reflections, wR2 = 0.1065 (all data); 2: M = 1448.13, orthorhombic, space
and a W–W single bond consistent with ligand reduction and
oxidation of the metal centre from (WMW)6+ to (W–W)10+ 10
˚
˚
˚
group Fdd2 No. 43, a = 38.156(2) A, b = 50.415(3) A, c = 15.8144(8) A, a =
b = c = 90u, Z = 16, R1 = 0.0494 for 11475 (I . 2s(I)) reflections, wR2 =
0.0990 (all data).
.
TpiPr2CrO2C2Ph2 (TpiPr2 = hydrotris(3,5-diisopropylpyrazolyl)bor-
ato) a 1 : 1 chromium diolate adduct was formed by the reductive
coupling of benzaldehyde by TpiPr2CrCl?py.11 In our system two
diketone ligands have been fully reduced to their diolate form
corresponding to the oxidation of three equivalents of Na metal
and one FeII centre to FeIII. Cyclic voltammetry shows only one
reversible feature at 21.62 vs. Fc/Fc+ which we assign to the
reduction of FeIII to FeII. It appears that any oxidation of 2 leads
to decomposition of the dimer. Unlike all previously reported
mixed valent iron dimers the high spin state of the FeII
antiferromagnetically coupled to the low spin state of the FeIII
leads to a ground state of St = 3/2.
{ CCDC 658636. For crystallographic data in CIF or other electronic
format see DOI: 10.1039/b713062g
§ CCDC 658637. For crystallographic data in CIF or other electronic
format see DOI: 10.1039/b713062g
1 (a) D. M. Kurtz, Chem. Rev., 1990, 90, 585; (b) A. Neves, M. A.
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96, 2625; (d) E. I. Solomon, T. C. Brunold, M. I. Davis, J. N. Kemsley,
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2 C. Belle and J.-L. Pierre, Eur. J. Inorg. Chem., 2003, 4137.
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33, 887; (c) J. D. Cohen, S. Payne, K. S. Hagen and J. Sanders-Loehr,
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and T. Glaser, Coord. Chem. Rev., 2000, 200, 595; (e) S. Albedyhl,
M. T. Averbuch-Pouchot, C. Belle, B. Krebs, J.-L. Pierre, E. Saint-
Aman and S. Torelli, Eur. J. Inorg. Chem., 2001, 1457.
4 (a) S. Dru¨eke, P. Chaudhuri, K. Pohl, K. Wieghardt, X.-Q. Ding, E. Bill,
A. Sawaryn, A. X. Trautwein, H. Winkler and S. J. Gurman, J. Chem.
Soc., Chem. Commun., 1989, 59; (b) D. R. Gamelin, E. L. Bominaar,
M. L. Kirk, K. Wieghardt and E. I. Solomon, J. Am. Chem. Soc., 1996,
118, 8085; (c) S. K. Dutta, J. Ensling, R. Werner, U. Flo¨rke, W. Haase,
P. Gu¨tlich and K. Nag, Angew. Chem., Int. Ed. Engl., 1997, 36, 152; (d)
J. R. Hagadorn, L. Que, Jr., W. B. Tolman, I. Prisecaru and E. Mu¨nck,
J. Am. Chem. Soc., 1999, 121, 9760; (e) D. Lee, C. Krebs, B. H. Huynh,
M. P. Hendrich and S. J. Lippard, J. Am. Chem. Soc., 2000, 122, 5000;
(f) A. Stubna, D.-H. Jo, M. Costas, W. W. Brenessel, H. Andres,
E. L. Bominaar, E. Mu¨nck and L. Que, Jr., Inorg. Chem., 2004, 43,
3067.
5 N. S. Nudelman and P. Outumuro, J. Org. Chem., 1982, 47, 4347.
6 (a) N. S. Hush, Prog. Inorg. Chem., 1967, 8, 391; (b) C. Creuz,
Prog. Inorg. Chem., 1983, 30, 1.
7 The broadening is apparently stronger for FeIII (S2 = 1/2) than for FeII
(S1 = 2), although the local spins are coupled by sizable exchange
interaction (J = 25.3 cm21), so that the paramagnetic relaxation rate
should be the same for both sites. We assign this effect to the larger
magnetic anisotropy expected for the ferric low-spin site, due to strong
spin–orbit coupling.
G.H.S. would like to thank the Alexander V. Humboldt
Foundation for the award of a Fellowship.
Notes and references
{ All manipulations except ligand workup were conducted under strict
exclusion of air and moisture in an atmosphere of dry argon or in vacuo
using Schlenk line and glovebox techniques. Li2(Et2O)2(C6H3-2,6-Pri2)2 was
prepared by modification of the procedure for Li2(Et2O)2(C6H2-2,4,6-
Pri3)2.12 ESI mass spectra were obtained on a Finnigan MAT 95 spectro-
meter. Elemental analyses were done by the H. Kolbe Mikroanalytisches
Laboratorium in Mu¨lheim an der Ruhr, Germany. Variable temperature
magnetic susceptibilities were measured on a Quantum Design SQUID
magnetometer in the range 2–300 K at an applied external field of 1000 G.
Data points were corrected for intrinsic diamagnetism of the sample, the
sample holder, and also for temperature-independent paramagnetism. The
magnetic data were simulated by using our own spin Hamiltonian program
julX for exchange-coupled systems (written by E.B.). X-Band EPR spectra
were recorded at 10 K on a Bruker ESP 300E spectrometer equipped with a
helium-flow cryostat (Oxford Instruments ESR 910). Mo¨ssbauer spectra
were recorded on a spectrometer with alternating constant-acceleration.
The minimum experimental line width was 0.24 mm s21. The sample
temperature was maintained constant by an Oxford Instruments Variox
cryostat. Isomer shifts (d) are referenced against iron metal at 300 K.
Bis(2,6-diisopropylphenyl)glyoxal, 1: A solution of Li2(Et2O)2(C6H3-2,6-
Pri2)2 (5 g, 12.2 mmol) in THF (20 mL) was cooled to 0 uC. CO was
bubbled through the solution resulting in a colour change from pale yellow
to dark red. The solution was allowed to warm to room temperature and
exposed to air. The solution was washed with quenched with water (20 mL)
and extracted with Et2O (50 mL). Removal of the solvent in vacuo resulted
in a pale yellow residue. This was extracted with hexane and recrystallised
8 The parameters render the sextet excited state manifold at about 25 cm21
above the quartet ground state, according to an exchange splitting DJ of
about 5|J|, as it would be expected for the limiting case of vanishing zfs.
However, the manifolds are actually mixed by the large zfs coming from
FeII, as can be seen from the energy level scheme shown in the inset of
Fig. 4. The ratio of the effective zfs D1(5/2) and D2(5/2) of the three
Kramers doublets of the excited sextet apparently deviates significantly
1
to give 1 as pale yellow crystals (Yield 1.5 g, 4.0 mmol, 32%). H NMR
(CDCl3, 300.08 MHz): d(ppm) 1.17 (d, 24H, J = 6.9 Hz, CHMe2), 2,61
(sept,. 4H, J = 6.6 Hz, CHMe2), 7.20 (d, 4H, Ar–H), 7.38 (t, 2H, Ar–H).
13C NMR (C6D6, 100.52 MHz): d(ppm) 22.6 (CHMe2), 32.1 (CHMe2),
123.1, 130.3, 134.5, 145.9 (unsaturated carbon) 199.5 (ArCO),. Mass
spectrum (ESI): m/z = 189, (COC6H3-2,6-Pri2, 100%), m/z = 161 (C6H3-2,6-
Pri2, 32%).
from the expected scheme 2D5/2/4D5/2
.
FeIIFeIII, 2: A solution of 1 (100 mg, 0.26 mmol) in DME (8 mL) was
added with stirring to FeBr2 (56 mg, 0.26 mmol) and Na (9.2 mg,
0.4 mmol). The pale yellow solution turned deep blue over 4 h. Removal of
the solvent in vacuo resulted in a deep blue residue which was extracted in
90 : 10 pentane–DME (3 mL) and filtered. Storage at 230 uC yielded 2 as
blue crystals in moderate yield (77 mg, 0.05 mmol, 41%). UV-Vis (DME):
702 nm (e = 2700). Elemental Analysis (2 + 2NaBr) Expected C 51.2% H
6.95% Found C 51.5% H 6.80%)
9 (a) P. Hofmann, M. Frede, P. Stauffert, W. Lasser and U. Thewalt,
Angew. Chem., Int. Ed. Engl., 1985, 24, 712; (b) G. Erker, P. Czisch,
R. Schlund, K. Angermund and C. Kru¨ger, Angew. Chem., Int. Ed.
Engl., 1986, 25, 364; (c) L.-C. Song, P.-C. Liu, C. Han and Q.-M. Hu,
J. Organomet. Chem., 2002, 648, 119.
10 M. H. Chisholm, J. C. Huffman and A. L. Ratermann, Inorg. Chem.,
1983, 22, 4100.
11 K.-I. Sugawara, S. Hikichi and M. Akita, J. Chem. Soc., Dalton Trans.,
2002, 4514.
˚
Crystal data for 1 and 2 at 100(2) K with MoKa (l = 0.71073 A). 1: M =
˚
378.53, orthorhombic, space group Pbca, a = 9.6205(3) A, b = 13.8569(5) A,
˚
12 R. A. Bartlett, H. V. R. Dias and P. P. Power, J. Organomet. Chem.,
1988, 341, 1.
˚
c = 16.7988(6) A, a = b = c = 90u, Z = 4, R1 = 0.0426 for 2031 (I . 2s(I))
This journal is ß The Royal Society of Chemistry 2007
Chem. Commun., 2007, 4339–4341 | 4341