Palladium-catalyzed cross-methylation of haloarenes possessing active hydrogen atoms by intramolecularly stabilized dimethylindium and dimethylaluminum reagents

Article abstract of DOI:10.1002/1099-0690(200205)2002:10<1628::aid-ejoc1628>3.0.co;2-c

While the intramolecularly stabilized aluminum complex [(CH₃)₂AlOCH₂CH₂ N(CH₃)₂]₂ (2a) reacts readily with 4-bromophenol to give methane and [(4-BrC₆H₄O)

Full text of DOI:10.1002/1099-0690(200205)2002:10<1628::aid-ejoc1628>3.0.co;2-c

FULL PAPER
Palladium-Catalyzed Cross-Methylation of Haloarenes Possessing Active
Hydrogen Atoms by Intramolecularly Stabilized Dimethylindium and
Dimethylaluminum Reagents
Nimer Jaber,[a] Dmitri Gelman,[a] Herbert Schumann,*[b] Sebastian Dechert,[b] and
Jochanan Blum*[a]
Keywords: Aluminum / Cross coupling / Indium / N,O ligands
While the intramolecularly stabilized aluminum complex
[(CH3)2AlOCH2CH2N(CH3)2]2 (2a) reacts readily with 4-bro-
mophenol to give methane and [(4-BrC6H4O)2Al-
The cross-methylation by 2c can be carried out under an am-
bient atmosphere. The ring-bound bromine atoms in 7 are
replaced by CH3 groups when treated with an excess of the
OCH2CH2N(CH3)2]2 (7), the demethylation of the analogous methylation reagent 2a, and the resulting aluminum cre-
indium complex [(CH3)2InOCH2CH2N(CH3)2]2 2c is very
slow. This inertness of 2c enables it to cross-methylate bromo-
phenols and other bromoarenes with active hydrogen atoms
in the presence of soluble palladium phosphane catalysts.
solate liberates 4-methylphenol upon hydrolysis.
( Wiley-VCH Verlag GmbH, 69451 Weinheim, Germany,
2002)
Introduction
compounds have lately been observed also with some other
organoindium complexes that, under oxygen-free condi-
In the course of our studies on cross-coupling processes tions, are quite stable, even in the presence of water.[6] Tak-
by intramolecularly stabilized group 13-metal alkylating ami et al.[7] found that triphenyl- and trivinylindium, as well
agents,[1Ϫ5] we found that in the presence of palladium cata- as bis(4-methoxyphenyl)indium chloride, react in wet THF
lysts, aryl chlorides, bromides and triflates react readily with with iodo- and bromoarenes that have active hydrogen
the aluminum reagents 1a and 2a to give the corresponding atoms. Trimethylindium, however, was found to form only
methylarenes. Aryl halides and pseudohalides that have vul- traces (3%) of methylated products. We now report on the
nerable substituents such as aldehyde, ketone or bromome- conditions for the smooth, selective cross-methylation of
thyl moieties, however, undergo cross-methylation in a non- haloarenes with active hydroxyl, carboxyl and amino
selective fashion as both reactive groups are affected by the groups under an ambient atmosphere by the intramolecul-
reagents. The gallium analogs of 1a and 2a (i.e. 1b and 2b) arly stabilized complexes 1c and 2c.
do not attack carbonyl, cyano, bromomethyl or nitro
groups,[1] but react rather slowly as cross-coupling reagents,
and are often deactivated by electron-releasing groups loc-
ated in the ortho or para positions.[4] The application of in-
tramolecularly stabilized indium complexes was shown to
overcome these shortcomings. Complexes 1c and 2c were
found to react nearly as fast as the aluminum compounds,
they are not deactivated by ring-bonded alkyl or alkoxyl
groups, and do not attack vulnerable groups other than the
ring-attached halide or triflate functions.[4] Diminished re-
activity and the ability to withstand the presence of active
functional groups that are known to destroy alkylmetal
[a]
Results and Discussion
Department of Organic Chemistry, Hebrew University,
Jerusalem 91904, Israel
Fax: (internat.) ϩ 972-2/651-3832
When the aluminum cross-methylation reagent 1a was
treated with halophenols, it reacted readily with the active
hydrogen atoms to give methane. Consequently, the ability
of 1a to participate in palladium-catalyzed cross-methyl-
E-mail: jblum@chem.ch.huji.ac.il
Institut für Chemie, Technische Universität Berlin,
10623 Berlin, Germany
Fax: (internat.) ϩ 49-(0)30/3142-2168
E-mail: schumann@chem.tu-berlin.de
[b]
1628
 WILEY-VCH Verlag GmbH, 69451 Weinheim, Germany, 2002 1434Ϫ193X/02/0510Ϫ1628 $ 20.00ϩ.50/0 Eur. J. Org. Chem. 2002, 1628Ϫ1632

Palladium-Catalyzed Cross-Methylation of Haloarenes
FULL PAPER
ation was destroyed. The analogous indium reagent 1c, of the transient reaction intermediates 3Ϫ6 has not been
however, was found to convert 4-bromophenol, under oxy- separated, although the formation of these methylalumi-
1
gen-free conditions, in the presence of [Pd(PPh3)4], into 4- num compounds has been confirmed by recording the H
methylphenol in quantitative yield. The dimethylaluminum NMR spectra of reaction mixtures of 2a in C6D6 during
aminoethoxide derivative 2a was found to react with 4-bro- gradual addition of limited quantities of 4-bromophenol.
mophenol, similarly to complex 1a, to give methane. How- While the CH3 signal of 2a at δ ϭ Ϫ0.57 decreases, signals
ever, the aluminum-containing product still proved capable at δ ϭ Ϫ0.556, Ϫ0.559, Ϫ0.560 (5), Ϫ0.561, and Ϫ0.63 (3)
of taking part in cross-coupling reactions in the presence appear and then disappear until, after addition of four
of an excess of methylation reagent. After quenching with equivalents of the phenol, no CH3 signals are left. During
hydrochloric acid the expected 4-methylphenol was formed. this operation, four transient AB quadruplets of 3Ϫ6 cent-
The dimethylindium aminoethoxide derivative 2c cross- ered at δ ϭ 7.048, 7.109, 7.165, and 7.396 are formed, and
methylates 4-bromophenol under an ambient atmosphere ultimately converted into the AB quadruplet of 7, centered
even when a relatively low [reagent]:[phenol] ratio was used at δ ϭ 7.035.
(see Table 1). The different behavior of 2a and 2c towards
4-bromophenol is rationalized in terms of two phenomena:
(i) the difference in rate of the reactions of the reagents with
the phenol, and (ii) the different mechanisms by which 2a
and 2c react. In a series of comparative experiments, we
have monitored the rate of methane formation from 4-bro-
mophenol and 2a, 2b and 2c by gasometric analysis. Ini-
tially, we treated a benzene solution of 0.38 mmol of 2a at
room temperature with 0.152 mmol of 4-bromophenol (i.e.
4 mol of the phenol was added for each mol of the dialumi-
num reagent). The reaction, which started immediately, af-
forded the first two equivalents (17 mL) of methane within
6 min, and the remaining two equivalents within the next
18 min. Realizing the difference in rate between the reaction
of the first and the second aluminum-attached CH3 groups,
we repeated the experiment with just 0.76 mmol of 4-
bromophenol per 0.38 mmol of the bimetallic reagent. The
calculated amount of 17 mL of methane was now evolved
Scheme 1
within 7 min. Replacement of 2a by the indium complex 2c
The structure of 7 has been determined by X-ray diffrac-
led to the formation of 17 mL of methane only after 5 h. tion analysis. The compound is dimeric in the solid state,
The gallium reagent 2b proved to react even more slowly, bridged by the oxygen atoms of the aminoethoxy ligand
and furnished only 8 mL of gas (47% of the calculated (see Figure 1). The coordination number of aluminum is
amount) after 15 h.
five and the coordination geometry corresponds to a dis-
During the evolution of methane in the reaction of 2a torted trigonal bipyramid with the coordinating oxygen and
and 4-bromphenol ([2a]:[4-BrC6H4OH] ϭ 1:4) the four CH3 nitrogen atoms in the axial positions. The equatorial posi-
groups are gradually replaced by 4-BrC6H4O moieties, as tions are occupied by the two oxygen atoms of the 4-bromo-
outlined in Scheme 1. When the evolution of methane is phenoxy ligand and the bridging alkoxide oxygen of the
complete pure 7 remains as the only product. The mixture aminoethoxy ligand. The shortest AlϪO distances are
Table 1. Effect of the molar ratio [substrate]:[methylation reagent] in cross-methylation of 4-BrC6H4OH with complexes of type 2 in the
[a]
presence of PdCl2(PPh3)2
Entry
Methylation
reagent
Molar ratio
Reaction time
(h)
Isolated
4-methylphenol (%)
reagent:4-BrC6H4OH[b]
1
2
3
4
5
6
7
8
9
2a
2a
2a
2a
2b
2c
2c
2c
2c
2c
0.5
1
1.5
2
3
0.5
1
1.5
2
3
24
2
2
2
24
2
2
2
2
2
0
Ͻ1[c]
57
96
0
15
37
54
75
96
10
[a]
[b]
Reaction conditions: 0.38 mmol 4-BrC6H4OH; ratio of [substrate]:[PdCl2(PPh3)2] ϭ 1:25, 2.2 mL benzene; 80 °C.
‘‘Molecular
[c]
weights’’ of monometallic rather than dimetallic reagents are used. Ͻ2% after 24 h.
Eur. J. Org. Chem. 2002, 1628Ϫ1632
1629

N. Jaber, D. Gelman, H. Schumann, S. Dechert, J. Blum
FULL PAPER
Figure 1. ORTEP diagram of 7; thermal ellipsoids are shown at the 30% probability level; hydrogen atoms are omitted for clarity; selected
˚
bond lengths (A) and bond angles ( °): AlϪO(1) 1.813(8), AlϪO(1)Ј 1.879(8), AlϪO(2) 1.727(9), AlϪO(3) 1.726(8), AlϪN 2.097(9);
AlϪO(1)ϪAlЈ 104.5(4), O(1)ϪAlϪN 81.5(4), O(1)ϪAlϪO(2) 120.2(4), O(1)ϪAlϪO(3) 121.8(4), O(1)ЈϪAlϪN 157.0(4), O(1)ЈϪAlϪO(2)
100.6(4), O(1)ЈϪAlϪO(3) 93.0(4), O(2)ϪAlϪO(3) 118.0(4), NϪAlϪO(2) 91.5(4), NϪAlϪO(3) 98.6(4); symmetry transformation used to
generate equivalent atoms: (Ј)Ϫx ϩ 1, Ϫy ϩ 1, Ϫz ϩ 1
˚
˚
found for the aluminum phenoxy bonds (1.73 A) and are AlϪN distance (2.10 A) and the OaxialϪAlϪN bond angle
similar to the bond lengths reported for similar com- (157.0°) are similar to the values found for [Me2Al-
[10]
pounds.[8] The central Al2O2 ring is perfectly planar. The (µ-OCH2CH2NMe2)]2 (2.13 A/151.7°).
˚
two AlϪO distances within the ring are different
In the presence of a palladium catalyst the bromine
(AlϪOequat. 1.81 A/AlϪOaxial 1.88 A). This is a typical fea- atoms in the bromophenoxy complexes 3Ϫ7 can react with
ture of five-coordinate dimeric aluminum alkoxides.[9] The excess 2a. Hydrolysis of the resulting aluminum-derived cre-
˚
˚
Table 2. Palladium-catalyzed cross-methylation of some halo- and pseudohaloarenes possessing active hydrogen atoms by the indium
reagent 2c[a]
Entry
Substrate
Ratio of
[2c]:[substrate]
Product
Yield after
2 h (%)[b]
1
2
3
4
5
2-bromophenol
3-bromophenol
4-bromophenol
4-iodophenol
2
2
2
2
2
2-methylphenol
3-methylphenol
4-methylphenol
4-methylphenol
4-methylphenol
33
99
75
33
8[c]
4-hydroxyphenyl
trifluoromethenesulfonate
4-bromo-1,3-benzenediol
4-bromobenzyl alcohol
4-bromobenzoic acid
5-bromo-2-hydroxybenzoic acid[3]
2-bromo-3,5-hydroxybenzoic acid[e]
4-bromoaniline
6
7
8
3
1
2
3
4
3
4
4-methyl-1,3-benzenediol[11]
4-methylbenzyl alcohol
4-methylbenzoic acid
40
39[d]
100
[12]
9
5-methyl-2-hydroxybenzoic acid
96
[f]
10
11
12
2-methyl-3,5-hydroxybenzoic acid[13]
4-methylaniline
93[g]
90[g]
5-bromo-2-aminobenzoic acid[d]
5-methyl-2-aminobenzoic acid[14]
[a]
[b]
[c]
[d]
Reaction conditions as in Table 1; 2 h.
The remaining percentage reflect on unchanged substrate. After 20 h.
96% after 22 h.
[e]
[f]
[g]
In THF. 9% after 73 h. The free amine was obtained after neutralization of the reaction mixture.
1630
Eur. J. Org. Chem. 2002, 1628Ϫ1632

Palladium-Catalyzed Cross-Methylation of Haloarenes
FULL PAPER
solates gives 4-methylphenol. Thus, the successful forma- this regard we would like to draw attention to the fact that,
tion of cresol from 4-bromophenol and 2a requires more in general, isolated trialkylindium compounds, prepared by
than one molecule of the reagent for every two molecules conventional methods,[16] react considerably slower than
of the bromophenol. Unlike the cross-methylation of 4-bro- those prepared in situ from organolithium or Grignard re-
mophenol with 2a, the reaction with the indium complex agents.[15] For example, 4Ј-bromoacetophenone, in the pres-
2c seems to proceed by the general mechanism outlined pre- ence of [PdCl2(PPh3)2], has been reported to yield 94% of
viously for cross-coupling of non-hydroxylated aryl halides 4Ј-methylacetophenone and 91% of 4Ј-butylacetophenone
and triflates with reagents of type 1 and 2.[1Ϫ4] Because of with trimethyl- and tributylindium (both prepared in situ),
the slow reaction of the indium complex with the OH group respectively,[15] but only 48 and 46% of the expected prod-
not much indium phenolate is formed. The cross-methyl- ucts under the reported experimental conditions with isol-
ation is not conditioned either by the presence of excessive ated pure trialkylindium reagents. The isolated reagents
reagent or by hydrolysis of the InϪOAr bonds. Indeed, lead to the formation of considerable amounts (21Ϫ25%)
while the monitoring of [PdCl2(PPh3)2]-catalyzed cross- of the homocoupling product 4,4Ј-bis(acetyl)-1,1Ј-biphenyl,
1
methylation of 4-bromophenol by 2c in C6D6 by H NMR along with unchanged starting material. Similar differences
spectroscopy revealed a gradual accumulation of 4-methyl- in yield between the expected cross-coupling products of in
phenol during the process, no phenolic product could be situ prepared, and of isolated, trialkylindium were observed
detected in the analogous reaction with 2a prior to quench- in the [NiCl2(PPh3)2]-catalyzed cross-coupling of 4Ј-chlo-
ing with aqueous hydrochloric acid.
roacetophenone. We therefore assume that the reactions of
The effect of the molar ratio [substrate]:[methylating re- haloarenes with RLi (or RMgX) and InCl3 are cross-coup-
agent] in the cross-methylation of 4-bromophenol with re- ling reactions of alkyllithium (or Grignard) reagents, prob-
agents 2 has been demonstrated by a series of experiments ably catalyzed by the indium salt.
that are summarized in Table 1.
This table indicates that cross-methylation with 2a takes
place at an appreciable rate only when [Al]:[bromophenol]
is greater than 1.5, whereas the indium reagent 2c yields
Conclusions
15% of 4-methylphenol after 2 h even when the ratio is 0.5.
At a [catalyst]:[substrate] ratio above 1:25 the cross-
methylation processes is independent of the amount of cata-
lyst. The rate depends to some extent, however, on the
structure and oxidation state of the palladium complex.
Comparative cross-methylation experiments of 4-bromo-
phenol by 2c at 80 °C in the presence of [PdCl2(PPh3)2],
[Pd(PPh3)4], [Pd(OAc)2(dppp)] and [Pd(dppp)2] under
identical conditions formed, after 2 h, 75, 68, 60, and 0%
cresol, respectively.
Complex 2c cross-methylates not only halo-monophenols
and hydroxy triflates, but also derivatives of resorcinol and
phloroglucinol, as well as other substrates with active hy-
drogen, such as benzylic alcohols, carboxylic acids and
primary amines. Some representative results are listed in
Table 2. Since the indium reagent reacts only slowly with
the active hydrogen atoms, the nature of the active function
has no big effect on the yield. In fact the cross-methylation
of 4-bromophenol, 4-bromobenzoic acid, 4-bromoaniline
and bromobenzene with 2c leads to similar yields of methyl-
ated products under identical conditions.
Direct [PdCl2(PPh3)2]-catalyzed cross-methylation of hal-
ophenols and other haloarenes with active hydrogen atoms,
is a unique feature of the intramolecularly stabilized di-
methylindium reagent 2c. At about 80 °C the interaction of
the reagent with the active hydrogen function is slow
enough to allow preferential attack at the ring-bound hal-
ogen atom. The reagent also withstands the presence of air
and can therefore be used under ambient atmospheric con-
ditions. Unlike the indium reagent, the analogous alumi-
num compound 2a is both air sensitive and reacts rapidly
with phenols to give methane and phenoxyaluminum deriv-
atives. Nevertheless it can also be utilized as a cross-coup-
ling reagent of bromophenol in the presence of an excess of
the dimethylaluminum complex, which initially serves as an
OH-protecting group. In the aluminum-induced cross-
methylation, methylated aluminum phenoxides are formed
and the liberation of the aluminum-free products takes
place only after hydrolysis.
Experimental Section
Attempts to block the OH group in 4-bromophenol with
lithium, sodium or potassium lowered the rate of the cross- General: 1H and 13C NMR spectra were recorded on Bruker AMX-
200, AMX-300, and AMX-400 instruments. MS measurements
were performed on a HewlettϪPackard model 4989A mass spectro-
meter with an HP gas chromatograph model 5890 series II. IR
spectra were recorded on a Bruker model Vector 22 FTIR instru-
ment, and HPLC separations were performed on a Jasco TRI-
ROTAR IV machine equipped with a DG-3510 degasser and
UVIDEC 100-VI UV spectrophotometer. Trimethylindium,[16] tri-
n-butylindium,[16] [3-(dimethylamino)propyl-C,N]dimethylalumi-
coupling, probably owing to the low solubility of the re-
sulting phenolates. Entries 1Ϫ3 in Table 2 indicate the ex-
istance of a mild electronic effect on the rate. A more pro-
nounced influence proved to be caused by steric constraints
(see entries 1, 6 and 10).
For comparison we examined the possibility to cross-
methylate 4-bromophenol (under argon) with trimethylind-
ium. The pure reagent gave only 4% of 4-methylphenol, and
num
(1a),[17]
[3-(dimethylamino)propyl-C,N]dimethylgallium
(1b),[18] [3-(dimethylamino)propyl-C,N]dimethylindium (1c),[18]
a reagent generated in situ from methyllithium and InCl3,
[15]
´
according to Perez et al,
did not form cresol at all. In bis{µ-[2-(dimethylamino)ethanolato-N,O:O]}tetramethyldi-
Eur. J. Org. Chem. 2002, 1628Ϫ1632
1631

N. Jaber, D. Gelman, H. Schumann, S. Dechert, J. Blum
FULL PAPER
aluminum (2a),[19] bis{µ-[2-(dimethylamino)ethanolato-N,O:O]}-
Cross-Coupling of 4-Bromophenol by 2c: In a typical experiment, a
mixture of 4-bromophenol (165 mg, 0.955 mmol), 2c (440 mg,
tetramethyldigallium (2b),[20] and bis{µ-[2-(dimethylamino)ethano-
lato-N,O:O]}tetramethyldiindium (2c)[21] were prepared as de- 0.950 mmol), [PdCl2(PPh3)2] (27 mg, 3.85 ϫ 10Ϫ2 mmol) and
scribed in the literature. 4-Hydroxyphenyl trifluoromethanesulfon-
11 mL of dry benzene was refluxed for 2 h. The cooled reaction
ate was synthesized from 4-aminophenol via the diazonium tetra- mixture was diluted with 50 mL of chloroform followed by acid-
fluoroborate.[22,23]
ification with 15% hydrochloric acid. After phase separation, ex-
traction of the aqueous layer with chloroform, concentration of the
organic phase, and chromatography on silica gel (using ether as
eluent), 70 mg (68%) of 4-methylphenol and 38 mg (23%) of un-
changed starting material were obtained.
Bis{µ-[2-(dimethylamino)ethanolato-N,O:O]}tetrakis(4-bromo-
phenoxy)dialuminum (7): A solution of freshly recrystallized 4-bro-
mophenol (2.81 g, 16.24 mmol) in a mixture of 15 mL of benzene
and 15 mL of hexane was added dropwise under argon at room
temperature to a stirred solution of 2a (1.19 g, 4.10 mmol) in 15 mL
n-hexane. Vigorous evolution of a gas started immediately. After
ca 30 min the formation of the methane was complete. The heavy
precipitate of colorless 7 was collected and recrystallized from tolu-
Experiments with air-sensitive aluminum and gallium reagents, as
well as those with bis(diphenylphosphanylpropane)palladium
[Pd(dppp)2], [Pd(AcO)2(dppp)], and [Pd(PPh3)4] were conducted
under argon in a thick-walled sealed pressure tube, thermostatted
at 80 Ϯ 0.2 °C. Some reactions were carried out in THF in the
same manner as in benzene but the workup required removal of
the solvent under reduced pressure prior to the quenching with
hydrochloric acid. Representative results of the cross-methylation
of 4-bromophenol under different conditions and the reaction of
some other haloarenes with active hydrogen atoms are summarized
in Table 1 and 2.
1
ene. Yield 3.27 g (87%); m.p. (sealed capillary) 231 °C.; H NMR
(300 MHz, CDCl3): δ ϭ 2.35 (s, 12 H, CH3), 2.55 (t, J ϭ 6.0 Hz,
4 H, NCH2), 3.73 (t, J ϭ 6.0 Hz, 4 H, OCH2), 6.81, 7.30 (ABq,
JAB ϭ 9 Hz, 16 H, ArH). 13C{1H} NMR (75 MHz, CDCl3): δ ϭ
45.31, 56.84, 58.17, 109.82, 120.98, 132.28, 159.21.
C32H36Al2Br4N2O6 (918.2): calcd. C 41.86, H 3.95, N 3.05; found
C 41.88, H 4.02, N 2.86.
A suitable crystal for X-ray diffraction analysis was obtained by
slow recrystallization from toluene. The X-ray data were obtained
by using a Siemens SMART-CCD diffractometer, ω-scans, Mo-Kα
˚
radiation (λ ϭ 0.71093 A), graphite monochromator, T ϭ 293 K,
Acknowledgments
SADABS[24] for absorption correction (Tmax ϭ 0.4080, Tmin
ϭ
0.1493), structure solution with direct methods and refinement
against F2 (SHELX-97)[25] with anisotropic thermal parameters for
all non-hydrogen atoms, hydrogen positions with fixed isotropic
We thank the United States-Israel Binational Science Foundation
(BSF, grant No. 2000013), the Fonds der Chemischen Industrie, the
Deutsche Forschungsgemeinschaft (Graduiertenkolleg ‘‘Syntheti-
sche und reaktionstechnische Aspekte von Metallkatalysatoren’’),
and the Exchange Program between the Hebrew University of Jeru-
salem and the Technische Universität, Berlin for financial support
of this study.
2
˚
thermal parameters (Uiso ϭ 0.08 A ) on calculated positions; crys-
tal dimensions 0.54 ϫ 0.36 ϫ 0.10 mm, orthorhombic, space group
˚
˚
˚
Pbca, a ϭ 12.6169(3) A, b ϭ 15.9490(2) A, c ϭ 18.9354(5) A, V ϭ
3810.31(14) A , Z ϭ 4, ρcalcd. ϭ 1.601 ϫ 103 kg mϪ3, µ ϭ 4.313
3
˚
mmϪ1, F(000) ϭ 1824; data collection 4.3θ Յ 2θ Յ 48.0θ, -13 Յ h
Յ 13, -18 Յ k Ͻ 17, -21 Յ l Յ 6, 9549 data were collected, 2938
unique data (Rint ϭ 0.1452), 1151 data with I Ͼ 2σ(I), 210 refined
parameters, GOF(F2) ϭ 1.007, final R indices (R1 ϭ Σ||F0| Ϫ |Fc||/
[1]
J. Blum, D. Gelman, W. Baidossi, E. Shakh, A. Rosenfeld, Z.
Aizenshtat, B. C. Wassermann, M. Frick, B. Heymer, S.
Schutte, S. Wernik, H. Schumann, J. Org. Chem. 1997, 62,
8681Ϫ8686.
Σ|Fo|, wR2 ϭ [Σw(F02 Ϫ F2c)2/Σw(F02)2]1/2), R1 ϭ 0.0898, wR2
ϭ
0.1736, max./min. residual electron density 0.688/Ϫ0.699 eAϪ3. An
ORTEP drawing of 7 is shown in Figure 1. CCDC-174124 contains
the supplementary crystallographic data for this paper. These data
can be obtained free of charge at www.ccdc.cam.ac.uk/conts/re-
trieving.html [or from the Cambridge Crystallographic Data
Centre, 12, Union Road, Cambridge CB2 1EZ, UK; Fax: (in-
ternat.) ϩ44-1223/336-033; E-mail: deposit@ccdc.cam.ac.uk].
˚
[2]
J. Blum, D. Gelman, Z. Aizenshtat, S. Wernik, H. Schumann,
Tetrahedron Lett. 1998, 39, 5611Ϫ5614.
J. Blum, O. Berlin, D. Milstein, Y. Ben-David, B. C. Wasserm-
[3]
ann, S. Schutte, Synthesis 2000, 571Ϫ575.
J. Blum, J. A. Katz, N. Jaber, M. Michman, H. Schumann, S.
[4]
Schutte, J. Kaufmann, B. C. Wassermann, J. Mol. Catal. A:
Chem. 2001, 165, 97Ϫ102.
D. Gelman, G. Höhne, H. Schumann, J. Blum, Synthesis
[5]
Monitoring of the Reaction of 4-Bromophenol with 2a, 2b and 2c: A
round bottomed flask equipped with a gasometer was charged at 24
°C under oxygen-free conditions with a solution of the aluminum
complex 2a (110 mg, 0.38 mmol) in 3 mL of dry benzene. A solu-
tion of 4-bromophenol (263 mg, 1.52 mmol) in 6 mL of the same
solvent was injected into this solution through a rubber septum.
Evolution of the calculated volume of the first 0.76 mmol (17 mL)
of methane took 6 min. The remaining 0.76 mmol of gas evolved
during the next 18 min. Upon repetition of the experiment with just
0.76 mmol of 4-bromophenol the evolution of the gas was complete
within 7 min.
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