Structural aspects of chlorine-aluminium alkoxides

Article abstract of DOI:10.1002/zaac.201100060

LiAlH₄ and AlCl₃ reacted in a ratio 1:3 to obtain Cl₂AlH, which is stabilised by the addition of two equivalents of N-methylpiperidine (nmp) to form dichloroalane (1) as bis adduct of nmp. Compound 1 was allowed to react with 2,6-tBu-4-MeC₆H₂OH and HO^cHex in a 1:1 ratio to get compounds 2 and 3, respectively. Cl₂Al(2,6-tBu-4-MeC₆H₂O)(nmp) (2) is a monomer in which the central aluminium atom is tetracoordinate. Contrary to the parent compound 1, compound 2 is stabilised by only one nmp molecule. The larger bulk of the alkoxide in 2 prevents the second nmp molecule to reach the aluminium atom. Compound 3 crystallises as unique anionic tri-nuclear aluminium entity [Al₃Cl₆(OR)₄]^- [nmp ₂H]⁺ with a protonated nmp as countercation. The lesser bulk of the cyclohexanolate leads to a higher oligomerisation of ROAlCl ₂ (R = cyclohexyl). When a relatively bulkier alcohol, 1-methylcyclohexanol, was allowed to react with mixtures of LiAlH₄ and AlCl₃ prepared in 1:1 and 1:3 ratios in solution, compounds 4 and 5, respectively, were obtained. Both compounds ((HClAlOR)₂ (4) and (Cl₂AlOR)₂ (5), R = ^cHexMe-1)) are dimers with oxygen as bridging atom in the Al₂O₂ rings. All compounds 2, 3, 4, and 5 were structurally characterised by X-ray diffraction on single crystals. Copyright

Full text of DOI:10.1002/zaac.201100060

ARTICLE
DOI: 10.1002/zaac.201100060
Structural Aspects of Chlorine-Aluminium Alkoxides
Michael Veith,*[a,b] Hameed Ullah Wazir,[a,b] Tatjana Kirs,[a,b] Volker Huch,[b] and
Michael Zimmer[b]
In Memory of Professor Hans Georg von Schnering
Keywords: Alanes; Alcohols; Amines; Chlorine; X-ray diffraction
Abstract. LiAlH4 and AlCl3 reacted in a ratio 1:3 to obtain Cl2AlH, ium entity [Al3Cl6(OR)4]– [nmp2H]+ with a protonated nmp as counter-
which is stabilised by the addition of two equivalents of N-methylpi- cation. The lesser bulk of the cyclohexanolate leads to a higher oligo-
peridine (nmp) to form dichloroalane (1) as bis adduct of nmp. Com- merisation of ROAlCl2 (R = cyclohexyl). When a relatively bulkier
pound 1 was allowed to react with 2,6-tBu-4-MeC6H2OH and HOcHex alcohol, 1-methylcyclohexanol, was allowed to react with mixtures of
in a 1:1 ratio to get compounds 2 and 3, respectively. Cl2Al(2,6-tBu- LiAlH4 and AlCl3 prepared in 1:1 and 1:3 ratios in solution, com-
4-MeC6H2O)(nmp) (2) is a monomer in which the central aluminium pounds 4 and 5, respectively, were obtained. Both compounds
atom is tetracoordinate. Contrary to the parent compound 1, compound ((HClAlOR)2 (4) and (Cl2AlOR)2 (5), R = cHexMe-1)) are dimers with
2 is stabilised by only one nmp molecule. The larger bulk of the alkox- oxygen as bridging atom in the Al2O2 rings. All compounds 2, 3, 4,
ide in 2 prevents the second nmp molecule to reach the aluminium and 5 were structurally characterised by X-ray diffraction on single
atom. Compound 3 crystallises as unique anionic tri-nuclear alumin- crystals.
ligand(s) (bases) and the intermolecular interaction is hindered
Introduction
by the high bulk of the alkoxy group.[5,6] In the oligomers the
Alkoxy-aluminium chlorides of the general formula
oxygen of the alkoxy group acts as stabilising base towards
aluminium putting the chlorine ligands into terminal bonding
Clx(OR)3–xAl are of general interest due to their role in organic
synthesis. The high Lewis-acidic aluminium center is believed
positions. The degree of oligomerisation/polymerisation de-
to be responsible for catalytic activity in organic reactions, for
pends upon the steric bulk of the alkyl moiety. The most com-
example in ring opening polymerisations.[1,2] On the other
mon structural motif of aluminium chloride alkoxides are di-
hand, compounds containing Al–Cl and Al–OR bonds are of
mers and trimers. The dimeric alkoxy-aluminium chloride dis-
high interest as precursors for the synthesis of alumina through
playing a central four-membered Al2O2 ring also exists in
non-aqueous sol-gel processes.[3] Hydrid-modified alkoxyalu-
solution.[7,8] The trinuclear alkoxy-aluminium chlorides exhibit
minium chloride has been used successfully as single source
three different types of structures (Scheme 1). One of them has
precursor for preparation of metastable Hx(X)1–xAlO
material.[4] The hydride ligand leads to a significant decrease
in the decomposition temperature of the precursor upon a sub-
strate in a CVD (chemical vapour deposition) process.
a central six-membered cyclic skeleton which is puckered due
to the repulsion among the exocyclic chlorine and alkyl moie-
ties (Scheme 1; A).[9] The other tri-nuclear alkoxy-aluminium
chlorides have bicyclic four-membered Al2O2 structures in
which the central aluminium atoms are penta- (Scheme 1; B)
and hexacoordinate (Scheme 1; C) alongside with tetracoordi-
The molecular structures for alkoxy-aluminium chlorides are
primarily dominated by intermolecular oligomerisation
through Lewis acid-base interactions leading to dimers and tri-
mers. Very few examples of monomeric alkoxy-aluminium nate terminal aluminium atoms.[7,10,11] These types of molecu-
chlorides have been reported so far, in which the electron-defi-
cient aluminium metal atom is stabilised by electron donating
lar structures of alkoxy-aluminium chlorides may differ in their
Cl/Al/OR ratio to that of the starting compounds.[11] This pecu-
liarity is often ascribed to ligand scrambling and redistribution.
Here we report upon the synthesis and single crystal analysis
of different alkoxy-aluminium chlorides as well as hydride-
modified alkoxy-aluminium chlorides. The alkoxy groups
carry alkyl moieties of different steric bulk. Therefore, the mo-
lecular structures found are monomeric or oligomeric with the
aluminium metal atoms displaying coordination numbers of 4,
5, and even 6.
* Prof. Dr. Dr. M. Veith
E-Mail: michael.veith@inm-gmbh.de
[a] INM – Leibniz Institute for New Materials
Campus D2 2
66123 Saarbruecken, Germany
[b] Institute for Inorganic Chemistry
Saarland University
Postfach 15 11 50
66041 Saarbruecken, Germany
Z. Anorg. Allg. Chem. 2011, 637, 923–929
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M. Veith, H. Ullah Wazir, T. Kirs, V. Huch, M. Zimmer
ARTICLE
structures for 4 and 5 both displaying a central four-membered
Al2O2 ring (following section). The organic pendant groups are
1
confirmed by H and 13C NMR spectroscopy. From the num-
bers of resonances in the NMR spectrum of 4 it can be deduced
that it exists in two isomeric forms in solution with cis- and
trans-orientations of hydrogen and chlorine with respect to the
four-membered Al2O2 cycle. The Al–H bond in 4 is confirmed
by characteristic stretching vibration at 1905 cm–1 in its IR
spectrum.[4]
Scheme 1. Different structures exhibited by the tri-nuclear alkoxy-alu-
minium chlorides.[7,10–11]
Results and Discussion
Synthesis and Spectroscopic Analysis
The title compounds (2–5) were synthesised under nitrogen
using different synthetic routes. The precursor compound di-
chloroalane 1 is obtained as a monomeric bis adduct of N-
methylpiperidine (nmp). Following routes for similar
reactions,[12,13] AlCl3 and LiAlH4 in diethylether are mixed to-
gether in a 3:1 ratio to which nmp is added as stabilising base
(Equation (1)).
Scheme 2. Two step reactions for synthesis of 4 and 5.
In the 27Al NMR spectrum of 1 appears a single peak at
118 ppm in deutrated benzene; the peak does not fall into the
characteristic region of pentacoordinate aluminium atoms with
oxygen and halides as ligands. Therefore, we recorded the
spectrum in different solvents like e.g. diethylether as a poten-
tial base, but obtained almost the same δ-value. We attribute
this unusual shift (far from the usual value of 50 20 ppm)
to the double nitrogen coordination following arguments and
findings of Benn et al.[16] who described several pentacoordi-
nate complexes with nitrogen on the aluminium atom in the
range of more than 100 ppm. Of course, we cannot exclude
another explanation: the two nmp ligands may be in fast ex-
change so that the aluminium atom in 1 is tetracoordinate in
solution in contrast to the solid (see below).
Contrary to 1, the aluminium atom in 2 is tetracoordinate
deduced from the appearance of a single broad signal at
82.5 ppm in the 27Al NMR spectrum.[17] The bulky alkoxy
group (2,6-tBu-4-MeC6H2O) hinders the aluminium atom to be
accessed by a second stabilising base. Owing to the facile li-
gand scrambling in aluminium chloride alkoxides,[18] the solu-
tion NMR spectra of 3 are quite complex and difficult to corre-
late with the solid state data obtained from X-ray diffraction.
The 27Al NMR spectrum of 3 gives four signals at 4 ppm,
43 ppm, 92 ppm and 109 ppm. The signals at 92 ppm and
4 ppm correspond to that of tetracoordinate and hexacoordi-
nate aluminium atoms, respectively.[19] The third signal at
43 ppm is in the region of pentacoordinate aluminium
atoms.[19] It seems reasonable that 3 undergoes ligand scram-
1
The H and 13C NMR spectra clearly show the nmp ligand
in 1 and the Al–H bond is confirmed by a characteristic band
at 1785 cm–1 in the IR spectrum.[14] Compounds 2 and 3 can
be obtained from 1 by reaction of the corresponding alcohols,
c
HOR (R = 2,6-tBu-4-MeC6H2,2, and Hex,3) with elimination
of dihydrogen in a simple 1:1 ratio according to equation (2).
The hydrogen evolution is expressed by bubbles produced in
the reaction mixture after addition of alcohols to 1. Addition
of 2,6-tBu-4-MeC6H2OH to 1 gives rise to precipitation of col-
ourless crystals after reducing the volume of the soles which
are characterised as [Cl2Al(2,6-tBu-4-MeC6H2O)] with nmp as
further ligand on aluminium (2). Crystals of 3 are obtained at
room temperature as soon as the solution is concentrated by
pumping off the solvent. The obtained product 3 has a stoichi-
ometry, which deviates from the starting 1:1:2 ratio of Al/OR/
Cl. It indicates that some excess alcohol has reacted. The or-
1
ganic moieties in 2 and 3 are confirmed by H and 13C NMR
spectroscopy.
Compounds 4 and 5 are obtained following a two step reac- bling in solution giving two different products which are in
tion route (Scheme 2).[15] In a first step, appropriate amounts equilibrium to each other (Scheme 3). The fourth signal at
of LiAlH4 and AlCl3 are mixed in diethyl ether followed by 109 ppm is quite sharp and is thought to be due to the presence
the addition of alcohol in required stoichiometric amounts in of highly symmetrical [AlCl4]– (not shown in Scheme 3).[20]
the second step. Hydrogen evolution is indicated by the bub- The 27Al NMR spectrum recorded for compound 4 in deuter-
bles produced in the reaction mixtures. After storage, colour- ated benzene is unusual but matches well with the 27Al NMR
less crystals of 4 and 5 formed from the concentrated diethyle- spectra reported for structurally similar compounds.[17] Two
ther solutions at +4 °C. X-ray analyses reveal dimeric signals at 89 ppm and 100 ppm indicate two different alumin-
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Structural Aspects of Chlorine-Aluminium Alkoxides
ium atoms of coordination number 4. The signal at 100 ppm ure 2). The central aluminium atom has highly distorted tetra-
is due to the tetracoordinate aluminium atom of compound hedral arrangement. Substituting hydrogen by a bulky alkoxy
4.[17] The signal at 89 ppm could be due to the other cis/trans group, OC6H2But-2,6-Me-4, in 1 reduces the coordination
isomer but more likely seems to be compatible with the com- number from five (1) to four in 2 by expelling one of the nmp
pound [Cl2Al(OcHexMe-1)]2, which may be present in the so- ligands. Only very few examples of monomeric dichloroalu-
lution as a result of ligand exchange; as it is well-known, alu- minium aryloxides can be found in the literature.[5,6] Com-
minium chloride alkoxides are susceptible to rapid ligand pound 2 has a similar structure to that of Cl2Al(OR)·Et2O (R =
exchange in solution.[18] Unfortunately, we could not obtain C6H2But-2,6-Me-4),[5] the only difference being the stabilising
well-dissolved temperature dependent NMR spectra for 4. base. The Al–Cl bond lengths are in the range reported for
Contrary to that of 4, the 27Al NMR spectrum of 5 has a single terminal Al–Cl bonds.[5] The Al–Cl and Al–O bond lengths are
broad signal at 89 ppm, which corresponds to that of structur- longer by approximately 0.011(1) Å and 0.013(1) Å, respec-
ally identical compounds, [Cl2Al(OR)]2 also having tetracoor- tively, compared to those in Cl2Al(OR)·Et2O (R = C6H2But-
dinate aluminium atoms.[11,17]
.
2,6-Me-4). This may be due to the relatively bulky stabilising
base nmp.
Compound 3 crystallises at room temperature by concentra-
tion of the mother liquor. As result of X-ray structure determi-
nation, 3 (Figure 3) is found to be composed of a cation-anion
pair and a diethylether molecule in its crystal lattice. The re-
sulting stoichiometry of OR/Al/Cl differs from the starting
1:1:2
ratios.
The
anion
has
the
composition
Scheme 3. Proposed equilibrium in solution between the two com-
pounds,
[(Cl2Al)2(Cl2Al(OcHex)4)]–[H(NMP)2]+
and
[(Cl2Al)3(OcHex)4]– and is electronically neutralised by the
cation [H(nmp)2]+. The tri-nuclear anionic part of the com-
pound has almost C2 point symmetry with the pseudo twofold
axis running through Al(1). The hexacoordinate central atom
Al(1) has highly distorted octahedral arrangement composed
of two terminal chlorine atoms and four bridging oxygen at-
oms of the cyclohexoxy group. The bridging Al(1)–O bond
lengths are longer than the bridging Al(2)–O and Al(3)–O
bond lengths reflecting the higher coordination number at
Al(1) compared to Al(2) and Al(3). Another interesting feature
is the trans effect of the chlorine ligands at Al(1) on the Al–
O bond lengths, as we find longer distances for the alkoxy
groups which are trans-oriented to the terminal chlorine atoms.
As also found for Al–O, the Al–Cl bond lengths for the chlo-
rine atoms attached to the hexacoordinate aluminium atom are
longer than those attached to the tetra-coordinated aluminium
atoms. As usual, the most acute angles in the Al2O2 rings are
found at the bigger aluminium atoms (compared to oxygen).
The sum of angles around oxygen atoms are in the range of
359.8(2)–359.9(2)° indicating that all the oxygen atoms have
trigonal planar arrangement (sp2 hybridisation).[22] The anionic
molecule has a counterpart cation formed by the interaction of
a proton, which is split off the alcohol, with nmp. The so
formed ammonium type Hnmp+ is bonded to a second nmp
molecule through hydrogen bonding (N…N = 2.82 Å).
[(Cl2Al)2(ClAl(OcHex)4)]·nmp·HCl.
Single X-ray Structure Analyses
Single crystals of 1 and the title compounds (2–5) were iso-
lated and analysed by the single-crystal X-ray diffraction
method. The most relevant data for compounds 1–5 are sum-
marised in Table 1.
The pertinent bond angles and lengths of compounds 1–3 are
presented in Table 2 and those of compounds 4 and 5 are given
in Table 3.
The structure of compound 1 is new in the sense that there
is no reported example of the type, [Cl2AlH·2nmp]. The double
Lewis base adduct of Cl2AlH (Figure 1) has a crystallographic
symmetry plane running through the Al–H an Al–N bonds and
in approximation a C2v point symmetry. The molecular struc-
ture of 1 has resemblance to that of the earlier reported mono-
chloroalane.[14,21] The central aluminium atom is pentacoordi-
nate having distorted trigonal bipyramidal arrangement. The
nitrogen atoms are at the apical positions whereas the chlorine
atoms and hydrogen occupy the equatorial positions. Contrary
to the monochloroalane,[14] the N–Al–N entity of 1 has a re-
markable deviation from linearity (8.49(1)°). The relatively
higher degree of deviation from linearity could be related to
the presence of two chlorine atoms against one chlorine atom
in case of the monochloroalane.[14] The Al–Cl(1) bond length
is 2.196(1) Å, which is shorter by 0.03 Å to that in
H2AlCl · 2nmp. The Al–N(1) and Al–N(2) bond lengths of
2.163(1) Å and 2.175(1) Å, respectively are long for donor
bonds and are even longer than those observed in
H2AlCl·2nmp. This may be due to the second chlorine atom
which increases the steric demand around the aluminium atom
and repels the amine groups.
The molecular structures of 4 and 5 obtained from single
crystal analyses are depicted in Figure 4 and Figure 5, respec-
tively. Both molecules are centrosymmetric dimers with central
four-membered Al2O2 rings. The aluminium atoms are tetraco-
ordinated in 4 and 5 having distorted tetrahedral geometries.
The bridging Al–O and terminal Al–Cl bond distances are in
their characteristic ranges.[4,11] Whereas the aluminium atom
in 4 has three different ligands (H, Cl, OR), the aluminium
atom in 5 only has two (Cl, OR). In both compounds the Al–
O distances within the ring are almost identical. The sum of
The asymmetric compound 2, which is the derivative of
compound 1 by exchange of hydrogen through alkoxy, is a angles at oxygen atoms in 4 and 5 approaches 360°, which
monomer in which the aluminium atom is tetracoordinate (Fig- indicates sp2 hybridisation for the oxygen atoms.[22] The higher
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925

M. Veith, H. Ullah Wazir, T. Kirs, V. Huch, M. Zimmer
ARTICLE
Table 1. Crystallographic data for compounds 1–5.
compound number
1
2
3
4
5
Empirical formula
Formula weight
Temp /K
Wavelength /Å
Crystal system
Space group
a /Å
C12H27AlCl2N2
297.24
130(2) K
0.71073
orthorhombic
Pnma
10.9807(9)
10.4692(8)
14.132(1)
90
1624.6(2)
4
C21H36AlCl2NO
416.39
C40H81Al3Cl6N2O5
963.71
C14H28Al2Cl2O2
353.22
C14H26Al2Cl4O2
422.11
152(2)
142(2)
152(2)
152(2)
0.71073
monoclinic
P21/c
0.71073
monoclinic
P21/c
0.71073
monoclinic
P21/c
0.71073
monoclinic
P21/c
10.1847(6)
15.817(1)
14.824(1)
106.80(1)
2286.0(3)
4
11.9289(9)
17.069(1)
25.110(2)
94.975(4)
5093.5(7)
4
8.9335(6)
8.2062(6)
13.052(1)
105.054(3)
924.0(1)
2
9.0178(4)
8.6817(4)
13.1491(5)
104.821(2)
995.19(7)
2
b /Å
c /Å
β /deg
V /Å3
Z
Density calcd. /Mg·m-3 1.215
1.210
1.257
1.270
1.409
Abs coefficient /mm–1 0.438
0.333
0.429
0.445
0.686
F(000)
640
896
2064
376
440
Crystal size /mm
θ-range for data
collection /°
Index ranges
0.59 × 0.41 × 0.20
2.35 to 36.79
0.50 × 0.32 × 0.30
1.93 to 27.94°
0.40 × 0.10 × 0.09
1.44 to 27.14°
0.29 × 0.26 × 0.06
2.36 to 27.83°
0.47 × 0.37 × 0.31
2.34 to 34.95°
–18 ≤ h ≤ 18
–17 ≤ k ≤ 17
–23 ≤ l ≤ 11
–13 ≤ h ≤ 13
–13 ≤ k ≤ 20
–19 ≤ l ≤ 19
21609
–15 ≤ h ≤ 15
–21 ≤ k ≤ 20
–32 ≤ l ≤ 32
43139
–11 ≤ h ≤ 10
–10 ≤ k ≤ 7
–16 ≤ l ≤ 17
7751
–9 ≤ h ≤ 14
–13 ≤ k ≤ 10
–21 ≤ l ≤ 21
16344
Reflections collected 17621
Independent reflections 4237 [0.0237]
[I > 2σ(I)] (Rint)
5472[0.0451]
11234[0.0820]
2190[0.0464]
4356[0.0491]
Completeness to θ /% 99.9
Absorption correction Multiscan
99.8
99.5
99.9
99.8
Multiscan
Multiscan
Multiscan
Multiscan
Max. and min.
Transmission
Refinement method
0.9183 and 0.7815
0.9056 and 0.8521
0.9624 and 0.8480
0.9755 and 0.8802
0.8166 and 0.7406
Full-matrix least-
Full-matrix least-
squares on F2
5472 / 0 / 379
Full-matrix least-
squares on F2
11234 / 0 / 513
Full-matrix least-
squares on F2
2190 / 0 / 147
Full-matrix least-
squares on F2
4356 / 0 / 152
squares on F2
Data/restraints/ parame-4237 / 0 / 149
ters
GOF in F2
1.028
1.061
1.003
1.066
1.051
R1, wR2 [I > 2σ(I)]
R1, wR2 (all data),
largest diff peak
and hole /e·Å–3
0.0331, 0.0916
0.0456, 0.0999
0.377 and –0.547
0.0519, 0.1323
0.0715, 0.1447
0.784 and –0.629
0.0501, 0.0908
0.1073, 0.1076
0.666 and –0.671
0.0459, 0.1156
0.0719, 0.1288
0.474 and –0.415
0.0313, 0.0835
0.0394, 0.0880
0.413 and –0.296
chlorine content in 5 compared to 4 is reflected by a shorter of higher coordination oligomers. To satisfy the electronic defi-
Al–O distance (difference: 0.016(1) Å).
ciency at the aluminium atoms, the oxygen atom of the alkox-
ide group behaves as a bridging base. Contrarily, when a steri-
cally less bulky alkoxide, cyclohexanol, is used, the resulting
molecule 3 is a “trimer”, which had trapped a further alcohol,
split into RO– and H+ with the base nmp.
Conclusions
Either intermediate chloroalanes from the reaction of LiAlH4
and AlCl3 or the base stabilised chloroalane Cl2HAl·2nmp (1)
may be used to introduce alcohol groups by hydrogen elimina-
tion. As the chloroalanes are prone to ligand scrambling and
interconversion, not only simple chloro alkoxyalanes may be
Experimental Section
All reactions were carried out under dry nitrogen using modified
obtained as exemplified by compound 3. The electronic defi- Schlenk vacuum line techniques. LiAlH4 and 2,6-di-tert-butyl-4-meth-
ylphenol were purchased from Aldrich and used as such while AlCl3
from Aldrich was sublimed before use. Cyclohexanol and 1-methylcy-
clohexanol were distilled from magnesium turnings and kept over mo-
lecular sieves. Diethylether, benzene and all other hydrocarbon sol-
vents were freshly distilled from Na/benzophenone under N2 and kept
under N2/Na wires. NMR spectra (1H and 13C) were recorded with a
Bruker AC200 NMR spectrometer with TMS (0.00 ppm) as internal
ciency at the aluminium atom and the bulk of the stabilising
base and/or alkoxide control the degree of polymerisation of
the alkoxyalanes.
Compounds 1 and 2 are base-stabilised monomers in solution
as well as in solid state. The lower coordination number of
aluminium in 2 is due to the higher bulk of the alkoxy group.
When a stoichiometric amount of 1-methylcyclohexanol is
added into the stoichiometric solutions of LiAlH4 and AlCl3,
dimeric compounds 4 and 5 are obtained. The steric bulk of
1
standard. The H and 13C NMR spectra were referenced to the proton
signals and carbon resonances of [D6]benzene, 7.16 and 128.0 ppm,
respectively. The 27Al NMR spectra were recorded with a multinuclear
the alkoxide moiety is sufficient to prevent from the formation Bruker ACP 200 NMR spectrometer at 52.1 MHz. IR spectra (4000–
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Structural Aspects of Chlorine-Aluminium Alkoxides
Table 2. Pertinent Bond Lengths /Å and Angles /deg of Compounds 1–3.
compound 1
compound 2
Bond Length
Al1–N1
Bond Length
Al1–O1
2.163(1)
2.175(1)
Al1–Cl1
Al1–H1
2.1963(3)
1.535(1)
1.713(1)
1.998(2)
Al1–Cl1
Al1–Cl2
2.1258(9)
2.1422(9)
Al1–N2
Al1–N1
Angle
Angle
N1–Al1–N2
N1–Al1–Cl1
N2–Al1–Cl1
171.51(4)
92.61(2)
92.09(2)
O1–Al1–N1
O1–Al1–Cl1
N1–Al1–Cl1
107.74(8)
111.66(6)
113.00(7)
O1–Al1–Cl2
N1–Al1–Cl2
Cl1–Al1–Cl2
118.45(6)
97.40(7)
107.91(4)
Cl1a–Al1–Cl1
112.72(2)
compound 3
Bond Length
Al1–O3
1.928(2)
1.930(2)
1.976(2)
1.991(2)
Al1–Cl1
Al1–Cl2
Al2–O2
Al2–O1
2.265(2)
2.286(2)
1.761(1)
1.778(1)
Al2–Cl3
Al2–Cl4
Al3–O4
Al3–O3
2.117(1)
2.128(1)
1.764(2)
1.774(2)
Al3–Cl5
Al3–Cl6
2.117(1)
2.131(1)
1.93(3)
0.89(3)
Al1–O1
…
Al1–O2
Al1–O4
N1 H1
N2–H1
Angle
O3–Al1–O1
O3–Al1–O2
O1–Al1–O2
O3–Al1–O4
O1–Al1–O4
O2–Al1–O4
O3–Al1–Cl1
O1–Al1–Cl1
160.46(8)
90.93(8)
75.19(8)
74.76(7)
91.00(8)
88.81(8)
96.95(6)
96.92(6)
O2–Al1–Cl1
O4–Al1–Cl1
O3–Al1–Cl2
O1–Al1–Cl2
O2–Al1–Cl2
O4–Al1–Cl2
Cl1–Al1–Cl2
O2–Al2–O1
90.79(6)
171.79(6)
96.63(6)
96.85(6)
172.01(7)
90.69(6)
90.84(4)
84.66(8)
O2–Al2–Cl3
O1–Al2–Cl3
O2–Al2–Cl4
O1–Al2–Cl4
Cl3–Al2–Cl4
O4–Al3–O3
O4–Al3–Cl5
O3–Al3–Cl5
115.63(7)
116.43(7)
115.91(7)
114.29(7)
108.57(4)
84.53(8)
O4–Al3–Cl6
O3–Al3–Cl6
Cl5–Al3–Cl6
Al2–O1–Al1
Al2–O2–Al1
Al3–O3–Al1
Al3–O4–Al1
115.90(7)
114.09(7)
107.87(4)
100.60(9)
99.48(9)
101.38(9)
99.33(8)
116.47(7)
116.84(7)
Table 3. Pertinent bond lengths /Å and angles /deg of compounds 4 and 5.
compound 4
compound 5
Bond Length
Al–Cl
Bond Length
Al1–O1a
2.1197(9)
1.640(3)
1.822(2)
Al–Oa
1.823(2)
2.766(1)
1.8043(7)
1.8083(7)
Al1–Cl1
Al1–Cl2
2.0919(4)
2.0968(4)
Al–H
Al…Ala
Al1–O1
Al–O
Angle
O–Al–Oa
O–Al–Cl
Oa–Al–Cl
H–Al–Cl
H–Al–O
Angle
81.30(8)
C1–O–Al
C1–O–Ala
Al–O–Ala
130.1(1)
130.0(1)
98.70(8)
O1a–Al1–O1
O1a–Al1–Cl1
O1–Al1–Cl1
O1a–Al1–Cl2
O1–Al1–Cl2
82.34(3)
113.21(2)
114.90(3)
115.71(3)
113.72(3)
Cl1–Al1–Cl2
C1–O1–Al1a
C1–O1–Al1
Al1a–O1–Al1
113.47(2)
131.62(5)
130.27(5)
97.76(3)
111.35(6)
112.81(6)
109.67(5)
119.19(5)
Figure 1. Molecular structure of [Cl2Al(H)·2nmp] (1) with 50 % ther-
mal ellipsoids.
Figure 2. Molecular structure of [Cl2Al(2,6-tBu-4-MeC6H2O)]·nmp
(2) with 50 % thermal ellipsoids.
400 cm–1) were collected with a Varian 2000 FT-IR spectrometer. Ele-
mental (C, H and N) analyses were carried out using a LECO CHN
900 elemental analyser. The Al and Cl contents were determined by
complexometric and titrimetric techniques.[23,24]
ochromated Mo-Kα X-ray radiation (λ = 0.711 Å). The crystal struc-
The single-crystal X-ray diffraction analyses were performed with a tures were solved by direct methods and refined by full-matrix least-
BrukerAXS X8 Apex II diffractometer at –150 °C using graphite-mon- squares on F2 using the SHELX software package for crystal structure
Z. Anorg. Allg. Chem. 2011, 923–929
© 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
www.zaac.wiley-vch.de
927

M. Veith, H. Ullah Wazir, T. Kirs, V. Huch, M. Zimmer
ARTICLE
filtration and the volume of the solvents was reduced at low pressure
to allow the formation of 4.34 g (70 %) of colourless crystals of
Cl2AlH·2nmp (1).
1
NMR (C6D6, TMS): H NMR (200 MHz): δ = 2.42–2.37 (m, α-CH2–
, nmp), 2.08 (s, –CH3, nmp), 1.25–1.14 (m, β-CH2–, nmp), 1.08–1.00
(m, γ-CH2–, nmp). 13C NMR (50.3 MHz): δ = 54.17 (s, α-CH2–, nmp),
42.59 (s, –CH3, nmp), 23.14 (s, β-CH2–, nmp), 22.14 (s, γ-CH2–, nmp).
27Al NMR: δ = 118 (w1/2 = 810 Hz). IR: (Al–H) ν = 1785 cm–1.
Elemental Analysis: Calcd. C 48.49; H 9.16; N 9.42; Al 9.08; Cl
23.85. Found C 48.66; H 10.01; N 9.00; Al 8.90; Cl 24.20 %.
Figure 3. Molecular structure of [(Cl2Al)3(OcHex)4)]–[H(nmp)2]+·Et2O
(3) with 50 % thermal ellipsoids.
[Cl2Al(2,6-tBu-4-MeC6H2O)·nmp] (2): Compound 1 (Cl2AlH·2nmp)
(0.55 g, 1.85 mmol) was dissolved in diethyl ether (30 mL) and the
solution was added to 2,6-tBu-4MeC6H2OH (0.407 g, 1.85 mmol) in
diethyl ether (30 mL). Evolution of hydrogen was observed and the
reaction was completed by stirring for 6 hours at room temperature.
The solution was concentrated by removing the solvent under reduced
pressure. Fine crystals of 2 were obtained with a yield of 0.67 g (88 %)
after storing the concentrated solution for approximately 12 hours in a
refrigerator at +4 °C.
NMR (C6D6, TMS): 1H NMR (200 MHz): δ = 6.89 (s, γ-CH, aryl
ring), 2.24 (m, α-CH2–, nmp), 2.11 (s, –CH3, nmp), 2.10 (s, –CH3, aryl
ring), 1.35 (s, –CH3, tert-butyl), 1.88–1.42 (m, β- & γ-CH2–, nmp),
13C NMR (50.3 MHz): δ = 151.67 (s, α-C, alkoxy), 139.03 (s, β-C,
alkoxy), 125.76 (s, γ-C, alkoxy), 130.00 (s, δ-C, alkoxy), 53.61 (s, α-
CH2-, nmp), 39.16 (s, –CH3, alkoxy), 35.40 (s, –CH3, nmp), 34.05 (s,
C(CH3)3, alkoxy), 30.30 (s, C(CH3)3, alkoxy), 21.13 (s, β-CH2–, nmp),
17.97 (s, γ-CH2–, nmp). 27Al NMR: δ = 82.5 (w1/2 = 1550 Hz). Ele-
mental Analysis: Calcd. C 60.57; H 8.71; N 3.36; Al 6.48. Found C
61.79; H 8.67; N 2.34; Al 6.35 %.
Figure 4. Molecular structure of [ClAl(H)(OcHex-Me)]2 (4) with 50 %
thermal ellipsoids.
[(Cl2Al)3(μ-OcHex)4]– [H(nmp)2]+·Et2O (3): The alcohol HOcHex
(0.72 mL, 6.88 mmol) was dissolved in diethyl ether (30 mL) and the
solution was added to a solution of compound 1 (2.051 g, 6.88 mmol)
in diethyl ether (30 mL) under evolution of hydrogen. The reaction
was completed by stirring for 6 hours at room temperature. The solu-
tion was concentrated by removing the solvent under reduced pressure.
Fine crystals of 3 were obtained after storing the solution for approxi-
mately 12 hours in a refrigerator at +4 °C with a yield of 1.96 g
(89 %).
1
NMR (C6D6, TMS): H NMR (200 MHz): δ = 3.31–3.18 (q, –CH2–,
Figure 5. Molecular structure of [Cl2Al(OcHex-Me)]2 (5) with 50 %
thermal ellipsoids.
c
diethyl ether), 3.17 (m, α-CH, Hex), 2.21–2.17 (m, α-CH2–, nmp),
c
2.10–1.37 (m, –CH2–, Hex), 2.06 (s, –CH3, nmp), 1.49–1.40 (m, β-
CH2–, nmp), 1.27–1.21 (m, γ-CH2–, nmp), 1.01–0.95 (t, –CH3, diethyl
ether). 13C NMR (50.3 MHz): δ = 66.28 (s, –CH3, diethyl ether), 78.68
(s, α-CH, alkoxy), 36.30 (s, β-CH2–, alkoxy), 25.62 (s, δ-CH2–, al-
koxy), 22.56 (s, γ-CH2–, alkoxy), 53.89 (s, α-CH2–, nmp), 34.94 (s,
–CH3, nmp), 24.92 (s, β-CH2–, nmp), 21.41 (s, γ-CH2–, nmp), 15.92
(s, –CH2–, diethyl ether). 27Al NMR: δ = 4.5 (w1/2 = 150 Hz), 43.7
(w1/2 = 450 Hz), 92.3 (w1/2 = 890 Hz), 109.6 (w1/2 = 40 Hz). Elemen-
tal Analysis: Calcd. C 49.85; H 8.47; N 2.93; Al 8.40. Found C 50.79;
H 7.67; N 2.34; Al 8.69 %.
solution and refinement.[25] All non-hydrogen atoms were refined with
anisotropic thermal parameters in the later cycles of refinement. Fur-
ther details of crystal structure determination are available from
CCDC.[26]
Syntheses
[Cl2AlH·2nmp] (nmp = N-methylpiperidine) (1): To a suspension of [ClAl(H)(OcHexMe-1)]2 (4): To a suspension of lithium aluminium
lithium aluminium hydride (0.198 g, 5.22 mmol) in diethyl ether hydride (0.268 g, 7.06 mmol) in diethyl ether (75 mL) was added a
(50 mL) was added a solution of aluminium trichloride (2.086 g, solution of aluminium trichloride (0.940 g, 7.06 mmol) prepared in
15.7 mmol) in diethyl ether (50 mL). After 1 h stirring, an excess of diethyl ether (75 mL) under cooling. After 1 h stirring, 1-methylcyclo-
N-methylpiperidine (nmp) (5.07 mL, 41.7 mmol) was added drop by hexanol (1.76 mL, 14.12 mmol) was added drop by drop to the reac-
drop to the mixture with cooling (ice bath) and stirred for additional tion mixture and stirred for additional 3 h. The volume of this solution
1 h. Hexane (ca. 100 mL) was added to the resulting mixture to com- was reduced to its half by removing the solvent under low pressure
plete the precipitation of lithium chloride salt, which was separated by and afterwards hexane (50 mL) was added to the resulting mixture to
928
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© 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
Z. Anorg. Allg. Chem. 2011, 923–929

Structural Aspects of Chlorine-Aluminium Alkoxides
[4] M. Veith, N. Köhler, Proc. Electrochem. Soc. 2005, 768.
[5] M. D. Healy, J. W. Ziller, A. R. Barron, Organometallics 1992,
11, 3041.
complete the precipitation of lithium chloride. The lithium chloride
salt was separated by filtration and the volume of the filtrate was re-
duced under reduced pressure to allow the formation of 2.15 g
(86.34 %) of colourless crystals of [ClAl(H)(OR)]2 (4) at +4 °C.
[6] S. Schulz, H. W. Roesky, M. Noltemeyer, H.-G. J. Schmidt, J.
Chem. Soc., Dalton Trans. 1995, 177.
[7] S. Szumacher, A. R. Kunicki, I. Madura, J. Zachara, J. Orga-
nomet. Chem. 2003, 682, 196.
[8] K. B. Starowieyski, S. Pasynkiewicz, M. Skowronska, J. Orga-
nomet. Chem. 1971, 31, 149.
[9] N. W. Mitzel, C. Lustig, Z. Naturforsch. 2003, 58b, 489.
[10] A. I. Yanovsky, V. A. Kozunov, N. Ya. Turova, N. G. Furmanova,
Y. T. Struchkov, Dokl. Akad. Nauk SSSR (Russ.) 1999, 244, 119.
[11] Z. Moravec, R. Sluka, M. Necas, V. Jancik, J. Pinkas, Inorg.
Chem. 2009, 48, 8106.
NMR (C6D6, TMS): 1H NMR (C6D6): δ = 1.34 (s, –CH3), 1.36 (s,
–CH3), 1.7–0.9 (m, –CH2–ring). 13C NMR (C6D6): δ = 82.25 (s, α-
CH, ring), 82.27 (s, α-CH2–), 39.74 (s, β-CH2–, ring), 39.56 (s, β-
CH2–, ring), 24.31 (s, –CH3), 22.78 (s, –CH3). 27Al NMR: δ = 100.9.
IR: (Al–H) ν = 1905 cm–1; Elemental Analysis: Calcd. C 47.60; H
7.99; Al 15.28; Cl 20.07. Found C 42.45; H 7.29; Al 15.36; Cl 19.72
%.
[Cl2Al(OcHexMe-1)]2 (5): To a suspension of lithium aluminium hy-
dride (0.104 g, 2.77 mmol) in diethyl ether (75 mL) was added a solu-
tion of aluminium trichloride (1.099 g, 8.24 mmol) in diethyl ether
(75 mL) under cooling. After 1 h stirring, 1-methylcyclohexanol
(1.36 mL, 10.95 mmol) was added drop by drop to the above mixture
and stirred for additional 3 h. The volume of the solution mixture was
reduced to its half by removing diethylether under reduced pressure
and afterwards hexane (50 mL) was added to the resulting mixture to
complete the precipitation of lithium chloride. The lithium chloride
salt was separated by filtration and the volume of the filtrate was re-
duced under low pressure to allow the formation 1.75 g (75.75 %) of
colourless crystals of [Cl2Al(OR)]2 (5).
[12] E. Wiberg, M. Schmidt, Z. Naturforsch. 1951, 6b, 333.
[13] E. Wiberg, M. Schmidt, Z. Naturforsch. 1951, 6b, 458.
[14] M. Veith, D. Kolano, T. Kirs, V. Huch, J. Organomet. Chem.
2010, 695, 1074.
[15] H. Nöth, H. Suchy, Z. Anorg. Allg. Chem. 1968, 358, 44.
[16] R. Benn, A. Rufinska, Angew. Chem. 1986, 98, 851.
[17] N. Köhler, Dissertation, Saarland University, 2007.
[18] F. Belanger-Gariepy, K. Hoogsteen, V. Sharma, J. D. Wuest, In-
org. Chem. 1991, 30, 4140.
[19] R. Benn, E. Janssen, H. Lehmkuh, A. Rufinska, J. Organomet.
Chem. 1987, 333, 155.
[20] Z. Cerny, J. Machacek, J. Fusek, B. Casensky, O. Kriz, D. G.
Tuck, Inorg. Chim. Acta 2000, 300–302, 556.
[21] C. Jones, P. C. Junk, M. L. Cole, Main Group Met. Chem. 2001,
24, 249.
1
NMR (C6D6, TMS): H NMR (C6D6): δ = 1.47 (s, –CH3), 1.87–1.41
(m, ring-CH2–). 13C NMR: δ = 87.44 (s, α-CH), 40.62 (s, β-CH2–),
25.21 (s, γ-CH2–), 24.17 (s, δ-CH2–). 27Al NMR: δ = 89. IR: (C–H)
ν = 2936 cm–1. Elemental Analysis: Calcd. C 39.83; H 6.21; Al 12.78;
Cl 33.59. Found C 38.46; H 5.40; Al 11.99; Cl 34.05 %.
[22] H. Nöth, A. Schlegel, J. Knizek, H. Schwenk, Angew. Chem. Int.
Ed. Engl. 1997, 36, 2640.
[23] Komplexometrische Bestimmungsmethoden mit Titriplex, Merck,
3. Auflage.
[24] E. Gerdes, Qualitative Anorganische Analyse, Verlag Vieweg,
Braunschweig, Germany, 1995.
[25] G. M. Sheldrick, Acta Crystallogr., Sect. A 2008, 64, 112.
[26] Full data of the X-ray structure determinations can be obtained
by the Cambridge Crystallographic Data Centre, 12 Union Road,
Cambridge CB2 1EZ, UK (Fax: +44-12233-36066; E-Mail: de-
posit@ccdc.cam.ac.uk): 1: 808694, 2: 808695, 3: 808696, 4:
808697, 5: 808698.
References
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ecules 2001, 34, 3159.
[2] M. H. Chisholm, J. Gallucci, D. Navarro-Llobet, H. Zhen, Poly-
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[3] Y. De. Hazan, G. E. Shter, Y. Cohen, C. Rottman, D. Avnir, G. S.
Grader, J. Sol-Gel Sci. Technol. 1999, 14, 233.
Received: January 31, 2011
Published Online: April 14, 2011
Z. Anorg. Allg. Chem. 2011, 923–929
© 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
www.zaac.wiley-vch.de
929