Reactions of β-diketiminatoaluminum hydrides with tert-butyl hydrogenperoxide - Facile formation of dialuminoxanes containing Al-O-Al groups

Article abstract of DOI:10.1016/j.jorganchem.2008.09.036

Treatment of diphenyl-β-diketiminatoaluminum dihydride, LAlH₂ [1, L = {H₅C₆-N{double bond, long}C(Me)}₂CH] with neopentyl- or trimethylsilylmethyllithium afforded the corresponding alkylderivatives LAlH(R) [R = CH₂-SiMe₃ (2), CH₂-CMe₃ (3)] by the precipitation of lithium hydride. Deprotonation of a methyl group instead of salt elimination occurred by the similar reaction of the more basic alkyllithium compound LiC(SiMe₃)₃. The reactions of the hydrides 1-3 with tert-butyl hydrogenperoxide did not yield the expected peroxo derivatives, instead the dialuminoxanes LAl(R)-O-Al(R)L [R = OCMe₃ (5), CH₂SiMe₃ (6), CH₂CMe₃ (7)] were isolated in high yields. Their Al-O-Al bridges deviated from linearity and had Al-O-Al bond angles of about 155° on average.

Full text of DOI:10.1016/j.jorganchem.2008.09.036

Journal of Organometallic Chemistry 694 (2009) 1101–1106
Contents lists available at ScienceDirect
Journal of Organometallic Chemistry
journal homepage: www.elsevier.com/locate/jorganchem
Reactions of b-diketiminatoaluminum hydrides with tert-butyl hydrogenperoxide
– Facile formation of dialuminoxanes containing Al–O–Al groups
*
Werner Uhl , Barun Jana
Institut für Anorganische und Analytische Chemie, Universität Münster, D-48149 Münster, Germany
a r t i c l e i n f o
a b s t r a c t
Article history:
Treatment of diphenyl-b-diketiminatoaluminum dihydride, LAlH2 [1, L = {H5C6–N@C(Me)}2CH] with neo-
pentyl- or trimethylsilylmethyllithium afforded the corresponding alkylderivatives LAlH(R) [R = CH2–
SiMe3 (2), CH2–CMe3 (3)] by the precipitation of lithium hydride. Deprotonation of a methyl group
instead of salt elimination occurred by the similar reaction of the more basic alkyllithium compound
LiC (SiMe3)3. The reactions of the hydrides 1–3 with tert-butyl hydrogenperoxide did not yield the
expected peroxo derivatives, instead the dialuminoxanes LAl(R)–O–Al(R)L [R = OCMe3 (5), CH2SiMe3
(6), CH2CMe3 (7)] were isolated in high yields. Their Al–O–Al bridges deviated from linearity and had
Al–O–Al bond angles of about 155° on average.
Received 25 July 2008
Received in revised form 15 September
2008
Accepted 22 September 2008
Available online 27 September 2008
Dedicated to Prof. Christoph Elschenbroich
on the occasion of his 70th birthday
Ó 2008 Elsevier B.V. All rights reserved.
Keywords:
Aluminum
Peroxides
Dialumoxanes
Diketiminates
1. Introduction
were bridged by three peroxo groups [6,7]. Furthermore, we were
able to isolate even an organoaluminum peroxide (Scheme 1)
Persistent organoelement peroxides of the heavier elements of
the third main-group are extremely rare because the conflicting
properties of oxidizing peroxo groups in close proximity to reduc-
ing E–C bonds result in very fast quenching reactions and the for-
mation of alkoxy derivatives [1]. Nevertheless, those compounds
were postulated to occur as intermediates and were employed
in secondary reactions as oxygen transfer reagents at low temper-
ature [2]. Structurally characterized organoelement peroxides,
which had a tert-butylperoxo ligand beside a strongly reducing
and generally very oxygen sensitive Al–C bond [8]. All compounds
had CH(SiMe3)2 groups attached to their aluminum or gallium
atoms. That particular alkyl group may contribute to the stability
of these peroxides by the reduction of the negative charge at the
a-carbon atoms through hyperconjugation and, hence, a diminu-
tion of the reducing power of the E–C bonds. We report here on
some systematic investigations into the generation of further
compounds of that type.
[(Me3C)2E(l-OOCMe3)2E(CMe3)2, E = Ga, In], were first reported
by the group of Barron [3]. However, they proved to be explosive
in the solid state. We isolated trace quantities of an organoele-
ment peroxide, in which a peroxo ligand was terminally coordi-
nated by two alkylgallium groups [4,5]. Despite their inherent
instability, such compounds are of particular interest because
they may find broader application as oxygen transfer reagents
soluble in non-coordinating solvents. Furthermore, they may
show unique coordination behaviour similar to transition metal
compounds. In recent investigations we found an easy access to
those peroxides by the treatment of the corresponding organoel-
ement hydrides with different hydrogenperoxides and by the re-
lease of elemental hydrogen [6–8]. One compound possessed
Ga3(O2)3 heterocycles (Scheme 1) in which three gallium atoms
2. Results and discussion
2.1. Syntheses of alkyl(b-diketiminato)aluminum hydrides
The particular stability of the organoelement tert-butylper-
oxoaluminum compound described before [8] may be due to
(i) the coordinative saturation of the aluminum atom by the
coordination to a chelating b-diketiminato ligand and (ii) by
the diminution of the negative charge at the
*
r -orbitals of C–Si bonds. We hoped to
a-carbon atom by
hyperconjugation with
apply this strategy for a more systematic approach to this new
class of compounds. The b-diketiminato coordinated aluminum
dihydride, {HC[C(Me)N–C6H5]2}AlH2 (1), represents
starting compound for the generation of alkylaluminum interme-
a suitable
* Corresponding author. Tel.: +49 251 8336610; fax: +49 251 8336660.
E-mail address: uhlw@uni-muenster.de (W. Uhl).
0022-328X/$ - see front matter Ó 2008 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2008.09.036

1102
W. Uhl, B. Jana / Journal of Organometallic Chemistry 694 (2009) 1101–1106
selectively the corresponding aluminum tert-butylperoxide by
_
2
hydrogen release [8]. However, the reactions described here pro-
ceeded on a completely different route, Eq. (3). Crystalline prod-
ucts (5 to 7) were isolated in up to 83% yield, which were
identified by NMR spectroscopy, mass spectrometry and crystal
structure determination as dialuminoxanes having bent Al–O–
Al bridges. While the Al–C bonds of 2 and 3 were not affected,
the second Al–H bond of 1 was replaced by a tert-butoxy group.
Thus, in these cases the peroxo starting compound did not yield
a peroxoaluminum compound by replacement of a hydrogen
atom, but reacted as an oxidant and inserted an oxygen atom
into the strongly reducing Al–H bond. The resulting Al–OH group
may be deprotonated in a secondary step by the reaction with
an intact Al–H species to afford the dialuminoxane by hydrogen
release. tert-Butanol may be formed as a by-product, which gave
the Al–OCMe3 moiety of 5 by the reaction with the second Al–H
bond. Thus, only the bulky CH(SiMe3)2 substituent gave a rela-
tively persistent alkylaluminum peroxide, LAl(R)–O–O–CMe3.
Owing to the close proximity of peroxo and bis(trimethyl-
silyl)methyl groups in geminal positions we do not believe that
steric shielding plays an important role for the stabilization of
this singular peroxide. However, the reaction pathway may be
influenced. The bulky bis(trimethylsilyl)methyl group may force
the hydrogenperoxo group to approach the Al–H bond via its
protic hydrogen atom and may, thus, favour the hydrogen re-
lease, while an approach via the oxygen atoms may be facilitated
by the smaller alkyl groups and may allow the insertion of oxy-
gen atoms
R
H3C
HC
C6H5
Ga
C
C
N
N
CH(SiMe3)2
O
O
Al
O
O
O
O
O
CMe3
Ga
Ga
H3C
C6H5
R
R
O
O
[R = CH(SiMe3)2]
Scheme 1.
diates. It is easily available by the reaction of the free, proton-
ated ligand with aluminum trihydride by hydrogen release [8].
Its reaction with equimolar quantities of trimethylsilylmethyl-
and neopentyllithium afforded the alkylhydrido derivatives 2
and 3 by LiH elimination in 80–90% yield, Eq. (1). The NMR spec-
troscopic parameters of these compounds (integration ratio,
chemical shifts) are in accordance to the molecular structures
and do not require a detailed discussion. The Al–H stretching
vibrations were detected in the IR spectra as broad absorptions
at 1791 and 1782 cmꢀ1
.
ð1Þ
The corresponding reaction of the dihydride 1 with the steri-
cally shielded alkyllithium compound [Li(THF)2][C(SiMe3)3] gave
a mixture of products from which few crystals of an orange com-
pound (4) could be isolated by recrystallization. Crystal structure
determination revealed that a methyl group of the b-ketiminato li-
gand was deprotonated by the strongly basic tris(trimethyl-
silyl)methyl anion. Ligand exchange afforded compound 4, Eq.
(2), in which an intact, monoanionic ligand and its dianionic form
are coordinated to the central aluminum atom. H-C(SiMe3)3 was
detected as a major by-product by NMR spectroscopy. In accor-
dance with the schematic formula given in Eq. (2) the 1H NMR
spectrum of 4 is relatively complicated. Beside the resonances
characteristic of the intact b-diketiminato ligand the 1H NMR spec-
trum showed resonances of the deprotonated form with two reso-
nances for the chemically different hydrogen atoms attached to the
exocyclic C@C double bond
ð3Þ
ð2Þ
2.2. Synthesis of the dialuminoxanes 5–7
The aluminum hydrides 1–3 were subsequently treated with
tert-butyl hydrogenperoxide at low temperature. In the case of
the bis(trimethylsilyl)methyl derivative a similar reaction gave

W. Uhl, B. Jana / Journal of Organometallic Chemistry 694 (2009) 1101–1106
1103
2.3. Crystal structure determinations
The molecular structure of compound 2 is depicted in Fig. 1.
A chelating b-diketiminato ligand is coordinated to the central
aluminum atom via its both nitrogen atoms. The metal atom is
further bonded to a hydrogen atom and a trimethylsilylmethyl
group. The aluminum atom is slightly above the plane spanned
by the five atoms of the N2C3 chelate (11 pm; 72 pm for the
minor component of the disordered molecule). All C–C
(140.0 pm) and C–N distances (132.9 pm) of the C3N2 moiety
are consistent with a delocalized
p-bonding. Al–N (190.7 pm)
and Al–C distances (196.9 pm) are in the expected range.
Although b-diketiminatoaluminum compounds are known in
the literature in a great number [5c,8,9], similar compounds hav-
ing an alkyl group and a hydrogen atom attached to their alumi-
num atoms are rare [8,10]. The molecular structure of 4 (Fig. 2)
comprises an unchanged and a deprotonated, dianionic b-dike-
timinato ligand coordinated to the central metal atom. The un-
changed one has structural parameters quite similar to those
of compound 2 which verify electronic delocalization. The sec-
ond one has a negative charge at each nitrogen atom. Accord-
ingly, the Al–N bonds are shortened to 182.2 pm on average.
Both C–N bond lengths in the heterocycle (140.7 pm) may be
interpreted in terms of localized single bonds, while the alternat-
ing C–C distances in that part of the molecule (C04–C05 134.2;
C05–C06 145.6; C06–C061 of the exocyclic C@C double bond
135.5 pm) correspond quite well to the situation of butadiene
[11]. The C–C bond length to the terminal methyl group is
150.2 pm. The Al atoms are 16 and 43 pm above the planes of
the respective ligands.
Fig. 2. Molecular structure of 4. The thermal ellipsoids are drawn at the 40%
probability level. Hydrogen atoms are omitted. Only the ipso-carbon atoms of the
phenyl rings are shown. Important bond lengths (pm) and angles (°): Al1–N1
185.8(3), Al1–N2 187.5(3), Al1–N3 181.7(3), Al1–N4 182.6(3), N1–C01 134.1(5),
C01–C02 138.5(5), C02–C03 139.1(5), C03–N2 134.0(5), N3–C04 140.8(5), C04–C05
134.2(5), C05–C06 145.6(5), C06–N4 140.6(5), C04–C041 150.2(5), C06–C061
135.5(6), N1–Al1–N2 97.1(2), N3–Al1–N4 103.3(2), C01–C02–C03 128.6(4), C04–
C05–C06 132.0(4).
age) resulted for the tert-butoxy derivative 5. The last ones
correspond to the bond lengths observed for the linear dialuminox-
ane cited before [12]. An approximate syn-arrangement across the
Al–O–Al axes resulted for the alkyl groups or the b-diketiminato li-
gands of all compounds. Few similar dialuminoxanes have been re-
ported in the literature [12,13], but they were generated on
different routes which do not involve an oxygen transfer from a
peroxo starting compound and the insertion of oxygen atoms into
Al–H bonds. A recent report described the application of those
compounds as catalysts in ring-opening polymerization reactions
[14].
The aluminum atoms of the dialuminoxanes 5–7 (Fig. 3–5) are
coordinated to both nitrogen atoms of the chelating b-diketiminato
ligands with quite normal Al–N distances (188.8 to 192.2 pm).
Each metal atom is further attached to terminal alkyl (6 and 7)
or alkoxy groups (5) and to the bridging oxygen atom. The Al–O–
Al angles are 159.2/154.3° (5), 155.9° (6) and 155.8° (7). A strictly
linear arrangement of those dialuminoxanes was observed only for
a
singular tetraalkyldialuminoxane possessing tricoordinated,
coordinatively unsaturated aluminum atoms shielded by very
bulky subtituents [12]. The Al–O distances to the bridging oxygen
atoms are close to the average value of 169.9 pm for the com-
pounds 6 and 7, while slightly shorter distances (167.9 pm on aver-
3. Experimental
All procedures were carried out under purified argon. n-Pentane,
n-hexane and cyclopentane were dried over LiAlH4, toluene over Na/
benzophenone. The aluminum dihydride 1 [8], neopentyllithium
[15], trimethylsilylmethyllithium [16] and LiC(SiMe3)3 ꢁ 2THF [17]
were obtained according to literature procedures. Commercially
available solutions of tert-butyl hydrogenperoxide (5.5 M in nonane,
Aldrich) were stored over molecular sieves prior to use.
3.1. Synthesis of LAl(H)–CH2SiMe3 [2, L = {H5C6–N@C(Me)}2CH]
A
cooled solution (ꢀ78 °C) of the dihydride
1 (1.99 g,
7.16 mmol) in 50 ml of n-hexane was treated with solid tri-
methylsilylmethyllithium (0.674 g, 7.16 mmol) in small portions.
The resulting suspension was vigorously stirred and slowly
warmed to room temperature. An almost clear solution was ob-
tained after 6 h. The solvent was removed in vacuum, and the res-
idue was treated with 10 ml of toluene. After filtration yellow
crystals of compound 2 precipitated at room temperature. Yield:
2.11 g (81%). Mp (argon, sealed capillary): 93 °C. 1H NMR (C6D6,
400 MHz, 298 K): = 7.09 (4 H, pseudo-t, m-H of phenyl), 7.06 (4
H, pseudo-d, o-H of phenyl), 6.94 (2 H, pseudo-t, p-H of phenyl),
4.92 (1 H, s, br., AlH), 4.72 (1 H, s, CH of the chelate), 1.54 (6 H,
s, CH3 of the chelate), 0.00 (9 H, s, SiMe3), ꢀ0.75 (2 H, s, AlCH2).
13C NMR (C6D6, 100 MHz, 298 K): d = 168.5 (C@N), 145.6 (i-C of
phenyl), 129.6 (m-C of phenyl), 126.4 (o-C of phenyl), 126.2 (p-C
Fig. 1. Molecular structure of 2. The thermal ellipsoids are drawn at the 40%
probability level. CH3 and CH2 hydrogen atoms are omitted. Only the ipso-carbon
atoms of the phenyl rings are shown. Important bond lengths (pm) and angles (°):
Al1–N1 189.6(2), Al1–N2 191.8(2), Al1–C4 196.9(3), C4–Si1 183.7(3), N1–C01
133.4(3), N2–C03 132.4(3), C01–C02 139.5(3), C02–C03 140.5(3), N1–Al1–N2
95.56(8), Al1–C4–Si1 116.0(1), C01–C02–C03 127.7(2).

1104
W. Uhl, B. Jana / Journal of Organometallic Chemistry 694 (2009) 1101–1106
Fig. 3. Molecular structure of 5. The thermal ellipsoids are drawn at the 40%
probability level. Hydrogen atoms are omitted. Only the ipso-carbon atoms of the
phenyl rings are shown. Important bond lengths (pm) and angles (°) (data of the
second molecule in square brackets): Al1–O1 167.8(2) [168.2(2)], Al1–O2 170.5(2)
[170.3(2)], Al1–N11 189.4(2) [189.1(2)], Al1–N12 189.0(2) [188.9(2)], Al2–O1
167.7(2) [168.0(2)], Al2–O3 169.7(2) [170.5(2)], Al2–N21 189.2(2) [188.5(2)], Al2–
N22 189.5(2) [188.8(2)], Al1–O1–Al2 159.2(1) [154.3(1)], N11–Al1–N12 95.43(9)
[95.56(8)], N21–Al2–N22 95.96(9) [95.75(9)].
Fig. 5. Molecular structure of 7. The thermal ellipsoids are drawn at the 40%
probability level. Hydrogen atoms are omitted. Only the ipso-carbon atoms of the
phenyl rings are shown. Important bond lengths (pm) and angles (°): Al1–O1
170.1(2), Al1–C7 193.4(3), Al1–N1 191.3(2), Al1–N2 191.7(2), Al2–O1 169.7(2),
Al2–C8 195.6(2), Al2–N3 191.6(2), Al2–N4 191.7(2), Al1–O1–Al2 155.8(1), N1–Al1–
N2 94.09(9), N3–Al2–N4 93.39(9).
3.2. Synthesis of LAl(H)-CH2CMe3 [3, L = {H5C6–N@C(Me)}2CH]
A
cooled solution (ꢀ40 °C) of the dihydride
1 (0.900 g,
3.24 mmol) in 20 ml of cyclopentane was treated with solid neo-
pentyllithium (0.253 g, 3.24 mmol) in small portions. The mixture
was slowly warmed to room temperature and stirred over night.
The solvent was removed in vacuum, and the residue was treated
with n-pentane. Colorless crystals of compound 3 were obtained
after filtration and cooling of the filtrate to ꢀ30 °C. Yield: 1.02 g
(90%). Mp (argon, sealed capillary): 79 °C. 1H NMR (C6D6,
400 MHz, 298 K): = 7.09 (4 H, pseudo-t, m-H of phenyl), 7.07 (4
H, pseudo-d, o-H of phenyl), 6.94 (2 H, pseudo-t, p-H of phenyl),
AlH not detected, 4.71 (1 H, s, CH of the chelate), 1.55 (6 H, s,
CH3 of the chelate), 0.93 (9 H, s, CMe3), 0.36 (2 H, s, AlCH2). 13C
NMR (C6D6, 100 MHz, 298 K): d = 168.5 (C@N), 145.7 (i-C of phe-
nyl), 129.5 (m-C of phenyl), 126.5 (o-C of phenyl), 126.2 (p-C of
phenyl), 97.6 (CH of the chelate), 34.1 (CMe3), 30.8 (CMe3), 29.6
(br., AlC), 22.8 (CH3 of the chelate). IR (cmꢀ1; paraffin; CsBr):
1942 vw; 1782 w, br.
CN, (phenyl); 1458 s (paraffin); 1396 s dCH3; 1377 s (paraffin);
1300 vw, 1256 w dCH3; 1227 vw, 1196 vw, 1153 vw, 1123 vw,
1070 vw, 1024 w, 982 m dCH3, CC, NC; 860 vw, 814 vw, 754
m; 721 m (paraffin); 698 m; 592 vw, 559 w, 525 w, 473 m, br. AlC,
AlN, (phenyl). MS (EI, 20 eV): m/z (%) = 348 (2) M+; 277 (100) M+
mAlH; 1653 w, 1597 w, 1558 m, 1530 w
m
m
m
Fig. 4. Molecular structure of 6. The thermal ellipsoids are drawn at the 40%
probability level. Hydrogen atoms are omitted. Only the ipso-carbon atoms of the
phenyl rings are shown. Important bond lengths (pm) and angles (°): Al1–O1
170.0(2), Al1–C7 196.1(2), Al1–N1 192.2(2), Al1–N2 192.2(2), Al2–O1 169.9(2),
Al2–C8 195.4(2), Al2–N3 192.1(2), Al2–N4 192.2(2), Al1–O1–Al2 155.9(1), N1–Al1–
N2 93.43(8), N3–Al2–N4 93.38(8).
m
m
–CH2CMe3. Anal. Calc. for C22H29N2Al (348.5): C, 75.8; H, 8.4; N, 8.0.
Found: C, 75.3; H, 8.2; N, 7.8%.
3.3. Synthesis of the compound LAl[N(C6H5)–C(Me)@C(H)–C(@CH2)–
N(C6H5)] [4, L = {H5C6–N@C(Me)}2CH]
of phenyl), 97.7 (CH of the chelate), 22.8 (CH3 of the chelate), 2.1
(SiMe3), ꢀ3.3 (br., AlC). 29Si NMR (C6D6, 400 MHz, 298 K): = 0.2.
IR (cmꢀ1; paraffin; CsBr): 1946 vw; 1791 m, br.
mAlH; 1683 w,
A
cooled solution (ꢀ78 °C) of the dihydride
1 (0.720 g,
1556 vs
(paraffin); 1352 sh, 1339 m, 1304 w dCH3; 1070 s, br. dCH3,
NC; 970 vw, 930 vw, 889 vw, 851 m, 814 w CH3(Si); 719 s (par-
AlC, AlN,
m
CN, (phenyl); 1452 vs (paraffin); 1402 s dCH3; 1377 s
2.59 mmol) in 20 ml of n-hexane was treated with solid LiC
(SiMe3)3 ꢁ 2THF (0.990 g, 2.59 mmol) in small portions. The suspen-
sion was vigorously stirred and slowly warmed to room tempera-
ture. After 1 h at room temperature a clear red solution was
obtained, which was stirred for further 12 h. The mixture was
filtered. The filtrate was stored at ꢀ45 °C. A colorless solid precipi-
tated which was separated. The solution was concentrated to about
m
CC,
m
q
affin); 667 w
m
asSiC; 592 w, 559 m, 513 w, 467 s, br.
m
m
(phenyl). MS (EI, 20 eV): m/z (%) = 364 (17) M+; 363 (45) M+ – H;
277 (100) M+ – CH2SiMe3. Anal. Calc. for C21H29N2AlSi (364.5): C,
69.2; H, 8.0; N, 7.7. Found: C, 68.9; H, 7.9; N, 7.5%.

W. Uhl, B. Jana / Journal of Organometallic Chemistry 694 (2009) 1101–1106
1105
Table 1
Crystal data and structure refinement for 2, 4, 5, 6, and 7a
2
4
5
6
7
Formula
C21H29N2AlSi
153(2)
C34H33AlN4
153(2)
C42H52N4O3Al2
153(2)
C42H56N4OAl2Si2
153(2)
C44H56N4OAl2
153(2)
Temperature (K)
Crystal system
Space group [19]
a (pm)
b (pm)
c (pm)
Monoclinic
P21/c (no. 14)
998.42(3)
2127.79(6)
1080.93(3)
90
106.836(2)
90
2197.9(1)
4
Monoclinic
P21/n (no. 14)
1330.1(1)
1609.3(1)
1362.1(1)
90
100.119(2)
90
2870.1(4)
4
Monoclinic
P21/n (no. 14)
2102.7(4)
1903.8(3)
2125.9(4)
90
112.193(3)
90
7880(10)
8
Triclinic
Monoclinic
P21/n (no. 14)
1146.86(6)
1977.5(1)
1863.1(1)
90
90.503(1)
90
4225.2(4)
4
ꢀ
P1 (no. 2)
1181.93(2)
1184.66(2)
1801.51(4)
95.945(1)
105.519(1)
115.200(1)
2129.64(7)
2
a
(°)
b (°)
c
(°)
V (10ꢀ30 m3)
Z
Dcalc (g cmꢀ3
)
1.102
1.355
1.214
0.100
1.205
0.117
1.159
1.426
1.118
0.105
l
(mmꢀ1
)
Crystal size (mm)
Radiation
0.40 ꢂ 0.28 ꢂ 0.14
0.10 ꢂ 0.06 ꢂ 0.05
0.23 ꢂ 0.11 ꢂ 0.06
0.20 ꢂ 0.15 ꢂ 0.06
0.22 ꢂ 0.18 ꢂ 0.12
Cu K
a
Mo K
a
Mo K
a
Cu K
a
Mo K
a
Theta range (°)
Index ranges
4.16 6 h 6 72.28
ꢀ12 6 h 6 12
ꢀ26 6 k 6 24
ꢀ10 6 l 6 12
4079 [Rint = 0.0370]
3043
1.97 6 h 6 19.68
ꢀ12 6 h 6 12
ꢀ15 6 k 6 15
ꢀ12 6 l 6 12
2554 [Rint = 0.0867]
1799
1.16 6 h 6 30.13
ꢀ29 6 h 6 29
ꢀ26 6 k 6 26
ꢀ29 6 l 6 29
22997 [Rint = 0.1082]
11098
1.21 6 h 6 26.07
ꢀ13 6 h 6 14
ꢀ13 6 k 6 13
ꢀ22 6 l 6 20
7260 [Rint = 0.0268]
5849
1.50 6 h 6 24.08
ꢀ13 6 h 6 13
ꢀ22 6 k 6 22
ꢀ21 6 l 6 21
6682 [Rint = 0.0760]
4473
Independent reflections
Reflections observed
Parameters
258
363
1001
470
470
R =
wR2 = {
R
||Fo|ꢀ|Fc||/
R
|Fo| [I > 2
r
(I)]
0.0505
0.1435
0.395/ꢀ0.213
0.0415
0.1041
0.181/ꢀ0.200
0.0679
0.1820
0.398/ꢀ0.365
0.0463
0.1318
0.402/ꢀ0.256
0.0487
0.1213
0.269/ꢀ0.262
R
w(|Fo|2ꢀ|Fc|2)2/
R
|Fo|2}1/2 (all data)
Max./min. residual (1030 e mꢀ3
)
a
Programme SHELXL-97 [18]; solutions by direct methods, full-matrix refinement with all independent structure factors.
5 ml and cooled to ꢀ45 °C to obtain an orange solid. Repeated
recrystallization yielded few crystals of 4. Mp (argon, sealed capil-
lary): 143 °C. 1H NMR (C6D6, 400 MHz, 298 K): = 7.44 to 6.66 (sev-
eral multiplets of phenyl hydrogen atoms), 5.13 and 4.81 (each 1 H,
s, CH of the chelates), 4.31 and 4.05 (each 1 H, s, br., C@CH2), 1.68
(3 H, s, CH3 of the chelate having the exocyclic C@C double bond),
1.46 (6 H, s, Me of the intact chelat ligand). MS (EI, 20 eV): m/z
the hydride 2 (0.432 g, 1.18 mmol) in 10 ml of n-hexane. The mix-
ture was slowly warmed to ꢀ20 °C and concentrated at this tem-
perature to approximately 8 ml. Colorless crystals of the
dialuminoxane 6 were obtained after storing of the solution at
ꢀ15 °C over night. Yield: 0.367 g (83%). Mp (argon, sealed capil-
lary): 179 °C. 1H NMR (C6D6, 400 MHz, 298 K): = 7.26 (8 H, pseu-
do-d, o-H of phenyl), 7.17 (8 H, pseudo-t, m-H of phenyl), 6.99 (4
H, m, p-H of phenyl), 4.91 (2 H, s, CH of the chelate), 1.76 (12 H,
s, CH3 of the chelate), ꢀ0.02 (18 H, s, SiMe3), ꢀ0.94 (4 H, s, AlCH2).
13C NMR (C6D6, 100 MHz, 298 K): d = 166.9 (C@N), 146.6 (i-C of
phenyl), 129.1 (m-C of phenyl), 126.9 (o-C of phenyl), 125.6 (p-C
of phenyl), 97.9 (CH of the chelate), 23.4 (CH3 of the chelate), 2.7
(SiMe3), ꢀ6.0 (AlCH2). 29Si NMR (C6D6, 79.5 MHz, 298 K):
d = ꢀ0.5. IR (cmꢀ1; paraffin; CsBr): 1940 w, 1879 w, 1798 w,
(%) = 524 (58) M+, 523 (100) M+
3.4. Synthesis of {LAl(OCMe3)}2O [5, L = {H5C6–N@C(Me)}2CH]
solution of Me3C–O–O–H in nonane (5.5 M, 0.23 ml,
–
H, 250 (38) LH+.
A
1.26 mmol) was added drop wise to a cooled solution (ꢀ60 °C) of
the dihydride 1 (0.351 g, 1.26 mmol) in 15 ml of n-hexane. The mix-
ture was slowly warmed to room temperature and stirred for
30 min. The solution was concentrated and cooled to ꢀ15 °C to ob-
tain bright yellow crystals of 5. Yield: 0.252 g (56%). Mp (argon,
sealed capillary): 204 °C. 1H NMR (C6D6, 400 MHz, 298 K): = 7.24
(8 H, pseudo-d, o-H of phenyl), 7.13 (8 H, m, m-H of phenyl), 6.99
(4 H, m, p-H of phenyl), 4.82 (2 H, s, CH of the chelate), 1.66 (12
H, s, CH3 of the chelate), 1.06 (18 H, s, CMe3). 13C NMR (C6D6,
100 MHz, 298 K): d = 167.3 (C@N), 146.2 (i-C of phenyl), 128.7 (m-
C of phenyl), 127.1 (o-C of phenyl), 125.6 (p-C of phenyl), 96.3 (CH
of the chelate), 33.9 (CMe3), 26.8 (CMe3), 23.1 (CH3 of the chelate).
1750 w, 1630 w, 1595 m, 1575 m, 1558 s, 1517 w mCN, (phenyl);
1458 vs, 1375 s (paraffin); 1298 w, 1260 w dCH3; 1239 m, 1193
w, 1168 w, 1070 m, 1022 s, 984 s, 970 s, 935 m, 918 m dCH3,
m
CC,
SiC; 640 w, 604 w
AlN,
AlO, (phenyl). MS (EI, 20 eV): m/z (%) = 727 (3) M+ – CH3;
655 (100) M+
CH2SiMe3; 250 (45) LH. Anal. Calc. for
m
NC; 854 s, 822 s, 746 s
q
CH3(Si); 723 s (paraffin); 698 s mas-
m
sSiC; 551 s, 540 m, 519 s, 495 w, 465 m
m
AlC,
m
m
–
C42H56N4OAl2Si2 (743.1): C, 67.9; H, 7.6; N, 7.5. Found: C, 67.5; H,
7.4; N, 7.4%.
IR (cmꢀ1; paraffin; CsBr): 1578 s, 1560 m, 1530 w
mCN, (phenyl);
3.6. Synthesis of the compound {LAl(CH2CMe3)}2O [7, L = {H5C6–
N@C(Me)}2CH]
1458 vs (paraffin); 1300 w dCH3; 1377 s (paraffin); 1302 w, 1256
w dCH3; 1217 w, 1112 w, 1047 m, 1024 m, 984 w, 943 w, 918 w
dCH3,
m
CC,
m
NC; 861 w, 851 w, 814 vw, 754 m; 721 m (paraffin);
A solution of Me3C–O–O–H in nonane (5.5 M, 0.08 ml,
642 w, 590 w, 561 w, 522 w, 470 m, br.
m
AlC,
m
AlN,
m
AlO, (phenyl).
0.44 mmol) was added drop wise to a cooled solution (ꢀ78 °C) of
the hydride 3 (0.149 g, 0.43 mmol) in 10 ml of n-hexane. The mix-
ture was slowly warmed to ꢀ10 °C and concentrated at this tem-
perature to approximately 6 ml. Colorless crystals of the
dialuminoxane 7 were obtained by storing of the solution at
ꢀ15 °C for 2 d. Yield: 0.123 g (79%). Mp (argon, sealed capillary):
214 °C. 1H NMR (C6D6, 400 MHz, 298 K): = 7.31 (8 H, br., o-H of
phenyl), 7.15 (4 H, m, p-H of phenyl), 6.97 (4 H, m, m-H of phenyl),
4.91 (2 H, s, CH of the chelate), 1.79 (12 H, s, CH3 of the chelate),
0.98 (18 H, s, CMe3), 0.15 (4 H, s, AlCH2). 13C NMR (C6D6,
MS (EI, 20 eV): m/z (%) = 714 (9) M+; 641 (100) M+ – OCMe3, 585 (9)
M+ – OCMe3 – butene, 250 (25) LH. Anal. Calc. for C42H52N4O3Al2
(714.8): C, 70.6; H, 7.3; N, 7.8. Found: C, 70.2; H, 7.3; N, 7.6%.
3.5. Synthesis of the compound {LAl(CH2SiMe3)}2O [6, L = {H5C6–
N@C(Me)}2CH]
A
solution of Me3C–O–O–H in nonane (5.5 M, 0.21 ml,
1.16 mmol) was added drop wise to a cooled solution (ꢀ60 °C) of

1106
W. Uhl, B. Jana / Journal of Organometallic Chemistry 694 (2009) 1101–1106
[2] Y.A. Aleksandrov, N.V. Chikinova, J. Organomet. Chem. 418 (1991) 1.
[3] (a) W.M. Cleaver, A.R. Barron, J. Am. Chem. Soc. 111 (1989) 8966;
(b) M.B. Power, W.M. Cleaver, A.W. Apblett, A.R. Barron, J.W. Ziller, Polyhedron
11 (1992) 477;
(c) M.B. Power, J.W. Ziller, A.R. Barron, Organometallics 12 (1993) 4908;
(d) A.R. Barron, Chem. Soc. Rev. 22 (1993) 93.
[4] W. Uhl, S. Melle, M. Prött, Z. Anorg. Allg. Chem. 631 (2005) 1377.
[5] (a) Aluminum peroxides without Al–C bonds J. Lewinski, J. Zachara, E. Grabska,
J. Am. Chem. Soc. 118 (1996) 6794;
100 MHz, 298 K): d = 166.8 (C@N), 147.0 (i-C of phenyl), 129.0 (m-
C of phenyl), 126.9 (o-C of phenyl), 125.6 (p-C of phenyl), 98.1 (CH
of the chelate), 34.7 (CMe3), 30.6 (GaC), 29.0 (CMe3), 23.6 (CH3 of
the chelate). IR (cmꢀ1; paraffin; CsBr): 1558 s, 1524 s
mCN, (phe-
nyl); 1456 vs (paraffin); 1402 w dCH3; 1377 s (paraffin); 1300 w,
1263 w dCH3; 1227 w, 1194 w, 1153 w, 1123 w, 1070 w, 1022
w, 980 w dCH3,
m
CC,
m
NC; 920 w, 858 w, 814 w, 752 m; 719 m (par-
AlC,
(b) J. Lewinski, J. Zachara, P. Gos, E. Grabska, T. Kopec, I. Madura, W. Marciniak,
I. Prowotorow, Chem. Eur. J. 6 (2000) 3215;
affin); 698 m, 656 w, 640 vw, 613 w; 559 m, 527 w, 471 m
m
m
AlN, (phenyl). MS (EI, 20 eV): m/z (%) = 640 (100) M+ – CHCMe3;
(c) S.S. Kumar, S. Singh, H.W. Roesky, J. Magull, Inorg. Chem. 44 (2005) 1199.
[6] W. Uhl, M.R. Halvagar, Angew. Chem. 120 (2008) 1981;
W. Uhl, M.R. Halvagar, Angew. Chem. Int. Ed. 47 (2008) 1955.
[7] W. Uhl, M. R. Halvagar, W. Massa, unpublished.
[8] W. Uhl, B. Jana, Chem. Eur. J. 14 (2008) 3067.
583 (2) M+ – CH2CMe3 – CMe3; 250 (7) LH. Anal. Calc. for
C44H56N4OAl2 (710.9): C, 74.3; H, 7.9; N, 7.9. Found: C, 74.0; H,
8.1; N, 7.8%.
[9] (a) Few examples B. Twamley, N.J. Hardman, P.P. Power, Acta Cryst. E 57
(2001) m227;
3.7. Crystal structure determinations of compounds 2 and 4 to 7
(b) C. Cui, H.W. Roesky, H. Hao, H.-G. Schmidt, M. Noltemeyer, Angew. Chem.
112 (2000) 1885. Angew. Chem. Int. Ed. 39 (2000) 1815;
(c) N. Kuhn, S. Fuchs, M. Steimann, Z. Anorg. Allg. Chem. 626 (2000)
1387;
Single crystals were obtained from toluene at room tempera-
ture (2) or from the concentrated reaction mixtures on cooling to
ꢀ15 °C (5–7); crystals of 4 from saturated solutions in n-hexane
(ꢀ15 °C). The crystallographic data were collected with a BRUKER
apex diffractometer. The structures were solved by direct methods
and refined with the program SHELXL-97 [18] by a full-matrix
least-squares method based on F2. Crystal data, data collection
parameters and structure refinement details are given in Table 1.
The crystals of 2 showed a disorder. The Al(H)–CH2SiMe3 group
occupied two positions. Their atoms were refined with occupancy
factors of 0.88 and 0.12; the last ones with isotropic displacement
(d) G. Bai, Y. Peng, H.W. Roesky, J. Li, H.-G. Schmidt, M. Noltemeyer,
Angew. Chem. 115 (2003) 1164. Angew. Chem. Int. Ed. 42 (2003) 1132.
[10] Quantum-chemical calculation C.-H. Chen, M.-L. Tsai, M.-D. Su,
Organometallics 25 (2006) 2766.
[11] J. March, Advanced Organic Chemistry, 3rd ed., Wiley, New York, 1985.
[12] W. Uhl, M. Koch, W. Hiller, M. Heckel, Angew. Chem. 107 (1995) 1122;
W. Uhl, M. Koch, W. Hiller, M. Heckel, Angew. Chem. Int. Ed. Engl. 34 (1995)
989.
[13] (a) N. Kuhn, S. Fuchs, E. Niquet, M. Richter, M. Steimann, Z. Anorg. Allg. Chem.
628 (2002) 717;
(b) Y. Peng, G. Bai, H. Fan, D. Vidovic, H.W. Roesky, J. Magull, Inorg. Chem. 43
(2004) 1217;
(c) G. Bai, H.W. Roesky, J. Li, M. Noltemeyer, H.-G. Schmidt, Angew. Chem. 115
(2003) 5660. Angew. Chem. Int. Ed. 42 (2003) 5502;
(d) Z. Yang, H. Zhu, X. Ma, J. Chai, H.W. Roesky, C. He, J. Magull, H.-G. Schmidt,
M. Noltemeyer, Inorg. Chem. 45 (2006) 1823;
(e) S. Gonzalez-Gallardo, V. Jancik, R. Cea-Olivares, R.A. Toscano, M. Moya-
Cabrera, Angew. Chem. 119 (2007) 2895. Angew. Chem. Int. Ed. 46 (2007)
2895;
parameters. Only very small crystals of compound
4 were
obtained. Therefore, data were collected only up to 2h = 39.4°.
The asymmetric unit of 5 contains two independent molecules.
Two tert-butyl groups of 5 were disordered (CT2 and CT6); the
methyl groups were refined with occupancy factors of 0.7 and 0.3.
(f) Dialuminoxanes bearing miscellaneous ligands Y. Kushi, Q. Fernando,
Chem. Commun. (1969) 555;
(g) W. Uhl, M. Koch, S. Pohl, W. Saak, W. Hiller, M. Heckel, Z. Naturforsch. 50b
(1995) 635;
4. Supplementary material
CCDC numbers 696067, 696068, 696069, 696070 and 696071
contain the supplementary crystallographic data for compounds
2, 4–7. These data can be obtained free of charge from The Cam-
bridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/
data_request/cif.
(h) M.R. Mason, J.M. Smith, S.G. Bott, A.R. Barron, J. Am. Chem. Soc. 115 (1993)
4971;
(i) K.J. Wynne, Inorg. Chem. 24 (1985) 1339;
(j) P.L. Gurian, L.K. Cheatham, J.W. Ziller, A.R. Barron, J. Chem. Soc. Dalton
Trans. (1991) 1449;
(k) Y. Wang, S. Bhandari, S. Parkin, D.A. Atwood, J. Organomet. Chem. 689
(2004) 759;
(l) R.J. Wehmschulte, P.P. Power, J. Am. Chem. Soc. 119 (1997) 8387;
(m) D. Rutherford, D.A. Atwood, Organometallics 15 (1996) 4417;
(n) H. Hatop, M. Schiefer, H.W. Roesky, R. Herbst-Irmer, T. Labahn,
Organometallics 20 (2001) 2643.
Acknowledgments
We are grateful to the Deutsche Forschungsgemeinschaft, the
Fonds der Chemischen Industrie and the NRW Graduate School of
Chemistry for generous financial support.
[14] S. Gong, H. Ma, Dalton Trans. (2008) 3345.
[15] R.R. Schrock, J.D. Fellmann, J. Am. Chem. Soc. 100 (1978) 3359.
[16] G.D. Vaughn, K.A. Krein, J.A. Gladysz, Organometallics 5 (1986) 936.
[17] M.A. Cook, C. Eaborn, A.E. Jukes, D.R.M. Walton, J. Organomet. Chem. 24 (1970)
529.
[18] SHELXTL-Plus, REL. 4.1; Siemens Analytical X-ray Instruments Inc.: Madison, WI,
1990. G.M. Sheldrick, SHELXL-93, Program for the Refinement of Structures;
Universität Göttingen, 1993.
[19] T. Hahn (Ed.), International Tables for Crystallography, Space-Group
Symmetry, vol. A, Kluwer Academic Publishers, Dordrecht-Boston-London,
1989.
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