Perras Frédéric A, Bryce David L
Department of Chemistry and CCRI, University of Ottawa, Ottawa, Ontario, Canada K1N 6N5.
J Am Chem Soc. 2013 Aug 28;135(34):12596-9. doi: 10.1021/ja407138b. Epub 2013 Aug 9.
Chemically informative J couplings between pairs of quadrupolar nuclei in dimetallic and dimetalloid coordination motifs are measured using J-resolved solid-state NMR experiments. It is shown that the application of a double-quantum filter is necessary to observe the J splittings and that, under these conditions, only a simple doublet is expected. Interestingly, the splitting is amplified if the spins are magnetically equivalent, making it possible to measure highly precise J couplings and unambiguously probe the symmetry of the molecule. This is demonstrated experimentally by chemically breaking the symmetry about a pair of boron spins by reaction with an N-heterocyclic carbene to form a β-borylation reagent. The results show that the J coupling is a sensitive probe of bonding in diboron compounds and that the J values quantify the weakening of the B-B bond which occurs when forming an sp(2)-sp(3) diboron compound, which is relevant to their reactivity. Due to the prevalence of quadrupolar nuclei among transition metals, this work also provides a new approach to probe metal-metal bonding; results for Mn2(CO)10 are provided as an example.
利用 J 分辨固态核磁共振实验测量了双金属和双准金属配位结构中一对四极核之间具有化学信息的 J 耦合。结果表明，应用双量子滤波器对于观察 J 分裂是必要的，并且在这些条件下，预计只会出现简单的双峰。有趣的是，如果自旋在磁场上是等效的，分裂会被放大，这使得测量高精度的 J 耦合并明确探测分子的对称性成为可能。通过与 N - 杂环卡宾反应形成 β - 硼化试剂，化学破坏一对硼自旋周围的对称性，实验证明了这一点。结果表明，J 耦合是二硼化合物中键合的敏感探针，并且 J 值量化了形成 sp(2)-sp(3)二硼化合物时 B - B 键的弱化，这与其反应性相关。由于过渡金属中四极核的普遍性，这项工作还提供了一种探测金属 - 金属键合的新方法；以 Mn2(CO)10 的结果为例进行了说明。
