3260
M.J. da Silva et al. / Journal of Organometallic Chemistry 694 (2009) 3254–3261
L
O
=
-
NOn
O
Pd(OAc)2 / Fe(NO3)3
HOAc / O2
Fe(III)
Pd(II)
L
L
L
L
-
L = OAc, NOn
L
-
NOn
L
L
Fe(III)
L
Pd(II)
L
- H2O
-Fe(NOn)n
-Pd(OAc)2
-
L = OAc, NOn ; n = 3, 2
Scheme 2. Proposal of the main steps involved in Pd(OAc)2/Fe(NO3)3-catalyzed oxidative coupling of camphene.
intermediate formed on the slow stage of the reaction. We propose
that a possible intermediate in the slow step or reaction could in-
clude the dioxygen coordinated to the Fe(III), which in turn could
be coordinated to the Pd(II), via a nitro/and or acetate ligands,
while simultaneously coordinated to camphene, as shown in the
Fig. 10 [40,41].
this alternative Wacker-type catalytic system. Additional mecha-
nism studies will be presented in due course.
Acknowledgements
We gratefully acknowledge financial support of this research by
FUNARBE, CNPq and FAPEMIG (Brazil).
Thus, once this key intermediate is formed, the Fe(III) could act
decreasing the eleÀctronic density around the Pd(II), via electron-
withdrawing NO3 ligands, favoring the coordination of the
camphene to palladium (Fig. 10). Such interaction probably in-
volves Fe(III) bonding to Pd(II) via bridging ligands, and seems to
be responsible for the increased effect of Fe(NO3)3 in the palla-
dium-catalyzed oxidation of the camphene. Simultaneously, the
Fe(III) also could coordinate to dioxygen promoting the recovery
of the reduced nitrogen species. The direct activation of dioxygen
by an Fe(III) metallic center in a coordination compound, has been
previously documented. This synergic effect, resulting from coop-
eration between Pd(II) and Fe(III) species, was recently described
by Potemkim on the investigation of alcohol oxidations catalyzed
by palladium (II) tetraaqua complexes and Fe(II)–Fe(III) aqua ions
[42].
Thus, based on kinetic experiments performed we thinking that
the palladium-catalyzed oxidative coupling can be rationalized by
the reaction sequence described in Scheme 2.
Recently, we have reported an oxidative system based on palla-
dium where high selectivities and yields were also reached on
terpenes oxidation [43]. However, the final oxidant employed
was hydrogen peroxide in acetonitrile solutions. Since the hydro-
gen peroxide is able of active the palladium, that system no need
metal reoxidant. Nevertheless, despites the nice results obtained,
long time reactions were requiring for achieve high conversion.
References
[1] J.L.F. Monteiro, C.O. Veloso, Top. Catal. 27 (2004) 169–180.
[2] T.J. Maimone, P.S. Baran, Nat. Chem. Biol. 3 (2007) 396–407.
[3] P. Gallezot, Catal. Today 121 (2007) 76–91.
[4] K.A.D. Swift, Top. Catal. 27 (2004) 1–4. 143–155.
[5] B.V. Popp, J.L. Thorman, S.S. Stahl, J. Mol. Catal. A 251 (2006) 2–7.
[6] J.M. Thomas, R. Raja, Annu. Rev. Mater. Res. 35 (2005) 315–350.
[7] J.A. Kovacs, Science 299 (2003) 1024.
[8] J. Muzart, Tetrahedron 63 (2007) 7505–7521.
[9] I.I. Moiseev, M.N. Vargaftik, Coord. Chem. Rev. 248 (2004) 2381–2391.
[10] S.S. Stahl, Angew. Chem., Int. Ed. 43 (2004) 3400–3420.
[11] K.P. Peterson, R.C. Larock, J. Org. Chem. 63 (1998) 3185–3189.
[12] C.N. Cornell, M.S. Sigman, Inor. Chem. 46 (2007) 1903–1907.
[13] T. Nishimura, T. Onoue, K. Ohe, S. Uemura, J. Org. Chem. 64 (1999) 6750–6755.
[14] M. Yoshizawa, T. Kusukawa, K. Yamaguchi, M. Fujita, J. Am. Chem. Soc. 122
(2000) 6311–6314.
[15] J.A. Keith, R.J. Nielsen, J. Oxgaard, W.A. Goddard, J. Am. Chem. Soc. 129 (2007)
12342–12343.
[16] J.A. Gonçalves, E.V. Gusevskaya, Appl. Catal. A 258 (2004) 93–98.
[17] T. Punniyamurthy, S. Velusamy, J. Iqbal, Chem. Rev. 105 (2005) 2329–2364.
[18] T.J. Collins, Science 291 (2001) 48–49.
[19] A.K. El-Qisiari, H.A. Qaseer, P.M. Henry, Tetrahedron Lett. 43 (2002) 4229–
4231.
[20] M. Misono, Catal. Today 100 (2005) 95–100.
[21] Z. Zhang, X. Ma, J. Zhang, F. He, S. Wang, J. Mol. Catal. A 227 (2005) 141–
146.
[22] N.H. Kiers, B.L. Feringa, Tetrahedron Lett. 33 (1992) 2403–2406.
[23] A. Heumann, F. Chauvet, B. Waegell, Tetrahedron Lett. 23 (1982) 2767–2768.
[24] I.E. Beck, A.V. Golovin, V.A. Likholobov, E.V. Gusevskaya, J. Organomet. Chem.
689 (2004) 2880–2887.
4. Conclusions
[25] M.J. da Silva, P.R. Dutenhefner, L. Menini, E.V. Gusevskaya, J. Mol. Catal. A 201
(2003) 71–77.
The catalytic performance of the Pd(OAc)2/M(NO3)n (M = Cu(II),
Fe(III); n = 2, 3) multicomponent system in the oxidation of terp-
enes, especially camphene, was evaluated. The nature of the co-
catalyst affects both product distribution and reaction rate. Among
the catalytic systems evaluated, the Pd(OAc)2/Fe(NO3)3 combina-
tion present the highest stability/activity besides being the most
efficient nitrate reoxidant. Moreover, Fe(III) is capable of increasing
the rate of both steps (oxidative coupling of camphene into diene
and oxidation of the diene into ketone) in the camphene catalyzed
oxidation. The dependence of the rate-determining step on camph-
ene, palladium, nitrate and Fe(III) is another important feature of
[26] M.J. da Silva, L. Menini, M.F.F. Lelis, J.D. Fabris, R.M. Lago, E.V. Gusevskaya,
Appl. Catal. A 269 (2004) 117–121.
[27] M.J. da Silva, E.V. Gusevskaya, J. Mol. Catal. A 176 (2001) 23–27.
[28] E.V. Gusevskaya, M.J. da Silva, J. Braz. Chem. Soc. 14 (2003) 83–89.
[29] E.M. Beccalli, G. Broggini, M. Martinelli, S. Sottocornola, Chem. Rev. 107 (2007)
5318–5365.
[30] A.D. Silva, M.L. Patitucci, H.R. Bizzo, E. D’Elia, O.A.C. Antunes, Catal. Commun.
(2002) 435–440.
[31] M.J. da Silva, J.A. Gonçalves, R.B. Alves, O.W. Howarth, E.V. Gusevskaya, J.
Organomet. Chem. 689 (2004) 302–308.
[32] P. Boontanonda, R. Krigg, Chem. Commun. 471 (1977) 583–584.
[33] Y. Peng, D. Fu, R. Liu, F. Zhang, X. Xue, Q. Xu, X. Liang, Appl. Catal. B 79 (2007)
163–170.
[34] D. Narog, A. Szczepanik, A. Sobkowiak, Catal. Lett. 120 (2008) 320–325.