Synthesis and structural characterization of a novel aluminum amidato derivative exhibiting a rare 16-membered wheel containing four aluminum centers

Article abstract of DOI:10.1021/om1005963

Reaction of 2 equiv of AlMe₃ with 1,2-C₆H ₄{NHC(t-Bu)O}₂ gives the tetranuclear aluminum compound [{AlMe₂(1,2-C₆H₄{NC(t-Bu)O}₂)} AlMe₂]₂ (1), the molecular structure of which exhibits a novel central 16-membered ring formed by four AlMe₂ units and four NCO fragments. Treatment of 1 with 1 equiv of B(C₆F₅) ₃ affords the ionic species [{(AlMe₂)₃(AlMe)(1, 2-C₆H₄{NC(t-Bu)O}₂)₂][MeB(C ₆F₅)₃] (2).

Full text of DOI:10.1021/om1005963

3642 Organometallics 2010, 29, 3642–3646
DOI: 10.1021/om1005963
Synthesis and Structural Characterization of a Novel Aluminum Amidato
Derivative Exhibiting a Rare 16-Membered Wheel Containing Four
Aluminum Centers
ꢀ
Vanessa Tabernero, Marta E. G. Mosquera,* and Tomas Cuenca*
´
ꢀ
Departamento de Quımica Inorganica, Universidad de Alcala, Campus Universitario,
ꢀ
ꢀ
E-28871 Alcala de Henares, Spain
Received June 18, 2010
Reaction of 2 equiv of AlMe3 with 1,2-C6H4{NHC(t-Bu)O}2 gives the tetranuclear aluminum com-
pound [{AlMe2(1,2-C6H4{NC(t-Bu)O}2)}AlMe2]2 (1), the molecular structure of which exhibits a novel
central 16-membered ring formed by four AlMe2 units and four NCO fragments. Treatment of 1 with 1
equiv of B(C6F5)3 affordstheionicspecies[{(AlMe2)3(AlMe)(1,2-C6H4{NC(t-Bu)O}2)2][MeB(C6F5)3] (2).
Aluminum derivatives bearing oxygen donor ligands play
important roles in a broad array of areas ranging from
catalysis to biochemistry and material chemistry.1-8 In
particular, aluminum carboxylato complexes have been used
as precursors for aluminum oxides9,10 and exhibit biological
relevance.11,12 Species containing N,O-donor ligands are
also of interest in catalytic reactions; thus alkoxido and
amino-alkoxido aluminum derivatives are very active species
in many catalytic polymerization processes.13-16 Neverthe-
less, the chemistry of aluminum with the related amidato
ligands has been far less explored. After the initial studies
published by Wade17 and Lappert18 in 1968, only a few of
these complexes have been reported,19-23 despite the excel-
lent properties that some of these derivatives have shown in
polymerization processes of polar monomers.24
We have investigated the reactivity of aluminum compounds
toward N,N0-alkyl-1,2-phenylenediamines and the related
amide reagents due to the interesting steric and donor char-
acteristics exhibited by this kind of ligand.25,26 The diamines 1,2-
C6H4(NHR)2 (R=CH2t-Bu, n-Pr) react with 2 equiv of AlMe3
in toluene solution, affording amido aluminum dinuclear com-
pounds [Al2{1,2-C6H4(NCH2R)2}Me4].25 The extension of our
investigations to the related diamide reagent 1,2-C6H4{NHC-
(t-Bu)O}2 has allowed us to isolate a novel tetranuclear deriva-
tive that shows a rare 16-membered ring structure; its synthesis,
structural characterization, and reactivity toward tris(penta-
fluorophenyl)borane are described in this report.
*Corresponding authors. Tel: þ34-918854655. Fax: þ34-918854683.
E-mail: tomas.cuenca@uah.es; martaeg.mosquera@uah.es.
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Results and Discussion
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The diamide 1,2-C6H4{NHC(t-Bu)O}2 was prepared by
lithiation of the corresponding commercially available 1,2-
phenylenediamine, and further reaction with pivaloyl chlor-
ide was carried out according to the methods described in the
literature.27-29 Addition of 2 equiv of AlMe3 to 1,2-C6H4-
{NHC(t-Bu)O}2 in toluene at room temperature affords the
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C. R. Polyhedron 2009, 28, 2545–2554.
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1992, 40, 1793–1798.
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ꢀ
r
pubs.acs.org/Organometallics
Published on Web 07/28/2010
2010 American Chemical Society

Article
Organometallics, Vol. 29, No. 16, 2010 3643
Scheme 1
reaction toward B(C6F5)3 as a Lewis acid reagent.30 One
equivalent of B(C6F5)3 was added to a solution of 1 in bromo-
benzene (C6D5Br) at room temperature, and the spectroscopic
study of the reaction suggested the formation of the ionic species
[{(AlMe2)3(AlMe)(1,2-C6H4{NC(t-Bu)O}2)2][MeB(C6F5)3] (2)
(Scheme 1). Unfortunately it was not possible to obtain sui-
table crystals of 2for a structure determination by X-ray diffrac-
tion methods, and complex 2 was characterized in solution by
NMR spectroscopy. The elemental analysis of this compound
shows that the contents of C and H are slightly lower than the
calculated values due to its high air sensitivity at room tempera-
ture. The 1H NMR spectrum of 2 (CDCl3 at -40 °C or C6D5Br
at room temperature) indicates methyl abstraction, resulting in
two nonequivalent sides derived from the initial symmetric ring
present in molecule 1. Subsequently, four signals of the phenyl
ligand, two singlets of the tert-butyl group protons, and six
resonances for the methyl groups (one integrating for 6 protons)
are observed with the presence of a broad singlet at δ 0.39
corresponding to a methyl group bonded to the boron atom.
In order to study the nature of complex 2, we carried out a
diffusion-ordered NMR (DOSY) study to deduce the con-
nection between the cationic and anionic units in solution.
1
The H DOSY spectrum of 2 in C6D5Br solution at room
temperature resolves into 2D peaks placed in one single
horizontal line in the diffusion dimension, indicating that
the signal corresponding to the methylborate group protons
has the same diffusion coefficient as the cation fragment
resonances. Estimating the expected volume of the corre-
sponding ionic species in compound 2 and consequently the
related different hydrodynamic radius of the diffusing ionic
fragments, this qualitative PGSE NMR result at room tem-
perature is consistent with the existence of a cation-anion
interaction. Cation-anion interactions depend on the struc-
tural and chemical characteristics of the ionic fragments.
Ion-pairing effects have been claimed to have an important
role in stoichiometric and catalytic reactions mediated by
ionic transition metal complexes.31 As an example, ion-
pairing phenomena in the single-site group 4 metal deriva-
tives as a precatalyst system for the olefin polymerization
reaction exhibit a strong influence on the properties of the
resulting polyolefinic polymer.32-34
To achieve a better knowledge of the structure of 2 for
studying the position of the methyl borate anion in this com-
pound, 2D NOESY NMR measurements in C6D5Br at room
temperature and in CDCl3 at -40 °C were carried out. Ex-
change cross-peaks between the resonances assigned to the
protons of the methyl group abstracted by boron to form the
anionic unit and those corresponding to the methyl groups
attached to the aluminum atoms in the cationic fragment are
revealed. Although the crystal structure of the neutral com-
pound 1 shows the methyl groups pointing out of the 16-mem-
bered ring, in solution at room temperature an alternative
conformation could be easily induced. In this conformation
the aluminum atoms, and consequently the methyl groups, are
directed toward the core of the wheel, allowing a proximity that
might favor the exchange process. Exchange between terminal
tetranuclear aluminum compound [{AlMe2(1,2-C6H4{NC-
(t-Bu)O}2)}AlMe2]2 (1), as shown in Scheme 1. The route to 1
involves an initial aminolysis process of aluminum-carbon
bonds with loss of methane to create the aluminum-nitro-
gen and aluminum-oxygen bonds. Four “AlMe2” units are
connected through four amidato functionalities to adopt the
final structure. The same complex is obtained even when the
reaction is performed using different reagent stoichiometries
under analogous reaction conditions. Compound 1 is iso-
lated in 59% yield as an analytically pure colorless solid, air-
and moisture-sensitive but thermally stable in solution and in
the solid state. Spectroscopic data and elemental analysis
concur with the proposed structure. Single crystals for X-ray
diffraction were obtained, and the molecular structure was
confirmed (see below).
The 1H NMR spectrum of 1 (CDCl3 at room temperature)
shows a resonance for the tert-butyl group protons at δ 1.38
accompanied by two multiplets corresponding to an AA0BB0
spin system for the aromatic phenyl ring protons at δ 7.18
and 6.77. Three resonances for the methyl groups coordi-
nated to the aluminum atoms are observed, one signal at δ
-0.76 integrating for 12 protons and two singlets at δ -0.36
and -0.81 for six protons each. The same spectroscopic
features are observed in the 13C{1H} NMR spectral data. On
the basis of this spectroscopic pattern and the elemental
analysis, the suggested structure of 1 in solution is the tetra-
nuclear disposition shown in Scheme 1. This structure was
confirmed by X-ray diffraction studies, which shows each
amidato group coordinating two aluminum atoms through
both nitrogen and oxygen atoms (see below). Thus, the four
methyl ligands linked to the aluminum coordinated through
the oxygen atom are equivalent, while the methyl groups
attached to the diamido-aluminum fragment have different
chemical environments, with the two located near the phe-
nylene ring experiencing the anisotropic effect of the ring.
We were interested in exploring the acid/base properties of
this new aluminum macrocycle derivative. Thus we analyzed the
(31) Macchioni, A. Eur. J. Inorg. Chem. 2003, 195–205.
(32) Zuccaccia, C.; Stahl, N. G.; Macchioni, A.; Chen, M. C.;
Roberts, J. A.; Marks, T. J. J. Am. Chem. Soc. 2004, 126, 1448–1464.
(33) Song, F. Q.; Lancaster, S. J.; Cannon, R. D.; Schormann, M.;
Humphrey, S. M.; Zuccaccia, C.; Macchioni, A.; Bochmann, M. Orga-
nometallics 2005, 24, 1315–1328.
(34) Beck, S.; Lieber, S.; Schaper, F.; Geyer, A.; Brintzinger, H. H.
(30) Chen, E. Y. X.; Marks, T. J. Chem. Rev. 2000, 100, 1391–1434.
J. Am. Chem. Soc. 2001, 123, 1483–1489.

3644 Organometallics, Vol. 29, No. 16, 2010
Tabernero et al.
Figure 1. ORTEP view of the structures of the diamide 1,2-C6H4{NH(CO)t-Bu}2 (a) and compound 1 (b) with ellipsoids of 30%
probability. Hydrogen atoms bonded to carbon atoms are omitted for clarity.
˚
Table 1. Selected Bond Lengths (A) and Angles (deg) for Com-
pound 1
ligands (COAlOC), while the other two AlMe2 fragments are
bonded to two nitrogen atoms (CNAlNC) within a diamido
environment. Thus, the phenylene-bis-amidato groups be-
have as tetradentate ligands bridging two dimethylaluminum
units through the two oxygen atoms and chelating a central
aluminum moiety through the two nitrogen atoms.
molecule I
molecule II
Al(3)-O(4)
Al(3)-O(3)
Al(4)-N(3)
N(4)-Al(4)b
O(3)-C(3)
N(3)-C(3)
O(4)-C(4)
C(4)-N(4)
Al(2)-O(1)
1.804(2)
1.812(2)
1.973(2)
1.983(2)
1.288(3)
1.341(4)
1.277(3)
1.336(4)
1.800(2)
1.805(2)
1.987(3)
1.972(3)
1.286(4)
1.331(4)
1.281(4)
1.341(4)
Al(2)-O(2)a
Al(1)-N(1)
Al(1)-N(2)
O(1)-C(1)
C(1)-N(1)
O(2)-C(2)
C(2)-N(2)
A crystallographic study of 1,2-C6H4{NHC(t-Bu)O}2
(Figure 1a) showed that the C-N distances are slightly lon-
˚
ger (1.346(4) and 1.348(4) A) and the bond lengths for C-O
˚
slightly shorter (1.227(3)-1.221(3) A) in the free ligand in com-
parison with the coordination disposition in 1. As such, bond
˚
lengths for C-N are 1.341(4) and 1.336(4) A in molecule I and
1.331(4) and 1.341(4) A in the chemically equivalent molecule
O(1)-Al(2)-O(2)a
C(1)-O(1)-Al(2)
C(2)-O(2)-Al(2)a
O(1)-C(1)-N(1)
O(2)-C(2)-N(2)
C(1)-N(1)-Al(1)
C(1)-N(1)-C(15)
C(15)-N(1)-Al(1) 107.48(17)
C(2)-N(2)-Al(1) 131.6(2)
C(21)-N(2)-Al(1) 107.54(17)
96.93(10) O(4)-Al(3)-O(3)
98.77(11)
162.2(2)
163.6(2)
121.8(3)
122.5(3)
132.7(2)
119.2(2)
106.80(18)
131.3(2)
107.79(18)
119.2(2)
87.46(10)
˚
161.2(2)
163.42(19)
121.0(3)
121.4(3)
131.8(2)
119.1(2)
C(3)-O(3)-Al(3)
C(4)-O(4)-Al(3)
O(4)-C(4)-N(4)
O(3)-C(3)-N(3)
C(3)-N(3)-Al(4)
C(3)-N(3)-C(49)
C(49)-N(3)-Al(4)
C(4)-N(4)-Al(4)b
C(44)-N(4)-Al(4)b
C(4)-N(4)-C(44)
II, and the bond lengths for C-O fall in the range 1.277(3)-
1.288(3) A, indicating a partially delocalized structure within
˚
the OCN fragment.37 Distances of 1.308(2) A for C-N bonds
˚
˚
and 1.302(2) A for C-O bonds have been found in analogous
aluminum compounds with formato bridging ligands, for
which a delocalized structural disposition within the OCN frag-
ment is suggested.23 The distances Al-N (1.972(3)-1.987(3) A
˚
C(2)-N(2)-C(21)
N(1)-Al(1)-N(2)
119.2(2)
range) are shorter than those reported for donor N-Al
bonds.38 On the basis of these structural findings, we propose
that complex 1 could be described as a zwitterionic compound,
formed by two anionic moieties [AlMe2(1,2-C6H4{NC(t-Bu)-
O}2)]- linked by the CdO groups to two cationic fragments
[AlMe2]þ, rendering a 16-membered macrocycle.
In view of this zwitterionic structure with its anionic
contribution from the aluminum-diamido fragment and its
cationic contribution from the aluminum centers connected
to the oxygen atoms, the Lewis acid B(C6F5)3 in the reaction
described in Scheme 1 should attack on the more nucleophi-
lic aluminum-methyl bond, suggesting the abstraction of
one methyl group bonded to the aluminum-amido unit to
generate the structural disposition shown in Scheme 1.
In the side view of the ring, the atoms forming the inner
core (COAlOC)2 are nearly coplanar, while the nitrogen
atoms come slightly out of that plane in a chair orientation
87.47(10) N(4)b-Al(4)-N(3)
a -x, -yþ2, -zþ1. b -xþ1, -yþ1, -zþ2.
and abstracted methyl groups has been extensively studied for
zirconocene-borate systems.32,34-36
Single-Crystal Structure. The molecular structure of 1 has
been determined by X-ray crystallography. The crystal
structure of 1 is shown in Figure 1b, and Table 1 summarizes
selected bond lengths and angles. In the asymmetric unit, two
half molecules (molecules I and II in Table 1) are observed,
and the whole structures are generated by an inversion center,
rendering two chemically equivalent but crystallographically
independent 16-membered rings. Figure 2a highlights the
structure of the central 16-membered-ring core formed by
four AlMe2 units and four NCO fragments. Two AlMe2 units
are coordinated to two oxygen atoms from different amidato
(35) Stahl, N. G.; Zuccaccia, C.; Jensen, T. R.; Marks, T. J. J. Am.
Chem. Soc. 2003, 125, 5256–5257.
(36) Stahl, N. G.; Salata, M. R.; Marks, T. J. J. Am. Chem. Soc. 2005,
127, 10898–10909.
(37) Maetzke, T.; Seebach, D. Organometallics 1990, 9, 3032–3037.
(38) Eaborn, C.; Farook, A.; Hitchcock, P. B.; Smith, J. D. Organo-
metallics 1998, 17, 3135–3137.

Article
Organometallics, Vol. 29, No. 16, 2010 3645
Figure 2. (a) Central 16-membered ring of the structure of 1. (b) Side view of the ring disposition. (c) Side view showing the methyl
groups and phenyl rings disposition. In (a) and (c) H atoms and t-Bu groups have been omitted for clarity. In (b) H atoms, Ph, and t-Bu
groups have been omitted for clarity.
(Figure 2b), which is the preferred disposition for this kind of
derivative.39 The distance between the aluminum centers in
˚
the “CNAlNC” fragments in the central ring is 8.195 A for
˚
molecule I (8.222 A for molecule II), and that between
˚
aluminum centers in the “COAlOC” moieties is 8.630 A
˚
for molecule I (8.593 A for molecule II). This central cavity is
Several coordination modes for the amidato ligand bonded to
aluminum are possible,17,18,23,40,41 and the factors affecting the
different coordination modes have been studied.23 It is note-
worthy to point out that few molecular Al4 rings have been des-
cribed where the aluminum atoms are connected by symmetric
bridges.2,42 The unusual 16-membered ring arrangement ob-
served in 1with a partially delocalized “Al-N-C-O” unit seems
to be imposed by the particular nature of this bis-amidato ligand.
Polymerization Studies. The electrophilicity of 2 could
enhance substrate coordination to the cationic aluminum center
and is active in the polymerization behavior. An initial test of
cyclohexene oxide (CHO) polymerization with compound 2 in
the standard conditions was carried out (25 °C; catalyst/CHO,
1/2000; 30 min; 5.6 ꢀ 10-5 moles of Al), showing low activity
(5% yield, Mn=2.9ꢀ104; Mw=7.0ꢀ104, polydispersity=2.5).
The broad polydispersity index suggests multiple reaction sites
or a low exchange of the growing chain between aluminum
centers.43,44 These preliminary results are in accordance with the
cationic-anionic interactions and the methyl exchange effect of
the ion pairs observed for compound 2 in solution. The low
activity could be attributed to the fact that the initiation step in
this polymerization process requires the coordination of the
monomer molecule to the active metal centers, and in com-
pound 2 these centers seem to be blocked by the coordination of
the methylborate anion.
covered by the two phenylene rings (Figure 2a and c). The
disposition of the rings suggests the existence in the solid
state of π-stacking intramolecular interactions, although the
distances between the centroids of these aligned rings are
˚
relatively long, 4.198 and 4.299 A, indicating that this effect
probably occurs for steric rather than electronic reasons. The
methyl groups bonded to the Al centers are oriented toward
the outside of the ring. They are placed in two perpendicular
planes that are also nearly perpendicular to the plane formed
by the central core, surrounding it on four sides in a wall-like
fashion (Figure 2b and c).
The five-membered chelate aluminum-diamido rings are
not planar, and the phenylenediamido ligand is folded along
the N-N vector with a fold angle, Θ, of 17.55° and 18.33°.
Similar folding has been previously observed in analogous
compounds.26,29 Both phenyl ligands are placed in an anti
direction (see Figure 2c).
Metal-carboxylato interactions have been addressed be-
cause of their biological interest, and attempts have been made
to determine which lone pair of the oxygen atoms of the carbo-
xylato group is preferred for metal binding.2 Upon comparison
with these carboxilato derivatives, an analysis of the structure of
1indicates that the aluminum moieties are bonded to the oxygen
atoms in an anti-anti disposition. This orientation has proven
to be the most likely disposition in carboxylato compounds.2
In conclusion, the polyfunctional diamide 1,2-C6H4-
{NHC(t-Bu)O}2 behaves as a good precursor for the forma-
tion of novel high-nuclearity macrocycle derivatives in the
(41) Power, M. B.; Bott, S. G.; Clark, D. L.; Atwood, J. L.; Barron,
A. R. Organometallics 1990, 9, 3086–3097.
(42) Bird, C. M.; Breheny, C.; Davidson, M. G.; Edwards, A. J.;
Llewellyn, S. C.; Raithby, P. R.; Snaith, R. Angew. Chem., Int. Ed. Engl.
1993, 32, 1483–1484.
(43) Inoue, S. J. Polym. Sci., Polym. Chem. 2000, 38, 2861–2871.
(44) Zevaco, T. A.; Sypien, J. K.; Janssen, A.; Walter, O.; Dinjus, E.
J. Organomet. Chem. 2007, 692, 1963–1973.
(39) Gerstner, F.; Hausen, H. D.; Weidlein, J. J. Organomet. Chem.
1980, 197, 135–146.
(40) Kai, Y.; Yasuoka, N.; Kasai, N.; Kakudo, M. J. Organomet.
Chem. 1971, 32, 165–179.

3646 Organometallics, Vol. 29, No. 16, 2010
Tabernero et al.
reaction with trialkyl aluminum compounds. It is expected
that the use of bulky ligands would produce low nuclearity
derivatives; however the electronic and steric characteristics
of this diamide generate multinuclear metal rings. The ring
structure of the tetranuclear 1 (both in solution and in the
solid state) displays potential donor and acceptor sites, and it
is expected to show wide coordinative abilities that could
lead to interesting catalytic properties.
Bu), 27.2, 27.1 (t-Bu), 10.0 (br, BMe), 0.42, -1.54, -2.60, -9.34,
-10.81, -10.96, -11.72 (AlMe). 19F NMR (376.40 MHz., CDCl3
-40 °C): δ-133.5 (d, J= 23.5 Hz, o-C6F5),-164.4 (t, J= 20.0 Hz,
p-C6F5), -167.1 (s br, m-C6F5). Compound 2 could not be isolated
as a pure substance since decomposition occurs in solution at
room temperature, which prevented us from obtaining correct
elemental analysis.
Single-Crystal X-ray Structure Determination of 1,2-C6H4-
{NHC(t-Bu)O}2 and Compound 1. Details of the X-ray experiment,
data reduction, and final structure refinement calculations are
summarized in the table in the Supporting Information. Suitable
single crystals of 1,2-C6H4{NHC(t-Bu)O}2 and 1 for the X-ray
diffraction study were selected. Data collection was performed at
200(2) K on a crystal covered with perfluorinated ether oil. The
crystals were mounted on a Bruker-Nonius Kappa CCD single-
crystal diffractometer equipped with graphite-monochromated Mo
Experimental Section
General Considerations. All manipulations were conducted
using Schlenk techniques or in an inert atmosphere glovebox.
All solvents were rigorously dried prior to use. NMR spectra
were recorded at 400.13 (1H), 376 (19F), and 100.60 (13C) MHz
on a Bruker AV400. Chemical shifts (δ) are given in ppm using
CDCl3 or C6D5Br as solvent. 1H and 13C resonances were
measured relative to solvent peaks considering TMS δ = 0
ppm, while 19F was measured relative to external CFCl3. Ele-
mental analyses were obtained on a Perkin-Elmer Series II 2400
CHNS/O analyzer. All reagents were commercially obtained
(Aldrich) and used without further purification. The diamide
1,2-C6H4{NHC(t-Bu)O}2 was prepared according to the re-
ported methods.27,28
Synthesis of [{AlMe2(1,2-C6H4{NC(t-Bu)O}2)}AlMe2]2 (1). A
0.434 mL amount of AlMe3 (2 M, 0.869 mmol) was added to a
solution of 1,2-C6H4{NHC(t-Bu)O}2 (0.120 g, 0.434 mmol) in
toluene at room temperature. After 4 h, the solvent was removed
in vacuo to give a solid, which was recrystallized in hexanes. Com-
pound 1 was obtained as a colorless solid. Yield: 59% (0.200 g,
0.258 mmol). Anal. Calcd (%) for C40H68Al4N4O4 (776.32 g/mol):
C, 61.87; H, 8.76; N, 7.21. Found: C, 61.33; H, 8.88; N, 7.80. 1H
NMR (400 MHz, CDCl3, 25 °C): δ 7.18 (AA0BB0 spin system, 4H,
Ph), 6.77 (AA0BB0 spin system, 4H, Ph), 1.38 (s, 36H, t-Bu), -0.36
(s, 6H, Me), -0.76 (s, 12H, Me), -0.81 (s, 6H, Me). 13C NMR
(100.60 MHz., CDCl3, 25 °C): δ 183.5 (CO), 137.3 (ipso-Ph),
124.9, 124.4 (Ph), 42.0 (ipso-t-Bu), 28.5 (t-Bu), -0.46, -6.99,
-7.52 (AlMe).
KR radiation (λ = 0.71073 A). Multiscan45 absorption correction
˚
procedures were applied to the data. The structures were solved,
using the WINGX package,46 by direct methods (SHELXS-97) and
refined by using full-matrix least-squares against F2 (SHELXL-
97).47,48 All non-hydrogen atoms were anisotropically refined.
Hydrogen atoms were geometrically placed and left riding on their
parent atoms except for the ones bonded to the nitrogen atoms in
1,2-C6H4{NHC(t-Bu)O}2, which were found in the difference Four-
ier map and refined. Half of a toluene molecule per molecule of 1 is
present in the unit cell. This solvent molecule was found in the
difference Fourier map but was very disordered, and it was not
possible to get a chemically sensible model for it; therefore, the
Squeeze procedure49 was used to remove its contribution from the
structure factors. Full-matrix least-squares refinements were carried
P
out by minimizing w(Fo2 - Fc2)2 with the SHELXL-97 weighting
scheme and stopped at shift/err < 0.001. The final residual electron
density maps showed no remarkable features.
Acknowledgment. Financial support for this research
ꢀ
by Direccion General de Investigacion Cientıfica y
Tecnica (Project MAT2007-60997) and Comunidad
ꢀ
ꢀ
ꢀ
Autonoma de Madrid (Project S-0505-PPQ/0328-02) is
gratefully acknowledged.
Synthesis of [{(AlMe2)3(AlMe)(1,2-C6H4{NC(t-Bu)O}2)2][MeB-
(C6F5)3] (2). In the drybox an PTFE-valved J-Young NMR tube
was charged with B(C6F5)3 (0.010 g, 0.019 mmol) and compound 1
(0.014 g, 0.019 mmol). Then the mixture was taken out of the
drybox, and CDCl3 was added at -78 °C, affording a dark solution.
Supporting Information Available: General procedure for the
polymerization experiments and table of crystallographic data,
including fractional coordinates, bond lengths and angles,
anisotropic displacement parameters, and hydrogen atom co-
ordinates in CIF format of the diamide 1,2-C6H4{NHC(t-Bu)-
O}2 and complex 1. This material is available free of charge via
the Internet at http://pubs.acs.org.
1
NMR monitoring was done at -40 °C. H NMR (400 MHz,
CDCl3, -40 °C): δ 7.25 (m, 2H, Ph), 7.15 (m, 2H, Ph), 6.93 (m, 2H,
Ph), 6.86 (m, 2H, Ph), 1.42 (s, 18H, t-Bu), 1.35 (s, 18H, t-Bu), 0.39
(br, 3H, BMe), -0.34(s, 3H, AlMe), -0.48 (s, 3H, AlMe), -0.78 (s,
6H, AlMe), -0.76 (s, 3H, AlMe), -0.81 (s, 3H, AlMe), -1.65 (s,
3H, AlMe). 13C NMR (400 MHz, CDCl3 -40 °C): δ 190 (CO),
188.3 (CO), 148.8, 146.6, 137.9, 137.1, 135.9, 134.9 (C6F5), 137.9,
137.6 (ipso-Ph), 128.8, 127.9, 124.3, 123.8 (Ph), 41.7, 41.8 (ipso-t-
(46) Farrugia, L. J. J. Appl. Crystallogr. 1999, 32, 837–938.
€
€
€
(47) Sheldrick, G. M. SHELXL-97; Universitat Gottingen: Gottingen,
Germany, 1998.
(48) Sheldrick, G. M. Acta Crystallogr., Sect. A 2008, 64, 112–122.
(49) Van der Sluis, P.; Spek, A. L. Acta Crystallogr., Sect. A 1990, 46,
194–201.
(45) SORTAV. Blessing, R. H. Acta Crystallogr., Sect. A 1995, 51,
33–38.