Department of Chemistry , The University of Texas at Austin , Austin , Texas 78712 , United States.
Inorg Chem. 2019 Oct 7;58(19):12689-12699. doi: 10.1021/acs.inorgchem.9b01530. Epub 2019 Sep 9.
We report syntheses and H activation involving model complexes of mono-iron hydrogenase (Hmd) derived from acyl-containing pincer ligand precursors bearing thioether () or phosphine () donor sets. Both complexes feature pseudo-octahedral iron(II) dicarbonyl units. While the pincer adopts the expected -CNS (pincer) geometry, the ligand unexpectedly adopts the -CNP coordination geometry. Both complexes exhibit surprisingly acidic methylene C-H bond (reversibly de/protonated by a bulky phenolate), which affords a putative dearomatized pyridinate-bound intermediate. Such base treatment of also results in deligation of the thioether sulfur donor, generating an open coordination site from the acyl unit. In contrast, maintains a CO ligand from the acyl site both in the parent and dearomatized complexes (the -PPh donor is to acyl). The dearomatized - was competent for H activation (5 atm D plus phenolate as base), which is attributed to both the basic site on the ligand framework and the open coordination site to the acyl donor. In contrast, the dearomatized - was for H activation, which is ascribed to the blocked coordination site from acyl (occupied by CO ligand). These results highlight the importance of both (i) the open coordination site to the organometallic acyl donor and (ii) a pendant base in the enzyme active site.
我们报告了单铁氢化酶（Hmd）模型配合物的合成和 H 活化，这些配合物源自含有酰基的钳形配体前体，带有硫醚（）或膦（）供体。这两个配合物都具有拟八面体的铁（II）二羰基单元。虽然 配体采用了预期的 -CNS（钳形）几何构型，但 配体却出人意料地采用了 -CNP 配位几何构型。这两个配合物都表现出非常酸性的亚甲基 C-H 键（可被大体积的酚盐可逆地去质子化/质子化），这提供了一个假定的去芳构化的吡啶基结合的中间产物。这种碱基处理 也导致硫醚供体的解配，从酰基单元生成一个开放的配位位点 。相比之下，在母体和去芳构化的配合物中， 都保留了一个 CO 配体 来自酰基位点（-PPh 供体在酰基侧）。去芳构化的 - 能够进行 H 活化（5 atm D 加上酚盐作为碱），这归因于配体骨架上的碱性位点和开放的配位位点 到酰基供体。相比之下，去芳构化的 - 不适合 H 活化，这归因于酰基的配位位点被封闭（被 CO 配体占据）。这些结果突出了两个因素的重要性：（i）开放的配位位点 到有机金属酰基供体和（ii）酶活性位点中的悬垂碱。
