Rapid Entry to Functionalized Boratabenzene Complexes through Metal-Induced Hydroboration at the Anionic 1-H-Boratabenzene Ligand

The hydroboration of alkenes, alkynes, imines, and carbodiimides using the anionic 1-H-boratabenzene ligand bound to rare-earth (RE = Y, Lu), transition (Zr and Rh), and main-group (Li) metals is reported. This hydroboration is metal ion dependent; in the case of 1-H-boratabenzene transition metal complexes, the reactivity follows the trend RE > Zr > Rh. Hydroboration with 1-H-boratabenzene rare-earth metal complexes works well for a range of unsaturated substrates, including 1-hexene, allyl propyl ether, allyl ether, 3-hexyne, benzylidene-n-propylamine, and N,N′-diisopropylcarbodiimide, thus generating a series of new alkyl-, alkenyl-, amino-, or amidino-functionalized boratabenzene rare-earth metal complexes in high yields. The reactions are highly anti-Markovnikov selective, and the mechanism has been investigated by deuterium-labeling experiments. In comparison, a 1-H-boratabenzene Zr complex reacts with benzylidene-n-propylamine and N,N′-diisopropylcarbodiimide, and a 1-H-boratabenzene Rh complex reacts with N,N′-diisopropylcarbodiimide. In contrast, the 1-H-boratabenzene lithium salt reacts only with the activated substrate benzylidene-n-propylamine at elevated temperature to give the corresponding hydroboration product. Boratabenzene Y complexes undergo ligand redistribution with Rh chlorides to give boratabenzene Rh complexes. Studies of the novel monoanionic amidino-boratabenzene ligand by X-ray diffraction and DFT calculations have revealed interesting structural features.

本文报道了使用结合于稀土金属（RE=钇Y、镥Lu）、过渡金属（锆Zr与铑Rh）及主族金属（锂Li）的阴离子1-氢-硼杂苯配体，实现烯烃、炔烃、亚胺与碳二亚胺的硼氢化反应（hydroboration）。该硼氢化反应具有金属离子依赖性；对于1-氢-硼杂苯过渡金属配合物，其反应活性遵循RE＞Zr＞Rh的顺序。采用1-氢-硼杂苯稀土金属配合物的硼氢化反应，可适用于多种不饱和底物，包括1-己烯、烯丙基丙基醚、烯丙基醚、3-己炔、亚苄基正丙胺以及N,N′-二异丙基碳二亚胺，最终以高收率得到一系列烷基、烯基、氨基或脒基官能化的硼杂苯稀土金属配合物。该类反应具备极高的反马氏选择性，研究团队通过氘标记实验对反应机理进行了探究。相比之下，1-氢-硼杂苯锆配合物可与亚苄基正丙胺及N,N′-二异丙基碳二亚胺发生反应，而1-氢-硼杂苯铑配合物仅能与N,N′-二异丙基碳二亚胺反应。与之不同的是，1-氢-硼杂苯锂盐仅能在高温条件下与活性底物亚苄基正丙胺反应，得到对应的硼氢化产物。硼杂苯钇配合物可与氯化铑发生配体重分配反应，生成硼杂苯铑配合物。通过X射线衍射（X-ray diffraction）与密度泛函理论（DFT, Density Functional Theory）计算对新型单阴离子脒基-硼杂苯配体开展的研究，揭示了其有趣的结构特征。