Functional Model for the [Fe] Hydrogenase Inspired by the Frustrated Lewis Pair Concept
Functional Model for the [Fe] Hydrogenase Inspired by the Frustrated Lewis Pair Concept
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DOI：
10.1021/ja509186d
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发表时间：
2014-11-26
影响因子：
15
通讯作者：
Meyer, Franc
中科院分区：
文献类型：
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作者：
Kalz, Kai F.;Brinkmeier, Alexander;Meyer, Franc
[Fe]氢化酶（Hmd）通过在其活性部位使用独特的有机金属铁-鸟苷基吡啶醇（FeGP）辅因子和作为氢化物受体的底物亚甲基四氢甲蝶呤（亚甲基-H4 MPT+）来催化H-2的异裂。FeGP/亚甲基-H4 MPT+的组合及其反应性与受抑刘易斯对（FLP）的概念相似，其中一些已被证明异相裂解活化H2。本工作通过使用刘易斯碱性钌金属化物，即K[CpRu（CO）（2）]（KRp）和相关的聚合物Cp/Ru/CO化合物（Rs）与新的咪唑啉盐1，3-bis的组合来利用Hmd反应性的这种解释。（2，6-二氟苯基）-2-（4-甲苯基）咪唑啉溴化物（[（Tol）Im（F4）]Br-+（-）），其被设计为模拟亚甲基-H4 MPT+的氢化物受体性质。[（Tol）Im（F4）]Br-+（-）和相应的咪唑烷H（Tol）Im（F4）的固态结构表明，杂环经历了与生物底物类似的结构变化。密度泛函理论计算表明，在极性溶剂中，FLP的Rp（-）/[（Tol）Im（F4）]（+）异裂反应是放热的，但初始刘易斯对的形成是不利的.因此，组合Rp（-）/[（Tol）Im（F4）]（+）不与H-2反应，而是导致亲核取代的副产物（室温下k = 4 × 10（-2）L mol（-1）s（-1））。相比之下，当使用D-2时，异质组合Rs/[（Tol）Im（F4）]（+）确实异源裂解H-2以得到H（Tol）Im（F4）和HRuCp（CO）（2）（HRp）或D（Tol）Im（F4）和DRp。该反应通过H-1/H-2和F-19 NMR光谱以及IR光谱进行跟踪，并且在1天后达到96%的转化率。H（Tol）Im（F4）在这些条件下的形成表明，通过质子化的超亲电活化（已经提出用于次甲基-H4 MPT+以增加其碳阳离子特性）对于咪唑啉离子充当氢化物受体不是必需的。这种前所未有的[Fe]氢化酶的功能模型，使用刘易斯酸性咪唑啉盐作为仿生氢化物受体结合有机金属刘易斯碱，可能会提供新的灵感仿生H-2激活。
[Fe] hydrogenase (Hmd) catalyzes the heterolytic splitting of H-2 by using, in its active site, a unique organometallic iron-guanylylpyridinol (FeGP) cofactor and, as a hydride acceptor, the substrate methenyltetrahydromethanopterin (methenyl-H4MPT+). The combination FeGP/methenyl-H4MPT+ and its reactivity bear resemblance to the concept of frustrated Lewis pairs (FLPs), some of which have been shown to heterolytically activate H2. The present work exploits this interpretation of Hmd reactivity by using the combination of Lewis basic ruthenium metalates, namely K[CpRu(CO)(2)] (KRp) and a related polymeric Cp/Ru/CO compound (Rs), with the new imidazolinium salt 1,3-bis(2,6-difluorophenyl)-2-(4-tolyl)imidazolinium bromide ([(Tol)Im(F4)]Br-+(-)) that was designed to emulate the hydride acceptor properties of methenyl-H4MPT+. Solid-state structures of [(Tol)Im(F4)]Br-+(-) and the corresponding imidazolidine H(Tol)Im(F4) reveal that the heterocycle undergoes similar structural changes as in the biological substrate. DFT calculations indicate that heterolytic splitting of dihydrogen by the FLP Rp(-)/[(Tol)Im(F4)](+) is exothermic, but the formation of the initial Lewis pair should be unfavorable in polar solvents. Consequently the combination Rp(-)/[(Tol)Im(F4)](+) does not react with H-2 but leads instead to side products from nucleophilic substitution (k = 4 x 10(-2) L mol (-1) s(-1) at room temperature). In contrast, the heterogeneous combination Rs/[(Tol)Im(F4)](+) does split H-2 heterolytically to give H(Tol)Im(F4) and HRuCp(CO)(2) (HRp) or D(Tol)Im(F4) and DRp when using D-2. The reaction has been followed by H-1/H-2 and F-19 NMR spectroscopy as well as by IR spectroscopy and reaches 96% conversion after 1 d. Formation of H(Tol)Im(F4) under these conditions demonstrates that superelectrophilic activation by protonation, which has been proposed for methenyl-H4MPT+ to increase its carbocationic character, is not necessarily required for an imidazolinium ion to serve as a hydride acceptor. This unprecedented functional model for the [Fe] hydrogenase, using a Lewis acidic imidazolinium salt as a biomimetic hydride acceptor in combination with an organometallic Lewis base, may provide new inspiration for biomimetic H-2 activation.