Tungstacyclopentane Ring Contraction Yields Olefin Metathesis Catalysts
Tungstacyclopentane Ring Contraction Yields Olefin Metathesis Catalysts
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DOI：
10.1021/jacs.2c03732
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发表时间：
2022-06-22
影响因子：
15
通讯作者：
Carta，Veronica
中科院分区：
文献类型：
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作者：
Boudjelel，Maxime;Riedel，Rene;Carta，Veronica
在22°C的环境（荧光）光下，将方形金字塔型钨环戊烷配合物W(NAr)(OSiPh3)2(C4H8) （Ar = 2,6-i- pr2c6h3）溶液暴露于乙烯中，缓慢地形成丙烯和方形金字塔型钨环戊烷配合物W(NAr)(OSiPh3)2（C3H6）。在黑暗中没有反应发生，但在蓝色LED光（λmax约450 nm）下，反应在约15分钟内完成了bbb90 %。中间体首先是α甲基钨环丁烷配合物(W(NAr)(OSiPh3)2(α mec3h5))，然后是β甲基。每一种TBP版本都可以失去丙烯并形成亚甲基配合物，在乙烯存在下，未取代的钨环丁烷配合物W(NAr)(OSiPh3)2（C3H6）。在不可见的TBP W(NAr)(OSiPh3)2（C4H8）异构体（C4H8环为赤道环）中，W - c - α键被光均匀切割。当W和C3之间的键形成时，一个氢原子从C3移动到丁基链末端的C4碳上，形成TBP α甲基钨环丁烷络合物。本质上，W(NCPh3)(OSiPh3)2（C4H8）的行为与W(NAr)(OSiPh3)2（C4H8）相同，只是W(NCPh3)(OSiPh3)2（C4H8）的消耗速度大约是W(NAr)(OSiPh3)2（C4H8）的一半。在这种情况下，观察到α甲基取代的钨环丁烷中间体，从W(NCPh3)(OSiPh3)2（C4H8）生成W(NCPh3)(OSiPh3)2（C3H6）和丙烯的总速率比NAr体系慢约20倍。这些结果构成了从金属环戊烷环（环收缩）形成金属环丁烷环的第一个实验记录的例子，并建立了如何在乙烯存在下形成和重组具有合成活性的亚甲基和金属环丁烷配合物。他们还提出了一种可能性，即环境光可能在一些涉及乙烯和钨基亚胺烷基烯烃催化的复分解反应中发挥作用，如果不是其他的。
Exposure of a solution of the square pyramidal tungstacyclopentane complex W(NAr)(OSiPh3)2(C4H8) (Ar = 2,6-i-Pr2C6H3) to ethylene at 22 °C in ambient (fluorescent) light slowly leads to the formation of propylene and the square pyramidal tungstacyclobutane complex W(NAr)(OSiPh3)2(C3H6). No reaction takes place in the dark, but the reaction is >90% complete in ∼15 min under blue LED light (∼450 nm λmax). The intermediates are proposed to be (first) an α methyl tungstacyclobutane complex (W(NAr)(OSiPh3)2(αMeC3H5)), and then from it, a β methyl version. The TBP versions of each can lose propylene and form a methylene complex, and in the presence of ethylene, the unsubstituted tungstacyclobutane complex W(NAr)(OSiPh3)2(C3H6). The W–Cαbond in an unobservable TBP W(NAr)(OSiPh3)2(C4H8) isomer in which the C4H8ring is equatorial is proposed to be cleaved homolytically by light. A hydrogen atom moves or is moved from C3 to the terminal C4 carbon in the butyl chain as the bond between W and C3 forms to give the TBP α methyl tungstacyclobutane complex. Essentially, the same behavior is observed for W(NCPh3)(OSiPh3)2(C4H8) as for W(NAr)(OSiPh3)2(C4H8), except that the rate of consumption of W(NCPh3)(OSiPh3)2(C4H8) is about half that of W(NAr)(OSiPh3)2(C4H8). In this case, an α methyl-substituted tungstacyclobutane intermediate is observed, and the overall rate of formation of W(NCPh3)(OSiPh3)2(C3H6) and propylene from W(NCPh3)(OSiPh3)2(C4H8) is ∼20 times slower than in the NAr system. These results constitute the first experimentally documented examples of forming a metallacyclobutane ring from a metallacyclopentane ring (ring contraction) and establish how metathesis-active methylene and metallacyclobutane complexes can be formed and reformed in the presence of ethylene. They also raise the possibility that ambient light could play a role in some metathesis reactions that involve ethylene and tungsten-based imido alkylidene olefin metathesis catalysts, if not others.