Synthesis characterisation of neutral cationic alkyl aluminium complexes bearing N,O-Schiff base chelates with pendant donor arms

Article abstract of DOI:10.1039/b106131n

The Schiff base ligands [3,5-Bu₂^t-2-(OH)C₆H₂CH=NL] [L = CH₂CH₂NMe₂ (1a), 2-(PhO)C₆H₄ (1b), 2-CH₂C₅H₃N (1c), 8-C₉H₆N (quinoline) (1d) and 2-(PPh₂)C₆H₄ (1e)] are accessed in good yields (>85%) via standard imine condensation reactions. Reaction of 1a-e with Me₃Al at room temperature affords the corresponding complexes [(3,5-Bu₂^t-2-(O)C₆H₂CH=NL)AlMe ₂] (2a-e); in the case of L = 8-quinoline, the same reaction conducted in refluxing toluene affords binuclear {[3,5-Bu₂^t-2-(O)C₆H₂CHMeN-8-C ₉H₆N]AlMe}₂ (3) by methyl migration from metal to ligand. Further reaction of the dimethyl compounds with B(C₆F₅)₃ in CD₂Cl₂ or C₆D₆ affords the cationic systems [(3,5-Bu₂^t-2-(O)C₆H₂CH=NL)AlMe] ⁺ (4a-e). The crystal structures of 2a, 2c, 2e and 3 have been determined. In 2a and 2c the respective ligands bind to the metal centre via all three heteroatoms, the aluminium having a trigonal bipyramidal geometry, whereas in 2e coordination is via nitrogen and oxygen only, and the aluminium is tetrahedral. Complex 3 has a dimeric structure with the ligand adopting both tridentate and binucleating roles; the aluminium centres are trigonal bipyramidal.

Full text of DOI:10.1039/b106131n

View Article Online / Journal Homepage / Table of Contents for this issue
Synthesis and characterisation of neutral and cationic alkyl
aluminium complexes bearing N,O-Schiff base chelates with
pendant donor arms
Paul A. Cameron, Vernon C. Gibson,* Carl Redshaw, John A. Segal, Andrew J. P. White and
David J. Williams
Department of Chemistry, Imperial College, South Kensington, London, UK SW7 2AY
Received 10th July 2001, Accepted 14th November 2001
First published as an Advance Article on the web 8th January 2002
The Schiff base ligands [3,5-But -2-(OH)C H CH᎐NL] [L = CH CH NMe (1a), 2-(PhO)C H (1b), 2-CH C H N
᎐
2
6
2
2
2
2
6
4
2
5
3
(1c), 8-C9H6N (quinoline) (1d) and 2-(PPh2)C6H4 (1e)] are accessed in good yields (>85%) via standard imine
condensation reactions. Reaction of 1a–e with Me3Al at room temperature affords the corresponding complexes
[(3,5-But -2-(O)C H CH᎐NL)AlMe ] (2a–e); in the case of L = 8-quinoline, the same reaction conducted in refluxing
᎐
2
6
2
2
toluene affords binuclear {[3,5-But2-2-(O)C6H2CHMeN-8-C9H6N]AlMe}2 (3) by methyl migration from metal to
ligand. Further reaction of the dimethyl compounds with B(C6F5)3 in CD2Cl2 or C6D6 affords the cationic systems
[(3,5-But -2-(O)C H CH᎐NL)AlMe]ϩ (4a–e). The crystal structures of 2a, 2c, 2e and 3 have been determined. In 2a
᎐
2
6
2
and 2c the respective ligands bind to the metal centre via all three heteroatoms, the aluminium having a trigonal
bipyramidal geometry, whereas in 2e coordination is via nitrogen and oxygen only, and the aluminium is tetrahedral.
Complex 3 has a dimeric structure with the ligand adopting both tridentate and binucleating roles; the aluminium
centres are trigonal bipyramidal.
the weakly bonding or non-bonding donor arm in the neutral
Introduction
precursor becomes a normal ligand occupying the fourth
In recent years there has been considerable and growing interest
coordination position in the cation, thereby stabilising the
in the coordination chemistry of bulky bi- and tridentate
electropositive aluminium centre. These cations were found to
ligands, in part because these ligands can be used to provide
be active in the catalysis of ethylene polymerisation and this
protective shields for catalytically active metal centres. This
work has been the subject of a preliminary communication.5
protection strategy is one which we and others have recently
Here we report the synthesis and characterisation of the
employed in late transition metal systems.1 In other studies, we
series of new potentially tridentate Schiff-base ligands [3,5-
have demonstrated2 the use of tridentate N,N,N-bis(imino)-
But -2-(OH)C H CH᎐NL] [L = CH CH NMe (1a), 2-(PhO)-
᎐
2
6
2
2
2
2
pyridines, bearing bulky substituents, in the formation of new
[ligand]aluminium dialkyl complexes, from which cationic
monoalkyl aluminium species can be readily generated by reac-
tion with B(C6F5)3. These cationic complexes were shown to be
active ethylene polymerisation catalysts.2 Coles and Jordan
reported3 a similar use of bidentate ligands, i.e. bulky N,N-
dialkylamidinates, in the formation of aluminium dialkyls
which could also be converted to polymerisation-active cationic
aluminium alkyls. In seeking to extend these studies to N,O
chelates, we developed the synthesis of novel Schiff base
dialkylaluminium compounds derived from salicylaldimines
bearing bulky groups.4 However, our initial findings showed4
that these bidentate N,O-salicylaldiminato complexes could
not be converted to stable alkylaluminium cations in the
absence of another donor ligand. We reasoned that the targeted
monoalkylaluminium cation, presumed to be formed as an
intermediate, would be a highly reactive and coordinatively
unsaturated 3-coordinate system which would be likely to
abstract an anion either from the boron counter ion or from
the solvent. It was thus anticipated that the provision of one
additional donor ligand would lead to a much more stable
4-coordinate methylaluminium cation, and to this purpose
we synthesised a series of potentially tridentate salicylaldimine
ligands each bearing a pendant O, N, or P donor arm attached
to the imine nitrogen. These ligands were then employed in the
synthesis of [N,O-salicylaldiminato]aluminium dialkyl com-
plexes which have, accordingly, the additional weakly bonding
N- or O-donor, or non-bonding P-donor, pendant arms. As
expected, reactions of these compounds with B(C6F5)3 lead to
the formation of stable alkylaluminium cations. In each case,
C6H4 (1b), 2-CH2C5H3N (1c), 8-C9H6N (quinoline) (1d) and
2-(PPh2)C6H4 (1e)], the corresponding dimethylaluminium
complexes [(3,5-But -2-(O)C H CH᎐NL)AlMe ] (2a–e), and
᎐
2
6
2
2
the cations [(3,5-But -2-(O)C H CH᎐NL)AlMe]ϩ (4a–e). A
᎐
2
6
2
dimeric complex 3, resulting from methyl migration from the
metal to the ligand when L = 8-quinoline, is also described.
Results and discussion
Ligands of the form 3,5-But -2-(OH)C H CH᎐NL
᎐
2
6
2
The ligands 1a–e (Fig. 1) were prepared via the condensation
Fig. 1 Ligands 1a–e.
reaction between 3,5-di-tert-butylsalicylaldehyde and the rele-
vant amine, and obtained as yellow to orange solids in good
1
yield (>85% isolated yield). The H NMR spectra of these
ligands exhibit resonances in the region δ 7.84–8.63 for the CH
DOI: 10.1039/b106131n
J. Chem. Soc., Dalton Trans., 2002, 415–422
This journal is © The Royal Society of Chemistry 2002
415

View Article Online
Scheme 1 Formation of aluminium complexes 2a–e and corresponding cations 4a–e. Reagents: i. AlMe3, toluene; ii. B(C6F5)3, C6D6 or CD2Cl2.
imine protons, with the corresponding 13C NMR resonances
occurring in the range δ 164.9–168.4. The phenolic resonances
appear at characteristically low field (δ 13–15). The infrared
absorption bands of the imine C᎐N stretch occur in the region
᎐
1615–1634 cmϪ1. In all cases the parent ion is observed by elec-
tron ionisation mass spectrometry, and all the compounds gave
satisfactory microanalyses.
Complexes of the form (3,5-But -2-(O)C H CH᎐NL)AlMe
᎐
2
6
2
2
Treatment of 1a–e with trimethylaluminium in toluene at room
temperature caused the evolution of methane and afforded (see
Scheme 1) the corresponding dimethyl complexes [3,5-But2-2-
(O)C H CH᎐NCH CH NMe ]AlMe (2a–e). Compounds 2a,
᎐
6
2
2
2
2
2
2c and 2e were obtained in good yields as yellow or pale orange
crystalline solids from hot saturated MeCN solutions on cool-
ing. Complexes 2b and 2d, however, were obtained as orange
oily solids from MeCN at Ϫ30 ЊC. Drying of the oils in vacuo
Fig. 2 1H NMR spectrum (250 MHz) of 2c in C6D6.
stability of these cations which have also been formed chem-
ically (vide infra). The X-ray structural data which follow show
that in compounds 2a and 2c the pendant arm donor groups
behave as weakly bound fifth ligands, and we infer that this
weak bonding will also pertain to the O and N donor arms in
compounds 2b and 2d. However, the pendant PPh2 group in 2e
is found to be non-bonding in the solid state.
1
yielded 2b and 2d as glassy solids (>95% pure by H NMR
spectroscopy). Satisfactory microanalyses were obtained on
all the compounds except 2d (see Experimental section). In
general, the 1H NMR spectra of compounds 2a–e exhibit
resonances in the region δ 7.40–8.11 for the imine CH protons,
with corresponding signals in the 13C NMR spectrum in the
range δ 169.1–172.8. The resonances attributable to the
aluminium-bound methyl groups occur at δ Ϫ0.05 to Ϫ0.29,
with corresponding 13C NMR resonances at δ Ϫ4.0 to Ϫ9.0. A
representative 1H NMR spectrum (compound 2c, C6D6, 298 K)
The molecular structure of 2a is shown in Fig. 3, and selected
4
is illustrated in Fig. 2. Two doublets (δ 7.70 and 6.83, J (HH)
ca. 2.5 Hz) are present for the salicylaldehyde derived aromatic
signals. The imine CH᎐N group is seen as a singlet at δ 7.42, and
᎐
there are several multiplets between δ 8.3 and δ 6.2, which are
due to the pyridyl protons. The backbone NCH2 group gives
rise to a singlet at δ 3.86. The tert-butyl groups afford two
singlets at δ 1.76 and 1.37 and the methyls attached to
aluminium occur at high field (δ Ϫ0.19). The characteristic
infrared absorption band for the imine C᎐N stretch in 2a–e
᎐
occurs in the region 1614–1623 cmϪ1. In all cases the envelope
corresponding to m/z = [M Ϫ CH3]ϩ is observed by electron
ionisation mass spectrometry; for 2d the parent ion, and
for 2e the parent ϩ Hϩ is also observed. In many cases
the [M Ϫ CH3]ϩ lines are very intense, e.g. for 2e they are
the strongest in the mass spectrum, indicating the relative
Fig.
3
The molecular structure of 2a, showing the trigonal
bipyramidal geometry at aluminium and the very long Al–N(amino)
linkage.
416
J. Chem. Soc., Dalton Trans., 2002, 415–422

View Article Online
Table 1 Selected bond lengths (Å) and angles (Њ) for 2a
Table 3 Selected bond lengths (Å) and angles (Њ) for 2e
Al–N(1)
Al–O(12)
Al–C(14)
2.413(5)
1.854(4)
1.976(5)
Al–N(4)
Al–C(13)
N(4)–C(5)
1.998(4)
1.978(6)
1.294(6)
Al–N
Al–C(1)
N–C(9)
1.973(4)
1.949(6)
1.300(5)
Al–O
Al–C(2)
1.754(3)
1.942(6)
O(12)–Al–C(14)
C(14)–Al–C(13)
C(14)–Al–N(4)
O(12)–Al–N(1)
C(13)–Al–N(1)
96.6(2)
123.7(3)
116.0(2)
163.0(2)
89.5(2)
O(12)–Al–C(13)
O(12)–Al–N(4)
C(13)–Al–N(4)
C(14)–Al–N(1)
N(4)–Al–N(1)
98.3(2)
88.2(2)
118.4(2)
91.4(2)
74.9(2)
O–Al–C(2)
C(2)–Al–C(1)
C(2)–Al–N
114.5(3)
116.9(3)
106.5(3)
O–Al–C(1)
O–Al–N
C(1)–Al–N
108.9(3)
94.57(14)
113.4(2)
the six-membered chelate ring the aluminium lies 0.58 Å out of
the plane of other five atoms which are co-planar to within 0.05
Å. The only intermolecular interactions of note are a pair of
short C–H ؒ ؒ ؒ π contacts between one of the C(7) methylene
hydrogen atoms in one molecule and the 3,5-di-tert-butylphenyl
ring of its centrosymmetrically related neighbour and vice versa
(H ؒ ؒ ؒ π 2.56 Å, C–H ؒ ؒ ؒ π 174Њ). The shortest “equivalent”
interaction in 2a is from C(2)–H, but with a much longer
H ؒ ؒ ؒ π separation of 2.99 Å and with a C–H ؒ ؒ ؒ π angle of
139Њ.
Table 2 Selected bond lengths (Å) and angles (Њ) for 2c
Al–N(1)
Al–O(16)
Al–C(18)
2.254(2)
1.854(2)
1.975(2)
Al–N(8)
Al–C(17)
N(8)–C(9)
1.999(2)
1.982(3)
1.295(3)
O(16)–Al–C(18)
C(18)–Al–C(17) 123.69(12)
C(18)–Al–N(8)
O(16)–Al–N(1)
C(17)–Al–N(1)
98.97(10)
O(16)–Al–C(17)
O(16)–Al–N(8)
C(17)–Al–N(8)
C(18)–Al–N(1)
N(8)–Al–N(1)
98.61(11)
88.11(7)
115.47(10)
89.78(10)
74.41(8)
118.18(10)
162.52(8)
88.87(11)
The X-ray analysis of 2e (Fig. 5, Table 3) shows the ligand
bond lengths and angles are given in Table 1. The geometry at
aluminium is best described as trigonal bipyramidal, with N(4),
C(13) and C(14) occupying the equatorial sites, the aluminium
atom lying 0.16 Å out of the equatorial plane in the direction of
O(12). Importantly, the relatively weak interaction of the NMe2
pendant group with the aluminium centre is apparent from
the long Al–N(1) bond length of 2.413(5) Å. Within the
six-membered chelate ring the binding to aluminium is unsym-
metrical, with the bond to the oxygen atom being typical of an
alkoxide [1.854(4) Å], whilst that to the imino nitrogen atom is,
as expected, appreciably longer at 1.998(4) Å. Both these dis-
tances, however, are statistically significantly longer than their
counterparts in simple chelate analogues,4 e.g. [3,5-But2-2-
(O)C H CH᎐N(2,6-Me C H )]AlMe , reflecting the presence of
᎐
6
2
2
6
3
2
the additional donor in 2a with subsequent competition for
electron density. This effect is more pronounced in the alkoxide
case [Al–O: 1.854(4) Å cf. 1.773(3) Å for the above simple chel-
ate], due to this ligand being trans to the NMe2 group. As in the
simple chelates, the chelate C᎐N bond retains its double bond
᎐
character, being 1.294(6) Å. The six-membered metallacycle has
a half-boat conformation, the aluminium lying 0.50 Å out of
the plane of the other five atoms, these being coplanar to within
0.03 Å. The five-membered chelate ring has an envelope con-
formation, the NCH2CH2N portion of the ligand adopting
a gauche geometry. There are no intermolecular packing
interactions of note.
Fig. 5 The molecular structure of 2e showing the tetrahedral
geometry at aluminium and the non-coordination of the phosphorus
centre.
The structure of 2c (Fig. 4, Table 2) is very similar to that of
coordination to be via only the oxygen and nitrogen atoms, the
phosphorus being remote (4.56 Å) from the aluminium centre,
its lone pair being directed over the N᎐C(9) bond. The geom-
᎐
etry at aluminium is distorted tetrahedral with angles ranging
between 94.57(14) and 116.9(3)Њ, the most “acute” angle being
associated with the bite angle of the chelating ligand. As in 2a,
the metal–donor bonds within the six-membered chelate ring
are unsymmetrical [Al–O 1.754(3), Al–N 1.973(4) Å], these dis-
tances being in close accord with those of the similar bidentate
ligand complexes4 referred to above. The ring has a slightly
folded conformation with the aluminium lying 0.28 Å out of
the plane of the other five atoms which are co-planar to
within 0.02 Å; the chelate C᎐N bond retains its double bond
character [1.300(5) Å]. There are no noteworthy intermolecular
᎐
Fig. 4 The molecular structure of 2c.
interactions.
2a, retaining a distorted trigonal bipyramidal geometry at
aluminium with N(1) and O(16) occupying the axial posi-
tions. The only major difference is a significant shortening of
the bond from the pendant arm heteroatom N(1) to the
aluminium centre, Al–N(1) 2.254(2) Å, cf. 2.413(5) Å in 2a. In
The dimeric complex {[3,5-But2-2-(O)C6H2CHMeN-8-C9H6N]-
AlMe}2 (3)
In refluxing toluene, the interaction of AlMe3 with the
J. Chem. Soc., Dalton Trans., 2002, 415–422
417

View Article Online
Table 4 Selected bond lengths (Å) and angles (Њ) for the two crystallographically independent dimers (A and B) present in the structure of 3
A
B
A
B
Al(1)–O(1)
Al(1)–C(1)
Al(1)–N(2)
Al(2)–O(2)
Al(2)–N(3)
1.944(3)
1.968(5)
2.064(4)
1.918(3)
1.880(5)
1.964(3)
1.955(5)
2.089(4)
1.951(3)
1.871(4)
Al(1)–N(1)
Al(1)–O(2)
Al(2)–O(1)
Al(2)–C(2)
Al(2)–N(4)
1.882(4)
1.866(3)
1.881(3)
1.967(6)
2.077(4)
1.879(3)
1.856(3)
1.870(3)
1.963(5)
2.067(4)
O(2)–Al(1)–N(1)
N(1)–Al(1)–O(1)
N(1)–Al(1)–C(1)
O(2)–Al(1)–N(2)
O(1)–Al(1)–N(2)
N(3)–Al(2)–O(1)
O(1)–Al(2)–O(2)
O(1)–Al(2)–C(2)
N(3)–Al(2)–N(4)
O(2)–Al(2)–N(4)
Al(1)–O(1)–Al(2)
123.4(2)
89.9(2)
113.0(2)
94.3(2)
160.2(2)
125.3(2)
75.61(14)
122.3(3)
82.0(2)
160.0(2)
99.6(2)
124.7(2)
89.37(14)
114.2(2)
94.4(2)
158.7(2)
123.3(2)
75.88(13)
122.8(2)
81.3(2)
O(2)–Al(1)–O(1)
O(2)–Al(1)–C(1)
O(1)–Al(1)–C(1)
N(1)–Al(1)–N(2)
C(1)–Al(1)–N(2)
N(3)–Al(2)–O(2)
N(3)–Al(2)–C(2)
O(2)–Al(2)–C(2)
O(1)–Al(2)–N(4)
C(2)–Al(2)–N(4)
Al(1)–O(2)–Al(2)
75.32(14)
123.6(2)
104.2(2)
81.7(2)
95.6(2)
89.9(2)
112.4(3)
103.5(2)
94.3(2)
96.5(2)
101.1(2)
75.85(13)
120.9(2)
101.6(2)
80.7(2)
99.6(2)
89.8(2)
113.7(2)
101.2(2)
94.7(2)
98.1(2)
100.89(14)
160.7(2)
99.92(14)
Scheme 2 The preparation of 3.
quinoline ligand 1d did not follow the room temperature reac-
tion above (to yield the dimethylaluminium complex 2d), but
instead afforded the dimeric complex {[3,5-But2-2-(O)C6H2-
CHMeN-8-C9H6N]AlMe}2 (3). This product is the result of a
methyl migration from the aluminium centre to the parent
ligand backbone, see Scheme 2; such migrations have been
noted previously.2,6–8 A dimeric structure is indicated by elec-
tron ionisation MS, which displays the envelope corresponding
to the parent ion (m/z = 832). The methyl migration to the imine
carbon is revealed by the absence of a signal in the infrared or
13C NMR spectrum for this group. Also, the 1H NMR spectrum
of 3, shows signals corresponding to a CH(CH3) group, i.e. a
quartet [3J(HH) 6.8Hz] at δ 4.77 and a corresponding doublet
[3J(HH) 6.8Hz] at δ 0.79.
Crystals of 3 suitable for an X-ray structure determination
were grown from a saturated acetonitrile solution at room
temperature. The X-ray analysis (Fig. 6, Table 4) reveals a
dimeric complex to have been formed where the Schiff base
ligands adopt both tridentate and binucleating roles. The
asymmetric unit contains two independent, but geometrically
very similar, dimers each of which exhibits approximate
molecular C2 symmetry. The phenolic oxygens are seen to
bridge adjacent aluminium centres to form a slightly folded
(ca. 27Њ about the non-bonded O ؒ ؒ ؒ O vector) Al2O2 ring.
The Al–O–Al bridges are slightly asymmetric, the Al–O dis-
tances falling into two distinct groupings, averaging 1.868(3)
and 1.944(3) Å. The non-bonded Al ؒ ؒ ؒ Al separations in the
two independent molecules are 2.922(2) and 2.936(2) Å,
respectively. The geometries at the aluminium centres are
distorted trigonal bipyramidal, with the phenolic oxygen
and the quinoline nitrogen occupying the axial positions. The
equatorial Al–N(amido) bonds [av. 1.878(4) Å] are, as expected,
significantly shorter than those to the axial quinoline nitro-
gens [av. 2.074(4) Å]. The aluminium atoms do not deviate
significantly out of the plane of their three equatorial
substituents. The six-membered chelate rings again adopt
Fig. 6 One of the two independent dimeric molecules present in the
structure of 3.
half-boat conformations, but with their phenolic oxygen atoms
(rather than the metal centres) lying out of the ring plane by
ca. 0.76 Å. An interesting feature of the methyl migration
and the consequent loss of the imino function is the reten-
tion within each molecule of a common chirality at each of
these stereogenic centres, i.e. in the crystal we have only the
RR and SS diastereomers and not the meso-SR or RS species.
Inspection of molecular models reveals that a simple inver-
sion at each of these centres would result in a severely steric-
ally congested geometry with overlap of the methyl and
quinoline hydrogen atoms. The only intermolecular inter-
action of note is a partial stacking of the quinoline ring
systems.
418
J. Chem. Soc., Dalton Trans., 2002, 415–422

View Article Online
Cations of the form [(3,5-But -2-(O)C H CH᎐NL)AlMe]؉
or CsI windows) were run on Perkin-Elmer 577 and 457 grating
᎐
2
6
2
spectrophotometers and mass spectra were measured on either
a VG Autospec or a VG Platform II spectrometer. The reagent
1,2-(NH2)(PPh2)C6H4 was prepared by a previously described
procedure.10 All other chemicals were obtained commercially
and used as received unless stated otherwise.
The reaction of the dimethyl complexes 2a–e with a molar
equivalent of B(C6F5)3, in CD2Cl2 or C6D6, resulted in the
formation of the cations [(3,5-But -2-(O)C H CH᎐NL)AlMe]ϩ
᎐
2
6
2
(4a–e). Whereas the reaction of 2a with B(C6F5)3 could be
carried out successfully in CD2Cl2 and gave the cation 4a in
high purity, this was not the case for the formation of the
remaining cations 4b–e. In CD2Cl2 slightly impure products
were obtained, and it was generally found best to conduct the
reaction with B(C6F5)3 in C6D6. Using this solvent the cations
formed lower oily layers which were separated and pumped to
dryness. The cations 4a–e were thus formed in high purity,
as demonstrated by their 1H, 13C, and 19F NMR spectra
recorded in CD2Cl2. Crystalline materials could not however be
Preparation of ligands
3,5-But -2-(OH)C H CH᎐NCH CH NMe (1a). To a stirred
᎐
2
6
2
2
2
2
solution of 3,5-di-tert-butyl-2-hydroxybenzaldehyde (5.00 g,
21.3 mmol) in methanol (100 cm3) was added N,N-dimethyl-
ethylenediamine (2.34 cm3, 21.3 mmol). The solution was
heated at reflux for 12 h, and was then dried over MgSO4 and
filtered. Removal of the volatile components in vacuo yielded a
yellow oil. Repeated washing of the oil with pentane (5 × 5 cm3)
at Ϫ78 ЊC afforded 1a as a yellow solid. Yield 6.1 g, 94%. Found
C, 75.1; H, 10.7; N, 8.9. C19H32N2O requires C, 75.0; H, 10.6; N,
1
obtained. The H NMR spectra of this series of cations have
the imine resonance appearing in the range δ 8.16 to 8.67 and
the resonance of the remaining aluminium methyl in the range
δ Ϫ0.12 to Ϫ0.47; the corresponding 13C NMR signals lie
between δ 166.1 and 176.5 and between δ Ϫ9.4 and Ϫ14.8
respectively. The 1H NMR resonance of the methyl group in the
[CH3B(C6F5)3]Ϫ counter ions, which is broadened by the boron
quadrupole, is seen in the range δ 0.38 to 0.48, with the similarly
broadened carbon resonance at ca δ 10.5 throughout the series.
The 19F NMR spectra show a single set of three signals in a 2 : 1
: 2 ratio (at δ Ϫ135, Ϫ167, and Ϫ170 respectively) as anticipated
for a C6F5 group. These data for the [CH3B(C6F5)3]Ϫ groups are
consistent9 with their formulation, and therefore the formu-
lation of the aluminium cations, as separated ions. The observ-
ation for cation 4e of 31P coupling from the ligand PPh2 group
9.2%. IR: 1732 (w), 1694 (w), 1634 (m, C᎐N stretch), 1362 (s),
᎐
1275 (s), 1253 (s), 1203 (s), 1173 (s), 1133 (w), 1041 (m), 969 (w),
933 (w), 877 (m), 828 (m), 773 (m), 730 (m), 645 (m). MS (EI):
1
m/z 304 [M]ϩ, 289 [M Ϫ CH3]ϩ, 260 [M Ϫ NMe2]. H NMR:
4
δ 14.26 (s, 1H, OH ), 7.84 (s, 1H, CH᎐N), 7.56 [d, 1H, J(HH)
᎐
4
2.4 Hz, C6H2], 6.98 [d, 1H, J(HH) 2.4 Hz, C6H2], 3.31 [t, 2H,
3J(HH) 6.8 Hz, CH2CH2], 2.28 [t, 2H, 3J(HH) 6.8 Hz,
CH2CH2], 2.02 (s, 6H, N(CH3)2), 1.65 (s, 9H, C(CH3)3), 1.32
(s, 9H, C(CH3)3). 13C NMR: δ 166.8 (CH᎐N), 158.9, 140.0,
᎐
137.1, 126.7, 126.3, 118.7 (4 quaternary ϩ 2 CH resonances,
C6H2), 60.1 (CH2), 57.8 (CH2), 45.7 [N(CH3)2], 35.4 (CMe3),
34.3 (CMe3), 31.7 [C(CH3)3], 29.8 [C(CH3)3].
1
to the methyl bound to the aluminium centre in both the H
and 13C NMR spectra [J(PH) 1.9 Hz, J(PC) 35.3 Hz respec-
tively] indicates that a bond exists between the metal and the
phosphorus atom. By contrast, no similar coupling is seen
for the dimethylaluminium precursor compound 2e where the
PPh2 group is not bonded to the aluminium centre. This evi-
dence confirms our description of the cations 4a–e as the
formally coordinatively saturated 4-coordinate species shown in
Scheme 1.
3,5-But -2-(OH)C H CH᎐N-2-OPhC H (1b). As for 1a but
᎐
2
6
2
6
4
with 2-phenoxyaniline (3.95 g, 21.3 mmol) in place of the ethyl-
enediamine and using formic acid (2 drops) as catalyst. Slow
concentration of the resulting dried methanolic solution led
to crystallisation of the product. 1b was obtained as a yellow
solid by filtration. Yield 7.25 g, 85%. Found C, 80.7; H, 7.8;
N, 3.3. C27H31NO2 requires C, 80.8; H, 7.6; N, 3.5%. IR: 1620
(s, C᎐N stretch), 1582 (m), 1378 (s), 1363 (m), 1276 (m),
᎐
1243 (s), 1216 (m), 1202 (m), 1168 (s), 1102 (m), 1075 (w), 1035
(w), 981 (w), 940 (w), 887 (m), 853 (m), 824 (w), 797 (w),
777 (w), 761 (s), 749 (s), 688 (m). MS (EI): m/z 401 [M]ϩ,
Concluding remarks
386 [M Ϫ CH3]ϩ, 344 [M Ϫ C(CH3)3]ϩ. 1H NMR: δ 13.83
This work demonstrates that the provision of a pendant
donor group significantly alters the course of the reaction of
the aluminium dimethyl compounds with B(C6F5)3, allowing
the cationic aluminium monomethyl systems to be isolated.
Corresponding cations could not be formed in the absence of
these additional donors. The donor arms which, in the dimethyl
aluminium systems, are weakly bonding (2a–d) or non-bonding
(2e) become normal donor groups in the cations 4a–e and
thereby stabilise these species.
4
(s, 1H, OH ), 8.18 (s, 1H, CH᎐N), 7.56 [d, 1H, J(HH) 2.4 Hz,
᎐
C6H2], 7.05–6.79 (m, 10H, Ar-H ), 1.56 (s, 9H, C(CH3)3), 1.29
(s, 9H, C(CH3)3). 13C NMR: δ 164.9 (CH᎐N), 164.6, 163.8,
᎐
159.2, 158.2, 150.0, 141.2, 140.3, 137.5, 129.9, 127.3, 124.7,
123.0, 121.3, 121.0, 119.0, 118.0 (7 quaternary ϩ 9 CH reson-
ances, C6H2 ϩ C6H4 ϩ C6H5), 35.4 (CMe3), 34.2 (CMe3), 31.6
[C(CH3)3], 29.7 [C(CH3)3].
3,5-But -2-(OH)C H CH᎐N-2-CH C H N (1c). As for 1a but
᎐
2
6
2
2
5
4
using 2-(methylamino)pyridine (2.12 cm3, 21.3 mmol) in place
of the diamine and with methanol (50 cm3). After the reflux, the
volatile components were removed in vacuo affording a yellow
oily solid. Washing with pentane (5 × 5 cm3) at Ϫ78 ЊC afforded
1c as a yellow solid. Yield 6.0 g, 87%. Found C, 77.9; H, 8.5; N,
8.6. C21H28N2O requires C, 77.7; H, 8.7; N, 8.6%. IR: 1631 (s,
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
C᎐N stretch), 1591 (s), 1571 (m), 1378 (s), 1362 (s), 1342 (m),
᎐
1314 (w), 1297 (w), 1271 (m), 1252 (s), 1203 (m), 1174 (m), 1148
(m), 1133 (w), 1098 (w), 1058 (m), 1048 (m), 1005 (m), 993 (w),
963 (w), 928 (w), 883 (m), 853 (m), 827 (m), 802 (w), 769 (s), 750
(m), 729 (m), 705 (w), 645 (w). M.S. (EI): m/z 324 [M]ϩ, 309
[M Ϫ CH3]ϩ, 267 [M Ϫ C(CH3)3]ϩ, 232 [M Ϫ CH2C5H4N]ϩ.
1H NMR: δ 14.12 (s, 1H, OH ), 8.44–8.41 (m, 1H, C5H4N), 7.86
Imperial College or by Medac Ltd. H, 13C, 19F and 31P NMR
1
spectra were recorded in C6D6 for the ligands and neutral com-
pounds, and in CD2Cl2 for the cationic complexes, on Bruker
AM500, DRX400 or AC250 machines at ambient temperature.
1H and 13C chemical shifts were referenced via the solvent sig-
nals to TMS, and 19F and 31P shifts were referenced to external
standards (CFCl3 and H3PO4). 13C chemical shift assignments
were based on DEPT experiments. IR spectra (nujol mulls, KBr
(s, 1H, CH᎐N), 7.57 [d, 4J(HH) 2.5 Hz, C6H2], 7.01–6.98
᎐
4
(m, 2H, C5H4N), 6.93 [d, J(HH) 2.5 Hz, C6H2], 6.61–6.56
(m, 1H, C5H4N), 4.63 (s, 2H, CH2), 1.63 [s, 9H, C(CH3)3],
1.32 [s, 9H, C(CH3)3]. 13C NMR: δ 168.4 (CH᎐N), 163.7, 158.9,
᎐
149.6, 140.3, 137.1, 136.3, 127.1, 126.8, 122.0, 121.6, 118.7
J. Chem. Soc., Dalton Trans., 2002, 415–422
419

View Article Online
(5 quaternary ϩ 6 CH resonances, C6H2 ϩ C5H4N), 65.2 (CH2),
35.4 (CMe3), 34.3 (CMe3), 31.7 [C(CH3)3], 29.8 [C(CH3)3].
obscured by solvent, C6H2), 57.8 (CH2), 54.1 (CH2), 45.2
[N(CH3)2], 35.4 (CMe3), 34.1 (CMe3), 31.6 [C(CH3)3], 29.6
[C(CH3)3], Ϫ8.3 (br, AlCH3). Crystal data for 2a:
C21H37N2OAl, M = 360.5, monoclinic, P21/c (no. 14), a =
10.332(2), b = 24.982(4), c = 9.729(2) Å, β = 115.98(1)Њ, V =
3,5-But2-2-(OH)C6H2CH-N-8-C9H6N (1d). As for 1c but
using 8-aminoquinoline (3.07 g, 21.3 mmol) in place of the
pyridine and with formic acid (2 drops). After the reflux,
the resulting rust-coloured precipitate was filtered off and was
washed with methanol (10 cm3) to provide 1d as an orange
powder. Yield 6.9 g, 90%. Found C, 79.7; H, 8.0; N, 7.6.
2257.4(7) Å3, Z = 4, Dc = 1.061 g cmϪ3, µ(Mo-Kα) = 1.00 cmϪ1
,
T = 293 K, yellow platy needles; 2934 independent measured
reflections, F 2 refinement, R1 = 0.067, wR2 = 0.156, 1646
independent observed reflections [|Fo| > 4σ(|Fo|), 2θ ≤ 45Њ], 226
parameters.
C H N O requires C, 80.0; H, 7.8; N, 7.8%. IR: 1615 (s, C᎐N
᎐
24 28
2
CCDC reference number 134423.
stretch), 1563 (m), 1498 (m), 1378 (s), 1367 (s), 1325 (m), 1312
(m), 1274 (m), 1250 (s), 1201 (m), 1179 (m), 1163 (m), 1088 (m),
1055 (m), 1026 (w), 980 (w), 930 (w), 906 (w), 885 (w), 826 (m),
805 (w), 791 (s), 774 (m), 756 (m), 728 (w). MS (EI): m/z (EI,
m/z) 360 [M]ϩ, 345 [M Ϫ CH3]ϩ, 303 [M Ϫ C(CH3)3]ϩ. 1H
AlMe [3,5-But -2-(O)C H CH᎐N-2-OPhC H ] (2b). Tri-
᎐
2
2
6
2
6
4
methylaluminium in toluene (2.0 M, 1.37 cm3, 2.74 mmol) was
added dropwise to a solution of 1b (1.00 g, 2.49 mmol) in tolu-
ene (30 cm3). After refluxing for 12 h, the volatiles were removed
in vacuo, and the product extracted into MeCN (10 cm3). Cool-
ing to Ϫ30 ЊC resulted in the formation of an orange oil. On
drying the oil under reduced pressure, a bright yellow glassy
solid, 2b, was formed. Yield 0.72 g, 63%. Found: C, 75.8; H, 7.9;
N, 3.4. C29H36AlNO2 requires C, 76.1; H, 7.9; N, 3.1%. (satisfac-
tory analysis not obtained; ascribed to oily nature of product).
NMR: δ 14.82 (s, 1H, OH ), 8.68–8.65 (m, 1H, C9H6N), 8.63 (s,
4
1H, CH᎐N), 7.65 [d, J(HH) 2.4 Hz, C H ], 7.53–7.48 (m, 1H,
᎐
6
2
4
C9H6N), 7.25–7.02 (m, 3H, C9H6N), 7.15 [d, J(HH) 2.4 Hz,
C6H2], 6.75–6.70 (m, 1H, C9H6N), 1.69 (s, 9H, C(CH3)3), 1.32 (s,
9H, C(CH3)3). 13C NMR: δ 166.8 (CH᎐N), 163.3, 159.5, 150.1,
᎐
146.0, 142.6, 140.0, 139.6, 137.3, 135.3, 129.1, 126.3, 125.4,
121.3, 119.7, 119.1 (7 quaternary ϩ 8 CH resonances, C6H2 ϩ
C9H6N), 35.3 (CMe3), 34.0 (CMe3), 31.4 [C(CH3)3], 29.6
[C(CH3)3].
IR: 1622 (s, C᎐N stretch), 1575 (w), 1555 (w), 1538 (m), 1504
᎐
(w), 1488 (w), 1424 (s), 1363 (m), 1353 (m), 1336 (m), 1286 (m),
1257 (m), 1237 (m), 1225 (m), 1200 (m), 1174 (s), 1070 (m), 1050
(m), 1019 (w), 1007 (w), 917 (w), 881 (w), 846 (w), 792 (w),
763 (m), 752 (w), 727 (m), 660 (s), 639 (s). MS (EI): m/z 442
[M Ϫ CH ]ϩ. 1H NMR: δ 7.73 (s, 1H, CH᎐N), 7.70 [d, 4J(HH)
3,5-But -2-(OH)C H CH᎐N-2-PPh C H (1e). As for 1b but
᎐
2
6
2
2
6
4
with 3,5-di-tert-butyl-2-hydroxybenzaldehyde (3.00 g, 12.8
mmol) and 2-diphenylphosphinoaniline (3.55 g, 12.8 mmol) in
ethanol (100 ml). Slow concentration of the dried ethanolic
solution resulted in crystallisation of the product. 1b was
obtained by filtration as a yellow crystalline solid. Yield 5.5 g,
87%. Found C, 79.7; H, 7.3; N, 2.8. C33H36NPO requires C,
᎐
3
2.6 Hz, C6H2], 6.97–6.61 (m, 10H, C6H2 ϩ C6H4 ϩ C6H5), 1.58
[s, 9H, C(CH3)3], 1.27 [s, 9H, C(CH3)3], Ϫ0.19 (s, 6H, AlCH3).
13C NMR: δ 172.7 (CH᎐N), 163.8 (Ar–C), 155.7 (Ar–C), 151.1
᎐
(Ar–C), 141.3 (Ar–C), 139.0 (Ar–C), 137.8 (Ar–C), 133.0
(Ar–C), 130.3 (Ar–C), 130.2 (Ar–C), 129.6 (Ar–C), 126.7
(Ar–C), 124.6 (Ar–C), 123.8 (Ar–C), 123.4 (Ar–C), 120.4
(Ar–C), 119.5 (Ar–C), 117.9 (Ar–C), 35.6 (CMe3), 34.1
(CMe3), 31.4 [C(CH3)3], 29.6 [C(CH3)3], Ϫ9.0 (br, AlCH3).
80.3; H, 7.4; N, 2.8%. IR: 1616 (s, C᎐N stretch), 1595m, 1595m,
᎐
1311w, 1283m, 1248m, 1199w, 1163m, 1135w, 1092w, 1023w,
979w, 936w, 887w, 802w, 760s, 739s, 689s, 668w. MS (EI): m/z
493 [M]ϩ. 1H NMR: δ 13.46 (s, 1H, OH ), 7.97 (s, 1H, CH᎐N),
᎐
7.54 [d, 4J(HH) 2.4 Hz, C6H2] 7.55–6.65 (several m, 14H, C6H4
4
AlMe [3,5-But -2-(O)C H CH᎐N-2-CH C H N] (2c). As for
᎐
2
2
6
2
2
5
4
ϩ C6H5), 6.88 [d, J(HH) 2.4 Hz, C6H2] 1.61 [s, 9H, C(CH3)3],
2a but with trimethylaluminium (2.0 M, 1.69 cm3, 3.39 mmol)
and 1c (1.00 g, 3.08 mmol). The product was extracted into hot
MeCN and filtered. Concentration of this solution to 15 cm3
and cooling to Ϫ30 ЊC resulted in the formation of 2c as pale
orange crystals. Yield 0.74 g, 63%. Found: C, 72.2; H, 8.7; N,
6.9. C23H33AlN2O requires C, 72.6; H, 8.7; N, 7.4%. (%C con-
1.27 [s, 9H, C(CH3)3]. 13C NMR: δ 163.81 (HC᎐N), 158.89,
᎐
140.18, 137.29, 118.80 (4 quaternaries of C6H2), 152.14 [d,
J(PC) 19.1 Hz, PAr–CN], 136.90 [d, J(PC) 11.9 Hz, P(C6H5)
quaternary), 134.50 [d, J(PC) 13.9 Hz, PC6H4 quaternary],
134.68 [d, J(PC) 20.6 Hz], 133.35, 129.88, 128.90 [d, J(PC)
12.2 Hz], 128.71, 128.22 [d, J(PC) 16.7 Hz], 127.38, 126.77,
118.00 (9 CH resonances, C6H2 ϩ C6H4 ϩ C6H5), 35.39 (CMe3),
34.16 (CMe3), 31.58 [C(CH3)], 29.65 [C(CH3)]. 31P NMR
δ 13.53 (s).
sistently low. Sample pure spectroscopically). IR: 1615 (s, C᎐N
᎐
stretch), 1587 (s), 1556 (m), 1540 (s), 1490 (s), 1438 (s), 1410
(m), 1363 (m), 1324 (m), 1278 (m), 1252 (s), 1200 (s), 1175 (s),
1136 (w), 1111 (m), 1072 (w), 1025 (w), 987 (w), 930 (w), 894
(w), 876 (w), 857 (m), 787 (m), 761 (m), 750 (m), 687 (s). MS
(EI): m/z 365 [M Ϫ CH3]ϩ. 1H NMR: δ 8.31–8.28 (m, 1H,
C5H4N), 7.72 [d, 1H, 4J(HH) 2.6, C6H2], 7.38 [t, 1H, 4J(HH) 1.3,
Preparation of complexes
AlMe [3,5-But -2-(O)C H CH᎐NCH CH NMe ] (2a). Tri-
᎐
2
2
6
2
2
2
2
methylaluminium in toluene (2.0 M, 1.81 cm3, 3.61 mmol) was
added dropwise to a solution of 1a (1.00 g, 3.28 mmol) in tolu-
ene (30 cm3). The reaction was stirred at room temperature for
12 h, then the volatiles removed in vacuo. The product was
extracted into hot MeCN (30 cm3). Filtration and cooling to
room temperature afforded 2a as large yellow platy needles.
Yield 0.83 g. 70%. Found C, 69.8; H, 10.3; N, 7.8. C21H37AlN2O
CH᎐N), 6.83 [d, 1H, J(HH) 2.5, C H ], 6.80 [dt, 1H, J(HH)
᎐
6 2
4
3
7.7, 4J(HH) 1.7, C5H4N], 6.50–6.39 (m, 1H, C5H4N), 6.22–6.14
(m, 1H, C5H4N), 3.81 (br. s, 2H, CH2), 1.76 (s, 9H, C(CH3)3),
1.38 (s, 9H, C(CH3)3), Ϫ0.15 (s, 6H, AlCH3). 13C NMR: δ 172.5
(CH᎐N), 166.1, 153.8, 146.6, 141.3, 137.5, 136.5, 131.5, 123.0,
᎐
120.5, 118.1 (10 Ar–CC resonances, 11th obscured by solvent,
C6H2 ϩ C5H4N), 59.3 (CH2), 35.7 (CMe3), 34.1 (CMe3), 31.6
[C(CH3)3], 29.8 [C(CH3)3], Ϫ5.1 (br, AlCH3). Crystal data for
2c: C23H33N2OAl, M = 380.5, monoclinic, P21/c (no. 14),
a = 15.009(2), b = 12.207(2), c = 14.129(1) Å, β = 116.36(1)Њ,
V = 2319.5(4) Å3, Z = 4, Dc = 1.090 g cmϪ3, µ(Mo-Kα) = 1.01
cmϪ1, T = 293 K, yellow prisms; 5299 independent measured
reflections, F 2 refinement, R1 = 0.054, wR2 = 0.136, 3526
independent observed reflections [|Fo| > 4σ(|Fo|), 2θ ≤ 55Њ], 245
parameters.
requires C, 69.6; H, 10.3; N, 7.4%. IR: 1623 (s, C᎐N stretch),
᎐
1607 (m), 1555 (m), 1540 (m), 1422 (m), 1360 (m), 1347 (m),
1335 (m), 1279 (w), 1260 (s), 1239 (m), 1202 (m), 1178 (s), 1135
(w), 1098 (w), 1082 (m), 1066 (w), 1045 (w), 1027 (m), 995 (w),
982 (w), 948 (w), 929 (w), 896 (m), 880 (w), 847 (m), 814 (w),
791 (m), 751 (w), 690 (s), 667 (s), 639 (s). MS (EI): m/z 345
1
4
[M Ϫ CH3]ϩ. H NMR: δ 7.66 [d, 1H, J(HH) 2.4 Hz, C6H2],
7.39 (s, 1H, CH᎐N), 6.80 [d, 1H, 4J(HH) 2.6 Hz, C H ], 2.86 [t,
᎐
6
2
3
3
2H, J(HH) 6.8 Hz, CH2CH2], 2.08 [t, 2H, J(HH) 6.2 Hz,
CH2CH2], 1.85 [s, 6H, N(CH3)2], 1.63 [s, 9H, C(CH3)3], 1.30 [s,
CCDC reference number 134424.
9H, C(CH3)3], Ϫ0.26 (s, 6H, AlCH3). 13C NMR: δ 172.8 (CH᎐
AlMe [3,5-But -2-(O)C H CH᎐N-9-C H N] (2d). As for 2a
᎐
᎐
2
2
6
2
9
6
N), 163.3, 140.9, 137.9, 131.4, 118.5 (5 Ar-C resonances, 6th
but with trimethylaluminium in toluene (2.0 M, 0.76 cm3, 1.53
420
J. Chem. Soc., Dalton Trans., 2002, 415–422

View Article Online
mmol) and 1d (0.50 g, 1.39 mmol) in toluene (15 cm3). The
resulting solution was evaporated to dryness in vacuo affording
2d as a dark red glassy solid. Approx. yield 0.39 g, 67%. Found:
C, 71.9; H, 7.7; N, 6.2. C26H33AlN2O requires C, 75.0; H, 8.0; N,
6.7%. (satisfactory analysis not obtained; ascribed to oily
1057 (m), 977 (w), 957 (w), 938 (w), 918 (w), 904 (w), 879 (w),
830 (m), 817 (s), 805 (m), 785 (s), 777 (m), 744 (m), 738 (m), 674
(m), 621 (s). MS (EI): m/z 832 [M]ϩ, 817 [M Ϫ CH3]ϩ, 416 [1/2
1
M]ϩ, 401 [1/2 M Ϫ CH3]ϩ. H NMR (integrals as for mono-
4
meric unit): δ 8.03–8.00 (m, 2H, C9H6N), 7.58 [d, 2H, J(HH)
nature of product). IR: 1618 (s, C᎐N stretch) 1600 (m), 1587 (s),
2.6 Hz, C6H2], 7.36–7.24 (m, 4H, C9H6N), 6.79 [d, 2H, 4J(HH)
2.6 Hz, C6H2], 6.55–6.38 (m, 6H, C9H6N), 4.77 [q, 2H, 3J(HH)
6.8 Hz, CH(CH3)], 2.00 [s, 18H, C(CH3)3], 1.26 [s, 18H,
C(CH3)3], 0.79 [d, 6H, 3J(HH) 6.8 Hz, CH(CH3)], Ϫ0.19 (s, 3H,
AlCH3). 13C NMR: δ 149.6 (Ar–C), 149.1 (Ar–C), 144.4
(Ar–C), 143.5 (Ar–C), 140.2 (Ar–C), 139.1 (Ar–C), 138.8
(Ar–C), 137.6 (Ar–C), 140.2 (Ar–C), 139.1 (Ar–C), 138.8
(Ar–C), 137.6 (Ar–C), 130.8 (Ar–C), 129.6 (Ar–C), 119.9
(Ar–C), 108.6 (Ar–C), 106.2 (Ar–C), 57.1 (CHMe) 37.1
(CMe3), 34.5 (CMe3), 34.2 [C(CH3)3], 31.6 [C(CH3)3], 20.6 [CH-
(CH3)]. AlCH3 not observed. Crystal data for 3: C52H66-
᎐
1537 (s), 1505 (s), 1439 (s), 1412 (s), 1363 (m), 1339 (m), 1319
(w), 1253 (m), 1234 (m), 1202 (m), 1182 (m), 1169 (m), 1132 (w),
1088 (m), 1069 (w), 1027 (w), 980 (w), 921 (w), 875 (w), 846 (w),
831 (w), 794 (m), 756 (w), 730 (w), 766 (m). MS (EI): m/z 416
[M]ϩ, 401 [M Ϫ CH3]ϩ. 1H NMR: δ 8.48–8.45 (m, 1H, C9H6N),
4
8.11 (s, 1H, CH᎐N), 7.77 [d, 1H, J(HH) 2.6 Hz, C H ], 7.32–
᎐
6
2
7.28 (m, 1H, C9H6N), 7.06–6.96 (m, 2H, C9H6N), 6.94 [d, 1H,
4J(HH) 2.6 Hz, C6H2], 6.66–6.58 (m, 2H, C9H6N), 1.79 [s, 9H,
C(CH3)3], 1.39 [s, 9H, C(CH3)3], Ϫ0.05 (s, 6H, AlCH3). 13C
NMR: δ 169.1 (HC᎐N), 165.9, 146.5, 142.4, 142.0, 139.7, 137.2,
᎐
¯
136.7, 133.2, 129.3, 128.7, 127.8, 124.2, 122.6, 118.7, 114.9
(7 quaternary ϩ 8 CH resonances, C6H2 ϩ C9H6N), 35.7
(CMe3), 34.2 (CMe3), 31.5 [C(CH3)3], 29.8 [C(CH3)3], Ϫ4.0
(AlCH3).
N4O2Al2, M = 833.1, triclinic, P1 (no. 2), a = 13.617(1), b =
18.114(2), c = 22.065(1) Å, α = 113.61(1), β = 96.62(1), γ =
95.98(1)Њ, V = 4885.5(7) Å3, Z = 4 (2 independent molecules),
Dc = 1.133 g cmϪ3, µ(Cu-Kα) = 8.56 cmϪ1, T = 293 K, orange
blocky needles; 13981 independent measured reflections, F 2
refinement, R1 = 0.071, wR2 = 0.181, 9453 independent observed
reflections [|Fo| > 4σ(|Fo|), 2θ ≤ 120Њ], 1170 parameters.
CCDC reference number 171205.
AlMe [3,5-But -2-(O)C H CH᎐N-2-PPh C H ] (2e). As for
᎐
2
2
6
2
2
6
4
2b but with trimethylaluminium in toluene (2.0 M, 1.12 cm3,
2.24 mmol) and (1e) (1.00 g, 2.03 mmol). After removal of
the volatiles in vacuo the product was extracted into MeCN
(10 cm3). Cooling and prolonged standing (1–2 days) at ambi-
ent temperature resulted in the formation of yellow crystalline
2e. Yield 0.79 g, 71%. Found: C, 76.4; H, 7.3; N, 3.1. C35H41-
See http://www.rsc.org/suppdata/dt/b1/b106131n/ for crystal-
lographic data in CIF or other electronic format.
Preparation of cations
AlNPO requires C, 76.5; H, 7.5; N, 2.6%. IR: 1614 (s, C᎐N
᎐
{AlMe[3,5-But -2-(O)C H CH᎐NCH CH NMe ]}{MeB-
᎐
2
6
2
2
2
2
stretch) 1598 (m), 1584 (s), 1559 (s), 1543 (s), 1461 (s), 1437 (s),
1407 (w), 1388 (s), 1362 (m), 1320 (m), 1279 (w), 1256 (s), 1241
(m), 1178 (s), 1137 (w), 1126 (w), 1092 (w), 1068 (w), 1027 (w),
998 (w), 952 (w), 929 (w), 885 (m), 869 (w), 852 (s), 812 (w), 786
(w), 766 (s), 746 (s), 698 (s), 680 (s), 664 (m). MS (EI): m/z 550
(C6F5)3} (4a). A solution of B(C6F5)3 (25.6 mg, 0.05 mmol) in
CD2Cl2 (0.20 ml) was added dropwise to a vigorously shaken
solution of 3a (18.0 mg, 0.05 mmol) in CD2Cl2 (0.30 ml) result-
ing in an essentially NMR-pure yellow–green solution of the
1
4
product. 1H NMR: δ 8.55 (s, 1H, CH᎐N), 7.76 [d, 1H, 4J(HH)
[M ϩ H]ϩ, 534 [M Ϫ CH3]ϩ. H NMR: δ 7.69 [d, 1H, J(HH)
᎐
4
2.6 Hz, C6H2], 7.27 [d, 1H, J(HH) 2.6 Hz, C6H2], 4.0 (br.s,
2.6 Hz, C H ], 7.35 [d, 1H, J(PH) 3.4 Hz, CH᎐N], 7.38–7.29 (m,
᎐
6
2
CH2CH2), 3.0 (br.s, CH2CH2), 2.77 (br.s, 6H, N(CH3)2), 1.41 (s,
9H, C(CH3)3), 1.31 (s, 9H, C(CH3)3), 0.47 (s, 3H, BCH3), Ϫ0.31
1H, PC6H4), 7.22–7.16 (complex m, 5H, PAr-H ), 7.03–6.90
(complex m, 7H, PAr-H ), 6.82 [dt, 1H, J(HH) 7.5 Hz, J(PH)
1.4 Hz, PAr-H], 6.19 [d, 1H, 4J(HH) 2.6 Hz, C6H2], 1.58 [s, 9H,
C(CH3)3], 1.23 [s, 9H, C(CH3)3], Ϫ0.04 (s, 6H, Al-CH3). 13C
(s, 3H, AlCH3). 13C NMR: δ (cation part only) 175.83 (HC᎐N),
᎐
158.88, 143.78, 141.65, 120.00 (4 quaternaries, C6H2), 135.44,
129.33 (2 CH resonances, C6H2), 58.42 (CH2), 48.86 (CH2),
46.23 [br, N(CH3)2], 35.79 (CMe3), 34.60 (CMe3), 31.10
[C(CH3)3], 29.45 [C(CH3)3], Ϫ14.78 (br, AlCH3), also CH3B of
anion seen as broad resonance at δ 10.4. 19F NMR: δ Ϫ135.4
(6F), Ϫ167.3 (3F), Ϫ170.0 (6F).
NMR: δ 173.87 [d, J(PC) 5.7 Hz, HC᎐N], 163.26, 151.66 [d,
᎐
J(PC) 24.4 Hz], 141.09, 138.86, 136.96 [d, J(PC) 11.30 Hz],
132.76 [d, J(PC) 18.8 Hz], 118.17 (7 quaternary aryl reson-
ances), 136.50, 134.33 [d, J(PC) 20.4 Hz], 133.00, 130.15.
129.74, 128.98 [d, J(PC) 11.0 Hz], 128.89, 127.55, 124.68 (9 aryl
CH resonances from C6H2, PC6H4 and P(C6H5)2), 35.59
(CMe3), 34.03 (CMe3), 31.42 (C(CH3)3), 29.58 (C(CH3)3),
Ϫ8.57 (AlCH3). 31P NMR: δ Ϫ18.14 (s). Crystal data for 2e:
C35H41NOPAl ؒ 0.5MeCN, M = 570.2, monoclinic, P21/n (no.
14), a = 15.329(1), b = 13.366(1), c = 17.575(1) Å, β = 108.81(1)Њ,
V = 3408.5(4) Å3, Z = 4, Dc = 1.111 g cmϪ3, µ(Cu-Kα) = 11.7
cmϪ1, T = 293 K, yellow prisms; 5019 independent measured
reflections, F 2 refinement, R1 = 0.069, wR2 = 0.167, 3187
independent observed reflections [|Fo| > 4σ(|Fo|), 2θ ≤ 120Њ], 359
parameters.
{AlMe[3,5-But -2-(O)C H CH᎐N-2-OPhC H ]}{MeB(C F ) }
᎐
2
6
2
6
4
6
5 3
(4b). A solution of B(C6F5)3 (51.2 mg, 0.10 mmol) in C6D6 (0.50
ml) was added dropwise to a vigorously shaken solution of 2b
(45.8 mg, 0.10 mmol) in C6D6 (0.40 ml). During the addition
the solution became cloudy and an oil began to separate. C6D6
(0.20 ml) was used to wash the residual B(C6F5)3 into the
shaken reaction mixture. After standing for 0.5 h the super-
natant C6D6 solution was decanted and the residual oil was
evacuated to yield a foamed solid which was dissolved in
1
4
CD Cl . H NMR: δ8.58 (s, 1H, CH᎐N), 8.16 [d, 1H, J(HH)
᎐
CCDC reference number 171206.
2
2
4
2.5, C6H2], 7.71 [d, 1H, J(HH) 2.5, C6H2], 7.6–6.9 (several m,
9H, C6H4 ϩ C6H5), 1.46 (s, 9H, C(CH3)3), 1.26 (s, 9H, C(CH3)3),
0.43 (br s, 3H, BCH3), Ϫ0.35 (s, 3H, AlCH3). 13C NMR:
{AlMe[3,5-But2-2-(O)C6H2CHMe-N-8-C9H6N]}2 (3). Tri-
methylaluminium in toluene (2.0 M, 1.53 cm3, 3.05 mmol) was
added dropwise to a solution of 1d (1.00 g, 2.77 mmol) in tolu-
ene (20 cm3). After refluxing for 12 h, the volatiles were removed
in vacuo, and the product extracted into MeCN (20 cm3). Cool-
ing to ambient temperature afforded an orange crystalline
product consisting of ∼81% 3 and ∼19% 2d. Pure 3 was
obtained as orange crystals at room temperature after a
recrystallisation from hot MeCN (50 cm3). Overall yield 0.42 g,
36%. Found: C, 74.8; H, 8.1; N, 6.7. C52H66Al2N4O2 requires C,
75.0; H, 8.0; N, 6.7%. IR: 1598 (m), 1575 (s), 1505 (s), 1429 (m),
1338 (s), 1287 (w), 1273 (w), 1261 (w), 1235 (m), 1220 (m), 1199
(m), 1174 (m), 1148 (m), 1129 (m), 1104 (m), 1081 (w), 1069 (w),
δ (cation part only) 167.23 (HC᎐N), 152.08, 150.04, 149.74,
᎐
149.01, 143.65, 128.59, 123.56 (7 quaternaries, C6H2 ϩ C6H4 ϩ
C6H5), 139.85, 134.24, 133.42, 132.92, 131.04, 130.59, 127.53,
123.17, 117.59, (9 CH resonances, C6H2 ϩ C6H4 ϩ C6H5), 36.54
(CMe3), 35.45 (CMe3), 31.79 [C(CH3)3], 31.01 [C(CH3)3],
Ϫ10.67 (AlCH3), also CH3B of anion seen as broad resonance
at δ 10.5. 19F NMR: δ Ϫ135.4 (6F), Ϫ167.3 (3F), Ϫ170.0 (6F).
{AlMe[3,5-But -2-(O)C H CH᎐N-2-CH C H N]}{MeB-
᎐
2
6
2
2
5
4
(C6F5)3} (4c). As for 4b, but using 2c (38.0 mg, 0.10 mmol). 1H
NMR: δ 8.46 (s, 1H, CH᎐N), 8.05 [dt, 1H, 3J(HH) 7.9, 4J(HH)
᎐
J. Chem. Soc., Dalton Trans., 2002, 415–422
421

View Article Online
1.5, C5H4N], 8.00 [d, 1H, 4J(HH) 2.5, C6H2], 7.82 [d, 1H,
3J(HH) 5.3, C5H4N], 7.51 [d, 1H, 3J(HH) 8.0, C5H4N], 7.20 [m,
[d, (J(PC) 6.3 Hz], 130.85, 130.75, 119.89 [d, J(PC) 3.5 Hz]
(9 aryl CH resonances C6H2, C6H4 and C6H5), 35.71 (CMe3),
34.58 (CMe3), 31.02 [C(CH3)], 29.41 [C(CH3)], Ϫ11.00 [d,
J(PC) 35.3 Hz, AlCH3], also CH3B of anion seen as broad
resonance at δ 10.4. 19F NMR: δ Ϫ135.5 (6F), Ϫ167.5 (3F),
Ϫ170.1 (6F).
3
4
1H, C5H4N], 7.20 [dt, 1H, J(HH) 6.3, J(HH) 1.1, C5H4N],
4
3
7.07 [d, 1H, J(HH) 2.5, C6H2], 5.15 [AB q, 2H, J(HH) 1.5,
3
CH2CH2], 4.98 [AB q, 2H, J(HH) 1.5, CH2CH2], 1.75 (s, 9H,
C(CH3)3), 1.26 (s, 9H, C(CH3)3), 0.48 (br s, 3H, BCH3), Ϫ0.47
(s, 3H, AlCH3). 13C NMR: δ (cation part only) 176.45 (HC᎐N),
᎐
151.78, 150.25, 149.84, 145.20, 143.77, 142.74, 138.49, 132.95,
125.74, 123.89, 122.98 (6 CH and 5 quaternary resonances,
C6H2 ϩ C5H4N), 56.06 (CH2), 37.11 (CMe3), 34.95 (CMe3),
32.95 [C(CH3)3], 30.94 [C(CH3)3], Ϫ9.45 (AlCH3), also CH3B
of anion seen as broad resonance at δ 10.5. 19F NMR: δ Ϫ135.4
(6F), Ϫ167.1 (3F), Ϫ169.8 (6F).
Acknowledgements
BP-Amoco Chemicals and ICI Acrylics are thanked for
financial support and the Royal Society & Leverhulme Trust
for Fellowships (J. A. S. & C. R., respectively).
{AlMe[3,5-But -2-(O)C H CH᎐N-8-C H N]}{MeB(C F ) }
References
᎐
2
6
2
9
6
6
5 3
(4d). As for 4b, but using B(C6F5)3 (30.7 mg, 0.60 mmol) and 2d
1 See S. D. Ittel, L. K. Johnson and M. Brookhart, Chem. Rev., 2000,
100, 1203 and references therein; also see e.g. (a) B. L. Small and
M. Brookhart, J. Am. Chem. Soc., 1998, 120, 7143; (b) B. L. Small,
M. Brookhart and A. M. A. Bennett, J. Am. Chem. Soc, 1998,
120, 4049; (c) G. J. P. Britovsek, V. C. Gibson, B. S. Kimberley,
P. J. Maddox, S. J. McTavish, G. A. Solan, A. J. P. White and
D. J. Williams, Chem. Commun., 1998, 849; (d ) C. Wang,
S. Friedrich, T. R. Younkin, R. T. Li, R. H. Grubbs, D. A. Bansleben
and M. W. Day, Organometallics, 1998, 17, 3149; (e) T. R. Younkin,
E. F. Conner, J. I. Henderson, S. K. Friedrich, R. H. Grubbs
and D. A. Bansleben, Science, 2000, 287, 460; ( f ) L. K. Johnson,
C. M. Killian and M. Brookhart, J. Am. Chem. Soc., 1995, 117,
6414; (g) L. K. Johnson, S. Mecking and M. Brookhart, J. Am.
Chem. Soc., 1996, 118, 267.
2 M. Bruce, V. C. Gibson, C. Redshaw, G. A. Solan, A. J. P. White and
D. J. Williams, Chem. Commun., 1998, 2523.
3 M. P. Coles and R. F. Jordan, J. Am. Chem. Soc., 1997, 119, 8125.
4 P. A. Cameron, V. C. Gibson, C. Redshaw, J. A. Segal, G. A. Solan,
A. J. P. White and D. J. Williams, J. Chem. Soc., Dalton Trans., 2001,
1472.
5 P. A. Cameron, V. C. Gibson, C. Redshaw, J. A. Segal, M. Bruce,
A. J. P. White and D. J. Williams, Chem. Commun., 1999, 1883.
6 V. C. Gibson, C. Redshaw, A. J. P. White and D. J. Williams,
J. Organomet. Chem., 1998, 550, 453.
7 J. M. Klerks, D. J. Stufkens, G. van Koten and K. Vrieze,
J. Organomet. Chem., 1979, 181, 271.
8 G. van Koten and K. Vrieze, Adv. Organomet. Chem., 1982, 21, 151.
9 X. Yang, C. L. Stern and T. J. Marks, J. Am. Chem. Soc., 1994, 116,
10015.
10 M. K. Cooper, J. M. Downes, P. A. Duckworth, M. C. Kerby,
R. J. Powell and M. D. Soucek, Inorg Synth., 1989, 25, 129.
(25.0 mg, 0.60 mmol). 1H NMR: δ 8.67 [dd, 1H, J(HH) 8.4 Hz,
J(HH) 1.3 Hz, C9H6N], 8.26–8.16 9 (m, 2H, C9H6N), 8.08 [d,
4
1H, J(HH) 2.5 Hz, C H ], 8.02 (s, 1H, HC᎐N), 7.91 (t, 1H,
᎐
6
2
J(HH) 8.0, C9H6N), 7.48 [dd, J(HH) 8.4 Hz, J(HH) 8.4 Hz,
C9H6N], 7.33 [d, 1H, J(HH) 7.6, C9H6N], 6.94 [d, 4J(HH)
2.5 Hz, C6H2], 1.83 [s, 9H, C(CH3)3], 1.25 [s, 9H, C(CH3)3], 0.38
(br s, 3H, BCH3), Ϫ0.35 (s, 3H, AlCH3). 13C NMR: δ (cation
part only) 166.10 (HC᎐N), 150.57, 150.49, 142.93, 137.59,
᎐
134.52, 129.04, 123.08 (7 quaternaries, C6H2 ϩ C9H6N), 148.36,
143.34, 131.12, 129.73, 123.93, 117.94 (6 CH resonances of
C9H6N), 139.09, 133.30 (2 CH resonances of C6H2), 37.02
(CMe3), 34.98 (CMe3), 32.75 [C(CH3)3], 30.86 [C(CH3)3],
Ϫ9.82 (AlCH3), also CH3B of anion seen as broad resonance at
δ 10.5. 19F NMR: δ Ϫ135.4 (6F), Ϫ167.1 (3F), Ϫ169.8 (6F).
{AlMe[3,5-But -2-(O)C H CH᎐N-2-PPh C H ]}{MeB(C F ) }
᎐
2
6
2
2
6
4
6
5 3
(4e). As for 4b, but using B(C6F5)3 (41.0 mg, 0.80 mmol) in C6D6
1
(0.5 ml) and 2e (44.0 mg, 0.80 mmol) in C6D6 (0.5 ml). H
NMR: δ 8.59 [d, J(PH) 2.0 Hz, HC᎐N), 7.95–7.85 (m, 1H,
᎐
PC6H4), 7.79 [d, 1H, 4J(HH) 2.6 Hz, C6H2], 7.75–7.30 (complex
mЈs, 13H, Ar Ϫ H ), 7.26 [d, 1H, 4J(HH) 2.6 Hz, C6H2], 1.49 (s,
9H, C(CH3)3), 1.29 (s, 9H, C(CH3)3), 0.46 (br.s, 3H, BCH3),
Ϫ0.12 [d, 3H, J(PH) 1.9 Hz, AlCH3]. 13C NMR: δ (cation part
only) 172.59 (HC᎐N), 160.27, 148.11 [d, J(PC) 12.6 Hz], 143.97,
᎐
141.74, 120.73 [d, J(PC) 40.2 Hz], 119.46 (6 aryl quaternaries,
7th is obscured), 136.79, 136.59, 134.66, 134.11, 133.54, 131.47
422
J. Chem. Soc., Dalton Trans., 2002, 415–422