Catalytic Hydrogenation of Alkenes and Alkynes by a Cobalt Pincer Complex: Evidence of Roles for Both Co(I) and Co(II)
Catalytic Hydrogenation of Alkenes and Alkynes by a Cobalt Pincer Complex: Evidence of Roles for Both Co(I) and Co(II)
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DOI：
10.1021/acs.organomet.1c00053
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发表时间：
2021-03-15
期刊：
影响因子：
2.8
通讯作者：
Tonzetich, Zachary J.
中科院分区：
文献类型：
--
作者：
Alawisi, Hussah;Arman, Hadi D.;Tonzetich, Zachary J.
Co（I）配合物[Co（N-2）（（PNP）-P-Cy）]（（PNP）-P-Cy = 2，5-双（二环己基膦甲基）吡咯的阴离子）在室温下，在2 bar的H2（g）下，对末端烯烃的催化氢化和内炔的半氢化具有活性。炔半氢化的产物是E和Z-烯烃的混合物。相比之下，使用相关的钴（I）预催化剂[Co（PMe 3）-（（TNP）-T-Cy）]导致仅形成Z-烯烃。半稳定的Co（II）物质[CoH（（PNP）-P-Cy）]也可以通过用H-2处理[Co（N-2）（（TNP）-T-Cy）]的脱气溶液来产生。Co-II-氢化物显示出对烯烃氢化和异构化的活性，但其不稳定性阻碍了作为催化剂的实施。已经在溶液中分离并检测到与潜在催化中间体相关的几种物质。这些化合物包括Co（I）的烯和炔加合物以及Co（III）二氢化物物质。与化合物的催化结果检查是最一致的一个过程，涉及钴（I）和钴（III）状态之间的穿梭。然而，产生少量的钴（II）在催化营业额似乎是负责观察到的异构化的炔半氢化。钴氧化态在相同的催化剂体系中的相互作用进行了讨论的背景下，催化加氢的机制方案。
The Co(I) complex, [Co(N-2)((PNP)-P-Cy)] ((PNP)-P-Cy = anion of 2,5-bis-(dicyclohexylphosphinomethyl)pyrrole), is active toward the catalytic hydrogenation of terminal alkenes and the semi-hydrogenation of internal alkynes under 2 bar of H-2 (g) at room temperature. The products of alkyne semi-hydrogenation are a mixture of E : and Z-alkenes. By contrast, use of the related cobalt(I) precatalyst, [Co(PMe3)-((TNP)-T-Cy)], results in formation of exclusively Z-alkenes. A semi-stable Co(II) species, [CoH((PNP)-P-Cy)], can also be generated by treatment of degassed solutions of [Co(N-2)((TNP)-T-Cy)] with H-2. The Co-II-hydride displays activity toward both alkene hydrogenation and isomerization, but its instability hampers implementation as a catalyst. Several species relevant to potential catalytic intermediates have been isolated and detected in solution. These compounds include alkene and alkyne adducts of Co(I) as well as a Co(III) dihydride species. Catalytic results with the compounds examined are most consistent with a process involving shuttling between Co(I) and Co(III) states. However, generation of small quantities of Co(II) during catalytic turnover appears to be responsible for the isomerization observed for alkyne semi-hydrogenation. The interplay of cobalt oxidation states within the same catalyst system is discussed in the context of mechanistic scenarios for catalytic hydrogenation.