Synthesis and characterization of aluminum- and gallium-bridged [1.1]chromarenophanes and [1.1]molybdarenophanes

Article abstract of DOI:10.1021/ic800336f

The synthesis and structural characterization of the first [1.1]chromarenophanes and the first [1.1]molybdarenophanes are described. A salt-metathesis reaction of [2-(Me₂NCH₂)C ₆H₄]AlCl₂ with freshly prepared [Cr(LiC ₆H₅)₂]·TMEDA (TMEDA = N,N,N′,N′-tetramethylethylenediamine) resulted in the dialumina[1.1]chromarenophane [{2-(Me₂NCH₂)-C ₆H₄}Al(η⁶-C₆H₅) ₂Cr]₂ (2a). The poor solubility of 2a in organic solvents prompted us to synthesize the new intramolecularly coordinated aluminum- and gallium dichlorides [5-tBu-2-(Me₂NCH₂)C₆H ₃]ECl₂ [E = Al (3a), Ga (3b)] in which the phenyl group was equipped with a tert-butyl group. Salt-metathesis reactions of 3a and 3b, respectively, with freshly prepared [M(LiC₆H₅) ₂]·TMEDA (M = Cr, Mo) resulted in four new [1.1]metallarenophanes of the general type [{5-tBu-2-(Me₂NCH ₂)C₆H₃}E(η⁶-C₆H ₅)₂M]₂ [E = Al, M = Cr (4a); E = Ga, M = Cr (4b); E = Al, M = Mo (5a); E = Ga, M = Mo (5b)]. 2a, 4a,b, and 5a,b have been structurally characterized by single-crystal analysis [2a·1/2C ₆H₁₂: C₄₈H₅₆Al₂Cr ₂N₂, monoclinic, P2₁/c, a = 9.9117(9) A, b = 19.9361(16) A, c = 10.638(2) A, α = 90°, β = 112.322(5)°, γ = 90°, Z = 2; 4a·2C₆H ₆: C₆₂H₇₂Al₂Cr₂N ₂, monoclinic, P2₁/c, a = 10.9626(9) A, b = 19.3350(18) A, c = 12.4626(9) A, α = 90°, β = 100.756(5)°, γ = 90°, Z = 2; 4b·2C₆H ₆: C₆₂H₇₂Cr₂Ga₂N ₂, monoclinic, P2₁/c, a = 10.8428(2) A, b = 19.4844(4) A, c = 12.4958(2) A, α = 90°, β = 100.6187°, γ = 90°, Z = 2; 5a·2C₆H₆: C₆₂H₇₂Al₂Mo₂N₂, triclinic, P1, a = 10.4377(4) A, b = 11.6510(4) A, c = 11.6514(4) A, α = 73.545(3)°, β = 89.318(2)°, γ = 76.120(2)°, Z = 1; 5b·2C₆H₆: C ₆₂H₇₂Ga₂Mo₂N₂, triclinic, P1, a = 10.3451(5) A, b = 11.6752(6) A, c = 11.6900(5) A, α = 73.917(3)°, β = 89.550(3)°, γ = 76.774(2)°, Z = 1]. All five [1.1]metallarenophanes 2a, 4a,b, and 5a,b crystallize as anti isomers with both Me₂N donor groups in exo positions (C_i point group symmetry). The new [1.1]metallarenophanes show NMR spectra that can be interpreted as being caused by time-averaged C_2h symmetrical species, which is consistent with the findings of their molecular structures in the solid state. Variable-temperature ¹H NMR measurements for 4a,b and 5a,b (500 MHz; -90 to 90 °C) revealed only peak broadening in the lower temperature range of -70 to -90 °C. ¹H NMR saturation transfer difference experiments did not show an expected anti-to-anti isomerization, rendering the new [1.1]metallacyclophanes rigid on the NMR time scale. Electrochemical measurements were performed for 4a,b and 5a,b. However, reproducible cyclic voltammograms could only be obtained for the two gallium species 4b and 5b, revealing the expected weak communication between the two transition-metal atoms in both compounds (class II).

Full text of DOI:10.1021/ic800336f

Inorg. Chem. 2008, 47, 5992-6000
Synthesis and Characterization of Aluminum- and Gallium-Bridged
[1.1]Chromarenophanes and [1.1]Molybdarenophanes
Clinton L. Lund,† Jo¨rg A. Schachner,† Ian J. Burgess,† J. Wilson Quail,‡ Gabriele Schatte,‡
and Jens Mu¨ller*,†
Department of Chemistry and Saskatchewan Structural Sciences Centre, UniVersity of
Saskatchewan, 110 Science Place, Saskatoon, Saskatchewan S7N 5C9, Canada
Received February 21, 2008
The synthesis and structural characterization of the first [1.1]chromarenophanes and the first [1.1]molybdarenophanes
are described. A salt-metathesis reaction of [2-(Me2NCH2)C6H4]AlCl2 with freshly prepared [Cr(LiC6H5)2] · TMEDA
(TMEDA ) N,N,N′,N′-tetramethylethylenediamine) resulted in the dialumina[1.1]chromarenophane [{2-(Me2NCH2)-
6
C6H4}Al(η -C6H5)2Cr]2 (2a). The poor solubility of 2a in organic solvents prompted us to synthesize the new
intramolecularly coordinated aluminum- and gallium dichlorides [5-tBu-2-(Me2NCH2)C6H3]ECl2 [E ) Al (3a), Ga
(3b)] in which the phenyl group was equipped with a tert-butyl group. Salt-metathesis reactions of 3a and 3b,
respectively, with freshly prepared [M(LiC6H5)2] · TMEDA (M ) Cr, Mo) resulted in four new [1.1]metallarenophanes
6
of the general type [{5-tBu-2-(Me2NCH2)C6H3}E(η -C6H5)2M]2 [E ) Al, M ) Cr (4a); E ) Ga, M ) Cr (4b); E )
Al, M ) Mo (5a); E ) Ga, M ) Mo (5b)]. 2a, 4a,b, and 5a,b have been structurally characterized by single-crystal
analysis [2a· 1/2C6H12: C48H56Al2Cr2N2, monoclinic, P21/c, a ) 9.9117(9) Å, b ) 19.9361(16) Å, c ) 10.638(2) Å,
R ) 90°, ꢀ ) 112.322(5)°, γ ) 90°, Z ) 2; 4a·2C6H6: C62H72Al2Cr2N2, monoclinic, P21/c, a ) 10.9626(9) Å, b
) 19.3350(18) Å, c ) 12.4626(9) Å, R ) 90°, ꢀ ) 100.756(5)°, γ ) 90°, Z ) 2; 4b·2C6H6: C62H72Cr2Ga2N2,
monoclinic, P21/c, a ) 10.8428(2) Å, b ) 19.4844(4) Å, c ) 12.4958(2) Å, R ) 90°, ꢀ ) 100.6187°, γ ) 90°,
¯
Z ) 2; 5a·2C6H6: C62H72Al2Mo2N2, triclinic, P1, a ) 10.4377(4) Å, b ) 11.6510(4) Å, c ) 11.6514(4) Å, R )
¯
73.545(3)°, ꢀ ) 89.318(2)°, γ ) 76.120(2)°, Z ) 1; 5b·2C6H6: C62H72Ga2Mo2N2, triclinic, P1, a ) 10.3451(5) Å,
b ) 11.6752(6) Å, c ) 11.6900(5) Å, R ) 73.917(3)°, ꢀ ) 89.550(3)°, γ ) 76.774(2)°, Z ) 1]. All five
[1.1]metallarenophanes 2a, 4a,b, and 5a,b crystallize as anti isomers with both Me2N donor groups in exo positions
(Ci point group symmetry). The new [1.1]metallarenophanes show NMR spectra that can be interpreted as being
caused by time-averaged C2h symmetrical species, which is consistent with the findings of their molecular structures
1
in the solid state. Variable-temperature H NMR measurements for 4a,b and 5a,b (500 MHz; -90 to 90 °C)
1
revealed only peak broadening in the lower temperature range of -70 to -90 °C. H NMR saturation transfer
difference experiments did not show an expected anti-to-anti isomerization, rendering the new [1.1]metallacyclophanes
rigid on the NMR time scale. Electrochemical measurements were performed for 4a,b and 5a,b. However, reproducible
cyclic voltammograms could only be obtained for the two gallium species 4b and 5b, revealing the expected weak
communication between the two transition-metal atoms in both compounds (class II).
Introduction
rocenophanes was reviewed in 1986 by Mueller-Westerhoff.2
Usually, carbon-bridged [1.1]ferrocenophanes prefer the syn
conformation (Figure 1, E ) C); however, in 1993 the first
structural evidence for the existence of the second isomer,
the anti isomer (Figure 1), was reported.3 In this particular
case, CHMe moieties bridged the two ferrocene units and
Since their first appearance in the literature in 1966,1
[1.1]ferrocenophanes have been the subject of intensive
investigations. The chemistry of the carbon-bridged [1.1]fer-
* To whom correspondence should be addressed. E-mail: jens.mueller@
usask.ca.
†
Department of Chemistry, University of Saskatchewan.
‡ Saskatchewan Structural Sciences Centre, University of Saskatchewan.
(2) Mueller-Westerhoff, U. T. Angew. Chem., Int. Ed. Engl. 1986, 25,
(1) Watts, W. E. J. Am. Chem. Soc. 1966, 88, 855–856.
702–717.
5992 Inorganic Chemistry, Vol. 47, No. 13, 2008
10.1021/ic800336f CCC: $40.75  2008 American Chemical Society
Published on Web 06/05/2008

[1.1]Chromarenophanes and [1.1]Molybdarenophanes
bridged species, with the knowledge about heteroatom-
bridged [1.1]ruthenocenophane being limited to a SiMe2-
bridged species published in 1995 by Herberhold et al.12
In the course of our investigation into strained [1]metal-
lacyclophanes with heavier group 13 elements in bridging
positions,17 we found that dilithioferrocene reacts with
intramolecularly coordinated group 13 element halides
Ar′EX2 (Ar′ ) 2-(Me2NCH2)C6H4; E ) Al,8,9 Ga,9 In9) to
give [1.1]ferrocenophanes. Even though [1.1]ferrocenophanes
are unstrained and, therefore, cannot be used for ring-opening
polymerizations, they serve as model compounds for the
investigation of metal-metal interactions. Using cyclic
voltammetry, we have shown that two isostructural [1.1]fer-
rocenophanes, a gallium- and an aluminum-bridged species,
show distinctively different redox behavior. Whereas the
digalla[1.1]ferrocenophane9 showed the expected class II18
behavior (two one-electron oxidation waves) similar to other
[1.1]ferrocenophanes, the dialumina[1.1]ferrocenophane9
showed an unexpected class I18 behavior (one two-electron
oxidation wave). On the basis of these findings, we wanted
to explore reactions of other dilithio sandwich compounds
with intramolecularly coordinated alanes and gallanes of the
type Ar′EX2. We were hoping to obtain [1.1]metallacyclo-
phanes to further investigate metal-metal interactions.
In contrast to the large number of [1.1]metallocenophanes,
it is surprising that not a single example of a [1.1]metal-
larenophane is described in the literature. Within this article,
we fill this gap by reporting on the synthesis and character-
ization of the first [1.1]chromarenophanes and the first
[1.1]molybdarenophanes.
Figure 1. Isomerism in [1.1]metallocenophanes.
gave rise to endo/exo isomers (Figure 1). [1.1]Ferro-
cenophanes are highly dynamic in solution and have been
coined “molecular acrobats”.2,4 A distanna[1.1]ferrocenophane
(E ) SnBu2)5 was the first heteroatom bridged [1.1]ferro-
cenophane and since its discovery, the group of heteroatom
containing [1.1]ferrocenophanes has grown significantly and
is now known for groups 13 (boron,6 aluminum,7–9 gal-
lium,9,10 indium,9), 14 (silicon,11,12 tin,5,13 lead14), 15 (phos-
phorus15), and 16 (sulfur16).
The knowledge about [1.1]ruthenocenophanes and mixed
Ru-Fe [1.1]metallocenophanes is mainly limited to carbon-
¨
(3) Lo¨wendahl, M.; Davidsson, O.; Ahlberg, P.; Håkansson, M. Orga-
nometallics 1993, 12, 2417–2419.
¨
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1983, 75, 139–144.
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Angew. Chem., Int. Ed. 2003, 42, 924–927.
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2005, E61, m682-m684.
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Radacki, K. Inorg. Chem. 2005, 44, 4906–4908.
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J. Inorg. Chem. 2006, 45, 454–459.
(10) (a) Jutzi, P.; Lenze, N.; Neumann, B.; Stammler, H. G. Angew. Chem.,
Int. Ed. 2001, 40, 1424–1427. (b) Uhl, W.; Hahn, I.; Jantschak, A.;
Spies, T. J. Organomet. Chem. 2001, 637, 300–303. (c) Althoff, A.;
Jutzi, P.; Lenze, N.; Neumann, B.; Stammler, A.; Stammler, H.-G.
Organometallics 2002, 21, 3018–3022. (d) Althoff, A.; Jutzi, P.; Lenze,
N.; Neumann, B.; Stammler, A.; Stammler, H. G. Organometallics
2003, 22, 2766–2774. (e) Althoff, A.; Eisner, D.; Jutzi, P.; Lenze, N.;
Neumann, B.; Schoeller, W. W.; Stammler, H.-G. Chem.sEur. J.
2006, 12, 5471–5480.
Results and Discussion
We started to investigate the reaction of dilithiobis(ben-
zene)chromium with Ar′AlCl2 (1a). After several attempts
using various reaction conditions, we obtained red crystals
from this reaction (eq 1). Interestingly, once 2a crystallized
it could not be redissolved in common organic solvents.
(11) (a) Park, J. W.; Seo, Y. S.; Cho, S. S.; Whang, D. M.; Kim, K. M.;
Chang, T. Y. J. Organomet. Chem. 1995, 489, 23–25. (b) Zechel, D. L.;
Foucher, D. A.; Pudelski, J. K.; Yap, G. P. A.; Rheingold, A. L.;
Manners, I. J. Chem. Soc., Dalton Trans. 1995, 1893–1899. (c) Ni,
Y. Z.; Rulkens, R.; Pudelski, J. K.; Manners, I. Macromol. Rapid
Commun. 1995, 16, 637–641. (d) Reddy, N. P.; Choi, N.; Shimada,
S.; Tanaka, M. Chem. Lett. 1996, 649–650. (e) MacLachlan, M. J.;
Zheng, J.; Thieme, K.; Lough, A. J.; Manners, I.; Mordas, C.; LeSuer,
R.; Geiger, W. E.; Liable-Sands, L. M.; Rheingold, A. L. Polyhedron
2000, 19, 275–289. (f) Calleja, G.; Carre´, F.; Cerveau, G. Organo-
metallics 2001, 20, 4211–4215. (g) Berenbaum, A.; Lough, A. J.;
Manners, I. Organometallics 2002, 21, 4415–4424. (h) Bao, M.;
Hatanaka, Y.; Shimada, S. Chem. Lett. 2004, 33, 520–521.
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(b) Dong, T. Y.; Hwang, M. Y.; Wen, Y. S.; Hwang, W. S. J.
Organomet. Chem. 1990, 391, 377–385. (c) Ja¨kle, F.; Rulkens, R.;
Zech, G.; Foucher, D. A.; Lough, A. J.; Manners, I. Chem.sEur. J.
1998, 4, 2117–2128. (d) Ja¨kle, F.; Rulkens, R.; Zech, G.; Massey, J.;
Manners, I. J. Am. Chem. Soc. 2000, 122, 4231–4232. (e) Baumgartner,
T.; Ja¨kle, F.; Rulkens, R.; Zech, G.; Lough, A. J.; Manners, I. J. Am.
Chem. Soc. 2002, 124, 10062–10070.
However, the compound is sparingly soluble in THF, and
a small amount of single crystals of sufficient quality for
X-ray single-crystal analysis were obtained from highly
diluted THF solution in the presence of cyclohexane (Figure
2, Table 1). The structural analysis clearly revealed that 2a
is a [1.1]chromarenophane. To the best of our knowledge, it
(14) Utri, G.; Schwarzhans, K. E.; Allmaier, G. M. Z. Naturforsch. B 1990,
45, 755–762.
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2000, 601, 211–219. (b) Mizuta, T.; Onishi, M.; Miyoshi, K.
Organometallics 2000, 19, 5005–5009. (c) Mizuta, T.; Imamura, Y.;
Miyoshi, K. Organometallics 2005, 24, 990–996.
(17) Lund, C. L.; Schachner, J. A.; Quail, J. W.; Mu¨ller, J. J. Am. Chem.
Soc. 2007, 129, 9313–9320.
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422.
Inorganic Chemistry, Vol. 47, No. 13, 2008 5993

Lund et al.
Scheme 1
Figure 2. Molecular structure of 2a with thermal ellipsoids at the 50%
probability level. Hydrogen atoms are omitted for clarity. Selected
atom-atom distances [angstroms] and bond angles [degrees]: Al1-N1 )
2.072(3), Al1-C1 ) 1.972(4), Al1-C7 ) 1.962(4), Al1-C13 ) 1.978(4),
Cr1-Cr1′ ) 5.0866(10), C1-Al1-C7 ) 121.22(16), N1-Al1-C13 )
85.78(14), C7-Al1-C13 ) 120.44(16), C1-Al1-C13 ) 113.65(16),
C7-Al1-N1 ) 103.15(14), C1-Al1-N1 ) 101.95(14), R ) 4.9(2).
were isolated and purified by crystallizations from toluene
solutions and crystals suitable for single crystal X-ray
structural determination were obtained from benzene solu-
1
tions (Figures 3 and 4, Table 1). According to H NMR
measurements of the reaction mixtures, the formation of the
[1.1]metallacyclophanes proceeds relatively cleanly for this
type of sensitive chemistry (estimated conversions of
80-90%). In all cases, we detected only small amounts of
the parent bis(benzene)metal complex among the products.
However, N,N,N′,N′-tetramethylethylenediamine (TMEDA),
which is required for the dilithiation of the parent sandwich
compounds, results in the formation of TMEDA · LiCl. It is
the latter compound that is difficult to separate from the
[1.1]metallacyclophanes, and, therefore, we isolated pure
4a,b and 5a,b in yields of only 20-30%.
is the first [1.1]chromarenophane known to date. 2a crystal-
lizes as an anti isomer with both NMe2 donor groups in exo
positions (Figure 1 and 2). Further structural details will be
discussed below.
The poor solubility of 2a made its separation from the
simultaneously produced LiCl difficult, and, in addition,
prevented investigations into metal-metal interactions in
solution, hence, rendering electrochemical methods unsuit-
able. Therefore, we attempted to increase the solubility of
the targeted [1.1]metallacyclophanes by using one-armed
phenyl ligands Ar′ equipped with an additional alkyl group
on the aromatic ring. From the ample possibilities, we picked
an Ar′ derivative with one tBu group para to the donor arm.
Starting from commercially available p-(tert-butyl)benzyl-
bromide (p-tBuC6H4CH2Br) a known two-step synthesis
Solid-State Structures of 2a, 4a,b, and 5a,b. As in the
case of the [1.1]ferrocenophanes investigated recently,8,9 the
new [1.1]chromarenophanes 2a (Figure 2) and 4a,b (Figure
3, Figure S1 in the Supporting Information) and the new
[1.1]molybdarenophanes 5a,b (Figure 4, Figure S2 in the
Supporting Information) crystallize as anti isomers with the
two NMe2 donor groups in exo positions (Figure 1). All five
species exhibit Ci point-group symmetries in the crystal
lattice. The geometries around the bridging atoms can be
best described as trigonal pyramids, with the three carbon
atoms C1, C7, and C13 at the base and the nitrogen atom
N1 at the tip of the pyramid. With respect to an ideal
tetrahedron, these pyramids are flattened as it can be deduced
from the sum over the three C-E-C angles (E ) Al, Ga),
which are 355.31 (2a), 354.14 (4a), 356.25 (4b), 354.12 (5a),
and 355.79° (5b). Respective atom-atom distances in 2a,
4a,b, and 5a,b are very similar; for example, the Cr-Cr
distances are 5.9866(10), 5.9921(11), and 6.0251(6) Å for
2a, 4a, and 4b, respectively, and the Mo-Mo distances are
5.9983(7) and 6.0277(6) Å for 5a and 5b, respectively. These
metal-metal distances are larger for the gallium species as
compared to the aluminum species, which is partly due to
differences in E-C bond lengths: Ga1-C1 and Ga1-C7
bonds being slightly longer than respective Al-C bonds
(Figures 3 and 4). Only the E-N donor bonds are very
different for aluminum compared with gallium-bridged
species, with Al-N donor bonds being shorter than Ga-N
bonds (for 4a and 4b, the difference is 0.103(4) Å; for 5a
and 5b it is 0.111(4) Å). Similar differences between E-N
donor bond lengths were found for the [1.1]ferro-
yielded (p-tBuAr′)Li19 [p-tBuAr′
)
5-tBu-2-(Me2-
NCH2)C6H3] that was used to synthesize the new intramo-
lecularly coordinated aluminum and gallium dichlorides 3a
and 3b, respectively (eq 2). Expectedly, both species show
1H and 13C NMR spectra that can be interpreted as being
caused by Cs symmetrical species. The 27Al NMR shift of δ
131 for 3a is very similar to δ 127 reported for the
monomeric Ar′AlCl2 (1a)20 and shows that 3a is a mono-
meric species with a 4-fold coordinated aluminum atom.
With the alane 3a and the gallane 3b in hand, novel
[1.1]chromarenophanes and [1.1]molybdarenophanes with
improved solubility were prepared through reactions with
freshly dilithiated bis(benzene)chromium or -molybdenum
(Scheme 1). The four [1.1]metallarenophanes 4a,b and 5a,b
(19) Cope, A. C.; Gourley, R. N. J. Organomet. Chem. 1967, 8, 527–533.
(20) Mu¨ller, J.; Englert, U. Chem. Ber. 1995, 128, 493–497.
5994 Inorganic Chemistry, Vol. 47, No. 13, 2008

[1.1]Chromarenophanes and [1.1]Molybdarenophanes
Table 1. Crystal and Structural Refinement Data for 2a, 4a,b, and 5a,b
b
b
2a·1/2C6H12
4a·2C6H6
4b·2C6H6
5a·2C6H6
5b·2C6H6
empirical formula
C48H56Al2Cr2N2
818.91
C62H72Al2Cr2N2
1003.18
C62H72Cr2Ga2N2
1088.66
C62H72 Al2Mo2N2
1091.06
C62H72Ga2Mo2N2
1176.54
fw
cryst size, mm3
0.20 × 0.20 × 0.12 0.12 × 0.10 × 0.10 0.20 × 0.18 × 0.15 0.13 × 0.13 × 0.10 0.08 × 0.08 × 0.050.71073
j
j
cryst. system, space group
Z
monoclinic, P21/c
2
monoclinic, P21/c
2
monoclinic, P21/c
2
triclinic, P1
triclinic, P1
1
1
a, Å
b, Å
c, Å
R, deg
ꢀ, deg
γ, deg
V, Å3
9.9117(9)
19.9361(16)
10.638(2)
90
112.322(5)
90
1944.6(4)
1.399
173(2)
10.9626(9)
19.3350(18)
12.4626(9)
90
100.756(5)
90
2595.2(4)
1.284
173(2)
10.8428(2)
19.4844(4)
12.4958(2)
90
100.6187
90
2594.72(8)
1.393
173(2)
10.4377(4)
11.6510(4)
11.6514(4)
73.545(3)
89.318(2)
76.120(2)
1316.82(8)
1.376
10.3451(5)
11.6752(6)
11.6900(5)
73.917(3)
89.550(3)
76.774(2)
1318.36(11)
1.482
F
calcd, mg/m3
T, K
173(2)
0.551
173(2)
1.517
µ
calcd, mm-1
0.642
0.494
1.477
e` range, deg
2.44 to 26.02
21561/3825
ψ-scan
3825/96/273
1.052
3.46 to 25.01
8155/4567
none
4567/0/294
1.032
3.32 to 27.47
41481/5916
ψ-scan
5916/0/313
1.072
2.64 to 25.68
8528/4967
multiscan
4967/0/312
1.069
3.21 to 27.47
10303/6021
multiscan
6021/0/312
1.059
reflns collected/ unique
absorption correction
data/restraints/params
GOF on F2
final R indices [I > 2σ(I)]a 0.0544
0.0653
0.1452
0.0368
0.0848
0.0453
0.1046
0.0412
0.0941
wR2 (all data)a
0.1387
largest diff. peak and hole,
0.975 and -0.761
0.278 and -0.304
0.326 and -0.376
0.462 and -0.660
0.690 and -0.801
∆Felect, Å-3
a R1 ) [Σ|Fo| - |Fc|]/[Σ|Fo|] for [Fo2 > 2σ(Fo )], wR2 ) {[Σw(Fo2 - Fc )2]/[Σw(Fo )2]}1/2 [all data]. b These compounds had been crystallized from C6D6
(Experimental Section). The deuterium atoms attached to the benzene solvent molecule were included as hydrogen atoms in the refinement. Chemical
formula and derived quantities fw, Fcalcd, µcalcd, and F(000) were not corrected.
2
2
2
Figure 4. Molecular structure of 5a with thermal ellipsoids at the 50%
Figure 3. Molecular structure of 4b with thermal ellipsoids at the 50%
probability level. Hydrogen atoms are omitted for clarity. For an ORTEP
plot of 4a, see the Supporting Information. Selected atom-atom distances
[angstroms] and bond angles [degrees] for 4a: Al1-N1 ) 2.089(4), Al1-C1
) 1.969(5), Al1-C7 ) 1.978(5), Al1-C13 ) 1.988(4), Cr1-Cr1′ )
5.9921(11), C1-Al1-C7 ) 119.96(19), N1-Al1-C13 ) 85.09(17),
C7-Al1-C13 ) 114.0(2), C1-Al1-C13 ) 120.18(18), C7-Al1-N1 )
100.59(18), C1-Al1-N1 ) 107.54(18), R ) 3.21(14). Selected atom-atom
distances [angstroms] and bond angles [degrees] for 4b: Ga1-N1 )
2.192(2), Ga1-C1 ) 1.980(2), Ga1-C7 ) 1.979(2), Ga1-C13 ) 1.984(2),
Cr1-Cr1′ ) 6.0251(6), C1-Ga1-C7 ) 121.99(10), N1-Ga1-C13 )
83.41(9), C7-Ga1-C13 ) 120.40(9), C1-Ga1-C13 ) 113.86(10),
C7-Ga1-N1 ) 105.71(9), C1-Ga1-N1 ) 99.04(9), R ) 2.67(7).
probability level. Hydrogen atoms are omitted for clarity. For an ORTEP
plot of 5b, see the Supporting Information. Selected atom-atom distances
[angstroms] and bond angles [degrees] for 5a: Al1-N1 ) 2.096(3), Al1-C1
) 1.968(4), Al1-C7 ) 1.968(4), Al1-C13 ) 1.981(4), Mo1-Mo1′ )
5.9983(7), C1-Al1-C7 ) 120.49(18), N1-Al1-C13 ) 85.06(15),
C7-Al1-C13 ) 120.80(17), C1-Al1-C13 ) 112.83(17), C7-Al1-N1
) 106.47(15), C1-Al1-N1 ) 101.73(15), R ) 2.7(3). Selected atom-atom
distances [angstroms] and bond angles [degrees] for 5b: Ga1-N1 )
2.207(3), Ga1-C1 ) 1.978(3), Ga1-C7 ) 1.967(3), Ga1-C13 ) 1.983(3),
Mo1-Mo1′ ) 6.0277(6), C1-Ga1-C7 ) 122.38(14), N1-Ga1-C13 )
83.08(13), C7-Ga1-C13 ) 120.27(14), C1-Ga1-C13 ) 113.14(14),
C7-Ga1-N1 ) 105.75(12), C1-Ga1-N1 ) 100.32(12), R ) 2.2(3).
frameworks of the two coordinated π ligands. Aluminum- and
gallium-bridged [1]metallacyclophanes exhibit R angles from
11.81(9)°22 for an alumina[1]chromarenophane to 21.24(10)°17
for an galla[1]molybdarenophane. [1.1]Metallacyclophanes are
expected to be unstrained sandwich compounds, with tilt angles
R close to 0°. For the new complexes 2a, 4a,b and 5a,b, R
angles of 4.9(2), 3.21(14), 2.67(7), 2.7(3), and 2.2(3)°, respec-
tively, were determined. In all cases, the two planes intersect
on the opposite side of the bridging atom, which could be
indicated by adding a negative sign to all R angles.
cenophanes8,9 mentioned before and are a testament of the
higher Lewis acidity of aluminum compared with gallium
for an amine donor.
For metallacyclophanes, a set of angles can be given to show
the distortion with respect to the parent sandwich species.21 The
most illustrative angle is the tilt angle R which is the angle
between the two intersecting planes defined by the carbon
(21) Herbert, D. E.; Mayer, U. F. J.; Manners, I. Angew. Chem., Int. Ed.
2007, 46, 5060–5081.
1
NMR Spectroscopy of 2a, 4a,b, and 5a,b. H and 13C
(22) Lund, C. L.; Schachner, J. A.; Quail, J. W.; Mu¨ller, J. Organometallics
2006, 25, 5817–5823.
NMR spectra of 4a,b and 5a,b measured at ambient
Inorganic Chemistry, Vol. 47, No. 13, 2008 5995

Lund et al.
temperatures, can be interpreted as being caused by time-
1
averaged C2h symmetrical species. For example, H NMR
spectra show one set of signals for the p-tBuAr′ ligands and
five signals of equal intensities for the η6-C6H5 moieties. In
addition to the signal pattern, the 13C NMR spectra show
that the chemical shifts of the ipso-C atom of the η6-C6H5
moieties at δ 76.0 (4a), 79.9 (4b), 76.6 (5a), and 79.8 (5b)
are very similar to those of the parent compounds bis(ben-
zene)chromium (δ 74.8)23 and bis(benzene)molybdenum (δ
75.3).24 The absence of an upfield shift clearly shows that
the [1.1]metallacyclophanes are unstrained, corroborated by
the molecular structures of the species in the solid state. As
mentioned earlier, the aluminum-bridged [1.1]chromar-
enophane 2a was not soluble in organic solvents anymore
once it had crystallized; hence, we could not measure NMR
spectra of the isolated product. However, a 1H NMR
spectrum was measured from the reaction mixture and
showed a pattern comparable to those discussed for 4a,b and
5a,b (Experimental Section), but the low solubility of 2a
prevented the measurement of reliable 13C NMR data.
Five-membered rings such as those present in the [1.1]met-
allarenophanes 2a, 4a,b, and 5a,b show envelope conforma-
tions in the solid state. In solution, these rings would be
expected to have conformational flexibility, and fast envelope
inversions should result in five-membered rings which are
Cs symmetrical on time average. Against this background,
one expects that a Ci symmetrical [1.1]metallarenophane
shows a C2h symmetry in solution, meaning that our NMR
results suggest that the molecular structures of 2a, 4a,b, and
5a,b are similar in solution and in the crystal lattice.
Figure 5. Cyclic voltammogram of 4b in THF/0.1 M [Bu4N][PF6] using
a glassy carbon working electrode at a scan rate of 100 mV/s. The measured
E°′ for the two principal peaks are -0.440 and -0.225 V, respectively
[E°′ ) 1/2(Epa + Epc)].26 The asterisk denotes a smaller set of voltammetric
signals in the CV, which is due to small amounts of [(C6H6)2Cr].
Figure 6. Cyclic voltammogram of 5b in THF/0.1 M [Bu4N][PF6] using
a glassy carbon working electrode at a scan rate of 100 mV/s. The measured
E°′ for the two principal peaks is -0.600 and -0.380 V, respectively [E°′
) 1/2(Epa + Epc)].26 The asterisk denotes a smaller set of voltammetric
signals in the CV, which are due to small amounts of [(C6H6)2Mo]. At
very cathodic potentials (ca. -1.0 V), an additional redox process is
observed (reversible couple denoted by uox and ured).
As mentioned in the introduction, [1.1]ferrocenophanes
had been coined “molecular acrobats”.4 Consequently, we
measured 1H NMR spectra of 4a,b and 5a,b in C6D5CD3 in
the temperature range of -90 to 90 °C (500 MHz). Except
for small shifts of signals, the high temperature spectra are
very similar to those at ambient temperature. In the lower
temperature range, a significant broadening of peaks between
-70 and -90 °C occurred. However, even though some
peaks are very broad at -90 °C, the signal pattern is still
similar to that at ambient temperature. The low temperature
spectra indicate that the molecular dynamics is slowed down
with respect to the NMR time scale, but it is still fast enough
at the lowest accessible temperature so that only one time-
averaged C2h symmetrical species is observed. One feasible
dynamic process for [1.1]metallacyclophanes is a degenerate
isomerization of one anti isomer to another anti isomer; a
process comparable to a chair-to-chair isomerization of
cyclohexane. If such a process would be occurring, with
indication that an anti-to-anti isomerization takes place even
at temperatures of 80 °C (Experimental Section for details).
Electrochemistry of 4a,b and 5a,b. Electrochemical
measurements were undertaken for the four metallarenophanes
to determine the extent of communication between the two
transition-metal redox centers. In the first attempts, we used
a small three-neck Schlenk flask with three electrodes
inserted through septa (supporting information in ref 9).
However, we did not obtain reproducible CVs; in particular,
the two aluminum compounds showed only CVs of the
parent bis(benzene) complexes, which suggested that mois-
ture had degraded 4a and 5a, respectively. Consequently,
all subsequent measurements were done inside a glovebox.
Extra precautions were taken to dry the solvent THF and
the electrolytes used (Experimental Section for details). With
these efforts, we obtained reproducible data for the two
gallium species 4b and 5b (Figures 5 and 6) but were
unsuccessful in obtaining reproducible data for the respective
aluminum compounds 4a and 5a. The measurements of the
latter species indicated that significant amounts of the parent
bis(benzene) complexes were always present in solution.
Therefore, additional measurements of aluminum compounds
1
saturation transfer difference H NMR experiments one
should be able to see magnetization transfer from one ortho
to the other ortho proton, similarly, from one meta to the
other meta proton.25 However, these experiments gave no
(23) Elschenbroich, C.; Koch, J. J. Organomet. Chem. 1982, 229, 139–
158.
(24) Measured in C6D6 at 25 °C referenced to the signal at δ 128.00.
(25) Berger, S.; Braun, S. 200 and More NMR Experiments, 3rd expanded
ed.; Wiley-VCH: Weinheim, Germany, 2004; p 298.
5996 Inorganic Chemistry, Vol. 47, No. 13, 2008

[1.1]Chromarenophanes and [1.1]Molybdarenophanes
4a and 5a were performed using [Bu4N][BF4] instead of
[Bu4N][PF6] as an electrolyte; however, their CVs varied
significantly by this change. Furthermore, it seemed that the
concentration of the parent sandwich compounds in a sample
of 4a or 5a strongly influenced the position and intensities
of the other oxidation and reduction waves and the obtained
electrochemical data for 4a and 5a were inconclusive.
Figures 5 and 6 show the CVs of the gallium-bridged
species 4b and 5b, respectively. 4b shows two one-electron
oxidation and two one-electron reduction waves. The shoul-
ders at lower potential correspond to the redox couple of
[(C6H6)2Cr] (asterisks in Figure 5). Similarly, species 5b
shows two redox couples which are due to one-electron
events (Figure 6). As in the case of the chromium compound
4b, the CV of the gallium-bridged molybdenum species 5b
reveals a pair of shoulders corresponding to the presence of
[(C6H6)2Mo] (asterisks in Figure 6). In contrast to 4b,
however, an additional second reversible redox couple at high
cathodic potentials was detected (uox and ured in Figure 6),
but we are unable to assign it to a compound. In summary,
the two CVs can be interpreted consistently: both compounds,
4b and 5b, are oxidized at similar potentials compared to
the respective parent sandwich compound [(C6H6)2M] (Sup-
porting Information). According to the Robin-Day clas-
sification,18 both species are class II compounds.
Figure 7. Illustration of two pairs of inner R protons pointing towards
each other. Drawing is based on the experimentally determined molecular
structure of compound 4b (ligand p-tBuAr′ removed for clarity).
approximately a tetrahedral angle for the Cipso-Si-Cipso
linkage. In [1.1]metallacyclophanes, there are two pairs of
inner R protons, which are oriented toward each other
(Figure 7). If all other structural parameters are kept constant,
the distance between those R protons must be larger in
[1.1]metallocenophanes, where two five-membered rings are
linked, than in [1.1]metallarenophanes, where two six-
membered rings are linked. It might be that, so far, steric
repulsion between R protons prevented the formation of
silicon-bridged [1.1]metallarenophanes. On the other hand,
with aluminum- and gallium moieties in bridging positions
the wider Cipso-E-Cipso angles of around 120° reduce a
possible repulsion between the R protons to allow the
formation of [1.1]metallarenophanes [C1-E-C7 ) 121.22(16)
(2a), 119.96(19) (4a), 121.99(10) (4b), 120.49(18) (5a),
122.38(14) (5b); Figures 2, 3, and 4]. A second factor that
might have contributed to the lack of reports about [1.1]met-
allarenophanes might be the low solubility of such com-
pounds; 2a showed unusual solubility properties in organic
solvents. One can speculate that other [1.1]metallarenophanes
might have been formed in salt-metathesis reactions but were
not identified because of their insolubility.
Conclusion
The first [1.1]metallarenophanes have been synthesized
and fully characterized. The aluminum-bridged species (2a,
4a, 5a) and the gallium-bridged species (4b, 5b) crystallize
as anti isomers with the dimethylamino groups in exo
positions (Figure 1). Structural parameters like atom-atom
distances and bond angles are very similar in all five species.
Expectedly, the E-N donor bonds are the only bonds that
differ significantly: aluminum as the better Lewis acid for
Me2N donor groups possesses Al-N bonds that are shorter
by 0.10 - 0.11 Å compared to the respective Ga-N bonds.
1H and 13C NMR spectra can be interpreted as being caused
by C2h symmetrical compounds. In contrast to their highly
dynamic [1.1]metallocenophane cousins, these new [1.1]met-
allarenophanes do not show anti-to-anti isomerization in
solution. [1.1]Metallacyclophanes can serve as model com-
pounds to investigate metal-metal interactions; however, the
extreme sensitivity of aluminum species 4a and 5a prevented
us from obtaining reproducible electrochemical data. On the
other hand, the gallium-bridged species 4b and 5b showed
an expected class II behavior.
Experimental Section
Electrochemistry. A computer controlled system, consisting of
a HEKA potentiostat PG590 (HEKA, Mahone Bay, NS, Canada)
was used for the cyclic voltammetry experiments. Data was
collected using a multifunction DAQ card (PCI 6251 M Series,
National Instruments Austin, Texas) and in-house software written
in the LabVIEW environment. Glassy carbon (BAS, 3 mm) was
used as the working electrode. The quasi-reference electrode (QRE)
was a silver wire (E°′ ) 0.645 V vs Fc/Fc+ with E°′ ) 1/2(Epa
+
Epc); Supporting Information). All measurements were made against
the QRE and subsequently rescaled to the ferrocene/ferrocenium
formal potential26 E°′. A loop of gold wire was used as the auxiliary
electrode. Before each measurement, 1 mM solutions of 4a, 4b,
5a, and 5b were freshly prepared in dry THF with 0.1 M
[Bu4N][PF6] as the supporting electrolyte. Extra efforts were
undertaken to remove moisture and oxygen from the solvent. THF
was first dried using a Braun Solvent Purification System and then
filled into a 1L flask, which was part of a specialty Schlenk line,
equipped with greaseless Young valves. To the so-predried THF,
small amounts of 1,1-diphenylethylene and butyllithium were added,
resulting in a red solution, which indicated the absence of moisture.
By flask-to-flask condensation under reduced static pressure, a small
amount of THF was condensed into a Schlenk tube from the THF
reservoir flask. The inert gas (N2 4.8) used for this Schlenk line
was purified by conducting it through two columns before feeding
it into the Schlenk line (one column equipped with a copper(I)
It is surprising that no other [1.1]metallarenophanes are
known in the literature. The most common route for the
synthesis of metallacyclophanes is the salt-metathesis be-
tween a dilithiated sandwich compound and an element
dihalide.21 In many cases, researchers used R2SiCl2; these
compounds are commercially available and are very reactive
toward nucleophilic substitutions. However, silicon in a
bridging position of a [1.1]metallacyclophane would dictate
(26) Bard, A. J.; Faulkner, L. R. Electrochemical Methods, 2nd ed.; John
Wiley & Sons, Inc.: New York, 2001, Chap. 6.
Inorganic Chemistry, Vol. 47, No. 13, 2008 5997

Lund et al.
catalyst and one column equipped with 4 Å molecular sieves; both
materials purchased from MBraun). A so-prepared Schlenk tube
filled with freshly condensed THF was moved into the glovebox.
The electrolytes were dried overnight under high vacuum
([Bu4N][PF6] at 100 °C and [Bu4N][BF4] at 70 °C). Unless
otherwise specified, the scan rate for all of the CVs reported was
100 mV/s. All of the measurements were conducted inside a
glovebox and taken at ambient temperature (24-25 °C).
4.26 (d, 4H, o-H), 4.29 (pst, 4H, m-H), 4.45 (pst, 4H, m-H), 4.62
(pst, 4H, p-H), 5.57 (d, 4H, o-H), 7.01 (d, 2H, 3-H), 7.37 (t, 2H,
4-H), 7.48 (t, 2H, 5-H), 8.47 (d, 2H, 6-H). MS (70 eV, EI +): m/z
(%) 208 (21) [Cr(C6H6)2]+, 135 (27) [C9H13N]+, 130 (24)
[C6H6Cr]+, 91 (15) [C7H7]+, 78 (100) [C6H6]+, 58 (33). Anal. Calcd
for C42H44Al2Cr2N2 (734.7674): C, 68.65; H, 6.04; N, 3.81. Found:
C, 68.91; H, 6.12; N, 3.59.
Synthesis of [5-tBu-2-(Me2NCH2)C6H3]AlCl2 (3a). A solution
of AlCl3 (2.477 g, 18.58 mmol) in Et2O (30 mL, -80 °C) was
added to a solution of [5-tBu-2-(Me2NCH2)C6H3]Li (3.670 g, 18.60
mmol) in Et2O (20 mL, -80 °C) followed by stirring at room
temperature for 6 h. The suspension was filtered to remove LiCl,
the filtrate was collected, and the remaining product was extracted
with an additional 30 mL of Et2O from the LiCl filter cake. All
volatiles were removed from the combined filtrates, and subsequent
sublimation of the resulting solid under high vacuum (110 °C) gave
3a as a white crystalline solid (4.692 g, 88%). 1H NMR: δ 1.19 (s,
9H, tBu), 1.87 (s, 18 H, 2 SiMe3), 3.05 (s, 6H, NMe2), 6.73 (d,
1H, 3-H), 7.32 (d, 1H, 4-H), 7.86 (s, 1H, 6-H). 13C NMR: δ 31.5
(tBu), 45.3 (NMe2), 65.3 (CH2), 124.4 (3-C), 126.7 (4-C), 133.6
(6-C), 139.9 (2-C, ipso-C), 150.5 (5-C, ipso-C). 27Al NMR: δ 131
(w1/2 ) 2500 Hz). MS (70 eV, EI +): m/z (%): 287 (26) [M]+, 272
(100) [M - CH3]+, 191 (45) [MH - AlCl2]+, 147 (30) [MH - NMe2
- AlCl2]+, 140 (34), 131 (50) [M - NMe2 - AlCl2 - CH3]+, 117 (12)
[M - CH2 - NMe2 - AlCl2 - CH3]+, 91 (19) [C7H7]+, 58 (52)
[C4H10]+. Anal. Calcd for C13H20AlCl2N (288.1921): C, 54.18; H,
6.99; N, 4.86. Found: C, 54.11; H, 6.80; N, 5.03.
Synthesis. All of the syntheses were carried out using standard
Schlenk techniques. An MBraun glovebox (O2 < 1 ppm, H2O < 1
ppm) was used to manipulate the very sensitive bis(benzene)
complexes including 2a, 4a,b, and 5a,b. Solvents were dried using
a MBraun solvent purification system and stored under nitrogen
over 4 Å molecular sieves. All solvents for NMR spectroscopy were
degassed prior to use and stored under nitrogen over 4 Å molecular
sieves. [Cr(C6H6)2],27 [Mo(C6H6)2],17 [Cr(LiC6H5)2] · TMEDA,28
[Mo(LiC6H5)2]·TMEDA,29 [5-tBu-2-(Me2NCH2)C6H3]Li,19 and
[2-(Me2NCH2)C6H4]AlCl2 (1a)20 were synthesized as described in
1
the literature. H, 13C, and 27Al NMR spectra were recorded on a
Bruker 500 MHz Avance NMR spectrometer at 25 °C in C6D6,
unless noted differently. 1H chemical shifts were referenced to the
residual protons of the deuterated solvent (δ 7.15 for C6D6); 13C
chemical shifts were referenced to the C6D6 signal at δ 128.00;
27Al NMR spectra were referenced to [Al(acac)3] dissolved in C6D6
as an external standard. Mass spectra were measured on a VG 70SE
(m/z > 10% are listed for signals of the most abundant ions).
Elemental analyses were performed on a PerkinElmer 2400 CHN
Elemental Analyzer using V2O5 to promote complete combustion.
For the saturation transfer difference experiments,25 two spectra
were measured, first a control spectrum and then one from a
selective irradiation. Subtraction of the second from the first
spectrum resulted in a difference spectrum displaying whether any
protons exchange with the irradiated one. The pulse sequence used
for the saturation transfer experiment was supplied by Bruker. 4b
(C7D8) was measured at 25 and 80 °C, and 5b (C6D6) was measured
at 25 °C without any detectable magnetization transfer. Selected
parameters include presaturation time (d1 ) 5.0 s), pulse power
(pl14 ) 95 dB), and number of data points (TD ) 65536). T1 times
[s] for 5b (C6D6): o-H ) 0.6324; m-H ) 1.315; p-H ) 1.563; m-H
) 1.490; o-H ) 1.297.
Synthesis of [5-tBu-2-(Me2NCH2)C6H3]GaCl2 (3b). A solution
of GaCl3 (3.2315 g, 18.352 mmol) in Et2O (40 mL, -80 °C) was
added to a solution of [5-tBu-2-(Me2NCH2)C6H3]Li (3.6133 g,
18.319 mmol) in toluene (40 mL, -80 °C) followed by stirring at
room temperature for 16 h. LiCl was filtered off, the filtrate
collected, and remaining product was extracted with CH2Cl2 (2 ×
20 mL) from LiCl filter cake. The combined filtrates were reduced
to dryness under vacuum to give a white solid. Subsequent
sublimation under high vacuum (120 °C) gave 3b as a white
1
crystalline solid (5.331 g, 88%). H NMR: δ 1.14 (s, 9H, tBu),
1.88 (s, 18 H, 2 SiMe3), 2.95 (s, 6H, NMe2), 6.69 (d, 1H, 3-H),
7.26 (d, 1H, 4-H), 7.73 (s, 1H, 6-H). 13C NMR: δ 31.4 (tBu), 45.3
(NMe2), 64.5 (CH2), 125.2 (3-C), 126.9 (4-C), 132.5 (6-C), 138.0
(2-C, ipso-C), 151.6 (5-C, ipso-C). MS (70 eV, EI +): m/z (%):
314 (10) [M - CH3]+, 191 (81) [MH - GaCl2]+, 175 (10) [MH -
CH3 - GaCl2]+, 147 (57) [MH - NMe2 - GaCl2]+, 132 (20) [M -
CH2 - NMe2 - GaCl2]+, 117 (19) [M - CH2 - NMe2 - GaCl2 - CH3]+,
105 (11) [C8H9]+, 92 (19) [C7H8]+, 58 (100) [C4H10]+. Anal. Calcd
for C13H20AlCl2N (330.9336): C, 47.18; H, 6.09; N, 4.23. Found:
C, 46.86; H, 6.19; N, 4.19.
Synthesis of [{5-tBu-2-(Me2NCH2)C6H3}Al(η6-C6H5)2Cr]2
(4a). A slurry of [Cr(LiC6H5)2] · TMEDA (1.142 g, 3.396 mmol)
in benzene (30 mL, 0 °C) was added to a solution of 3a (0.976,
3.39 mmol) in benzene (10 mL, 0 °C). The cooling bath was
removed, and the mixture was stirred for 1 h. All volatiles were
removed in vacuum. The product was extracted with toluene (2 ×
10 mL), filtered to remove LiCl, and storage of the filtrate at -25
°C led to the formation of dark-red crystals of 4a (0.425 g, 30%).
Single crystals for X-ray analysis were obtained from benzene at 6
°C. 1H NMR: δ 1.58 (s, 18H, tBu), 1.75 (s, 12 H, NMe2), 3.42 (s,
4H, CH2), 4.30 (br. s, 8H, o-H, m-H), 4.48 (pst, 4H, p-H), 4.73
(pst, 4H, m-H), 5.77 (d, 4H, o-H), 7.05 (d, 2H, 3-H), 7.50 (d, 2H,
4-H), 8.69 (s, 2H, 6-H). 13C NMR: δ 32.1 (tBu), 46.8 (NMe2), 67.1
(CH2), 75.0 (p-C), 75.6 (m-C or o-C), 76.0 (ipso-C), 76.5 (m-C),
80.6 (o-C), 81.9 (o-C or m-C), 123.9 (3-C), 124.7 (4-C), 135.0 (6-
C), 142.8 (2-C, ipso-C), 149.2 (5-C, ipso-C). MS (70 eV, EI +):
Synthesis of [{2-(Me2NCH2)C6H4}Al(η6-C6H5)2Cr]2 (2a). A
slurry of [Cr(LiC6H5)2]·TMEDA (1.527 g, 4.541 mmol) in benzene
(30 mL, 0 °C) was added to a solution of 1a (1.016 g, 4.378 mmol)
in benzene (10 mL, 0 °C). The cooling bath was removed, and the
mixture was stirred for 30 min. LiCl was filtered off, and the filtrate
containing the product was collected. The product was extracted
with an additional (2 × 10 mL) of hot benzene from the LiCl filter
cake, and the combined filtrates were reduced in volume to 10 mL,
during which time a red precipitate formed that was separated by
cannula transfer of the filtrate (0.201 g, 0.274 mmol). The mother
liquor was stored at 6 °C to give additional red precipitate (0.138
g, 0.188 mmol). The total yield of 2a was 0.339 g (21%). Single
crystals for X-ray analysis were obtained from a highly diluted
solution of 2a in 1 mL of cyclohexane and 5 mL of THF at 25 °C.
A
1H NMR spectrum was obtained from the reaction mixture
because dissolving the precipitate in common organic solvents was
not successful. 1H NMR: δ 1.71 (s, 12 H, NMe2), 3.37 (s, 4H, CH2),
(27) Synthetic Methods of Organometallic and Inorganic Chemistry;
Herrmann, W. A., Ed.; Georg Thieme Verlag Stuttgart: New York,
1997; Vol. 8.
(28) Elschenbroich, C.; Hurley, J.; Metz, B.; Massa, W.; Baum, G.
Organometallics 1990, 9, 889–897.
(29) Green, M. L. H.; Treurnicht, I.; Bandy, J. A.; Gourdon, A.; Prout, K.
J. Organomet. Chem. 1986, 306, 145–165.
5998 Inorganic Chemistry, Vol. 47, No. 13, 2008

[1.1]Chromarenophanes and [1.1]Molybdarenophanes
m/z (%) 208 (43) [Cr(C6H6)2]+, 191 (100) [C13H21N]+, 175 (10)
[C12H17N]+, 154 (12), 147 (71) [C11H15]+, 134 (14) [C9H12N]+, 132
(25) [C10H12]+, 130 (49) [C6H6Cr]+, 119 (11), 117 (27) [C9H9]+,
105 (11). Anal. Calcd for C50H60Al2Cr2N2 (846.9801): C, 70.90;
H, 7.14; N, 3.31. Found: C, 70.70; H, 6.98; N, 3.12.
CH2), 4.40 (d, 4H, o-H), 4.47 (t, 4H, m-H), 4.82 (t, 4H, p-H), 4.98
(t, 4H, m-H), 5.83 (d, 4H, o-H), 7.02 (d, 2H, 3-H), 7.39 (d, 2H,
4-H), 8.13 (s, 2H, 6-H). 13C NMR: δ 32.0 (tBu), 46.9 (NMe2), 66.8
(CH2), 74.5 (p-C), 76.5 (m-C), 77.5 (m-C), 79.8 (ipso-C), 81.5 (o-
C), 81.7 (o-C), 124.1 (4-C), 124.2 (3-C), 133.8 (6-C), 142.0 (2-C,
ipso-C), 149.2 (5-C, ipso-C). MS (70 eV, EI +) m/z (%): 414 (10)
[C25H30GaN]+, 338 (100), 337 (51) [C19H26GaN]+, 336 (93)
[C19H25GaN]+, 296 (21), 294 (21), 293 (18) [C17H20Ga]+, 191 (23)
[C13H21N]+, 190 (19) [C13H20N]+, 147 (16) [C11H15]+. Anal. Calcd
for C50H60Ga2Mo2N2 (1020.3508): C, 58.86; H, 5.93; N, 2.75.
Found: C, 58.65; H, 5.43; N, 2.49.
Crystal Structure Determination. Crystal data of 2a, 4a,b, and
5a,b were collected at -100 °C on a Nonius Kappa CCD
diffractometer, using monochromated Mo KR radiation (λ )
0.71073 Å) at -100 °C. An initial orientation matrix and cell was
determined by scans, and the X-ray data were measured using
and ω scans.30 Data reduction was performed with HKL DENZO
and SCALEPACK software.31 Structures were solved by direct
methods (SIR-97)32 and refined by full-matrix least-squares methods
on F2 with SHELX-97.33 Unless otherwise stated, the non-hydrogen
atoms were refined anisotropically; hydrogen atoms were included
at geometrically idealized positions but not refined. The isotropic
thermal parameters of the hydrogen atoms were fixed at 1.2 times
that of the preceding carbon atom. Neutral atom scattering factors
for non-hydrogen atoms and anomalous dispersion coefficients are
contained in the SHELXTL-NT 6.14 program library.34 Crystal-
lographic data are summarized in Table 1. ORTEP-3 for Windows35
was used for molecular graphics and PLATON36 was used to prepare
material for publication.
For 2a, a disordered cyclohexane molecule in the lattice was
modeled with restraints to hold its geometry. The cyclohexane
molecule is lying on a symmetry center in the lattice, which
generates the superimposed mirror image of the cyclohexane
molecule and results in some very short H · · · H distances (as short
as 1.84 Å) to hydrogen atoms in the 2a molecule. For 4b, the
disordered benzene molecule in the structure was modeled as a
rigid molecule with anisotropic displacement parameters.
5a,b were crystallized from C6D6, which was incorporated into
their lattices. The deuterium atoms attached to the benzene solvent
molecule were included as hydrogen atoms at geometrically
idealized positions and were not refined. The chemical formula and
the derived quantities fw, Fcalcd, µcalcd, and F(000) were not corrected,
to account for the presence of these deuterium atoms.
Synthesis of [{5-tBu-2-(Me2NCH2)C6H3}Ga(η6-C6H5)2Cr]2
(4b). A slurry of [Cr(LiC6H5)2] · TMEDA (1.072 g, 3.188) in
benzene (30 mL) was added to a solution of 3b (1.073 g, 3.242
mmol) in benzene (10 mL, 0 °C). The cooling bath was removed,
and the mixture was immediately warmed to ambient temperature
and stirred for 1 h. All volatiles were removed in vacuum. The
dark-red product was extracted with toluene (2 × 10 mL) and
filtered to remove LiCl. The filtrate was concentrated to 10 mL
and kept at -25 °C to yield dark-red crystals of 4b (0.410 g, 28%).
Single crystals suitable for X-ray analysis were obtained from
benzene at 6 °C. 1H NMR: δ 1.57 (s, 18H, 2 tBu), 1.72 (s, 12H, 2
NMe2), 3.35 (s, 4H, 2 CH2), 4.28 (pst, 4H, m-H), 4.31 (d, 4H, o-H),
4.44 (pst, 4H, p-H), 4.73 (pst, 4H, m-H), 5.73 (d, 4H, o-H), 7.08
(d, 2H, 3-H), 7.46 (d, 2H, 4-H), 8.58 (s, 2H, 6-H). 13C NMR: δ
32.1 (tBu), 46.6 (NMe2), 66.7 (CH2), 75.0 (p-C), 75.8 (m-C), 76.6
(m-C), 79.9 (ipso-C), 80.7 (o-C), 81.6 (o-C), 124.2 (3-C), 124.4
(4-C), 134.1 (6-C), 142.2 (2-C, ipso-C), 149.5 (5-C, ipso-C). MS
(70 eV, EI +): m/z (%): 208 (19) [Cr(C6H6)2]+, 191 (100)
[C13H21N]+, 175 (10) [C12H17N]+, 147 (71) [C11H15]+, 134 (13)
[C9H12N]+, 132 (25) [C10H12]+, 130 (22) [C6H6Cr]+, 119 (13), 117
(32) [C9H9]+, 115 (13), 105 (13). Anal. Calcd for C50H60Cr2Ga2N2
(932.463): C, 64.40; H, 6.49; N, 3.00. Found: C, 64.42; H, 5.89;
N, 3.02.
Synthesis of [{5-tBu-2-(Me2NCH2)C6H3}Al(η6-C6H5)2Mo]2
(5a). A slurry of [Mo(LiC6H5)2] · TMEDA (1.192 g, 3.135 mmol)
in benzene (30 mL) was added to a solution of 3a (0.914 g, 3.17
mmol) in benzene (10 mL, 0 °C). The cooling bath was removed,
and the mixture was stirred for 1 h resulting in a red-brown solution.
All volatiles were removed in vacuum. The product was extracted
with toluene (4 × 5 mL), and the solution was filtered to remove
LiCl. The filtrate was concentrated to 10 mL and kept at -25 °C
to yield green crystals, which were washed with benzene (2 × 3
mL) and dried on high vacuum to give 5a (0.428 g, 29%). Single
crystals for X-ray analysis were obtained from C6D6 at 25 °C from
1
an NMR tube. H NMR: δ 1.51 (s, 18H, 2 tBu), 2.01 (s, 9H, 2
NMe2), 3.45 (s, 4H, 2 CH2), 4.38 (d, 4H, o-H), 4.46 (pst, 4H, m-H),
4.86 (pst, 4H, p-H), 4.96 (pst, 4H, m-H), 5.82 (d, 4H, o-H), 6.99
(d, 2H, 3-H), 7.43 (d, 2H, 4-H), 8.24 (s, 2H, 6-H). 13C NMR: δ
32.0 (tBu), 47.1 (NMe2), 67.3 (CH2), 74.1 (p-C), 76.3 (m-C), 76.6
(ipso-C), 77.4 (m-C), 81.8 (o-C), 81.9 (o-C), 123.8 (3-C), 124.6
(4-C), 134.7 (6-C), 142.6 (2-C, ipso-C), 148.9 (5-C, ipso-C). MS
(70 eV, EI +): m/z (%): 191 (100) [C13H21N]+, 190 (88)
[C13H20N]+, 175 (10) [C12H17N]+, 154 (16), 147 (73) [C11H15]+,
134 (11) [C9H12N]+, 132 (25) [C10H12]+, 119 (10), 117 (24) [C9H9]+,
105 (12). Anal. Calcd for C50H60Al2Mo2N2 (934.8679): C, 64.24;
H, 6.47; N, 3.00. Found: C, 64.03; H, 6.33; N, 3.32.
Acknowledgment. We thank G. A. Orlowski (University
of Guelph) and H.-B. Kraatz (University of Western Ontario)
for their help with electrochemical measurements in the initial
stage of the project. We thank K. Brown (University of
Saskatchewan) for NMR measurements. We thank the
Natural Sciences and Engineering Research Council of
Canada (NSERC Discovery Grant, J.M.), the Department of
Synthesis of [{5-tBu-2-(Me2NCH2)C6H3}Ga(η6-C6H5)2Mo]2
(5b). A slurry of [Mo(LiC6H5)2] · TMEDA (1.071 g, 2.817) in
benzene (30 mL) was added to a solution of 3b (0.917 g, 2.77
mmol) in benzene (10 mL, 0 °C). The cooling bath was removed,
and the mixture was stirred for 1 h, resulting in a red-brown
solution. All volatiles were removed in vacuum. The product was
extracted with toluene (4 × 5 mL) and filtered to remove LiCl.
The filtrate was concentrated to 10 mL and kept at -25 °C to yield
green crystals, which were washed with benzene (2 × 3 mL) and
dried to give 5b (0.283 g, 20%). Single crystals for X-ray analysis
(30) Nonius, B. V. Nonius Collect; Delft, The Netherlands, 1998.
(31) Otwinowski, Z.; Minor, W. In Macromolecular Crystallography; Part
A; Carter, C. W., Sweet, R. M., Eds.; Academic Press: London, 1997;
Vol. 276, pp 307-326..
(32) Altomare, A.; Burla, M. C.; Camalli, M.; Cascarano, G.; Giacovazzo,
C.; Guagliardi, A.; Moliterni, A. G. G.; Polidori, G.; Spagna, R.
J. Appl. Crystallogr. 1999, 32, 115–119.
(33) Sheldrick, G. M. SHELXL97-2: Program for the Solution of Crystal
Structures; UniVersity of Go¨ttingen: Go¨ttingen, Germany, 1997.
(34) SHELXTL-NT 6.14: Program Library for Structure Solution and
Molecular Graphics; 2000.
(35) Farrugia, L. J. J. Appl. Crystallogr. 1997, 30, 565.
(36) Spek, A. L. PLATON, A Multipurpose Crystallographic Tool;
UniVersity of Utrecht: The Netherlands, 2001.
1
were obtained from C6D6 at 25 °C from an NMR tube. H NMR:
δ 1.23 (s, 18 H, 2 tBu), 1.97 (s, 12 H, 2 NMe2), 3.38 (s, 4H, 2
Inorganic Chemistry, Vol. 47, No. 13, 2008 5999

Lund et al.
H6)2Mo] with respect to the silver quasi-reference electrode. This
material is available free of charge via the Internet at http://
pubs.acs.org. Crystallographic data for all of the structures in this
article have been deposited with the Cambridge Crystallographic
Data Centre, under CCDC 675591 (2a), CCDC 675592 (4a), CCDC
675593 (4b), and CCDC 675594 (5a), and CCDC 675595 (5b).
These data can be obtained free of charge from The Cambridge
Crystallographic Data Centre via www.ccdc.cam.ac.uk/data_request/
cif.
Chemistry, the Saskatchewan Structural Sciences Centre, and
the University of Saskatchewan for their generous support.
We thank the Canada Foundation for Innovation (CFI) and
the government of Saskatchewan for funding of the X-ray
and NMR facilities in the Saskatchewan Structural Sciences
Centre (SSSC).
Supporting Information Available: ORTEP plots for com-
pounds 4a and 5b; X-ray crystallographic data for 2a, 4a,b, and
5a,b in CIF format; CVs of [(C5H5)2Fe], [(C6H6)2Cr], and [(C6-
IC800336F
6000 Inorganic Chemistry, Vol. 47, No. 13, 2008