Synthesis and reactivity of Bi-, Tri-, and hexametallic and zwitterionic methyl aluminum complexes containing a phenoxide/imine ligand system

Article abstract of DOI:10.1021/om010773b

Addition of 3 equiv of trimethylaluminum to tris(3,5-di-tert-butyl-2-hydroxyphenyl)methane, 1H₃, affords the simple, C₃-symmetric, trimetallic species [1(AlMe₂)₃], 2. To disrupt the Al₃O₃ b

Full text of DOI:10.1021/om010773b

418
Organometallics 2002, 21, 418-428
Syn th esis a n d Rea ctivity of Bi-, Tr i-, a n d Hexa m eta llic
a n d Zw itter ion ic Meth yl Alu m in u m Com p lexes
Con ta in in g a P h en oxid e/Im in e Liga n d System
Andrew Cottone III, Dolores Morales, J ennifer L. Lecuivre, and Michael J . Scott*
Department of Chemistry and Center for Catalysis, University of Florida, P.O. Box 117200,
Gainesville, Florida 32611-7200
Received August 23, 2001
Addition of 3 equiv of trimethylaluminum to tris(3,5-di-tert-butyl-2-hydroxyphenyl)-
methane, 1H3, affords the simple, C3-symmetric, trimetallic species [1(AlMe2)3], 2. To disrupt
the Al3O3 bridging unit, one of the ortho-alkyl substituents from the tris(2-hydroxyphenyl)-
methane platform of 1H3 was substituted with a reactive aldehyde group to afford the ligands
3-(2,2′-methylenebis(4-methyl-6-tert-butylphenol)-5-methyl-2-hydroxybenzaldehyde, 3H3, and
3-(2,2′-methylenebis(4,6-di-tert-butylphenol)-5-methyl-2-hydroxybenzaldehyde, 4H3, respec-
tively. Benzylamine reacts independently with both 3H3 and 4H3 specifically at the aldehyde
functionality, affording the mixed donor ligands 3-(2,2′-methylenebis(4-methyl-6-tert-bu-
tylphenol)-5-methylsalicylidenebenzylimine, 5H3, and 3-(2,2′-methylenebis(4,6-di-tert-bu-
tylphenol)-5-methylsalicylidenebenzylimine, 6H3, in high isolable yields. Furthermore, the
Salen-type ligand, 7H6, can be prepared from the reaction of 1,2-ethylenediamine and 4H3.
Two equivalents of trimethylaluminum will react with 5H3 and 6H3 to produce the binuclear
aluminum compounds [(5)Al2Me3], 8, and [(6)Al2Me3], 9, respectively. If an additional
equivalent of trimethylaluminum is added to 9, the trimetallic species [(6)Al3Me6], 10, albeit
as a slightly impure material, is observed, while 7H6 reacts in an analogous manner to afford
[(7)Al6Me12], 11. Treatment of 8 with 1 equiv of DMSO produces the new complex [(5){AlMe2}-
{AlMe(OSMe2)}], 12, wherein the substrate is coordinated to only one of a possible two
aluminum centers. In contrast to this simple transformation, the separate reactions of 8
and 9 with either cyclopentanone or cyclohexanone afford the zwitterionic mononuclear
complexes [(5H)+AlMe-], 13, and [(6H)+AlMe-], 14. Solid-state structures are reported for
2, 6H3, 7H6, and 9-13.
In tr od u ction
The preparation of Lewis acidic complexes with
multiple metal centers has attracted much attention in
recent years since complexes of this type could have
utility in many important areas of chemistry including
organic catalysis and anionic complexation.1-3 If two
Lewis acidic centers simultaneously bind a single Lewis
base, the resulting complex should exhibit significantly
enhanced reactivity relative to a similar monomeric
species.4 Given the Lewis acidity inherent in many
group 13 complexes, cooperative binding of a substrate
by these species offers the prospect for generation of
extremely reactive compounds. Many new ligands have
been designed solely for the task of placing two or more
metals in proximity with the intention of binding Lewis
bases.1,5 With multiple donor groups, the mixed N2O2
* Corresponding author. Fax: 352-392-3255. E-mail: mjscott@
chem.ufl.edu.
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10.1021/om010773b CCC: $22.00 © 2002 American Chemical Society
Publication on Web 12/21/2001

Methyl Aluminum Complexes
Organometallics, Vol. 21, No. 2, 2002 419
and Salan7 derivatives would seem, at first glance, to
be ideal framework for the preparation of multimetallic
group 13 complexes, but the majority of work with this
type of ligand has involved the preparation of monome-
tallic group 13 complexes8-12 for purposes such as
selective addition of organic substrates.13-15 In addition,
these species include a number of interesting examples
of cationic aluminum complexes16-18 which may possess
utility as polymerization cocatalysts. Apparently, the
orientation and proximity of the four donor atoms in
Salen-type ligands tend to favor the complexation of a
single metal center in a square planar geometry. Mon-
omeric group 13 complexes with high coordination
numbers have been relatively popular, while,19 until
recently, relatively little attention has been devoted to
multinuclear complexes,20 specifically, binuclear moi-
eties.21 Contrary to initial studies,22 more recent work
has shown that binuclear complexes of mixed donor
types NxOy are readily accessible and isolable.21 Taking
inspiration from the Salen platform and with the intent
to prepare bimetallic group 13 complexes, we have
developed a new class of ligand that contains one-half
of the familiar phenol-imine donor set and a sterically
encumbering, robust 2,2′-methylenebis(4-tert-butyl-6-
alkylphenol) group. The two subunits of the ligand have
been designed to each hold a single metal center, thus
affording a novel binuclear aluminum species. Herein,
we report the synthesis and characterization of alumi-
num complexes with these NO3 donor ligands and the
reactivity of the resulting complexes with Lewis bases.
Resu lts a n d Discu ssion
Initial work in the development of simple multifunc-
tional Lewis acid catalysts concentrated on a study of
the reactivity of various Lewis acids with tris(3,5-di-
tert-butyl-2-hydroxyphenyl)methane, 1H3. This versa-
tile, C3-symmetric platform contains three phenolic
donors all linked at the ortho-position to a central
methine group. With three arms surrounding a central
carbon, two distinct conformations can be envisaged for
the ligand, type 1 and 2. In our extensive work with
this class of ligand, a distinct preference for the type 1
conformer, with all three hydroxide groups aligned with
the central methine hydrogen, has been noted.23 The
ligand can, however, be coaxed to adopt the type 2
conformer to bind atoms such as phosphorus and
arsenic.24 Nevertheless, when the ligand adopts the type
1 conformer, a single metal center cannot simulta-
neously bind all three phenolic arms since the atoms
are separated by more than 4 Å and the methine
hydrogen points directly between the donor groups.
Consequently, deprotonation of 1H3 with akali metal25
or zinc26 reagents produces multimetallic clusters with
the phenoxide donors bridging between adjacent metal
sites. In these complexes, the metal sites are often
buried within a hydrophobic pocket created by the tert-
butyl substituents and the aryl rings. Due to their Lewis
acidity, these species exhibit interesting properties
including the ability to recognize molecules with a
specific size and shape.25 Unfortunately, despite their
promise in the area of selective recognition, the com-
plexes have thus far proven to be poor catalysts, and
accordingly, we turned our attention to the reaction of
1H3 with significantly stronger Lewis acids such as
aluminum, particularly in view of the spectacular utility
of aluminum phenoxide complexes like methylalumi-
num 2,6-di-tert-butyl-4-methylphenolate (MAD).27
When a solution of trimethylaluminum is added to
1H3, the trimetallic species 2 is isolated in high yield
as outlined in Scheme 1, and in sharp contrast to the
diverse architectures produced when 1H3 is treated with
dialkylzinc reagents,26 the reaction with trimethylalu-
minum appears to form only the trimetallic species
regardless of the stoichiometry and conditions. In 2,
each of the three phenoxides bridge between two
{AlMe2} groups, forming a C3-symmetric complex with
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grahi, B.; Atwood, D. A. J . Am. Chem. Soc. 1999, 121, 6747-6748. (f)
Liu, S.; Mun˜oz-Herna´ndez, M.-AÄ .; Atwood, D. A. J . Organomet. Chem.
2000, 596, 109-114. (g) Atwood, D. A.; Harvey, M. J . Chem. Rev. 2001,
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1977, 55, 2540-2546.

420 Organometallics, Vol. 21, No. 2, 2002
Ta ble 1. X-r a y Str u ctu r a l Da ta a for Com p ou n d s 2, 6H3, 7H6, a n d 9
6H3 7H6‚3THF
22 551 9885
Cottone et al.
2
9‚CH2Cl2‚C5H12
total no. of reflns
no. of unique reflns
R(int)
17 529
44 361
6987
0.1192
23.00
11 891
0.0424
29.42
7520
0.1082
26.00
C44H57NO3
647.91
monoclinic
P21/n
0.069
11.5753(8)
11.2030(7)
29.5529(19)
90.359(1)
3832.3(4)
5893
0.0534
23.00
θmax (deg)
chemical formula
fw
C
49H79Al3O3
C88H128N2O9
1357.92
triclinic
P1h
C53H77NAl2Cl2O3
901.02
orthorhombic
Pbcn
797.06
cryst syst
triclinic
P1h
0.112
space group
µ(Mo KR) (mm-1
a (Å)
)
0.067
0.206
11.4957(2)
13.1039(2)
17.1580(2)
75.540(1)
89.467(1)
89.489(1)
2502.61(6)
2
10.1422(13)
12.3607(16)
17.630(3)
84.566(6)
75.120(5)
88.961(6)
2126.4(5)
1
28.448(2)
17.2688(13)
20.4503(14)
10046.4(12)
b (Å)
c (Å)
R (deg)
â (deg)
γ (deg)
Vc (Å3)
Z
4
8
R1 [I g 2σ(I) data]b
wR2 (all data)c
0.0688 [6843]
0.1719
0.0624 [3185]
0.1921
0.0740 [2784]
0.1912
0.0866 [4774]
0.2233
0.577, -0.322
larg diff peak, hole (e/Å3)
0.320,-0.355
0.276,-0.408
0.228,-0.226
a
b
2
Obtained with monochromatic Mo KR radiation (λ ) 0.71073 Å) at 173 K. R1 ) ∑||Fo| - |Fc||/∑|Fo|. c wR2 ) {∑[w(Fo
-
Fc2)2/∑[w(Fo2)2]}1/2 where w ) 1/[σ2(Fo2) + (XP)2 + YP] where P ) (Fo + 2Fc2)/3}.
2
Sch em e 1
Ta ble 2. Selected Bon d Len gth s (Å) a n d An gles
(d eg) for 2
Bond Lengths
Al(1)-O(1)
Al(1)-O(2)
Al(1)-C(44)
Al(1)-C(45)
Al(2)-O(2)
Al(2)-O(3)
Al(1)‚‚‚Al(2)
Al(1)‚‚‚Al(3)
1.903(2)
1.895(2)
1.947(3)
1.943(3)
1.897(2)
1.906(2)
3.3747(12)
3.3726(12)
Al(2)-C(46)
Al(2)-C(47)
Al(3)-O(1)
Al(3)-O(3)
Al(3)-C(48)
Al(3)-C(49)
Al(2)‚‚‚Al(3)
1.947(3)
1.945(3)
1.918(2)
1.908(2)
1.948(3)
1.948(3)
3.3576(12)
F igu r e 1. Diagram of the structure of 2 (30% probability
ellipsoids). Hydrogen atoms have been omitted for clarity.
are in very different environments, and the shielding
provided by the aryl rings is evident in the 1.52 ppm
1
disparity in the two H NMR resonances arising from
Bond Angles
100.92(8) O(2)-Al(2)-C(47) 106.48(12)
the aluminum-methyl groups.
O(1)-Al(1)-O(2)
O(1)-Al(1)-C(44) 107.21(12) O(3)-Al(2)-C(46) 107.40(12)
O(2)-Al(1)-C(44) 108.83(12) O(3)-Al(2)-C(47) 110.77(12)
O(1)-Al(1)-C(45) 110.84(12) O(1)-Al(3)-O(3) 102.80(8)
O(2)-Al(1)-C(45) 106.40(12) Al(1)-O(2)-Al(2) 125.70(10)
C(44)-Al(1)-C(45) 120.82(15) Al(1)-O(1)-Al(3) 123.90(10)
Since the aluminum centers in 2 are coordinately
saturated and sterically congested by the tert-butyl
substituents, the reactivity of the complex was not
extensively investigated, but given the proximity of the
metal centers, we reasoned the basic platform should
allow for the preparation of reactive Lewis acid catalysts
if the stabilizing Al3O3 ring structure is disrupted. The
addition of a donor group at the periphery of the
platform would effectively break the symmetry of the
platform and preclude the formation of the Al3O3 unit,
and efforts to derivatize 1H3 were undertaken. Several
synthetic pathways have been used to prepare 1H3
including the acid-catalyzed condensation of 3,5-di-tert-
butyl-2-hydroxybenzaldehyde with 2 equiv of 2,4-di-tert-
butylphenol,23a,24 and in an attempt to incorporate a
reactive functionality at the periphery of the ligand,
O(2)-Al(2)-O(3)
100.84(8)
Al(2)-O(3)-Al(3) 123.36(10)
O(2)-Al(2)-C(46) 109.11(12)
an average Al-O distance of 1.905 Å (Table 2). In
contrast to the familiar Al2O2 unit normally found when
aluminum alkyls are bound by simple phenoxides or
more complex ligands containing multiple phenoxide
arms,1,28,29 the methine hydrogen allows only the forma-
tion of an Al3O3 ring structure.5b,30 As illustrated in
Figure 1, the two alkyl groups bound to the metal center
(28) (a) Aitken, C. L.; Barron, A. R. J . Chem. Cryst. 1996, 26, 293-
295. (b) Rennekamp, C.; Wessel, H.; Roesky, H.; Muller, P.; Schmidt,
H.; Noltemeyer, M.; Uson, I.; Barron, A. Inorg. Chem. 1999, 38, 5235-
5240. (c) Francis, J .; Bott, S.; Barron, A. J . Organomet. Chem. 2000,
597, 29-37. (d) Taden, I.; Kang, H.; Massa, W.; Spaniol, T. P.; Okuda,
J . Eur. J . Inorg. Chem. 2000, 441-445.
(30) (a) Hausen, H. D.; Schmoger, G.; Schwarz, W. J . Organomet.
Chem. 1978, 153, 271-279. (b) Mason, M. R.; Smith, J . M.; Bott, S.
G.; Barron, A. R. J . Am. Chem. Soc. 1993, 115, 4971-4984. (c) Storre,
J .; Schnitter, C.; Roesky, H. W.; Schmidt, H.-G.; Noltemeyer, M.;
Fleischer, R.; Stalke, D. J . Am. Chem. Soc. 1997, 119, 7505-7513.
(29) Atwood, J . L.; Gardiner, M. G.; J ones, C.; Raston, C. L.; Skelton,
B. W.; White, A. H. Chem. Commun. 1996, 2487-2488.

Methyl Aluminum Complexes
Sch em e 2
Organometallics, Vol. 21, No. 2, 2002 421
Sch em e 3
In view of the limited examples of mixed donor
bimetallic aluminum complexes21 and the potential of
bimetallic Lewis acid catalysts,1,2,4 the reactivity of 5H3,
6H3, and 7H6 with trimethylaluminum was examined.
Initially, 2 equiv of trimethylaluminum was added to
5H3 and 6H3, independently (Scheme 3), and in both
cases, comparable bimetallic products [(L)Al2Me3], 8 (L
) 5), and 9 (L ) 6), were isolated in high yield from
pentane solutions. As can be seen in the diagram, the
phenolic arms have adopted a type 2 orientation in order
to bind both metal centers simultaneously. Moreover,
with the formation of the type 2 geometry about the
central methine carbon, a single metal, Al(1), coordi-
nates all three oxygen donors and one methyl group in
a tetrahedral arrangement. The imine arm in conjunc-
tion with one of the phenolic donors coordinates the
second aluminum center, Al(2). The bridging phenoxide
oxygen, O(3), is nearly equidistant between Al(1) and
Al(2), with bond distances typical for phenoxide groups
joining two aluminum centers32,33 of 1.874(3) and 1.870-
(3) Å, respectively. For comparison, the two remaining
Al(1)-O(1) bonds are more than a 0.1 Å shorter (Al-
(1)-O(1) ) 1.742(3) and Al(1)-O(2) ) 1.741(3) Å).
Straddling the salicylidene phenolic oxygen and the
imine donor, Al(2) fulfills its tetrahedral geometry with
the incorporation of two methyl groups at an average
distance of 1.940 Å similar to the metal sites observed
in [Salcen(tBu){AlMe2}2] and [SalpenN3H{AlMe2}2].21f
In contrast to the values reported for the Salcen and
Salpen species, the Al(2)-O(3) distance in 9 increases
significantly to 1.870(3) Å due to the bridging interaction
of O(3) with Al(1). There is, however, no significant
change in the distance of the metal to the imine nitrogen
in 9 relative to [Salcen(tBu){AlMe2}2] or [Sal(tBu)-
AlEt2].34
2-hydroxy-5-alkyl-1,3-benzene dicarboxaldehydes were
substituted for the normal salicylaldehyde precursor
used to prepare 1H3. As outlined in Scheme 2, the
reaction of the dialdehyde with 2,4-disubstituted phe-
nols in trifluoroacetic acid will, under the proper condi-
tions, afford 2-hydroxy-3-(2,2′-methylenebis(4-methyl-
6-tert-butylphenol)-5-methylbenzaldehyde, 3H3, and
2-hydroxy-3-(2,2′-methylenebis(4,6-di-tert-butylphenol)-
5-methylbenzaldehyde, 4H3, in which only one of the
two aldehyde arms has reacted with the phenolic
precursors. Although minor amounts of the product with
four phenolic arms can be generated using a large excess
of phenol, the insolubility of the product with one
unreacted aldehyde arm in the reaction mixture allowed
for its isolation in high yield and purity. Thus far, only
ligands derived from 2,6-di-tert-butylphenol (3H3) and
2-tert-butyl-4-methylphenol (4H3) have been isolated
and fully characterized, but the condensation reaction
appears to be quite general.
With one aldehyde group tethered to the polyphenolic
platform, mixed NO3 donor ligands and even Salen-type
complexes with N2O6 donors can easily be prepared with
both 3H3 and 4H3 via nucleophilic attack by primary
amines. Indeed, when 3H3 and 4H3 were reacted with
benzylamine or ethylenediamine in ethanol, the Schiff
base products 5H3, 6H3, and 7H6 were isolated in high
yields as outlined in Scheme 2.31 Much like 1H3, the
three phenoxide donors in 5H3-7H6 are aligned in a
type 1 configuration in the solid state even with the
imine groups bound to the framework as demonstrated
in Figures 2 and 3. Interestingly, the ethylene backbone
in 7H6 resides on an inversion symmetry position in the
solid state with the two sets of phenoxide donors
pointing in opposite directions. These groups are each,
in turn, hydrogen-bonded to adjacent molecules, forming
infinite polymeric chains of the ligand in the solid state.
(32) Applet, A. W.; Barron, A. R. Organometallics 1990, 9, 2137-
2141.
(33) Haaland, A.; Stokkeland, O. J . Organomet. Chem. 1975, 94,
345-352.
(31) Cottone, A.; Lecuivre, J . L.; Scott, M. J . Unpublished results.

422 Organometallics, Vol. 21, No. 2, 2002
Cottone et al.
F igu r e 2. Diagram of the structure of 6H3 (30% prob-
ability ellipsoids). Hydrogen atoms have been omitted for
clarity.
F igu r e 4. Diagram of the structure of 9 (30% probability
ellipsoids; carbon atoms drawn with arbitrary radii). The
tert-butyl methyl groups and all hydrogen atoms have been
omitted for clarity.
F igu r e 3. Diagram of the structure of 7H6 (30% prob-
ability ellipsoids). Primed and unprimed atoms are related
by a center of inversion.
1
The H NMR spectra of the crude reaction mixture
after the addition of 2 equiv of trimethylaluminum to
5H3 and 6H3 consistently exhibited resonances arising
from a very minor byproduct, which could be removed
from the bimetallic products by recrystallization. If 3
equiv of trimethylaluminum were added to solutions of
5H3 and 6H3 or, alternatively, an additional equivalent
of trimethylaluminum was added to solutions of 8 or 9,
the ratios of the signals arising from these byproducts
increased markedly to the point where the bimetallic
species was only a contaminant. The interpretation of
F igu r e 5. Diagram of the structure of 10 (30% probability
ellipsoids; carbon atoms drawn with arbitrary radii). The
tert-butyl methyl groups and all hydrogen atoms have been
omitted for clarity.
Ta ble 3. Selected Bon d Len gth s (Å) a n d An gles
(d eg) for 9
Bond Lengths
1
the H NMR spectra of the solutions was complicated
Al(1)-O(1)
Al(1)-O(2)
Al(1)-O(3)
Al(1)-C(45)
Al(1)‚‚‚Al(2)
1.742(3)
1.741(3)
1.874(3)
1.935(5)
3.3722(19)
Al(2)-O(3)
Al(2)-C(46)
Al(2)-C(47)
Al(2)-N(1)
1.870(3)
1.939(6)
1.941(5)
1.968(4)
due to the presence of two different products, but five
distinct sets of resonances arising from Al-methyl
groups could be identified. Unfortunately, every attempt
to purify these materials was unsuccessful. Although
single crystals of the complexes could be isolated, the
product was consistently contaminated with small
amounts of either 8 or 9. The crystal structure of the
product from the reaction of 9 and 1 equiv of trimethy-
laluminum was obtained, and the structure is presented
in Figure 5 and Table 4. As depicted in Scheme 3, the
product of the reaction is a trimetallic species [(6)Al3-
Me6], 10, wherein the incoming aluminum center has
caused Al(1) to lose one of the three phenoxide bonds
found in 9, allowing the arm to bind the incoming
aluminum. The ligand has also inverted to adopt the
type 1 orientation found in 6H3. Although 2 and 10 both
contain three {AlMe2} groups, the incorporation of the
imine functionality has indeed disrupted the Al3O3 core
as originally intended. The bond distances of the
aluminum coordinated to the imine in 10 are indistin-
Bond Angles
O(1)-Al(1)-O(2) 107.59(15) O(3)-Al(2)-C(46) 111.7(2)
O(1)-Al(1)-O(3) 102.65(14) O(3)-Al(2)-C(47) 107.57(19)
O(2)-Al(1)-O(3) 103.08(14) C(46)-Al(2)-C(47) 124.0(3)
O(1)-Al(1)-C(45) 116.3(2)
O(3)-Al(2)-N(1)
92.23(16)
O(2)-Al(1)-C(45) 113.74(19) C(46)-Al(2)-N(1) 106.1(2)
O(3)-Al(1)-C(45) 112.15(19) C(47)-Al(2)-N(1) 110.7(2)
guishable from the analogous distances in 9, but the
remaining aluminum oxygen distances in 10 are all
significantly longer than corresponding bonds in 9,
ranging from 1.757(2)° for Al(1)-O(1) to 1.931(3)° for
Al(1)-O(2). Compounds 9 and 10 appear to be in equil-
ibrium, and repeated recrystallization of solutions con-
taining predominately 10 only increased the ratio of 9.
In an attempt to obtain a clean sample of a product
with this trimetallic unit, 6 equiv of trimethyl-
aluminum was added to a solution of the Salen ligand
7H6 (Scheme 4). Earlier work had indicated that each
imine/trisphenoxide half of this ligand reacts with
(34) Hill, M. S.; Hutchison, A. R.; Keizer, T. S.; Parkin, S.; VanAel-
styn, M. A.; Atwood, D. A. J . Organomet. Chem. 2001, 628, 71-75.

Methyl Aluminum Complexes
Organometallics, Vol. 21, No. 2, 2002 423
Ta ble 4. X-r a y Str u ctu r a l Da ta a for Com p ou n d s 10-13
10‚C5H12 11‚2CHCl3
12‚11/4CH2Cl2
23 758 23 326 32 324
13‚2CH2Cl2
20 355
total no. of reflns
no. of unique reflns
R(int)
8481
7227
11 290
6093
0.0746
23.50
0.1047
23.00
0.0893
28.34
0.1080
23.50
θ
max (deg)
chemical formula
fw
C
55H84Al3NO3
C90H136N2Al6Cl6O6
1716.59
C44.25H59.5NAl2Cl2.5O4S
844.07
C41H50NAlCl4O3
773.60
888.17
cryst syst
space group
triclinic
P21/n
0.112
monoclinic
P21/c
0.262
13.3899(19)
21.173(3)
18.885(3)
104.594(3)
5181.0(13)
2
monoclinic
P21/n
0.292
12.7251(8)
15.7782(10)
23.4282(14)
99.951(1)
4633.1(5)
4
monoclinic
P21/c
0.346
9.5604(9)
25.373(2)
17.1538(16)
98.415(12)
4116.4(7)
4
µ(Mo KR) (mm-1
)
a (Å)
b (Å)
c (Å)
11.3973(6)
22.8557(12)
22.6521(12)
103.1290(10)
5746.5(5)
4
0.0729 [5753]
0.1786
0.246,-0.215
â (deg)
Vc (Å3)
Z
R1 [I g 2σ(I) data]b
wR2 (all data)c
larg diff peak, hole (e/Å3)
0.0889 [3854]
0.2194
0.467,-0.412
0.0549 [6103]
0.1419
0.418, -0.364
0.0705 [3066]
0.1522
0.244, -0.222
a
b
2
Obtained with monochromatic Mo KR radiation (λ ) 0.71073 Å) at 173 K. R1 ) ∑||Fo| - |Fc||/∑|Fo|. c wR2 ) {∑[w(Fo
-
Fc2)2/∑[w(Fo2)2]}1/2 where w ) 1/[σ2(Fo2) + (XP)2 + YP] where P ) (Fo + 2Fc2)/3}.
2
Sch em e 4
F igu r e 6. Diagram of the structure of 11 (30% probability
ellipsoids; carbon atoms drawn with arbitrary radii). The
tert-butyl methyl groups and all hydrogen atoms have been
omitted for clarity. Primed and unprimed atoms are related
by a center of inversion.
resonances arising from methyl groups coordinated to
an aluminum center, and these two peaks integrated
in a ratio of 2:1. As illustrated in the solid-state
structure of the complex depicted in Figure 7, the DMSO
substrate disrupts the aryloxide bridge, Al(1)-O(3)-Al-
(2), in 8 and coordinates to Al(1) in a η1-O mode with a
bond distance of 1.8238(16) Å. The geometry about this
metal remains tetrahedral, with angles ranging between
100.36(7)° and 115.11(7)°, and there is a small but
perceptible shortening of the bond between Al(1) and
O(1) to 1.7169(16) Å. As expected, the disruption of the
bridging interaction significantly shortens the distance
from Al(2) to O(3) to 1.7726(15) Å, but in comparison to
8, the remaining distances to Al(2) are not perturbed
to any statistically significant extent. The inclusion of
a coordinated DMSO molecule has induced the inversion
of the phenolic arms with respect to the central methine
carbon to a type 1 configuration with all three oxygen
donors aligned with the methine hydrogen. The two
metal centers are situated at a distance of 5.419(1) Å
from each other.
aluminum in a manner exactly analogous to both 5H3
and 6H3,31 and indeed, the C2 symmetric hexametallic
species [(7)Al6Me12], 11, consisting of two separate
trimetallic species was isolated as shown in Figure 6.
As highlighted in Table 5, the bond distances in 10 and
11 are identical and the data warrant no further
discussion. Fortunately, the solubility properties of 11
allowed for a more detailed characterization of the
compound relative to 10, but presumably due to the
presence of trace amounts of the bimetallic species [(7)-
Al4Me6], crystalline 11 still failed to analyze satisfac-
torily.
In sharp contrast to reaction with DMSO, the addition
of either cylcohexanone or cyclopentanone to 8 produced
With the intent to probe the interactions of Lewis
bases with the binuclear aluminum complexes, the
electron-rich DMSO compound was introduced into a
solution of 8 (Scheme 5), and the clean conversion of 8
to a new species [(5){AlMe2}{AlMe(OSMe2)}], 12, was
1
the same aluminum product, and the H and 13C NMR
spectra of the material exhibited only a single resonance
for a methyl group bound to aluminum. Moreover, the
1H and 13C NMR spectra indicated the isolated metal
product did not contain the ketone substrate, and in the
case of the reaction with cyclohexanone, the organic
1
clearly evident in the H NMR spectrum of the reaction
mixture. Moreover, the spectrum exhibited only two

424 Organometallics, Vol. 21, No. 2, 2002
Cottone et al.
Ta ble 5. Selected Bon d Len gth s (Å) a n d An gles
(d eg) for 10 a n d 11
Bond Lengths
10
11
Al(1)-O(1)
Al(1)-O(2)
Al(1)-C(45)
Al(1)-C(46)
Al(2)-O(2)
Al(2)-O(3)
Al(2)-C(47)
Al(2)-C(48)
Al(3)-O(3)
Al(3)-C(49)
Al(3)-C(50)
Al(3)-N(1)
Al(1)‚‚‚Al(2)
Al(2)‚‚‚Al(3)
1.757(2)
1.931(3)
1.952(4)
1.947(4)
1.859(2)
1.914(3)
1.954(4)
1.948(4)
1.879(3)
1.937(4)
1.935(4)
1.976(3)
3.4015(15)
3.5043(18)
Al(1)-O(1)
Al(1)-O(2)
Al(1)-C(39)
Al(1)-C(40)
Al(2)-O(2)
Al(2)-O(3)
Al(2)-C(41)
Al(2)-C(42)
Al(3)-O(3)
Al(3)-C(43)
Al(3)-C(44)
Al(3)-N(1)
Al(1)‚‚‚Al(2)
Al(2)‚‚‚Al(3)
1.768(4)
1.957(4)
1.961(6)
1.956(6)
1.842(4)
1.930(4)
1.954(6)
1.946(6)
1.858(4)
1.911(7)
1.953(7)
1.980(6)
3.420(2)
3.441(3)
F igu r e 7. Diagram of the structure of 12 (30% probability
ellipsoids; carbon atoms drawn with arbitrary radii).
Hydrogen atoms have been omitted for clarity.
Bond Angles
10
11
O(1)-Al(1)-O(2)
O(1)-Al(1)-C(45)
O(1)-Al(1)-C(46)
O(2)-Al(1)-C(45)
O(2)-Al(1)-C(46)
109.40(12) O(1)-Al(1)-O(2)
107.03(14) O(1)-Al(1)-C(39)
112.20(15) O(1)-Al(1)-C(40)
107.68(15) O(2)-Al(1)-C(39)
106.14(15) O(2)-Al(1)-C(40)
106.88(18)
108.9(2)
111.0(3)
106.6(2)
104.1(2)
C(45)-Al(1)-C(46) 114.26(19) C(39)-Al(1)-C(40) 118.6(3)
O(2)-Al(2)-O(3)
O(2)-Al(2)-C(47)
O(2)-Al(2)-C(48)
O(3)-Al(2)-C(47)
O(3)-Al(2)-C(48)
104.60(11) O(2)-Al(2)-O(3)
108.78(16) O(2)-Al(2)-C(41)
112.29(15) O(2)-Al(2)-C(42)
104.55(14) O(3)-Al(2)-C(41)
107.65(17) O(3)-Al(2)-C(42)
107.07(17)
110.6(2)
108.2(2)
101.2(2)
109.5(2)
C(47)-Al(2)-C(48) 117.85(19) C(41)-Al(2)-C(42) 119.6(3)
O(3)-Al(3)-C(49)
O(3)-Al(3)-C(50)
C(49)-Al(3)-C(50) 121.4(2)
O(3)-Al(3)-N(1)
C(49)-Al(3)-N(1)
C(50)-Al(3)-N(1)
Al(1)-O(2)-Al(2)
Al(2)-O(3)-Al(3)
117.82(18) O(3)-Al(3)-C(43)
107.09(15) O(3)-Al(3)-C(44)
106.9(3)
119.2(3)
C(43)-Al(3)-C(44) 119.8(3)
88.91(12) O(3)-Al(3)-N(1)
89.5(2)
110.5(3)
106.6(3)
128.3(2)
130.6(2)
107.84(17) C(43)-Al(3)-N(1)
108.71(16) C(44)-Al(3)-N(1)
127.62(15) Al(1)-O(2)-Al(2)
135.04(13) Al(2)-O(3)-Al(3)
F igu r e 8. Diagram of the structure of 13 (30% probability
ellipsoids; carbon atoms drawn with arbitrary radii).
Hydrogen atoms have been omitted for clarity.
Sch em e 5
Ta ble 6. Selected Bon d Len gth s (Å) a n d An gles
(d eg) for 12
Bond Lengths
Al(1)-O(1)
Al(1)-O(2)
Al(1)-O(4)
Al(1)-C(39)
Al(1)‚‚‚Al(2)
1.7169(16)
1.7553(15)
1.8238(16)
1.949(2)
Al(2)-O(3)
Al(2)-C(40)
Al(2)-C(41)
Al(2)-N(1)
1.7726(15)
1.943(3)
1.961(3)
1.980(2)
5.4191(9)
Bond Angles
O(1)-Al(1)-O(2) 115.11(7)
O(1)-Al(1)-O(4) 107.31(7)
O(2)-Al(1)-O(4) 100.36(7)
O(1)-Al(1)-C(39) 111.10(10) O(3)-Al(2)-N(1)
O(2)-Al(1)-C(39) 114.43(9) C(40)-Al(2)-N(1) 110.19(11)
O(4)-Al(1)-C(39) 107.42(11) C(41)-Al(2)-N(1) 105.32(11)
Al(1)-O(4)-S(1) 123.01(9)
O(3)-Al(2)-C(40) 110.39(10)
O(3)-Al(2)-C(41) 110.37(10)
C(40)-Al(2)-C(41) 122.84(13)
93.66(8)
Ta ble 7. Selected Bon d Len gth s (Å) a n d An gles
(d eg) for 13
Bond Lengths
Al(1)-O(1)
Al(1)-O(2)
1.742(3)
1.751(3)
Al(1)-O(3)
Al(1)-C(39)
1.797(3)
1.944(4)
Bond Angles
O(1)-Al(1)-O(2) 108.04(16) O(1)-Al(1)-C(39) 113.50(19)
O(1)-Al(1)-O(3) 102.80(15) O(2)-Al(1)-C(39) 115.5(2)
O(2)-Al(1)-O(3) 107.43(15) O(3)-Al(1)-C(39) 108.68(19)
AlMe-], 13, in addition to the aldol condensation product
bicyclohexyliden-2-one, which was isolated and charac-
terized. Similar aldol condensation chemistry has been
seen with Cl2AlCH2TiCl3,35 and no attempt was made
to ascertain the fate of the AlMe2 unit lost from 8 during
product bicyclohexyliden-2-one was isolated and char-
acterized from the reaction mixture. As illustrated in
the solid-state structure of 13 (Figure 8; Table 7) and
in Scheme 6, the reaction with cyclohexanone produced
a mononuclear zwitterionic aluminum complex, [(5H)+-

Methyl Aluminum Complexes
Sch em e 6
Organometallics, Vol. 21, No. 2, 2002 425
mixed donor ligands of the type NO3 have been synthe-
sized and used to prepare a new class of bifunctional
aluminum species 8 and 9 containing a stabilizing
phenoxide bridge between the two metal centers. De-
spite the presence of the bridge, the complexes are
susceptible to further reactivity, as evidenced by the
formation of the unusual trimetallic species 10 upon the
addition of 1 equiv of aluminum to solutions of 9.
Moreover, Lewis bases such as DMSO will induce the
cleavage of one of the aluminum oxygen bonds involved
in the bridging interaction in the bimetallic species,
allowing for the isolation of new bimetallic species
containing a coordinated Lewis base in proximity to the
second aluminum center. Both 8 and 9 will also react
with the Lewis bases cyclopentanone and cyclohexanone
to afford a monometallic, zwitterionic product as well
as the organic aldol condensation product. Work has
now begun on a study of the ability of the bimetallic
complexes 8 and 9 to catalyze organic transformations,
and efforts to adjust the constraints of the ligand system
to enhance cooperativity in these reactions are also
underway.
Exp er im en ta l Section
Unless otherwise stated, all manipulations were carried out
under an inert atmosphere of N2 in a drybox or on a vacuum
line using standard Schlenk techniques. All solvents used were
dried and distilled prior to use. All NMR spectra were recorded
on a Varian Mercury 300 MHz spectrometer at 299.95 and
75.47 MHz for the proton and carbon channels, respectively,
or on a Varian VXR 300 MHz spectrometer at 78.17 MHz for
the aluminum channel. Chemicals shifts (δ) are reported with
reference to [Al(H2O)6]Cl3 for 27Al spectra. IR spectra were
recorded as KBr pellets on a Bruker Vector instrument at a
resolution of 2 cm-1. Elemental analyses were performed at
Atlantic Microlab Inc., Norcross, GA, or Complete Analysis
Laboratories Inc., Parsippany, NJ . Tris(3,5-di-tert-buyl-2-
hydroxyphenyl)methane23 and 2-hydroxy-5-methyl-1,3-benzene
dicarboxaldehyde37 were prepared as previously described.
Syn th esis of [(Tr is(3,5-d i-ter t-bu tyl-2-p h en oxy)m eth -
a n e)Al3Me6], 2. A 2.0 M solution of trimethylaluminum in
toluene (2.38 mmol, 1.19 mL) was added to a cooled (0 °C)
solution of 0.50 g (0.79 mmol) of tris(3,5-di-tert-butyl-2-
hydroxyphenyl)methane in 20 mL of toluene. The mixture was
slowly allowed to warm to room temperature, and the solution
was stirred overnight. The solvent was removed in vacuo, and
the residue was redissolved in a minimal amount of pentane
and filtered. The filtrate was stored at -30 °C, and the
resultant crystalline material was collected by filtration and
dried to yield 0.50 g of product. Yield: 78%. Anal. Calcd for
the course of the reaction. Compound 9 reacted with
cyclohexanone in an analogous manner to afford
[(6H)+AlMe-], 14.
Unlike the transformation from 8 to 12, the conver-
sion of 8 to 13 conserves the geometry about the central
methine carbon. Once again, the angles around the
aluminum center are unspectacular and range from
102.81(15)° to 115.5(2)°. The Al(1)-O(1) and Al(1)-O(2)
distances are 1.742(3) and 1.751(3) Å, respectively, and
are shorter than the corresponding Al(1)-O(3) bond
distance of 1.797(3) Å. We attribute this slight elonga-
tion of the Al(1)-O(3) bond to the formation of a
hydrogen bond to the protonated imine and not proto-
nation of the oxygen atom. During the refinement of the
X-ray crystal structure, the largest peak in the final
difference Fourier map was located ∼1.0 Å from the
imine nitrogen atom, and this position isotropically
refined to a distance of 0.92(6) and 1.88(6) Å from N(1)
and O(1), respectively. Further suggesting the formation
of zwitterions in 13 and 14, Barron and co-workers have
identified a preference for a zwitterionic alkoxide/
ammonium species rather than the alcohol/amine com-
plex in the case of the reaction of HOCH2CH2CH2NMe2
with Al(tBu)3.36
C
49H79Al3O3: C, 73.83; H, 9.99. Found: C, 74.12; H, 10.16. 1H
NMR (CD2Cl2): δ 8.42 (s, 1H, CH), 7.81 (d, J ) 2.44 Hz, 3H,
t
aryl-H), 7.27 (d, J ) 2.44 Hz, 3H, aryl-H), 1.39 (s, 27H, Bu),
t
1.32 (s, 27H, Bu), -0.18 (s, 9H, Al-CH3), -1.70 (s, 9H, Al-
CH3). 13C NMR (CD2Cl2): δ 150.9 (aryl), 148.3 (aryl), 139.1
(aryl), 136.1 (aryl), 124.9 (aryl), 123.7 (aryl), 36.3 (tBu), 35.0
(tBu), 32.6 (tBu), 31.7 (tBu), 27.9 (CH), -6.2 (Al-Me), -8.7 (Al-
Me). 27Al NMR (CD2Cl2): δ 63 ω1/2 3.9 kHz.
Con clu sion s
The reaction of trimethylaluminum with the ligand
tris(3,5-di-tert-butyl-2-hydroxyphenyl)methane affords
a C3-symmetric trimetallic complex wherein the metals
are coordinatively saturated and sterically congested.
With the intention of disrupting the formation of a
stabilizing Al3O3 unit found in this species, several
Syn th esis of 3-(2,2′-Meth ylen ebis(4-m eth yl-6-ter t-bu -
tylp h en ol)-5-m eth yl-2-h yd r oxyben za ld eh yd e, 3H3. A 2.20
g (13.4 mmol) portion of 2-hydroxy-5-methyl-1,3-benzene di-
carboxaldehyde was added to 2-tert-butyl-4-methylphenol (5.50
g, 33.5 mmol). Trifluoroacetic acid (10 mL) was added in 1 mL
aliquots over a period of several minutes, and the mixture was
stirred for 3 h. The resultant pink precipitate was isolated and
washed with cold methanol and dried in vacuo to yield 4.53 g
(35) Piotrowski, A. M.; Malpass, D. B.; Boleslawski, M. P.; Eisch, J .
J . J . Org. Chem. 1988, 53, 2829-2835.
(36) McMahon, C. N.; Bott, S. G.; Barron, A. R. J . Chem. Soc., Dalton
Trans. 1997, 3129-3137.
(37) Taniguchi, S. Bull. Chem. Soc. J pn. 1984, 57, 2683-2684.

426 Organometallics, Vol. 21, No. 2, 2002
Cottone et al.
(72%) of product as an off-white powder. Anal. Calcd for
(s, CH, 1H), 5.58 (s, OH, 2H), 4.77 (s, N-CH2, 2H), 2.22 (s, Me,
t
C
ν
31H38O4: C, 78.44; H, 8.07. Found: C, 77.97; H, 8.35. IR (KBr,
3H), 1.37 (s, Me, 6H), 1.19 (s, Bu, 18H). 13C NMR: δ 165.6
max/cm-1): 3462m, 3299m, 3000m, 2954s, 2866m, 1634s,
(NdCH), 158.0 (aryl), 151.1 (aryl), 142.1 (aryl), 137.7 (aryl),
136.9 (aryl), 134.5 (aryl), 130.9 (aryl), 129.2 (aryl), 129.0 (aryl),
128.1 (aryl), 127.9 (aryl), 127.8 (aryl), 127.1 (aryl), 124.2 (aryl),
123.0 (aryl), 118.2 (aryl), 62.3 (N-CH2), 38.7 (CH), 35.2 (tBu),
34.5 (tBu), 31.8 (tBu), 30.1 (tBu), 20.8 (Me).
1443s, 1389m, 1306m, 1254s, 1234s, 1213s, 1163s, 1003s,
884m, 764m, 711m, 669m, 502m. 1H NMR (CDCl3): δ 11.32
(br s, OH, 1H), 9.88 (s, HCdO, 1H), 7.32 (d, aryl-H, J ) 2.1
Hz, 1H), 7.06 (d, aryl-H, J ) 1.9 Hz, 1H), 7.05 (d, aryl-H, J )
1.9 Hz, 2H), 6.53 (d, aryl-H, J ) 1.7 Hz, 2H), 5.92 (s, CH, 1H),
4.94 (br s, OH, 2H), 2.28 (s, Me, 3H), 2.19 (s, Me, 6H), 1.35 (s,
tert-Bu, 18H). 13C NMR: δ 196.8 (HCdO), 156.9 (aryl), 151.2
(aryl), 138.8 (aryl), 137.8 (aryl), 133.0 (aryl), 129.7 (aryl), 129.6
(aryl), 129.3 (aryl), 127.6 (aryl), 127.5 (aryl), 127.0 (aryl), 120.5
(aryl), 39.3 (CH), 34.9 (tBu), 30.0 (tBu), 21.3 (Me), 20.8 (Me).
High-resolution FAB-MS: calcd 474.277 (M+), found 474.276.
Syn th esis of 3-(2,2′-Meth ylen ebis(4,6-di-ter t-bu tylph en -
ol)-5-m eth yl-2-h yd r oxyben za ld eh yd e, 4H3. A 2.20 g (13.4
mmol) portion of 2-hydroxy-5-methyl-1,3-benzene dicarboxal-
dehyde was added to 2,4-di-tert-butylphenol (6.90 g, 33.5
mmol), and the reaction mixture was treated in a manner
similar to 1H3 to yield 5.75 g (77%) of product as a pink solid.
Crystals suitable for elemental analysis were obtained from
an evaporation of a saturated acetone solution. Anal. Calcd
for C37H50O4‚C3H6O: C, 77.87; H, 9.16. Found: C, 77.97; H,
9.50. IR (KBr, νmax/cm-1): 3627w, 3528m, 2964s, 2904s, 2871s,
1659s, 1619m, 1599m, 1459s, 1360s, 1310s, 1264s, 1181s,
Syn th esis of N,N′-Bis{3-[2,2′-m eth ylen ebis(4,6-d i-ter t-
b u t ylp h e n ol)-5-m e t h ylsa licylid e n e ]}-1,2-e t h yle n e d i-
a m in e, 7H6. A 1.00 g portion of 4H3 (1.79 mmol) was dissolved
in 40 mL of ethanol, and 59 µL (0.89 mmol) of 1,2-ethylene-
diamine was added. The mixture was refluxed for 12 h and
cooled to room temperature, and the yellow microcrystalline
solid was collected by filtration. The product was washed with
cold methanol (4 × 10 mL) and dried under vacuum to yield
0.85 g of solid. Yield: 83%. Anal. Calcd for C76H104N2O6: C,
79.96; H, 9.18; N, 2.45. Found: C, 80.13; H, 9.23; N, 2.34. IR
(KBr, νmax/cm-1): 3562m, 3522m, 3451w, 2952s, 2910m,
2871m, 1636s (CdN stretch), 1599w, 1470s, 1443m, 1319m,
1363m, 1290m, 1268m, 1189s, 1029w, 980w, 888w, 770w,
658w, 569w, 471w. 1H NMR (CDCl3): δ 14.07 (s, br, 2H, OH),
8.25 (s, 2H, NdCH), 7.23 (d, J ) 1.95 Hz, 4H, Ar-H), 6.97 (s,
2H, Ar-H), 6.93 (s, 2H, Ar-H), 6.85 (d, J ) 1.95 Hz, 4H, Ar-H),
6.00 (s, 2H, CH), 5.51 (s, 4H, OH), 3.91 (s, 4H, N-CH2), 2.16
t
t
(s, 6H, CH3), 1.37 (s, 36H, Bu), 1.17 (s, 36H, Bu). 13C NMR
(CDCl3): δ 166.9 (NdCH), 157.1 (aryl), 151.0 (aryl), 142.1
(aryl), 136.8 (aryl), 134.5 (aryl), 131.1 (aryl), 128.6 (aryl), 128.1
(aryl), 127.0 (aryl), 124.1 (aryl), 122.9 (aryl), 118.0 (aryl), 59.0
(N-CH2), 38.4 (CH), 35.2 (tBu), 34.5 (tBu), 31.7 (tBu), 30.0 (tBu),
20.7 (Me). A crystal suitable for an X-ray determination was
obtained by slow evaporation of a solution of 7 in THF.
P r ep a r a t ion of [(5)Al2Me3], 8. A 2.0 M solution of tri-
methylaluminum in toluene (0.95 mL, 1.90 mmol) was added
to a solution of 5H3 (0.53 g, 0.95 mmol) in toluene (50 mL) at
0 °C. The reaction was held at 0 °C for 1 h and was gradually
allowed to warm to room temperature. After 4 h, the solvent
was removed, and the residue was dissolved in pentane (25
mL) and stirred at ambient conditions for an additional hour.
A precipitate formed and was isolated and dried to yield 0.39
g of a yellow powder (63%). Crystals suitable for X-ray and
elemental analysis were obtained from a saturated methylene
chloride solution. Anal. Calcd for C41H51NAl2O3: C, 74.63; H,
1
885m, 768m, 668m, 476w. H NMR (CDCl3): δ 11.39 (s, OH,
1H). 9.83 (s, HCdO, 1H), 7.31 (s, aryl-H, 1H), 7.27 (d, aryl-H,
J ) 2.0 Hz, 1H), 7.02 (s, aryl-H, 1H), 6.69 (d, aryl-H, J ) 1.8
Hz, 2H), 6.07 (s, CH, 1H), 3.95 (br s, OH, 2H), 2.26 (s, Me,
3H), 1.39 (s, tBu, 18H), 1.17 (s, tert-Bu, 18H). 13C NMR: δ 197.1
(HCdO), 156.8 (aryl), 150.6 (aryl), 142.5 (aryl), 138.5 (aryl),
137.1 (aryl), 132.7 (aryl), 130.4 (aryl), 129.3 (aryl), 127.4 (aryl),
124.0 (aryl), 122.9 (aryl), 120.2 (aryl), 38.3 (CH), 35.0 (tBu),
34.3 (tBu), 31.5 (tBu), 29.6 (tBu), 20.5 (Me). High-resolution
FAB-MS: calcd 558.371 (M+), found 558.370.
Syn th esis of 3-(2,2′-Meth ylen ebis(4-m eth yl-6-ter t-bu -
tylp h en ol)-5-m eth ylsa licylid en eben zylim in e, 5H3. A por-
tion of 3H3 (2.61 g, 5.50 mmol) was dissolved in ethanol (100
mL) with benzylamine (0.60 mL, 5.54 mmol). The reaction was
refluxed for 12 h, resulting in the formation of a yellow
precipitate. The solid was collected and dried in vacuo over-
night to afford 2.85 g of product (92%). Anal. Calcd for C38H45
-
NO3: C, 80.95; H, 8.05; N, 2.49. Found: C, 80.94; H, 8.46; N,
2.15. IR (KBr, νmax/cm-1): 3497s, 3127m (O-H stretch), 2950s,
2917m, 2871m, 1636s (CdN stretch), 1443s, 1400s, 1362m,
1247m, 1181m, 866w, 767w, 699w. 1H NMR (CDCl3): δ 14.22
(s, OH, 1H), 8.31 (s, HCdN, 1H), 7.25-7.36 (m, benzyl-H, 5H),
7.02 (d, aryl-H, J ) 1.9 Hz, 2H), 6.98 (d, aryl-H, J ) 1.9 Hz,
2H), 6.65 (d, aryl-H, J ) 1.9 Hz, 2H), 5.94 (s, CH, 1H), 5.42
(br s, OH, 2H), 4.75 (s, H2C-N, 2H), 2.21 (s, Me, 3H), 2.18 (s,
Me, 6H), 1.35 (s, tBu, 18H). 13C NMR: δ 165.5 (NdCH), 158.0
(aryl), 151.2 (aryl), 137.7 (aryl), 137.6 (aryl), 134.5 (aryl), 131.0
(aryl), 129.1 (aryl), 128.9 (aryl), 128.7 (aryl), 128.1 (aryl), 127.8
(aryl), 127.7 (aryl), 127.6 (aryl), 127.5 (aryl), 127.1 (aryl), 118.2
(aryl), 62.3 (N-CH2), 39.2 (CH), 34.9 (tBu), 29.9 (tBu), 21.3 (Me),
20.8 (Me). High-resolution FAB-MS: calcd 563.340 (M+), found
563.341.
Syn t h esis of 3-(2,2′-Met h ylen eb is(4,6-d i-ter t-b u t yl-
p h en ol)-5-m eth ylsa licylid en eben zylim in e, 6H3. A portion
of 4H3 (2.40 g, 4.30 mmol) was dissolved in ethanol (100 mL)
with benzylamine (0.47 mL, 4.30 mmol). The reaction was
heated under reflux overnight, resulting in the formation of a
precipitate. The yellow solid was collected by filtration and
dried in vacuo to afford 2.31 g of product (83%). Anal. Calcd
for C44H57NO3: C, 81.56; H, 8.87; N, 2.16. Found: C, 81.34;
H, 9.25; N, 2.15. IR (KBr, νmax/cm-1): 3386m (O-H stretch),
2950s, 2865m, 1636s (CdN stretch), 1535m, 1477s, 1360s,
1294m, 1198s, 1149m, 880w, 757w, 702m, 661w. 1H NMR
(CDCl3): δ 14.36 (s, OH, 1H), 8.33 (s, HCdN, 1H), 7.25-7.37
(m, benzyl-H, 5H), 7.23 (d, aryl-H, J ) 2.1 Hz, 2H), 7.00 (d,
aryl-H, J ) 3.9 Hz, 2H), 6.88 (d, aryl-H, J ) 2.3 Hz, 2H), 6.02
7.79; N, 2.12. Found: C, 74.52; H, 7.79; N, 2.09. IR (KBr, νmax/
cm-1): 3438w, 3151w, 2958s, 2923m, 2858m, 1624s (CdN
stretch), 1583m, 1554w, 1470s, 1444s, 1397m, 1352w, 1293m,
1270m, 1208m, 1163w, 1065w, 1026w, 895w, 863s, 801s, 758m,
752m, 698s, 674s, 556w, 497w, 445w. 1H NMR (CDCl3): δ 8.17
(s, NdCH, 1H), 7.37 (d, aryl-H, J ) 1.8 Hz, 1H), 7.16-7.34
(m, benzyl-H, 6H), 6.96 (d, aryl-H, J ) 1.7 Hz, 1H), 6.90 (br s,
aryl-H, 2H), 6.82 (br s, aryl-H, 1H), 6.75 (br s, aryl-H, 1H),
5.16 (s, CH, 1H), 4.67-4.85 (m, N-CH2, 2H), 2.23 (s, Me, 3H),
t
2.14 (s, Me, 3H), 1.29 (s, Bu, 18H), -0.59 (s, Al-CH3, 3H),
-0.68 (s, Al-CH3, 3H), -1.91 (s, Al-CH3, 3H). 13C NMR: δ 170.5
(NdCH), 156.4 (aryl), 155.9 (aryl), 149.9 (aryl), 140.9 (aryl),
139.5 (aryl), 139.2 (aryl), 138.9 (aryl), 133.9 (aryl), 133.1 (aryl),
132.5 (aryl), 131.3 (aryl), 130.2 (aryl), 129.7 (aryl), 129.5 (aryl),
129.4 (aryl), 129.0 (aryl), 126.9 (aryl), 126.4 (aryl), 125.7 (aryl),
125.6 (aryl), 121.7 (aryl), 61.7 (N-CH2), 57.6 (CH), 35.2 (tBu),
34.8 (tBu), 30.7 (tBu), 30.3 (tBu), 20.9 (Me), 20.8 (Me), 20.4 (Me),
-10.0 (Al-Me), -11.8 (Al-Me), -13.9 (Al-Me). 27Al NMR
(CDCl3): δ 61 ω1/2 5.8 kHz. High-resolution FAB-MS: calcd
659.350 (M+), found 659.350.
P r ep a r a t ion of [(6)Al2Me3], 9. A 2.0 M solution of tri-
methylaluminum in toluene (0.77 mL, 1.54 mmol) was added
to a solution of 6H3 (0.50 g, 0.772 mmol) in toluene (50 mL) at
0 °C. The sealed reaction vessel was immersed in an ice-water
bath for 1 h and slowly allowed to warm to room temperature.
The solvent was removed under vacuum after 4 h, and the
residue was redissolved in pentane (25 mL) and stirred at
ambient conditions for an additional hour. A precipitate formed
and was isolated, washed with cold pentane, and dried to yield

Methyl Aluminum Complexes
Organometallics, Vol. 21, No. 2, 2002 427
0.50 g of product as a yellow powder (77%). Crystals suitable
for elemental analysis were obtained from a saturated chlo-
roform solution. Anal. Calcd for C47H63NAl2O3: C, 75.88; H,
to a solution of 8 (0.10 g, 0.154 mmol) in CH2Cl2 (4 mL), and
the mixture was stirred overnight. The volume was reduced
to half, and the solution was stored at -30 °C. Crystals formed
over several days and were isolated, washed with cold pentane,
and dried to yield 0.064 g of product as a yellow solid (58%).
Anal. Calcd for C43H57NAl2O4S: C, 69.99; H, 7.79; N, 1.90.
Found: C, 69.89; H, 7.71; N, 1.71. IR (KBr, νmax/cm-1): 3395w,
3131w, 2948s, 2919s, 2861w, 1620s (CdN stretch), 1551s,
1473s, 1443s, 1310m, 1248m, 1177m, 1030w, 991m, 959m,
895m, 869s, 811m, 794m, 684s, 650s, 573w, 496w. 1H NMR
(CDCl3): δ 8.05(s, NdCH, 1H), 7.59 (s, aryl-H, 1H), 7.18-7.34
(m, benzyl-H, 5H), 6.82 (s, aryl-H, 1H), 6.78 (s, aryl-H, 2H),
6.76 (s, aryl-H, 2H), 6.01 (s, CH, 1H), 4.60 (s, N-CH2, 2H), 2.68
(br s, S-CH3, 6H), 2.18 (s, Me, 3H), 2.14 (s, Me, 18H), 1.35 (s,
tBu, 18H), -0.69 (s, Al-CH3, 3H), -1.35 (s, Al-CH3, 6H). 13C
NMR: δ 170.8 (NdCH), 165.3 (aryl), 161.5 (aryl), 153.8 (aryl),
138.2 (aryl), 138.1 (aryl), 137.6 (aryl), 136.5 (aryl), 135.4 (aryl),
132.5 (aryl), 131.3 (aryl), 129.1 (aryl), 128.7 (aryl), 125.2 (aryl),
123.5 (aryl), 120.5 (aryl), 118.2 (aryl), 60.4 (N-CH2), 37.8 (CH),
35.4 (S-Me), 34.3 (S-Me), 35.0 (tBu), 30.4 (tBu), 21.4 (Me), 20.9
(Me), -10.6 (Al-Me), -12.7 (Al-Me). 27Al NMR (CDCl3): δ 61
ω1/2 2.8 kHz.
P r ep a r a tion of [(5H)+AlMe-], 13. A 0.20 g (0.303 mmol)
portion of 8 was dissolved in methylene chloride (5 mL) and
cooled to -30 °C. In a separate flask, the desired ketone
(cyclopentanone: 52.0 µL, 0.606 mmol or cyclohexanone: 49.4
µL, 0.606 mmol) was dissolved in 2 mL of methylene chloride
and cooled to -30 °C. The two chilled solutions were mixed
and allowed to stir at room temperature for 12 h. The volume
of methylene chloride was reduced to ca. 2 mL, and the mixture
was stored at -30 °C until a crystalline solid formed. The solid
was isolated and dried to yield 0.10 g of yellow crystals (52%).
Anal. Calcd for C39H46NAlO3: C, 77.58; H, 7.68; N, 2.32.
Found: C, 77.19; H, 7.51; N, 2.06. IR (KBr, νmax/cm-1): 3477w
(N-H stretch), 3145w, 2949s, 2923m, 2865m, 1647s (CdN
stretch), 1626m, 1556m, 1470s, 1443s, 1404m, 1352m, 1290m,
1256m, 1202m, 1032w, 861m, 801m, 698m, 659m, 550w, 497w.
1H NMR (CD2Cl2): δ 7.93 (d, NdCH, J ) 14.4 Hz, 1H), 7.52
(d, aryl-H, J ) 1.8 Hz, 1H), 7.34-7.48 (m, benzyl-H, 5H), 7.32
(d, aryl-H, J ) 2.1 Hz, 1H), 6.96 (br s, HNdC, 1H), 6.92 (d,
aryl-H. 4J ) 2.0 Hz, 2H), 6.81 (d, aryl-H, J ) 1.9 Hz, 2H), 5.12
(s, CH, 1H), 4.73 (d, N-CH2, J ) 5.4 Hz, 2H), 2.24 (s, Me,
3H), 2.16 (s, Me, 6H), 1.33 (s, tBu, 18H), -0.80 (s, Al-CH3, 3H).
13C NMR: δ 166.1 (NdCH), 157.2 (aryl), 145.0 (aryl), 139.8
(aryl), 137.7 (aryl), 134.0 (aryl), 132.3 (aryl), 132.0 (aryl), 131.4
(aryl), 130.2 (aryl), 130.1 (aryl), 129.6 (aryl), 129.2 (aryl), 126.9
(aryl), 125.8 (aryl), 116.3 (aryl), 59.4 (N-CH2), 56.2 (CH), 35.2
(tBu), 30.3 (tBu), 20.8 (Me), 20.2 (Me), -13.3 (Al-Me). 27Al NMR
(CD2Cl2): δ 61 ω1/2 3.2 kHz.
8.54; N, 1.88. Found: C, 75.82; H, 8.59; N, 1.80. IR (KBr, νmax
/
cm-1): 3425w, 3158w, 2956s, 2904m, 2865s, 1628m (CdN
stretch), 1580w, 1554w, 1476s, 1444s, 1360w, 1301m, 1202m,
1163w, 1026w, 857m, 804m, 779m, 767m, 707m, 680m, 654m,
1
563w, 491w. H NMR (CDCl3): δ 8.27 (s, NdCH, 1H), 7.15-
7.40 (m, benzyl-H, 5H), 7.14 (br s, aryl-H, 2H), 7.02 (d, aryl-
H, J ) 2.1 Hz, 1H), 6.85 (br s, aryl-H, 1H), 6.80 (br s, aryl-H,
1H), 5.24 (s, CH, 1H), 4.80 (m, N-CH2, 2H), 2.29 (s, Me, 3H),
t
t
1.33 (s, Bu, 18H), 1.24 (s, Bu, 18H), -0.58 (s, Al-CH3, 3H),
-0.65 (s, Al-CH3, 3H), -1.94 (s, Al-CH3, 3H). 13C NMR: δ 170.5
(NdCH), 150.0 (aryl), 141.4 (aryl), 139.3 (aryl), 138.7 (aryl),
133.9 (aryl), 133.2 (aryl), 132.3 (aryl), 131.8 (aryl), 129.9 (aryl),
129.5 (aryl), 129.4 (aryl), 129.1 (aryl), 127.5 (aryl), 126.5 (aryl),
123.0 (aryl), 121.6 (aryl), 61.7 (N-CH2), 58.6 (CH), 32.0
(overlapping primary carbons), 32.0 (tBu), 30.8 (tBu), 30.4 (tBu),
20.5 (Me), -9.7 (Al-Me), -11.9 (Al-Me), -13.6 (Al-Me). 27Al
NMR (CDCl3): δ 66 ω1/2 3.2 kHz.
Syn th esis of [(6)Al3Me6], 10. (a) A 2.0 M solution of
trimethylaluminum in toluene (0.88 mL, 1.76 mmol) was
added to a solution of 6H3 (0.30 g, 0.44 mmol) in toluene (10
mL) at 0 °C. The reaction was allowed to warm to room
temperature, stirring overnight. The solvent was removed
under vacuum, and the residue was redissolved in a minimum
amount of pentane. Storage of the mixture for several days at
-30 °C produced a yellow microcrystalline solid. Although
predominately 10, the 1H NMR spectrum of the material
indicates that the solid was contaminated with small amounts
of 9.
(b) In an alternative method, a 2.0 M solution of trimethyl-
aluminum (64 µL, 0.13 mmol) was added to a solution of 9
(0.08 g, 0.10 mmol) in 5 mL of toluene. After stirring overnight
the solvent was removed, and the residue was redissolved in
pentane and stored at -30 °C. As before, the resulting
crystalline solid was a mixture of 10 and a small amount of 9.
Repeated attempts to purify 10 were unsuccessful. 1H NMR
(CDCl3): δ 8.32 (s, 1H, NdCH), 8.02 (s, 1H, CH), 7.4-7.1 (m,
10H, aryl), 6.68 (s, 1H, aryl), 4.93 (m, 2H, N-CH2), 2.44 (s, 3H,
t
t
t
Me), 1.37 (s, 9H, Bu), 1.33 (s, 9H, Bu), 1.31 (s, 9H, Bu), 1.27
(s, 9H, tBu), -0.44 (s, 3H, Al-Me), -0.72 (s, 3H, Al-Me), -0.91
(s, 3H, Al-Me), -1.36 (s, 3H, Al-Me), -1.66 (s, 3H, Al-Me),
-1.85 (s, 3H, Al-Me).
Syn th esis of [(7)Al6Me12], 11. In an attempt to improve
the synthesis of the trinuclear species, a 2.0 M solution of
trimethylaluminum in toluene (1.05 mL) was added to a cooled
(0 °C) solution of 0.40 g of 7H3 (0.35 mmol) in 20 mL of toluene.
The yellow mixture was allowed to warm to room temperature
and was stirred overnight. The solvent was removed in vacuo,
and the residue was redissolved in 2 mL of dichloromethane.
The mixture was stored at -30 °C overnight, and the resultant
yellow microcrystalline solid was collected, washed with cold
dichloromethane, and dried to yield 0.35 g of product. In
comparison to the synthesis of 10, the crystalline solid contains
significantly smaller amounts of the impurity [(7)Al4Me6].
Yield: 67%. IR (KBr, νmax/cm-1): 3484w, 3125w, 2950s, 2871m,
1621s (CdN stretch), 1580w, 1547w, 1477s, 1436s, 1417w,
1397w, 1362m, 1306m, 1201m, 1156w, 1130w, 1097w, 1039w,
P r ep a r a tion of [(6H)+AlMe-], 14. A 0.20 g (0.269 mmol)
portion of 9 was dissolved in methylene chloride (5 mL) and
cooled to -30 °C. In a separate flask, the desired ketone
(cyclopentanone: 46.0 µL, 0.538 mmol; cyclohexanone: 45.8
µL, 0.538 mmol) was dissolved in 2 mL of methylene chloride
and cooled to -30 °C. The two cooled solutions were mixed
and allowed to stir at room temperature for 12 h. The
methylene chloride solvent was reduced to ca. 2 mL and stored
at -30 °C until a crystalline solid formed. The solid was
isolated and dried to yield 0.18 g of a yellow solid (66%). Anal.
Calcd for C45H58NAlO3‚1/2CH2Cl2: C, 75.06; H, 8.17; N, 1.93.
1
980w, 878m, 817m, 780m, 688s. H NMR (CDCl3): δ 8.12 (s,
2H, NdCH), 8.04 (s, 2H, CH), 7.12, 7.00, 6.89, 6.69 (s, 18 H,
1
Found: C, 75.57; H, 7.48; N, 2.25. H NMR (CD2Cl2): δ 8.02
Ar-H), 4.13 (br, 4H, NCH2), 2.38 (s, 6H, CH3), 1.34 (s, 36H,
t
tBu), 1.19 (s, 36H, Bu), -0.27 (s, 12H, Al-CH3), -0.53 (s, 6H,
(d, NdCH, J ) 14.3 Hz, 1H), 7.37 (br s aryl-H, 1H),7.28-7.40
(m, benzyl-H, 5H), 7.26 (br s, aryl-H, 1H), 7.07 (d, aryl-H, J )
2.1 Hz, 2H), 7.01 (br s, HNdC, 1H), 6.90 (d, aryl-H, J ) 1.8
Hz, 2H), 5.11 (s, CH, 1H), 4.72 (d, N-CH2, J ) 5.3 Hz, 2H),
Al-CH3), -0.70 (s, 6H, Al-CH3), -1.45 (br, 12H, Al-CH3). 13C
NMR (CDCl3): δ 173.3 (NdCH), 150.0 (aryl), 140.6 (aryl),
137.6 (aryl), 137.4 (aryl), 134.9 (aryl), 132.2 (aryl), 122.8 (aryl),
57.7 (N-CH2), 36.1 (tBu), 34.4 (tBu), 32.1 (tBu), 31.7 (tBu), 31.3
(CH), 20.9 (Me), -5.7 (Al-Me), -6.4 (Al-Me), -8.4 (Al-Me), -9.7
(Al-Me). 27Al NMR (CDCl3): δ 62 ω1/2 3.1 kHz.
t
t
2.16 (s, Me, 3H), 1.25 (s, Bu, 18H), 1.17 (s, Bu, 18H), -0.88
(s, Al-CH3, 3H). 13C NMR: δ 166.4 (NdCH), 157.1 (aryl), 145.2
(aryl), 139.2 (aryl), 139.1 (aryl), 138.0 (aryl), 134.0 (aryl), 132.2
(aryl), 131.3 (aryl), 130.3 (aryl), 130.2 (aryl), 129.7 (aryl), 129.4
(aryl), 127.7 (aryl), 123.4 (aryl), 116.5 (aryl), 60.4 (N-CH2), 56.3
P r ep a r a tion of [(5){AlMe2}{AlMe(OSMe2)}], 12. A solu-
tion of DMSO (11 µL, 0.154 mmol) in CH2Cl2 (1 mL) was added

428 Organometallics, Vol. 21, No. 2, 2002
Cottone et al.
(CH), 35.6 (tBu), 34.4 (tBu), 32.0 (tBu), 30.3 (tBu), 20.2 (Me),
-12.7 (Al-Me).
density, while fixing their geometry. In several cases, the
crystals contained severely disordered solvate molecules, and
in instances where a suitable model could not be constructed
for the solvates, their contribution to the diffraction were
removed (“squeezed”) from the data by the Platon for Windows
software program.39 Experimental details are contained in the
Supporting Information.
X-r a y Cr ysta llogr a p h y. Unit cell dimensions and intensity
data for all the structures are contained in Table 1. The data
were obtained on a Siemens CCD SMART diffractometer at
-100 °C, with monochromatic Mo KR X-rays (λ ) 0.71073 Å).
The data collections nominally covered over a hemisphere of
reciprocal space, by a combination of three sets of exposures;
each set had a different φ angle for the crystal, and each
exposure covered 0.3° in ω. The crystal to detector distance
was 5.0 cm. The data sets were corrected empirically for
absorption using SADABS.38 All the structures were solved
using the Bruker SHELXTL software package for the PC,
using the direct methods option of SHELXS. The space groups
for all of the structures were determined from an examination
of the systematic absences in the data, and the successful
solution and refinement of the structures confirmed these
assignments. Except for the phenolic hydrogen atoms and
hydrogen atoms involved in H-bonding interactions, all hy-
drogen atoms were assigned idealized locations and were given
a thermal parameter equivalent to 1.2 or 1.5 times the thermal
parameter of the carbon atom to which it was attached. For
the methyl groups, where the location of the hydrogen atoms
was uncertain, the AFIX 137 card was used to allow the
hydrogen atoms to rotate to the maximum area of residual
Ack n ow led gm en t. We thank the University of
Florida, the National Science Foundation (CAREER
Award 9874966), and the donors of the American
Chemical Society Petroleum Research Fund for funding
this research. We would also like to express our grati-
tude to Dr. Khalil Abboud at the University of Florida
for granting access to X-ray instrumentation, and we
thank Dr. Ion Ghiviriga, Dr. Lidia Matveeva, and Dr.
David H. Powell for their assistance.
Su p p or tin g In for m a tion Ava ila ble: Complete crystal-
lographic information (excluding structure factors) for all
compounds. This material is available free of charge via the
Internet at http://pubs.acs.org.
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