Vanadium-based, extended catalytic lifetime catechol dioxygenases: evidence for a common catalyst.
In 1999, a catechol dioxygenase derived from a V-polyoxometalate was reported which was able to perform a record >100 000 total turnovers of 3,5-di-tert-butylcatechol oxygenation using O2 as the oxidant (Weiner, H.; Finke, R. G. J. Am. Chem. Soc. 1999, 121, 9831). An important goal is to better understand this and other vanadium-based catechol dioxygenases. Scrutiny of 11 literature reports of vanadium-based catechol dioxygenases yielded the insight that they all proceed with closely similar selectivities. This, in turn, led to a "common catalyst hypothesis" for the broad range of vanadium based catechol 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-based polyoxometalate precatalysts, (n-Bu4N)4H5PV14O42, (n-Bu4N)7SiW9V3O40, (n-Bu4N)5[(CH3CN)(x)Fe(II).SiW9V3O40], (n-Bu4N)9P2W15V3O62, (n-Bu4N)5Na2[(CH3CN)(x)Fe(II).P2W15V3O62], and (n-Bu4N)4H2-gamma-SiW10V2O40; (ii) three vanadium catecholate complexes, [V(V)O(DBSQ)(DTBC)]2, [Et3NH]2[V(IV)O(DBTC)2].2CH3OH, and [Na(CH3OH)2]2[V(V)(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-mass spectrometry (negative ion ESI-MS), and kinetic studies provided compelling evidence for a common catalyst or catalyst resting state, namely, Pierpont's structurally characterized vanadyl semiquinone catecholate dimer complex, [VO(DBSQ)(DTBC)]2, formed from V-leaching from the precatalysts. The results provide a considerable simplification and unification of a previously disparate literature of V-based catechol dioxygenases.
Yin
Cindy-Xing
CX
Department of Chemistry, Colorado State University, Ft. Collins, Colorado 80523, USA.
Finke
Richard G
RG
D002384:Catalysis; D002396:Catechols / Q000138:chemical synthesis* / Q000737:chemistry; D018360:Crystallography, X-Ray; D049308:Dioxygenases / Q000737:chemistry*; D004578:Electron Spin Resonance Spectroscopy; D007700:Kinetics; D009682:Magnetic Resonance Spectroscopy; D008958:Models, Molecular; D008968:Molecular Conformation; D009942:Organometallic Compounds / Q000737:chemistry*; D010100:Oxygen / Q000737:chemistry; D014639:Vanadium / Q000737:chemistry*
D002396:Catechols; D009942:Organometallic Compounds; D014639:Vanadium; D049308:Dioxygenases; D010100:Oxygen