Tetrametallic D3-symmetric alkoxide molecules containing aluminum

Article abstract of DOI:10.1021/om980900c

A new series of aluminum alkoxide molecules of formula [Al{(μ-OEt)₂AlR₂}₃], where R = Me (1), Et (2), ⁱBu (3), and [Al{(μ-OEt)₂GaR₂}₃], where R = Me (4) and Et (5), have been synthesized and fully characterized. In pure form 1, 2, and 4 are crystalline solids. However, in the presence of a small amount of solvent or impurity all of the compounds exist as oils. They were characterized by ¹H NMR, IR, elemental analysis, mp, and single-crystal X-ray diffractometry for compounds 1, 2, and 4.

Full text of DOI:10.1021/om980900c

976
Organometallics 1999, 18, 976-981
Tetr a m eta llic D3-Sym m etr ic Alk oxid e Molecu les
Con ta in in g Alu m in u m
David A. Atwood,* J olin A. J egier, Shengming Liu, Drew Rutherford,
Pingrong Wei, and Robert C. Tucker†
Department of Chemistry, The University of Kentucky, Lexington, Kentucky 40506-0055, and
Praxair Surface Technologies, Inc., 1500 Polco Street, Indianapolis, Indiana 46224
Received November 3, 1998
A new series of aluminum alkoxide molecules of formula [Al{(µ-OEt)2AlR2}3], where R )
i
Me (1), Et (2), Bu (3), and [Al{(µ-OEt)2GaR2}3], where R ) Me (4) and Et (5), have been
synthesized and fully characterized. In pure form 1, 2, and 4 are crystalline solids. However,
in the presence of a small amount of solvent or impurity all of the compounds exist as oils.
1
They were characterized by H NMR, IR, elemental analysis, mp, and single-crystal X-ray
diffractometry for compounds 1, 2, and 4.
In tr od u ction
ies7,10,11 into the structure12 of [Al(OiPr)3]4, which is
tetrametallic (below). A wide range of heterobimetallic
complexes [M{(µ-OR)2Al(OR)2}3] (where M ) gallium,
indium, transition metal,13 or lanthanide14 and R )
alkyl) also adopt a Mitsubishi structure. These previ-
ously reported complexes may be viewed as homoleptic
metal alkoxides, whereas those reported herein are alkyl
group 13 alkoxides.
The search for a unimolecular precursor to Al2O3 is
somewhat problematic since any relevant molecules
must be crafted to incorporate an Al/O ratio of 2:3. This
is a rare ratio for the group 13/16 elements, which
generally form compounds having stoichiometries of 1:1
1
([R2AlOR′]n or [RAlO]n ), 1:2 ([RAl(OR′)2]n), and 1:3 ([Al-
(OR′)3]n) (where n is commonly 2, 3, and 4).2 Previously
employed precursors to Al2O3 have almost always
contained an excess of oxygen (or have been used with
a second oxygen source such as H2O). This is true in
some recently reported precursors of the type Al(acac)3,3
Al(OOCR)3,4 and Al(OR)3 (R ) alkyl). These types of
5
precursors, which were all used in the gas phase, have
met with a measure of success in the fabrication of
aluminum oxide thin films for use as passivating layers
and insulating films in electronic devices.6
This article details attempts to synthesize molecules
that contain a group 13:oxygen stoichiometry of 2:3. The
resulting complexes are tetrameric with a core of group
13 element and O atoms in the shape of the emblem of
the Mitsubishi company.7 They are of formula [Al{(µ-
OEt)2AlR2}3], where R ) Me (1), Et (2), iBu (3), and [Al-
{(µ-OEt)2GaR2}3], where R ) Me (4) and Et (5). Only
two such molecules, [Al[{2-(OCH2)SC4H3)2}2AlMe2]3]8
and [Al{(µ-OR)2AlMe2}3] (where R ) 10-undecene),9
have been previously reported. However, as a class these
molecules have as a foundation the extensive stud-
Resu lts a n d Discu ssion
Syn th esis a n d Ch a r a cter iza tion . Compounds 1-5
(below) are prepared by combining the appropriate alkyl
group 13 reagent with aluminum triethoxide. The initial
(8) Oliver, J . P.; Kumar, R. Polyhedron 1990, 9, 409. Kumar, R.;
del Mel, V. S. J .; Sierra, M. L.; Hendershot, D. G.; Oliver, J . P.
Organometallics 1994, 13, 2079.
(9) Turunen, J .; Pakkanen, T. T.; Lofgren, B., J . Mol. Catal. A 1997,
123, 35.
(10) J oung, W. G.; Hartung, W. H.; Krossley, F. S. J . Am. Chem.
Soc. 1936, 58, 100.
(11) It was first proposed to be tetrametallic by: Bradley, D. C.
Nature 1958, 182, 1211. Bradley, D. C. Adv. Chem. Ser. 1959, 23, 10.
(12) Turova, N. Y.; Kozunov, V. A.; Yanovskii, A. I.; Bokii, N. G.;
Struchkov, Y. T.; Tarnopol’ski, B. L. J . Inorg. Nucl. Chem. 1979, 41,
5.
(1) Mason, M. R.; Smith, J . M.; Bott, S. G.; Barron, A. R. J . Am.
Chem. Soc. 1993, 115, 4971, and references therein.
(2) Oliver, J . P. In Coordination Chemistry of Aluminum; Robinson,
G. H., Ed.; VCH Publishers: New York, 1993; Chapter 4. Taylor, M.
J .; Brothers, P. J . In Chemistry of Aluminum, Gallium, Indium and
Thallium; Downs, A. J ., Ed.; Chapman and Hall: London, 1993; pp
148-152 (and references therein).
(3) Temple, D.; Reisman, A. J . Electron. Mater. 1990, 19, 995. Kim,
J . S.; Marzouk, H. A.; Reucroft, P. J .; Robertson, J . D.; Hamrin, C. E.,
J r. Appl. Phys. Lett. 1993, 62, 681.
(4) Maruyama, T.; Nakai, T. Appl. Phys. Lett. 1991, 58.
(5) van Corbach, H. D.; Haanappel, V. A. C.; Fransen, T.; Gellings,
P. J . Thin Solid Films 1994, 239, 31. Saraie, J .; Ono, K.; Takeuchi, S.
J . Electrochem. Soc. 1989, 136, 3139.
(6) Kobayashi, T.; Okamura, M.; Yamaguchi, E.; Shinoda, Y.; Hirota,
Y. J . Appl. Phys. 1981, 52, 6434.
(7) They were first called by that name in: Folting, K.; Streib, W.
E.; Caulton, K. G.; Poncelet, O.; Hubert-Pfalzgraf, I. G. Polyhedron
1991, 10, 1639.
(13) Singh, J . V.; J ain, N. C.; Mehrotra, R. C. Synth. React. Inorg.
Met.-Org. Chem. 1979, 9, 79.
(14) Mehrotra, R. C.; Mehrotra, A. Inorg. Chim. Acta 1971, 5, 127.
Mehrotra, R. C.; Mehrotra, A. Ind. J . Chem. 1972, 10, 532. Mehrotra,
R. C.; Agrawal, M. M.; Mehrotra, A. Synth. Inorg. Met-Org. Chem.
1973, 3, 181. Mehrotra, R. C.; Agrawal, M. M.; Mehrotra, A. Synth.
Inorg. Met-Org. Chem. 1973, 3, 407. Mehrotra, R. C.; Kapoor, P. N.;
Batwara, J . M. Coord. Chem. Rev. 1980, 31, 67. Wijk, M.; Norrestam,
R.; Nygren, M.; Westin, G. Inorg. Chem. 1996, 35, 1077.
10.1021/om980900c CCC: $18.00 © 1999 American Chemical Society
Publication on Web 02/20/1999

Tetrametallic Alkoxide Molecules
Organometallics, Vol. 18, No. 6, 1999 977
mixture is prepared in an inert atmosphere glovebox
using toluene as the solvent. It is then taken out of the
drybox, connected to a vacuum line, and refluxed for a
minimum of 4 h. The heating may be conducted for a
longer period of time with no detrimental effect. As the
reflux begins, the originally insoluble Al(OEt)3 becomes
soluble and a clear solution results. After terminating
the reflux, filtration, and solvent removal, viscous oils
result. For 1-3 the synthesis involves the 1:1 addition
F igu r e 1. ORTEP view (30% probability) of [Al{(µ-
OEt)2AlMe2}3] (1).
of the reagents with no additional byproducts. For 4 and
5 the optimal stoichiometry was 3 GaR3 with 2 Al(OEt)3
with the consequent elimination of AlR3 from the
reaction. By the existence of [Al{(µ-OiPr)2Al(OiPr)2}3] it
would appear that the synthesis of the complexes
[Al{(µ-OiPr)2AlR2}3], where R ) Me, Et, iBu, would also
be possible. However, under the same conditions em-
ployed in the synthesis of 1-3, these complexes were
not accessible. Rather, the reactions led to isolation of
the tetrameric starting material, {iPrO2Al(µ-OiPr)2}3Al.
This may imply that such tetramers do not easily
redistribute to give the desired products in the same
manner as dimeric [Al(OEt)3]2. Additionally, attempts
to form derivatives stemming from the use of AlH3-
NMe3 were not successful, perhaps due to the sensitivity
of the Al-H group for thermal decomposition.15
1
These oils give very clean H NMR spectra. A primary
feature in the spectra for 1-3 is the presence of one set
of resonances for the Al-R group and one for the
OCH2CH3 protons. These data are consistent with a
symmetrical structure like that shown above. However,
the OCH2 groups are manifested as two closely spaced
multiplets. This type of behavior is consistent with the
presence of diastereotopic methylene groups which
would be a consequence of the D3 symmetry of the
molecule. The fact that two resonances are not observed
for the CH3 groups may be attributed to an averaging
process or coincidence of the two resonances. Thus, it
is likely that the compounds are not interconverting to
other species in solution.
F igu r e 2. ORTEP view (30% probability) of [Al{(µ-
OEt)2GaMe2}3] (4).
solution for 3, which has a more complex 1H NMR
spectrum than was observed for 1 and 2. It contains
three peaks in the 27Al NMR, which can be assigned to
four-, five-, and six-coordinate species. This could be
interpreted as resulting from a tetramer-trimer equi-
librium, the trimer giving rise to the five-coordinate
27Al resonance (Scheme 2).
A different situation is observed in the NMR spectra
of the mixed-metal derivatives, 4 and 5. For these
compounds, the 27Al spectra contained resonances for
more than one six-coordinate aluminum atom in solu-
tion (in the range δ 11-16 ppm). There were no peaks
in the regions associated with four- and five-coordinate
aluminum species. This was an indication that the
central atom was aluminum and that the peripheral
atoms were gallium (confirmed in a crystal structure of
4; see below). Based upon the elemental analyses it was
clear that 4 and 5 were pure. Moreover the 1H NMR
data did not indicate other products in solution. Obtain-
ing 27Al NMR data at low temperatures had little effect
on the positions of the multiple six-coordinate reso-
nances until -90 °C. At this temperature only one
Furthermore, the 27Al NMR of 1 and 2 consists of two
peaks in the expected range for six-coordinate (∼11
ppm) and four-coordinate aluminum atoms (∼150 ppm).
This is in contrast to the behavior of [Al(OiPr)3]4 and
16
others of general formula [Me2Al(OR)]2,3
,
which do
undergo interconversion in solution. For [Al(OiPr)3]4
there is interconversion between the tetramer and a
trimer (Scheme 1).13 This may also be occurring in
(15) Kovar, R. A.; Callaway, J . O. Inorg. Synth. 1990, 17, 36.
(16) Rogers, J . H.; Apblett, A. W.; Cleaver, W. M.; Tyler, A. N.;
Barron, A. R. J . Chem. Soc., Dalton Trans. 1992, 3179.

978 Organometallics, Vol. 18, No. 6, 1999
Sch em e 1. Tetr a m er -Tr im er Equ ilibr iu m for [Al(OiP r )3]4
Atwood et al.
Sch em e 2. P r op osed Equ ilibr iu m for [Al{(µ-OEt)2AliBu 2}3] (3)
resonance was observed for 4 and 5 at a value of δ 15
ppm for both and W1/2 of 140.2 and 112.3 Hz, respec-
tively. An explanation for the multiple resonances at
warmer temperatures could be that the GaR2 groups
are rapidly dissociating and reattaching in solution.
That this does not occur for the all-aluminum analogues
could be attributed to the greater Al-O bond strength
when compared to a Ga-O bond.17
of combinations of 1 and 2, and 2 and 3, no solidification
occurred over the course of 3 months.
Molecu la r Str u ctu r es of 1, 2, a n d 4. In several
instances the solids that crystallized from the original
oils were of sufficient crystallinity to warrant an X-ray
crystallographic investigation. This was successfully
performed for 1, 2, and 4. Compounds 1 and 2 were
isomorphous, so only the strucutre of 2 will be described
(Figure 1). The central six-coordinate Al atom is che-
lated in a bidentate fashion through the oxygens of the
three R2Al(OEt)2 groups. The Al-O distances (Table 1)
are longer around the central six-coordinate aluminum
(av 1.9 Å) than for the terminal four-coordinate alumi-
nums (av 1.8 Å). This is in keeping with the increase in
atomic radii with increasing coordination number. All
of the Al2O2 four-membered rings are planar. They
adopt a propeller-type arrangement around the central
aluminum atom. The Al2O2 rings form dihedral angles
of 59.2°(av) for 1 and 60.5°(av) for 2 with the coplanar
aluminum atoms. The structure of 4 (Figure 2) is
unusual in that the heavier element occupies the
peripheral positions in the tetramer. All of the other
heterobimetallics have the heavier element in the
central position.11,12 This is apparently a consequence
of these elements being able to better accommodate a
six-coordinate rather than four-coordinate geometry. In
4 this might be an indication that Ga(III) (six-coordi-
nate) is, indeed, smaller than aluminum(III) (due to the
contraction of the d orbitals on the fourth period).
However, textbook values indicate that this is not the
case with Al ) 0.68 Å and Ga ) 0.73 Å.17 The Al-O
distances (av 1.9 Å) are similar to what was observed
in 1 and 2. The O-Ga distances (av 1.92 Å) are
somewhat longer than those observed to the terminal
Al atoms in 1 and 2.
Initial work found that the oils originally isolated for
1-4 slowly became crystalline over the course of days
to months. Compound 5 remains indefinitely as an oily
1
solid. The H NMR spectra of the resulting crystalline
material were close to being identical to that shown for
the oils. Upon closer inspection and after obtaining
numerous examples, two observations could be made.
The oils that did not solidify within one or 2 days had
at least one of two features in common. The first was
an impurity 1H NMR resonance falling close to that seen
for the OCH2CH3 groups. The second was the presence
of a toluene peak at δ 2.1 ppm. In cases where neither
1
of these peaks were observed in the H NMR, the oils
crystallized within 24 h. Moreover, the occurrence of oils
with greater longevity took place more frequently as the
bottle of Al(OEt)3 aged. Thus, the maintenance of an
oil for an extended period of time for 1-3 could be
attributed to the presence of solvent or the use of aged
Al(OEt)3. The as-prepared oils (after being evacuated
to 10-3 Torr for 3 h) contained one molecule of toluene
for every 10 tetramers for 1 and 2, and one toluene for
every 20 tetramers for 3 and 4. Compound 5, which does
not solidify, contains substantially more toluene, with
one molecule of toluene for four tetramers. An alternate
means of preventing solidification of the pure oils is to
mix two of them immediately after synthesis. In the case
(17) Inorganic Chemistry, Principles of Structure and Reactivity, 4th
ed.; Huheey, J . E., Keiter, E. A.; Keiter, R L., Eds.; Harper Collins:
New York, 1993; p 114.
The tetrametallic Mitsubishi structural motif is not
limited to metals supported by alkoxide groups. Other

Tetrametallic Alkoxide Molecules
Organometallics, Vol. 18, No. 6, 1999 979
Ta ble 1. Bon d Len gth s (Å) for 1, 2 (Isom or p h ou s to 1), a n d 4
1
2
3
Al(1)-O(1)
Al(1)-O(2)
Al(1)-O(3)
Al(1)-O(4)
Al(1)-O(5)
Al(1)-O(6)
Al(2)-O(1)
Al(2)-O(2)
Al(2)-C(3)
Al(2)-C(4)
Al(3)-O(3)
Al(3)-O(4)
Al(3)-C(9)
Al(3)-C(10)
Al(4)-O(5)
Al(4)-O(6)
Al(4)-C(15)
Al(4)-C(16)
1.896(8)
1.904(8)
1.891(8)
1.900(7)
1.888(9)
1.904(7)
1.815(8)
1.813(9)
1.952(12)
1.960(13)
1.816(8)
1.815(8)
1.920(15)
1.944(13)
1.807(8)
1.813(9)
1.941(15)
1.923(15)
Al(1)-O(1)
Al(1)-O(2)
Al(1)-O(3)
Al(1)-O(4)
Al(1)-O(5)
Al(1)-O(6)
Al(2)-O(1)
Al(2)-O(2)
Al(2)-C(3)
Al(2)-C(5)
Al(3)-O(3)
Al(3)-O(4)
Al(3)-C(11)
Al(3)-C(13)
Al(4)-O(5)
Al(4)-O(6)
Al(4)-C(19)
Al(4)-C(21)
1.875(20)
1.852(25)
1.837(25)
1.908(19)
1.863(20)
1.862(25)
1.811(22)
1.781(26)
1.856(35)
1.874(41)
1.752(24)
1.802(22)
1.968(43)
1.919(56)
1.826(22)
1.757(28)
1.952(49)
1.889(37)
Al(1)-O(1)
Al(1)-O(2)
Al(1)-O(3)
Al(1)-O(4)
Al(1)-O(5)
Al(1)-O(6)
Ga(1)-O(1)
Ga(1)-O(2)
Ga(1)-C(1)
Ga(1)-C(2)
Ga(2)-O(3)
Ga(2)-O(4)
Ga(2)-C(3)
Ga(2)-C(4)
Ga(3)-O(5)
Ga(3)-O(6)
Ga(3)-C(15)
Ga(3)-C(16)
1.898(4)
1.905(4)
1.888(4)
1.903(4)
1.903(4)
1.909(4)
1.915(4)
1.922(4)
1.938(8)
1.939(9)
1.927(4)
1.913(4)
1.946(8)
1.934(8)
1.922(4)
1.915(4)
1.920(10)
1.950(11)
Ta ble 2. Bon d An gles (d eg) for 1, 2 (Isom or p h ou s to 1), a n d 4
2
1
3
O(1)-Al(1)-O(2)
O(1)-Al(1)-O(3)
O(2)-Al(1)-O(3)
O(1)-Al(1)-O(4)
O(2)-Al(1)-O(4)
O(3)-Al(1)-O(4)
O(1)-Al(1)-O(5)
O(2)-Al(1)-O(5)
O(3)-Al(1)-O(5)
O(4)-Al(1)-O(5)
O(1)-Al(1)-O(6)
O(2)-Al(1)-O(6)
O(3)-Al(1)-O(6)
O(4)-Al(1)-O(6)
O(5)-Al(1)-O(6)
O(1)-Al(2)-O(2)
O(1)-Al(2)-C(3)
O(2)-Al(2)-C(3)
O(1)-Al(2)-C(4)
O(2)-Al(2)-C(4)
C(3)-Al(2)-C(4)
O(3)-Al(3)-O(4)
O(3)-Al(3)-C(9)
O(4)-Al(3)-C(9)
O(3)-Al(3)-C(10)
O(4)-Al(3)-C(10)
C(9)-Al(3)-C(10)
O(5)-Al(4)-O(6)
O(5)-Al(4)-C(15)
O(6)-Al(4)-C(15)
O(5)-Al(4)-C(16)
O(6)-Al(4)-C(16)
C(15)-Al(4)-C(16)
Al(1)-O(1)-Al(2)
Al(1)-O(2)-Al(2)
Al(1)-O(3)-Al(3)
Al(1)-O(4)-Al(3)
Al(1)-O(5)-Al(4)
Al(1)-O(6)-Al(4)
75.8(3)
165.7(4)
95.0(4)
94.3(3)
96.2(3)
75.4(3)
94.6(4)
165.7(4)
96.2(4)
95.2(3)
96.7(3)
94.3(3)
94.9(4)
166.3(4)
75.9(3)
O(1)-Al(1)-O(2)
O(1)-Al(1)-O(3)
O(2)-Al(1)-O(3)
O(1)-Al(1)-O(4)
O(2)-Al(1)-O(4)
O(3)-Al(1)-O(4)
O(1)-Al(1)-O(5)
O(2)-Al(1)-O(5)
O(3)-Al(1)-O(5)
O(4)-Al(1)-O(5)
O(1)-Al(1)-O(6)
O(2)-Al(1)-O(6)
O(3)-Al(1)-O(6)
O(4)-Al(1)-O(6)
O(5)-Al(1)-O(6)
O(3)-Al(3)-O(4)
O(3)-Al(3)-C(11)
O(4)-Al(3)-C(11)
O(3)-Al(3)-C(13)
O(4)-Al(3)-C(13)
C(11)-Al(3)-C(13)
O(1)-Al(2)-O(2)
O(1)-Al(2)-C(3)
O(2)-Al(2)-C(3)
O(1)-Al(2)-C(5)
O(2)-Al(2)-C(5)
C(3)-Al(2)-C(5)
O(5)-Al(4)-O(6)
O(5)-Al(4)-C(19)
O(6)-Al(4)-C(19)
O(5)-Al(4)-C(21)
O(6)-Al(4)-C(21)
C(19)-Al(4)-C(21)
Al(1)-O(1)-Al(2)
Al(1)-O(2)-Al(2)
Al(1)-O(3)-Al(3)
Al(1)-O(4)-Al(3)
Al(1)-O(5)-Al(4)
Al(1)-O(6)-Al(4)
74.2(9)
95.4(9)
98.1(11)
164.0(10)
97.0(9)
72.3(9)
93.4(8)
162.5(10)
95.2(10)
97.8(9)
O(1)-Al(1)-O(2)
O(1)-Al(1)-O(3)
O(2)-Al(1)-O(3)
O(1)-Al(1)-O(4)
O(2)-Al(1)-O(4)
O(3)-Al(1)-O(4)
O(1)-Al(1)-O(5)
O(2)-Al(1)-O(5)
O(3)-Al(1)-O(5)
O(4)-Al(1)-O(5)
O(1)-Al(1)-O(6)
O(2)-Al(1)-O(6)
O(3)-Al(1)-O(6)
O(4)-Al(1)-O(6)
O(5)-Al(1)-O(6)
O(1)-Ga(1)-O(2)
O(1)-Ga(1)-C(1)
O(2)-Ga(1)-C(1)
O(1)-Ga(1)-C(2)
O(2)-Ga(1)-C(2)
C(1)-Ga(1)-C(2)
O(3)-Ga(2)-O(4)
O(3)-Ga(2)-C(4)
O(4)-Ga(2)-C(4)
O(3)-Ga(2)-C(3)
O(4)-Ga(2)-C(3)
C(3)-Ga(2)-C(4)
O(5)-Ga(3)-O(6)
O(6)-Ga(3)-C(5)
O(5)-Ga(3)-C(5)
O(6)-Ga(3)-C(6)
O(5)-Ga(3)-C(6)
C(5)-Ga(3)-C(6)
Al(1)-O(1)-Ga(1)
Al(1)-O(2)-Ga(1)
Al(1)-O(3)-Ga(2)
Al(1)-O(4)-Ga(2)
Al(1)-O(5)-Ga(3)
Al(1)-O(6)-Ga(3)
77.1(2)
167.9(2)
94.5(2)
94.8(2)
97.0(2)
77.3(2)
93.9(2)
166.7(2)
95.8(2)
93.5(2)
96.3(2)
93.7(2)
93.0(2)
166.0(2)
77.3(2)
98.4(10)
95.7(11)
162.7(11)
95.7(10)
73.6(10)
76.9(10)
112.4(15)
113.6(14)
113.7(19)
116.4(19)
117.3(22)
77.5(10)
119.7(17)
112.9(15)
117.1(15)
113.8(15)
111.5(19)
77.1(10)
112.0(16)
115.2(14)
116.2(13)
116.5(15)
114.6(17)
103.1(9)
105.2(11)
107.9(12)
102.9(10)
103.2(10)
106.0(11)
80.1(4)
76.3(2)
115.2(5)
113.8(5)
114.3(5)
115.4(5)
113.9(6)
79.4(4)
115.0(5)
115.3(6)
114.2(5)
114.5(5)
114.0(7)
80.2(4)
114.9(5)
114.6(5)
115.2(5)
113.6(5)
114.2(7)
102.1(4)
101.9(4)
102.7(4)
102.4(4)
102.3(4)
101.5(4)
112.3(3)
111.7(3)
112.3(3)
114.1(3)
121.5(4)
76.2(2)
111.3(3)
112.7(3)
112.9(4)
113.2(3)
121.8(4)
76.7(2)
112.8(4)
113.2(4)
112.0(3)
113.5(3)
120.6(5)
102.1(4)
101.9(4)
102.7(4)
102.4(4)
102.3(4)
101.5(4)
group 13 element complexes have demonstrated an
Al4E6 central core (E ) O or N). For instance, these
species can occur when the stoichiometry of the het-
eroatom containing starting material is in a 3:2 ratio
with the aluminum reagent.18 Structurally character-
ized examples include [{(CH3)3Si}2Al(NH2)2]3Al,19 as
well as those with open chain amines,20 and alu-
matranes.21
The fact that group 13 alkoxides can take this
geometry is somewhat surprising in view of the pre-
dominance of the bridged dimeric type of structures. For
instance, Al(OEt3)3 and Al(OSiMe3)37 (where the SiMe3
group may be envisioned to have the steric effect of a
tBu) have been shown to be dimeric. The OiPr group is
(20) Robinson, G. H.; Sangokoya, S. A. J . Am. Chem. Soc. 1987, 109,
6852. Robinson, G. H.; Self, M. F.; Pennington, W. T.; Sangokoya, S.
A. Organometallics 1988, 7, 2424. Robinson, G. H.; Moise, F.; Pen-
nington, W. T.; Sangokoya, S. A. Polyhedron 1989, 8, 1279. Lee, B.;
Pennington, W. T.; Robinson, G. H.; Rogers, R. D. J . Organomet. Chem.
1990, 396, 269. Robinson, G. H.; Pennington, W. T.; Lee, B.; Self, M.
F.; Hrncir, D. C. Inorg. Chem. 1991, 30, 809.
(18) Eisch, J . J . In Comprehensive Organometallic Chemistry, Vol
1; Wilkinson, G. A., Stone, F. G. A., Abel, E., Eds.; Pergamon Press:
New York 1983; p 555.
(19) J anik, J . F.; Duesler, E. N.; Paine, R. T. Inorg. Chem. 1988,
27, 4335.

980 Organometallics, Vol. 18, No. 6, 1999
Atwood et al.
Ta ble 3. Su m m a r y of X-r a y Da ta for 1, 2, a n d 4
or Strem and used as received. Caution: R3Al and R3Ga
reagents are highly pyrophoric and must be handled under
an inert atmosphere. This is not the case for compounds 1-5,
which decompose slowly over the course of hours to days when
exposed to the atmosphere.
1
2
4
formula
fw
cryst syst
space group
a (Å)
C
468.5
18H48Al4O6
C24H60Al4O6 C18H48AlGa3O6
552.6
monoclinic
P21/c
596.70
triclinic
P1h
monoclinic
P21/c
11.646(1)
11.444(2)
22.759(2)
90
98.51(1)
90
2999.9(6)
4
[Al{(µ-OEt)2AlMe2}3] (1). To a stirred suspension of alu-
minum triethoxide (30.83 mmol, 5.000 g) in toluene (30 mL)
at 25 °C was added a solution of trimethylaluminum (30.83
mmol, 2.223 g) in toluene (30 mL). The mixture was then
brought to reflux and the solid dissolved after 20 min. The
solution was refluxed for a total of 4 h, cooled to 25 °C, and
filtered to remove a small amount of insoluble material. The
volatiles were removed under reduced pressure, yielding a
nearly colorless, viscous oil (6.742 g, 93%), which crystallized
in a period of time from 1 day to 3 months. Single crystals
suitable for X-ray analysis were obtained from a sample which
was allowed to sit undisturbed for 3 months at 25 °C. Mp:
12.205(2)
12.248(1)
24.440(2)
90
98.75(1)
90
8.3373(6)
10.6313(8)
17.339(1)
89.835(1)
89.993(1)
76.309(1)
1493.1(2)
2
b (Å)
c (Å)
R (deg)
â (deg)
g (deg)
V (Å3)
Z
3611.3(7)
4
D
calc (g/cm3)
1.037
1.016
1.327
cryst size (mm)
temp (K)
0.7 × 0.4 × 0.4 (0.5)3
(0.4)3
298
298
298
2θ range (deg)
3.5-45
2θ-θ
10-60
3.5-45
2θ-θ
8-60
2.34-38
2θ-θ
1
scan type
162-65 °C. H NMR (C6D6): δ -0.43 (s, 18H, AlCH3), 1.12 (t,
scan speed
(deg/min)
18H, OCH2CH3), 3.59 (m, 6H, OCHaHb), 3.83 (m, 6H, OCHaHb).
27Al NMR (C6D6): 12 (W1/2 19.6 Hz) 151 (W1/2 5.62 kHz), IR
(KBr): ν 2984 s, 2943 m, 2906 m, 2818 m, 1471 m, 1390 m,
1197 s, 1103 s, 1060 s, 900 s, 680 s(br), 582 s, 523 m. Analysis
based on C18H48O6Al4: calcd, C 46.15, H 10.33; found, C 46.23,
H 10.29.
scan range (deg) 0.31
0.40
no. of reflns
collected
5182
5182
4168
no. of indp reflns 3937
no. of obsd reflns 1588
(F > 4.0σ(F))
4754
1021
2377
2364
[Al{(µ-OEt)2AlEt2}3] (2). The procedure was as for 1 using
aluminum triethoxide (30.83 mmol, 5.000 g), toluene (60 mL),
and triethylaluminum (30.83 mmol, 21.336 g of a 1 M solution
in hexanes), yielding a nearly colorless, viscous oil (8.308 g,
98%). This oil also crystallized in a period of time from 3 days
to several months. Single crystals suitable for X-ray analysis
no. of
parameters
253
307
253
R
Rw
0.0776
0.0765
2.51
0.0896
0.0876
3.79
0.0561
0.1684
1.422
GOF
lar diff peak
0.23
0.21
0.470
were obtained from
a sample which was allowed to sit
(e/Å3)
undisturbed for 5 days at 25 °C. Mp: 124-27 °C. 1H NMR
(C6D6): δ 0.17 (m, 12H, AlCH2CH3), 1.12 (t, 18H, AlCH2CH3),
1.38 (t, 18H, OCH2CH3), 3.56 (m, 6H, OCHaHb), 3.78 (m, 6H,
OCHaHb). 27Al NMR (C6D6): 12 (W1/2 24.9 Hz) 148 (W1/2 5.31
kHz). IR (KBR): ν 2978 s, 2939 s, 2911 s, 2817 m, 1452 m,
1408 s, 1321 m, 1195 m, 1165 m, 1101 s, 1060 s, 896 s, 640
s(br). Analysis based on C24H60O6Al4: calcd, C 52.16, H 10.94;
found, C 52.09, H 10.85.
clearly intermediary in steric encumbrance between the
groups used in these two examples but gives the
tetrameric structure.
Con clu sion
A series of tetrametallic alkyl group 13 alkoxide
molecules have been synthesized and fully character-
ized. They possess D3 symmetric structures and have
the appropriate metal:oxygen stoichiometry for use as
unimolecular precursors to metal oxide materials. Pre-
liminary results indicate that 1-3 can be decomposed
to form relatively pure Al2O3 at ambient temperatures.
[Al{(µ-OEt)2AliBu 2}3] (3). The procedure was as for 1 using
aluminum triethoxide (30.83 mmol, 5.000 g), toluene (60 mL),
and triisobutylaluminum (30.83 mmol, 6.115 g), yielding a
nearly colorless, viscous oil (10.528 g, 95%). Crystalline mate-
rial was never obtained from this reaction. 1H NMR (C6D6): δ
0.15 (d, 12H, AlCH2CH(CH3)2), 1.08 (d, 18H, AlCH2CH(CH3)2),
1.19 (t, 18H, OCH2CH3), 2.01 (m, 6H, AlCH2CH(CH3)2), 3.73
(m, 6H, OCHaHb), 3.92 (m, 6H, OCHaHb), 27Al NMR (C6D6):
12 (W1/2 25.5 Hz) 41 (W1/2 1.18 kHz) 164 (W1/2 6.02 kHz), IR
(neat): ν 2949 s, 2866 s, 2773 m, 1462 s, 1390 s, 1359 s, 1340
m, 1160 s, 1059 s, 896 s, 871 s(br). Analysis based on
Exp er im en ta l Section
Gen er a l Con sid er a tion s. All manipulations were con-
ducted using Schlenk techniques in conjunction to an inert
atmosphere glovebox. All solvents were rigorously dried prior
to use. NMR data were obtained on J EOL-GSX-400 and -270
instruments at 270.17 (1H), 62.5 (13C), and 104.5 (27Al) MHz.
Chemical shifts are reported relative to SiMe4 and are in ppm.
Elemental analyses were obtained on a Perkin-Elmer 2400
analyzer and were found to be within acceptable limits for
crystalline 1-5. The oils analyzed were found to include a
certain amount of toluene as described in the text. Infrared
data were recorded as KBr pellets on a Matheson Instruments
C
36.68H84.78O6Al4 (tetramer with 1/10 toluene): calcd, C 60.36,
H 11.72; found, C 60.31, H 11.69.
[Al{(µ-OEt)2Ga Me2}3](4). The procedure was as for 1 using
aluminum triethoxide (18.5 mmol, 3.00 g), toluene (40 mL),
and trimethylgallium (27.7 mmol, 3.19 g), yielding a nearly
colorless, viscous oily solid (5.12 g, 93%). Crystals of 4 were
grown from a separate reaction (in a 1:1 stoichiometry) which
1
was left standing at 25 °C for 10 days. Mp: 130-133 °C. H
NMR (C6D6): δ -0.29 (s, 18H, GaCH3), 1.02 (t, 18H, OCH2CH3),
3.74 (m, 6H, OCHaHb), 4.02 (m, 6H, OCHaHb). 27Al NMR
(C6D6): 12.55 (W1/2 38.2 Hz) 12.78 (W1/2 25.5 Hz) 13.95 (W1/2
47.3 Hz) 15.12 (W1/2 21.8 Hz) at -94 °C ) 15.36 (W1/2 140.2
Hz). IR (neat): ν 2949 s, 2866 s, 2773 m, 1462 s, 1390 s, 1359
s, 1340 m, 1160 s, 1059 s, 896 s, 871 s(br). Analysis based on
2020 Galaxy Series spectrometer and are reported in cm-1
.
X-ray powder diffraction data were collected on a Philips
diffractometer. Thermogravimetric and elemental analyses (C
and H) were conducted on Perkin-Elmer analyzers. R3Al,Me3-
Ga, Et3Ga, and Al(OEt)3 were purchased from either Aldrich
C
18H48O6Ga3Al: calcd, C 36.23, H 8.11; found, C 36.41, H 8.28.
[Al{(µ-OEt)2Ga Et2}3] (5). The procedure was as for 1 using
(21) Pinkas, J .; Verkade, J . G. Polyhedron 1996, 15, 1567. Shklover,
V. E.; Struchkov, Y. T.; Voronkov, M. G.; Ovchinnikova, Z. A.;
Baryshok, V. P. Dokl. Acad. Nauk SSSR (Engl. Trans.) 1984, 277, 723.
Pinkas, J .; Verkade, J . G. Inorg. Chem. 1993, 32, 2711. Paz-Sandoval,
M. A.; Fernandez-Vincent, C.; Vribe, G.; Contreras, R.; Klaebe, A.
Polyhedron 1988, 71, 679.
aluminum triethoxide (19.2 mmol, 3.12 g), toluene (40 mL),
and triethylgallium (28.9 mmol, 4.53 g), yielding a nearly
1
colorless, viscous oily solid (6.42 g, 98%). H NMR (C6D6): δ
0.29-0.71 (m, 18H, GaEt), 1.35 (t, 18H, OCH2CH3), 3.74 (m,
6H, OCH2). 27Al NMR (C6D6): 13 (d, W1/2 23.7 and 19.1 Hz) 14

Tetrametallic Alkoxide Molecules
Organometallics, Vol. 18, No. 6, 1999 981
(W1/2 69.9 Hz) 15 (W1/2 23.7 Hz) at -94 °C ) 15 (W1/2 112.3
Hz). IR (neat): ν 2968 s, 2940 s, 2914 m, 2870 s, 1451 s, 1385
s, 1163 m, 1101 s, 1065 s, 999 s, 895 m, 637 m, 561 m, 515 m.
Analysis based on C25.75H62O6Ga3Al (one tetramer with 1/4
toluene): calcd, C 43.94, H 8.88; found, C 44.02, H 8.91.
X-r a y Exp er im en ta l Da ta . In each of the data collections
the check reflections indicated a less than 5% decrease in
intensity over the course of data collection, and hence, no
correction was applied. All calculations were performed on a
personal computer using the Siemens software package SHELX-
TL-Plus. The structures were solved by direct methods and
successive interpretation of difference Fourier maps, followed
by least-squares refinement. All non-hydrogen atoms were
refined anisotropically. The hydrogen atoms were included in
the refinement in calculated positions using fixed isotropic
parameters. With the exception of having a weakly diffracting
crystal for 2, which exacerbated the problem of ethyl group
motion, there were no other problems in the structure solu-
tions.
Ack n ow led gm en t. This work was supported by
Praxair Surface Technologies, Inc., the Petroleum Re-
search Fund (Grant 31901-AC3), and the National
Science Foundation (CAREER Program, Grant CHE
9625376).
Su p p or tin g In for m a tion Ava ila ble: Tables of bond
lengths and angles, positional parameters, anisotropic thermal
parameters, and unit cell views for 1, 2, and 4. This material
is available free of charge via the Internet at http://pubs.acs.org.
OM980900C