Department of Chemistry and Polymer Science , Stellenbosch University , Private Bag X1, Stellenbosch , 7602 Western Cape , South Africa.
Inorg Chem. 2018 Aug 6;57(15):8909-8922. doi: 10.1021/acs.inorgchem.8b00840. Epub 2018 Jul 24.
Herein, we present a DFT computational study of the trans-[OsO(OH)] and [OsO(OH) ] ( n = 1, 2 cis) comproportionation reaction mechanism that occurs in a basic aqueous matrix. The reaction pathway where [OsO(OH)] reacts with trans-[OsO(OH)] via an intermediate mediated concerted electron-proton transfer yielded the best agreement with experiment (Δ H°, Δ S° and Δ G° experimental data for the forward reaction are 10.3 ± 0.5 kcal mol, -2.6 ± 1.6 cal mol K, and 11.1 ± 0.9 kcal mol and for the reverse reaction are -6.7 ± 1.0 kcal mol, -63.6 ± 3.4 cal mol K, and 12.2 ± 2.0 kcal mol, respectively, where at the PBE-D3 level for the forward reaction are 11.3 kcal mol, -9.8 cal mol K, and 14.2 kcal mol and for the reverse reaction are -11.8 kcal mol, -80.7 cal mol K, and 12.3 kcal mol, respectively) and consists of (i) formation of a (singlet spin state) noncovalent adduct, [Os═O···HO-Os], (ii) spin-forbidden, concerted electron-proton transfer (i-EPT) from the trans-[OsO(OH)] donor to the Os acceptor to form a second (triplet spin state) noncovalent adduct, [Os-OH···O═Os], (iii) separation of the Os monomers, and finally (iv) interconversion of the separated species to form trans-[OsO(OH)] and mer-[OsO(OH)] stereoisomer species. i-EPT from Os to the Os species was found to be the rate-determining step, which corroborated the experimental evidence (kinetic isotope effect) that the rate-determining step involves the transfer of a proton.
在此，我们提出了一个 DFT 计算研究，涉及在碱性水基质中发生的 trans-[OsO(OH)] 和 [OsO(OH)] ( n = 1, 2 cis) 自衡反应机制。[OsO(OH)] 通过中间体协同电子-质子转移与 trans-[OsO(OH)] 反应的反应途径与实验结果吻合得最好（正向反应的Δ H°、Δ S° 和 Δ G° 实验数据分别为 10.3 ± 0.5 kcal mol、-2.6 ± 1.6 cal mol K 和 11.1 ± 0.9 kcal mol，而逆向反应的Δ H°、Δ S° 和 Δ G° 实验数据分别为-6.7 ± 1.0 kcal mol、-63.6 ± 3.4 cal mol K 和 12.2 ± 2.0 kcal mol，其中正向反应在 PBE-D3 水平下的Δ H°、Δ S° 和 Δ G° 分别为 11.3 kcal mol、-9.8 cal mol K 和 14.2 kcal mol，而逆向反应在 PBE-D3 水平下的Δ H°、Δ S° 和 Δ G° 分别为-11.8 kcal mol、-80.7 cal mol K 和 12.3 kcal mol），它由以下步骤组成：（i）形成非共价加合物[Os═O···HO-Os]（单重自旋态）；（ii）从 trans-[OsO(OH)] 给体到 Os 受体的自旋禁阻、协同电子-质子转移（i-EPT），形成第二个非共价加合物[Os-OH···O═Os]（三重自旋态）；（iii）Os 单体的分离；最后（iv）分离物种的互变，形成 trans-[OsO(OH)] 和 mer-[OsO(OH)] 立体异构体。从 Os 到 Os 物种的 i-EPT 被发现是速率决定步骤，这与实验证据（动力学同位素效应）相符，即速率决定步骤涉及质子的转移。
