Formation and characterization of the first monoalumoxane, LAlO·B(C6F5)3

Article abstract of DOI:10.1002/1521-3773(20021115)41:22<4294::AID-ANIE4294>3.0.CO;2-W

Stabilization of the presumed Al-O double bond in LAlO · B(C₆F₅)₃, the simplest member of the alumoxane series, was achieved by the strong Lewis acid B(C₆F₅)3. LAlO. B(C₆F₅)

Full text of DOI:10.1002/1521-3773(20021115)41:22<4294::AID-ANIE4294>3.0.CO;2-W

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[1] For reviews, see: a) G. W. Gribble, S. J. Berthel in Studies in Natural
Products Chemistry, Vol. 12 (Ed.: Atta-Ur-Rahman), Elsevier, New
York, 1993, pp. 365 409; b) J. Bergman, T. Janosik, N. Wahlstrˆm in
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[2] P. Moreau, F. Anizon, M. Sancelme, M. Prudhomme, D. Sevõre, J. F.
Riou, J. F. Goossens, J. P. Hÿnichart, C. Bailly, E. Labourier, J. Tazzi,
D. Fabbro, T. Meyer, A. M. Aubertin, J. Med. Chem. 1999, 42, 1816
1822.
Formation and Characterization of the First
Monoalumoxane, LAlO¥B(C6F5)3**
Dante Neculai, Herbert W. Roesky,*
Ana Mirela Neculai, Jˆrg Magull, Bernhard Walfort,
and Dietmar Stalke
Dedicated to Professor Heribert Offermanns
on the occasion of his 65th birthday
[3] P. Schupp, C. Eder, P. Porksch, V. Wray, B. Schneider, M. Herderich, V.
Paul, J. Nat. Prod. 1999, 62, 959 962.
[4] For a review, see: U. Pindur, Y. S. Kim, F. Mehrabani, Curr. Med.
Chem. 1999, 6, 29 69.
[5] a) K. P. C. Vollhardt, Angew. Chem. 1984, 96, 525; Angew. Chem. Int.
Ed. Engl. 1984, 23, 539 556; b) A. J. Fletcher, S. D. R. Christie, J.
Chem. Soc. Perkin Trans. 1 2000, 1657 1668; c) S. Saito, Y. Yama-
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[6] a) H. N. C. Wong, T. K. Ng, T. Y. Wong, Heterocycles 1983, 20, 1815
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1984, 22, 875 890; c) C. O. Kappe, S. S. Murphree, A. Padwa,
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O. Arjona, Tetrahedron 1999, 55, 13521 13642.
[7] Recent selected examples: metal-catalyzed: a) B. Witulski, T. Stengel,
Angew. Chem. 1999, 111, 2521 2524; Angew. Chem. Int. Ed. 1999, 38,
2426 2430; b) D. Suzuki, H. Urabe, F. Sato, J. Am. Chem. Soc. 2001,
123, 7925 7926; c) T. Sugihara, A. Wakabayashi, Y. Nagai, H. Takao,
H. Imagawa, M. Nishizawa, Chem. Commun. 2002, 576 577; d) M.
Petit, G. Chouraqui, P. Phansavath, C. Aubert, M. Malacria, Org. Lett.
2002, 4, 1027 1029; cycloaddition: e) A. Padwa, J. P. Snyder, E. A.
Curtis, S. M. Sheehan, K. J. Worsencroft, C. O. Kappe, J. Am. Chem.
Soc. 2000, 122, 8155 8167.
It has been shown that alumoxanes of the general formula
(RAlO)n for n > 1 can be obtained by the controlled reaction
of organoaluminum compounds with either water or water
contained in hydrated salts or (Me2SiO)3.[1] Although the
simplest member of the series, namely (RAlO), was predicted
to be obtainable based on the analogy with aluminum
imides,[2] its formation and characterization has remained
ꢀ
elusive, presumably because it implies the presence of an Al
O double bond, which is likely to be very unstable even
though p interactions between Al and O atoms have been
invoked by several groups.[3] However, compounds with such
bonds may be either sterically (by using bulky ligands bonded
to the aluminum) or electronically (by using Lewis acids)
stabilized. Our approach for the stabilization was to use
H2O¥B(C6F5)3, which has been shown to act as a strong
Br˘nsted acid,[4] and whose ability to protonate M R bonds
ꢀ
has been verified.[5] Furthermore if a monoalumoxane is
formed, B(C6F5)3 may hinder the aggregation owing to its
strong Lewis acid character.[6]
[8] a) J. Drews, Science 2000, 287, 1960 1964; b) W. Wess, M. Urmann, B.
Sickenberger, Angew. Chem. 2001, 113, 3443 3453; Angew. Chem.
Int. Ed. 2001, 40, 3341 3350.
[9] For recent reviews on multicomponent reactions, see: a) G. H. Posner,
Chem. Rev. 1986, 86, 831 844; b) L. Weber, K. Illgen, M. Almstetter,
Synlett 1999, 366 374; c) A. Domling, I. Ugi, Angew. Chem. 2000,
112, 3300 3344; Angew. Chem. Int. Ed. 2000, 39, 3168 3210; d) H.
Bienaymÿ, C. Hulme, G. Oddon, P. Schmitt, Chem. Eur. J. 2000, 6,
3321 3329.
[10] For recent reviews on domino process, see: a) L. F. Tietze, Chem. Rev.
1996, 96, 115 136; b) M. H. Filippini, J. Rodriguez, Chem. Rev. 1999,
99, 27 76; c) R. A. Bunce, Tetrahedron 1995, 51, 13103 13160;
d) L. F. Tietze, F. Haunert in Stimulating concepts in Chemistry (Eds.:
M. Shibasaki, J. F. Stoddart, F. Vˆgtle), 2000, pp. 39 64.
[11] X. Sun, P. Janvier, G. Zhao, H. Bienaymÿ, J. Zhu, Org. Lett. 2001, 3,
877 880.
Indeed, the reaction of LAlMe2 (where L is a monoanionic
b-diketiminato ligand, Scheme 1)[7] and H2O¥B(C6F5)3 in
toluene gave LAlO¥B(C6F5)3 (1), which was filtered off at
room temperature and crystallized from dichloromethane
(ꢀ268C). In contrast, when the same reagents were allowed to
react in THF at 558C for 2 h, after the solvent had been
removed, an oily product was formed which crystallized as an
isomer of 1, formulated as LAl(C6F5)OB(C6F5)2 (2;
Scheme 1).
[12] a) For a review on the intramolecular Diels Alder reaction of oxazole
and acetylene, see: P. A. Jacobi in Advances in Heterocyclic Natural
Product Synthesis, Vol. 2 (Ed.: W. H. Pearson), 1992, pp. 251 298; for
a recent application in natural product synthesis, see: b) B. Liu, A.
Padwa, Tetrahedron Lett. 1999, 40, 1645 1648; c) P. A. Jacobi, K. Lee,
J. Am. Chem. Soc. 2000, 122, 4295 4303; d) L. A. Paquette, I.
Efremov, J. Am. Chem. Soc. 2001, 123, 4492 4501.
[13] 3-Arylpropiolic acid was synthesized fromthe corresponding cinna-
mate according to a literature procedure: K. J. Schofield, J. C. E.
Simpson, J. Chem. Soc. 1945, 512 520.
[14] E. Gonzalez-Zamora, A. Fayol, M. Bois-Choussy, A. Chiaroni, J. Zhu,
Chem. Commun. 2001, 1684 1685.
Scheme 1. Synthesis of compounds 1 and 2.
[15] a) P. Cristau, J.-P. Vors, J. Zhu, Org. Lett. 2001, 3, 4079 4082; b) P.
Janvier, X. Sun, H. Bienaymÿ, J. Zhu, J. Am. Chem. Soc. 2002, 124,
2560 2567.
[16] For a five-component synthesis of a-acylaminocarbonamide, see: a) I.
Ugi, C. Steinbr¸ckner, Chem. Ber. 1961, 94, 2802 2814; for a seven-
component reaction, see: b) A. Dˆmling, I. Ugi, Angew. Chem. 1993,
105, 634 635; Angew. Chem. Int. Ed. Engl. 1993, 32, 563 564.
[17] a) S. L. Schreiber, Science 2000, 287, 1964 1969; b) P. Arya, D. T. H.
Chou, M. G. Baek, Angew. Chem. 2001, 113, 351 358; Angew. Chem.
Int. Ed. 2001, 40, 339 346.
[*] Prof. Dr. H. W. Roesky, D. Neculai, A. M. Neculai, Prof. Dr. J. Magull
Institut f¸r Anorganische Chemie
Universit‰t Gˆttingen
Tammannstrasse 4, 37077 Gˆttingen (Germany)
Fax : (þ 49)551-393-373
E-mail: hroesky@gwdg.de
Dr. B. Walfort, Prof. Dr. D. Stalke
Institut f¸r Anorganische Chemie
Universit‰t W¸rzburg
AmHubland, 97074 W¸rzburg (Germany)
[**] This work was supported by the Deutsche Forschungsgemeinschaft.
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0044-8249/02/4122-4294 $ 20.00+.50/0
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Both complexes were characterized by multinuclear NMR
spectroscopy, elemental analysis, and X-ray structural analy-
sis.[8] However, contrary to the 1H NMR spectra of 1 and 2 in
solution, which are consistent with the equivalency of the
dangling arms of the ligand, the solid-state structures of 1 and
2 reveal that only one armof the ligand is coordinated to the
Al atom(see Figure 1 and 2). One possible explanation for
this equivalency is a rapid interconversion in solution.
Figure 2. Structure of 2 (30% thermal ellipsoids; hydrogen atoms omitted
for clarity). Selected bond lengths [ä] and angles [8]: Al(1)-O(1) 1.780(2),
O(1)-B(1) 1.311(2), Al(1)-N(1) 1.964(2), Al(1)-N(2) 1.890(2), Al(1)-N(3)
2.195(2), N(1)-C(2) 1.322(2), N(2)-C(3) 1.346(3), C(2)-C(3) 1.384(3), C(3)-
C(4) 1.409(3), Al(1)-C(31) 2.043(2); Al(1)-O(1)-B(1) 141.69(13), C(3)-
C(2)-N(1) 122.50(17), N(2)-Al(1)-N(1) 94.11(7), Al(1)-N(1)-C(2)
125.19(13), Al(1)-N(2)-C(4) 125.62(13), N(2)-Al(1)-N(3) 82.48(6), N(2)-
C(4)-C(3) 123.68(17), C(31)-Al(1)-O 123.43(7), C(2)-C(3)-C(4) 127.43(18).
ꢀ
ꢀ
For complex 2, the Al O and B O bond lengths of 1.780(2)
and 1.311(2) ä (Figure 2), respectively, are in the range of
those in previously reported compounds.[1,6c]
Figure 1. Structure of 1 (50% thermal ellipsoids; hydrogen atoms omitted
for clarity). Selected bond lengths [ä] and angles [8]: Al(1)-N(1) 1.853(2),
Al(1)-N(2) 1.857(4), Al(1)-N(3) 1.988(4), N(2)-C(4) 1.356(3), C(3)-C(2)
1.401(3), C(4)-C(3) 1.402(0), N(1)-C(2) 1.334(4), Al(1)-O(1) 1.659(3), B(1)-
O(1) 1.444(3); Al(1)-O(1)-B(1) 163.76(2), N(2)-C(4)-C(3) 123.45(2), N(2)-
Al(1)-N(1) 96.69(1), C(4)-C(3)-C(2) 126.79(2), N(1)-Al(1)-N(3) 86.50(1),
C(3)-C(2)-N(1) 119.68(2), Al(1)-N(2)-C(4) 118.02(2), C(2)-N(1)-Al(1)
123.44(2).
In both complexes the Al atom is a member of two
ꢀ
nonplanar, five- and six-membered heterocycles. The Al N
bond lengths for 1 (av 1.855 ä) are somewhat shorter than
those previously reported for similar compounds (av
1.90 ä).[9] In 2 the Al N distances have normal values (av
ꢀ
1.925 ä).[9,10] A similar trend is observed for the coordinative
ꢀ
ꢀ
Al N bond lengths; the Al N(3) bond length in 1 (1.988(4)) is
ꢀ
ꢀ
The Al O bond length in 1 is 1.659(3) ä, which is, to the
shorter than the Al N(3) bond length in 2 (2.195(29),
ꢀ
best of our knowledge, the shortest Al O bond reported for a
however they are in the range found for previously reported
similar compounds.[11] The b-diketiminato C N and C C ring
distances of both compounds have values (av 1.34 and 1.40 ä)
corresponding to a delocalized p-electron system.[9] In the
ꢀ
ꢀ
ꢀ
tetracoordinate Al atom(Figure 1); an Al O distance of
1.6877(4) ä was reported for a tricoordinate Al atom.[3] This
short bond can be explained by considering the resonance
structures given in Scheme 2. Resonance forms A and C can
ꢀ
light of the different Al O bond order for the complexes 1
ꢀ
be considered with regard to the shortness of the Al O bond,
and imply a certain double-bond character. These resonance
structures can also be taken into account to explain the B O
bond length (1.444(3) ä), which is intermediate between the
coordinative B O bond in H2O¥B(C6F5)3 (1.597(2) ä)[4d] and a
B O covalent bond (1.311(2) ä for 2). Even so the B(C6F5)3
group stabilizes the monoalumoxane by dispersing the
negative charge fromoxygen ( B, C, and D; Scheme 2). The
b-diketiminato ligand must also be taken into consideration
because it reduces the positive charge on the Al center by
acting as a Lewis base.[7] In addition these resonance
structures support the irreversible isomerization of 1 to 2.
and 2 (seen fromthe different bond lengths), deviation of the
Al-O-B angles from163.76(2) ( 1) to 141.69(13) (2) is
expected.
In conclusion, we have provided evidence for the existence
of the monomeric member of the (RAlO)n series. Never-
ꢀ
ꢀ
ꢀ
ꢀ
theless it has to be stated that the nature of the Al O bond in
complex 1 is still under debate; additional insights fromfuture
calculations may make things clearer. H2O¥B(C6F5)3 has been
shown to be an excellent reagent for the synthesis of the first
monoalumoxane, and its further application towards the
synthesis and stabilization of other unusual compounds with
ꢀ
multiple M O bonds is in progress.
Experimental Section
O
LAl
O
O
LAl
O
LAl
LAl
B(C6F5)3
B(C6F5)3
B(C6F5)3
B(C6F5)3
All operations involving air- and moisture-sensitive com-
pounds were performed by using standard Schlenk line and
dry box techniques under a purified nitrogen atmosphere.
H2O¥B(C6F5)3 was prepared according to the procedure
A
B
C
D
Scheme 2. Proposed resonance structures for 1.
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described in reference [4a]. Toluene, THF, hexane, and CH2Cl2 were dried
fromappropriate drying agents, Na/K alloy (toluene, THF, hexane), CaH 2
(CH2Cl2), and distilled under nitrogen prior to use. C6D6 and [D8]THF were
dried over Na/K alloy and degassed. 1H, 13C, 19F, 11B, and 27Al NMR spectra
were recorded at ambient temperature on a Bruker AM 200. Chemical
shifts are reported in d units downfield fromTMS ( 1H, 13C), C6F6 (19F),
Et2O¥BF3 (11B), AlCl3 (27Al), with the solvent as the reference signal.
Elemental analyses were carried out at the Analytical Laboratory of the
Institute of Inorganic Chemistry of the University of Gˆttingen. Melting
points were determined in sealed capillary tubes under nitrogen and are
uncorrected.
McMahon, C. J. Harlan, A. R. Barron, Organometallics 2001, 20, 460;
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1994, 33, 969; b) J. D. Fisher, P. J. Shapiro, G. P. A. Yap, A. L.
Rheingold, Inorg. Chem. 1996, 35, 271; c) N. J. Hardman, C. Cui,
H. W. Roesky, W. H. Fink, P. P. Power, Angew. Chem. 2001, 113, 2230;
Angew. Chem. Int. Ed. 2001, 40, 2172.
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1123; Angew. Chem. Int. Ed. Engl. 1995, 34, 989; b) M. A. Petrie,
M. M. Olmstead, P. P. Power, J. Am. Chem. Soc. 1991, 113, 8705.
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Bridgewater, C. J. Harlan, K. R. Norton, R. A. Friesner, G. Parkin, J.
Am. Chem. Soc. 2000, 122, 10581; c) T. Beringhelli, D. Maggioni, G.
D©Alfonso, Organometallics 2001, 20, 4927; d) L. D. Doerrer, M. L. H.
Green, J. Chem. Soc. Dalton Trans. 1999, 4325.
[5] a) G. S. Hill, L. Manojlovic-Muir, K. W. Muir, R. J. Puddephatt,
Organometallics 1997, 16, 525; b) M. Stender, A. D. Philips, P. P.
Power, Inorg. Chem. 2001, 40, 5314.
[6] a) A. K. Dash, R. F. Jordan, Organometallics 2002, 21, 777; b) J. M.
Blackwell, W. E. Piers, M. Parvez, R. McDonald, Organometallics
2002, 21, 1400; c) D. Vagedes, R. Frˆhlich, G. Erker, Angew. Chem.
1999, 111, 3561; Angew. Chem. Int. Ed. 1999, 38, 3362.
LAlMe2: Dry hexane (50 mL) was added to LH (1.553 g, 5.24 mmol; for L
see Scheme 1) in a 100 mL Schlenk flask. The mixture was cooled to ꢀ788C
and a solution of AlMe3 (7.38 mL, 5.3 mmol of a 1.42m solution in hexane)
was added dropwise. The mixture was stirred for 2 h at ꢀ788C, and then
stirred overnight at room temperature until the methane evolution had
ceased. The solvent was removed and the yellowish oil obtained (1.832 g;
99%) was used without any further purification. Elemental analysis (%)
calcd for C17H41AlN4: C 64.73, H 11.72, N 15.89; found: C 64.50, H 11.80, N
16.30; 1H NMR (200 MHz, TMS; C6D6): d ¼ 4.45 (s, 1H; CH), 3.26 (m, 4H;
NCH2CH2NEt2), 2.41 (m, 12H; CH2N(CH2CH3)2), 1.72 (s, 6H; CHCCH3),
0.91 (t, J ¼ 7.07 Hz, 12H; CH2CH3,), ꢀ0.47 ppm(s, 6H; Al(CH 3)2);
13C NMR (125.75 MHz, TMS, C6D6): d ¼ 167.91 (CCHC), 96.938 (CH),
54.20 (CNCH2), 47.90 (NCH2CH2), 46.69 (NCH2CH3), 20.84 (CHCCH3),
12.58 (NCH2CH3), ꢀ8.73 ppm(Al CH3); 27Al NMR (65 MHz, AlCl3 in D2O,
C6D6): d ¼ 150.36 ppm.
[7] D. Neculai, H. W. Roesky, A. M. Neculai, J. Magull, H.-G. Schmidt, M.
Noltemeyer, J. Organomet. Chem. 2002, 643, 47.
[8] Unfortunately, 27Al NMR spectra for 1 and 2 could not be recorded.
The 13C resonances of the C atoms from C6F5 groups fromboth
complexes could not be assigned. a) Crystal data for 1, C35H35AlBF15-
N4O, Mr ¼ 850.46, T¼ 130(2) K, monoclinic, space group P2(1)/n; a ¼
10.618(3), b ¼ 17.108(4), c ¼ 20.457(6) ä, b ¼ 100.402(6)8, V¼
3655.0(18) ä3, Z ¼ 4, 1cald ¼ 1.546 gcmꢀ3, m ¼ 0.169 mmꢀ1, R ¼ 0.0614
for 8646 independent reflections (R1 ¼ 0.0823 for all 28476 data),
GOF ¼ 0.977. The data were collected fromshock-cooled crystals on a
Bruker Smart-Apex diffractometer (graphite-monochromated MoKa
radiation, l ¼ 0.71073 ä) equipped with a low-temperature device at
130(2) K. a) D. Stalke, Chem. Soc. Rev. 1998, 27, 171; b) T. Kottke,
R. J. Lagow, D. Stalke, J. Appl. Crystallogr. 1996, 29, 465; c) T. Kottke,
D. Stalke, J. Appl. Crystallogr. 1993, 26, 615. For the refinement of the
data of compound 1, which crystallized as a non meroedric twin, two
separate matrices of the two domains were determined. Every domain
was integrated on its own. The structure solution was performed by
direct methods by using the data of the first domain. A new hklf5 file
with the reflections of both domains was then written. The reflections
are divided into five overlapping ranges, and the data was refined well
with 10 scaling factors (one for each range and domain). b) Crystal
data for 2, C35H35AlBF15N4O, Mr ¼ 850.46, T¼ 133(2) K, monoclinic,
space group P2(1)/n; a ¼ 9.8994(6), b ¼ 21.4678(17), c ¼
LAlO¥B(C6F5)3 (1): A solution of LAlMe2 (0.217 g, 0.61 mmol) in toluene
(15 mL) was allowed to react with H2O¥B(C6F5)3 (0.326 g, 0.61 mmol) in
toluene (10 mL) at 08C. The mixture was stirred for 1 h at 08C, and then
stirred overnight at room temperature until the methane evolution had
ceased. The suspension was filtered and the precipitate was redissolved in
CH2Cl2 (10 mL). Colorless crystals were obtained by cooling the CH2Cl2
solution at ꢀ268C. Then the crystals were filtered off. Yield 0.317 g (60%);
m.p. 1568C; elemental analysis (%) calcd for 1, C35H35AlBF15N4O: C 49.43,
1
H 4.15, N 6.59; found: C 49.81, H 4.33, N 6.63; H NMR (200 MHz, TMS;
C6D6/[D8]THF): d ¼ 4.82 (s, 1H; CH), 3.11 (t, J ¼ 6.85 Hz, 4H;
NCH2CH2NEt2), 2.41 (m, J ¼ 7.19 Hz, 12H; CH2N(CH2CH3)2), 1.76 (s,
6H; CHCCH3), 0.78 ppm(t,
J ¼ 7.1 Hz, 12H; CH2CH3); 13C NMR
(125.75 MHz, TMS, C6D6): d ¼ 171.82 (CCHC), 98.32 (CH),54.31
(CNCH2), 51.78 (NCH2CH2), 45.58 (NCH2CH3), 20.95 (CHCCH3),
10.17 ppm(NCH 2CH3); 19F NMR (188 MHz, ext. C6F6, C6D6/[D8]THF)
d ¼ ꢀ134.5 (m, 6 F; ortho), ꢀ163.7 (t, 3F; para), ꢀ166.5 ppm(m, 6F; meta);
11B NMR (80 MHz, ext. Et2O¥BF3, C6D6/[D8]THF): d ¼ ꢀ4.83 ppm.
LAl(C6F5)OB(C6F5)2 (2): A solution of LAlMe2 (0.25 g, 0.71 mmol) in THF
(15 mL) was allowed to react in a solution of H2O¥B(C6F5)3 (0.375 g,
0.71 mmol) in THF (10 mL) at 558C for 2 h. The solvent was removed and
the oily product was left to crystallize at roomtemperature. The crystals
formed were washed with cold hexane. Yield 0.44 g (73%); m.p. 85 878C;
elemental analysis (%) calcd for 2, C35H35AlBF15N4O: C 49.43, H 4.15, N
6.59; found: C 49.75, H 4.27, N 6.46; 1H NMR (200 MHz, TMS; C6D6): d ¼
4.28 (s, 1H; CH), 3.22 (m, 2H, NCH2CH2N(CH2)2), 2.95 (m, 2H,
NCH2CH2NEt2), 2.19 (q, J ¼ 7.53 Hz, 8H; CH2CH3), 1.85 (m, 2H;
NCH2CH2NEt2), 1.51 (s, 6H; CHCCH3), 0.70 ppm(t, 12H; CH 2CH3);
13C NMR (125.75 MHz, TMS, C6D6): d ¼ 168.61 (CCHC), 97.29 (CH), 50.51
(CNCH2), 45.48 (NCH2CH2), 45.28 (NCH2CH3), 21.57 (CHCCH3),
18.1143(12) ä, b ¼ 104.315(5)8, V¼ 3730.09(4) ä3, Z ¼ 4, 1cald
¼
1.514 gcmꢀ3, m ¼ 0.166 mmꢀ1 R ¼ 0.0388 for 5121 reflections with I >
2s(I) (R1 ¼ 0.0492 for all 28476 data), GOF ¼ 1.021. Data for crystal
structure of 2 were collected on a Stoe Image Plate IPDS II-System.
Both structures were solved by direct methods (SHELXS-97) (G. M.
Sheldrick, Acta Crystallogr. Sect. A 1990, 46, 467) and refined by full-
matrix least-squares methods against F2 (SHELXL-97), (G. M.
Sheldrick, SHELXL-97, Programfor Crystal Structure Refinement,
University of Gˆttingen, Gˆttingen (Germany), 1997). CCDC-187737
(1) and 187738 (2) contain the supplementary crystallographic data for
this paper. These data can be obtained free of charge via www.ccdc.ca-
m.ac.uk/conts/retrieving.html (or from the Cambridge Crystallo-
graphic Data Centre, 12, Union Road, Cambridge CB21EZ, UK;
fax: (þ 44)1223-336-033; or deposit@ccdc.cam.ac.uk).
9.62 ppm(NCH CH3); 19F NMR (188 MHz, ext. C6F6, C6D6): d ¼ ꢀ118.09
2
(m2F; AlC F5 ortho), ꢀ133.2 (m, 4F; BC6F5 ortho), ꢀ152.5 (t, 2F; BC6F5
6
para), ꢀ155.3 (t, 1F; AlC6F5 para), ꢀ159.7 (m, 2F; AlC6F5 meta),
ꢀ161.5 ppm(m, 4F; AlC 6F5 meta); 11B NMR (80 MHz, ext. Et2O¥BF3,
C6D6): d ¼ 36.83 ppm.
Received: June 21, 2002 [Z19578]
[9] C. Cui, S. Kˆpke, R. Herbst-Irmer, H. W. Roesky, M. Noltemeyer, H.-
G. Schmidt, B. Wrackmeyer, J. Am. Chem. Soc. 2001, 123, 9091.
[10] B. Qian, D. L. Ward, M. R. Smith III, Organometallics 1998, 17, 3070.
[11] C. N. McMahon, A. R. Barron, J. Chem. Soc. Dalton Trans. 1998, 3693.
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Coordination Chemistry of Aluminium (Ed.: G. H. Robinson), VCH,
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Barron, J. Am. Chem. Soc. 1993, 115, 4971; d) C. J. Harlan, M. R.
Mason, A. R. Barron, Organometallics 1994, 13, 2957; e) J. Storre, C.
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4296
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