state as well as in Et2O to afford a paramagnetic orange
compound Fe2(L)2(CO)2 3 quantitatively. Irradiation of 3
resulted in regeneration of 2 concomitant with the loss of CO.
According to X-ray analysis (Fig. 2),‡ the homochiral binuclear
frame was retained during the reaction. A crystallographic C2
axis again runs though the two iron atoms. Complex 3 contains
the two different iron atoms: one iron atom [Fe(1)] is placed in
the center of a disordered octahedron defined by four nitrogen
atoms of two benzamidinate groups and two carbonyl ligands;
the other iron atom [Fe(2)] adopts a distorted tetrahedral
geometry with two amidinate groups. The solid structure of 3 is
consistent with its 1H NMR spectrum in solution, which shows
two SiMe3 protons as well as 16 resonances attributable to
phenyl and cyclohexane groups. In the IR spectrum, the n(CO)
bands of 3 are observed at 2018 and 1944 cm21 and are shifted
to higher frequencies than those of Fe[ButC(NCy)2]2(CO)2
(1999, 1929 cm21).8
The dihedral angles between the two Fe–amidinates of 85.4
and 84.8° for Fe(1) and Fe(2) in 3 are lager than those of 2 (59.9
and 68.1°). The geometrical parameters within the FeN2C rings
in 3 are comparable to those found in 2. However, the tethering
of the amidinate groups in 3 restricts the N(4)–Fe(2)–N(4A)
angle at the tetrahedral iron site, which is 128.9(2)° and acute
compared with the corresponding angles at 3 [154.2(1) and
140.2(1)°]. The Fe–Fe separation of 3 was elongated by 0.94 Å
compared with that of the parent complex 2, indicating that the
size of the cage created by the L22 ligands is flexible. The
stability of 3 deserves comment. Although 3 contains a
14-electron iron site, it is found to be stable in the solid state for
a few minutes under air. In contrast, 2 immediately decomposes
in air. This is ascribed to the rigid conformation, which is locked
by the CO ligands and prevents 3 from undergoing further
reaction. This reason is related to the formation of 3, and
coordination of additional CO is hampered in the remaining
tetrahedral iron site. Studies of the reactivity of binuclear iron
complexes 2 and 3 are in progress.
Notes and references
†
Preparation of 2: all manipulations were carried out under an
atmosphere of argon. A solution of Li2(L) (2.31 mmol) in THF (40 mL) was
added to a slurry of FeCl2 (0.29 g, 2.31 mmol) in THF (20 mL) at 0 °C. The
solution was stirred for 18 h. The solvent was evaporated to dryness, and the
red residue was extracted with Et2O. Concentration and cooling to 230 °C
gave 0.56 g of 2 as yellow crystals in 47% yield. 1H NMR (C6D6, 500 MHz):
d 127.8 (2H), 31.6 (2H), 21.1 (4H, Ph), 13.3 (4H, Ph), 10.6 (2H), 5.9 (2H),
2.5 (18H, SiMe3 + 2H), 2.0 (2H). Anal. calc. for C52H76N8Si4Fe2: C, 60.21;
H, 7.39; N, 10.80. Found: C, 59.67; H, 7.33; N, 10.51%.
Preparation of 3: a solution of 2 (0.14 g, 0.14 mmol) in Et2O (20 mL) was
stirred under 1atm of CO at room temperature for 16 h, after which the
solvent was removed in vacuo. The remaining orange crystalline solid was
rinsed with hexane and dried to give 0.14 g of 3 in 95% yield. IR (Nujol,
KBr)/cm21: 2018 (s), 1944 (s). 1H NMR (C6D6, 500 MHz): d 127.5 (1H),
26.3 (1H), 23.5 (2H, Ph), 22.8 (1H), 19.3 (2H, Ph), 11.0 (1H), 3.6 (9H,
SiMe3), 2.6 (1H), 2.0 (1H), 0.9 (1H), 0.2 (2H, Ph), 0.1 (2H, Ph), 20.1 (1H),
22.0 (9H, SiMe3), 24.4 (1H), 25.6 (1H), 26.8 (1H), 27.6 (1H). Anal.
calc. for C54H76N8O2Si4Fe2: C, 59.33; H, 7.01; N, 10.25. Found: C, 59.02;
H, 6.85; N, 9.89%.
‡
Crystal data: for 2: C52H76N8Si4Fe2, M = 1037.26, monoclinic, space
group C2/c, a = 23.6648(9), b = 18.6585(9), c = 13.5164(5) Å, b =
92.4516(10)°, V = 5962.7(4) Å3, Z = 4, T = 193 K, m(Mo-Ka) = 6.05
cm21, Rigaku Mercury, 28 006 measured reflections (2qmax = 55°), 6822
unique, 337 variables, R1 = 0.038 [I > 2s(I)], wR2 = 0.111 (all data), and
GOF = 1.03.
For 3: C54H76N8O2Si4Fe2, M = 1093.28, monoclinic, space group C2/c,
a = 23.912(4), b = 18.384(2), c = 13.4886(5) Å, b = 92.6946(9)°, V =
5923.0(9) Å3, Z = 4, T = 193 K, m(Mo-Ka) = 6.15 cm21, Rigaku
Mercury, 27 945 measured reflections (2qmax = 55°), 6690 unique, 355
variables, R1 = 0.041 [I > 2s(I)], wR2 = 0.127 (all data), and GOF =
1.00. All structures were solved by direct methods and refined on F2 by full-
matrix, least squares using the CrystalStructure software package.
suppdata/cc/b1/b111651g/ for crystallographic data in CIF or other
electronic format.
1 Polynuclear Metal Cluster Complexes, R. D. Adams and F. A. Cotton,
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Jordan, J. Am. Chem. Soc., 1997, 119, 8125; E. A. C. Brussee, A.
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Fig. 2 Structure of D,D-Fe2(LSS)2(CO)2 3. Phenyl groups (except for the
ipso carbon) and methyl groups on Si are omitted for clarity. Selected
interatomic distances (Å) and angles (°): Fe(1)–Fe(2) 4.4550(10), Fe(1)–
N(1) 2.029(3), Fe(1)–N(2) 2.036(3), Fe(2)–N(3) 2.034(3), Fe(2)–N(4)
2.076(3), N(1)–C(1) 1.344(4), N(2)–C(1) 1.313(4), N(3)–C(2) 1.322(4),
N(4)–C(2) 1.340(4), Fe(1)–C(27) 1.764(4), C(27)–O(1) 1.146(4); N(1)–
Fe(1)–N(2) 65.77(11), N(3)–Fe(2)–N(4) 65.80(11), N(1)–C(1)–N(2)
112.3(3), N(3)–C(2)–N(4) 114.0(3), Fe(1)–C(27)–O(1) 176.1(3), C(27)–
Fe(1)–C(27A) 87.2(2).
7 J. R. Hagadorn and J. Arnold, Inorg. Chem., 1997, 36, 132.
8 B. Vendemiati, G. Prini, A. Meetsma, B. Hessen, J. H. Teuben and O.
Traverso, Eur. J. Inorg. Chem., 2001, 707.
CHEM. COMMUN., 2002, 958–959
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