Dialkylaluminium complexes derived from 1,8-diphenyl-3,6- dimethylcarbazole: A new sterically hindered monodentate ligand system

Article abstract of DOI:10.1016/S0022-328X(03)00174-8

A new type of sterically hindered, monodentate ligand system based on the carbazolide frame is introduced. (1,8-diphenyl-3,6- dimethylcarbazolide)AlR₂ (4, R=Me; 5, R=Et) complexes have been prepared by N-lithiation of the carbazole, followed by

Full text of DOI:10.1016/S0022-328X(03)00174-8

Journal of Organometallic Chemistry 673 (2003) 95ꢂ101
/
www.elsevier.com/locate/jorganchem
Dialkylaluminium complexes derived from 1,8-diphenyl-3,6-
dimethylcarbazole: a new sterically hindered monodentate ligand
system
Stefan K. Spitzmesser, Vernon C. Gibson *
Department of Chemistry, Imperial College, South Kensington, Exhibition Road, London SW7 2AZ, UK
Received 10 February 2003; received in revised form 18 March 2003; accepted 19 March 2003
Abstract
A new type of sterically hindered, monodentate ligand system based on the carbazolide frame is introduced. (1,8-diphenyl-3,6-
dimethylcarbazolide)AlR2 (4, RꢀMe; 5, RꢀEt) complexes have been prepared by N-lithiation of the carbazole, followed by
reaction with the appropriate dialkylaluminium chloride. Treatment of the dialkyl complexes 4 and 5 with B(C6F5)3 or
/
/
[H(OEt2)2][B{3,5-(CF3)2C6H3}4] affords [LAlR]ꢁ species followed by products arising from alkyl/ArF exchange. The cationic
alkylaluminium species are found to oligomerise ethylene to C4Ã
/C10 olefinic products.
# 2003 Elsevier Science B.V. All rights reserved.
Keywords: Aluminium; Carbazole; Ethylene; Polymerisation
1. Introduction
where the presumed active species involves three or
four-coordinate cationic alkylaluminium centres, respec-
tively. Their ethylene polymerisation activities, however,
have proved to be relatively low [20], and recent
computational studies by Budzelaar and co-workers
have indicated that the barriers to ethylene insertion
may be too high to allow efficient chain propagation
Low-coordinate metal complexes are of great interest
in coordination chemistry and catalysis for their ability
to generate highly reactive metal centres capable of
mediating unusual transformations. Recently a two-
coordinate AlI complex [1] and a three-coordinate FeII
species [2] based on sterically demanding b-diketiminate
ligands have been isolated and structurally charac-
terised. These bulky ligands have also been successfully
[21ꢂ23]. We, therefore, decided to target aluminium pre-
/
?
catalysts of the type R2NAlR2 where the amide is a
sterically hindered carbazolide ligand with the potential
not only to stabilise mononuclear three-coordinate
employed to stabilise three-coordinate Mg [3,4], Zn [5ꢂ
7] and Sn [8] centres, and complexes of this type show
remarkable activities in the polymerisation of lactide [7ꢂ
/
precatalysts but also two-coordinate cationic alkyl
ꢁ
/
?
species of the type [R2NAlR] . Complexes of the type
10], methylmethacrylate [11] and for the co-polymerisa-
tion of CO2 with epoxides [5].
?
R2NAlR2 generally form aggregates ranging from
dimers to higher oligomers [24], but with bulky sub-
stituents R and/or R?, rare examples of monomeric
complexes with three-coordinate aluminium centres
We [12,13], and others [14ꢂ19], have been investigat-
/
ing the possible use of cationic alkylaluminium species
in the polymerisation of olefins. To date, these studies
have involved bi- and tri-dentate N-donor ligands,
have been isolated and structurally characterised [25ꢂ
/
29]. A potentially useful additional facet of the diphe-
nylcarbazole system is the positioning of phenyl sub-
stituents close to the metal centre, which may be able to
lend stability to cationic species through weak AlÁ Á ÁPh
interactions. Here we describe the synthesis of alumi-
* Corresponding author. Tel.: ꢁ
7594-5810.
E-mail address: v.gibson@imperial.ac.uk (V.C. Gibson).
/
44-20-7594-5830; fax: ꢁ44-20-
/
0022-328X/03/$ - see front matter # 2003 Elsevier Science B.V. All rights reserved.
doi:10.1016/S0022-328X(03)00174-8

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S.K. Spitzmesser, V.C. Gibson / Journal of Organometallic Chemistry 673 (2003) 95ꢂ101
/
nium complexes bearing the novel sterically demanding
1,8-diphenyl-3,6-dimethylcarbazolide ligand, their reac-
tivity towards Lewis and Brønsted acids and their
potential as ethylene polymerisation catalysts.
was isolated as a bright yellow, air and moisture
sensitive solid, which is highly fluorescent in solution.
Since the reaction was carried out in heptane no
additional donor is coordinated to the Li atom, as
1
confirmed by H-NMR and 13C-NMR spectroscopy as
well as by elemental analysis. Compound 3 is, therefore,
tentatively formulated as a mononuclear base-free
lithium species. Additional stabilisation of the one-
coordinate lithium atom might be provided through
interactions with the p-system of the phenyl rings. All
attempts to obtain single crystals suitable for an X-ray
analysis were unsuccessful.
2. Results and discussion
2.1. Synthesis of diphenylcarbazolide Al complexes
1,8-Diphenyl-3,6-dimethylcarbazole (2) is readily pre-
pared from the corresponding 1,8-dibromocarbazole 1
The lithium carbazolide species 3 is a useful precursor
for the synthesis of the Al complexes 4 and 5 via salt
[30] via
a Suzuki cross-coupling reaction using
Pd(PPh3)4 as the catalyst under typical reaction condi-
tions [31] (Scheme 1).
metathesis using R2AlCl (RꢀEt, Me). Both complexes
/
were isolated in moderate yields as yellow, air sensitive
Several attempts were made to form metal complexes
directly via the reaction of ligand precursor 2 with
trialkylaluminium reagents. Reactions were carried out
with 2 and one equivalent Me3Al or Me3Al(CH3CN) in
C6D6, CD3CN and d8-toluene solutions in NMR tubes
at elevated temperatures. In all cases no complexation
was observed as indicated by the persistence of the
1
solids. In the H-NMR spectrum of 4 (Fig. 1), a singlet
resonance for the aluminium bonded methyl protons
(Ha) is found at ꢃ
the range (typically ꢃ
/
1.33 ppm, which is shifted upfield of
0.23 to ꢃ0.99 ppm) usually
/
/
observed for neutral LAlMe2 complexes, e.g. those
containing imino-amide [14], troponiminate [15], b-
diketiminate [32] and amidinate [33] ligands. This is
possibly due to a ring-current effect arising from the
proximal phenyl substituents, which may lead to mag-
resonance for the NÃ/H proton in C6D6 and d8-toluene
solutions, even after several days. This was unexpected
since aluminium alkyls generally react with amines and
alcohols readily at ambient temperature with concomi-
netic shielding of the AlÃ
/
Me protons. The 13C-NMR
8.5 ppm, lies
resonance for the AlÃMe carbons, at ꢃ
/
/
tant elimination of the corresponding alkane [13ꢂ15].
/
within the range typically found for LAlMe2 complexes.
The 1H-NMR spectrum of the diethylaluminium
complex 5 is analogous to that for 4. A quartet at
When the reaction of 2 with the Me3Al(CH3CN)
precursor was carried out in CD3CN solution in a
sealed NMR tube, the resonance for the NÃ
/
H proton
ꢃ0.95 ppm is attributed to the aluminium-bonded
/
diminished in intensity but no signal attributable to an
2
aluminium methyl species appeared. H-NMR spectro-
methylene protons along with an associated triplet at
0.56 ppm due to the CH3 protons of the ethyl unit. Both
of these resonances are shifted considerably upfield
compared with the usual chemical shift ranges found
scopy confirmed the formation of the N-deuterated
carbazole, 2-d1, indicated by a resonance for the N-
bound deuterium at 8.40 ppm (in CH2Cl2).
Deprotonation of 2 was achieved using nBuLi in
heptane solution and the corresponding lithium salt 3
for the methyl (0.91ꢂ
/
1.21 ppm) and methylene units
(0.14ꢂ0.52 ppm) of diethylaluminium species [14,15,33].
/
Solution structures for 4 and 5 in which the phenyl
substituents lie orthogonal to the carbazolide backbone
and with the aluminium centres sandwiched between the
aromatic groups, are proposed.
2.2. Reactivity towards Lewis and Brønsted acids
In earlier reports of ethylene polymerisation catalysts
based on aluminium, the dialkyl precursors are con-
verted into cationic alkyl complexes by alkyl abstraction
or protonation with suitable Lewis or Brønsted acids
such as B(C6F5)3, [CPh3][B(C6F5)4], [PhNMe2H]-
[B(C6F5)4] or [H(OEt2)2][B{3,5-(CF3)2C6H3}4] [12ꢂ16].
/
These cationic alkylaluminium complexes are readily
1
characterised by H-NMR and 19F-NMR spectroscopy
[17,18,33,34], and in rare cases the molecular structure
has been determined by X-ray analysis [19].
In a NMR-scale experiment, equimolar quantities of 4
and B(C6F5)3 were dissolved in CD2Cl2. Within 15 min a
Scheme 1. Synthesis of diphenylcarbazolide complexes 4 and 5.

S.K. Spitzmesser, V.C. Gibson / Journal of Organometallic Chemistry 673 (2003) 95ꢂ
/101
97
Fig. 1. 1H-NMR spectrum of 4 in CD2Cl2 (*CHDCl2).
broad singlet at 0.44 ppm was apparent along with
cationic methylaluminium intermediate 6 is highly
reactive and abstracts C6F5 from [MeB(C6F5)3] to give
7 and MeB(C6F5)2. Similar reactivity has been observed
in the reaction of B(C6F5)3 with dimethylaluminium
complexes bearing amidinate [18,33], salicylaldimine [34]
and b-diketiminate [39] ligands.
resonances at ꢃ
/
167.5, ꢃ
/
164.8 and ꢃ133.5 ppm in the
/
19F-NMR spectrum. These chemical shifts are consistent
with the formation of a non-coordinated [MeB(C6F5)3]
1
anion rather than a contact ion pair [16,35]. In the H-
NMR spectrum, a singlet resonance at ꢃ1.11 ppm is
/
A NMR tube containing a solution mixture of 6 and 7
was charged with ethylene (1 bar) and sealed. Over a
period of several days, very slow conversion of ethylene
to higher olefins was observed. A 1H-NMR spectrum on
the volatile products revealed multiplets centred at 0.90,
1.61 and 5.45 ppm, in a ratio of 2:28:5, respectively,
consistent with internal olefins. This was confirmed by
attributed to the aluminium-bonded methyl group of the
counter-cation [LAlMe]ꢁ present in 6, while a reso-
nance at 7.88 ppm is assigned to the aromatic protons of
the carbazolide ligand. Monitoring the progress of the
reaction over a period of 24 h revealed that the
aluminium-bonded methyl protons of 4 slowly disap-
peared, but the signal corresponding to the non-coordi-
nated anion [MeB(C6F5)3] did not gain in intensity. The
1H-NMR spectrum of the solution after 24 h (Fig. 2)
reveals that a further reaction has taken place (the
residual signals due to 6 are indicated by #) (Scheme 2).
The spectrum is consistent with LAl(Me)C6F5 (7) as
the predominant product. Notably, the high-field triplet
GC and GCꢂ
showed the presence of exclusively internal C4Ã
/
MS analysis of the NMR solution, which
C10
/
olefins (all isomers). The mechanism of formation of
internal olefins has not been elucidated, but initial
formation of terminal olefins followed by an aluminium
catalysed dimerisation or isomerisation process is prob-
able. Olefin dimerisation reactions catalysed by alumi-
nium compounds are well documented and they
generally proceed at slow rates [40].
Reaction of the diethyl complex 5 with B(C6F5)3 leads
to similar results to those obtained with 4, but the major
reaction product 8 is less stable and partial decomposi-
tion of this species to unidentified products occurs as the
reaction proceeds. Complex 8 gives rise to characteristic
resonances for the aluminium-bonded ethyl unit (a
resonance at ꢃ
/
1.02 ppm is characteristic of an AlÃ
/Me
group (Ha) coupled to the two equivalents ortho-
fluorines of a coordinated C6F5 unit. The MeB(C6F5)2
side product of this reaction gives rise to a characteristic
quintet at 1.68 ppm for the protons of the boron-bonded
methyl group (Hb) coupled to four equivalents ortho-
phenyl fluorines along with anticipated resonances in
the 19F-NMR spectrum [36ꢂ
38]. These observations,
/
together with the initial formation of the [MeB(C6F5)3]
anion, indicates a reaction pathway involving abstrac-
tion of an aluminium-bonded methyl group from 4 by
B(C6F5)3. The resultant coordinatively unsaturated
quartet at ꢃ0.61 ppm and a triplet at 0.69 ppm), and
/
the EtB(C6F5)2 side product (a triplet at 1.13 ppm and a
quartet at 2.10 ppm) is clearly evident [37,41]. There also

98
S.K. Spitzmesser, V.C. Gibson / Journal of Organometallic Chemistry 673 (2003) 95ꢂ101
/
Fig. 2. 1H-NMR spectrum (CD2Cl2) arising from reaction of 4 with B(C6F5)3: *, residual protio impurity in CD2Cl2; $, signal corresponding to non-
coordinated anion [MeB(C6F5)3]; #, signals attributable to 6.
remains some unreacted B(C6F5)3, as well as [(1,8-
diphenyl-3,6-dimethylcarbazolide)AlEt][EtB(C6F5)3]
which, according to the 19F-NMR spectrum (resonances
spectrum corresponding to the AlMe2 protons in 4 is
replaced instantaneously by a new singlet at ꢃ1.02 ppm,
/
along with a resonance at 0.21 ppm due to methane [42].
Resonances are also present corresponding to free and
coordinated Et2O [43], the latter showing characteristic
quartet (4.60 ppm) and triplet (1.60 ppm) resonances
[38]. These observations are consistent with the forma-
tion of an ether-stabilised cationic methyl species 9
(Scheme 3) arising by protonation of one of the methyl
groups of 4 and elimination of methane [44]. This
species is evidently not very stable and decomposes
over a period of ca. 60 min, as indicated by the
at ꢃ
/
167.7 ꢃ
/
165.0 and ꢃ132.7 ppm), is present as a
/
separated ion pair.
A mixture of several products is obtained upon
reaction of 4 with one equivalent of [CPh3][B(C6F5)4].
1
None of the reaction products can be identified by H-
NMR spectroscopy, but several new signals in the
chemical shift range 0 to ꢃ1.3 ppm indicate the
/
formation of new methylaluminium species. Addition
of ethylene (1 bar) to the product mixture in a NMR-
tube sealed with a Young’s tap results in the formation
of oligomers at a rate and with a product distribution
disappearance of the AlÃ
/
Me resonance at ꢃ1.02 ppm.
/
The decomposition product(s) show no high-field reso-
nances for Al methyl protons, but signals corresponding
to coordinated Et2O remain in evidence. Given the
similar to those observed for 4ꢂB(C6F5)3.
/
A much faster reaction is observed when equimolar
amounts (0.05 mmol) of 4 and [H(OEt2)2][B{3,5-
(CF3)2C6H3}4] are combined in CD2Cl2 at room tem-
propensity for MeꢂC6F5 exchange in cationic systems
/
containing the diphenylcarbazolide ligand, it seems
likely that the main decomposition product of 9 is the
perature. The signal at ꢃ
/
1.33 ppm in the 1H-NMR
Scheme 2. Reaction of the dialkylaluminium complexes 4 and 5 with B(C6F5)3.

S.K. Spitzmesser, V.C. Gibson / Journal of Organometallic Chemistry 673 (2003) 95ꢂ
/101
99
Scheme 3. Reaction of 4 with [H(OEt2)2][B{3,5-(CF3)2C6H3}4].
LAl[C6H3(CF3)2](Et2O) (10) (Scheme 3). However,
H activation involving the
phenyl substituents with concomitant formation of
zole (1) [30], Me3Al(CH3CN) [45], B(C6F5)3 [46,47] and
[H(OEt2)2][B{3,5-(CF3)2C6H3}4] [48]. All other reagents
are commercially available and were used without
further purification.
decomposition of 9 via CÃ
/
methane can not be excluded.
2.3. Conclusions
3.3. 1,8-Diphenyl-3,6-dimethyl-9H-carbazole (2)
A new type of monodentate, anionic ligand derived
from 1,8-disubstituted carbazole has been described.
1,8-Diphenyl-3,6-dimethylcarbazole offers very good
To a solution of 310 mg (0.88 mmol) 1,8-dibromo-3,6-
dimethyl-9H-carbazole (1) and 100 mg (0.09 mmol)
Pd(PPh3)4 in 50 ml toluene was added a solution of 1.52
g (12.5 mmol) phenylboronic acid in 30 ml ethanol,
followed by 9 ml 1 M aqueous Na2CO3 solution. The
resulting yellow suspension was degassed in a stream of
nitrogen and stirred at 80 8C for 16 h. The reaction
mixture was filtered hot and the filtrate was washed with
steric protection of the carbazole NÃ
demonstrated by its reluctance to react with alkylalu-
H deprotonation. Deprotona-
/H proton as
minium reagents via NÃ
/
tion can be achieved using nBuLi as a base and
dialkylaluminium complexes are readily obtained via
salt metathesis reactions using R2AlCl compounds. The
dialkylaluminium products can be converted to cationic
species of the type [LAlR]ꢁ which readily abstract ArF
from the counter-anion. [LAlR]ꢁ species show low
activities for the oligomerisation of ethylene to low
2ꢄ
/
30 ml 1 M aqueous NaOH and 2ꢄ30 ml H2O, dried
/
over MgSO4, filtered, and the solvent was removed on a
rotary evaporator. The crude product was purified by
recrystallisation from hot ethanolꢂ
off-white solid. Yield: 260 mg (85%). M.p. 160ꢂ
RF (SiO2, hexaneꢂ
EtOAc 10:1) 0.40. 1H-NMR (250
/hexane to afford an
/
161 8C.
molecular weight (C4Ã/C10) olefinic products.
/
MHz, CDCl3, room temperature (r.t.)): d (ppm) 2.57 (s,
6H, CH3), 7.25 (s, 2H, Ar-H), 7.37 (m, 2H, Ph-H), 7.49
(m, 4H, Ph-H), 7.64 (m, 4H, Ph-H), 7.86 (s, 2H, Ar-H),
8.32 (br, 1H, NH). 13C{1H}-NMR (63 MHz, CDCl3,
r.t.): d (ppm) 21.4 (CH3), 119.5, 124.1, 124.6, 127, 127.4,
128.1, 129.2, 135.7, 139.1, 139.9 (all Ar-C). IR (KBr):
3. Experimental
3.1. General considerations
3482 (w, n(NÃ
/
H)) cmꢃ1. EIMS (m/e): 347 [M]ꢁ. Anal.
All manipulations of water and/or moisture sensitive
compounds were performed using standard Schlenk and
cannula techniques. 1H- and 13C-NMR spectra were
recorded on a Bruker AC-250 spectrometer. Infrared
Calc. for C26H21N: C, 89.88; H, 6.09; N, 4.03. Found: C,
89.81; H, 5.99; N, 3.91%.
spectra were obtained as KBr discs using a Perkinꢂ
/
3.4. (1,8-Diphenyl-3,6-dimethylcarbazolide)Li (3)
Elmer 1760X FTIR spectrometer. Mass spectra were
recorded on either a VG Autospec or a VG Platform II
spectrometer. Elemental analyses were performed by the
microanalytical services of the Chemistry Departments
of the University of North London and University
College London.
4.3 ml (10.8 mmol) nBuLi (2.5 M in hexane) was
added at r.t. to a solution of 3.06 g (8.8 mmol) 1,8-
diphenyl-3,6-dimethyl-9H-carbazole (2) in 200 ml hep-
tane. The resulting yellow suspension was stirred for 3 h
and then concentrated to 40 ml. The supernatant
solution was separated by filtration and the residue
3.2. Solvents and reagents
washed with 3ꢄ40 ml pentane. After drying in vacuo
/
the product was obtained as a bright yellow, amorphous
1
solid. Yield: 2.6 g (84%). H-NMR (250 MHz, CD2Cl2,
Solvents were purified by standard methods. The
following compounds were prepared according to pub-
lished procedures: 1,8-dibromo-3,6-dimethyl-9H-carba-
r.t.): d (ppm) 2.47 (s, 6H, CH3), 6.97 (s, 2H, Ar-H), 7.27
(m, 2H, Ph-H), 7.41 (m, 4H, Ph-H), 7.63 (m, 4H, Ph-

100
S.K. Spitzmesser, V.C. Gibson / Journal of Organometallic Chemistry 673 (2003) 95ꢂ101
/
H), 7.68 (s, 2H, Ar-H). 13C{1H}-NMR (63 MHz,
CD2Cl2, r.t.): d (ppm) 21.5 (CH3), 119.8, 124.3, 125.1,
127.6, 127.8, 128.4, 129.6, 136.1, 138.7, 139.4 (all Ar-C).
Anal. Calc. for C26H20LiN: C, 88.37; H, 5.70; N, 3.96.
Found: C, 88.26; H, 5.69; N, 3.80%.
and CD2Cl2 was added. This resulted in the formation
of a dark orange solution. The reaction mixture was
kept at r.t. over a period of 24 h and was monitored by
1
1H- and 19F-NMR spectroscopy. H-NMR (250 MHz,
CD2Cl2, r.t.) for (1,8-diphenyl-3,6-dimethylcarbazoli-
5
de)AlMe(C6F5) (7): d (ppm) ꢃ
/
1.02 (t, 3H, J(FH)ꢀ
/
3.5. (1,8-Diphenyl-3,6-dimethylcarbazolide)AlMe2 (4)
1.6 Hz, AlCH3), 2.57 (s, 6H, CH3), 7.12 (s, 2H, Ar-H),
7.06ꢂ
7.68 (m, 10H, Ph-H), 7.93 (s, 2H, Ar-H). 19F-
NMR (235 MHz, CD2Cl2, r.t.) for 7: d (ppm) ꢃ162.8
(2F, m-C6F5), ꢃ154.2 (1F, p-C6F5), ꢃ123.2 (2F, o-
C6F5). 1H-NMR (250 MHz, CD2Cl2, r.t.) for
MeB(C6F5)2: d (ppm) 1.68 (quint, 3H, 5J(FH)ꢀ
1.8
Hz, BCH3). 19F-NMR (235 MHz, CD2Cl2, r.t.) for
MeB(C6F5)2: d (ppm) ꢃ161.9 (4F, m-C6F5), ꢃ147.9
(2F, p-C6F5), ꢃ129.6 (4F, o-C6F5).
The atmosphere in the NMR-tube was replaced after
24 h with ethylene (1 bar). Over a period of 7 days the
formation of internal olefins could be observed,
although not all ethylene was consumed. All volatiles
were then vacum-transferred into another NMR-tube.
1H-NMR (250 MHz, CD2Cl2, r.t.): d (ppm) 0.90 (m,
2H), 1.61 (m, 28H), 5.45 (m, 5H).
/
606 mg (1.80 mmol) 1,8-diphenyl-3,6-dimethylcarba-
zolide)Li (3) were suspended in 50 ml toluene and 1.8 ml
(1.8 mmol) Me2AlCl (1.0 M in hexane) was added at
0 8C. The resulting orange solution was stirred at r.t. for
3 h after which the solvent was removed in vacuo. The
residue was extracted with CH2Cl2. This CH2Cl2 solu-
tion was concentrated to 10 ml and the product
precipitated by the addition of 50 ml pentane. The
supernatant solution was separated by filtration and,
after drying in vacuo, the product obtained as a yellow,
/
/
/
/
/
/
/
1
amorphous solid. Yield: 480 mg (47%). H-NMR (250
MHz, CD2Cl2, r.t.): d (ppm) ꢃ1.33 (s, 6H, AlCH3), 2.56
/
(s, 6H, CH3), 7.10 (s, 2H, Ar-H), 7.45 (m, 2H, Ph-H),
7.60 (m, 8H, Ph-H), 7.90 (s, 2H, Ar-H). 13C{1H}-NMR
(63 MHz, CD2Cl2, r.t.): d (ppm) ꢃ8.5 (AlCH3), 21.3
/
(CH3), 119.8, 126.3, 126.4, 127.1, 127.2, 128.1, 129.3,
136.7, 144.4, 145.3 (all Ar-C). Anal. Calc. for
C28H26AlN: C, 83.35; H, 6.49; N, 3.47. Found: C,
83.27; H, 6.57; N, 3.37%.
3.8. Reaction of 5 with B(C6F5)
27.7 mg (0.064 mmol) (1,8-diphenyl-3,6-dimethylcar-
bazolide)AlEt2 (5) and 32.9 mg (0.064 mmol) B(C6F5)3
were placed into a NMR-tube sealed with a Young’s tap
and CD2Cl2 was added. This resulted in the formation
of a dark orange solution. The reaction mixture was
kept at r.t. over a period of 9 h and was monitored by
3.6. (1,8-diphenyl-3,6-dimethylcarbazolide)AlEt2 (5)
340 mg (0.96 mmol) 1,8-diphenyl-3,6-dimethylcarba-
zolide)Li (3) were suspended in 30 ml toluene and 560 ml
(1.01 mmol) Et2AlCl (1.8 M in toluene) was added at
1H- and 19F-NMR spectroscopy. H-NMR (250 MHz,
1
CD2Cl2, r.t.) for (1,8-diphenyl-3,6-dimethylcarbazoli-
3
ꢃ78 8C. The resulting orange solution was stirred at r.t.
/
de)AlEt(C6F5) (8): d (ppm) ꢃ
/
0.61 (q, 2H, J(HH)ꢀ
/
for 2 h after which the solvent was removed in vacuo.
The residue was extracted with CH2Cl2. After evapora-
tion of the solvent the residue was washed with cold
8.0 Hz, AlCH2CH3), 0.69 (t, 3H, 3J(HH)ꢀ
AlCH2CH3), 2.58 (s, 6H, CH3). 19F-NMR (235 MHz,
CD2Cl2, r.t.) for 8: d (ppm) ꢃ162.7 (2F, m-C6F5),
154.2 (1F, p-C6F5), ꢃ122.6 (2F, o-C6F5). H-NMR
(250 MHz, CD2Cl2, r.t.) for EtB(C6F5)2: d (ppm) 1.13 (t,
3H, 3J(HH)ꢀ
7.5 Hz, BCH2CH3), 2.10 (q, 2H,
3J(HH)ꢀ7.5 Hz, BCH2CH3). 19F-NMR (235 MHz,
CD2Cl2, r.t.) for EtB(C6F5)2: d (ppm) ꢃ161.8 (4F, m-
C6F5), ꢃ148.7 (2F, p-C6F5), ꢃ130.3 (4F, o-C6F5).
/
8.0 Hz,
/
(ꢃ78 8C) pentane. After drying in vacuo the product
/
1
ꢃ
/
/
was obtained as a yellow, amorphous solid. Yield: 178
1
mg (43%). H-NMR (250 MHz, CD2Cl2, r.t.): d (ppm)
/
3
ꢃ
/
0.95 (q, 4H, J(HH)ꢀ
/
7.9 Hz, AlCH2CH3), 0.56 (t,
/
3
6H, J(HH)ꢀ
/
7.9 Hz, AlCH2CH3), 2.56 (s, 6H, CH3),
7.10 (m, 2H, Ar-H), 7.47 (m, 2H, Ph-H), 7.63 (m, 8H,
Ph-H), 7.89 (m, 2H, Ar-H). 13C{1H}-NMR (63 MHz,
/
/
/
CD2Cl2, r.t.):
d
(ppm) 0.9 (AlCH2CH3), 9.1
(AlCH2CH3), 21.3 (CH3), 119.8, 126.3, 126.4, 126.8,
127.2, 128.1, 129.2, 133.3, 144.6, 145.2 (all Ar-C).
Accurate elemental analysis could not be obtained due
to the extreme air and moisture sensitivity of the
compound.
Acknowledgements
The authors are grateful to BP Chemicals Ltd. for
financial support of this work.
3.7. Reaction of 4 with B(C6F5)3 and ethylene
References
14.9 mg, 0.037 mmol (1,8-diphenyl-3,6-dimethylcar-
bazolide)AlMe2 (4) and 18.9 mg (0.037 mmol) B(C6F5)3
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