Inorganic Chemistry
Communication
Press: Boca Raton, FL, 2007. (d) Rehder, D. Bioinorganic Vanadium
Chemistry; Wiley: Chichester, U.K., 2008.
operate via a common type of mechanism, with involvement of
HO• radicals.
(2) (a) Mondal, S.; Ghosh, P.; Chakravorty, A. Inorg. Chem. 1997, 36,
59. (b) Dutta, S. K.; Kumar, S. B.; Bhattacharyya, S.; Tiekink, E. R. T.;
Chaudhury, M. Inorg. Chem. 1997, 36, 4954. (c) Holwerda, R. B.;
Whittlesey, B. R. Inorg. Chem. 1998, 37, 64. (d) Dutta, S. K.; Samanta,
S.; Kumar, S. B.; Han, O. H.; Burckel, P.; Pinkerton, A. A.; Chaudhury,
M. Inorg. Chem. 1999, 38, 1982. (e) Mahroof-Tahir, M.; Keramidas, A.
D.; Goldfarb, R. B.; Anderson, O. P.; Miller, M. M.; Crans, D. C. Inorg.
Chem. 1997, 36, 1657. (f) Ghosh, S.; Nanda, K. K.; Addison, A. W.;
Butcher, R. J. Inorg. Chem. 2002, 41, 2243. (g) Wang, D.; Behrens, A.;
Farahbakhsh, M.; Gatjens, J.; Rehder, D. Chem.Eur. J. 2003, 9, 1805.
(h) Dinda, R.; Sengupta, P.; Mak, T. C. W.; Ghosh, S. Inorg. Chem.
2002, 41, 1684. (i) Dinda, R.; Sengupta, P.; Sutradhar, M.; Mak, T. C.
W.; Ghosh, S. Inorg. Chem. 2008, 47, 5634. (j) Chen, C.-Y.; Zhou, Z.-
H.; Chen, H.-B.; Huang, P.-Q.; Tsai, K.-R.; Chow, Y. L. Inorg. Chem.
2008, 47, 8714.
The mixed-valence character of 1 can be favorable because it
exhibits both 4+ and 5+ vanadium oxidation states, which are
required4a−d,j,k for the metal-promoted generation of HO• from
H2O2. However, because 1 and 1/PCA exhibit different
efficiencies and kinetic rates under identical reaction conditions,
different catalytic species can be involved. PCA can possibly
displace one or more N,O-donor ligands in 1,4c,d,j as suggested
by electrospray ionization mass spectrometry (see the SI), thus
resulting in the formation of catalytically more active species
than 1 itself. Besides, PCA can play a key role as a stabilizer in
hydrogen-transfer steps in the ‘‘water-assisted” mechanism of
free-radical generation, as was recently disclosed, based on DFT
4j
−
calculations, for H2O2/VO3 /PCA-catalyzed alkane oxidation.
The acidity of the reaction medium (due to the presence of
PCA or any other acid) is crucial for the formation of
oligovanadates, which reveal higher catalytic activity without
the requirement of an additive, in contrast to a simple
monovanadate.4k The high activity of the polynuclear complex
1 suggests that multinuclearity can be a favorable feature with a
more general character, valid for vanadium centers of other
types, besides vanadates.
(3) (a) Codd, R.; Hambley, T. W.; Lay, P. A. Inorg. Chem. 1995, 34,
877. (b) Johnson, J. W.; Johnston, D. C.; King, H. E., Jr.; Halbert, T.
R.; Brody, J. F. Inorg. Chem. 1988, 27, 1646. (c) Jin, Y.; Lee, H.-I.;
Pyoc, M.; Lah, M. S. Dalton Trans. 2005, 797. (d) Biswas, B.;
Weyhermuller, T.; Bill, E.; Chaudhuri, P. Inorg. Chem. 2009, 48, 1524.
̈
(4) (a) Shilov, A. E.; Shul’pin, G. B. Chem. Rev. 1997, 97, 2879.
(b) Shul’pin, G. B. Oxidations of C−H Compounds Catalyzed by
Metal Complexes. In Transition Metals for Organic Synthesis, 2nd ed.;
Beller, M., Bolm, C., Eds.; Wiley-VCH: Weinheim/New York, 2004;
Vol. 2, Chapter 2.2, p 215. (c) Shul’pin, G. B. J. Mol. Catal. A 2002,
189, 39. (d) Shul’pin, G. B. Mini-rev. Org. Chem. 2009, 6, 95. (e) da
In summary, a unique hexanuclear oxovanadium compound
has been synthesized and fully characterized, revealing the first
example of a high-nuclearity mixed-valence vanadium complex
bearing an N,O-donor ligand. It exhibits remarkably high
activity toward mild alkane oxidations by H2O2, in the presence
of a PCA cocatalyst, leading to good yields and exceptionally
high TONs (up to ca. 25 × 103 or ca. 4.2 × 103 if recalculated
for the number of V atoms), with the latter being
unprecedented for any vanadium-catalyzed alkane oxidations
Silva, J. A. L.; Frausto da Silva, J. J. R.; Pombeiro, A. J. L. Coord. Chem.
́
Rev. 2011, 255, 2232. (f) Mizuno, N.; Kamata, K. Coord. Chem. Rev.
2011, 225, 2358. (g) Ligtenbarg, A. G. J.; Hage, R.; Feringa, B. L.
Coord. Chem. Rev. 2003, 237, 89. (h) Conte, V.; Floris, B. Dalton
Trans. 2011, 40, 1419. (i) Kirillova, M. V.; Kuznetsov, M. L.; Reis, P.
M.; da Silva, J. A. L.; Frausto da Silva, J. J. R.; Pombeiro, A. J. L. J. Am.
́
Chem. Soc. 2007, 129, 10531. (j) Kirillova, M. V.; Kuznetsov, M. L.;
−
Romakh, V. B.; Shul’pina, L. S.; Frausto da Silva, J. J. R.; Pombeiro, A.
́
by H2O2, including also an efficient state-of-the-art VO3 /
PCA/H2O2 system.4a−d Such a high activity of 1 deserves
further exploration and elucidation. The extension of this type
of study to the synthesis and catalysis of other multinuclear
mixed-valence vanadium(IV/V) complexes, as well as to other
alkanes, and a detailed kinetic and mechanistic investigation will
be pursued.
J. L.; Shul’pin, G. B. J. Catal. 2009, 267, 140. (k) Kirillova, M. V.;
Kuznetsov, M. L.; Kozlov, Y. N.; Shul’pina, L. S.; Kitaygorodskiy, A.;
Pombeiro, A. J. L.; Shul’pin, G. B. ACS Catal. 2011, 1, 1511. (l) Reis,
P. M.; Silva, J. A. L.; Frausto da Silva, J. J. R.; Pombeiro, A. J. L. Chem.
́
Commun. 2000, 1845.
(5) (a) Guo, Q.-X.; Wu, Z.-J.; Luo, Z.-B.; Liu, Q.-Z.; Ye, J.-L.; Luo, S.-
W.; Cun, L.-F.; Gong, L.-Z. J. Am. Chem. Soc. 2007, 129, 13927.
(b) Liu, Q.-Z.; Xie, N.-S.; Luo, Z.-B.; Cui, X.; Cun, L.-F.; Gong, L.-Z.;
Mi, A.-Q.; Jiang, Y.-Z. J. Org. Chem. 2003, 68, 7921. (c) Luo, Z.; Liu,
Q.; Gong, L.; Cui, X.; Mi, A.; Jiang, Y. Angew. Chem., Int. Ed. 2002, 41,
4532. (d) Luo, Z.; Liu, Q.; Gong, L.; Cui, X.; Mi, A.; Jiang, Y. Chem.
Commun. 2002, 8, 914. (e) Nakajima, K.; Kojima, M.; Toriumi, K.;
Saito, K.; Fujita, J. Bull. Chem. Soc. Jpn. 1989, 62, 760.
ASSOCIATED CONTENT
* Supporting Information
■
S
X-ray crystallographic files of 1 (CCDC 884049) in CIF format,
experimental details, Figures S1−S7, Schemes S1 and S2, and
Tables S1−S3. This material is available free of charge via the
AUTHOR INFORMATION
Corresponding Author
■
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
We acknowledge the FCT (Project PTDC/QUI/102150/
2008), Portugal, for financial support.
■
REFERENCES
■
(1) (a) Crans, D. C.; Smee, J. J.; Gaidamauskas, E.; Yang, L. Chem.
Rev. 2004, 104, 849. (b) Frausto da Silva, J. J. R.; Williams, R. J. P. The
Biological Chemistry of the Element; Oxford University Press: Oxford,
U.K., 2001. (c) Tracey, A. S.; Willsky, G. R.; Takeuchi, E. S. Vanadium
Chemistry, Biochemistry, Pharmacology and Practical Applications; CRC
́
C
dx.doi.org/10.1021/ic3017062 | Inorg. Chem. XXXX, XXX, XXX−XXX