Group of Inorganic Materials Chemistry, Department of Chemistry, University of Turku, FI-20014 Turku, Finland.
Laboratory of Molecular Science and Technology, Åbo Akademi University, FI-20500 Turku, Finland.
Dalton Trans. 2021 May 11;50(18):6088-6099. doi: 10.1039/d1dt00419k.
Six known aminophenolate vanadium complexes V1-V6 were examined in 3,5-di-tert-butylcatechol (1, 3,5-DTBC) oxidation. From the complexes V1-V5 have been previously shown to demonstrate catechol oxidase (catecholase) like behavior, catalytically oxidizing 1 to 3,5-di-tert-butyl-1,2-benzoquinone (2, 3,5-DTBQ). A critical re-evaluation of V1-V5, including V6 not assessed earlier, in the aerobic oxidation of 1 has revealed that several catechol dioxygenase products are obtained in addition to 2, which is produced partly by autoxidation. Mechanistic investigations into the V1-V6 catalyzed oxidation of 1 by EPR, negative mode ESI-MS and 51V NMR, in addition to semi-quantitative product distribution analyses with GC and column chromatography afford compelling evidence in support of the "common catalyst hypothesis" earlier proposed by Finke and co-workers. During the reaction, V1-V6 are partially converted in situ by H2O2 assisted leaching to vanadium catecholate complexes [V(3,5-DTBC)2(3,5-DTBSQ˙)] and [VO(3,5-DTBC)(3,5-DTBSQ˙)], where 3,5-DTBSQ˙ = 3,5-di-tert-butyl-1,2-semiquinone, the latter of which has been implicated as the common true active catalyst in catechol dioxygenation as per the common catalyst hypothesis. The results herein suggest that vanadium aminophenolate complexes are sensitive to H2O2 mediated leaching in the presence of strong σ and π donating ligands such as 1 and 2. Furthermore, based on these results, the use of vanadium aminophenolate complexes as catechol oxidase mimics is not as warranted as previously understood.
六种已知的氨基酚钒配合物 V1-V6 在 3,5-二叔丁基邻苯二酚（1,3,5-DTBC）氧化中进行了研究。先前已经表明，配合物 V1-V5 具有儿茶酚氧化酶（儿茶酚酶）样行为，可催化氧化 1 生成 3,5-二叔丁基-1,2-苯醌（2,3,5-DTBQ）。对 V1-V5 进行了重新评估，包括之前未评估的 V6，发现除了部分由自动氧化生成的 2 之外，还获得了几种儿茶酚双加氧酶产物。通过 EPR、负模式 ESI-MS 和 51V NMR 对 V1-V6 催化 1 氧化的机制研究，以及通过 GC 和柱色谱进行半定量产物分布分析，为 Finke 及其同事早期提出的“通用催化剂假说”提供了令人信服的证据。在反应过程中，V1-V6 通过 H2O2 辅助浸出原位部分转化为钒儿茶酚配合物 [V(3,5-DTBC)2(3,5-DTBSQ˙)] 和 [VO(3,5-DTBC)(3,5-DTBSQ˙)]，其中 3,5-DTBSQ˙ = 3,5-二叔丁基-1,2-半醌，后者被认为是儿茶酚双加氧酶作用中的通用真实活性催化剂，根据通用催化剂假说。结果表明，在强 σ 和 π 供体配体如 1 和 2 的存在下，钒氨基酚配合物对 H2O2 介导的浸出敏感。此外，基于这些结果，以前被认为是合理的，钒氨基酚配合物作为儿茶酚氧化酶模拟物的使用并不像以前理解的那样有保证。
