Synthesis and characterisation of neutral dialkylaluminium complexes stabilised by salicylaldiminato ligands, and their conversion to monoalkylaluminium cations

Article abstract of DOI:10.1039/b100743m

Treatment of the salicylaldimine ligands 3,5-Bu^t₂-2-(OH)C₆ H₂CHNR [R = 2,6-Me₂C₆H₃ (1a), 2,6-Prⁱ₂C₆H₃ (1b), 3,5-(CF₃)₂

Full text of DOI:10.1039/b100743m

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Synthesis and characterisation of neutral dialkylaluminium
complexes stabilised by salicylaldiminato ligands, and their
conversion to monoalkylaluminium cations †
Paul A. Cameron, Vernon C. Gibson,* Carl Redshaw, John A. Segal, Gregory A. Solan,
Andrew J. P. White and David J. Williams
Department of Chemistry, Imperial College, South Kensington, London, UK SW7 2AY
Received 22nd January 2001, Accepted 8th March 2001
First published as an Advance Article on the web 3rd April 2001
Treatment of the salicylaldimine ligands 3,5-But2-2-(OH)C6H2CHNR [R = 2,6-Me2C6H3 (1a), 2,6-Pri2C6H3 (1b),
3,5-(CF3)2C6H3 (1c), 4-(NO2)C6H4 (1d), 4-ClC6H4 (1e), 1-naphthyl (1f), But (1g)] with Me3Al in toluene yields, after
work-up, the highly crystalline (except 2c – an oil) complexes {3,5-But -2-(O)C H CH᎐NR}AlMe [R = 2,6-Me C H
᎐
2
6
2
2
2
6
3
(2a), 2,6-Pri2C6H3 (2b), 3,5-(CF3)2C6H3 (2c), 4-(NO2)C6H4 (2d), 4-ClC6H4 (2e), 1-naphthyl (2f), But (2g)] respectively.
Reaction of these systems with B(C F ) in the presence of THF leads smoothly to [{3,5-But -2-(O)C H CH᎐NR}-
᎐
6
5
3
2
6
2
AlMe(THF)]+ [R = 2,6-Me2C6H3 (3a), 2,6-Pri2C6H3 (3b), 3,5-(CF3)2C6H3 (3c), 4-(NO2)C6H4 (3d), 4-ClC6H4 (3e),
1-naphthyl (3f), But (3g)], as the B(C6F5)3MeϪ salts. By contrast, the same reaction performed in dichloromethane
solution without THF gives complex mixtures: the NMR spectrum of the product mixture obtained from the
reaction of 2g with B(C F ) in CD Cl indicated, inter alia, the presence of both {3,5-But -2-(O)C H CH᎐NBut}-
᎐
6
5
3
2
2
2
6
2
AlMe(C6F5)] and B(C6F5)2Me. Compounds 2a and 2b have been characterised by single crystal X-ray structure
determinations and shown to have virtually identical conformations. In both systems there is a marked distortion
in the tetrahedral geometry at the aluminium centre.
ligand such as THF. Here we report the synthesis and character-
isation of a series of neutral aluminium alkyls stabilised by
bidentate salicylaldimine ligands and the conversion of these to
the corresponding THF-coordinated monoalkylaluminium
cations.
Introduction
Organoaluminium complexes are currently generating con-
siderable interest due to their increasing role in polymerisation
chemistry, e.g., in cationic,1,2 anionic3–6 and ring-opening7
polymerisation, and as cocatalysts/activators in transition
metal-catalysed olefin polymerisation.8 In addition, neutral
aluminium alkyls have long been known to promote the oligo-
merisation of ethylene to α-olefins at elevated temperature and
pressure.9 More recently, cationic aluminium alkyls have been
shown to polymerise ethylene under mild conditions.10,11 These
polymerisation-active cationic aluminium alkyls are stabilised
by means of monoanionic ligands, namely the bidentate N,N
amidinate ligand and the tridentate N,N,N pyridylimineamide
ligand as reported by Jordan et al.10 and ourselves11, respec-
tively. We have subsequently described12 an extension of this
work to include a series of aluminium alkyl cations employing
tridentate O,N,N and O,N,O Schiff base ligands derived from
salicylaldimine and bearing a pendant donor arm joined at the
imine nitrogen. These monoalkylaluminium cations, which are
formed from the corresponding neutral dialkylaluminium
systems, were similarly found to be active in the polymerisation
of ethylene.
The readily accessible potentially bidentate salicylaldimine
ligand family is closely related to the tridentate family referred
to above but, by having no pendant arm, the former constitutes
a simpler N,O ligand type. In our programme directed at stabil-
ising both mono- and di-alkylaluminium systems we decided to
target these simpler chelates. We noted in an earlier communi-
cation12 that it appeared possible to employ the N,O bidentate
ligands to stabilise cationic monoalkylaluminium species pro-
vided they were used in conjunction with an independent donor
Results and discussion
All of the salicylaldimine ligands studied were prepared in good
yields (61–95%) as yellow to orange crystalline solids by
condensation of 3,5-di-tert-butyl-4-hydroxybenzaldehyde with
the appropriate aniline in refluxing ethanol in the presence
of a catalytic amount of formic acid. Satisfactory elemental
analyses were obtained for all of the ligands. Spectroscopic
data are consistent with the formulations depicted in Scheme 1.
The 1H NMR spectra of 1a–1g in C6D6 exhibit resonances in
the region δ 7.60–8.13 for the imine CH proton, with the
corresponding 13C NMR signals occurring in the range δ 161.1–
168.4. Ligands 1a–1g also display two characteristic doublets
(4J(HH) ca. 2.5 Hz) in the 1H NMR for the aromatic ring
protons of the But2C6H2(OH)CHNR ring, whilst the phenolic
protons appear as low field resonances in the region δ 13.1–
14.9. The infrared absorption band of the imine is clearly
visible between 1587 and 1655 cmϪ1, and molecular ion peaks
are observed in the EI mass spectrum for all of the compounds.
Reaction of these new ligands 1a–1g with Me3Al (one
equivalent) in toluene at ambient temperature affords, after
work-up, the corresponding highly crystalline yellow to orange/
red complexes {3,5-But -2-(O)C H CH᎐NR}AlMe , 2a–2g; the
᎐
2
6
2
2
exception is the 3,5-(CF3)2C6H2 derivative 2c which is an orange
oil (see Scheme 1). The complexes are presumed to form via
formal loss of methane, and their spectroscopic data indicate
that all are constituted similarly to the crystallographically
characterised examples (vide infra).
Crystals of 2a and 2b suitable for X-ray analysis were grown
from acetonitrile at room temperature. The structures of 2a and
† Electronic supplementary information (ESI) available: further syn-
thetic details and characterisation for ligands and for aluminium com-
pounds and cations. See http://www.rsc.org/suppdata/dt/b1/b100743m/
1472
J. Chem. Soc., Dalton Trans., 2001, 1472–1476
This journal is © The Royal Society of Chemistry 2001
DOI: 10.1039/b100743m

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Table 1 Selected bond lengths (Å) and angles (Њ) for 2a and 2b
2a
2b
2a
2b
Al–O
1.755(3)
1.950(5)
1.319(5)
1.457(5)
1.433(6)
1.773(3)
1.959(5)
1.321(4)
1.460(5)
1.442(5)
Al–N
1.972(3)
1.960(5)
1.285(5)
1.411(5)
1.972(3)
1.948(5)
1.300(5)
1.413(5)
Al–C(1)
O–C(3)
N–C(10)
C(4)–C(9)
Al–C(2)
N–C(9)
C(3)–C(4)
O–Al–C(1)
O–Al–C(2)
C(2)–Al–N
C(1)–Al–C(2)
C(9)–N–C(10)
C(10)–N–Al
C(3)–C(4)–C(9)
111.8(2)
111.8(2)
111.2(2)
114.5(3)
117.4(3)
120.7(3)
122.2(4)
114.0(2)
110.4(2)
112.2(2)
115.1(2)
117.2(3)
120.3(2)
122.0(3)
O–Al–N
93.9(2)
111.8(2)
133.5(3)
121.9(3)
120.7(4)
127.7(4)
93.6(1)
109.7(2)
132.2(2)
122.6(3)
121.3(3)
126.8(4)
C(1)–Al–N
C(3)–O–Al
C(9)–N–Al
O–C(3)–C(4)
N–C(9)–C(4)
Scheme 1 Reagents: (i) AlMe3, C7H8; (ii) B(C6F5)3, THF in C6D6 or C7H8.
two structures with that in 2b having a slightly folded, sofa
conformation (the aluminium atom lying 0.17 Å out of the
plane of the other five atoms which are co-planar to within 0.04
Å) whereas in 2a the chelate ring is essentially planar (the
maximum deviation from planarity being only 0.02 Å).
In both structures the pendant 2,6-dialkylphenyl rings are
oriented virtually orthogonally (89Њ) to the plane of the six-
membered metallocyclic ring. There is evidence in 2b that this
conformation is stabilised by a pair of weak C–H ؒ ؒ ؒ N(pπ)
interactions between the isopropyl methine hydrogen atoms
and the non-bonding p orbitals of the ring nitrogen atom (link-
ages a and b in Fig. 1).13 In neither structure are there any
notable intermolecular interactions, the packing being domin-
ated by the hydrophobic methyl and tert-butyl groups resulting
in very low packing densities (Dc = 1.047 and 1.053 g cmϪ3 in 2a
and 2b respectively).
Fig. 1 The molecular structure of 2b (that of 2a has an essentially
identical conformation) showing also the weak C–H ؒ ؒ ؒ N(pπ)
stabilising interactions; the H ؒ ؒ ؒ N distances (Å) and C–H ؒ ؒ ؒ N
angles (Њ) are a, 2.46, 109; b, 2.48, 108.
The 1H NMR spectra (in C6D6) of compounds 2a–2g exhibit
resonances in the region δ 7.05–7.83 due to the imine groups,
with corresponding 13C NMR signals between δ 169.1 and
174.8. Characteristic Al–Me signals appear in the region
2b show the complexes to have virtually identical geometries,
the principal difference being in the relative orientations of the
tert-butyl groups – Fig. 1. In both structures the aluminium
centre has a distorted tetrahedral geometry with angles ranging
between 93.9(2) and 114.5(3)Њ in 2a and 93.6(1) and 115.1(2)Њ in
2b, the most “acute” angle in each case being associated with
the bite of the chelating ligand (Table 1). The chelate ligand in
each structure binds to the aluminium in an unsymmetrical
fashion with the bond to the oxygen atom being typical of an
alkoxide [1.755(3) and 1.773(3) Å in 2a and 2b respectively],
whilst that to the imino nitrogen atom is, as expected, appre-
ciably longer at 1.972(3) Å in each complex. In both structures
1
δ Ϫ0.20 to Ϫ0.36 in the H NMR, and δ Ϫ6.4 to Ϫ9.1 in the
13C NMR. The NMR data for the structurally characterised
systems 2a and 2b indicate that the solid state forms remain
essentially unchanged in solution. The infrared absorption
band for the imine C᎐N stretches of 2a–2g occur in the region
᎐
1613–1618 cmϪ1. Satisfactory elemental analyses were obtained
for all the compounds.
Arene solutions of the dimethyl complexes 2a–2g, when
treated sequentially with one equivalent of tetrahydrofuran and
then with one equivalent of B(C6F5)3, were observed to separate
into two layers. Isolation of the lower layer and evaporation
of this to dryness yielded the cationic systems [{3,5-But2-2-
the chelate C᎐N bond retains its double bond character, being
᎐
1.285(5) Å in 2a and 1.300(5) Å in 2b. There are small differ-
ences in the geometries of the six-membered chelate rings in the
(O)C H CH᎐NR}AlMe(THF)]+, 3a–3g, with [MeB(C F ) ]Ϫ as
᎐
6
2
6
5 3
J. Chem. Soc., Dalton Trans., 2001, 1472–1476
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ca. δ 10.4) and the C6F5 19F resonances (at δ Ϫ135.5, Ϫ167.5,
Ϫ170.0) in the anion are virtually identical throughout the
series is further evidence that this charge separated arrange-
ment occurs in all the products 3a–3g.
When excess THF is added to CD2Cl2 solutions of the
cations 3a–3g, the original two resonances of the coordinated
THF are replaced by two more intense resonances shifted
towards those of free THF (i.e. δ 3.68, 1.82 in CD2Cl2). With 3c,
for example, a 1.5 molar excess of THF led to a shift in the
resonance positions from δ 4.21, 2.15 to δ 3.90, 1.95. The fact
that only one set of resonances is seen in the presence of excess
THF implies that a rapid intermolecular exchange process
occurs between the bound and the free ligand. This behaviour
demonstrates the highly labile nature of the coordinated THF
which we anticipate will be important in chemical processes
involving these cationic species.
Fig. 2 The 1H NMR spectrum of 3e in CD2Cl2.
Concluding remarks
This work provides an extension of our earlier study12 of
aluminium alkyl systems employing salicylaldiminate ligands
bearing pendant donor arms. Here we have shown that it is
possible to access cleanly and in high yield a family of cationic
aluminium alkyls bearing an independent donor ligand (THF),
as opposed to one that is pendant to the salicylaldiminate
group. The synthetic pathway is crucial to the successful
isolation of these bidentate cationic alkylaluminium species;
the reactions are best carried out by addition of one mole
equivalent of THF to the neutral precursor in an aromatic
solvent prior to the addition of B(C6F5)3. In the absence of the
donor ligand, abstraction of C6F5 by the electron-deficient
aluminium centre occurs. The ability to use an independent
rather than a pendant donor group to stabilise the (L,X)AlMe+
system broadens appreciably the scope and potential of the
original study as now, clearly, a much wider array of other
potential donors may be employed. We are currently exploring
the role of these cations and their derivatives in facilitating
various polymerisation processes; the results of these studies
will be presented elsewhere.
the counter ion (see Scheme 1). It was also found possible
to generate the cations by adding the THF donor after the
addition of B(C6F5)3, but the cleanest products were obtained
when the donor was added first. However, in the absence of the
THF donor, no immediate reaction was observed, e.g. when 2b
and B(C6F5)3 were mixed in C6D6 solution at ambient temper-
ature. In CD2Cl2, by contrast, all of 2a–2g reacted rapidly with
B(C6F5)3 to form complex mixtures. For example, the 1H NMR
spectrum of a solution of 2g and B(C6F5)3 in CD2Cl2 (after
standing for 24 hours at ambient temperature) revealed inter
alia a high field triplet at δ Ϫ0.31 [J(HF) 1.5 Hz] characteristic
of an Al–Me resonance coupled to the α-fluorines of a
coordinated C6F5 group. This suggests the presence of the
species {3,5-But -2-(O)C H CH᎐NBut}AlMe(C F ) which is
᎐
2
6
2
6
5
formed, presumably, by abstraction of a C6F5 group from
[B(C6F5)3Me]Ϫ by the first-formed coordinatively unsaturated
and therefore highly reactive cationic intermediate (i.e. not
having the THF donor to stabilise it). Further evidence for the
abstraction of a C6F5 group is the appearance of a quintet in
the same 1H NMR spectrum at δ 1.33 [J(HF) 1.8 Hz] which is
assigned to the methyl of the resulting MeB(C6F5)2, this methyl
being coupled to the four equivalent α-fluorines of the C6F5
groups. Our observations parallel those of Smith and co-
workers14 for the similar reaction of the β-diketiminato com-
plex [(2,6-Pri2C6H3)NC(Me)CHC(Me)N(2,6-Pri2C6H3)]AlMe2
with B(C6F5)3, in the absence of a donor, which led to the
isolation and characterisation of the analogous [ligand]-
AlMe(C6F5) system.
Experimental
General
All manipulations were carried out under an atmosphere of dry
nitrogen either using standard Schlenk and cannula techniques,
or in a conventional nitrogen-filled glove-box. Solvents were
refluxed over an appropriate drying agent, and distilled and
degassed prior to use. Elemental analyses were performed by
the microanalytical services of the Department of Chemistry at
Imperial College or by Medac Ltd. 1H, 13C and 19F NMR
spectra were recorded in C6D6 for the ligands and neutral com-
pounds (unless stated otherwise), and in CD2Cl2 for the cationic
complexes, on Bruker DRX400 or AC250 machines at ambient
temperature; chemical shifts were referenced to the residual
protio impurity of the deuterated solvent; 13C chemical shift
assignments were based on DEPT experiments. Infrared
spectra (Nujol mulls, KBr/CsI windows) were run on Perkin-
Elmer 577 and 457 grating spectrophotometers and mass
spectra were measured either on a VG Autospec or a VG
Platform II spectrometer. Selected synthetic details are given
below, the remainder are supplied as ESI.†
The THF coordinated aluminium methyl cations, 3a–3g,
1
were formed in high purity, as demonstrated by their H, 13C
(and in some cases 19F) NMR spectra recorded in CD2Cl2.
1
Crystalline materials were however not obtained. A typical H
NMR spectrum is shown in Fig. 2 (i.e. as obtained for 3e). The
1H NMR spectra of this series of cations have the imine reson-
ance appearing in the range δ 8.74 to 8.41 and the resonance of
the remaining aluminium methyl in the range δ Ϫ0.16 to Ϫ0.43;
the corresponding 13C NMR signals lie between δ 174.8 and
179.9 and between δ Ϫ10.9 and Ϫ14.5 respectively. A com-
1
parison of the H NMR spectra of e.g. 2a and 3a (both run in
CD2Cl2) shows that the resonances for the cation are shifted
downfield relative to the corresponding resonances for the
neutral AlMe2 precursor compound, with the largest shift
being that for the Al–Me resonance (from δ Ϫ0.83 to Ϫ0.43).
This effect is ascribed principally to the presence of the positive
charge in 3a. The methyl resonance of [B(C6F5)3Me]Ϫ in 3a–3g,
which is broadened by the boron quadrupole, is seen in the
range δ 0.39 to 0.44, as is anticipated for the free ion.15 This
observation supports our formulation of the complexes as sep-
arated ions as opposed to the ion pairs (i.e. with Al ؒ ؒ ؒ Me–B
association) observed by Coles and Jordan.16 Moreover, the
fact that the positions of the broad BMe 13C resonance (at
Preparation of ligands
3,5-But2-2-(OH)C6H2CHN-2,6-Me2C6H3 (1a). 2,6-Dimethyl-
aniline (5.72 cm3, 46.4 mmol) was added via syringe to a solu-
tion of 3,5-di-tert-butyl-4-hydroxybenzaldehyde (10.88 g, 46.4
mmol) in EtOH (120 cm3). Formic acid (5 drops) was added,
and the solution refluxed for 20 h. The resulting solution was
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J. Chem. Soc., Dalton Trans., 2001, 1472–1476

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dried over MgSO4 and filtered. Slow concentration of the
EtOH solution yielded large yellow plates of 1a. Yield 14.47 g,
92%. Found C 81.6; H 9.0; N 4.2%; C23H31NO requires C 81.9;
H 9.3; N 4.2%. IR/cmϪ1: 3375w, br (O–H stretch), 1774m,
dropwise to a solution of 1b (1.00 g, 2.54 mmol) in toluene
(30 cm3). The reaction was stirred at room temperature for 12 h
and then the volatiles were removed in vacuo. The product was
extracted into hot MeCN (10 cm3). Filtration and cooling to
room temperature afforded 2b as bright yellow crystals. Yield
0.99 g, 87%. Found C 77.6; H 9.6; N 3.1%. C29H44AlNO
requires C 77.5; H 9.9; N 3.1%. IR/cmϪ1: 1614s, 1598s, 1587s,
1557m, 1541s, 1407m, 1364s, 1321s, 1276m, 1256s, 1235m,
1202m, 1190m, 1170s, 1134m, 1109m,1097m, 1057m, 1043m,
1029m, 935m, 921m, 889w, 876m, 854m, 800m, 785m, 764s,
723m, 700m, 678s, 659m, 641m, 608m, 544w, 525w.1H NMR:
δ 7.85 (s, 1H, p-NAr–H), 7.73 [d, 1H, 4J(HH) 2.5 Hz, OAr–H],
1748s, 1705s, 1655m (C᎐N stretch), 1625s, 1588s, 1312m,
᎐
1287m, 1274s, 1252s, 1216s, 1193s, 1171s, 1133m, 1095m,
1026m, 979m, 919w, 887w, 863s, 825s, 803s, 768s, 734m, 646m,
602m. 1H NMR: δ 13.84 (br s, 1H, –OH), 7.66 (s, 1H, CH᎐N),
᎐
7.65 [d, 1H, 4J(HH) 2.5 Hz, OAr–H], 6.99 [d, 1H, 4J(HH)
2.5 Hz, OAr–H], 6.94–6.91 (m, 3H, NAr–H), 1.97 (s, 6H,
Ar–CH3), 1.65 [s, 9H, C(CH3)3], 1.33 [s, 9H, C(CH3)3]. 13C
NMR: δ 168.4 (CH᎐N), 158.1, 148.9, 140.9, 137.6, 128.6, 128.4,
᎐
127.6, 127.2, 125.0, 118.8 (all Ar–C), 35.5 [C(CH3)3], 34.3
[C(CH3)3], 31.7 [C(CH3)3], 29.8 [C(CH3)3], 18.4 (NAr–CH3).
MS (EI, m/z) 337 [M]+, 322 [M Ϫ CH3]+.
7.15–7.0 (m, 2H, NAr–H), 7.05 (s, 1H, CH᎐N), 6.91 [d, 1H,
᎐
4J(HH) 2.6 Hz, OAr–H], 3.16 [sept., 2H, 3J(HH) 6.8 Hz,
CH(CH3)2], 1.59 [s, 9H, C(CH3)3], 1.25 [s, 9H, C(CH3)3], 1.19 [d,
3
3
6H, J(HH) 6.8 Hz, CH(CH3)2], 0.81 [d, 6H, J(HH) 6.8 Hz,
CH(CH3)2], Ϫ0.27 (s, 6H, Al–CH3). 13C NMR: δ 174.5
3,5-But2-2-(OH)C6H2CHN-2,6-Pri2C6H3 (1b). 2,6-Diiso-
propylaniline (4.19 cm3, 22.2 mmol) was added via syringe to a
solution of 3,5-di-tert-butyl-4-hydroxybenzaldehyde (5.21 g,
22.2 mmol) in EtOH (100 cm3). Formic acid (5 drops) was
added, and the solution refluxed for 20 h. The solution was
dried over MgSO4, filtered, and the volatiles removed under
reduced pressure. Extraction into pentane (5 cm3) followed by
cooling to Ϫ30 ЊC afforded yellow crystals of 1b. Yield 5.30 g,
61%. Found C 82.5; H 10.0; N 3.4%; C27H39NO requires C 82.4;
H 10.0; N 3.4%. IR/cmϪ1: 3397w, br (O–H stretch), 1776m,
(CH᎐N), 163.2, 142.83, 142.76, 141.6, 139.8, 133.3, 129.0,
᎐
124.5, 118.8 (all Ar–C, one peak obscured), 35.7 [C(CH3)3], 34.1
[C(CH3)3], 31.3 [C(CH3)3], 29.6 [C(CH3)3], 28.4 [CH(CH3)2],
25.8 [CH(CH3)2], 22.8 [CH(CH3)2], Ϫ9.0 (Al–CH3).MS (EI,
m/z) 434 [M Ϫ CH3]+.
Preparation of cations
[{3,5-But -2-(O)C H CH᎐N-2,6-Me C H }AlMe(THF)]؉
᎐
2
6
2
2
6
3
[B(C6F5)3Me]Ϫ (3a). The compound 2a (23.6 mg, 0.06 mmol)
was dissolved in C6D6 (0.5 ml). THF (4.86 µl, 0.06 mmol) was
added to the solution via syringe and then a solution of
B(C6F5)3 (30.72 mg, 0.06 mmol) in C6D6 (0.8 ml) was added
dropwise; this caused the formation of two layers. The solution
of the aluminium compound was agitated during the addition.
Residual B(C6F5)3 was washed into the reaction solution using
C6D6 (0.6 ml). The resulting mixture was shaken briefly and was
then left to stand for 20 minutes. After this period the upper
layer was carefully separated and discarded. The lower layer
1749m, 1705s, 1654m, 1624s (C᎐N stretch), 1586s, 1322m,
᎐
1274s, 1251s, 1231m, 1203s, 1169s, 1133m, 1109m, 1058m,
1043m, 1026m, 980m, 933m, 881m, 862s, 823m, 796s, 773m,
1
758s, 731m, 720m, 644w, 603w. H NMR: δ 13.94 (br s, 1H,
–OH), 7.98 (s, 1H, CH᎐N), 7.64 [d, 1H, 4J(HH) 2.5 Hz, OAr–
᎐
4
H], 7.14–7.10 (m, 3H, NAr–H), 7.09 [d, 1H, J(HH) 2.5 Hz,
OAr–H], 3.02 [sept., 2H, J(HH) 6.9 Hz, CH(CH3)2], 1.64 [s,
3
3
9H, C(CH3)3], 1.30 [s, 9H, C(CH3)3], 1.06 [d, 12H, J(HH) 6.9
Hz, CH(CH3)2]. 13C NMR: δ 168.4 (CH᎐N), 159.2, 147.1,
᎐
141.0, 139.1, 137.8, 127.2, 127.1, 125.7, 123.5, 118.6 (all Ar–C),
35.5 [C(CH3)3], 34.3 [C(CH3)3], 31.6 [C(CH3)3], 29.8 [C(CH3)3],
28.5 [CH(CH3)2], 23.5 [CH(CH3)2]. MS (EI, m/z) 393 [M]+, 378
[M Ϫ CH3]+
1
was evaporated to dryness leaving a yellow foam (37 mg). H
NMR: δ 8.44 (s, 1H, CH᎐N), 7.91 [d, 1H, 4J(HH) 2.5 Hz,
᎐
C6H2], 7.30 [d, 1H, 4J(HH) 2.5 Hz, C6H2], 7.30 (m, 3H,
C6H3Me2), 4.25 (m, 4H, OCH2CH2), 2.21 (m, 4H, OCH2CH2),
2.19 [s, 6H, C6H3(CH3)2], 1.49 (s, 9H, C4H9), 1.32 (s, 9H, C4H9),
0.45 (br s, 3H, BCH3), Ϫ0.43 (s, 3H, AlCH3). 13C NMR:
Preparation of complexes
{3,5-But -2-(O)C H CH᎐N-2,6-Me C H }AlMe (2a). Tri-
δ (cation part only) 179.86 (CH᎐N), 160.53, 144.08, 141.25,
᎐
᎐
2
6
2
2
6
3
2
118.88 [four quaternary resonances of C6H2But2(O)C ring],
141.98 (one quaternary of C6H3Me2 ring, the other is
obscured), 137.30, 131.38 [2 CH resonances of C6H2But2(O)C
ring], 130.26, 129.45 (two CH resonances of C6H3Me2N ring),
75.76 (OCH2), 35.69 (CMe3), 34.65 (CMe3), 31.03 [C(CH3)3],
29.57 [C(CH3)3], 25.70 (OCH2CH2), 18.46 [C6H3(CH3)2],
Ϫ14.50 (br, AlCH3), also CH3B of anion seen as broad reson-
ance at δ 10.3. 19F NMR: δ Ϫ135.5 (6F, BC6F5), Ϫ167.6 (3F,
BC6F5), Ϫ170.2 (6F, BC6F5).
methylaluminium (2.0 M, 1.60 cm3, 3.2 mmol) was added
dropwise to a solution of 1a (1.05 g, 3.11 mmol) in toluene (30
cm3) at Ϫ78 ЊC. The reaction was allowed to warm to room
temperature and then stirred for 12 h. Volatiles were removed in
vacuo, and the product was extracted into hot MeCN (20 cm3).
Filtration followed by cooling to room temperature afforded
large golden blocks of 2a. Yield 0.87 g, 71%. Found C 75.9; H
9.1; N 3.7%. C25H36AlNO requires C, 76.3; H 9.2; N 3.6%. IR/
cmϪ1: 1613s, 1598s, 1588s, 1555s, 1540s, 1408m, 1359m, 1336m,
1323m, 1279m, 1257s, 1237m, 1211m, 1199m, 1173s, 1137m,
1097m, 1025w, 996w, 966w, 927w, 918w, 878m, 857s, 813w,
[{3,5-But -2-(O)C H CH᎐N-2,6-Pri C H }AlMe(THF)]؉
᎐
2
6
2
2
6
3
1
4
[B(C6F5)3Me]Ϫ (3b). This complex was prepared similarly to 3a
783m, 768s, 760m. H NMR: δ 7.72 [d, 1H, J(HH) 2.6 Hz,
OAr–H], 7.17 (s, 1H, CH᎐N), 6.92–6.80 (m, 3H, NAr–H), 6.71
᎐
but using 2b (27.0 mg, 0.06 mmol ) and toluene was used in
[d, 1H, 4J(HH) 2.6 Hz, OAr–H], 1.97 (s, 6H, Ar–CH3), 1.60 [s,
9H, C(CH3)3], 1.28 [s, 9H, C(CH3)3], Ϫ0.32 (s, 6H, Al–CH3). 1H
1
place of benzene-d . H NMR: δ 8.41 (s, 1H, CH᎐N), 7.91 [d,
᎐
6
1H, 4J(HH) 2.5 Hz, C6H2], 7.49 [dd, 1H, 3J(HH) 8.7 Hz, 3J(HH)
NMR (CD Cl ): δ 8.07 (s, 1H, CH᎐N), 7.61 [d, 1H, 4J(HH) 2.6
3
᎐
2
2
6.7 Hz, C6H3Pri2], 7.36 [d, 1H, J(HH) 8.7 Hz, C6H3Pri2], 7.36
4
[d, 1H, J(HH) 6.7 Hz, C6H3Pri2], 7.26 [d, 1H, J(HH) 2.5 Hz,
3
4
Hz, OAr–H], 7.15 (m, 3H, NAr–H), 7.05 [d, 1H, J(HH) 2.6
Hz, OAr–H], 2.22 (s, 6H, Ar–CH3), 1.44 [s, 9H, C(CH3)3], 1.30
[s, 9H, C(CH3)3], Ϫ0.83 (s, 6H, Al–CH3). 13C NMR: δ 174.8
3
C6H2], 4.25 (m, 4H, OCH2), 2.68 (sept., 2H, J(HH) 6.8 Hz,
CHMe2), 2.21 (m, 4H, OCH2CH2), 1.49 (s, 9H, C4H9), 1.32 (s,
9H, C4H9), 1.32 [d, 6H, 3J(HH) 6.8 Hz, CH(CH3)2], 1.14 [d, 6H,
3J(HH) 6.8 Hz, CH(CH3)2], 0.44 (br s, 3H, BCH3), Ϫ0.37 (s, 3H,
(CH᎐N), 163.0, 145.2, 141.3, 139.3, 133.0, 131.9, 129.4, 129.0,
᎐
127.3, 119.1 (all Ar–C), 35.6 [C(CH3)3], 34.2 [C(CH3)3], 31.5
[C(CH3)3], 29.6 [C(CH3)3], 18.5 (NAr–CH3), Ϫ8.5 (Al–CH3).
AlCH3). 13C NMR: δ (cation part only) 179.02 (CH᎐N),
᎐
+
MS (EI, m/z) 379 [M Ϫ CH3]; (CI, NH4 ) 395 [M Ϫ CH3 +
160.61, 144.38, 141.32, 118.51 [four quaternary resonances
of C6H2But2(O)C ring], 137.60, 131.05 [2 CH resonances of
C6H2But2(O)C ring], 130.42, 125.57 (2 CH resonances of
C6H3Pri2N ring), 129.32, 128.52 (two quaternary resonances
of C6H3Pri2N ring), 75.82 (OCH2), 35.74 (CMe3), 34.71
NH4]+, 378 [M Ϫ CH3 + H]+.
{3,5-But -2-(O)C H CH᎐N-2,6-Pri C H }AlMe (2b). Tri-
᎐
2
6
2
2
6
3
2
methylaluminium (2.0 M, 1.30 cm3, 2.6 mmol) was added
J. Chem. Soc., Dalton Trans., 2001, 1472–1476
1475

View Article Online
2 M. Bochmann and D. M. Dawson, Angew. Chem., Int. Ed. Engl.,
1996, 35, 2226.
3 M. Kuroki, T. Aida and S. Inoue, J. Am. Chem. Soc., 1987, 109,
4737; M. Kuroki, T. Watanabe, T. Aida and S. Inoue, J. Am. Chem.
Soc., 1991, 113, 5903.
(CMe3), 31.05 [C(CH3)3], 29.62 [C(CH3)3], 29.33 (CHMe2),
26.00 [(CH(CH3)2], 25.69 (OCH2CH2), 22.76 [(CH(CH3)2],
Ϫ14.52 (br, AlCH3), also CH3B of anion seen as broad
resonance at δ 10.3.
4 D. Mardare, K. Matyjaszewski and S. Coca, Macromol. Rapid
Commun., 1994, 15, 37.
5 M. Dimonie, D. Mardare, S. Coca, V. Dragutan and I. Ghiviriga,
Macromol. Rapid Commun., 1992, 13, 283.
6 F. Coslédan, P. B. Hitchcock and M. F. Lappert, Chem. Commun.,
1999, 705.
7 See e.g. S. Inoue, J. Polym. Sci., Part A: Polym. Chem., 1998, 21,
3114 and refs therein; J. A. Jegier and D. A. Atwood, Inorg. Chem.,
1997, 36, 2034.
8 For recent reviews see: W. Kaminsky, J. Chem. Soc., Dalton Trans.,
1998, 1413; R. M. Waymouth, Chem. Rev., 1998, 98, 2587; G. J. P.
Britovsek, V. C. Gibson and D. F. Wass, Angew. Chem., Int. Ed.,
1999, 38, 428.
9 (a) K. Ziegler and H. G. Gellert, Justus Liebigs Ann. Chem., 1950,
567, 195; (b) W. A. Skinner, E. Bishop, P. Cambour, S. Fuqua and
P. Lim, Ind. Eng. Chem., 1960, 52, 695; (c) J. Skupinska, Chem. Rev.,
1991, 91, 613; A. M. Al-Jarallah, J. A. Anabtawi, M. A. B. Siddiqui
and A. W. Al-Sa’doun, Catal. Today, 1992, 14, 42.
10 (a) M. P. Coles and R. F. Jordan, J. Am. Chem. Soc., 1997, 119,
8125; (b) E. Ihara, V. G. Young, Jr and R. F. Jordan, J. Am. Chem.
Soc., 1998, 120, 8277; (c) S. Dagorne, I. A. Guzei, M. P. Coles and
R. F. Jordan, J. Am. Chem. Soc., 2000, 122, 274.
11 M. Bruce, V. C. Gibson, C. Redshaw, G. A. Solan, A. J. P. White and
D. J. Williams, Chem. Commun., 1998, 2523.
12 P. A. Cameron, V. C. Gibson, C. Redshaw, J. A. Segal, M. D.
Bruce, A. J. P. White and D. J. Williams, Chem. Commun., 1999,
1883.
13 This has been observed previously, see: P. N. Jagg, P. F. Kelly,
H. S. Rzepa, D. J. Williams, J. D. Woollins and W. Wylie, J. Chem.
Soc., Chem. Commun., 1991, 942; V. C. Gibson, C. Newton,
C. Redshaw, G. A. Solan, A. J. P. White and D. J. Williams,
Eur. J. Inorg. Chem., in press.
Crystallography
Crystal data for 2a: C25H36NOAl, M = 393.5, orthorhombic,
Pbca (no. 61), a = 13.865(2), b = 15.721(3), c = 22.912(4) Å,
V = 4994(1) Å3, Z = 8, Dc = 1.047 g cmϪ3, µ(Mo-Kα) = 0.95
cmϪ1, T = 293 K, orange prisms; 4355 independent measured
reflections, F2 refinement, R1 = 0.066, wR2 = 0.141, 2118
independent observed reflections [|Fo| > 4σ(|Fo|)], 2θ ≤ 50Њ], 254
parameters.
Crystal data for 2b: C29H44NOAl, M = 449.6, orthorhombic,
P212121 (no. 19), a = 9.316(2), b = 10.277(1), c = 29.617(1) Å,
V = 2835.5(6) Å3, Z = 4, Dc = 1.053 g cmϪ3, µ(Cu-Kα) = 7.52
cmϪ1, T = 203 K, yellow plates; 2616 independent measured
reflections, F2 refinement, R1 = 0.052, wR2 = 0.129, 2257
independent observed reflections [|Fo| > 4σ(|Fo|), 2θ ≤ 126Њ], 290
parameters. The absolute structure was determined by a com-
bination of R-factor tests [R1+ = 0.0524, R1Ϫ = 0.0531] and by
use of the Flack parameter [x+ = +0.22(8), xϪ = +0.78(8)].
CCDC reference numbers 157073 and 157074. See http://
www.rsc.org/suppdata/dt/b1/b100743m/ for crystallographic
data in CIF or other electronic format.
Acknowledgements
ICI, BP-Amoco, The Leverhulme Trust (Special Research
Fellowship to CR) and the Royal Society (Industry Fellowship
to JAS) are thanked for financial support.
14 B. Qian, D. L. Ward and M. R. Smith, III, Organometallics, 1998,
17, 3070.
15 X. Yang, C. L. Stern and T. J. Marks, J. Am. Chem. Soc., 1994, 116,
10015.
References
1 Cationic Polymerisations: Mechanisms, Synthesis and Applications,
ed. K. Matyjaszewski, Marcel Dekker, New York, 1996.
16 M. P. Coles and R. F. Jordan, J. Am. Chem. Soc., 1997, 119,
8125.
1476
J. Chem. Soc., Dalton Trans., 2001, 1472–1476