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experiments performed in the deoxygenation reaction of sulfox-
ides, pyridine N-oxide, arsenium oxide, and hydrogenation of
nitroarenes indicated that no radicals are involved in these reduc-
tion reactions, since addition of radical traps does not affect the
reaction.26
In conclusion, an efficient method for the reduction of aromatic
nitro compounds and pyridine N-oxides employing H2 as reducing
agent and MoO2Cl2 as catalyst is reported. This catalytic system is
simple, inexpensive, clean, reusable, and applicable for preparing
different substituted aromatic amines and pyridines with excellent
conversion and chemoselectivity. This method does not generate
any harmful and/or wasteful co-products, only water is generated
in the reaction.
Acknowledgments
This work was supported by FCT through project PTDC/QUI/
64458/2006. P.M.R. thanks FCT for a postdoctoral grant SFRH/
BPD/20655/2004. We thank Professor Carlos C. Romão for helpful
discussions. We thank M. C. Almeida and Dr. A. Coelho for provid-
ing data from the Elemental Analyses and Mass Spectrometry Ser-
vices at ITQB. We thank FC&T for REDE/1517/RMN/2005 and REDE/
1504/REM/2005.
21. Corma, A.; Serna, P. Science 2006, 313, 332–334; Corma, A.; Serna, P.;
Concepción, P.; Calvino, J. J. J. Am. Chem. Soc. 2008, 130, 8748–8753. and
references therein.
22. In
a typical experiment, a mixture of MoO2Cl2 (0.1 mmol) and substrate
(1.0 mmol) in ethanol (8 mL) was added to the reactor, previously degassed
with nitrogen, and provided with a magnetic stirrer. The reactor was flushed
with 50 atm of H2 pressure and heated to 120 °C for 20 h. Conversion was
determined by gas chromatography (GC).
23. Arnáiz, F. J.; Aguado, R.; Pedrosa, M. R.; Cian, A. D. Inorg. Chim. Acta 2003, 347,
33–40.
24. Characterization of Mo2O3Cl4(tBuBipy)2: IR(cmꢀ1):
m
(Mo@O) 965(s);
m
(Mo–O–
References and notes
3
Mo) 786(m). 1H NMR (CD2Cl2): 9.09 ppm (d, JH–H = 6.1 Hz, 2H); 8.88 ppm (d,
3JH–H = 5.8 Hz, 2H); 8.16 ppm (s, 2H); 8.10 ppm (s, 2H); 7.59 ppm (d, JH–
3
1. Holm, R. H. Chem. Rev. 1987, 87, 1401–1449.
2. Lu, X.; Sun, J.; Tao, X. Synthesis 1982, 185.
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3
H = 6.0 Hz, 2H); 7.53 ppm (d, JH–H = 5.1 Hz, 2H); 1.49 ppm (s, 18H); 1.42 ppm
(s, 18H). Anal. Calcd for C36H48Mo2Cl4N4O3: C, 47.07; H, 5.26; N, 6.1. Found: C,
47.14; H, 5.08; N 6.21. MS (ES): m/z 884 [M]+ꢀCl. MoO2Cl2(tBuBipy) catalyzes
the redution of PhMeSO to PhMeS with 80% yield.
25. Aguado, R.; Escribano, J.; Pedrosa, M. R.; Cian, A. D.; Sanz, R.; Arnáiz, F. J.
Polyhedron 2007, 26, 3842–3848.
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1629–1632.
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213–214.
26. The spin traps 2,6-di-tert-butyl-4-methylphenol (BHT) and 5,50-dimethyl-4,5-
dihydro-3H-pyrrole-N-oxide (DMPO) were added to the catalytic reaction
mixture, and the catalytic essay was performed under similar reaction
conditions.