Synthesis, characterization and reactivity of dinuclear and trinuclear aluminum-bridged ferrocenophanes

Article abstract of DOI:10.1002/ejic.200900273

Ferrocene derivatives bearing substituents with aluminum, in the 1,1'-positions, in the absence of donor ligands, possess rather unusual structural features. Starting from various dipyridine adducts of such 1,1'-disubstituted ferrocene derivatives, it pro

Full text of DOI:10.1002/ejic.200900273

FULL PAPER
DOI: 10.1002/ejic.200900273
Synthesis, Characterization and Reactivity of Dinuclear and Trinuclear
Aluminum-Bridged Ferrocenophanes
Bernd Wrackmeyer,*[a] Elena V. Klimkina,[a] and Wolfgang Milius[a]
Keywords: Metallocenes / Aluminum / NMR spectroscopy / Structure elucidation / Cyclophanes
Ferrocene derivatives bearing substituents with aluminum in
the 1,1Ј-positions, in the absence of donor ligands, possess
rather unusual structural features. Starting from various di-
NMR spectroscopy. For the first time, the dynamic behaviour
of such complexes was studied and a complete set of NMR
spectroscopic data has been reported. The dinuclear complex
pyridine adducts of such 1,1Ј-disubstituted ferrocene deriva- [Fe(η5-C5H4)2]2Al3Et5 was characterized by X-ray structural
tives, it proved possible to trap the pyridine as the adducts
R3Al(py) and monitor the formation of dinuclear and trinu-
clear aluminum-bridged ferrocenophanes in solution by
analysis.
(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim,
Germany, 2009)
In the present work, we have taken advantage of our ex-
perience with pyridine adducts of ferrocenylaluminum com-
pounds as well as dipyridine adducts 1–3[1] to find alterna-
tive routes to compounds of type 4 and 5. Indeed, these
dinuclear and trinuclear complexes should be somehow re-
lated to species 2 and 3. Their formation in equilibria is
feasible, if it proves possible to offer another suitable ac-
ceptor for the pyridine ligands. It will be shown that AlMe3
or AlEt3 can play this role.
Introduction
The chemistry of ferrocene derivatives bearing aluminum
in the 1,1Ј-positions appears to be complex and fairly un-
predictable in the absence of donors. In previous work,[1]
we successfully introduced rational synthetic methods to
prepare dipyridine adducts 1, 2 and 3 (Scheme 1), which, in
contrast to their gallium congeners,[2–5] had not been
known. Interestingly, other attempts in this field, in the ab-
sence of pyridine, have produced compounds such as 4[6]
and 5[7] (Scheme 1), in which at least the central aluminum
atoms possess rather unusual surroundings. Although the
molecular structures of 4a and 5b were determined by X-
ray structural analysis,[6,7] their solution-state structures
Results and Discussion
We studied the reactivity of starting materials 1–3[1]
were not studied in detail, as the reported NMR spectro- towards AlMe3 and AlEt3, respectively, in order to form
scopic data sets were incomplete and some data were proba- the pyridine adducts AlR3(py) and monitor the fate of the
bly misinterpreted.
pyridine-free ferrocenediylaluminum compounds. The most
Scheme 1. Some known 1,1Ј-disubstituted ferrocene derivatives with aluminum, as dipyridine adducts 1–3[1] and as pyridine-free com-
pounds 4[6] and 5.[7]
important results are summarized in Scheme 2. Indepen-
[a] Anorganische Chemie II, Universität Bayreuth,
dent of starting material 1, 2 or 3, the use of AlMe3 or
AlEt3 resulted in the formation of 4a or 4b as the final
products in solution. Compounds 4a and 4b could be iso-
lated as crystalline solids. The molecular structure of 4a has
95440 Bayreuth, Germany
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E-mail: b.wrack@uni-bayreuth.de
Supporting information for this article is available on the
WWW under http://dx.doi.org/10.1002/ejic.200900273.
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B. Wrackmeyer, E. V. Klimkina, W. Milius
FULL PAPER
Scheme 2. Three different routes to the dinuclear, threefold-aluminum-bridged ferrocenophane of type 4, of which 4a has been isolated
previously by treatment of AlMe2Cl with 1,1Ј-dilithioferrocene.[6]
already been described, and that of 4b was determined in ria is illustrated in Figure 1 by 1H–1H NOE difference spec-
the present work (vide infra). Compounds 4 are stable in tra, which, in addition to NOE, also give rise to numerous
[D8]toluene under an atmosphere of argon for prolonged intensities caused by inter- and intramolecular exchange
periods of time at –20 °C and decompose slowly in CD2Cl2. processes. In contrast, as shown in Figure 2, for pure com-
Clearly, the pyridine ligands are caught by the trialkylal- pound 4b (isolated and redissolved crystalline sample), the
uminum, as shown by NMR spectra of the reaction mix- analogous experiments reveal solely intramolecular ex-
tures (see Table 1 for NMR spectroscopic data of pure com- change between the AlEt(a,b) groups.
pounds 4a,b). The formation of 4 is the result of complex
The bonding of the central aluminum atom in 4 is of
rearrangements in the equilibrated mixtures in order to re- major interest, as the structure in the solid state shows
duce electron deficiency and coordinative unsaturation of markedly different Al–C(ferrocene) distances, two shorter
the aluminum atoms. The presence of slow dynamic equilib- and two longer ones, which therefore may imply a coordina-
Table 1. 13C NMR spectroscopic data[a,b,c] of compounds 4 and 5.
4a
4b
5a
5b
R = Me
[D8]toluene
R = Et
[D8]toluene
R = Me
[D8]toluene
R = Et
[D8]toluene CD2Cl2
C6D6[d]
CD2Cl2
CD2Cl2
CD2Cl2
δ13C(fc-C1)
56.6 [br.]
56.9 [br.]
56.6 [br.]
55.8 [br.]
55.8 [br.]
δ13C(fc-C1)
δ13C(fc-C6)
58.5 [br.]
86.0 [br.]
80.4 (br.)
80.0 (br.)
58.9 [br.]
86.0 [br.]
80.4 (br.)
79.9 (br.)
56.8 [br.]
85.7 [br.]
80.2 (br.)
79.9 (br.)
n.o.
δ13C(fc-C2)
δ13C(fc-C5)
82.0
82.3
82.5
82.7
82.0
82.4
81.7
82.0
81.7
82.1
δ13C(fc-C2,5
δ13C(fc-
)
80.3 (br.)
79.8 (br.)
C7,10
)
δ13C(fc-C3)
δ13C(fc-C4)
δ13C: R(a)
δ13C: R(b)
δ13C: R(c)
78.5
77.4
–4.2 [br.]
–5.3 [br.]
–5.7 [br.]
78.9
77.9
–3.8 [br.]
–4.8 [br.]
–5.1 [br.]
78.9
78.0
–4.9 [br.]
–5.3 [br.]
–5.8 [br.]
78.4
77.4
5.7 [br.], 10.2
3.6 [br.], 9.9
5.1 [br.], 11.1
78.7
77.8
δ13C(fc-C3,4
δ13C(fc-C8,9
)
)
76.1 (br.)
76.5 (br.)
76.2 (br.)
76.4 (br.)
5.2 [br.], 9.7 (br.) δ13C: AlR2
3.2 [br.], 9.4 (br.) δ13C: AlR
4.4 [br.], 10.8
–4.8 [br.]
–2.8 [br.]
–5.1 [br.]
–3.5 [br.]
n.o., 9.9
n.o., 10.0
3.5 [br.], 8.7
3.5 [br.], 9.1
1
1
[a] The assignment of the NMR signals is based on H{1H} NOESY[9] and 2D H–13C gHSQC[10] experiments. [b] [br.] denotes broad
13C resonances of aluminum-bonded atoms; (br.) denotes broad 13C resonances due to dynamic effects. [c] n.o. = not observed. [d] NMR
spectroscopic data from ref.[6] 13C NMR (75.46 MHz, C6D6): δ = –8.0, –4.8, –2.8, 68.2, 77.5, 82.0, 82.3 ppm. 1H NMR (300.13 MHz,
C6D6): δ = –0.69 (s, 3 H), –0.67 (s, 6 H), –0.40 (s, 6 H), 4.21, 4.37 (m, 8 H), 4.49 (m, 8 H) ppm. Some of these data correspond to those
found here for 5a.
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Dinuclear and Trinuclear Aluminum-Bridged Ferrocenophanes
Figure 1. 399.8 MHz 1H{1H} NOE difference spectra (gradient en-
hanced[9]) of the reaction mixture containing 4b, AlEt3 and Et3-
Al(py) (in [D8]toluene at 23 °C, relaxation delay 2.0 s, mixing time
0.6 s). The irradiated resonance signals (arrows) give rise to inten-
sities (NOE or Exchange) as indicated. (A) Normal 1H NMR spec-
trum. (B) Irradiation of 1H[AlCH2(b)]; response: magnetization
transfer[11] between AlCH2 groups of AlEt(a), AlEt(b) and AlEt3,
whereas NOE is observed for 1H(AlCH2) of AlEt(c), 1H(Me) of
AlEt(b), AlEt(a) and AlEt(c) groups, and (fc)1H5 and (fc)1H2. (C)
Irradiation of 1H(Me) of AlEt(a); response: magnetization transfer
between Me of AlEt(a), AlEt(b) and AlEt3. (D) Irradiation of (fc)
1H5; response: magnetization transfer between (fc)1H5 and (fc)1H2,
whereas NOE is observed for (fc)1H3,4, 1H(AlCH2) and 1H(Me) of
AlEt(a) and AlEt(b). (E) Irradiation of (fc)1H2; response: magne-
tization transfer between (fc)1H5 and (fc)1H2, whereas NOE is ob-
Figure 2. 399.8 MHz 1H{1H} NOE difference spectra (gradient en-
hanced[9]) of 4b (in [D8]toluene at 23 °C, relaxation delay 2.0 s, mix-
ing time 0.6 s). The irradiated resonance signals (arrows) give rise
to the indicated respective intensities (NOE or Exchange). (A) Nor-
mal 1H NMR spectrum. (B) Irradiation of 1H[AlCH2(a)]: response:
magnetization transfer[11] between AlCH2(a) and AlCH2(b),
1
whereas NOE is observed for (fc)1H5 and (fc)1H2, and H(Me) of
AlEt(a). (C) Irradiation of 1H(Me) of AlEt(c); response: (fc)1H2,
1H(AlCH2) of AlEt(c). (D) Irradiation of (fc)1H5; response: (fc)
1
1H3,4, and weaker for H(AlCH2) of the AlEt(a) and AlEt(b). (E)
Irradiation of (fc)1H2; response: 1H3,4 and 1H(Me) and 1H(AlCH2)
of AlEt(c), and weaker for 1H(AlCH2) of AlEt(a) and AlEt(b). (F)
Irradiation of (fc)1H3,4; response: (fc)1H5 and (fc)1H2.
served for (fc)1H3,4 1H(AlCH2) and 1H(Me) of AlEt(c), and for
,
1H(AlCH2) of AlEt(a) and AlEt(b).
groups.[8] Hence, this strongly supports fast exchange of the
central aluminum between all four C1(fc) carbon atoms in
order to relieve this aluminum atom from electronic and
coordinative strain, as indicated in the formula for 4.
tion number of three for the aluminum. The reported NMR
spectroscopic data set[6] is incomplete and inconclusive in
this respect. The 13C NMR spectra of 4a,b (see Figure 3 for
4b) show all expected 13C NMR signals in agreement with
the proposed structure.
Broad 13C NMR signals are expected for 13C nuclei
linked to aluminum owing to partially relaxed scalar 27Al–
13C spin–spin coupling as a result of efficient scalar nuclear
relaxation [short values T2SC(13C)] of the second kind.
However, there is only one broad 13C(fc)–Al NMR signal.
This is in the region typical of bridging Al–C(fc)–Al
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B. Wrackmeyer, E. V. Klimkina, W. Milius
FULL PAPER
Figure 3. 125.8 MHz 13C{1H} NMR spectrum of 4b (in [D8]toluene at 23 °C). Note the broad 13C(Al) NMR signals; there are three for
13C(Et)Al and only one 13C(fc)Al.
Considering the solution-state structure of 4, it was Table 2. 13C NMR spectroscopic data[a,b,c] of compounds 6b and
7.
tempting to offer another nucleophile such as a carbanion
6b[d]
R = Et
[D8]toluene, py
7a
7b
to the central aluminum. Thus, the reactions of 4b with
EtLi in benzene/cyclohexane were studied. Mixtures con-
taining 4b and small amounts of Et3Al(py) reacted
smoothly with EtLi (Scheme 3). The formation of 6b to- δ13C(fc-C1)
R = Me
[D8]toluene
R = Et
[D8]toluene
n.o.
72.3 [br.]
73.2 [br.]
76.2
71.0
76.1
71.8 [br.]
72.6 [br.]
76.5
71.0
76.3
71.6
1.3 [br.], 10.87
2.5 [br.], 10.94
δ13C(fc-C6)
gether with Li[AlEt4] follows conclusively from the NMR
δ13C(fc-C2,5
)
)
)
)
76.3 (br.)
72.2 (br.)
–
–
3.2 (br.), 12.1 (br.) –9.1 [br.]
–8.2 [br.]
spectra (see Table 2), in particular from 27Al NMR spec-
troscopy.
δ13C(fc-C3,4
δ13C(fc-C7,10
δ13C(fc-C8,9
71.6
Having isolated compounds 4, it was of interest to study
their reactivity towards pyridine (Scheme 4). Addition of
pyridine opens the ferrocenophane systems to give 7a,b, as
shown by the NMR spectra (see Table 2) of the reaction
mixtures (see Figure 4 for 7b). These equilibria are finally
driven to 1a,b in the presence of R3Al(py). Therefore, com-
pounds 7a,b may also be of importance in the formation of
4 following Scheme 2.
δ13C: AlR2
AlR
δ13C(py)
124.3 (Cβ)
136.8 (Cγ)
149.8 (Cα)
123.8 (Cβ)
137.5 (Cγ)
150.1 (Cα)
124.1 (Cβ)
136.6 (Cγ)
149.2 (Cα)
[a] The assignment of the NMR signals is based on 1H{1H}
NOESY[9] and 2D 1H–13C gHSQC[10] experiments. [b] [br.] denotes
broad 13C resonances of aluminum-bonded atoms; (br.) denotes
broad 13C resonances due to dynamic effects. [c] n.o. = not ob-
served. [d] δ27Al{1H} 165 (h1/2 ≈ 1000 Hz).
When the reactions of 3 with AlR3 (Scheme 2) were care-
1
fully monitored by using H and 13C NMR spectroscopy,
the intermediate formation of another species was ob-
served. These intermediates are most likely compounds 5[7]
(NMR spectroscopic data of 5a,b are included in Table 1), must be considered as intermediates prior to the formation
and we propose Scheme 5 to explain their formation. Thus, of 4. Schemes 2, 4 and 5 emphasize the complex behaviour
AlR3 does not only abstract the pyridine ligands from 3, it of 1,1Ј-aluminum-substituted ferrocene derivatives.
also exchanges its alkyl groups with the aluminum atoms in
Although the NMR signals of 5 were rather weak relative
3 to give trinuclear complexes 5. Therefore, complexes 5 to those of 4, their regular appearance for R = Me, Et and
Scheme 3. Reaction of 4b with EtLi and pyridine.
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Dinuclear and Trinuclear Aluminum-Bridged Ferrocenophanes
Scheme 4. Reactivity of 4 towards pyridine and shifting the equilibria by addition of AlR3.
Scheme 5. Formation of trinuclear ferrocenophane 5 by abstracting
the pyridine ligands from 3 with the use of a slight excess amount
of AlR3.
correlation for the CH(fc) region. There are four different
1
CH(fc) units clearly evident from the H NMR spectra, of
which two corresponding signals overlap in the 13C NMR
spectra. There can be no doubt about the structure of 5b in
the solid state,[7] proving the presence of a three-coordinate
central aluminum and two terminal different four-coordi-
nate aluminum atoms bearing one and two ethyl groups,
respectively. Meaningful and conclusive NMR spectro-
scopic data of 5b were not reported.[7]
Assuming a rigid structure of 5 in solution, many more
signals than those observed (Figure 5) were expected. How-
ever, dynamic processes (Scheme 6) involving exchange of
the alkyl groups accompanied by exchange of the bonds
between the terminal aluminum atoms Al(1,3) and the
ferrocenediyl groups simplifies the situation. Then, the re-
quired four CH(fc) units with slightly exchange-broadened
signals fit to the dynamic structure of 5. Moreover, the dy-
namic structure requires on average two broad 13C(fc)Al
NMR signals at any time, one in the region for bridging
Al(1)–C(fc)–Al(2) and Al(2)–C(fc)–Al(3) units and the
other one for terminal C(fc)–Al(1) and C(fc)–Al(3) bonds.
1
Figure 4. Parts of the 399.8 MHz H{1H} NOE difference spectra
(gradient enhanced[9]) of a reaction mixture, in which 4b was con-
verted into 7b with Et3Al(py) (in [D8]toluene at 23 °C, relaxation
delay 1.0 s, mixing time 0.4 s). The irradiated transitions (arrows)
1
gave rise to intensities (NOE) as indicated. (A) Normal H NMR
1
spectrum. (B) Irradiation of AlCH2 of AlEt; response: H(Me) of
the AlEt, and (fc)1H7,10, (fc)1H2,5 and (fc)1H8,9. (C) Irradiation of
1H(Me) of AlEt; response: H(AlCH2) of AlEt, and (fc)1H2,5 and
1
(fc)1H8,9. (D) Irradiation of (fc)1H8,9; response: (fc)1H7,10, (fc)1H2,5
,
;
and H(Me) and H(AlCH2) of AlEt. (E) Irradiation of (fc)1H3,4
1
1
response: (fc)1H7,10, (fc)1H2,5, and 1H(Me) and 1H(AlCH2) of
AlEt2.
their peculiar somewhat broad features were striking. An These weak broad signals are observed. Unfortunately, the
example is shown for the 13C NMR spectra in Figure 5, limited solubility of compounds 5 did not allow their NMR
which also shows the inverse 1H–13C heteronuclear shift spectra to be recorded at low temperature.
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B. Wrackmeyer, E. V. Klimkina, W. Milius
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1
Figure 5. 100.5 MHz 13C{1H} NMR spectrum and contour plot of part of the 400 MHz 2D H–13C-correlated spectrum [recorded by
the gradient-selected (gs-)HSQC method[10]] of a mixture 4a/5a (in CD2Cl2 at 23 °C).
Scheme 6. Dynamic processes in 5. The exchange of the R groups and of the ferrocenediyl groups is indicated by arrows.
X-ray Structure Analysis of Aluminum-Bridged
Ferrocenophane 4b
angles are small, whereas the β angles are larger because of
the bridging nature of the carbon atoms linked to alumi-
num. The arrangement of the three aluminum atoms in 4b
enforce considerable twist angles τ[13] (39.8 and 22.8°) of
the cyclopentadienyl rings against an eclipsed structure.
The molecular structure of 4b is shown in Figure 6 and
selected structural data are given in Table 3 and compared
with those reported for 4a.[6] The AlEt2 units are linked
unsymmetrically to the ferrocenediyl groups. The surround-
ings of the central aluminum atom appears to be close to
trigonal planar {Σ[ЄAl(2)] = 357.5°}, and the distances to
the next ferrocenediyl carbon atoms are rather long (351.6,
253.6 pm). Major differences between the structures of 4b
and 4a may be found in the exact positions of the central
aluminum atom Al(2). This may be due to different steric
effects exerted by methyl (4a) and ethyl groups (4b). Other-
Experimental Section
General: All preparative work as well as handling of the samples
was carried out with precautions to exclude trace amounts of air
and moisture. Carefully dried solvents and oven-dried glassware
were used throughout. The deuterated solvent CD2Cl2 was distilled
from CaH2 under an atmosphere of argon. All other solvents were
distilled from Na metal under an atmosphere of argon. Starting
materials such as Me3Al (2.0  in hexanes), Et3Al (1.0  in hex-
anes), pyridine (anhydrous, 99.8%), EtLi (0.5  in benzene/cyclo-
wise, the important structural features are comparable.
[12,13]
Table 3 lists the α, β and τ angles
for 4b, describing
the distortions of the ferrocene geometry. Typically, the α hexane, 90:10) (all from Aldrich) were commercial products and
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Dinuclear and Trinuclear Aluminum-Bridged Ferrocenophanes
Table 3. Selected bond lengths [pm] and angles [°][a] of ferroceno-
phanes 4b and 4a[6] for comparison.
4b
4a
Al(1)–C(1)
Al(3)–C(11)
Al(1)–C(16)
Al(3)–C(6)
Al(2)–C(1)
Al(2)–C(11)
Al(2)···C(16)
Al(2)···C(6)
Al(1)–C(21)
Al(1)–C(23)
Al(3)–C(27)
Al(3)–C(29)
Al(2)–C(25)
Al(1)···Al(2)
Al(2)···Al(3)
Al(1)···Al(3)
218.6(6)
219.2(6)
199.4(7)
203.6(6)
205.5(6)
201.8(6)
321.6
Al(3)–C(31)
Al(1)–C(21)
Al(3)–C(11)
Al(1)–C(41)
Al(2)–C(31)
Al(2)–C(21)
Al(2)···C(11)
Al(2)···C(41)
Al(3)–C(5)
Al(3)–C(4)
Al(1)–C(1)
Al(1)–C(2)
Al(2)–C(3)
Al(3)···Al(2)
Al(2)···Al(1)
Al(1)···Al(3)
C(31)···C(21)
C(11)···C(41)
Al(2)···Fe(2)
Al(2)···Fe(1)
215.1(2)
216.0(2)
198.6(3)
203.8(2)
203.3(2)
201.5(2)
326.2
244.4(3)
196.6(5)
197.0(3)
197.7(3)
196.3(3)
193.8(2)
288.0
253.6
198.3(7)
197.8(8)
196.2(8)
199.0(8)
196.6(7)
312.4
284.5(3)
589.9
364.7
297
587
360.8
554.7
Figure 6. Molecular structure of 4b (ORTEP plot, 30% probabili-
ties; hydrogen atoms are omitted for clarity); see Table 3 for struc-
tural parameters. The methyl carbon of the ethyl group [C(23)–
C(24)] is statistically disordered. (The relatively large space require-
ment of the disordered methyl carbon atoms of the ethyl substitu-
ents in 4b may also be seen by the difference of the unit cell volumes
in 4a and 4b. By taking into account Z = 2 in 4b and Z = 4 in 4a
there is a difference of about 450 Å3 for five methyl C atoms).
C(1)···C(11)
C(16)···C(6)
Al(2)···Fe(1)
Al(2)···Fe(2)
556.9
270.8(2)
314.0
261.7
Al(1)–Al(2)–Al(3)
Al(1)–C(1)–Al(2)
Al(3)–C(11)–Al(2)
Al(1)–C(16)–Al(2)
Al(3)–C(6)–Al(2)
C(1)–Al(1)–C(16)
C(1)–Al(1)–C(21)
C(1)–Al(1)–C(23)
C(16)–Al(1)–C(21)
C(16)–Al(1)–C(23)
C(21)–Al(1)–C(23)
C(11)–Al(3)–C(6)
C(11)–Al(3)–C(27)
C(11)–Al(3)–C(29)
C(6)–Al(3)–C(27)
C(6)–Al(3)–C(29)
C(27)–Al(3)–C(29)
C(1)–Al(2)–C(11)
C(1)–Al(2)–C(25)
C(11)–Al(2)–C(25)
Σ[ЄAl(2)]
C(1)–Al(2)–C(16)
C(1)–Al(2)–C(6)
C(11)–Al(2)–C(6)
C(11)–Al(2)–C(16)
C(16)–Al(2)–C(25)
C(6)–Al(2)–C(25)
C5 / C5 (α1) [Fe(1)]
C5 / C5 (α2) [Fe(2)]
C5 [C(6)]/ Al(3) (β1)
C5 [C(16)]/ Al(1) (β2)
C5 [C(1)]/ Al(1) (β3)
C5 [C(1)]/ Al(2) (β4)
C5 [C(11)]/ Al(3) (β5)
C5 [C(11)]/ Al(2) (β6)
162.4
Al(3)–Al(2)–Al(1) 162.3
94.8(2)
84.9(2)
69.2
76.0
103.6(2)
103.2(3)
109.3(3)
110.9(3)
116.0(3)
112.6(3)
97.2(2)
105.9(3)
108.5(3)
110.3(3)
116.9(3)
115.8(4)
127.2(3)
113.4(3)
116.9(3)
357.5
73.5
95.2
87.5
78.9
105.4
104.0
4.0
5.9
C(31)–Al(3)–C(11) 103.63(9)
used as received. Compounds 1b, 2b and 3 were prepared by litera-
ture procedures.[1] Owing to the extreme sensitivity of the new or-
ganoaluminum compounds, elemental analysis did not give reliable
results. Attempts to measure mass spectra (EI MS, 70 eV) did not
reveal the respective molecular ions. Instead, the pattern of diferro-
cene (CpFeC5H4)2 was observed. NMR measurements: Varian
C(31)–Al(3)–C(5)
C(31)–Al(3)–C(4)
C(11)–Al(3)–C(5)
C(11)–Al(3)–C(4)
C(5)–Al(3)–C(4)
100.52(11)
110.34(12)
115.30(13)
C(21)–Al(1)–C(41) 97.03(9)
C(21)–Al(1)–C(1)
C(21)–Al(1)–C(2)
C(41)–Al(1)–C(1)
C(41)–Al(1)–C(2)
C(1)–Al(1)–C(2)
107.49(1)
1
1
INOVA 400: H, 13C, 27Al NMR; Bruker DRX 500: H, 13C, 27Al
NMR; chemical shifts are given with respect to SiMe4 [δ1H
(CHDCl2) = 5.31 ppm, δ1H (C6D5CD2H) = 2.08 ppm; δ13C
(CD2Cl2) = 53.8 ppm, δ13C(C6D5CD3) = 20.4 ppm]; external 1.1 
Al(NO3)3 in D2O [δ27Al = 0 ppm for Ξ(27Al) = 26.056890 MHz].
The melting points (uncorrected) were determined by using a Büchi
510 melting point apparatus.
105.33(9)
C(31)–Al(2)–C(21) 126.09(9)
C(31)–Al(2)–C(3)
C(21)–Al(2)–C(3)
Σ[ЄAl(2)]
116.62(11)
112.46(11)
355.2
[Fe(η5-C5H4)2]2Al3R5 (4) from 1,1Ј-Bis(dialkylalanyl)ferrocene Di-
pyridine Adduct 1b
4a (R = Me): To a solution of the dipyridine adduct of 1,1Ј-bis(di-
ethylalanyl)ferrocene (1b; 200 mg, 0.39 mmol) in [D8]toluene
(1 mL) cooled to –40 °C was added Me3Al (2.0  in hexanes,
2.0 mL, 4.0 mmol). The reaction mixture was allowed to reach am-
bient temperature and then stirred for 1 h. Readily volatile materi-
als were removed in vacuo. The resulting mixture contained 4a to-
gether with Me3Al, Me3Al(py), Et3Al(py) and several unidentified
side products (1H and 13C NMR). The brown oil thus obtained
was washed with hexane (2 mL), the residue oil after removal of
the hexane was dried in vacuo to give 73 mg (72%) of 4a (about
95%) (together with Me3Al(py) and several unidentified side prod-
25.4
11.1
55.6
49.5
66.2
32.4
C5 / C5 (twist) (τ1) Fe(1) 39.8
C5 / C5 (twist) (τ2) Fe(2) 22.8
[a] See Ref.[12,13] for the definition of the angles α, β and τ.
1
ucts). Data for 4a: H NMR (399.8 MHz, [D8]toluene, 23 °C): δ =
–0.88 [s, 6 H, CH3(a)Al], –0.25 [s, 6 H, CH3(b)Al], 0.21 [s, 3 H,
CH3(c)Al], 4.02 (m, 4 H, H5), 4.16 (m, 4 H, H2), 4.36 (m, 8 H,
1
H3,4) ppm. H NMR (399.8 MHz, C6D6, 23 °C): δ = –0.78 [s, 6 H,
CH3(a)Al], –0.16 [s, 6 H, CH3(b)Al], 0.29 [s, 3 H, CH3(c)Al], 4.08
(m, 4 H, H5), 4.21 (m, 4 H, H2), 4.36 (m, 8 H, H3,4) ppm. 1H NMR
(399.8 MHz, CD2Cl2, 23 °C): δ = –1.29 [br. s, 6 H, CH3(a)Al], –0.65
[br. s, 6 H, CH3(b)Al], 0.07 [s, 3 H, CH3(c)Al], 4.36 (m, 4 H, H5),
(s, CH3Al) ppm. 13C NMR (100.5 MHz, [D8]toluene, 25 °C): δ =
–7.3 [br., CH3Al] ppm.
4b (R = Et): The synthesis was carried out as described for 4a,
4.40 (m, 4 H, H2), 4.87 (m, 4 H, H4), 4.91 (m, 4 H, H3) ppm. Data starting from 1b (205 mg, 0.40 mmol) in [D8]toluene (1 mL) and a
for Me3Al: 1H NMR (399.8 MHz, [D8]toluene, 23 °C): δ = –0.40 solution of Et3Al (1.0  in hexane, 2.5 mL, 2.5 mmol). The re-
Eur. J. Inorg. Chem. 2009, 3163–3171
© 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
3169

B. Wrackmeyer, E. V. Klimkina, W. Milius
FULL PAPER
sulting mixture contained 4b together with Et3Al, Et3Al(py) and
several unidentified side products (1H and 13C NMR). The brown
oil thus obtained was washed with hexane (2 mL), and the orange
solid after removal of the hexane was dried in vacuo to give 108 mg
of 4b (about 50%) together with Et3Al(py) and Et3Al (1H and 13C
NMR). Single orange crystals of 4b for X-ray analysis were grown
from a [D8]toluene solution after 2 d at –24 °C. M.p. 145–150 °C.
to give 114 mg of 4b (about 45%) together with 5b (7%) and Et3-
Al(py) (47%) (1H and 13C NMR). The solid was washed with hex-
ane (0.5 mL) and dried under high vacuum to leave an orange pow-
der (75 mg), containing about 95% of 4b together with Et3Al(py)
(1H NMR). Data for 5b: 1H NMR (399.8 MHz, [D8]toluene,
23 °C): δ = –0.25 (q, 2 H, CH2Al), –0.16 (q, 4 H, 2 CH2Al), 0.89
(t, 3 H, CH3), 0.93 (t, 6 H, 2 CH3), 4.17 (br. m, 6 H, H2,5), 4.31
1
Data for 4b: H NMR (399.8 MHz, [D8]toluene, 23 °C): δ = –0.28
(br. m, 6 H, H7,10), 4.48 (m, 6 H, H8,9), 4.49 (m, 6 H, 6 H, H3,4
)
[q, 4 H, CH2(a)Al], 0.45 [q, 4 H, CH2(b)Al], 0.87 [q, 2 H, CH2(c)- ppm. 1H NMR (399.8 MHz, CD2Cl2, 23 °C): δ = –0.62 (q, 2 H,
Al], 0.93 [t, 6 H, CH3(b)], 1.30 [t, 6 H, CH3(a)], 1.59 [t, 3 H, CH2Al), –0.52 (q, 4 H, 2 CH2Al), 0.48 (t, 3 H, CH3), 0.56 (t, 6 H,
CH3(c)], 3.99 (m, 4 H, H5), 4.23 (m, 4 H, H2), 4.36 (m, 8 H, H3,4
)
2 CH3), 4.41 (m, 6 H, H2,5), 4.48 (br. m, 6 H, H7,10), 4.80 (m, 6 H,
1
ppm. H NMR (399.8 MHz, CD2Cl2, 23 °C): δ = –0.60 [br., 4 H, H8,9), 4.84 (m, 6 H, H3,4) ppm.
CH2(a)Al], 0.53 [br., 4 H, CH2(b)Al], 0.80 [q, 2 H, CH2(c)Al], 0.96
[Fe(η5-C5H4)2]3Al3R3 (5) from Tris(µ-ferrocene-1,1Ј-diyl)bis[N-pyr-
[br., 12 H, CH3(a), CH3(b)], 1.44 [t, 3 H, CH3(c)], 4.35 (m, 4 H,
H5), 4.40 (m, 4 H, H2), 4.89 (m, 4 H, H4), 4.91 (m, 4 H, H3) ppm.
Data for Et3Al(py): 1H NMR (399.8 MHz, [D8]toluene, 23 °C): δ
= 0.27 (q, 6 H, CH2Al), 1.32 (t, 9 H, CH3), 6.52 (m, py-Hβ), 6.87
(m, py-Hγ), 8.17 (m, py-Hα) ppm. 13C NMR (100.5 MHz, [D8]tolu-
ene, 25 °C): δ = 0.5 [br., CH2Al], 10.3 (CH3), 124.8 (py-Cβ), 137.5
(py-Cγ), 147.4 (py-Cα) ppm. Data for Et3Al: 1H NMR (399.8 MHz,
[D8]toluene, 23 °C): δ = 0.39 (q, 6 H, CH2Al), 1.17 (t, 9 H, CH3)
ppm. 13C NMR (100.5 MHz, [D8]toluene, 25 °C): δ = 0.6 (br.,
CH2Al), 8.7 (CH3) ppm.
idine]aluminum (3)
5a (R = Me): To a suspension of 3 (53 mg, 0.069 mmol) in CD2Cl2
(1.5 mL) cooled to –50 °C was added Me3Al (2.0  in hexanes,
0.07 mL, 0.14 mmol). After stirring the reaction mixture for 30 min
at ambient temperature, readily volatile materials were removed in
vacuo, and the remaining oil was dissolved in [D8]toluene (1.5 mL).
Solid materials were separated by centrifugation, and the superna-
tant liquid phase was collected. The resulting mixture contained 5a
(about 60%, which, in our hands, could not be further purified)
together with Me3Al(py), FcH and several unidentified side prod-
ucts (1H NMR).
5b (R = Et):[7] The synthesis was carried out as described for 5a
(vide supra), starting from 3 (40 mg, 0.052 mmol) in CD2Cl2
(1.5 mL) and a solution of Et3Al (1.0  in hexane, 0.11 mL,
0.11 mmol). The resulting mixture contained 5b/4b (≈1:2) together
with Et3Al(py) and FcH (1H NMR).
[Fe(η5-C5H4)2]2Al3Et5 (4b) from Bis(µ-ferrocene-1,1Ј-diyl)bis[ethyl-
(N-pyridine)aluminum] (2b): To
a suspension of 2b (25 mg;
0.039 mmol) in [D8]toluene (0.5 mL) cooled to –20 °C was added
a solution of Et3Al (1.0  in hexane, 0.1 mL, 0.1 mmol). This sus-
pension was stirred for 2 h. The resulting solution contained 4b,
Et3Al, Et3Al(py) and several unidentified side products (1H and
13C NMR).
[Fe(η5-C5H4)2]3Al3R3 (5) from 4 and 3
Reaction of Tris(µ-ferrocene-1,1Ј-diyl)bis[N-pyridine]aluminum (3)
with R3Al
5a (R = Me): A mixture containing 4a/[Me3Al(py),Me3Al] (80 mg;
from 3 and Me3Al, vide supra) was dissolved in [D8]toluene (2 mL)
and 3 (38 mg, 0.050 mmol) was added; this suspension was stirred
for 20 h. After centrifugation from 3, the supernatant liquid phase
was decanted and volatile materials were evaporated. The residue
was washed with hexane to leave an orange-red solid (95 mg) con-
taining about 70% of 5a [together with Me3Al(py), ferrocene and
4a/5a (R = Me): To a suspension of 3 (140 mg, 0.18 mmol) in [D8]-
toluene (1.2 mL) cooled to –20 °C was added Me3Al (2.0  in hex-
anes, 1.25 mL, 2.5 mmol). After stirring the reaction mixture for
5 h at ambient temperature, readily volatile materials were removed
in vacuo and the remaining oil was dissolved in [D8]toluene
(1.5 mL). Solid materials were separated by centrifugation, the su-
pernatant liquid phase was collected and volatile materials were
removed in vacuo. The resulting mixture (160 mg) contained 4a
together with Me3Al, Me3Al(py), FcH and several unidentified side
products (1H and 13C NMR). The orange-brown oil thus obtained
was washed with hexane (2 mL), the orange solid after removal of
the hexane was dried in vacuo to give 98 mg of 4a (about 60%)
together with Me3Al(py) (25%) and 5a (15%) (1H and 13C NMR).
1
several unidentified side products. H NMR].
5b (R = Et): The synthesis was carried out as described for 5a,
starting from a mixture containing 4b/Et3Al(py) (104 mg; from 3
and Et3Al, vide supra) in [D8]toluene (2 mL) and 3 (36 mg,
0.047 mmol). The orange-brown oil thus obtained was washed with
hexane (1.5 mL), and the orange solid obtained after removal of
the hexane was dried in vacuo to give 94 mg of 5b[7] (≈80%) to-
gether with Et3Al(py), ferrocene and several unidentified side prod-
ucts (1H NMR).
1
Data for 5a: H NMR (399.8 MHz, [D8]toluene, 23 °C): δ = –0.84
(s, 3 H, CH3), –0.81 (s, 6 H, 2 CH3), 4.19 (br. m, 6 H, H2,5), 4.32
(br. m, 6 H, H7,10), 4.49 (br. m, m, 6 H, 6 H, H3,4, H8,9) ppm. H
1
Dilithium 1,1Ј-Bis[triethyl(ferrocenyl)]alanate (6b) and Lithium Tet-
ra(ethyl)alanate: To a mixture containing 4b/Et3Al(py) (223 mg,
vide supra) dissolved in [D8]toluene (1 mL) cooled to –50 °C was
added LiEt (0.5  in benzene/cyclohexane, 90:10; 2.25 mL;
1.13 mmol]. The mixture was warmed to room temperature, stirred
for 1 h and the volatile materials were then removed in vacuo. The
remaining solid was dissolved in [D8]toluene (0.5 mL), and a layer
of brown-black oil was formed at the bottom. The oil after removal
of [D8]toluene was dissolved in pyridine (0.3 mL) at 5 °C. Then,
[D8]toluene (0.1 mL) was added. The solution thus obtained con-
NMR (399.8 MHz, CD2Cl2, 23 °C): δ = –1.24 (s, 3 H, CH3), –1.22
(s, 6 H, 2 CH3), 4.41 (m, 6 H, H2,5), 4.49 (br. m, 6 H, H7,10), 4.80
(br. m, 6 H, H8,9), 4.83 (br. m, 6 H, H3,4) ppm. Data for Me3Al(py):
1H NMR (399.8 MHz, [D8]toluene, 23 °C): δ = –0.35 (s, CH3Al),
1
6.46 (m, py-Hβ), 6.86 (m, py-Hγ), 8.16 (m, py-Hα) ppm. H NMR
(399.8 MHz, C6D6, 23 °C): δ = –0.31 (s, CH3Al), 6.35 (m, py-Hβ),
6.72 (m, py-Hγ), 8.11 (m, py-Hα) ppm. 13C NMR (100.5 MHz,
[D8]toluene, 25 °C): δ = –7.7 (br., CH3Al), 124.8 (py-Cβ), 137.5 (py-
Cγ), 147.1 (py-Cα) ppm.
1
4b/5b (R = Et): The synthesis was carried out as described for 4a,
starting from 3 (100 mg, 0.13 mmol) in [D8]toluene (1.2 mL) and a
solution of Et3Al (1.0  in hexane, 1.31 mL, 1.31 mmol). The
orange-brown oil thus obtained was washed with hexane (1.5 mL),
and the orange solid after removal of the hexane was dried in vacuo
tained 6b(x py) and Li(x py)AlEt4. Data for 6b (x py; x Ն 8): H
NMR (500.1 MHz, [D8]toluene, 23 °C): δ = 0.39 (br. q, 8 H,
CH2Al), 1.70 (br. t, 12 H, CH3), 4.49 (br. m, 8 H, H2,3,4,5), 6.90
(m, py-Hβ), 7.25 (m, py-Hγ), 8.42 (m, py-Hα) ppm. 27Al{1H} NMR
(130.3 MHz, [D8]toluene, 23 °C): δ = 165 (h1/2 ≈ 1000 Hz) ppm.
3170
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© 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Inorg. Chem. 2009, 3163–3171

Dinuclear and Trinuclear Aluminum-Bridged Ferrocenophanes
Data for LiAlEt4 (x py; x Ն 4): 1H NMR (500.1 MHz, [D8]toluene,
NMR). Product 7b decomposes slowly at room temperature to give
1
23 °C): δ = 0.39 (br. q, 8 H, CH2Al), 1.44 (br. t, 12 H, CH3), 6.90 1b (≈70% after 5 d), FcAlEt2(py) and FcH. Data for 7b: H NMR
(m, py-Hβ), 7.25 (m, py-Hγ), 8.42 (m, py-Hα) ppm. 13C NMR
(125.8 MHz, [D8]toluene, 23 °C): δ = 3.3 [1J(27Al,13C) = 73 Hz,
AlCH2], 12.0 (CH3), 124.3 (py-Cβ), 136.7 (py-Cγ), 149.8 (py-Cα)
ppm. 27Al{1H} NMR (130.3 MHz, [D8]toluene, 23 °C): δ = 169
(h1/2 = 12 Hz) ppm.
(399.8 MHz, [D8]toluene, 23 °C): δ = 0.54 (q, 8 H, CH2Al), 0.81
(q, 2 H, CH2Al), 1.45 (t, 12 H, CH3), 1.56 (t, 3 H, CH3), 4.29 (m,
4 H, H7,10), 4.50 (m, 4 H, H2,5), 4.63 (m, 4 H, H8,9), 4.72 (m, 4 H,
H3,4), 6.73 (m, py-Hβ), 7.08 (m, py-Hγ), 8.48 (m, py-Hα) ppm.
Crystal Structure Determination of Complex 4b: Data were col-
lected with a STOE IPDS I diffractometer with graphite mono-
chromated Mo-Kα (λ = 71.073 pm) radiation. All other details per-
tinent to the crystal structure determinations are listed in
Table 4.[14] A crystal of appropriate size was sealed under an atmo-
sphere of argon in a Lindemann capillary. The data collection was
carried out at 293 K.
1,1-Bis{1-[1Ј-dialkyl(pyridine)aluminum]ferrocenyl}-1-alkylalumi-
num Pyridine Adduct (7)
7a (Alkyl = Me): Pyridine (0.04 mL, ≈5 equiv.) was added to a reac-
tion mixture containing 4a/Me3Al(py) (50 mg, from 3 and Me3Al)
in [D8]toluene at 0 °C. The solution was stirred for 0.5 h. The re-
sulting mixture contained about 80% of 7a together with
Me3Al(py), FcH, FcAlMe2(py) and several unidentified side prod-
ucts (1H and 13C NMR). Product 7a decomposes at room tempera-
ture to give 1a (≈60% after 1 d), FcAlMe2(py) and FcH. Data for
Supporting Information (see footnote on the first page of this arti-
1
cle): H NMR spectrum of 4a is given.
1
7a: H NMR (399.8 MHz, [D8]toluene, 23 °C): δ = –0.13 (t, 12 H,
Acknowledgments
CH3), 0.17 (t, 3 H, CH3), 4.27 (m, 4 H, H7,10), 4.45 (m, 4 H, H2,5),
4.64 (m, 4 H, H8,9), 4.69 (m, 4 H, H3,4), 6.79 (m, py-Hβ), 7.12 (m,
py-Hγ), 8.51 (m, py-Hα) ppm. 1H NMR (399.8 MHz, C6D6, 23 °C):
δ = –0.11 (t, 12 H, CH3), 0.19 (t, 3 H, CH3), 4.30 (m, 4 H, H7,10),
4.48 (m, 4 H, H2,5), 4.68 (m, 4 H, H8,9), 4.72 (m, 4 H, H3,4), 6.70
(m, py-Hβ), 7.03 (m, py-Hγ), 8.52 (m, py-Hα) ppm.
This work was supported by the Deutsche Forschungsgemein-
schaft.
[1] B. Wrackmeyer, E. V. Klimkina, W. Milius, Eur. J. Inorg. Chem.
2009, 3155–3162, preceding publication.
7b (Alkyl = Et): The procedure was analogous to that described
for 7a, starting from a mixture containing 4b/Et3Al(py) (55 mg,
from 1b and Et3Al) and pyridine (0.04 mL). The resulting mixture
contained about 80% of 7b together with Et3Al(py) (1H and 13C
[2] A. Althoff, P. Jutzi, N. Lenze, B. Neumann, A. Stammler, H.-
G. Stammler, Organometallics 2002, 21, 3018–3022.
[3] A. Althoff, P. Jutzi, N. Lenze, B. Neumann, A. Stammler, H.-
G. Stammler, Organometallics 2003, 22, 2766–2774.
[4] P. Jutzi, N. Lenze, B. Neumann, H.-G. Stammler, Angew.
Chem. 2001, 113, 1469–1473; Angew. Chem. Int. Ed. 2001, 40,
1424–1427.
Table 4. Crystallographic data of dialuma[1.1]ferrocenophane 4b.
4b
[5] A. Althoff, D. Eisner, P. Jutzi, N. Lenze, B. Neumann, W. W.
Schoeller, H.-G. Stammler, Chem. Eur. J. 2006, 12, 5471–5480.
[6] H. Braunschweig, G. K. B. Clentsmith, S. Hess, T. Kupfer, K.
Radacki, Inorg. Chim. Acta 2007, 360, 1274–1277.
[7] H. Braunschweig, C. Burschka, G. K. B. Clentsmith, T. Kupfer,
K. Radacki, Inorg. Chem. 2005, 44, 4906–4908.
[8] B. Wrackmeyer, E. V. Klimkina, T. Ackermann, W. Milius, In-
org. Chem. Commun. 2007, 10, 743–747.
[9] K. Stott, J. Keeler, Q. N. Van, A. J. Shaka, J. Magn. Reson.
1997, 125, 302–324.
[10] T. Parella, J. Magn. Reson. 2004, 167, 266–272.
[11] A. E. Derome, Modern NMR Techniques for Chemistry Re-
search, Pergamon, Oxford, 1987, pp. 188–190.
[12] M. Herberhold, Angew. Chem. 1995, 107, 1985–1987; Angew.
Chem. Int. Ed. Engl. 1995, 34, 1837–1839.
[13] B. Wrackmeyer, E. V. Klimkina, H. E. Maisel, O. L. Tok, M.
Herberhold, Magn. Reson. Chem. 2008, 46, S30–S35.
[14] CCDC-723413 [for 4b at 293 K] contains the supplementary
crystallographic data for this paper. These data can be obtained
free of charge from The Cambridge Crystallographic Data
Centre via www.ccdc.cam.ac.uk/data_request/cif.
Formula
Crystal
Dimensions [mm]
Crystal system
Space group
a [pm]
b [pm]
c [pm]
C30H41Al3Fe2
red-orange prism
0.28ϫ0.22ϫ0.18
triclinic
¯
P1
1042.1(2)
1104.6(2)
1370.6(3)
75.11(3)
73.44(3)
77.90(3)
2
1.112
1.9–26.0
9976
α [°]
β [°]
γ [°]
Z
µ [mm–1]
Measuring range (θ)[°]
Reflections collected
Independent reflections [I Ͼ 2σ(I)]
Absorption correction
Refined parameters
wR2/R1 [I Ͼ 2σ(I)]
5191
none[a]
316
0.175/0.066
Max./min. res. e– dens. [10–6 ϫepm–3] 0.879 / –0.445
Received: March 22, 2009
[a] Absorption correction did not improve the data set.
Published Online: June 10, 2009
Eur. J. Inorg. Chem. 2009, 3163–3171
© 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
3171