Yin Cindy-Xing, Sasaki Yoh, Finke Richard G
Department of Chemistry, Colorado State University, Fort Collins, Colorado 80523, USA.
Inorg Chem. 2005 Nov 14;44(23):8521-30. doi: 10.1021/ic050717t.
In recent work, it was shown that V-containing polyoxometalates such as (n-Bu4N)7SiW9V3O40 or (n-Bu4N)9P2W15V3O62, as well as eight other V-containing precatalysts tested, evolve to a high activity, long catalytic lifetime (> or = 30,000-100,000 total turnovers) 3,5-di-tert-butylcatechol dioxygenase, in which Pierpont's complex [VO(DBSQ)(DTBC)]2 (where DBSQ is 3,5-di-tert-butylsemiquinone and DTBC is the 3,5-di-tert-butylcatecholate dianion) was identified as a common catalyst or catalyst resting state (Yin, C.-X.; Finke, R. G. Vanadium-Based, Extended Catalytic Lifetime Catechol Dioxygenases: Evidence For a Common Catalyst. J. Am. Chem. Soc. 2005, 127 (25), 9003-9013). Herein, those findings are followed up by studies aimed at answering the following questions about this record catalytic lifetime 3,5-di-tert-butylcatechol dioxygenase catalyst: (i) What is the key to how V leaches from, for example, seemingly robust V-containing polyoxometalate precatalysts? (ii) What is the key to the sigmoidal, apparently autocatalytic kinetics observed? (iii) What can be learned about the underlying reactions that form [VO(DBSQ)(DTBC)]2? (iv) Finally, do the answers to (i-iii) lead to any broader insights or concepts? Key findings from the present work include the fact that the reaction involves a novel, autoxidation-product-induced dioxygenase, that is, one in which the undesired autoxidation of the 3,5-di-tert-butylcatechol substrate to the corresponding benzoquinone and H2O2 turns on the desired dioxygenase catalysis via a V-leaching process which eventually yields Pierpont's complex, [VO(DBSQ)(DTBC)]2. Plausible reactions en route to [VO(DBSQ)(DTBC)]2 consistent with the kinetic data, the role of H2O2, and the relevant literature are provided. The results provide a prototype example of the little observed but likely more general concept of an autoxidation-product-initiated reaction. The results also provide considerable simplification of, and insight into, the previously disparate literature of V-based 3,5-di-tert-butylcatechol dioxygenase catalysis.
在最近的工作中，研究表明含钒多金属氧酸盐，如(n - Bu4N)7SiW9V3O40或(n - Bu4N)9P2W15V3O62，以及测试的其他八种含钒预催化剂，能演变成具有高活性、长催化寿命（总周转数≥30,000 - 100,000）的3,5 - 二叔丁基邻苯二酚双加氧酶，其中皮尔庞特配合物[VO(DBSQ)(DTBC)]2（其中DBSQ是3,5 - 二叔丁基半醌，DTBC是3,5 - 二叔丁基邻苯二酚二价阴离子）被确定为常见催化剂或催化剂静止状态（尹，C.-X.；芬克，R.G. 基于钒的、具有延长催化寿命的邻苯二酚双加氧酶：关于常见催化剂的证据。《美国化学会志》2005年，127(25)，9003 - 9013）。在此，针对这一创纪录催化寿命的3,5 - 二叔丁基邻苯二酚双加氧酶催化剂，通过旨在回答以下问题的研究对这些发现进行了跟进：(i) 例如，钒如何从看似稳定的含钒多金属氧酸盐预催化剂中浸出的关键是什么？(ii) 观察到的S形、明显自催化动力学的关键是什么？(iii) 关于形成[VO(DBSQ)(DTBC)]2的潜在反应能了解到什么？(iv) 最后，对(i - iii)的回答是否能带来更广泛的见解或概念？本工作的关键发现包括该反应涉及一种新型的、自氧化产物诱导的双加氧酶，即3,5 - 二叔丁基邻苯二酚底物意外自氧化为相应苯醌和H2O2的过程通过钒浸出过程开启了所需的双加氧酶催化，最终产生皮尔庞特配合物[VO(DBSQ)(DTBC)]2。给出了与动力学数据、H2O2的作用以及相关文献一致的、通往[VO(DBSQ)(DTBC)]2的合理反应。这些结果提供了一个自氧化产物引发反应这一较少观察到但可能更普遍概念的典型例子。结果还极大地简化了并深入了解了此前分散的基于钒的3,5 - 二叔丁基邻苯二酚双加氧酶催化的文献。
