A R T I C L E S
Miao et al.
respectively. Similar to the results of propargyl bromide 4a,
the yields observed for the hydrolysis products, 2-butyne and
1,2-butadiene, were only around 5% at the end of the reaction,
presumably due to the volatility of these compounds.
peaks at lower field could be observed. This was the set of
signals generated when 3-bromo-1-butyne (4c) was reacted with
indium bromide in deuterated THF under ultrasound irradiation,
thus confirming its allenylindium(III) 8c structure. The other
1
set of peaks at higher field in H NMR spectra was assigned
The relative reactivity of 5b and 6b toward aldehyde was
also tested in the same manner as that for 7a and 8a. At the
stage when both the indium(I) 5b and indium(III) 6b were in
almost equal amount, 0.1 equiv of 4-chlorobenzaldehyde was
added to the mixture as a THF-d8 solution. After 3 min, NMR
spectroscopy showed that most of the indium(I) intermediate
5b had reacted while the indium(III) 6b was still present. A
further quantity of 0.3 equiv of 4-chlorobenzaldehyde was then
added in one portion and this time, all the organoindium
intermediates disappeared in 2 min concomitant with the
formation of E-1-(4-chlorophenyl)-2, 5-dimethyl-2,5,6-hep-
tatrien-1-ol as the only product according to proton NMR
spectroscopy.14h The results are therefore similar to that of 7a
and 8a in that the reactions between organoindium intermediates
5b and 6b with aldehyde were fast processes, and the organo-
indium(I) intermediate 5b was a more reactive species than the
indium(III) intermediate 6b.
therefore to have the allenylindium(I) 7c structure.
Theoretical Calculations
Ab initio and density functional calculations were carried out
with the GAUSSIAN 98 program to study structures and relative
stabilities of allenylindium(I, III) and propargylindium(I, III).20
All geometries were first fully optimized by the HF/6-31+G*
method and then further optimized by the B3LYP/6-311+G*
method.21 The Lanl2dz basis set with Effective Core Potentials
(ECP)22 was used for indium and bromide in all calculations.
Vibration frequencies were calculated for each structure, based
on which free energies were calculated. As far as we are aware,
there have been no previous theoretical studies on the structures
and reactivities of organoindium compounds.
Propargyl/allenyl indiums. B3LYP/6-311+G* geometric
optimization of propargylindium(I) (5a) and allenylindium(I)
(7a) led to only one structure, which is a π-complex of
allenylindium(I) (7a-Pi).23 Propargylindium(III) dibromide (6a)
and allenylindium(III) dibromide (8a) were calculated to be
stable in σ-complexes with the B3LYP method. Allenylindium-
(III) dibromide (8a) is calculated to be more stable than
propargylindium(III) dibromide (6a) by 6.5 kcal/mol at the
B3LYP method. Recently, Reich provided evidence that some
allenyl-propargyllithium compounds may adopt localized or
bridged structures depending on the solvent used.24 We therefore
also calculated structures 5-8a(H2O) with one water molecule
coordinated to the indium atom. As shown in Figure 4, a
σ-complex is obtained for each structure. The coordination of
the water molecule reduces the energetic preference of the
allenylic form of both In(I) and In(III) species somewhat. In
any case, the calculations clearly suggest that allenylindium
should be much more stable than propargylindium for these
unsubstituted propargyl/allenyl systems, in agreement with the
experimental observation.
3-Bromo-1-Butyne (4c). The reaction of 4c (R2 ) R3 ) H,
R4 ) Me) with indium in aqueous media was also found to be
fast. In a mixed solvent of D2O/THF-d8 (4:1) and at low
temperature (3 °C), the reaction system became a gellike mixture
within one minute and therefore, was difficult to be monitored
by NMR spectroscopy. Nevertheless, using equal amounts of
THF-d8 and D2O, the reaction gave much better results. At 30
1
s, three new sets of peaks clearly showed up in the H NMR
spectra and one set was assigned to be 1,2-butadiene that should
be the hydrolysis product. The other two sets of peaks were at
4.98 (m, 1H), 4.46 (m, 1H), 1.56 (m, 3H) and 4.84 (m, 1H),
4.34 (m, 1H), 1.50 (m, 3H), respectively, and were consistent
with the allenic structure. When 4-chlorobenzaldehyde was
added to the mixture at this stage, 1-(4-chlorophenyl)-2-methyl-
3-butyne-1-ol 10c (R ) 4-ClC6H4-, R2 ) R3 ) H, R4 ) Me)
was the only product observed. When the ratio of THF-d8 to
D2O was changed to 3:2, the NMR spectra of the mixture could
be observed more clearly.
Effect of Methyl Substituent on Allenyl-In/Propargyl-In
Equilibrium. The calculated structures and relative energies
of methyl substituted propargyl-In (5b, 6b, 5c, 6c) and allenyl-
In (7b, 8b, 7c, 8c) are given in Figure 5. For the In(I) 5b and
7b species, the B3LYP method only leads to the 7b-π structure.
Water complexation leads to a more stable γ-methylpropar-
The reaction of 3-bromo-1-butyne 4c with indium in deuter-
ated tetrahydrofuran under ultrasonic irradiation was then carried
out and found to be slower than that of propargyl bromide 4a,
but faster than 1-bromo-2-butyne 4b. At 6 h, three new sets of
1
peaks showed up again in the H NMR spectra and one set of
them was attributed to 1, 2-butadiene. The other two sets of
peaks, which appeared around 4.88 (m, 1H), 4.40 (m, 1H), 1.61
(m, 3H) and 5.00 (m, 1H), 4.62 (m, 1H), 1.55 (dd, J ) 6.9, 3.3
Hz, 3H), respectively, were similar to those observed in aqueous
media reaction and consistent with the allenylindium structure.
Adding 4-chlorobenzaldehyde to the mixture resulted in the
propargylic alcohol 10c (R ) 4-ClC6H4-, R2 ) R3 ) H, R4 )
Me). We deduced therefore that the allenylindium species 7c
and 8c have been generated in THF-d8 as well as in aqueous
media. Their 13C NMR spectra, at 209.9, 83.8, 73.2, 14.2 ppm
and 210.3, 82.9, 75.8, 14.0 ppm and the subsequent 2D-NMR
experiments including COSY, HSQC, and HMBC, further
confirmed the allenic structures of these two organoindium
species. When the reaction was left to proceed further under
sonication, the set of peaks that was at higher field in proton
NMR disappeared gradually and eventually only that set of
(20) Frisch, M. J.; Trucks, G. W.; Schlegel, H. B.; Scuseria, G. E.; Robb, M.
A.; Cheeseman, J. R.; Zakrzewski, V. G.; Montgomery, J. A. Jr.; Stratmann,
R. E.; Burant, J. C.; Dapprich, S.; Millam, J. M.; Daniels, A. D.; Kudin,
K. N.; Strain, M. C.; Farkas, O.; Tomasi, J.; Barone, V.; Cossi, M.; Cammi,
R.; Mennucci, B.; Pomelli, C.; Adamo, C.; Clifford, S.; Ochterski, J.;
Petersson, G. A.; Ayala, P. Y.; Cui, Q.; Morokuma, K.; Malick, D. K.;
Rabuck, A. D.; Raghavachari, K.; Foresman, J. B.; Cioslowski, J.; Ortiz,
J. V.; Baboul, A. G.; Stefanov, B. B.; Liu, G.; Liashenko, A.; Piskorz, P.;
Komaromi, I.; Gomperts, R.; Martin, R. L.; Fox, D. J.; Keith, T.; Al-Laham,
M. A.; Peng, C. Y.; Nanayakkara, A.; Gonzalez, C.; Challacombe, M.;
Gill, P. M. W.; Johnson, B.; Chen, W.; Wong, M. W.; Andres, J. L.;
Gonzalez, C.; Head-Gordon, M.; Replogle, E. S.; Pople, J. A. Gaussian
98, Revision A.7; Gaussian, Inc.: Pittsburgh, PA, 1998.
(21) (a) Becke, A. D. Phys. ReV. 1988, A38, 3098. (b) Becke, A. D. J. Chem.
Phys. 1993, 98, 1372, 5648. (c) Lee, C.; Yang, W.; Parr, R. G. Phys. ReV.
1988, B37, 785. Since the B3LYP method gives better prediction than the
HF calculations, the HF computed values are provided as Supporting
Information.
(22) Wadt, W. R.; Hay, P. J. J. Chem. Phys. 1985, 82, 284.
(23) A similar π-complex structure was also obtained with MP2 geometric
optimization.
(24) Reich, H. J.; Thompson, J. L. Org. Lett. 2000, 2, 783.
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13330 J. AM. CHEM. SOC. VOL. 126, NO. 41, 2004