Dimeric Di(tert-butyl)haloalanes and a Monomeric Di(tert-butyl)phosphino- di(tert-butyl)alane

Article abstract of DOI:10.1515/znb-2008-0905

The di(tert-butyl)aluminum halides, tBu₂AlX (X = Br, I) have been prepared in yields ranging from 55 to 64 % from AlX3 and Lit Bu in a 1: 2 molar ratio in pentane. In the crystal these pyrophoric compounds are dimeric featuring Al-X-Al bridges. The reaction of AlCI₃ with LitBu in diethyl ether produced a volatile solvate of composition tBu₃Al-Cl- AltBu₂(OEt₂). Reaction of this species with AlCl ₃ at 120 °C yielded a separable mixture of tBu₂AlCl and tBu₂AlCl(OEt₂). tBu₂AlCl and tBu ₂GaCl react with tBu₂PLi to produce the monomeric compounds tBu₂E-PtBu₂ (E = Al, Ga). The aluminum compound decomposes at 111 °C to give a mixture of the cis/trans-isomers of [tBu(H) Al-PtBu₂]₂ while at 200 °C only the trans-isomer is formed.

Full text of DOI:10.1515/znb-2008-0905

Dimeric Di(tert-butyl)haloalanes and a Monomeric
Di(tert-butyl)phosphino-di(tert-butyl)alane
Ingo Krossing, Heinrich No¨th, and Siegfried Staude
Department of Chemistry and Biochemistry, University of Munich, Butenandtstr. 5 – 13,
D-81377 Mu¨nchen, Germany
Reprint requests to Prof. Dr. H. No¨th. E-mail: H.Noeth@lrz.uni-muenchen.de
Z. Naturforsch. 2008, 63b, 1045 – 1051; received May 14, 2008
The di(tert-butyl)aluminum halides, tBu2AlX (X = Br, I) have been prepared in yields ranging
from 55 to 64 % from AlX3 and LitBu in a 1 : 2 molar ratio in pentane. In the crystal these pyrophoric
compounds are dimeric featuring Al–X–Al bridges. The reaction of AlCl3 with LitBu in diethyl
ether produced a volatile solvate of composition tBu3Al–Cl–AltBu2(OEt2). Reaction of this species
◦
with AlCl3 at 120 C yielded a separable mixture of tBu2AlCl and tBu2AlCl(OEt2). tBu2AlCl and
tBu2GaCl react with tBu2PLi to produce the monomeric compounds tBu2E–PtBu2 (E = Al, Ga). The
aluminum compound decomposes at 111 ◦C to give a mixture of the cis/trans-isomers of [tBu(H)Al–
PtBu2]2 while at 200 ◦C only the trans-isomer is formed.
Key words: Di(tert-butyl)aluminum Halides, Chloro Penta(tert-butyl)dialuminum Diethyl Ether,
Di(tert-butyl)phosphino-di(tert-butyl)alane, NMR Spectra, Crystal Structures
Introduction
Schnepf [11]. Using this method we obtained the
tBu2AlX compounds (X = Br, I) according to
Eq. 1 from pentane solutions in moderate yields
(55 – 64 %).
Our attempts to synthesize tBu2AlCl analo-
gously in diethyl ether, expecting the formation of
tBu2AlCl·OEt2, led to a surprising result because the
reaction proceeded, irrespective of the ratio of AlCl3
to LitBu from 1 : 1.5 to 1 : 2.5, to compound 3, as de-
picted in Eq. 2.
It is well known that triorganylalanes like AlMe3
or AlEt3 are dimeric in hydrocarbon solvents as well
as in the gas phase [1, 2]. However, in the presence of
sterically demanding organyl groups such as tert-butyl
[3, 4] or mesityl [5] they stay monomeric in solu-
tion and in the solid state. Organylaluminum halides
of types RAlX2 and R2AlX are generally dimeric.
Dimerization occurs via Al–X–Al bonds [1, 2]. The
tBu2AlX halides (X = Cl, I) are also dimeric in the
solid state [6, 7] as well as in hydrocarbon solutions in
contrast to mesitylaluminum halides which are present
as monomers according to 27Al NMR data [8]. This has
also been demonstrated for bis(tetramethylpiperidino)-
aluminum halides [9], which retain their monomeric
character also in the solid state.
In contrast to aminoorganylalanes and amino-
aluminum halides little information exists on or-
ganylphosphinoalanes [1, 2, 10]. As far as we are
aware, no monomeric (organylphosphino)diorganyl-
alanes have been reported as yet. They are potential
precursors to AlP materials.
AlX3 +2LitBu → tBu2AlX+2LiX
(1)
X = Br,1,X = I,2
4AlCl3 +10LitBu +2OEt2
→ 2tBu3Al–Cl–AltBu2 ·OEt2 +10LiCl
(2)
3
2tBu3Al–Cl–AltBu2 ·OEt2 +AlCl3 →
→ 3tBu2AlCl+2tBu2AlCl·OEt2ꢀ
(3)
4
5
Compound 3 can be distilled without decomposition
in vacuo. It reacted with AlCl3 at 120 ◦C within 5 min
under formation of tBu2AlCl, 4, and its diethyl ether-
Results
Synthesis
A simple and efficient synthesis of di(tert- ate 5 (Eq. 3). These two compounds can be separated
butyl)aluminum halides was described by Uhl and by fractional crystallization from hexane.
c
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I. Krossing et al. · Dimeric Di(tert-butyl)haloalanes
tBu2ECl+LiPtBu2 → tBu2E–PtBu2 +LiCl
6 : E = Al, 7 : E = Ga
(4)
(5)
Reactions
While tBu3Al [3, 4] is a monomer, in contrast
NMR Spectra
The 27Al NMR spectrum of compound 3 shows
to the di(tert-butyl)haloalanes, we expected that two comparatively sharp signals of equal intensity at
subsituents X, which are sterically more demanding δ = 153 and 125 ppm. We attribute the latter to the
than a halogen atom might provide monomeric di(tert- Cl(tBu2)AlO unit and the former to the tBu3AlCl
butyl)alanes, tBu2AlX. To test this assumption we unit. This can be compared with the 27Al NMR spec-
reacted tBu2ECl (E = Al, Ga) with LiPtBu2, as shown trum for the anion [tBu3Al–Br–AltBu3]− with δ =
1
in Eq. 4.
154 ppm, h1/2 = 3000 Hz [14]. The H NMR spec-
Because tBu2AlCl forms readily a diethyl ether trum shows two sharp signals in a 3 : 2 ratio. The
adduct [5], we performed the reaction in hexane or compound also exhibits two sets of 13C NMR reso-
pentane solution obtaining 6 in 46 % yield. However, nances for the tBu groups in accord with formula 3.
we used an ether solution for the analogous reac- On the other hand, compound 5 shows a 27Al reso-
tion with tBu2GaCl, because this compound forms nance at δ = 95 ppm for a tetracoordinated Al atom.
only weak diethyl ether adducts. Compound 7 was In contrast, the 27Al NMR signal of 4 in C6D6 so-
isolated in 72 % yield. Cryoscopic molecular weight lution at δ = 161 ppm is rather broad with h1/2
=
determinations of 6 and 7 in cyclohexane showed 6000 Hz. This chemical shift lies still in the range
that both compounds are monomeric. They are highly for tetracoordinated Al atoms, i. e. the compound is
susceptible to hydrolysis, and they react explosively present as a dimer. The 27Al NMR signal of tBu2Al Br
with air.
was observed at δ = 160 ppm, h1/2 = 8400 Hz, and
It is known that tBu2Ga–AstBu2 decomposes that of tBu2AlI at δ = 162 ppm, h1/2 = 7900 Hz.
readily with formation of gallium arsenide [12]. Mitzel et al. [7] reported for the iodide a chemical shift
δ
27Al = 149 ppm, h1/2 = 6500 Hz. Large line widths
◦
Compound 7 decomposed on heating up to 400 C
but no pure product could be isolated. In contrast, the are not only typical for tricoordinated Al centers but
◦
aluminum compound 6 decomposed at 200 C with also for tetracoordinated organylaluminumcompounds
dehydroalumination under formation of all-trans- with low symmetry due to the large quadrupol mo-
hexa-tert-butyl-1,3-diphospha-2,4-dialumina-cyclo-
ment of the Al nucleus [15]. Typical examples are
butane 8a, as shown in Eq. 5. Heating to temperatures the monomeric 2,2,6,6-tetramethylpiperidino-alanes
higher than 230 ◦C led i. a. to the formation of metallic tmp2AlCl (134 ppm, 13 700 Hz), tmp2AlBr (130 ppm,
aluminum. However, when 6 was heated in toluene 9100 Hz), tmp2AlI (130 ppm, 10 000 Hz), [9], and
◦
(b. p. 111 C) the NMR spectra showed the presence tmp2AlMe (173 ppm, 3200 Hz) [16]. The line widths
of 8a, besides cis- hexa-tert-butyl-1,3-diphospha-2,4- for dimeric (AlMe3)2 (δ = 153 ppm, h1/2 = 850 Hz) or
dialumina-cyclobutane 8b. This indicates that 8b is a for (Et2AlNEt2)2 (δ = 160 ppm, h1/2 = 1220 Hz) are
kinetic reaction product. The two products could not significantly smaller [8].
be interconverted into each other in contrast to similar
1,3-diphospha-2,4-dibora-cyclobutanes [13].
The 27Al chemical shift of compound 6 of δ =
265 ppm shows it to be a monomeric di(tert-butyl)-
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I. Krossing et al. · Dimeric Di(tert-butyl)haloalanes
1047
Table 1. Structural parameters of bis(tert-butyl)haloalanes.
Compound
tBu2AlCl
tBu2AlBr
tBu2AlI
Al–X1
Al–X2
Al–C1
Al–C5
ref.
[6]
2.317(4)
2.463(3)
2.708(1)
2.711(1)
2.324(4)
2.466(3)
2.716(1)
2.717(1)
1.982(9)
1.975(9)
1.987(4)
1.985(2)
1.996(6)
2.01(1)
1.991(3)
1.986(2)
tBu2AlI
[5]
[6]
X1–Al1–X1A
Al1–X1–Al1A
C1–Al1–C5
C1–Al1–X1
C1–Al1–X1A
tBu2AlCl
tBu2AlBr
tBu2AlI
tBu2AlI
87.2(1)
90.07(9)
93.10(4)
95.2(7)
92.8(1)
89.93(9)
86.90(4)
95.9(7)
123.6(3)
122.9(4)
124.3(2)
124.2(1)
110.3(3)
108.6(3)
108.2(1)
108.6(1)
110.2(3)
109.1(3)
108.5(1)
108.2(1)
[15]
signals each in the 1H and 13C NMR spectrum for the
AltBu2 and PtBu2 groups. In the 31P NMR spectrum
two signals at δ = 28.2 and 15.7 ppm are observed in
consonance with the presence of rotamers.
The 27Al resonances of compounds 8a/8b were ob-
served at δ = 144 ppm, i. e. the two isomers show the
same chemical shifts. However, these two isomers can
be distinguished by their 31P NMR spectrum. The 31
P
resonance for the trans isomer 8a appears at 12.0 ppm,
and that of the cis isomer 8b at 3.5 ppm. More infor-
mation is obtained from the 1HMR spectra (see Fig. 1).
In 8a the tert-butyl groups at the P and Al atoms
each are equivalent. They are characterized by a
pseudotriplet [3J(31P1H) + 5J(31P1H)] while the AltBu
groups are represented by a single signal. The inten-
sity ratio of the two resonances is 2 : 1. The presence
of Al–H bonds in these isomers is demonstrated by an
Fig. 1. The 1H NMR
spectrum on top was
observed for the trans-
isomer 8a, the spectrum
at the bottom shows a
mixture of the cis- and
trans-isomers.
Al–H stretching band at 1770 cm−1
.
phosphinoalane in solution, the first one of its kind.
Its Al atom is similarly shielded as observed for
AltBu3 [8]. No 79Ga NMR signals could be observed
for the gallium compound 7. It is well known that
X-Ray structure determination
The structure of tBu2AlCl has been determined by
79Ga signals can be even broader than those of 27Al. Barron et al. in 1997 [6]. More recently, Mitzel et
The monomeric character of both compounds is as- al. [5] published the structure of tBu2AlI, 2, in 2005.
1
certained by the H and 13C NMR spectra. Only the Its structural data fit very well to those determined
coupling to a single P atom is observed. The PCMe3 for 2 by Krossing in 1997 [15]. Here we report on
3
group shows doublets with J(31P1H) = 11.8 Hz in the missing link tBu2AlBr, 1. The most relevant struc-
1
the H NMR spectrum but singlets in the 13C NMR tural parameters of the three species are summarized in
spectrum while the contrary happens for EtBu2 groups Table 1.
(E = Al, Ga), i. e. the 13C signals appear as dou-
Fig. 2 shows the molecular structure of dimeric 1
blets (3J(31P13C) = 12.6 Hz, 12.2 Hz for 6 and 7, re-
which crystallizes like 2 in the monoclinic space
1
spectively). Low temperature H NMR spectra of 6
show no rotational barrier for the Al–P bond down to
−80 ◦C.
group P21/n with Z = 2. A crystallographic center
of inversion is located in the Al2Br2 ring. The two
Al–Br bonds Al1–Br1 and Al1–Br1A are 2.643(3)
However, solutions of 6 in THF exhibit a 27Al NMR and 2.646(3) A long, i. e. they have virtually the same
signal at δ = 151 ppm, i. e. the presence of a tetraco- lengths. In contrast, the Al–C distances are slightly dif-
ordinated Al atom which is due to the formation of ferent with 1.975(3) and 2.010(9) A (see Table 1). As
˚
˚
◦
tBu2P–AltBu2 · THF. This adduct at 45 C shows no can be seen from these data, the four-membered ring
longer free rotation about the Al–P bond. There are two of 1 is almost a perfect square as the Br1–Al1–Br2
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1048
I. Krossing et al. · Dimeric Di(tert-butyl)haloalanes
mides besides (tBu2AlBr)2 to be compared in this con-
text, namely {[(3,5-iPr2C6H3)2iPrC]2AlBr}2 [22]. Its
˚
Al–Br bonds are slightly longer (2.473 and 2.502 A),
and its Al–Br–Al bond angles are larger than in 1
(92.73, 93.90◦). It is interesting to note that the ter-
minal Al–Cl bonds of (MeAlCl2)2 and [(Me3Si)2CH–
AlCl2]2 are as short as in gaseous Al2Cl6 while the
Al–Cl bond lengths in the bridge position are only
˚
slightly longer (2.21 and 2.06 A, respectively) [15].
The present data indicate that steric effects determine
the lengths of the Al–X bridge bonds, and, therefore,
the stability of the dimer.
Fig. 2. Molecular structure of (tBu2AlBr)2 in the solid state.
Displacement ellipsoids are depicted at the 25 % probability
level. Relevant bonding parameters are listed in Table 1.
In contrast to the chemistry of phosphinobo-
ranes [13, 25], little is known about the chemistry
of diorganylphosphino-diorganylalanes [1, 10]. Ac-
tually, the review of the structures of organoalu-
minum compounds by Holloway and Melnik [26]
refers only to trimeric [Me2Al–PPh2]3 [27]. The only
other trimeric species is [I2Al–PPh2]3 [28] although
a number of heterocycles containing one or two
R2Al–PR2 units are known as parts of ring systems
[29 – 32].
However, no mononuclear diorganylphosphino-
diorganylalane has been reported as yet. The same
is true for diorganylphosphino-diorganylgallanes. The
existence of compounds 6 and 7 demonstrates that
these kinds of compounds can be prepared provided
that the substituents at the Al and P atoms are bulky.
The absence of P–Al π bonding is demonstrated by
the free rotation about the Al–P bond even at low tem-
peratures. However, hindered rotation is observed for
the THF adduct of 6 due to steric overcrowding at the
Al atom. The only other monomeric phosphinoalane
so far reported is diphenylphosphino-bis(tetramethyl-
piperidino)alane [29]. As expected, both 6 and 7 are
thermally unstable and decompose in a first step by
loss of isobutene. In case of compound 6 the four-
membered 1,3-diphospha-2,4-dialumina-cyclobutane
could be analytically characterized as well by NMR
data. We had, however, not the possibility to study
the gas phase decomposition of compounds 6 and 7
in order to prepare thin films of AlP or GaP. We
are convinced that the di(tert-butyl)haloalanes of-
fer many opportunities for the preparation of new
materials.
and Al1–Br2–Al1A angles are both 90◦ within stan-
dard deviations. On the other hand, the C1–Al1–C5
bond angle of 1 is quite wide with 122.9(4)◦, while
the C1–Al1–Br1 and C1–Al1–C5 angles at 108.6(3)
and 110.2(3)◦, are close to the tetrahedral standard.
This demonstrates that amongst the (tBu2AlX)2 com-
pounds listed in Table 1 compound 1 is the most
symmetrical one. As one moves from (tBu2AlCl)2
to (tBu2AlI)2 the X–Al–X angles increase, and the
Al–X–Al angles decrease. This is the consequence of
the increasing Al–X bond lengths. Another typical fea-
ture of the structures of 1 and 2 is that Al–X bridg-
ing bonds are longer than in Al2Br6 [2.399(9) and
˚
˚
2.387(9) A] and Al2I6 [2.66(2), 2.67(2) A] [17], re-
spectively, while their terminal Al–X bonds are sig-
˚
nificantly shorter [2.205(9) and 2.20(1) A for Al2Br6,
and 1.482(2) and 2.49(2) A for Al2I6]. The longer
˚
bonds of solid di-tert-butylaluminum halides indicate
a weaker bonding situation which is a prerequisite for
the dissociation into monomeric units.
Discussion and Conclusion
Like tBu2AlX most other diorganylhaloalanes are
dimeric in the solid state even with rather bulky
substituents. Typical examples are [(Ph(Me3Si)2C)-
MeAlCl]2 [18], (Mes2AlCl)2 [19], (MeAlCl2)2 [20],
[(Me3Si)2CHAlCl2]2 [21], {[(3,5-iPrC6H2)2iPrC]Al-
Br}2 [22], [(F5C6)2AlCl]2 [23], or [(2,6-Mes2Ph)-
AlCl2]2 [24]. Amongst the dimeric dialkylaluminum
chlorides the Al–Cl bonds of the dimeric dime-
sitylaluminum chloride are the longest with 2.345
˚
and 2.316 A. Amongst the dimeric organylaluminum
dichlorides the difference in Al–Cl bond lengths is
smallest for (2,6-dimesitylphenyl)aluminum dichlo-
ride (0.057 and 0.070 A) [25]. There exists only one
Experimental Section
˚
All experiments were performed in an atmosphere of dry
other structure for dimeric diorganylaluminum bro- dinitrogen gas using Schlenk techniques. Solvents were dried
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I. Krossing et al. · Dimeric Di(tert-butyl)haloalanes
1049
by use of CaH2, P4O6 or LiAlH4, and distilled in dispensing 13.2 ppm (OCH2Me). – 27Al NMR: δ = 153.0, 125.0. –
bottles filled with dry dinitrogen gas. AlCl3 was sublimed C24H55OAl2Cl (429.09): calcd. Cl 7.89; found Cl 8.00.
prior to use, and AlBr3 as well as AlI3 were prepared from
the elements. Pentane and hexane solutions of LitBu were
supplied by Chemetall GmbH. 1H, 13C and 27Al NMR spec-
tra were recorded with a Jeol GSX 270 instrument.
Di(tert-butyl)chloroalane (4) and di(tert-butyl)chloroalane-
diethyl ether (5)
A mixture of 3 (4.03 g, 9 mmol) and AlCl3 (0.6 g) was
◦
heated to 120 C for 5 min. Fractional crystallization from
Di(tert-butyl)bromoalane (1)
hexane (15 mL) yielded tBu2AlCl, 4 (0.7 g, dec.: 126 ◦C). A
third fraction proved to be tBu2AlCl(OEt2), 5 (1.29 g, 57 %)
as a paste.
AlBr3 (20.9 g, 78.4 mmol) was suspended in pen-
tane (200 mL) and the suspension cooled to −78 ◦C.
Within 1 h a 1.55 M solution of LitBu in pentane (101.2 mL,
156.8 mmol) was added while stirring. The mixture was then
allowed to attain r. t. over night, and the solid was removed
by filtration and then washed with pentane (100 mL). The
volume of the combined filtrates was reduced to 1/5 by ap-
1
tBu2AlCl, 4: H NMR: δ = 1.13 – 13C NMR: δ = 29.9
CMe3, 18.2 CMe3. – 27Al NMR: δ = 161.6 ppm.
tBu2AlCl(OEt2), 5: 1H NMR: δ = 1.17 (CMe3), 3.58,
0.7 (3J(1H1H) 7.09 Hz). – 13C NMR: δ = 29.9 (CMe3),
18.4 (CMe3), 67.9, 13.3 (OCH2Me) – 27Al NMR: δ = 95. –
C12H28OAlCl (250.68): calcd. Al 10.76, Cl 14.14; found
Al 10.9, Cl 15.2.
◦
plying vacuum. After cooling the solution to −78 C color-
less crystals separated on standing over night. These crystals
are highly pyrophoric and need to be handled with proper
care in an atmosphere of N2: Yield: 8.75 g (55 %). – NMR
(C6D6): 1H NMR: δ = 1.10 ppm (s, CMe). – 13C NMR: δ =
Di(tert-butyl)-di(tert-butyl)phosphanylalan (6)
18.3 (CMe3), 29.9 (CMe3). – 27Al NMR: δ = 160 (h1/2
=
LitBu (0.80 g, 5.3 mmol) was suspended in hexane
(15 mL) and the stirred suspension cooled to −78 ◦C. Then a
solution of tBu2AlCl (920 mg, 5.2 mmol) in hexane (10 mL)
was slowly added. At r. t. the resulting suspension showed
a yellow green color. The solid (LiCl, 230 mg) was re-
moved by filtration and the hexane by evaporation in vacu-
um. The sticky residue yielded a colorless powder of 6 on
attempted crystallizati◦on from pentane. Yield of 6: 680 mg
(46 %), m. p. 55 – 57 C. The compound ignites in contact
with air. Solutions in Et2O, C6H6 or C6H14 showed a yellow-
green color. – Cryoscopic MW in cyclohexane: 231 g/mol,
(calcd. 286.4). – 1H NMR (C6D6): δ = 1.24 (AlCMe3),
1.35 (PCMe3, 3J(31P1H) = 11.8 Hz). – 13C NMR: δ =
31.0 (PCMe3), 35.4 (AlCMe3, 3J(31P13C) = 12.6 Hz). –
27Al NMR: δ = 265.0, v. br. – 31P NMR: δ = 9.5 ppm
(3J(31P13C) = 12.6 Hz).
8400 Hz). – C8H18AlBr (202.97): calcd. Al 13.3, Br 39.4;
found Al 13.0, Br 39.6.
Di(tert-butyl)iodoalane (2)
Prepared in analogy to compound 1. AlI3 (3.64 g,
◦
9.4 mmol) was suspended in pentane (60 mL). At −78 C
6.1 mL of a 1.55 M solution of LitBu in pentane (9.4 mmol)
was added. After stirring over night at ambient temperature
the solid was removed by filtration and washed with pentane
(30 mL). From the concentrated filtrate crystals of 2 sepa-
◦
rated on cooling to −78 C. Yield: 1.50 g (64 %) of color-
less pyrophoric crystals. – NMR (C6D6): 1H NMR: δ = 1.11
(s, CMe3). – 13C NMR: δ = 18.5 (CMe3), 30.0 (CMe3). –
27Al NMR: δ = 162 (h1/2 = 7900 Hz). – C8H18AlI (249.97):
calcd. Al 10.8, I 50.8; found Al 10.1, I 49.3.
Di(tert-butyl)-di(tert-butyl)phosphanylgallane (7)
Tris(tert-butyl)aluminum-µ-chloro-bis(tert-butyl)aluminum-
diethyl ether (3)
A solution of tBu2GaCl (1.26 g, 5.75 mmol) in diethyl
ether (10 mL) was treated at −78 ◦C with a solution of
◦
At 0 C AlCl3 (19 g, 140 mmol) was dissolved in di- LiPtBu2 (870 mg, 5.7 mmol) in diethyl ether (10 mL). The
ethyl ether (100 mL). To the stirred solution was dropwise color of the resulting suspension changed to yellow-green
added a 1.4 M solution of LitBu in pentane (200 mL, 1.4 M, on warming to ambient temperature. Insoluble LiCl was re-
280 mmol). The resulting suspension was stirred at ambi- moved by filtration and the solvent from the filtrate in vacu-
ent temperature over night. Insoluble material was then re- um. The residue, a yellow oil (1.57 g), solidified within 2 h,
◦
◦
moved by centrifugation. A sticky solid was left after re- m. p. 33 C. The compound sublimed at 60 C/10−5 Torr
moval of all volatiles from the filtrate under vacuum. Dis- to give colorless crystals. – Cryoscopic MW in cyclohex-
tillation at b. p. 130 ◦C/4 Torr led to a solid which on crystal- ane: 333 g/mol, (calcd. 325.2). – NMR (C6D6): 1H NMR:
lization from hexane gave a yi◦eld of 21.7 g of 3 (69 %), color- δ = 1.29 (GaCMe3), 1.30 (PCMe3, 3J(31P1H) = 13.2 Hz). –
less crystals, m. p. 130 – 134 C. – 1H NMR: δ = 1.15, 1.24 13C NMR: δ = 34.6 (GaCMe3, 3J(31P13C) = 12.2 Hz), 30.3
(CMe3, 2 : 3), 3.54, 0.73 (OCH2Me, 3J (1H1H) = 7.1 Hz; (PCMe3). – C16H33GaP (325.17): calcd. C 58.38, H 11.02;
4 : 6). – 13C NMR: 30.3, 31.6 (CMe3), 19.7 (br, CMe3), 68.0, found C 57.82, H 10.41.
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1050
I. Krossing et al. · Dimeric Di(tert-butyl)haloalanes
Table 2. Relevant crystallographic data and data related to
structure solution.
1.43 (cis, AlCMe3), 1.45 (trans, PCMe3, pseudo-t, N =
13.7 Hz), 1.43 – 1.438 (m, cis/trans), 4.58 ppm (Al–H). –
13C NMR: δ = 33.1 (trans, AlCMe3, 3J(31P13C) = 3.7 Hz),
32.2 (PCMe3). – 31P NMR: δ = 12.0 (trans), 3.5 (cis). –
27Al NMR: 144.0. – C24H56Al2P2 (460.62): calcd. C 62.58,
H 12.25; found C 62.21, H 11.8.
Compound
1
2
Chem. formula
Form. wght.
C16H36Al2Br2
442.22
0.2×0.3×0.3
monoclinic
P21/n
8.796(5)
12.120(7)
11.219(4)
109.86(1)
1125(1)
2
C16H36Al2I2
536.20
0.25×0.25×0.25
monoclinic
P21/n
8.644(5)
12.373(7)
11.419(5)
109.16(1)
1154(1)
2
Cryst. size, mm3
Cryst. system
Space group
X-Ray structure determinations
˚
a, A
˚
b, A
A Siemens P4 diffractometer equipped with a low-
temperature device and an area detector was used for de-
termining the unit cells and for collecting the data sets of
compounds 1 and 2. The micro chemical laboratory of the
Department supplied the elemental analyses.
˚
c, A
β, deg
3
˚
V, A
Z
ρ(calc.), mg m−3
1.306
3.674
456
1.543
2.795
528
µ, mm−1
Crystals of compounds 1 and 2 were covered in a Schlenk
tube with dry oxygen-free perfluoroether oil. Several speci-
mens were then transferred onto a glass platelet in the mi-
croscope which was cooled by a stream of dinitrogen gas
to −30 ◦C. The selected specimen was placed on the tip
of a glass fibre and as quickly as possibly transferred on
to the head of the goniometer which was flushed with dini-
F(000), e
hkl index range
11, 14,
−15 → +9
58.0
11, 15,
−10 → +15
57.4
2θ, deg
Temp., K
183
173
Refl. collect.
Refl. unique
Refl. observ. (4 σ)
Rint
No. variables
Wght. scheme. x/ya
GOOF
6353
1920
1215
0.0463
97
0.0450/6.7058
1.086
6380
2121
2018
0.0241
97
0.0139/2.1866
1.121
◦
trogen gas at −80 C. The unit cell dimensions were calcu-
lated from the positions of reflections on 20 frames collected
at 5 different orientations using the program SMART [33].
Data collection was performed in the hemisphere mode. A
total of 1200 frames were collected at two different χ set-
tings by changing ω by 0.3◦. Data were reduced with the
program SAINT [33]. SADABS [33] was applied for correct-
ing the data for absorption. The structures were solved and
refined by using the program package SHELXTL [33]. Po-
sitions of non-hydrogen atoms were refined anisotropically,
and the H atoms were added in calculated positions with Ui
equals 1.3 times that of the Ui j value of the respective carbon
atom.
Final R (4σ)
0.0677
0.1480
1.203
0.0232
0.0.547
0.753
Final wR2 (all data)−3
˚
Larg. res. peak, e A
a
w
−1 = σ2Fo2 +(xP)2 +yP; P = (Fo2 +2Fc2)/3.
1,2,2,3,4,4-Hexa(tert-butyl)-1,3,2,4-
dialuminadisphosphacyclobutane (8)
◦
Half of the product 6 (above) was heated to 200 C in
vacuum. A yellow melt formed, and after a minute the melt
became colorless. After 5 min the melt turned grey indicating
decomposition. Part of the residue dissolved in diethyl ether,
and the insoluble material was removed by filtration. From
the filtrate colorless crystals of the trans-isomer 8a separated,
m. p. 76 – 78 ◦C.
Table 2 contains relevant crystallographic data and data
related to data collection and structure solution. CCDC
681783 (1) and 681762 (2) contain the supplementary crys-
tallographic 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.
The second half of the product 6 (above) was dissolved in
toluene (8 mL) and kept for 12 h at reflux. Then the toluene
was removed from the solution in vacuum, and the yellow
brown, honey-like residue was “crystallized” from pentane.
This produced a colorless powder. Yield: 140 mg (55 %)
of a mixture of the cis/trans isomers, 8a, 8b; m. p. 70 –
75 ◦C. – NMR (C6D6): 1H NMR: δ = 1.40 (trans, AlCMe3),
Acknowledgements
We thank Fond der Chemischen Industrie and Chemet-
all GmbH for the support of our research. Mr. P. Mayer was
very helpful in recording NMR data. Finally, we thank the
team of the departmental microanalytical laboratory for the
analytical data.
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