Electronic Control of the Protonation Rates of Fe-Fe Bonds
Electronic Control of the Protonation Rates of Fe-Fe Bonds
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DOI：
10.1021/ja506693m
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发表时间：
2014-09-17
影响因子：
15
通讯作者：
Pickett, Christopher J.
中科院分区：
文献类型：
--
作者：
Jablonskyte, Ausra;Webster, Lee R.;Pickett, Christopher J.
在氢化酶和固氮酶的活性位点的功能的上下文中，在金属金属键处的质子化是基本的兴趣。在带有羰基和给电子配体的dfiron二硫纶配合物中，金属-金属键是具有“弯曲”几何形状的最高占据分子轨道（HOMO）。在这里，我们表明，实验测得的质子化率（k（H））的这个键和HOMO的能量，通过测量的复合物的氧化电位（E-1/2（ox））相关的线性自由能关系：在k（H）=（（F（c -β E-1/2（ox）/（RT）），其中c是一个常数和β是无量纲布朗斯台德系数。β值为0.68表明对HOMO能量的强烈依赖性：对于约1/2的E-1/2（ox）变化，测量的质子化速率变化超过6个数量级。0.55 V（ca. 11个数量级/V）。这种关系允许预测质子化率的系统，要么太快，以实验测量或拥有额外的质子化位点。它进一步表明，在二硫纶配体中的桥头的性质可以施加立体电子的影响：庞大的取代基不稳定的HOMO，从而增加质子化的速率。
Protonation at metal metal bonds is of fundamental interest in the context of the function of the active sites of hydrogenases and nitrogenases. In dfiron dithiolate complexes bearing carbonyl and electron-donating ligands, the metal-metal bond is the highest occupied molecular orbital (HOMO) with a "bent" geometry. Here we show that the experimentally measured rates of protonation (k(H)) of this bond and the energy of the HOMO as measured by the oxidation potential of the complexes (E-1/2(ox)) correlate in a linear free energy relationship: In k(H) = ((F(c - beta E-1/2(ox)))/(RT)), where c is a constant and beta is the dimensionless Bronsted coefficient. The value of beta of 0.68 is indicative of a strong dependence upon energy of the HOMO: measured rates of protonation vary over 6 orders of magnitude for a change in E-1/2(ox) of ca. 0.55 V (ca. 11 orders of magnitude/V). This relationship allows prediction of protonation rates of systems that are either too fast to measure experimentally or that possess additional protonation sites. It is further suggested that the nature of the bridgehead in the dithiolate ligand can exert a stereoelectronic influence: bulky substituents destabilize the HOMO, thereby increasing the rate of protonation.