Vanadium-Based, Extended Catalytic Lifetime Catechol Dioxygenases:  Evidence for a Common Catalyst

Abstract

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.

The application of electrospray ionization mass spectrometry to homogeneous catalysis

“…[43]. Through kinetic experiments the species corresponding to [V(DTBC) 3 ] -was ruled out as the catalytically active species and the neutral species that was shown to correspond to [VO(DTBC) 2 ] -, namely (VO(DBSQ)(DTBC)) 2 (DBSQ = 3,5-di-tert-butylsemiquinone anion) , was reported as a common catalyst for this reaction.…”

A 12-molybdophosphoric acid supramolecular compound: Synthesis, crystal structure and photochromic properties

“…Polyoxometalates (POMs), one species of transition-metal oxide clusters, have been attracted intense interest and extensive research for their fascinating structures and potential applications, such as catalysis [1][2][3], photochemistry [4], nonlinear optics [5], porous materials [6,7], molecular magnetism [8], biology [9], and medicine [10,11]. Recently, extensive efforts have been focused on the design and assembly of such kind of supramolecular architectures based on POMs and a few high-dimensional supramolecular architectures, which due to the spherical surface of the POM anions gives a better opportunity in forming hydrogen bonds with the organic-inorganic moieties [12][13][14][15].…”

New polydentate ligands based on sterically hindered o-benzoquinones (pyrocatechols) containing the 1,4-diazadiene group

“…[1][2][3][4] In recent three decades, sterical ly hindered o quinones and pyrocatechols found wide use in the chemistry of o semiquinone and catecholate metal complexes. 5- 7 The o quinone ligand in the o semiquino ne or catecholate form is valence bonded in mixed ligand metal complexes due to high differences in the values of reduction potentials of diazadienes and o quinones. 8, 9 To date there are no published data on bifunctional ligands containing simultaneously the diazadiene and o quinone groups.…”