pyramidalization at boron has been predicted computationally to be of central importance to the strength and selectivity of anion binding by triarylboranes. The role of steric factors in systems containing a ferrocenyl reporter unit has been systematically probed in the current study by comparison of the F(-)/CN(-) binding properties of FcB(o-Tol)(2) (1, o-Tol = C(6)H(4)Me-2), FcB(o-Xyl)(2) (2, o-Xyl = C(6)H(3)Me(2)-2,6) and FcBMes(2) (3, Mes = C(6)H(2)Me(3)-2,4,6)), both in solution and in the solid state. Somewhat surprisingly, the inclusion of an extra ortho-methyl aryl substituent (e.g. for 2/3vs.1) is found to have a relatively small effect on the binding affinities of these boranes (e.g. log(10)K(CN) = 5.94(0.02), 4.73(0.01), 5.56(0.02), for 1, 2 and 3 respectively). Consistent with this observation, the degree of pyramidalization at boron determined for the cyanide adducts [1·CN](-), [2·CN](-) and [3·CN](-) in the solid state is also found to be essentially invariant (∠C(aryl)-B-C(aryl) = 338, 337, 337°, respectively), as are the B-CN and mean B-C(aryl) distances. In the solid state at least, it is apparent that the adverse steric effects potentially brought about by increasing ortho substitution are mitigated by a greater degree of synchronous rotation of the aryl substituents about the B-C(aryl) bonds. Thus a mean inter-plane angle of 71° is observed for [1·CN](-) while the corresponding values for [2·CN](-) and [3·CN](-) are 78° and 79°.