Influence of Thiolate versus Alkoxide Ligands on the Stability of Crystallographically Characterized Mn(III)-Alkylperoxo Complexes
Influence of Thiolate versus Alkoxide Ligands on the Stability of Crystallographically Characterized Mn(III)-Alkylperoxo Complexes
复制标题
DOI：
10.1021/jacs.0c13001
复制
发表时间：
2021-04-14
影响因子：
15
通讯作者：
Kovacs, Julie A.
中科院分区：
文献类型：
--
作者：
Downing, Alexandra N.;Coggins, Michael K.;Kovacs, Julie A.
本文所述的工作证明了金属酶和过渡金属络合物的内配位层对反应性的精细控制。我们报告的几个晶体学特征的锰过氧配合物，并表明，测量和光谱参数之间的紧密相关性，建立了以前由我们组的硫醇盐连接RS-锰（III）-OOR配合物，可以扩展到包括一个烷氧基连接RO-锰（III）-OOR配合物。我们表明，醇盐连接的RO-Mn（III）-OOR络合物比其硫醇盐连接的RS-Mn（III）-OOR衍生物（t（1/2）（293）K = 249 s，k（1）（293）K = 2.78 × 10（-3）s（-1））。电子结构计算提供了关于这些稳定性差异的见解。最高占据轨道的硫醇连接的衍生物具有显着的硫特征和π-反馈从硫醇竞争与π-反馈从过氧pi*（O-O）。DFT计算的Mulliken电荷表明，醇盐连接的RO-Mn（III）-OOR的Mn离子刘易斯酸性（+0.451）大于硫醇盐连接的RS-Mn（III）-OOR的Mn离子路易斯酸性（+0.306），从而促进了反键过氧π *（O-O）轨道的π反馈并增加了其稳定性。这有助于解释为什么光合放氧Mn络合物，其催化O-O键的形成，而不是裂解，掺入O-和/或N-配体，而不是S-cys-配体。
The work described herein demonstrates the exquisite control that the inner coordination sphere of metalloenzymes and transition-metal complexes can have on reactivity. We report one of few crystallographically characterized Mn-peroxo complexes and show that the tight correlations between metrical and spectroscopic parameters, established previously by our group for thiolate-ligated RS-Mn(III)-OOR complexes, can be extended to include an alkoxide-ligated RO-Mn(III)-OOR complex. We show that the alkoxide-ligated RO-Mn(III)-OOR complex is an order of magnitude more stable (t(1/2)(298 K) = 6730 s, k(obs)(298 K) = 1.03 x 10(-4) s(-1)) than its thiolate-ligated RS-Mn(III)-OOR derivative (t(1/2)(293) K = 249 s, k(1)(293) K = 2.78 x 10(-3) s(-1)). Electronic structure calculations provide insight regarding these differences in stability. The highest occupied orbital of the thiolate-ligated derivative possesses significant sulfur character and pi-backdonation from the thiolate competes with pi-backdonation from the peroxo pi*(O-O). DFT-calculated Mulliken charges show that the Mn ion Lewis acidity of alkoxide-ligated RO-Mn(III)-OOR (+0.451) is greater than that of thiolate-ligated RS-Mn(III)-OOR (+0.306), thereby facilitating pi-backdonation from the antibonding peroxo pi*(O-O) orbital and increasing its stability. This helps to explain why the photosynthetic oxygen-evolving Mn complex, which catalyzes O-O bond formation as opposed to cleavage, incorporates O- and/or N-ligands as opposed to S-cys-ligands.