Aluminum pentafluorophenyl-amide complexes

Article abstract of DOI:10.1139/V07-003

The pentafluoroaryl amine (C₆F₅)₂NH (1) reacts with AlH₃·NEtMe₂ to give [(C ₆F₅)₂N]AlH₂·NEtMe ₂ (2) and [(C₆F₅)₂

Full text of DOI:10.1139/V07-003

135
Aluminum pentafluorophenyl–amide complexes
Carsten Cornelissen, Gigi Chan, Jason D. Masuda, and Douglas W. Stephan
Abstract: The pentafluoroaryl amine (C6F5)2NH (1) reacts with AlH3·NEtMe2 to give [(C6F5)2N]AlH2·NEtMe2 (2) and
[(C6F5)2N]2AlH·NEtMe2 (3). The related fluorinated-aryl amine (C6F5)(n-C4H9)NH (4) also reacts with AlH3·NEtMe2 to
give [(C6F5)(n-C4H9)N]3Al·NEtMe2 (5). This latter compound undergoes ligand exchange with PMe3 or N-
methylimidazole to form [(C6F5)(n-C4H9)N]3Al·PMe3 (6) and [(C6F5)(n-C4H9)N]3Al·(Me-imid) (7), respectively. The lat-
ter amine also reacts with AlMe3, affording [Me2AlN(C6F5)(n-C4H9)]2 (8).
Key words: almunium, amides, pentafluorophenylamine.
Résumé : L’amine pentafluorée (C6F5)2NH (1) réagit avec le complexe AlH3·NEtMe2 pour conduire à la formation du
[(C6F5)2N]AlH2·NEtMe2 (2) et du [(C6F5)2N]2AlH·NEtMe2 (3). L’amine aromatique fluorée apparentée (C6F5)(n-
C4H9)NH (4) réagit aussi avec le complexe AlH3·NEtMe2 pour conduire à la formation du [(C6F5)(n-
C4H9)N]3Al·NEtMe2 (5). Ce dernier produit subit une réaction d’échange de ligand avec le PMe3 ou le N-méthylimida-
zole pour conduire à la formation du [(C6F5)(n-C4H9)N]3Al·PMe3 (6) et du [(C6F5)(n-C4H9)N]3Al·(Me-imid) (7) respec-
tivement. Cette dernière amine réagit aussi avec le AlMe3 avec formation du [Me2AlN(C6F5)(n-C4H9)]2 (8).
Mots-clés : aluminium, amides, pentafluorophénylamine.
[Traduit par la Rédaction] Cornelissen et al. 140
Introduction
MBraun or Vacuum Atmospheres inert-atmosphere
glovebox. Solvents were purified, employing a Grubbs-type
solvent purification system, manufactured by Innovative
Technologies. All organic reagents were purified by conven-
Lewis acids play dominant roles as co-catalysts in olefin
polymerization and as catalysts in a variety of reactions in
organic chemistry. The borane B(C6F5)3 has been studied in
such applications (1, 2), and a number of studies have tar-
geted structural modifications. For example, Marks and co-
workers (3–9), as well as Piers and co-workers (1, 10–13),
have developed elegant syntheses to both elaborate the sub-
stituents on B or to access bis-borane compounds. Related
alanes have also been prepared and evaluated for a variety of
applications in catalysis (14–16). Generally, fluoroaryl-
alanes have been effective in these applications (17–23), al-
though they have proved to be dangerous, as species such as
Al(C6F5)3 are known to be heat and shock sensitive. In an ef-
fort to develop new Al-based Lewis acids, we began an
exploration of the Al–amide derivatives, incorporating
pentafluoroaryl substitutents. In this paper, we describe the
synthesis and structure of several such compounds. An ini-
tial attempt to apply these species to the activation of early
metal-catalyst precursors is also briefly described.
1
tional methods. H, 31P{1H}, 19F, and 13C{1H} NMR spectra
were recorded on Bruker Avance-300 and -500 spectrome-
ters. All spectra were recorded at 25 °C. Trace amounts of
1
protonated solvents were used as a reference for H NMR
spectra, while the solvent was used as a reference for
1
13C{1H} spectra, and chemical shifts for H and 13C{1H}
spectra were reported relative to SiMe4. 31P{1H} NMR spec-
tra were referenced to external 85% H3PO4. IR spectra were
recorded on a Bruker FTIR spectrometer. Combustion analyses
were done in-house, employing a PerkinElmer CHN Ana-
lyzer. (C6F5)2NH (1) was purchased from Aldrich Chemical
Co. (C6F5)(n-C4H9)NH (4) was prepared following a litera-
ture procedure (24).
Synthesis of [(C6F5)2N]AlH2·EtMe2 (2)
A solution of (C6F5)2NH (0.524 g, 1.5 mmol) in toluene
(10 mL) was added dropwise to a solution of AlH3·NEtMe2
(3.0 mL, 1.5 mmol, 0.5 mol/L in toluene) at 25 °C. The re-
action mixture was stirred overnight, and the solvent was re-
moved in vacuo to yield 0.653 g (1.45 mmol, 97%) of a light
Experimental section
General data
1
3
All preparations were done under an atmosphere of dry,
O2-free N2, employing both Schlenk line techniques and an
yellow oil. H NMR (CD2Cl2): 2.85 (q, JHH = 7 Hz, 2H,
3
NCH2Me), 2.48 (s, 6H, NMe2), 1.18 (t, JHH = 7.3 Hz, 3H,
NCH2Me). 1H NMR (CD2Cl2, –80 °C): 3.39 (br s, 2H, AlH),
the resonance for AlH was not observed. 13C{1H} NMR
Received 13 November 2006. Accepted 6 December 2006.
Published on the NRC Research Press Web site at
http://canjchem.nrc.ca on 27 February 2007.
1
(CD2Cl2): 144.9 (dm, JFC = 239 Hz, o-C6F5), 138.4 (dm,
1JFC = 246 Hz, m-C6F5), 138.0 (dm, 1JFC = 250 Hz, m-C6F5),
126.2 (m, C6F5), 54.4 (s, NCH2Me), 44.5 (s, NMe2), 8.6 (s,
C. Cornelissen, G. Chan, J.D. Masuda, and D.W.
Stephan.1 Department of Chemistry & Biochemistry,
University of Windsor, Windsor, ON N9B 3P4, Canada.
3
NCH2Me). 19F NMR (CD2Cl2): –149.2 (d, JFF = 23 Hz, o-
C6F5), –164.7 (t, 3JFF = 23 Hz, p-C6F5), –165.5 (m, m-C6F5).
Anal. calcd. for C16H13AlF10N2: C 42.68, H 2.91, N 6.22;
found: C 42.46, H 2.56, N 6.13.
1Corresponding author (e-mail: stephan@uwindsor.ca).
Can. J. Chem. 85: 135–140 (2007)
doi:10.1139/V07-003
© 2007 NRC Canada

136
Can. J. Chem. Vol. 85, 2007
3
nances was not detected. 19F NMR (C7D8): –149.4 (d, JFF
=
Synthesis of [(C6F5)2N]2AlH·NEtMe2 (3)
23 Hz, o-C6F5), –165.2 (m, m-C6F5, p-C6F5). 31P{1H} NMR
(C7D8): –50.3 (s, PMe3). Anal. calcd for C33H36AlF15N3P: C
48.48, H 4.44, N 5.14; found: C 48.22, H 4.21, N 5.01.
.
AlH3 NEtMe2 (5 mL, 2.5 mmol, 0.5 mol/L in toluene) was
added dropwise to a vigorously stirring solution of
(C6F5)2NH (2.618 g, 7.5 mmol) in toluene (5 mL) at 25 °C.
After stirring overnight, the white product was collected on a
frit, washed three times with pentane, and dried in vacuo.
For a second fraction, the solvent was removed in vacuo,
and the crude product 3 was recrystallized from pentane to
1
Compound 7: 162 mg, white solid (0.2 mmol, 100%). H
NMR (CD2Cl2): 8.00 (s, 1H, NCHN), 7.03 (s, 1H,
NCHCHN), 7.00 (s, 1H, NCHCHN), 3.82 (s, 3H, NMe),
3.09 (m, 6H, NCH2), 1.10 (m, 12H, CH2CH2Me), 0.76 (t,
1JHH1 = 7 Hz, 9H, CH2Me). 13C{1H} NMR (CD2Cl2): 146.2
(d, JCF = 234 Hz, o-C6F5), 139.6 (s, NCHN), 138.0 (m, m-
C6F5), 127,1 (s, NCHCHN), 122.4 (s, MeNCH), 49.6 (s,
NCH2), 35.6 (s, NMe), 33.7 (s, NCH2CH2), 20.5 (s,
CH2Me), 14.1 (s, CH2Me), resonances for p-C6F5 and ipso-
C6F5 were not detected. 19F NMR (CD2Cl2): –150.4 (d,
3JFF = 20 Hz, o-C6F5), –167.5 (m, m-C6F5), –168.7 (m, p-
C6F5). Anal. calcd. for C34H33AlF15N5: C 49.58, H 4.04, N
8.50; found: C 49.21, H 4.13, N 8.67.
1
yield 1.94 g (overall, 1.7 mmol, 68%) of a white solid. H
3
NMR (CD2Cl2): 2.98 (q, JHH = 7 Hz, 2H, NCH2Me), 2.52
(s, 6H, NMe2), 1.14 (t, 3JHH = 7 Hz, 3H, NCH2Me), the reso-
nance for AlH was not observed. 1H NMR (CD2Cl2, –80 °C):
3.21 (br s, 1H, AlH). 13C{1H} NMR (CD2Cl2): 145.6 (dm,
1
3
1JFC = 246 Hz, o-C6F5), 139.0 (dt, JFC = 251 Hz, JFC
=
1
13 Hz, p-C6F5), 138.0 (dm, JFC = 255 Hz, m-C6F5), 124.3
(m, i-C6F5), 53.0 (s, NCH2Me), 43.0 (s, NMe2), 6.7 (s,
NCH2Me). 19F NMR (CD2Cl2): –147.6 (d, JFF = 20 Hz, o-
3
C6F5), –161.7 (t, 3JFF = 21 Hz, p-C6F5), –164.7 (m, m-C6F5).
Anal. calcd. for C28H12AlF20N3: C 42.18, H 1.52, N 5.27;
found: C 41.66, H 1.56, N 5.73. Single crystals suitable for
X-ray diffraction experiments were obtained by cooling a
saturated pentane solution to –30 °C overnight.
Synthesis of [Me2AlN(C6F5)(n-C4H9)]2 (8)
A solution of (C6F5)(n-C4H9)NH (1.436 g, 6 mmol) in to-
luene (6 mL) was added slowly to a solution of AlMe3
(95 µL, 2 mmol) in toluene (3 mL) at –30 °C. The solution
was allowed to warm to 25 °C overnight. After the solvent
was reduced in vacuo to half of its volume, the solution was
stored at –30 °C overnight to yield colourless crystals. The
product was collected on a frit in dried in vacuo to yield
Synthesis of [(C6F5)(n-C4H9)N]3Al·NEtMe2 (5)
.
AlH3 NEtMe2 (5 mL, 2.5 mmol, 0.5 mol/L in toluene) was
added dropwise to a vigorously stirring solution of (C6F5)(n-
C4H9)NH (4) (1.794 g, 7.5 mmol) in toluene (5 mL) at
25 °C. After stirring overnight, the solvent was removed in
vacuo. The crude product was recrystallized from pentane to
1
862 mg (1.5 mmol, 73%). H NMR (C6D6): 3.18 (m, 4H,
NCH2), 1.23 (m, 4H, NCH2CH2), 0.97 (m, 4H, CH2Me),
3
0.73 (t, JHH = 7 Hz, 6H, CH2Me), –0.04 (m, 6H, AlMe2),
–0.73 (m, 6H, AlMe2). 13C{1H} NMR (C6D6): 145.3 (dm,
1
yield 1.466 g (1.8 mmol, 72%) of a white solid. H NMR
1JFC = 244 Hz, o-C6F5), 139.6 (dm, JFC = 255 Hz, p-C6F5),
1
(CD2Cl2): 3.18 (q, 3JHH = 7 Hz, 2H, NCH2Me), 2.92 (m, 6H,
1
3
138.0 (dm, JFC = 257 Hz, m-C6F5), 122.9 (m, ipso-C6F5),
NCH2CH2), 2.62 (s, 6H, NMe2), 1.17 (t, JHH = 7 Hz, 3H,
55.9 (s, NCH2), 29.6 (s, NCH2CH2), 20.3 (s, CH2Me), 13.7
NCH2Me), 1.04 (m, 6H, NCH2CH2), 0.92 (m, 6H,
(s, CH2Me), –9.6 (br, AlMe2), –10.5 (br, AlMe2). 19F NMR
CH2CH2Me), 0.76 (m, 9H, CH2CH2Me). 13C{1H} NMR
3
3
1
(C6D6): –140.3 (d, JFF = 23 Hz, o-C6F5), –155.2 (t, JFF
=
(CD2Cl2): 147.4 (dm, JFC = 235 Hz, o-C6F5), 138.2 (dm,
3
3
1JFC = 250 Hz, m-C6F5), 127.6 (m, ipso-C6F5), 52.1 (s,
NCH2Me), 51.5 (s, NMe2), 43.4 (s, NCH2CH2), 32.9 (s,
NCH2CH2), 20.5 (s, CH2CH2Me), 14.0 (s, CH2CH2Me), 5.3
(s, NCH2Me), the resonances for p-C6F5 were masked by the
23 Hz, p-C6F5), –161.9 (dd, JFF = 23 Hz, JFF = 23 Hz, m-
C6F5). Anal. calcd for C24H30Al2F10N2: C 48.82, H 5.12, N
4.74; found: C 48.61, H 5.11, N 4.65. Single crystals suit-
able for X-ray diffraction experiments were obtained by
storing a concentrated pentane solution at –30 °C overnight.
m-C6F5 signal. 19F NMR (CD2Cl2): –147.2 (d, JFF = 20 Hz,
3
3
o-C6F5), –165.1 (t, JFF = 21 Hz, p-C6F5), –166.6 (m, m-
C6F5). Anal. calcd. for C34H38AlF15N4: C 50.13, H 4.70, N
6.88; found: C 50.01, H 4.55, N 6.54. Single crystals suitable
for X-ray diffraction experiments were grown from pentane.
X-ray data collection and reduction
Crystals were manipulated and mounted in capillaries in a
glovebox, thus, maintaining a dry, O2-free environment for
each crystal. Diffraction experiments were performed on a
Siemens SMART System CCD diffractometer. The data
were collected in a hemisphere of data in 1329 frames with
10 s exposure times. The observed extinctions were consis-
tent with the space groups in each case. The data sets were
collected (4.5° < 2θ < 45–50.0°). A measure of decay was
obtained by recollecting the first 50 frames of each data set.
The intensities of reflections within these frames showed no
statistically significant change over the duration of the data
collections. The data were processed using the SAINT and
XPREP processing packages. An empirical absorption cor-
rection, based on redundant data, was applied to each data
set. Subsequent solution and refinement was performed, us-
ing the SHELXTL solution package.
Synthesis of [(C6F5)(n-C4H9)N]3Al·PMe3 (6) and
[(C6F5)(n-C4H9)N]3Al·(Me-imid) (7)
These compounds were prepared in a similar fashion, us-
ing the appropriate reagent; thus, only one preparation is de-
tailed. PMe3 (0.17 mL, 1.67 mmol) was added to a solution
of 5 (545 mg, 0.67 mmol) in toluene (5 mL) and stirred
overnight at 25 °C. The solvent was removed in vacuo, and
the crude product was recrystallized from pentane to yield
145 mg (0.18 mmol, 27%) of a white microcrystalline solid
1
6. H NMR (C7D8): 3.05 (m, 6H, NCH2), 1.06 (m, 12H,
3
CH2CH2Me), 0.78, (t, JHH = 7 Hz, 9H, CH2Me), 0.71 (d,
2JPH = 8 Hz, 9H, PMe3). 13C{1H} NMR (C7D8): 146.0 (dm,
1
1JFC = 240 Hz, o-C6F5), 137.9 (dm, JFC = 252 Hz, m-C6F5),
1
136.8 (dm, JFC = 253 Hz, p-C6F5), 136.2 (m, ipso-C6F5),
49.7 (s, NCH2), 33.3 (s, NCH2CH2), 20.2 (s, CH2Me), 13.7
(s, CH2Me), 10.7 (d, JPC = 23.2 Hz, PMe3), ipso-C6F5 reso-
Structure solution and refinement
Non-hydrogen atomic-scattering factors were taken from
1
© 2007 NRC Canada

Cornelissen et al.
Table 1. Crystallographic data.
137
Crystal
1
2·C6H5Me
4
8
Empirical formula
C12HF10N
C35H20AlF20N3
C34H38AlF15N4
C24H30Al2F10N2
Formula weight
Crystal system
a (Å)
b (Å)
c (Å)
349.14
889.52
814.66
590.46
Monoclinic
21.383(5)
5.9810(14)
4.5176(11)
Triclinic
12.3959(19)
12.7928(19)
13.306(2)
104.584(2)
106.602(2)
108.169(2)
1781.5(5)
P1
Monoclinic
23.36(3)
8.902(10)
19.97(2)
Monolcinic
14.713(3)
12.980(2)
15.085(3)
α (°)
β (°)
γ (°)
100.344(3)
112.660(15)
98.488(2)
Volume (Å3)
Space group
Dcalcd. (g cm–3)
568.4(2)
C2
1.02
3833(8)
P21/c
1.412
2849.3(9)
P21/n
1.376
1.658
Z
1
2
4
4
Absorption coefficient (µ) (mm–1)
0.118
2325
811
0.195
17357
6274
0.156
35570
6754
0.183
26972
5013
Reflections collected
Data Fo > 3σ(Fo )
2
2
Parameters
107
0.0291
536
0.0539
487
0.0577
349
0.0557
a
R1
b
wR2
0.0727
0.729
0.1112
0.997
0.1063
0.998
0.1272
1.019
Goodness-of-fit
aData collected at 20 °C with Mo Kα radiation (λ = 0.71069 Å), R1 = Σ|(|Fo| – |Fc|)|/Σ|Fo|.
bwR2 = [Σw(Fo -Fc2)2/Σ(wFc)2]1/2
.
2
the literature tabulations (25). The heavy-atom positions
were determined, using direct methods, employing the
SHELXTL direct methods routine. The remaining non-
hydrogen atoms were located from successive difference
Fourier map calculations. The refinements were carried out
by using full-matrix least-squares techniques on F, minimiz-
ing the function w(|Fo| – |Fc|)2, where the weight w is de-
fined as 4Fo /2σ(Fo ), and Fo and Fc are the observed and
calculated structure factor amplitudes, respectively. In the fi-
nal cycles of each refinement, all non-hydrogen atoms were
assigned anisotropic temperature factors in the absence of
disorder or insufficient data. In the latter cases, atoms were
treated isotropically. H-atom positions were calculated and
allowed to ride on the carbon to which they are bonded, as-
suming a C–H bond length of 0.95 Å. Hydrogen-atom tem-
perature factors were fixed at 1.10 times the isotropic
temperature factor of the C atom to which they are bonded.
The H-atom contributions were calculated but not refined.
The locations of the largest peaks in the final difference
Fourier map calculation, as well as the magnitude of the re-
sidual electron densities in each case, were of no chemical
significance. Additional details are provided in the supple-
mentary data.2 Crystallographic data for 1, 2, 4, and 8 are
given in Table 1.
frequently used as a ligand in main-group or tranisition-
metal chemistry. In initiating work with this species, we
were able to obtain X-ray quality crystals of 1 (Fig. 1). The
reaction of this amine with AlH3·NEtMe2 in a 1:1 ratio af-
1
fords a light-yellow oil 2 in 97% isolated yield. The H
NMR data were consistent with the presence of coordinated
NEtMe2, although resonances attributable to Al–H frag-
ments were not observed at 25 °C. At –80 °C, a resonance
appeared at 3.39 ppm, and it was attributed to two protons on
Al. The 19F NMR spectrum of 2 showed the resonances ex-
pected for the amide substituents. Based on these data and
2
2
elemental analyses, compound
2 was formulated as
[(C6F5)2N]AlH2·NEtMe2 (Scheme 1).
Using 1:3 stoichiometry, the reaction of AlH3·NEtMe2
with (C6F5)2NH proceeds upon stirring at 25 °C for 12 h to
afford the product 3 (Scheme 1). The product was
recrystallized from pentane to yield a white crystalline mate-
1
rial in 83% yield. For compound 3, the H NMR spectrum
showed resonance attributable to coordinated NEtMe2, al-
though no resonances attributable to AlH were observed.
Nonetheless, similar to 2, cooling to –80 °C resulted in the
observation of a 1H NMR resonance at 3.21 ppm attributable
to the single Al–H atom. The 13C{1H} NMR spectrum re-
vealed the corresponding 13C resonances, as well as signals
arising from C6F5 rings. Similarly, the 19F NMR data are
consistent with the presence of the (C6F5)2N fragments. Suit-
able crystals were obtained from a pentane solution at
Results and discussion
The pentafluoroaryl amine (C6F5)2NH (1) has not been
2 Supplementary data for this article are available on the journal Web site (http://canjchem.nrc.ca) or may be purchased from the Depository
of Unpublished Data, Document Delivery, CISTI, National Research Council Canada, Ottawa, ON K1A 0R6, Canada. DUD 5132. For more
information on obtaining material, refer to http://cisti-icist.nrc-cnrc.gc.ca/irm/unpub_e.shtml. CCDC 633717 and 633720 contain the crystal-
lographic data for this manuscript. These data can be obtained, free of charge, via http://www.ccdc.cam.ac.uk/conts/retrieving.html (or from
the Cambridge Crystallographic Data Centre, 12 Union Road, Cambridge CB2 1EZ, UK; fax +44 1223 336033; or de-
posit@ccdc.cam.ac.uk).
© 2007 NRC Canada

138
Can. J. Chem. Vol. 85, 2007
Scheme 1.
Fig. 1. ORTEP drawing of 1 (30% thermal ellipsoids are shown).
Selected distances (Å) and angles (°): N(1)—C(1), 1.389(3);
C(1)–N(1)–C(1), 127.7(3).
–30 °C, allowing the unambiguous determination of the
nature of 3, as [(C6F5)2N]2AlH·NEtMe2, by a single-crystal
X-ray diffraction study (Fig. 2). The geometry about Al is
pseudo-tetrahedral, with the amide Al—N distances averag-
ing 1.855(3) Å. The coordinated tertiary amine gives rise to
an Al—N distance of 2.006(3) Å. The resulting N–Al–N an-
gles range from 105.48(12)° to 113.78(13)°. The Al-bound
H atom was located and refined, giving rise to an Al–H dis-
tance of 1.62 Å. Similar Al—H distances have been reported
for (i-Pr2C6H3N)C(Me)CHPPh2(NC6H3-i-Pr2)AlH2 (26). Ad-
jacent arene rings on the two amide ligands are oriented in
an approximately parallel offset π-stacking arrangement. The
distance between these rings is 3.284 Å, while the angle be-
tween the planes is 2°.
The related fluorinated-aryl amine (C6F5)(n-C4H9)NH (4)
was prepared via a known method (24). Reactions of this
less bulky and more basic amine with AlH3·NEtMe2 in 1:1
and 2:1 ratios afforded unresolved mixtures of products.
© 2007 NRC Canada

Cornelissen et al.
139
Fig. 2. ORTEP drawing of 2 (30% thermal ellipsoids are shown).
All hydrogen atoms except the AlH are omitted for clarity. Se-
lected distances (Å) and angles (°): Al(1)—N(1), 1.855(3);
Al(1)—N(2), 1.856(3); Al(1)—N(3), 2.006(3); N(1)–Al(1)–N(2),
111.44(13); N(1)–Al(1)–N(3), 113.78(13); N(2)–Al(1)–N(3),
105.48(12).
Fig. 3. ORTEP drawing of 4 (30% thermal ellipsoids are shown).
Hydrogen atoms are omitted for clarity. Selected distances (Å)
and angles (°): Al(1)—N(1), 1.838(4); Al(1)—N(2), 1.833(3);
Al(1)—N(3), 1.827(3); Al(1)—N(4), 2.043(4); N(3)–Al(1)–N(2),
114.55(15); N(3)–Al(1)–N(1), 111.01(16); N(2)–Al(1)–N(1),
112.25(14); N(3)–Al(1)–N(4), 106.37(14); N(2)–Al(1)–N(4),
105.66(15); N(1)–Al(1)–N(4), 106.34(14).
However, the reaction of 4 in a 3:1 ratio with AlH3·NEtMe2
proceeded to give a white solid 5 in 72% isolated yield.
1H NMR data were consistent with a ratio of amide to
coordinated NEtMe2 of 3:1. 13C{1H} and 19F NMR data
also supported the formulation of
5 as [(C6F5)(n-
C4H9)N]3Al·NEtMe2 (Scheme 1). This view was subse-
quently confirmed via X-ray crystallography (Fig. 3). The
Al center in 5 has a pseudo-tetrahedral geometry with
Al—N distances for the amide ligands ranging from
1.827(3) Å to 1.838(4) Å. These distances are slightly
shorter than those reported earlier for 3, consistent with the
increased basicity of the amide derived from 4. The coordi-
nated amine NEtMe2 gave rise to an Al—N distance of
2.043(4) Å. Interestingly, this distance is significantly
shorter than that seen in 4, suggesting that although the Al in
5 has three amide ligands, the Al center is more accessible
to the donor, presumably because of the lesser steric de-
mands of the amide substituents.
the lesser steric congestion provided by the imidazole N-
atom donor.
In contrast to the reactions with AlH3·NEtMe2, the amine
4 reacts with AlMe3 in a 1:1 ratio to form the colorless crys-
1
talline product 8 in 73% isolated yield. The H NMR spec-
trum of 8 is consistent with replacement of one methyl
group by an amide ligand. However, this spectrum also
shows two resonances at –0.04 and –0.73 ppm, attributable
to Al-bound methyl groups. This suggests molecular
dissymmetry and the formulation of 8 as [Me2AlN(C6F5)(n-
C4H9)]2 (Fig 4, Scheme 2). The 13C{1H} and 19F NMR and
elemental analysis data were also consistent with this formu-
lation. Single crystals of 8, suitable for X-ray diffraction ex-
periments, were grown from a concentrated pentane solution
at –30 °C. The X-ray data confirmed the dimeric formula-
tion of 8, in which the amido-N atoms bridge the two Al
centers. The substituents on N are oriented such that the
C6F5 rings are on cis. It is this feature that accounts for the
inequivalent methyl groups on the Al atoms. The Al—N dis-
tances were found to range from 1.993(3) Å to 2.031(3) Å,
significantly longer than the terminal Al–amide distances
described earlier. The geometry and metric parameters are
similar to those recently reported for a series of Al-dimers
[Me2AlN(C6FnH5–n)H]2(n = 1, 2, 4, and 5) (27). The Al—C
distances range from 1.947(4) to 1.959(3) Å, similar to those
seen in the previously mentioned Al-dimers and in
[Me2Al(NPt-Bu3)]2 (28). The Al-centers are pseudo-
tetrahedral, with C–Al–C′ and N–Al–N′ angles averaging
122.4(2)° and 86.8(1)°, respectively. In addition, the Al2N2
Compound 5 reacts with other donors to afford the
replacement of the coordinated amine. For example, the re-
action with PMe3 results in the formation of the white micro-
crystalline product 6, albeit in a relatively low isolated yield
1
of 27%. H NMR confirms the displacement of the coordi-
nated NEtMe2 by PMe3. In addition, the observation of a
31P{1H} NMR signal at –50.3 ppm is consistent with coordi-
nation to Al, and thus, the formulation of 6 as [(C6F5)(n-
C4H9)N]3Al·PMe3 (Scheme 1). In a similar fashion, the
reaction of 5 with N-methylimidazole MeN2C3H3 results in
the displacement of the amine, affording the product
[(C6F5)(n-C4H9)N]3Al·(Me-imid) (7) in quantitative yields
(Scheme 1). NMR data supported this formulation, although
repeated attempts to isolate X-ray quality crystals of 7 were
unsuccessful. The dramatically higher yields of 7 than 6 are
consistent with hard–soft donor considerations, as well as
© 2007 NRC Canada

140
Can. J. Chem. Vol. 85, 2007
Fig. 4. ORTEP drawing of 8 (30% thermal ellipsoids are shown).
Hydrogen atoms are omitted for clarity. Selected distances (Å)
and angles (°): Al(1)—C(1), 1.947(4); Al(1)—C(2), 1.956(4);
Al(1)—N(2), 1.993(3); Al(1)—N(1), 2.031(3); Al(1)—Al(2),
2.8280(14); Al(2)—C(4), 1.958(3); Al(2)—C(3), 1.959(3);
Al(2)—N(1), 2.002(3); Al(2)—N(2), 2.030(3); C(1)–Al(1)–C(2),
123.70(18); C(1)–Al(1)–N(2), 112.08(15); C(2)–Al(1)–N(2),
109.36(14); C(1)–Al(1)–N(1), 111.89(14); C(2)–Al(1)–N(1),
106.70(15); N(2)–Al(1)–N(1), 86.87(10); C(4)–Al(2)–C(3),
121.04(18); C(4)–Al(2)–N(1), 110.78(14); C(3)–Al(2)–N(1),
113.11(14); C(4)–Al(2)–N(2), 107.39(14); C(3)–Al(2)–N(2),
112.50(14); N(1)–Al(2)–N(2), 86.65(10); Al(2)–N(1)–Al(1),
89.02(10); Al(1)–N(2)–Al(2), 89.33(10).
istry that will result in new activators for applications in
olefin polymerization catalysts.
Acknowledgements
Financial support from the Natural Sciences and Engi-
neering Research Council of Canada (NSERC) is gratefully
acknowledged.
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Summary
Several Al compounds incorporating hexafluoro-
phenylamido-ligands have been prepared and characterized.
The amides derived from the amines (C6F5)2NH and
(C6F5)(n-C4H9)NH react with AlH3.NEtMe2 to give the
momeric Al products 2, 3, and 5, with varying numbers of
amido-substituents. The degree of substitution appears to be
dominated by the steric demands of the amide subsitutents.
Donor exchange is facile for 5, readily affording 6 and 7.
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give the dimeric product 8. These Al–amido species proved
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© 2007 NRC Canada