Controlling Substrate Binding to Fe4S4 Clusters through Remote Steric Effects
Controlling Substrate Binding to Fe4S4 Clusters through Remote Steric Effects
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DOI：
10.1021/acs.inorgchem.9b00360
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发表时间：
2019-04-15
影响因子：
4.6
通讯作者：
Suess, Daniel L. M.
中科院分区：
文献类型：
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作者：
Brown, Alexandra C.;Suess, Daniel L. M.
许多Fe-S酶表现出的非凡反应性在很大程度上是由于蛋白质支架对底物结合和活化的影响。原则上，合成的Fe-S簇合物的配位化学可以类似地通过远程空间效应来控制。为此，我们报道了由具有可变空间构型的N-杂环卡宾（NHC）配体连接的3：1位置差异的[Fe_4S_4]簇合物的合成：IMes（1，3-dimesitylimidazol-2-ylidene）和'（IPrMe）-Pr-1（1，3-diisopropyl-4，5-dimethylimidazol-2-ylidene）。在醚溶剂（Et 2 O和THF）中用NaBAr 4F处理（IMes）（3）Fe 4S 4Cl导致形成醚加合物[（IMes）（3）Fe 4S 4（solv）][BAr 4F];溶剂可以通过添加（BuNC）-Bu-t来置换以形成不寻常的单异氰化物加合物[（IMes）（3）Fe 4S 4（CNTBu）][BAr 4F]。用空间位阻较小的簇（（IPrMe）-Pr-i）（3）Fe 4S 4Cl进行相同的反应导致更典型的反应性：不期望的配体重新分布以形成均配簇[（（IPrMe）-Pr-i）（4）Fe 4S 4][BAr 4F]和生成三异氰化物加合物[（（IPrMe）-Pr-i）（3）Fe 4S 4（（CNBu）-Bu-t）（3）][BAr 4F]。IMes配体的空间分布的增加不利于配体再分布，并在顶端Fe处限定了结合口袋，从而使得能够生成配位不饱和和取代不稳定的Fe位点。这种通过修改与相邻Fe位点结合的配体的空间位阻来控制顶端Fe位点处的配位化学的方法补充了现有的用于产生位点分化的Fe-S簇的策略，并提供了在立方体簇直接反应的新机会。
The extraordinary reactivity exhibited by many Fe-S enzymes is due in large part to the influence of the protein scaffold on substrate binding and activation. In principle, the coordination chemistry of synthetic Fe-S clusters could similarly be controlled through remote steric effects. Toward this end, we report the synthesis of 3:1 site-differentiated [Fe4S4] clusters ligated by N-heterocyclic carbene (NHC) ligands with variable steric profiles: IMes (1,3-dimesitylimidazol-2-ylidene) and '(IPrMe)-Pr-i (1,3-diisopropyl-4,5-dimethylimidazol-2-ylidene). Treatment of (IMes)(3)Fe4S4Cl with NaBAr4F in ethereal solvents (Et2O and THF) leads to the formation of an ether adduct, [(IMes)(3)Fe4S4(solv)][BAr4F]; solvent can be displaced by addition of (BuNC)-Bu-t to form the unusual monoisocyanide adduct [(IMes)(3)Fe4S4(CNtBu)][BAr4F]. Carrying out the same reactions with the less sterically encumbered cluster ((IPrMe)-Pr-i)(3)Fe4S4Cl results in more typical reactivity: undesired ligand redistribution to form the homoleptic cluster [((IPrMe)-Pr-i)(4)Fe4S4][BAr4F] and generation of the triisocyanide adduct [((IPrMe)-Pr-i)(3)Fe4S4((CNBu)-Bu-t)(3)][BAr4F]. The increased steric profile of the IMes ligands disfavors ligand redistribution and defines a binding pocket at the apical Fe, thereby enabling the generation of a coordinatively unsaturated and substitutionally labile Fe site. This method of controlling the coordination chemistry at the apical Fe site by modifying the sterics of ligands bound to adjacent Fe sites complements existing strategies for generating site-differentiated Fe-S clusters and provides new opportunities to direct reactivity at cuboidal metalloclusters.