A Comparison of Two Zinc Hydride Catalysts for Terminal Alkyne C-H Borylation/Hydroboration and the Formation of 1,1,1-Triborylalkanes by Tandem Catalysis Using Zn-H and B-H Compounds
A Comparison of Two Zinc Hydride Catalysts for Terminal Alkyne C-H Borylation/Hydroboration and the Formation of 1,1,1-Triborylalkanes by Tandem Catalysis Using Zn-H and B-H Compounds
复制标题
DOI：
10.1021/acs.organomet.0c00086
复制
发表时间：
2020-04-27
期刊：
影响因子：
2.8
通讯作者：
Ingleson, Michael J.
中科院分区：
文献类型：
--
作者：
Uzelac, Marina;Yuan, Kang;Ingleson, Michael J.
报道了由端炔和频哪醇硼烷（HBPin）合成1，1，1-三硼基烷烃的方法。该转化通过初始Zn催化的炔C-H硼基化进行，其可以使用NacNacZnH络合物实现。通过末端炔的C-H锌化形成的NacNacZn-炔基和HBPin的组合与炔基-BPin和NacNacZnH平衡存在。NacNacZnH通过与末端炔的不可逆反应释放H-2的消耗对于驱动炔C-H硼基化完成是必不可少的。炔基-BPin化合物在升高的温度下用{7 DIPP}ZnH（NTf 2）络合物（7 DIPP = 1，3-双（2，6-二异丙基苯基）-4，5，6，7-四氢-1H-1，3-二氮杂卓-3-鎓-2-化物）进行Zn-H络合物催化的硼氢化反应，所述{7 DIPP} ZnH（NTf 2）络合物是比NacNacZnH络合物更活性的硼氢化反应催化剂。计算表明，{7 DIPP}Zn-H同类物具有比NacNacZnH更明显的两亲性特征（在Zn上具有更大的亲电性，同时保持碱性氢化物）。在这两个硼氢化反应步骤中，炔基BPin的硼氢化反应由Zn-H络合物催化，而1，1-二硼基烯烃的硼氢化反应更有效地由含B-H的物种催化，包括由HBPin原位形成的硼烷。这些观察结果导致开发了一种用于将末端炔转化为1，1，1-三硼基烷烃的一锅法方案，该方案利用{7 DIPP}ZnPh（NTf 2）作为用于形成1，1-二硼基化烯烃的预催化剂，随后添加BH 3-THF作为最终步骤的催化剂。
The synthesis of 1,1,1-triborylalkanes from terminal alkynes and pinacolborane (HBPin) is reported. This transformation proceeds via initial Zn-catalyzed alkyne C-H borylation, which can be achieved using a NacNacZnH complex. Combinations of a NacNacZn-alkynyl formed via C-H zincation of a terminal alkyne and HBPin exist in equilibrium with the alkynyl-BPin and NacNacZnH. The consumption of NacNacZnH by irreversible reaction with a terminal alkyne evolving H-2 is essential for driving alkyne C-H borylation to completion. The alkynyl-BPin compounds undergo hydroboration catalyzed by Zn-H complexes at raised temperatures with a {7DIPP}ZnH(NTf2) complex (7DIPP = 1,3-bis(2,6-diisopropylpheny1)-4,5,6,7-tetrahydro-1H-1,3-diazepin-3-ium-2-ide) a more active catalyst for hydroboration than a NacNacZnH complex. Calculations indicate the {7DIPP}Zn-H congener has a more pronounced biphilic character than that of NacNacZnH (greater electrophilicity at Zn while maintaining a basic hydride). Of the two hydroboration steps, the hydroboration of alkynylBPin is catalyzed by Zn-H complexes, while the hydroboration of 1,1-diborylalkenes is catalyzed more effectively by B-H-containing species, including boranes formed in situ from HBPin. These observations led to a one-pot protocol being developed for converting terminal alkynes into 1,1,1-triborylalkanes that utilizes {7DIPP}ZnPh(NTf2) as a precatalyst for the formation of 1,1-diborylated alkenes with subsequent addition of BH3-THF as catalyst for the final step.