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Aza- and Oxadithiolates Are Proton Relays in Functional Models for the FeFe-Hydrogenases

机译:氮杂-和草二硫代硫酸盐是FeFe-加氢酶功能模型中的质子中继。

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摘要

The dithiolate cofactor for the [FeFe]-hydrogenase models, Fe2(xdt)(CO)2(dppv)2 (where xdt = 1,3-propanedithiolate (pdt), azadithiolate (adt), (SCH2)2NH, and oxadithiolate (odt), (SCH2)2O; dppv = cis-1,2-bis-(diphenylphosphino)ethylene) have been probed for their functionality as proton relays enabling formation and deprotonation of terminal hydrides. Compared to the propanedithiolate derivative, the azadithiolate and oxaditiholate show enhanced rates of proton transfer between solution and the terminal site on one Fe center. The results are consistent with the heteroatom of the dithiolate serving a gating role for both protonation and deprotonation. The pKa of the transiently formed ammonium (pK CD2Cl2 5.7–8.2) or oxonium (pK CD2Cl2 −4.7–1.6) regulates the proton transfer. As consequence, only the azadithiolate is capable of yielding the terminal hydride from weak acids. The aza- and oxadithiolates manifested the advantages of proton relays: the odt derivative proved to be a faster catalyst for hydrogen evolution than the pdt derivative as indicated from cyclic voltammetry plots of ic/ip vs. [H+]. The adt derivative was capable of proton reduction from the weak acid [HPMe2Ph]BF4 (pK CD2Cl2 = 5.7). The proton relay function does not apply to the isomeric bridged-hydrides [Fe2(xdt)(μ-H)(CO)2(dppv)2]+, where the hydride is too distant and too basic to interact to be affected by the heteroatomic relay site. None of these μ-H species can be deprotonated.
机译:[FeFe]-加氢酶模型的二硫醇盐辅因子Fe2(xdt)(CO)2(dppv)2(其中xdt = 1,3-丙二硫醇盐(pdt),氮杂二硫醇盐(adt),(SCH2)2NH和乙二硫醇草酸盐( odt),(SCH2)2O; dppv =顺式1,2-双(二苯基膦基)亚乙基)作为质子中继的功能已被探究,从而可形成末端氢化物并使其去质子化。与丙二硫醇盐衍生物相比,氮杂二硫醇盐和草二膦酸盐显示出溶液与一个Fe中心的末端位点之间质子转移的速率增加。结果与二硫醇盐的杂原子在质子化和去质子化中起门控作用一致。瞬时形成的铵(pK CD2Cl2 5.7-8.2)或氧鎓(pK CD2Cl2 -4.7-1.6)的pKa调节质子转移。结果,仅氮杂二硫醇盐能够从弱酸产生末端氢化物。硫杂和草二硫代硫酸盐具有质子传递的优势:如ic / ip与[H + 的循环伏安图所示,证明odt衍生物比pdt衍生物是更快的析氢催化剂。 ]。 adt衍生物能够从弱酸[HPMe2Ph] BF4还原质子(pK CD 2 Cl 2 = 5.7)。质子中继功能不适用于[Fe 2 (xdt)(μ-H)(CO) 2 (dppv) 2 < / sub>] + ,其中氢化物距离太远且太碱性,无法相互作用,因此不受杂原子中继位点的影响。这些μ-H物质均不能被去质子化。

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