Synthesis and structural characterization of m-terphenyl Schiff base ligands and their aluminum complexes

Article abstract of DOI:10.1139/v04-110

2,4,6-Triphenylbenzaldehyde 1 undergoes a condensation reaction with 2-aminophenol to give N-(2′,4′,6′-triphenylbenzylidene)-2- iminophenol (TPIP) 2. The imine 2 can be reduced with NaBH₄ in ethanol to form N-(2′,4′,6′-triphenylbenzyl)-2-aminop

Full text of DOI:10.1139/v04-110

1346
Synthesis and structural characterization of m-
terphenyl Schiff base ligands and their aluminum
complexes
Diane A. Dickie, Hanifa Jalali, Rahul G. Samant, Michael C. Jennings, and
Jason A.C. Clyburne
Abstract: 2,4,6-Triphenylbenzaldehyde 1 undergoes a condensation reaction with 2-aminophenol to give N-(2′,4′,6′-
triphenylbenzylidene)-2-iminophenol (TPIP) 2. The imine 2 can be reduced with NaBH4 in ethanol to form N-(2′,4′,6′-
triphenylbenzyl)-2-aminophenol (TPAP) 3. Addition of trimethylaluminum to 2 or 3 results in the formation of the
complexes TPIP-AlMe2·AlMe3 (4) or TPAP-AlMe2 (5). Compounds 2, 3, and 4 have been crystallographically charac-
terized.
Key words: N,O ligands, aluminum, m-terphenyl, Schiff bases, X-ray crystallography.
Résumé : Le 2,4,6-triphénylbenzaldéhyde 1 subit une réaction de condensation avec le 2-aminophénol qui conduit à la
formation du N-(2′,4′,6′-triphénylbenzylidène)-2-iminophénol (TPIP, 2). L’imine 2 peut être réduite à l’aide de NaBH4,
dans l’éthanol, pour conduire à la formation du N-(2′,4′,6′-triphénylbenzyl)-2-aminophénol (TPAP, 3). L’addition de tri-
méthylaluminium aux composés 2 ou 3 conduit à la formation de complexes TPIP-AlMe2·AlMe3 (4) ou TPAP-AlMe2
(5). Les composés 2, 3 et 4 ont été caractérisés par cristallographie par diffraction des rayons X.
Mots clés : ligands N,O, aluminium, m-terphényle, bases de Schiff, cristallographie par diffraction des rayons X.
[Traduit par la Rédaction] Dickie et al. 1352
Introduction
ies on m-terphenyl substituted compounds, we decided to in-
corporate other catalytically active functional groups into the
m-terphenyl pocket. An ideal candidate for the pocket ap-
peared to be a Schiff base. We chose phenyl as the aryl
substituent because it is less bulky than other substituted
aryls, and it is also affordably and reliably synthesized.
Multidentate ligands such as Schiff bases, which contain
both an imino (C=N) and a phenolic (OH) functional group,
are potentially useful monoanionic ligands. While they can
exhibit two different structural isomers (Fig. 2), the isomer
featuring a three-carbon bridge (A) between the heteroatoms
is much more common, with only a few published examples
of main group Schiff base complexes containing a bridge of
only two carbons (B) (15–18). Schiff bases are useful for
varying the coordination number of the metal centre as the
heteroatoms can bind in a monodentate fashion, chelate the
metal, or bridge multiple metal centres (Fig. 3) (19). The
tetradentate Salen family of ligands are perhaps the best
known Schiff bases, and the coordination chemistry of main
group elements with this class and the saturated Salan-type
ligands has been extensively reviewed (20, 21).
The chemistry of m-terphenyl ligands is a rapidly develop-
ing field of research (1, 2). These molecules feature a central
phenyl ring with two meta-aryl substituents that twist out of
the plane of the central ring to form a bowl-shaped pocket
into which numerous metals or functional groups can be
placed (Fig. 1). The steric demands of the ligand can be
tuned by varying the substituents of the aryl groups. Syn-
thetically, the steric demands of m-terphenyl ligands have
been used to stabilize unusual coordination environments
and multiple bonds between heavy main group elements (3–6).
Organoaluminum compounds are widely used as catalysts
or co-catalysts in numerous polymerization reactions (7–10).
When developing a new homogeneous catalyst, it is impor-
tant to have the ability to control the coordination environ-
ment around the metal centre (11). m-Terphenyl ligands,
because of their ability to protect the space around the metal
centre, have the potential to be useful in the field of cataly-
sis. We have previously used amidine-substituted m-terphenyl
ligands for the preparation of robust aluminum complexes
(12, 13) and related compounds have been used as olefin
polymerization catalysts (14). As a continuation of our stud-
In an attempt to incorporate Schiff bases onto an m-
terphenyl ligand, we have prepared and structurally charac-
Received 3 September 2003. Published on the NRC Research Press Web site at http://canjchem.nrc.ca on 23 October 2004.
D.A. Dickie, H. Jalali, R.G. Samant, and J.A.C. Clyburne.1 Department of Chemistry, Simon Fraser University, 8888 University
Dr., Burnaby BC V5A 1S6, Canada.
M.C. Jennings.2 Department of Chemistry, University of Western Ontario, 1151 Richmond Street, London ON N6A 5B7, Canada.
1Corresponding author (e-mail: clyburne@sfu.ca).
2Corresponding author (crystallography) (e-mail: mjenning@uwo.ca).
Can. J. Chem. 82: 1346–1352 (2004)
doi: 10.1139/V04-110
© 2004 NRC Canada

Dickie et al.
1347
Scheme 1. Synthesis of 1 and 2.
Fig. 1. Space-filling model of a m-terphenyl, 1,3-diphenylbenzene.
Note the bowl-shaped cavity formed by the flanking rings. For
clarity, only the hydrogen in the m-terphenyl pocket is shown.
Fig. 3. Schiff base coordination patterns.
1625 cm–1 in the IR spectrum. These values are consistent
with those reported by Yamamoto and co-workers (26) for
the related 2-(phenylmethylene)aminophenol (δ NH
8.68 ppm, ν C=N 1630 cm–1). The alcohol functionality was
1
Fig. 2. Structural isomers of a Schiff base.
observed as a sharp singlet at 5.49 ppm in the H NMR
spectrum and at 3419 cm–1 in the IR. The value of the OH
stretch in 2, while higher than that of Yamamoto and co-
workers at 3130 cm–1, is comparable to other molecules that
feature intramolecular [O-H···π] interactions, such as 2,6-
diphenylphenol with an OH stretch of 3565 cm–1 (27).
X-ray crystallographic studies of a single crystal of 2
were performed and the results are presented in Table 1. As
is typical in terphenyl molecules, the ortho phenyls are
twisted out of the plane of the central phenyl ring to form a
protective bowl around the imino functional group (Fig. 4).
As expected from the spectroscopic data, an [O-Hþ π] inter-
action is observed between the phenolic proton and the cen-
troid of one phenyl ring.
terized two ligands as well as a complex with aluminum.
These molecules are related to bulky Schiff base ligands and
complexes reported by Chisholm et al. (22), Gibson and co-
workers (23), and Grubbs and co-workers (24).
Reduction of the C=N double bond in TPIP was achieved
by the addition of NaBH4 in ethanol solution to give TPAP 3
1
(Scheme 2). The H NMR spectrum showed a peak for the
methylene protons at 4.05 ppm. This is consistent with data
presented by Endo et al. (28) for the related N-benzyl-2-
aminophenol where the methylene resonance is observed at
4.37 ppm. In the IR spectrum, the NH stretch appeared as a
sharp peak at 3321 cm–1 while the OH appeared as a weak
signal at 3391 cm–1. X-ray crystallographic studies of a sin-
gle crystal of 3 (Fig. 5) showed that the Cterphenyl—N bond
length increased from 1.222(4) Å in TPIP to 1.448(3) Å in
TPAP while the Cphenol—N bond shortened slightly from
1.427(4) to 1.394(3) Å. The [O-Hþ π] interaction noted in 2
is not observed in 3.
TPIP 2 reacts with 2 equiv. of trimethylaluminum to give
TPIP-AlMe2·AlMe3 (4) (Scheme 2), which features one alu-
minum chelated by the two heteroatoms as well as a second
aluminum coordinated in Lewis acid–base fashion to the ox-
ygen atom. In the presence of only 1 equiv. of AlMe3, com-
pound 4 is still formed, along with a yellow powder that was
not further characterized because of its insolubility in con-
ventional solvents.
Results and discussion
2,4,6-Triphenylbenzaldehyde 1 is readily synthesized on a
large scale with good yield (80%) according to a variation of
literature procedures (25) (Scheme 1). The white crystalline
product was characterized by NMR spectroscopy. The alde-
1
hyde H resonance is observed at 10.0 ppm in the H NMR
spectrum. In the 13C NMR, the aldehyde carbon signal ap-
pears at 193 ppm. Further confirmation of the assigned struc-
ture was provided by IR spectroscopy (ν C=O 1698 cm–1;
ν C-H 2747 cm–1).
Aldehyde 1 was treated with 2-aminophenol in ethanol so-
lution to form N-(2′,4′,6′-triphenylbenzylidene)-2-iminophenol
(TPIP) 2 (Scheme 1). The product was isolated in high yield
(>90%) as a yellow crystalline compound. Characterization
1
of 2 was achieved by H and 13C NMR spectroscopy. The
imine functionality was indicated by the peak at 8.59 ppm in
1
the H NMR spectrum as well as by the C=N stretch at
© 2004 NRC Canada

1348
Can. J. Chem. Vol. 82, 2004
Table 1. Crystal data.
TPIP (2)
TPAP (3)
TPIP-AlMe2·AlMe3 (4)
Empirical
formula
C31H23NO
C31H25NO
C36H37Al2NO
Formula weight
Crystal system
Space group
Temperature (K)
a (Å)
425.50
427.52
553.63
Triclinic
P-1
Monoclinic
P2(1)/c
297(2)
17.490 3(4)
5.702 9(1)
23.349 2(6)
90
99.234(1)
90
2298.79(9)
4
Monoclinic
P2(1)/n
296(2)
12.418 4(3)
10.637 4(2)
17.993 2(5)
90
101.353(1)
90
2330.38(10)
4
150(2)
10.060 5(2)
12.418 5(4)
13.886 3(5)
100.619(1)
97.415(1)
110.549(2)
1560.91(8)
2
b (Å)
c (Å)
α (°)
β (°)
γ (°)
Volume (Å3)
Z
Dcalcd (Mg m–1)
1.229
1.219
1.178
µ (mm–1)
R (2σ)
0.074
0.069 0
0.191 0
0.073
0.052 6
0.141 3
0.121
0.052 9
0.120 1
2
Rw (2σ)
Scheme 2. Synthesis of TPAP (3) and aluminum complexes TPIP-AlMe2·AlMe3 (4) and TPAP-AlMe2 (5).
1H NMR data indicated the presence of two different alu-
Fig. 4. The structure of TPIP (2) showing the numbering
scheme. Hydrogen atoms, except the phenolic H, have been re-
moved for clarity. Selected bond lengths (Å): C(1)—N(2)
1.222(4), C(1)—C(11) 1.505(5), N(2)—C(3) 1.427(4), C(8)—
O(9) 1.393(5), H(9a)···centroid 2.986, O(9)···centroid 3.562. Se-
lected bond angles (°): C(11)-C(1)-N(2) 123.2(4), C(1)-N(2)-C(3)
119.0(3), O(9)-H(9a)···centroid 139.73.
minum methyl environments with resonances observed at
−1.31 and –0.89 ppm, with relative integrated intensities of
2:3. These signals were assigned to a N,O-chelated di-
methylaluminum centre and the O-coordinated trimethylalu-
minum centre, respectively. Noticeably absent from the IR
spectrum of 4 was the OH stretch observed in 2. X-ray crys-
tallographic studies confirmed the proposed structure
(Fig. 6).
The coordination pattern observed in 4, while unexpected,
is not unprecedented (Fig. 7). Similar five-membered N-Al-
O heterocycles with a second trialkylaluminum coordinated
to the oxygen atom have been reported by Atwood et al.
(17), Barron and co-workers (29), and van Koten and co-
workers (30, 31). The Al—N and both Al—O bond lengths
of 4 are consistent with the literatures values (Table 2). The
environment around each aluminum centre in 4 is that of a
distorted tetrahedron, with bond angles ranging from
84.13°–120.30° in the chelated aluminum, Al(13), and
102.02°–115.47° for the other, Al(4). The large distortions
seen in the chelated centre are likely due to the steric con-
straints imposed by the formation of a five-membered ring,
as well as the presence of the bulky m-terphenyl fragment.
The aluminum complex TPIP-AlMe2·AlMe3 (4) was
tested as a catalyst in the ring-opening polymerization of ε-
© 2004 NRC Canada

Dickie et al.
1349
Fig. 5. The structure of TPAP (3) showing the numbering
scheme. Aryl hydrogen atoms have been removed for clarity. Se-
lected bond lengths (Å): C(10)—C(9) 1.517(3), C(9)—N(8)
1.448(3), N(8)—C(7) 1.394(3), C(2)—O(1) 1.375(3). Selected
bond angles (°): C(10)-C(9)-N(8) 112.14(17), C(9)-N(8)-C(7)
118.91(18).
Fig. 6. Structure of TPIP-AlMe2·AlMe3 (4) showing the number-
ing scheme. Hydrogen atoms have been removed for clarity. Se-
lected bond lengths (Å): C(21)—C(16) 1.470(3), C(16)—N(12)
1.289(3), N(12)—Al(13) 2.013(2), N(12)—C(11) 1.430(3),
C(6)—O(5) 1.386(3), O(5)—Al(4) 1.936(2), O(5)—Al(13)
1.870(2), Al(13)—C(15) 1.939(3), Al(13)—C(14) 1.932(3),
Al(4)—C(3) 1.972(3), Al(4)—C(1) 1.977(3), Al(4)—C(2)
1.970(3). Selected bond angles (°): C(21)-C(16)-N(12) 122.5(2),
C(16)-N(12)-C(11) 120.3(2), N(12)-Al(13)-O(5) 84.13(8), N(12)-
Al(13)-C(15) 108.27(12), N(12)-Al(13)-C(14) 115.13(12), C(15)-
Al(13)-C(14) 120.30(15), O(5)-Al(13)-C(15) 116.83(14), O(5)-
Al(13)-C(14) 106.74(12), C(6)-O(5)-Al(13) 112.72(16), C(6)-
O(5)-Al(4) 123.28(16), O(5)-Al(4)-C(1) 106.45(11), O(5)-Al(4)-
C(2) 102.01(12), O(5)-Al(4)-C(3) 105.25(12), C(1)-Al(4)-C(2)
112.31(15), C(1)-Al(4)-C(3) 115.47(15), C(2)-Al(4)-C(3)
113.82(17), Al(13)-O(5)-Al(4) 123.50(9).
caprolactone (9) and propylene oxide (7). Complex 4 was
found to give poly(caprolactone) with Mw = 10 964 and
polydispersity of 1.50. Under similar conditions, the bulky
alkylaluminum catalysts described by Okuda and co-workers
(9) produced polymers with Mw in the range of 50 000 with
polydispersities between 1.8–3.3. Complex 4 was not active
in the polymerization of propylene oxide. This is poor com-
pared with other alkylaluminum compounds featuring nitro-
gen and oxygen donors (7).
Polymerization of ε-caprolactone and propylene oxide
were attempted under similar conditions to those described
for 4 but no reaction was observed. The reasons for this dif-
ference in activity are not immediately clear.
Finally, when TPAP 3 was combined with trimethylalu-
minum, the anticipated product TPAP-AlMe·AlMe3 was not
detected. To our surprise, the mononuclear complex TPAP-
AlMe2 (5) was isolated (Scheme 2). Complex 5 was charac-
Summary
1
terized by IR, H and 13C NMR spectroscopy. The IR spec-
trum showed a peak assigned to an NH stretch at 3321 cm–1
Two new aminophenol m-terphenyl derivatives were syn-
thesized and characterized. The aluminum complexes of
these ligands were also synthesized. The activity of TPIP-
AlMe2·AlMe3 as a ring-opening polymerization catalyst was
examined. Poly(caprolactone) with Mw = 10 964 and
polydispersity of 1.50 was produced, however the molecule
was not catalytically active in the presence of propylene ox-
ide.
1
(cf. TPAP N-H observed at 3291 cm–1). In the H NMR
spectrum, the signal for the methylene protons was resolved
into a doublet (3JH-H = 7 Hz) and the NH signal appeared as
a triplet at 3.08 ppm (3JH-H = 7 Hz). Also observed in the 1H
NMR spectrum was a sharp singlet at –1.35 ppm that inte-
grated to six hydrogens. This signal was assigned to six alu-
minum methyl hydrogen atoms. Similarly, the signal at
−8.1 ppm in the 13C NMR spectrum was assigned to the two
aluminum methyl carbons. These spectroscopic observa-
tions, specifically the decreased frequency of νN-H in the IR
Experimental
3
1
spectrum and the NH-CH JH-H coupling constant in the H
NMR spectrum, are consistent with our suggested structure
5 and this structure is reminiscent of trialkylaluminum-
dialkylamine adducts previously reported by Bradley et al.
(32). Elemental analyses was performed on samples of 5,
and the results agree more closely with the suggested struc-
ture of 5 than any of the other likely reaction products. Un-
fortunately, despite numerous attempts in various solvents
and conditions, we were not able to grow crystals suitable
for X-ray crystallographic studies.
General
An MBraun UL-99–245 dry box and standard Schlenk
techniques on a double manifold vacuum line were used in
the manipulation of air and moisture sensitive compounds.
NMR spectra were recorded on a Bruker AMX 400 or a
1
Varian AS 500 spectrometer in 5 mm quartz tubes. H and
13C chemical shifts are reported in parts per million (ppm)
downfield from tetramethylsilane (TMS) and are calibrated
to the residual signal of the solvent. Infrared spectra were
obtained using a Bomem MB spectrometer with the % trans-
© 2004 NRC Canada

1350
Can. J. Chem. Vol. 82, 2004
Fig. 7. Coordination of aluminum in 4, 6 (17), 7 (29), 8 (30), and 9 (31).
Table 2. Comparison of bond lengths in structurally characterized C2NOAl rings exhibiting O-AlR3 complexation.
4
6
7
8
9
Bond lengths (Å)
Al1—N
2.013(2)
1.870(2)
1.936(2)
2.005(9)
1.807(9)
1.895(8)
2.039(2)
1.870(2)
1.895(2)
2.013(6)
1.837(4)
1.929(4)
2.002(6)
1.825(5)
1.910(5)
Al1—O
Al2—O
Bond angles (°)
N-Al1-O
84.13(8)
123.50(9)
This work
85.6(3)
126.4(3)
17
85.65(9)
126.6(1)
29
74.4(2)
135.5(2)
30
84.6(2)
120.3(3)
31
Al1-O-Al2
Reference
1
mittance values reported in cm–1. Melting points were mea-
sured using a Mel-Temp apparatus and are uncorrected.
Elemental analysis were obtained by M.K. Yang on a Carlo
Erba Model 1106 CHN analyzer.
(m), 699 (s). H NMR (400 MHz, CDCl3) δ: 5.49 (s, 1H,
OH), 6.68–6.72 (m, 1H), 6.76–6.79 (m, 2H), 7.01–7.06 (m,
1H), 7.38–7.53 (m, 15H), 7.65 (s, 2H), 8.59 (s, 1H, N=CH).
13C NMR (100 MHz, CDCl3) δ: 119.7, 127.2, 127.4, 127.7,
128.0, 128.2, 128.4, 128.9, 129.0, 129.4, 129.5, 193.0 (qua-
ternary carbons not observed). Anal. calcd. for C31H23NO: C
87.50, H 5.45, N 3.29; found: C 87.42, H 5.47, N 3.41.
2,4,6-Triphenylbenzaldehyde (25) (1)
2,4,6-Triphenylbromobenzene (20 g, 52 mmol) was sus-
pended in ca. 200 mL anhydrous ether and n-butyllithium
(1.6 mol L–1 in hexane, 36 mL, 57 mmol) was added drop-
wise. The reaction was stirred at room temperature for 3 h
and an excess of DMF (17 mL) was then added dropwise.
After 2 h, the reaction was quenched with H2O and extracted
with ether. The combined ether portions were dried with
MgSO4, concentrated under vacuum, and stored at −20 °C.
Yellow crystals were isolated and characterized as 2,4,6-
triphenylbenzaldehyde (13.8 g, 41 mmol, 80%), mp 128 to
129 °C. IR (Nujol): 2747 (m), 1698 (s), 1590 (s), 1343 (s),
N-(2′,4′,6′-Triphenylbenzyl)-2-aminophenol (TPAP) (3)
TPIP (4.05 g, 9.52 mmol) and sodium borohydride
(0.90 g, 23.8 mmol) were suspended in ca. 200 mL of
anhyd. EtOH. The mixture was heated slowly to reflux over
1 h and then allowed to cool to room temperature. The reac-
tion was quenched with H2O and extracted with CH2Cl2.
The organic layer was washed with H2O and a saturated so-
dium chloride solution and dried with MgSO4. The solvent
was removed under vacuum to give a brown powder that was
recrystallized from Et2O at room temperature (2.54 g,
5.94 mmol, 62.4%), mp 174–176 °C. IR (Nujol): 3391 (w),
3321 (m), 1595 (m), 1493 (m), 1480 (s), 1275 (m), 1251
1
1198 (s), 892 (m), 764 (vs). H NMR (400 MHz, CDCl3) δ:
7.40–7.71 (m, 17H), 10.00 (s, 1H). 13C NMR (100 MHz,
CDCl3) δ: 127.4, 127.7, 128.2, 128.5, 129.0, 129.1, 129.6,
131.6, 139.4, 139.8, 144.2, 145.2, 193.0.
1
(m), 886 (m), 702 (s). H NMR (400 MHz, CDCl3) δ: 4.06
(s, 2H, CH2), 5.06 (br s, 1H, OH), 6.24 (s, 1H, NH), 6.63 (s,
4H), 7.38–77.67 (m, 17H). 13C NMR (125 MHz) δ: 44.6,
114.2, 115.4, 119.5, 120.9, 127.1, 127.4, 127.5, 128.3,
128.8, 129.1, 132.8, 135.6, 139.9, 140.1, 141.3, 144.0,
145.5. Anal. calcd. for C31H25NO: C 87.09, H 5.89, N 3.28;
found: C 87.13, H 5.97, N 3.21.
N-(2′,4′,6′-Triphenylbenzylidene)2-iminophenol (TPIP) (2)
2,4,6,-Triphenylbenzaldehyde (10.0 g, 29.9 mmol) and 2-
aminophenol (3.7 g, 29.9 mmol) were suspended in ca.
200 mL of anhyd. EtOH and heated to reflux. Glacial acetic
acid (5 mL) was then added and reflux continued for 3 h.
The mixture was allowed to cool to room temperature and
bright yellow needle-like crystals were filtered off (11.5 g,
26.9 mmol, 90%), mp 158 to 159 °C. IR (Nujol): 3417 (m),
1625 (m), 1584 (m), 1297 (m), 1249 (m), 1212 (m), 887
TPIP-AlMe2AlMe3 (4)
TPIP (0.5 g, 1.18 mmol) was dissolved in ca. 15 mL of
anhydrous toluene under a N2 atmosphere. Trimethyl-
© 2004 NRC Canada

Dickie et al.
1351
aluminum (2.0 mol L–1 in toluene, 1.4 mL, 2.8 mmol) was
added dropwise to the stirred TPIP solution. Evolution of
methane was observed immediately but ceased after the half-
way point of the addition. The solution was allowed to stir
for 15 min and then the solvent was removed under vacuum.
The resulting yellow powder was recrystallized by slow
evaporation of a CH2Cl2 solution to give yellow crystals
(0.58 g, 1.05 mmol, 89%), mp 276 °C (dec.). IR (Nujol):
3058 (w), 3029 (w), 1596 (vs), 1575 (s), 1556 (m), 1485 (s).
1H NMR (400 MHz, CD2Cl2) δ: –1.31 (s, 6H), –0.89 (s, 9H),
7.19–7.54 (m, 17H), 7.73–7.82 (m, 4H), 8.98 (s, 1H).
13C NMR (100 MHz, CD2Cl2) δ: –10.5, −7.2, 25.6, 117.5,
119.2, 120.8, 127.6, 127.7, 128.7, 128.9, 129.2, 129.4,
129.5, 130.3, 131.8, 138.8, 129.5, 143.7. Anal. calcd. for
C36H37Al2NO: C 78.10, H 6.74, N 2.53; found: C 77.80, H
6.70, N 2.26.
to be located. The molecule was very well behaved. All of
the non-hydrogen atoms were refined with anisotropic ther-
mal parameters. The hydrogen atom positions were calcu-
lated geometrically and were included as riding on their
respective carbon atoms. The crystal data and refinement pa-
rameters are listed in Table 1. Thermal ellipsoids in Figs. 4–
6 are shown at 50% probability.
Acknowledgements
Funding for this research was provided by the Natural
Sciences and Engineering Research Council of Canada
(NSERC), Simon Fraser University, and the University of
Western Ontario. The authors would like to thank Zhiqing
(Ken) Shi and Marianne Rodgers for help with the polymer-
ization study, and Marcy Tracey and Madhvi Ramnial for the
collection of NMR data.
TPAP-AlMe2 (5)
TPAP (250 mg, 0.58 mmol) was dissolved in ca. 5 mL
anhyd. CH2Cl2. Trimethylaluminum (2.0 mol L–1 in hexane,
0.32 mL, 0.64 mmol) was added dropwise to the stirred
TPAP solution. Evolution of methane was observed and the
solution turned reddish brown. Upon completion of the addi-
tion, stirring was stopped and the flask was left to sit at
room temperature to allow slow evaporation of solvent to
give a pale brown powder (230 mg, 0.47 mmol, 82%), mp >
260 °C. IR (Nujol): 3291 (w), 1595 (s), 1574 (m), 1564 (m),
1493 (s). 1H NMR (400 MHz, CD2Cl2) δ: –1.35 (s, 6H,
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Al(CH3)2), 3.08 (t, JH-H = 7 Hz, 1H, NH), 4.01 (d, JH-H
=
7 Hz, 2H, CH2), 6.17 (d of d, JH-H = 8 Hz, 1 Hz, 1H), 6.54 (t
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Polymerization studies
TPIP-AlMe2·AlMe3 (4) (0.1 g, 0.2 mmol) was dissolved
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as a THF solution.
X-ray crystallography
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© 2004 NRC Canada