| Abstract
| - In 1999, a catechol dioxygenase derived from a V-polyoxometalate was reported which wasable to perform a record >100 000 total turnovers of 3,5-di-tert-butylcatechol oxygenation using O2 as theoxidant (Weiner, H.; Finke, R. G. J. Am. Chem. Soc.1999, 121, 9831). An important goal is to betterunderstand this and other vanadium-based catechol dioxygenases. Scrutiny of 11 literature reports ofvanadium-based catechol dioxygenases yielded the insight that they all proceed with closely similarselectivities. This, in turn, led to a “common catalyst hypothesis” for the broad range of vanadium basedcatechol dioxygenase precatalysts presently known. The following three classes of V-based compounds,10 complexes total, have been explored to test the common catalyst hypothesis: (i) six vanadium-basedpolyoxometalate precatalysts, (n-Bu4N)4H5PV14O42, (n-Bu4N)7SiW9V3O40, (n-Bu4N)5[(CH3CN)xFeII·SiW9V3O40],(n-Bu4N)9P2W15V3O62, (n-Bu4N)5Na2[(CH3CN)xFeII·P2W15V3O62], and (n-Bu4N)4H2-γ-SiW10V2O40; (ii) threevanadium catecholate complexes, [VVO(DBSQ)(DTBC)]2, [Et3NH]2[VIVO(DBTC)2]·2CH3OH, and [Na(CH3OH)2]2[VV(DTBC)3]2·4CH3OH (where DBSQ = 3,5-di-tert-butylsemiquinone anion and DTBC = 3,5-di-tert-butylcatecholate dianion), and (iii) simple VO(acac)2. Product selectivity studies, catalytic lifetime tests,electron paramagnetic resonance spectroscopy (EPR), negative ion mode electrospray ionization-massspectrometry (negative ion ESI-MS), and kinetic studies provided compelling evidence for a common catalystor catalyst resting state, namely, Pierpont's structurally characterized vanadyl semiquinone catecholatedimer complex, [VO(DBSQ)(DTBC)]2, formed from V-leaching from the precatalysts. The results provide aconsiderable simplification and unification of a previously disparate literature of V-based catecholdioxygenases.
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