Selective hydroboration of electron-rich isocyanates by an NHC-copper(I) alkoxide.
Selective hydroboration of electron-rich isocyanates by an NHC-copper(I) alkoxide.
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NHC-铜(I)醇盐选择性硼氢化富电子异氰酸酯。
DOI：
10.1039/d2cc04742j
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发表时间：
2023
期刊：
影响因子：
--
通讯作者：
English LE
中科院分区：
文献类型：
--
作者：
English LE
（IPr）CuOtBu催化的11种芳基和烷基异氰酸酯与频哪醇硼烷的还原在大多数情况下仅得到硼甲酰胺pinBN（R）C（O）H。阻碍几乎所有异氰酸酯硼氢化的过度还原仅限于贫电子的芳基异氰酸酯（4-NC-C6 H4 NCO、4-F3 C-C6 H4 NCO、3-O2 N-C6 H4 NCO）。计算分析表明，稳定的[（IPr）CuH]2，这被认为是催化剂的静止状态，驱动选择性，建议在未来的工作中，以防止过度还原的方法。在iPrNCO的情况下，这种物质的形成使得过度还原在动力学上不可接近。然而，对于4-NC-C6 H4 NCO，过度还原的第一步的势垒高度低得多，甚至相对于[（IPr）CuH]2，导致非选择性还原。
The (IPr)CuOtBu catalysed reduction of 11 aryl and alkyl isocyanates with pinacolborane gave only the boraformamides, pinBN(R)C(O)H, in most cases. Overreduction, which hampers almost all isocyanate hydroborations, was restricted to electron poor aryl isocyanates (4-NC-C6H4NCO, 4-F3C-C6H4NCO, 3-O2N-C6H4NCO). Computational analysis showed stability of [(IPr)CuH]2, which was proposed to be the catalyst resting state, drives selectivity, suggesting an approach to prevent overreduction in future work. In the case of iPrNCO, formation of this species renders overreduction kinetically inaccessible. For 4-NC-C6H4NCO, however, the barrier height for the first step of over-reduction is much lower, even relative to [(IPr)CuH]2, resulting in unselective reduction.