Kerns Spencer A, Seo Junhyeok, Lynch Vincent M, Shearer Jason, Goralski Sean T, Sullivan Eileen R, Rose Michael J
Department of Chemistry, The University of Texas at Austin Austin Texas 78712 USA
Department of Chemistry, Gwangju Institute of Science and Technology Gwangju 61005 Republic of Korea.
Chem Sci. 2021 Sep 10;12(38):12838-12846. doi: 10.1039/d0sc03154b. eCollection 2021 Oct 6.
We report the synthesis and reactivity of a model of [Fe]-hydrogenase derived from an anthracene-based scaffold that includes the endogenous, organometallic acyl(methylene) donor. In comparison to other non-scaffolded acyl-containing complexes, the complex described herein retains molecularly well-defined chemistry upon addition of multiple equivalents of exogenous base. Clean deprotonation of the acyl(methylene) C-H bond with a phenolate base results in the formation of a dimeric motif that contains a new Fe-C(methine) bond resulting from coordination of the deprotonated methylene unit to an adjacent iron center. This effective second carbanion in the ligand framework was demonstrated to drive heterolytic H activation across the Fe(ii) center. However, this process results in reductive elimination and liberation of the ligand to extrude a lower-valent Fe-carbonyl complex. Through a series of isotopic labelling experiments, structural characterization (XRD, XAS), and spectroscopic characterization (IR, NMR, EXAFS), a mechanistic pathway is presented for H/hydride-induced loss of the organometallic acyl unit ( pyCH-C[double bond, length as m-dash]O → pyCH+C[triple bond, length as m-dash]O). The known reduced hydride species [HFe(CO)] and [HFe(CO)] have been observed as products by H/H NMR and IR spectroscopies, as well as independent syntheses of PNP[HFe(CO)]. The former species ( [HFe(CO)]) is deduced to be the actual hydride transfer agent in the hydride transfer reaction (nominally catalyzed by the title compound) to a biomimetic substrate (Im = fluorinated imidazolium as hydride acceptor). This work provides mechanistic insight into the reasons for lack of functional biomimetic behavior (hydride transfer) in acyl(methylene)pyridine based mimics of [Fe]-hydrogenase.
我们报道了一种基于蒽骨架的[Fe]-氢化酶模型的合成及其反应活性，该模型包含内源性有机金属酰基（亚甲基）供体。与其他无骨架的含酰基配合物相比，本文所述的配合物在加入多当量的外源碱后仍保持分子结构明确的化学性质。用酚盐碱对酰基（亚甲基）C-H键进行完全去质子化，导致形成一种二聚体结构，该结构包含一个新的Fe-C（次甲基）键，这是由去质子化的亚甲基单元与相邻铁中心配位形成的。配体框架中这种有效的二级碳负离子被证明可驱动Fe(ii)中心的异裂氢活化。然而，这个过程会导致还原消除和配体的释放，从而挤出一个低价铁羰基配合物。通过一系列同位素标记实验、结构表征（XRD、XAS）和光谱表征（IR、NMR、EXAFS），提出了一条H/氢化物诱导有机金属酰基单元损失的机理途径（pyCH-C[双键，长度为m破折号]O → pyCH+C[三键，长度为m破折号]O）。通过H/H NMR和IR光谱以及PNP[HFe(CO)]的独立合成，已观察到已知的还原氢化物物种[HFe(CO)]和[HFe(CO)]作为产物。推断前一种物种（[HFe(CO)]）是氢化物转移反应（名义上由标题化合物催化）中向仿生底物（Im = 氟化咪唑鎓作为氢化物受体）转移氢化物的实际氢化物转移剂。这项工作为基于酰基（亚甲基）吡啶的[Fe]-氢化酶模拟物缺乏功能性仿生行为（氢化物转移）的原因提供了机理见解。
