Communications
Scheme 3. Plausible mechanism for the reversible conversion of 1 into 2. ET=electron transfer.
0.0808); GOF(F2) = 1.029, R1(I>2s(I)) = 0.0455, wR2 (all data) =
dioxygen, which then proceeds by a spin-forbidden step with
charge transfer from 1 to dioxygen to form 2. The available
data do not allow us to distinguish between these two possible
mechanisms. However, we suppose that the first mechanism is
more probable. The biradical complex is also the key
intermediate in the elimination of molecular oxygen. This
biradical complex is formed in the first step by the homolytic
0.0963; largest diff. peak and hole 0.597/À0.350 eꢀÀ3
.
2: Compound 1 (195 mg, 0.25 mmol) was dissolved in toluene and
left in air for 2 h. The solvent was removed by slow evaporation and
the residue was recrystallized from acetone over 3 days to yield
yellow–orange crystals of 2·C3H6O suitable for X-ray analysis which
were collected and dried in air (144 mg, 80%); m.p. 173–1768C
(decomp); IR (nujol): n˜ = 1715s, 1645s, 1600m, 1590m, 1570m, 1485s,
1435s, 1365s, 1315w, 1275w, 1260w, 1225s, 1180m, 1140s, 1080m,
1065m, 1030w, 1005w, 985w, 940w, 910m, 870m, 855w, 795 m, 760w,
À
splitting of the C O bond. The essential factor that assists this
process is the energy compensation because of the formation
of an o-iminobenzosemiquinonate chelate ligand bonded to
antimony.
745s, 730s, 705s, 665w, 625w, 570w, 545w, 535w, 490w, 460s cmÀ1
;
1H NMR (200 MHz, CDCl3, 258C, TMS): d = À0.02 (d, 3JH,H = 6.8 Hz,
3H; CH3 of iPr), 0.38 (d, 3JH,H = 6.8 Hz, 3H; CH3 of iPr), 0.78 (d,
3
3JH,H = 6.8 Hz, 3H; CH3 of iPr), 0.86 (d, JH,H = 6.8 Hz, 3H; CH3 of
iPr); 1.02, 1.36 (both s, both 9H; 2tBu), 2.58, 2.94 (both sept, 3JH,H
=
6.8 Hz, both 1H; 2 CH of 2iPr), 5.53, 6.51 (both d, 3JH,H = 1.5 Hz, both
1H; C6H2 aromatic), 6.8–7.6 ppm (m, 18H; aromatic); 1H NMR
(200 MHz, [D6]acetone, 258C, TMS): d = 0.01 (d, 3JH,H = 6.8 Hz, 3H;
Experimental Section
The starting materials used were from commercially available sources
(Aldrich, Fluka, Strem) unless otherwise noted. 4,6-Di-tert-butyl-N-
(2,6-diisopropylphenyl)-o-iminobenzoquinone was synthesized by
using a reported method.[14] Synthetic procedures were carried out
3
3
CH3 of iPr), 0.43 (d, JH,H = 6.8 Hz, 3H; CH3 of iPr), 0.81 (d, JH,H
=
6.8 Hz, 3H; CH3 of iPr), 0.88 (d, 3JH,H = 6.8 Hz, 3H; CH3 of iPr); 1.06,
1.36 (both s, both 9H; 2tBu), 2.68, 3.03 (both sept, 3JH,H = 6.8 Hz, both
1H; 2 CH of 2iPr), 5.60, 6.66 (both d, 4JH,H = 1.5 Hz, both 1H; C6H2
aromatic), 6.9–8.0 ppm (m, 18H; aromatic).
1
under vacuum (for 1) with dried, distilled solvents. H NMR spectra
were obtained on a Bruker DPX-200 spectrometer (200 MHz). IR
spectra (4000–400 cmÀ1) were recorded on Specord M-80 in nujol. X-
ray data were collected on a Bruker Smart Apex diffractometer.
1: A solution of 4,6-di-tert-butyl-N-(2,6-diisopropylphenyl)-o-
iminobenzoquinone (0.76 g, 2 mmol) in toluene (30 mL) was added
to a stirred solution of SbPh3 (0.71 g, 2 mmol) in toluene (15 mL). The
reaction was allowed to proceed over 3 h at room temperature, during
which time the mixture gradually changed color from cherry red to
orange. The resulting solution was concentrated to 15 mL and stored
for a day at 08C. The product was isolated by filtration and
recrystallized over a longer period from toluene to yield yellow, X-
ray-quality crystals (1.39 g, 89%); m.p. 170–1718C; Elemental anal-
ysis calcd (%) for C47.5H56ONSb (778.72 gmolÀ1): C 73.26, H 7.25,
Sb 15.63; found: C 72.88, H 6.96, Sb 15.60; IR (Nujol): n˜ = 1580w,
1570m, 1450s, 1440s, 1430s, 1415m, 1390s, 1360m, 1330m, 1315w,
1290m, 1240s, 1060s, 1055w, 1025w, 995s, 895w, 865w, 850 m, 825w,
Crystal data for 2·C3H6O: C47H58NO4Sb, Mr = 822.73, monoclinic,
space group P21/n, a = 13.2049(6), b = 21.8719(10), c = 14.8069(7) ꢀ;
b = 97.4860(10)8, V= 4240.0(3) ꢀ3, Z = 4, 1calcd = 1.289 gcmÀ3, T=
100(2) K, F(000) = 1720, l(MoKa) = 0.71073 ꢀ, m = 0.693 mmÀ1
;
yellow–orange crystal, 0.08 ꢁ 0.05 ꢁ 0.02 mm3, q = 1.67–25.008, 23334
reflections collected, 7455 independent reflections (Rint = 0.0619);
GOF(F2) = 0.970, R1(I>2s(I)) = 0.0370, wR2(all data) = 0.0727; larg-
est diff. peak and hole 0.613/À0.417 eꢀÀ3
.
CCDC 253414 (1) and 253415 (2) contain the supplementary
crystallographic data for this paper. These data can be obtained free
of charge from the Cambridge Crystallographic Data Centre via
Received: November 3, 2004
Published online: March 31, 2005
805w, 755w, 730s, 690s, 655m, 605w, 530w, 490w, 455m, 440m cmÀ1
.
1H NMR of 1·0.5C7H8 (200 MHz, CDCl3, 258C, TMS): d = 0.71,
0.94 (both d, 3JH,H = 6.8 Hz, both 6H; 2CH(CH3)2), 1.13, 1.44 (both s,
Keywords: antimony · N,O ligands · oxo ligands · oxygen ·
both 9H; 2tBu), 2.36 (s, 0.5 ꢁ 3H; CH3 of toluene), 3.07 (sept, 3JH,H
=
.
peroxides
6.8 Hz, 2H; 2CH(CH3)2), 5.91, 6.69 (both d, 4JH,H = 2.3 Hz, both 1H;
C6H2 aromatic), 6.8–8.3 ppm (m, 20.5H; 18 protons of aromatic
groups in 1 and 0.5 ꢁ 5 protons of toluene); 1H NMR of 1·0.5C7H8
3
(200 MHz, [D6]acetone, 258C, TMS): d = 0.78, 0.96 (both d, JH,H
=
[1] a) H. Mimoun in Comprehensive Coordination Chemistry, Vol. 6
(Eds.: G. Wilkinson, R. D. Gillard, J. A. McCleverty), Pergamon,
Oxford, 1987, pp. 317 – 410; b) L. I. Simꢂndi, Advances in
Catalytic Activation of Dioxygen By Metal Complexes, Catalysis
By Metal Complexes, Vol. 26, Kluwer, Boston, 2003.
[2] a) D. H. Busch, N. W. Alcock, Coord. Chem. Rev. 1994, 94, 585 –
623; b) A. Butler, M. J. Clague, G. E. Meister, Coord. Chem.
Rev. 1994, 94, 625 – 638; c) R. A. Sheldon, J. K. Kochi, Metal-
Catalyzed Oxidations of Organic Compounds, Academic Press,
New York, 1981; d) Oxygen Complexes and Oxygen Activation
by Transition Metals (Eds.: A. E. Martell, D. T. Sawyer), Plenum,
New York, 1988.
6.8 Hz, both 6H; 2CH(CH3)2), 1.11, 1.42 (both s, both 9H; 2tBu), 2.32
(s, 0.5 ꢁ 3H; CH3 of toluene), 3.16 (sept, 3JH,H = 6.8 Hz, 2H; 2
CH(CH3)2), 5.91, 6.70 (both d, 4JH,H = 2.3 Hz, both 1H; C6H2
aromatic), 6.9–7.8 ppm (m, 20.5H; 18 protons of aromatic groups in
1 and 0.5 ꢁ 5 protons of toluene).
Crystal data for 1·0.5C7H8: C47.5H56NOSb, Mr = 778.72, mono-
clinic, space group P21/n, a = 10.525(2), b = 14.861(3), c =
26.426(6) ꢀ; b = 99.855(5)8, V= 4072.5(15) ꢀ3, Z = 4, 1calcd
=
1.228 gcmÀ3, T= 293(2) K, F(000) = 1566, l(MoKa) = 0.71073 ꢀ, m =
0.710 mmÀ1. Yellow crystal, 0.50 ꢁ 0.04 ꢁ 0.04 mm3, q = 1.56–23.328,
27208 reflections collected, 5866 independent reflections (Rint
=
2770
ꢀ 2005 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Angew. Chem. Int. Ed. 2005, 44, 2767 –2771