in the former. The observation that the metal–nitrogen bond
˚
distances for 2 are y0.3 A longer than those for 1 and 3 is
consistent with the retention of the +2 oxidation state in 2. As
reflected by the sums of bond angles for the MNCCN rings, these
metallacycles are close to planar for 2 and 3. The significant
folding along the N–N vector in the case of 1 is attributable to the
steric demands of the mesityl substituents.
Scheme 1
The proposed structures for 1–3 are also in accord with IR,
1H NMR, and magnetic moment data. Thus, only 2 exhibits an
IR peak at 1636 cm21, which falls in the region reported for the
CLN stretching mode,10 therefore indicating that metal A ligand
electron transfer has not occurred in this case. Moreover, the
detection of a 1H NMR resonance for 3 at d 221.30 supports the
assignment of the +3 oxidation state in this complex since Evans
et al.11 reported a peak with a similar chemical shift (d 219.7) for
the Me5C5 protons of the Eu (+3) complex, [(C5Me5)Eu(OCMe3)-
(m-OCMe3)]2. The magnetic moment values (Evans method) of
1.82, 6.98, and 3.55 BM for 1, 2 and 3, respectively, also support
the oxidation state assignments proposed above.
arrangement is best represented by structure C (Scheme 1). The
angle between the N(1)–Sm–N(2) and N(1)–C(1)–C(12)–N(2)
planes (47.54u) is larger than that in 1 (42.80u) due to the
concerted effects of increased substituent bulk and optimization
of the interaction between Sm and the C(1)–C(12) double bond.
It is likely that the reaction of (C5Me5)2Sm?OEt2 with dpp-
BIAN proceeds via initial displacement of Et2O to form
(C5Me5)2SmII(dpp-BIAN), followed by intramolecular electron
transfer to generate (C5Me5)2SmIII(dpp-BIAN2), which eliminates
[C5Me5]2. In turn, [C5Me5]2 transfers the second electron to the
singly-reduced BIAN ligand.14 Support for this idea stems from
the detection of the oxidized product, [C5Me5]2, in the reaction
mixture by 1H NMR spectroscopy. This type of process has been
elegantly investigated by Evans and Davis15 and dubbed ‘‘sterically
induced reduction.’’
The reaction of (C5Me5)2Sm?OEt2 with one equivalent of the
sterically encumbered ligand, dpp-BIAN12 (dpp 5 2,6-diisopro-
pylphenyl) in THF solution at ambient temperature resulted in loss
of a C5Me5 group and formation of (C5Me5)Sm(dpp-BIAN)(thf)
(4) in 85% yield. Akin to 1 and 3, compound 4 features a five-
membered MNCCN ring. However, a single-crystal X-ray
analysis5 revealed that the ring structure of 4 differs significantly
from those of 1–3 (Fig. 2). Thus, the C(1)–C(12) separation in 4 is
In summary, we have prepared the first lanthanide 1,2-
bis(imino)acenaphthene complexes and demonstrated that the
metal A BIAN charge transfer process can be controlled by (a) the
choice of metal, (b) tuning of the BIAN ligand substituents, or (c)
use of a bulky BIAN ligand.
˚
y0.03 A less than those in 1 and 3. Furthermore, there are short
˚
contacts of 2.692(4) and 2.707(4) A between these carbon atoms
We are grateful to the Robert A. Welch Foundation (F-0003)
for financial support of this work.
˚
and the Sm center, and the N–C bond distances are y0.05 A
longer than those in 1 and 3. The Sm–C5Me5 ring centroid
˚
distance of 2.420(1) A is similar to that of 1 and therefore
Notes and references
indicative of a Sm(III) center in 4. Moreover, the N–C and C–C
bond distances in 4 are very similar to those of the dianionic dpp-
BIAN ligand in magnesium and calcium complexes.13 Overall, the
metrical parameters for 4 imply that two-electron reduction of the
dpp-BIAN ligand has taken place and that the bonding
1 For recent examples, see: (a) P. Preishuber-Pflugl and M. Brookhart,
Macromolecules, 2002, 35, 6074; (b) M. D. Leatherman, S. A. Svedja,
L. K. Johnson and M. Brookhart, J. Am. Chem. Soc., 2003, 125, 3068;
(c) A. E. Cherian, E. M. Lobkovsky and G. W. Coates, Chem.
Commun., 2003, 2566; (d) W. Liu and M. Brookhart, Organometallics,
2004, 23, 6099; (e) D. H. Camacho, E. V. Salo, J. W. Ziller and Z. Guan,
Angew. Chem., Int. Ed., 2004, 43, 1821; (f) B. S. Williams, M. D.
Leatherman, P. S. White and M. Brookhart, J. Am. Chem. Soc., 2005,
127, 5132; (g) A. M. Kluwer, T. S. Koblenz, T. Jonischkeit, K. Woelk
and C. J. Elsevier, J. Am. Chem. Soc., 2005, 127, 15470; (h) D. H.
Camacho and Z. Guan, Macromolecules, 2005, 38, 2544; (i) J. M. Rose,
A. E. Cherian and G. W. Coates, J. Am. Chem. Soc., 2006, 128, 4186.
2 R. van Asselt, C. J. Elsevier, W. J. J. Smeets, A. L. Spek and R. Bendix,
Recl. Trav. Chim. Pays-Bas, 1994, 113, 88.
3 J. A. Moore, K. Vasudevan, N. J. Hill, G. Reeske and A. H. Cowley,
Chem. Commun., 2006, 2913.
4 D. N. Coventry, A. S. Batsanov, A. E. Goeta, J. A. K. Howard and
T. B. Marder, Polyhedron, 2004, 23, 2789.
5 All X-ray data were collected at 153 K on a Nonius-Kappa CCD
diffractometer. Crystal data for 1: C64H74N2Sm, Mr 5 1021.60, triclinic,
¯
˚
space group P1, a 5 12.319(5), b 5 14.294(5), c 5 16.910(5) A, a 5
3
˚
70.589(5), b 5 82.726(5), c 5 69.084(5)u, V 5 2623.2(16) A , Z 5 2, T 5
153(2) K, m 5 1.161 mm21, reflections collected/independent 5 17880/
11973 (Rint 5 0.0373), R1(I . 2s(I)) 5 0.1107. For 2: C47H62EuN2,
Mr 5 806.95, monoclinic, space group P21/n, a 5 10.250(5),
Fig. 2 View of the Sm(III) complex (C5Me5)Sm(dpp-BIAN)(thf) (4)
showing the atom numbering scheme and thermal ellipsoids at 50%
probability (hydrogen atoms omitted for clarity). Selected bond distances
3
˚
˚
b 5 18.436(5), c 5 23.258(5) A, b 5 94.739(5)u, V 5 4380(3) A ,
Z 5 4, T 5 153(2) K, m 5 1.463 mm21, reflections collected/
independent 5 16952/10032 (Rint 5 0.0358), R1 (I . 2s(I)) 5 0.0443
and wR2 (I . 2s(I)) 5 0.1103. For 3: C46H50EuN2O2, Mr 5 814.88,
˚
(A) and angles (u): Sm(1)–N(1) 2.269(3), Sm(1)–N(2) 2.232(4), Sm(1)–C(1)
2.704(4), Sm(1)–C(12) 2.692(4), C(1)–N(1) 1.387(5), C(12)–N(2) 1.405(5),
C(1)–C(12) 1.414(6), N(1)–Sm(1)–N(2) 83.1(1), Sm(1)–N(1)–C(1) 92.4(2),
N(1)–C(1)–C(12) 119.3(3), C(1)–C(12)–N(2) 124.4(4), C(12)–N(2)–Sm(1)
92.6(2).
¯
˚
triclinic, space group P1, a 5 9.5567(19), b 5 10.286(2), c 5 20.283(4) A,
˚
3
a 5 101.15(3), b 5 94.09(3), c 5 104.01(3)u, V 5 1883.4(7) A , Z 5 2,
T
5
153(2) K,
m
5
1.706 mm21
independent 5 12045/8520 (Rint 5 0.0398), R1 (I . 2s(I)) 5 0.0476
,
reflections collected/
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Chem. Commun., 2007, 3464–3466 | 3465