Reversible alkene binding and allylic C-H activation with an aluminium(i) complex
Reversible alkene binding and allylic C-H activation with an aluminium(i) complex
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DOI：
10.1039/c8sc04865g
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发表时间：
2019-02-28
期刊：
影响因子：
8.4
通讯作者：
Crimmin, Mark R.
中科院分区：
文献类型：
--
作者：
Bakewell, Clare;White, Andrew J. P.;Crimmin, Mark R.
单体分子铝配合物1 [{（ArNCMe）（2）CH}Al]（Ar = 2，6-二异丙基苯基）与乙烯、丙烯、烯丙基苯和异戊烯等一系列末端和张力烯烃反应生成烯烃结合产物。值得注意的是，所有这些反应在温和条件下（298-353 K）是可逆的，由于正反应熵，在较高温度下不利于烯烃结合。Van 't霍夫分析允许定量Δ G（298）度K = -4至-8 kcal mol（-1）的结合事件。计算和单晶X-射线衍射研究是一致的，与烯烃结合的物种是二环丙烷配合物。烯烃结合涉及可逆的氧化还原过程，从+1到+3铝氧化态的变化。在更强制的条件下，二环丙烷络合物经历不可逆的烯丙基C-H键活化以生成铝（III）烯丙基氢化物络合物。这代表了基于氧化还原的主基团反应性的罕见实例，其中可逆底物结合之后是进一步的生产性键断裂事件。对该机制的分析揭示了一个反应网络，其中烯丙位C-H活化需要烯烃解离和1的重组，这一认识对于开发具有主族化合物的基于氧化还原的催化循环的长期目标具有重要意义。
The monomeric molecular aluminium(i) complex 1 [{(ArNCMe)(2)CH}Al] (Ar = 2,6-di-iso-propylphenyl) reacts with a series of terminal and strained alkenes including ethylene, propylene, allylbenzene and norbornene to form alkene bound products. Remarkably all these reactions are reversible under mild conditions (298-353 K) with alkene binding being disfavoured at higher temperatures due to the positive reaction entropy. Van't Hoff analyses have allowed quantification of the binding events with Delta G(298)degrees K = -4 to -8 kcal mol(-1). Calculations and single crystal X-ray diffraction studies are consistent with the alkene bound species being metallocyclopropane complexes. Alkene binding involves a reversible redox process with changes from the +1 to +3 aluminium oxidation state. Under more forcing conditions the metallocyclopropane complexes undergo non-reversible allylic C-H bond activation to generate aluminium(III) allyl hydride complexes. This represents a rare example of redox-based main group reactivity in which reversible substrate binding is followed by a further productive bond breaking event. Analysis of the mechanism reveals a reaction network in which alkene dissociation and reformation of 1 is required for allylic C-H activation, a realisation that has important implications for the long-term goal of developing redox-based catalytic cycles with main group compounds.