Reorientation dynamics within ion-paired allylic lithium compounds: Isolation of inversion processes

Article abstract of DOI:10.1021/jo982196f

Among the several ion-ion reorientational processes that take place within several newly studied allylic lithium compounds, the dynamics of transfer of TMEDA-coordinated lithium between the two ally1 faces has been determined independently by use of ¹³C NMR line shape studies of diastereotopic geminal methylsilyl groups strategically incorporated close to the chiral lithium in the organometallic species. With increasing temperature, the ¹³C shift between these methyls is progressively averaged due to faster rates of lithium transfer (inversion). Typical ΔH((+)) values of 5-7 kcal·mol^-1 with ΔS((+)) = ca. -20 eu are encountered. A faster process, the reorientation of coordinated TMEDA on one side of the allyl plane, has been monitored from the NCH₃ ¹³C resonance of TMEDA-coordinated Li⁺, with ΔH((+)) = 7 kcal·mol^-1 and ΔS((+)) = ca. -12 eu.

Full text of DOI:10.1021/jo982196f

1302
J . Org. Chem. 1999, 64, 1302-1310
Reor ien ta tion Dyn a m ics w ith in Ion -P a ir ed Allylic Lith iu m
Com p ou n d s: Isola tion of In ver sion P r ocesses
Gideon Fraenkel,*,† J ose Cabral,‡ Carolina Lanter,† and J inhai Wang†
Department of Chemistry, The Ohio State University, Columbus, Ohio 43210, and
The Ohio State University, Newark Campus, Newark, Ohio 43055
Received November 2, 1998
Among the several ion-ion reorientational processes that take place within several newly studied
allylic lithium compounds, the dynamics of transfer of TMEDA-coordinated lithium between the
two allyl faces has been determined independently by use of 13C NMR line shape studies of
diastereotopic geminal methylsilyl groups strategically incorporated close to the chiral lithium in
the organometallic species. With increasing temperature, the 13C shift between these methyls is
progressively averaged due to faster rates of lithium transfer (inversion). Typical ∆Hq values of
5-7 kcal‚mol-1 with ∆Sq ) ca. -20 eu are encountered. A faster process, the reorientation of
coordinated TMEDA on one side of the allyl plane, has been monitored from the NCH3 13C resonance
of TMEDA-coordinated Li+, with ∆Hq ) 7 kcal‚mol-1 and ∆Sq ) ca. -12 eu.
Allylic lithium compounds1 are among the simplest
structures have been shown to be aggregated. Possible
species with structures that lie between 1 and 2, i.e., 3,
have only recently been observed in studies of internally
coordinated allylic lithium compounds, such as 4. These
were proposed to be stablized by virtue of restricted
stereochemistry of lithium coordination.7
potentially conjugated carbanionic species. As a result
of extensive spectroscopic2,3 X-ray crystallographic4 and
calculational5 studies, two categories of structures have
been recognized. These are the delocalized contact ion-
pairs with lithium normal to the allyl plane and solvated
by ethers or tertiary amines 1, and then, there are the
unsolvated species, 2a b,6 whose 13C NMR shifts are more
in accord with a localized structure. Both kinds of
† The Ohio State University, Columbus.
‡ The Ohio State University, Newark.
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Chem. 1967, 8, C13. (c) Schlosser, M.; Stahle, N. Angew. Chem. 1980,
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neglected subject, let alone the dynamics of motion of ions
with respect to each other within the ion-pairs. Ion-pairs
were not believed to assume energetically favored struc-
tures. Our NMR studies provided the first direct support
for a sandwich structure of ion-pair dimers that contain9
triple ions A-Li+A-, Li+,9,10 in which only the outer
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1984, 17, 353-357. (d) Reichert, C. Solvents and Solvent Effects in
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10.1021/jo982196f CCC: $18.00 © 1999 American Chemical Society
Published on Web 01/15/1999

Reorientation Dynamics
J . Org. Chem., Vol. 64, No. 4, 1999 1303
lithium is solvated.10 Then, direct mapping of ion-pairs
has been recently accomplished with careful NMR NOE
experiments.11
of coordinated lithium between the two sides normal to
the allyl plane would average such a shift, so line shape
analysis should provide the dynamics of face transfer
alone, a process that is phenomenologically inversion of
the ion-pair. Herein we report the results of such a study,
the specific design and preparation of several model
allylic lithium compounds that incorporate a geminal
methyl silyl diastereotopic probe and how NMR line
shape analysis of the geminal methyl resonances sepa-
rates and identifies, the dynamics of inversion from all
other intra-ion pair reorientational effects.
Recently, we have reported that at low temperatures,
160 K, unexpected nonequivalences among 13C shifts of
several allylic lithium compounds implied that these ion-
paired species assume quite specific structural arrang-
12
ments, as shown in structures 5-7. Signal averaging
Resu lts a n d Discu ssion
Evidence for the ion-paired structure and reorientation
dynamics of ions with ion pairs was first obtained for 5.12a
To investigate whether this behavior is unique to silicon-
substituted allylic lithium compounds we have now
prepared the carbon analogue of 5, the di-tert-butyl
species 11.
effects seen in the NMR spectra with increasing temper-
ature were ascribed to the reorientation dynamics of ions
with respect to each other within the ion-pair. For
example, at 150 K in diethyl ether-d10 5‚TMEDA shows
a small 13C NMR shift between the terminal allyl carbons
and two well-separated broad peaks for the N-methyls,
which implied that complexed TMEDA is unsymmetri-
cally sited with respect to the allyl moiety. With increas-
ing temperature, these two doublets progressively aver-
age to single lines at their respective centers. Similar
behavior was observed for compounds 6-8.12 NMR line
shape analysis revealed first-order processes with ∆Hq
of 5-7 kcal‚mol-1, respectively. These effects were as-
cribed to reorientation of coordinated ligand with respect
to counterion within the ion-pairs. Reorientation could
result from several different processes. Thus, the averag-
ing observed in N-methyl 13C NMR of coordinated TME-
DA in 5 and 6 could come from rotation of coordinated
ligand on one side of the allyl plane, transfer of coordi-
nated ligand between two faces of the allyl plane, and
finally fast reversible local N-Li dissociation accompa-
nied by inversion at nitrogen and rotation about the
CH2-N bond. To determine, independently, the rates of
transfer of coordinated lithium between two sides of the
allyl plane, a process that is phenomenologically inver-
sion, we have chosen to exploit the diastereotopic proper-
ties of geminal methyls in a chiral environment.13
Assuming that in a 1-substituted allylic lithium com-
pound coordinated lithium is sited normal to the allyl
plane,7 then the system is chiral. The methyls of a
dimethylsilyl group near the chiral center would be
magnetically nonequivalent in 13C NMR. Fast transfer
Transformation of unsaturated ketone 914 via the
alcohol 10a and chloride 10b provided the desired phenyl
sulfide 10c. Cleavage of 10c with lithium (dimethylami-
no)naphthalenide, LDMAN, provided an impure sample
of 11 together with PhSLi.
Compound 11 was purified by conversion to its tri-
methyltin derivative 12 and cleavage of the latter with
CH3Li in diethyl ether. Compounds 9, 10a -c, and 12 are
assigned trans structures on the basis of vicinal proton
coupling constants across the double bonds of ca. 15 Hz.
We previously reported that 1,1,3,3-tetramethylallyl-
lithium added cleanly and rapidly to anthracene in
diethyl ether at -90 °C.15 Compound 11 behaves in a
similar fashion, except that the reaction requires a higher
temperature, -30 °C. Hydrolysis of the initial adduct 13
provided 14 in 81% yield. A vicinal proton coupling of
15.4 Hz across the allylic double bond of 14 confirms the
trans relationship shown and by implication that in the
precursor anion 13; see below.
Preparation of other starting materials and their
metalation (15-25) is summarized below. Four geminal
dimethylsilyl allylic lithium compounds have been pre-
pared, 16, 18, 21, and 25, via a series of metalation/
silylation cycles; see 15-25. Metalation has been accom-
plished using n-butyllithium in the presence of TMEDA
in diethyl ether or THF. It is a common feature of the
(11) (a) Mo, H.; Pochapsky, T. C. Prog. Nucl. Magn. Reson. Spectrosc.
1997, 30, 1-38. (b) Pochapsky, T. C.; Wang, A.-P.; Stone, P. M. J . Am.
Chem. Soc. 1993, 115, 11084-11091. (c) Pochapsky, T. C.; Stone, P.
M. Ibid. 1991, 113, 6714-6715. (d) Pochapsky, T. C.; Stone, P. M.;
Pochapsky, S. S. Ibid. 1991 113, 1460-1462.
(12) (a) Fraenkel, G.; Chow, A.; Winchester, W. R. J . Am. Chem.
Soc. 1990, 112, 1382-1386. (b) Fraenkel, G.; Winchester, W. A.; Chow,
A. Ibid. 1990, 112, 2582-2585. (c) Fraenkel, G.; Cabral, J . A. ibid.
1993, 115, 1551-1557. (d) Fraenkel, G.; Cabral, J . Ibid. 1992, 114,
9007-9015.
(13) (a) Saunders: M.; Yamada, F. J . Am. Chem. Soc. 1964, 85, 1882.
(b) Whitesides, G. M.; Roberts, J . D. Ibid. 1965, 87, 4878. (c) Pechhold,
E.; Adams, D. G.; Fraenkel, G. J . Org. Chem. 1971, 36, 1368-1374.
(14) (a) House, H. O.; Crumrine, D. S.; Teranishi, A. Y.; Olmstead,
H. D. J . Am. Chem. Soc. 1973, 95, 3318.
(15) Cabral, J . A.; Cohen, T.; Doubleday: W. W.; Duchelle, E. F.;
Fraenkel, G.; Guo, B. S.; Yu, S. H. J . Org. Chem. 1992, 57, 3680-
3684.

1304 J . Org. Chem., Vol. 64, No. 4, 1999
Fraenkel et al.
Ta ble 1. 13C a n d (1H) NMR Sh ifts, Allylic Lith iu m Com p ou n d s Com p lexed to TMEDA, Dieth yl Eth er -d 10 Solu tion ,
<180 K
C1
C2
C3
Si(CH3)2
SiCH2CH3
C(CH3)3
NCH3
NCH2
58.0
16
18
53.1
(1.94)
149.0
(6.41)
64.3
(2.65)
(2.75)
-0.441
0.001
8.6 CH2
11.8 CH3
(0.37) CH2
(0.92) CH3
46.0
49.0
67.43
(2.6)
155.21
(6.7)
67.43
(2.6)
0.215
-0.13
-0.32
(0.97)
8.53 CH2
11.32 CH3
(0.40) CH2
(0.91) CH3
49.4
45.0
(2.34)
58.0
(2.45)
21
25
50.28
(1.95)
149.7
(6.4)
65.3
(2.71)
(2.83)
-2.88
-5.01
29.25 CH3
20.0 q
50.66
46.56
(2.3)
57.86
(2.45)
68.8
(2.6)
155.2
(6.65)
67.1
(2.6)
-0.71
-0.35
(0.97)
8.58 CH2
11.36 CH3
(0.3) CH2
(0.9) CH3
49.27
44.84
57.85
(1.94)
2.12
(-0.1)
11
77.1
(2.54)
131.8
(6.42)
77.5
(2.54)
34.4 CH3
33.1 q
(2.33)
49.4
56.9
(2.45)
45.09
45.37
(2.33)
Ta ble 2. P r oton -P r oton Cou p lin g Con sta n ts, Hz, for
Allylic Lith iu m Com p ou n d s in Eth er -d 10
no.
AB
BC
BD
CD
11
13.7
19.4
15.6
15.6
15.2
13.7
15
15.6
14.9
15.2
17
16a
18
8.5
8.5
-2
-2
21a
25
a
X ) Hc.
chemistry reported here and previously published16 that
1-silylallyllithiums undergo further silylation at the
3-position resulting in trans products.16 Thus, herein 16
and 23 on silylation produce exclusively 17 and 24,
respectively, which are identified as the trans stereo-
chemistry due to vicinal proton proton coupling constants
across the double bonds of 18 and 19, Hz, respectively.
For NMR study, the solvent diethyl ether, THF, and
excess TMEDA were removed under vacuum from the
initial preparations of 11, 16, 18, 21, and 25 and replaced
via bulb-to-bulb distillation by dry oxygen-free diethyl
ether-d10 or THF-d8.
in Table 1 for all of the allylic lithium compounds
reported here. All of these compounds exhibit the alter-
nating allyl 13C shifts typical of delocalized carban-
ions.2,3,17 The three-bond proton-proton coupling con-
stants of ca. 15 Hz within the allyl moieties (Table 2)
show that all these species are exo substituted, as drawn,
and that endo isomers present are too dilute to detect.
The TMEDA that remains in these samples is clearly
bound to lithium, since the associated NMR behavior is
quite different from that of the free material. Finally,
geminal silyl methyls at low temperature all resolve into
simple doublets. These issues are elaborated upon below;
see Table 1.
Carbon-13 and proton chemical shifts, obtained at low
temperature, using diethyl ether-d10 solutions, are listed
(16) (a) Ayalon-Chass, D.; Ehlinger, E.; Magnus, P. J . Chem. Soc.,
Chem. Commun. 1977, 772. (b) Ehlinger, E.; Magnus, P. Tetrahedron
Lett. 1980, 11. (c) Ehlinger, E.; Magnus, P. J . Am. Chem. Soc. 1980,
102, 5004.
(17) Winchester, W. R.; Bauer, W.; Schleyer, P. v. R. J . Chem Soc.,
Chem. Commun. 1987, 177.

Reorientation Dynamics
J . Org. Chem., Vol. 64, No. 4, 1999 1305
(a )
F igu r e 2. Pattern of 13C NMR of NCH3 of 11, complexed to
TMEDA.
5‚TME DA. At low temperature, 175 K, there is a 13C
NMR shift difference between the terminal allyl carbons
of 0.4 ppm, Figure 1a. Further, at 175 K the N-methyls
give rise to three singlets of relative intensities 2:1:1.
With increasing temperature, the two multiplets progres-
sively average to single lines at their respective centers,
Figure 1b. We assume these resonances come from a
single molecular species. The C1, C3 resonance was
treated as a two-site equally populated uncoupled system
undergoing exchange, Figure 1a. As for the N-methyl
resonance, it was calculated as due to four equally
populated uncoupled sites (the four methyls) of which two
have the same shift; see Figure 2. The simplest model is
for each site to exchange with all of the others, all at the
same rate.18 This model nicely matched the calculated
to the observed resonances, as shown in Figure 1b. Thus,
comparison of observed and calculated line shapes gave
the rate constants and associated activation parameters;
∆Hqs, kcal/mol, of 8.0 and 6.6 were derived from the
N-methyl and C1, C3, 13C resonances, respectively.
Entropy and enthalpy tend to balance, since over the
temperature range investigated rate constants from the
C1, C3 resonance exceed those from N-CH3 by not more
than a factor of 2; see Table 3. The Eyring plot is shown
in Figure 3 for N-methyl 13C resonances.
(b)
At low temperature, the 13C NMR of geminal silyl
methyls of each of the compounds 16, 21, and 25 consists
of a single equal doublet. This is not the result of
nonequivalent methyls within slowly interconverting
rotamers about the allyl carbon silicon bonds since we
find that the starting silylpropenes show no such effects
at low temperature; their geminal silylmethyls give rise
to single peaks down to 160 K. Rather, the gem-silyl-
methyl doublets for the allylic organolithium compounds
are most likely due to the chiral character of these
compounds. With increasing temperature, the dimeth-
ylsilyl 13C doublets of 16, 21, and 25 progressively
average to single lines at their respective centers. This
behavior does not depend on concentration of the orga-
nolithium species and, hence, must be the result of a first-
order process, the transfer of coordinated lithium between
opposite sides normal to the allyl plane. Comparison of
observed and calculated line shapes (see Figure 4 for 21)
provides the rate constants. The Eyring plot is in Figure
5; the results are given in Table 3.
F igu r e 1. (a) 13C NMR, 11, 0.5 M, complexed to TMEDA in
diethyl ether-d10, C1, C3 allylic carbons: (left) observed, dif-
ferent temperatures; (right) calculated line shapes with rate
constants. (b) 13C NMR as in (a) NCH3 of complexed TMEDA:
(left) observed, different temperatures; (right) calculated line
shapes with rate constants.
Consider first the behavior of exo,exo-1,3-di(tert-butyl)-
allyllithium, 11, complexed to TMEDA, which was
chosen as a highly substituted species for comparison
with the1,3-disila analogue5‚TMEDA,reportedpreviously.12a
NMR data indicated that the coordinated ligand in 5‚
TMEDA is unsymmetrically sited with respect to the
allyl loop; i.e., the system assumes a single structure.
Then changes in NMR line shape were interpreted as
resulting from the dynamics of reorientiation of ions with
respect to each other within the ion-pair.
Compound 18 behaves in a fashion similar to that of
the others described above. The allyl 13C NMR shifts are
consistent with a delocalized carbanion. The C1 and C3
allyl resonance is a single broadened line (compared to
the other carbons), implying a small shift between them.
The 13C NMR spectrum down to 170 K shows no evidence
for more than one species. In contrast to 16, 21, and 25,
the geminal methyls of which give rise to 1:1 13C doublets,
(18) Kaplan, J . I.; Fraenkel, G. NMR of Chemically Exchanging
Systems; Academic Press: New York, 1980; Chapter 6.
Compound 11‚TMEDA behaves in fashion similar to

1306 J . Org. Chem., Vol. 64, No. 4, 1999
Fraenkel et al.
Ta ble 3. Dyn a m ics of Ion -Ion Reor ien ta tion w ith in
Allylic Lith iu m ‚TMEDA Com p lexes in Dieth yl Eth er -d 10
As Obta in ed fr om NCH3, Si(CH3)2, or C1, C3 13C NMR Lin e
Sh a p es
eu
a
b
Broadened doublet. Net inversion. c Reference 12a, recalcu-
F igu r e 4. 13C NMR, 21 complexed to TMEDA, gem-methyl-
silyl resonance: (right) observed, different temperatures; (left)
calculated, with rate constants.
lated. Broadened line. e Reorientation of complexed lithium on
one side normal to allyl plane.
d
F igu r e 3. Eyring plot, reorientation dynamics, 11‚TMEDA,
from N-methyl 13C NMR of complexed TMEDA diethyl ether-
d10 solution.
those of 18 exhibit three singlets, 2:1:1 at δ 0.215, -0.13,
and -0.32, respectively. The two silicons are labeled A
and B. Geminal methyls may be assigned A1, A2 at δ
0.215 with B1 and B2 at δ -0.13 and -0.34, respectively;
alternatively, A1, B1 at δ 0.215 with A2 and B2 at δ -0.13
and 0.32, respectively, diagrammed in Figure 6. Of these
two, only the latter assignment is consistent with the
results for 25, a compound with one less methylene than
18. Hence, both should have similar structures and
behave in a similar manner. The geminal silyl methyls
of 25 give rise to a clean 1:1 doublet in 13C NMR,
separation 0.19 ppm. Were the first assignments for 18
correct then the 13C NMR of 25 would have indicated two
species, one with a geminal silylmethyl 1:1 doublet and
the other with just a single line for these methyls. Clearly
the second assignment must be the more correct one.
With increasing temperature above 160 K, the 2:1:1
F igu r e 5. Eyring plot, reorientation dynamics for 21 com-
plexed to TMEDA from gem-silylmethyl resonance.
F igu r e 6. Assignment for gem-methyl 13C resonances of 18
complexed to TMEDA.
geminal silyl multiplet of 18 progressively undergoes
signal averaging, ultimately by 300 K to a single line.
These line shape changes are best fitted with two
different sets of rate constants, the faster set being

Reorientation Dynamics
J . Org. Chem., Vol. 64, No. 4, 1999 1307
responsible for averaging the 1:1 doublet (δ -0.13 and
-0.34) between 170 and 200 K. In terms of our proposed
model, Figure 6, that is the averaging of the two doublets,
A1A2 with B1B2 to a single doublet. Above 200 K with
increasing temperature, the latter doublet averages to a
single line, the slower process. We would like to propose
that this slower process involves transfer of coordinated
lithium between opposite sides normal to the allyl plane,
“inversion”, while the former, detected within the lower
temperature range, involves side to side motion of the
coordinated ligand or its rotation on one side of the silyl
plane only. Experimental and calculated line shapes are
compared in Figure 7a,b; associated activation param-
eters are in Table 3.
(a )
The 13C NMR of TMEDA in diethyl ether remains
unchanged between 150 and 300 K; the N-methyl reso-
nance consists of a sharp single line throughout this
entire temperature range. All of the compounds reported
herein, 11, 16, 18, 21, and 25, were prepared in the
presence of TMEDA. The TMEDA that remained in
these samples after all volatile components had been
pumped out exhibited NMR behavior quite differenct
from that of the free diamine. Below 180 K, 13C NMR for
N-methyls in each of the complexes 16, 18, 21, and 25
resolved into a 1:1 doublet unformally at δ 45 and 49,
respectively. The exception in this work is 11, which gave
a 2:1:1 triplet; see above. These results indicate that the
diamine is complexed to Li+ in each case and that
coordinated ligand is unsymmetrically sited with respect
to the allyl moiety, as proposed in previous reports.12
With increasing temperature, these N-methyl 13C mul-
tiplets progressively average to single lines at their
respective centers. NMR line shape analysis provides the
associated dynamic parameters. Figure 8 shows calcu-
lated line shapes for 21. Table 3 lists the activation
parameters ∆Hq and ∆Sq derived from the N-methyl 13C
resonance for all cases analyzed.
(b)
The nature of the dynamic process responsible for these
changes in the 13C NMR N-methyl line shapes for
complexed TMEDA in the above listed compounds is less
clear than that for the gem-silylmethyl 13C resonances
of 16, 18, 21, and 25. The latter changes are most likely
the result of transfer of coordinated lithium between two
sides normal to the allyl plane. In contrast, changes in
the TMEDA resonance may be the result of several
effects, including inversion as well as lateral motion of
complexed ligand and fast reversible N, Li dissociation
accompanied by inversion at nitrogen and rotation around
the N-CH2 bond. The latter process may be much faster
than the other two, fast relative to the NMR time scale,
even at the lowest temperature at which acceptable NMR
data could be obtained. This would account for the
observation of just two N-methyl 13C lines instead of the
expected four on the basis of our proposed structures,
discussed above.
Barriers to rotation in allylic lithium compounds have
been reported by several workers.4d-f Among the com-
pounds described herein, 11, 17, and 25 appear to assume
the exo-exo structures with no isomers detectable by
NMR. Hence, it is not possible to determine the barrier
to allyl rotation with NMR methods. However, the
dynamics of allyl rotation around the C2, C3 bond in 21
is accessible from proton NMR. Like all compounds
described here 21 is 1-exo. With increasing temperature
between 290 and 330 K there is partial averaging of the
cis and trans coupling constants between C2H and the
F igu r e 7. (a) 13C NMR, gem-methyl resonances of 18 com-
plexed to TMEDA, higher temperature range: (left) observed,
different temperatures; (right) calculated line shapes with rate
constants. (b) As in (a), lower temperature range: (left)
observed with temperatures; (right) calculated with rate
constants.
C3 methylene hydrogens. Analysis of the C2H12C proton
resonance provides the rates of C2, C3 rotation and
associated activation parameters. These are, in order,
∆Hq and ∆Sq for diethyl ether-d10 solution, 16 kcal‚mol-1
and +4.6 eu, while for THF solution these values are 14
kcal‚mol-1 and -2 eu. The latter are closely similar to
the corresponding parameters determined for 1-trimeth-
ylsilylallyllithium using THF solutions, 14.3 kcal‚mol-1
and ∼0 eu.12b Note that these barriers vary significantly
with the nature of the lithium ligand present.12b It has
been proposed that an increase in carbon lithium cova-
lence in the transition state for rotation, compared to the
ground state, is responsible for this effect.3c
It is now instructive to recapitulate what has been
found herein and how it relates to what is generally

1308 J . Org. Chem., Vol. 64, No. 4, 1999
Fraenkel et al.
Ta ble 4. NMR P a r a m eter s
parameter
13C
1H
frequency, MHz
transform, K
75
64
300
16
spectral width, Hz
resolution, Hz/point
acquisition time, s
transients
13514
0.231
2.16
1600-9600
4200
0.513
1.09
1600-9600
The available data do not provide a picture as to how
lithium transfers between two sides normal to the allyl
plane. The transfer is not accompanied by an increase
in C, Li covalence. That path would perturb the conjuga-
tion and thus facilitate rotation around the allyl carbon
carbon bonds, a process already known to involve higher
barriers with ∆Hq of 12-19 kcal‚mol-1, respectively. In
contrast, inversion could accompany allyl rotation.
Exp er im en ta l Section
Ma t er ia ls a n d P r oced u r es. Diethyl ether, tetrahydro-
furan, and pentane used in the organometallic procedures were
freshly distilled from sodium and benzophenone under an
argon atmosphere. Toluene was distilled from CaH2, and
TMEDA was distilled from KOH pellets and then from CaH2,
under argon or nitrogen. Organolithium compounds were
analyzed using our double titration procedure, previously
described.7a All glassware used for organometallic compounds
was baked in an oven, 120 °C, overnight, flamed out under
vacuum, and finally flushed out with argon.
NMR Sa m p les. The assembly consists of a 5 mm OD NMR
sample tube with an attached 2 mm straight bore stopcock,
the latter protected by a rubber serum cap, the whole system
previously dried with flaming in a current of argon. Within
the drybox (argon), the NMR tube was loaded by syringe with
ca. 1 mL of the allylic lithium solution. Solvent was removed
under vacuum and the assembly flushed with argon and then
attached to a high vacuum system (10-6 Torr) to remove
remaining volatile components. After 1 h, diethyl ether-d10 (1
mL) was vacuum transferred into the sample. The frozen
sample (liquid nitrogen) was then sealed under vacuum.
Samples were stored in dry ice prior to NMR study.
F igu r e 8. 13C NMR 21 complexed to TMEDA in diethyl ether-
d
10, N-methyl part: (right) observed, with temperatures; (left)
calculated with rate constants.
understood about allylic lithium compounds. The ex-
amples of solvated allylic lithium compounds reported
here and previously behave spectroscopically as delocal-
ized carbanions within contact ion pairs.3,4,6,12 Our NMR
data reported here and elsewhere indicated that several
of these compounds assume energetically favored struc-
tures,12 a concept rarely applied to ion-paired salts, as
evidenced by unexpected nonequivalences among the 13C
NMR shifts. At low temperature, 180 K, reorientation of
ions within the ion-pairs, with respect to each other, is
slow relative to the NMR time scale.
Signal averaging of nonequivalent N-methyl 13C reso-
NMR Equ ip m en t a n d Con d ition s. Conventional NMR
spectra were obtained with a Bruker AC-200 spectrometer. All
variable-temperature experiments with carried out using a
Bruker MSL-300 instrument. Table 4 lists typical parameters
used in this work.
nances due to bound TMEDA and of gem-methylsilyl 13
C
resonances are due to the dynamics of ion-ion reorienta-
tion. Whereas the data from TMEDA methyls may be
due to several effectssincluding inversion, rotation of the
coordinated ligand on one side of the allyl plane, and fast
reversible N5Li dissociation, that from the geminal me-
thyls on silicon comes from inversion alone, with one
exception (see below). These geminal methyls are non-
equivalent due to the chiral character of the ion-pair.
Their averaging with increasing temperature is due to
inversion of the ion-pair above and is more accurately
described as transfer of coordinated lithium between two
sides normal to the allyl plane. In the case of 18, the cis-
1,3-bis(dimethylethylsilyl) compound, the changes in the
geminal methyl 13C NMR line shape have been resolved
to result from two processessinversion and the faster
rotation of coordinated ligand on one side of the allyl
plane. This latter rate at 200 K is similar to the value
obtained from the N-methyl 13C resonance of TMEDA-
coordinated 18. Similar effects are seen for 5 where the
N-methyl and C1, C3 13C line shapes give rise to similar
rates at 200 K. In fact, the ∆Gq (200 K) values extracted
from two sets of resonances just described for 18 and 5
are remarkably similar, (9 × 6) ( 3 kcal‚mol-1. Thus in
cases where the dynamics of both inversion and one side
reorientation have been measured, inversion is the slower
process.
2,2,6,6-Tetr a m eth yl-4-h ep ten -3-on e, 9. Freshly distilled
5-hydroxy-2,2,6,6-tetramethyl-3-heptanone (37 g, 0.199 mol)
prepared by the method of House14 was introduced into a three-
neck round-bottom flask equipped with a reflux condensor, a
stopcock, an addition funnel, and a magnetic stirbar. p-
Toluenesulfonic acid (1.7 g, 8.5 mmol) dissolvd in 650 mL of
benzene was then added and the solution refluxed for 1 h. After
this time, the reflux condensor was replaced by a Vigreux
distillation column, and the H2O-benzene azeotrope was
allowed to distill out at atmospheric pressure (71 °C) until no
more water droplets came out. The remaining solution was
concentrated by rotary evaporation and the residue extracted
twice with 100 mL of CCl4 to separate the insoluble p-
toluenesulfonic acid. The rotary evaporator deposited 30.5 g
(91.3% yield) of the trans title ketone as white needles: mp
1
40-41 °C; H NMR (CDCl3, 20 MHz) δ 1.0 (9H, s, tBu), 1.07
(9H, s, tBu), 6.3 (1H, d, vinyl J ) 14.7 Hz), 6.8 (1H, d, vinyl J
) 14.7 Hz).
2,2,6,6-Tetr a m eth yl-4-h ep ten -3-ol, 10a . Into a 250 mL
three-neck round-bottom flask equipped with an addition
funnel, a glass stopcock, argon inlet, and a magnetic stirbar,
containing LiAlH4 (4.94 g, 0.13 mol) in 30 mL dry ether, was
added trans ketone 14 (20 g, 0.119 mol) dropwise. This reaction
mixture was stirred for 5 h and maintained at 20 °C with a
water bath. Then it was hydrolyzed very carefully with 12 mL
of distilled H2O, which was added over a period of 1 h. The

Reorientation Dynamics
J . Org. Chem., Vol. 64, No. 4, 1999 1309
reaction mixture was vacuum filtered in a Bu¨chner funnel,
and the residual slurry in the funnel was washed thoroughly
with ether (50 mL). The ethereal filtrate was next dried with
anhydrous MgSO4 powder, concentrated in the rotary evapora-
tor, and distilled twice to give 16.88 g (83.4% yield) of the clear
This mixture was then queched with 10 mL of H2O, the THF
was removed first in vacuo, and the remaining solution was
extracted twice with 10 mL portions of diethyl ether, washed
three times with 0.2 N KOH (aq) (to remove the thiophenol),
once with NaCl (sat.), and twice with 1 N HCl (aq) (to remove
the naphthalenamine). Next, the solution was dried (MgSO4)
and concentrated in the rotary evaporator. The product was
purified by flash column chromatography (SiO2, hexanes) to
separate 0.45 g (75% yield) of the pure stannyl title com-
pound: MS for C14H30Sn m+/e obsd 316.93965, calcd 316.9249;
IR (neat) cm-1 29573, 28.64.2, 1463.8, 1362.3, 1230.6, 971.0,
764.3; 1H NMR (CDCl3, 200 MHz) δ 0.07 (9H, s, Sn(CH3)3),
0.95 (9H, s, tBu), 1.01 (9H, s, tBu), 2.0 (1H, d, -SnCH-, J )
11.0 Hz), 5.25 (1H, d, vinyl, J ) 15.8 Hz), 5.44 (1H, dd, vinyl,
J ) 15.8, 11.0 Hz); 13C NMR (CDCl3, 50 MHz) δ -8.28, 30.20,
30.67, 32.87, 33.50, 49.21, 125.32, 138.04.
exo,exo-1,3-Di-ter t-bu tyla llyllith iu m . TMEDA, 11. A 50
mL flame-dried Schlenk flask containing a glass-coated stirbar
and a stopcock connected to an argon tube was charged by
syringe with tin compound 12 (0.35 g, 0.0011 mol) and
TMEDA (0.128 g, 0.0011 mol). After this step, the flask was
cooled with an acetone-dry ice bath (-78 °C). Next, a mixture
of 6.0 mL of anhydrous diethyl ether and 0.6 mL of THF was
introduced for solvation, followed by the addition of methyl-
lithium-6Li (1.2 mL, 1.27 M, 1.52 mmol) in diethyl ether. The
reaction mixture was stirred at -78 °C for 2 h and then slowly
warmed to room temperature. By ca. -30 °C, a yellow color
was observed, indicating the formation of the lithium com-
pound. It appeared to be stable even at room temperature. To
obtain NMR samples, aliquots of 0.8 and 1.2 mL were syringed
out very carefully and transferred to flame-dried, argon-filled
NMR tubes. The latter were attached to a vacuum system
(Torr), and the solvents allowed to distill into a liquid nitrogen
trap. Then when most of the solvent had been removed, the
tubes were transferred to a high vacuum line (5 × 10-6 mmHg)
and maintained there for 3 h to pump out completely all
volatile components. Diethyl ether-d10, up to 0.5 mL, was
vacuum transferred into the cooled NMR tubes (liquid nitro-
gen). The yellow-orange NMR samples were then frozen and
sealed off under vacuum with a torch. NMR samples were
stored in a liquid nitrogen bath in the freezer until NMR
studies began: 1H NMR (Et2O-d10, 300 MHz, 3.34 ppm) δ 0.96
(9H, s, tBu), 2.20 (s, TMEDA methyls), 2.34 (s, TMEDA-
methylenes), 2.5-2.6 (1H, d, J ) 13.2 Hz), 6.2-6.7 (1H, t, J )
13.2 Hz); 13C NMR (Et2O-d10, 75 MHz, 65.3 ppm) δ 32.676,
34.027, 46.849, 57.487, 77.814, 134.153.
9-(ter t-Bu tyl-4,4-d im eth yl-2-p en ten e)-9,10-d ih yd r oa n -
th r a cen e, 14. Into a flame-dried 50 mL round-bottom flask
equipped with a glass-coated stirring bar, a low-temperature
thermometer, and glass stopcock, the whole flushed with
argon, was introduced a mixture of 4.5 mL of diethyl ether
and 0.5 mL of THF together with TMEDA (0.128 g, 1.1 mmol)
freshly distilled from CaH2. Next, stannane 12 (0.35 g, 1.1
mmol) was introduced into the flask. The solution was then
cooled to -78 °C with a dry ice-acetone bath, and methyl-
lithium (1.2 mL, 1.24 M, 1.52 mmol) in diethyl ether was added
slowly via syringe. At -78 °C, no color change was observed,
so the mixture was left to warm slowly. At -30 °C, a yellow
coloration developed, and after 2 h at room temperature the
bright yellow color indicated the formation of the allyllithium
compound. The flask was chilled again to -78 °C, and
anthracene (0.392 g, 2.2 mmol) dissolved in 2 mL of THF was
added carefully from a syringe. After 1 h at -78 °C, the
reaction mixture was warmed slowly to -30 °C. At this
temperature, a dark orange color started to develop, which
intensified by room temperature, giving a dark red solution.
The reaction mixture was then quenched with 10 mL of
distilled H2O, washed twice with 10 mL each of 1 N HCl (aq),
dried (MgSO4), and concentrated in the rotary evaporator.
Further purification by flash chromatography on SiO2 using
a 10:1 hexanes-ethyl acetate eluent system afforded 0.296 g
(81.26%) of the addition product as white crystals: mp 67-68
°C; MS for C25H32 m+/e obsd 332.3435, calcd 332.5054; 1H NMR
(CDCl3, 200 MHz) δ 1.01 (9H, s, tBu), 0.76 (9H, s, tBu), 2.07
(1H, dd, J ) 9.8 and J ) 3.8), 3.65 (1H, d, J ) 17.7), 4.10 (1H,
1
title trans alcohol: bp 126-129 °C/60 Torr; H NMR (CDCl3,
200 MHz) δ 0.9 (9H, s, tBu), 1.01 (9H, s, tBu), 1.4-1.5 (1H, m
OH), 3.6-3.8 (1H, d, J ) 7.5 Hz), 5.4 (1H, dd, J ) 15.6, 7.5
Hz), 5.6 (1H, d, J ) 7.5 Hz).
tr a n s-2,2,6,6-Tetr am eth yl-3-ch lor o-4-h epten e,10b.Thion-
yl chloride (3.5 mL, 0.048 mol, distilled) was introduced into
a three-neck, 50 mL dry round-bottom flask equipped with an
addition funnel, a magnetic stirbar, and a glass stopcock
connected to a CaCl2 drying tube. Anhydrous diethyl ether,
30 mL, was added and the mixture stirred at room tempera-
ture for 15 min, Then trans alcohol, 10a (7.0 g, 0.041 mol),
dissolved in 10 mL of diethyl ether was added dropwise from
the addition funnel over a period of 30 min. The resulting
solution was allowed to stir for an additional 2 h. The reaction
mixture was then treated with 10 mL of 2 N KOH (aq), washed
twice with 10 mL each of NaHCO3 (sat.), dried with MgSO4,
and concentrated by rotary evaporation. Distillation afforded
5.4 g (69.6% yield) of the title chloride as a light yellow liquid:
bp 108-112 °C/57 Torr; 1H NMR CDCl3, 200 MHz) δ 0.99 (9H,
s, tBu), 1.02 (9H, s, tBu), 4.1 (1H, d, -CCl (tBu) J ) 9.3 Hz),
5.46 (1H, dd, vinyl J ) 15.5, 9.3 Hz), 5.65 (1H, d, vinyl J )
15.5 Hz); 1H NMR (CDCl3, 50 Hz); d, 26.68, 29.37, 32.98, 36.05,
75.06, 123.19, 145.11.
tr a n s-2,2,6,6-Tetr am eth yl-5-(ph en ylth io)-3-h epten e, 10c.
Into a flame-dried three-neck 50 mL round-bottom flask
equipped with an addition funnel, magnetic stirbar, glass
stopcock, and a reflux condenser connected to an argon inlet
was introduced 10 mL of dry THF and thiophenol (0.58 mL,
0.0053 mol). Next, the solution was cooled with an external
acetone-dry ice bath to -78 °C. When the desired temperature
had been reached, n-butyllithium (2.12 mL, 2.5 M, 0.0053 mol)
in hexanes was added very slowly from the addition funnel to
the mixture, which developed a blue-gray color. It was stirred
for 15 min and then allowed to warm to room temperature.
The chloride 10b (1.1 g, 0.058 mol) was then added dropwise
and the mixture stirred for an additional 1 h. After this, it
was refluxed for another hour, followed by the addition of 5
mL of 2 M KOH (aq), and finally it was refluxed overnight. At
this point, thin-layer chromatography indicated the total
conversion of the starting material to the title compound. The
solution was washed twice with 10 mL portions of 2 N KOH
(aq) to remove unreacted thiophenol. Then the THF was
removed in vacuo, and the reaction mixture was extracted
twice with ether (10 mL each), dried with MgSO4, and
concentrated. The crude product was purified by flash column
chromatography (SiO2, hexanes) to afford 0.8 g (62% yield) of
the pure title phenyl sulfide: MS for C17H26S m+/e 262.1758
1
obsd, calcd 262.1757; H NMR (CDCl3, 200 MHz) δ 0.84 (9H,
s), 1.07 (9H, s), 3.27 (1H, d, J ) 9.9 Hz), 5.05 (1H, d, J ) 15.4
Hz), 5.24 (1H, dd, J ) 15.4, 9.9), 7.18-7.38 (5H, m); 13C NMR
(CDCl3, 50 MHz) δ 28.07, 29.47, 32.20, 34.53, 65.79, 123.03,
126.82, 128.36, 133.99, 135.70, 143.61.
tr a n s-2,2,6,6-Tetr a m eth yl-5-(tr im eth ylsta n n yl)-3-h ep -
ten e, 12. The apparatus consisted of a three-neck 50 mL
round-bottom flask, previously flame dried and equipped with
a glass coated stirring bar, addition funnel, a glass stopcock,
and an argon inlet. It was placed in the drybox (argon) and
loaded with finely cut lithium slivers (6.3 mg, 9 mg atom).
Then, outside the drybox and under positive Ar pressure 10
mL of anhydrous THF was added by syringe very carefully.
The flask was cooled to -50 °C with a dry ice-acetone bath,
and 1-(N,N-dimethylamino)naphthalene (1.53 g, 8.9 mmol) was
added dropwise from the addition funnel with stirring. The
mixture was allowed to react for 12 h, developing a green-
black coloration. After all the lithium slivers had disappeared,
the system was cooled to -78 °C, and the sulfide 10c (0.5 g,
1.9 mmol), previously dissolved in 0.5 mL of THF in the
addition funnel, was added very slowly until the reaction
mixture turned red. The resulting solution was treated with
trimethyltin chloride (2.0 mL, 1 M,2 mmol) in diethyl ether.

1310 J . Org. Chem., Vol. 64, No. 4, 1999
Fraenkel et al.
2
d, J ) 17.7), 4.28 (1H, d, J ) 3.81), 4.8-4.9 (1H, dd, J ) 15.4,
9.9), 5.0 (1H, d, J ) 15.4), 7.1-7.4 (8H, m, ring); 13C NMR
(CDCl3, 200 MHz) δ 28.8, 29.11, 32.63, 34.60, 37.11, 47.58,
61.5, 124.49, 125.27, 125.68, 125.81, 127.64, 127.78, 129.15,
137.78, 138.45, 141.73.
1-(Dim eth yleth ylsilyl)a llyllith iu m , TMEDA Com p lex,
16. n-Butyllithium in pentane (1.36 mL, 2.5 M, 3.4 mmol) was
slowly added by syringe to a solution of TMEDA (0.39 g, 3.4
mmol) and 3-dimethylethylsilylpropene (0.43 g, 3.4 mmol) in
3 mL of THF at 0 °C. The mixture was warmed to room
temperature and stirred for 3 h. A 0.5 M solution of the title
compound in dimethyl ether-d10 was prepared for NMR study,
as described above.
and 4.87 (m, 2H, J (CH2d) ) -1.4 Hz); 13C NMR (CDCl3, 50
MHz) δ 6.59 (Si(CH3)2), 26.56 (C(CH3)3), 16.78 (C(CH3)3), 20.7
(CH2Si), 135.69 (-CHd), 112.68 (CH2d).
1-Dim eth yl-(ter t-bu tylsilyl)a llyllith iu m , 21. Compound
20 (0.035 g, 0.23 mmol) and TMEDA (0.023 g, 0.2 mmol) were
dissolved in 2 mL of dry diethyl ether in a 50 mL Schlenk tube
under an argon atmosphere. With external cooling to -68 °C,
n-butyllithium-6Li (3.5 mL, 0.57 M, 0.2 mmol) in pentane was
then added dropwise to the reaction mixture with stirring.
After the reaction was allowed to warm to room temperature,
4 h, neutral silane and diethyl ether were removed under high
vacuum and the residue dissolved in 1 mL of pentane. This
solution was transferred in a Schlenk tube to the drybox (argon
atmosphere) and then syringed into a 5 mm OD NMR tube.
Volatile components were removed under high vacuum, and
the NMR sample in diethyl ether was prepared as described
above: 1H NMR (diethyl ether-d10, 200 MHz, 293 K) δ 0.859
(s, 9H, C(CH3)), -0.036 (s, 6H, Si(CH3)2), 1.94 (1, CHSi), 6.46
(m, 1H, CHCH2), 2.81 (m, 2H, CH2CH), 2.71 (s, 6H, NCH3),
2.46 (s, 4H, NCH2); 13C NMR (75 MHz) δ -3.1 (Si(CH3)2), 27.85
(C(CH3)3), 50.87 (CHSi), 149.98 (CHCH2), 65.21 (CHCH2),
46.97 (NCH3), 57.93 (NCH2).
t r a n s-1-(Tr im e t h ylsilyl)-3-(d im e t h yle t h ylsilyl)p r o-
p en e, 24. To a solution of 3-(trimethylsilyl)propene (2.1 g,
0.018 mol) and TMEDA (2.05 g, 0.018 mol) in 30 mL of THF
was added at 0 °C n-butyllithium in pentane (7.1 mL, 2.5 M,
0.018 mol). The mixture was then warmed to room tempera-
ture and stirred for 3 h. Dimethylethylchlorosilane (2.17 g,
0.018 mol) was added dropwise over 1 min. Hydrolysis (excess
water) followed by ether extraction and drying of the extracts
with sodium sulfate yielded after rotary evaporation of solvent
and vacuum distillation of the residue 1.5 g of the title
compound in 42% yield: bp 97-98 °C/40 Torr; proton NMR
(CDCl3, 200 MHz) δ 6.04 (m, 1H), 5.44 (m, 1H), 1.63 (m, 2H),
0.94 (t, 6H), 0.51 (q, 4H), 0.018 (s, 9H), 0.0 (s, 6H); 13C NMR
(CDCl3, 50 MHz) δ 143.7, 127.9, 26.6, 73, 6.7, -0.98, -4.19.
tr a n s-1,3-Bis(d im eth yleth ylsilyl)p r op en e, 17. To a solu-
tion of 3-(dimethylethylsilyl)propene (5 g, 0.039 mol) and
TMEDA (4.54 g, 0.039 mol) in 70 mL of THF was added at 0
°C n-butyllithium (16 mL, 2.5 M, 0.039 mol) in pentane. The
mixture was warmed to room temperature and stirred for 3
h. Then 3-dimethylethylchlorosilane (4.8 g, 0.039 mol) was
added dropwise over 10 min. Hydrolysis with excess water
followed by ether extraction and drying the ether extracts with
sodium sulfate gave, after removal of solvent and vacuum
distillation of the residue, 4.0 g of the title compound in 48%
1
yield: bp 126-127 °C/40 Torr; H NMR (CDCl3, 200 MHz) δ
6.02 (m, 1H), 5.47 (m, 1H), 1.61 (m, 2H), 0.97 (t, 6H), 0.51 (q,
4H), 0.08 (s, 6H), -0.04 (s, 6H); 13C NMR (CDCl3, 50.0 MHz)
δ 144.2, 126.6, 26.7, 7.7, 7.4, 7.2, 6.7, -3.3, -4.2.
1,3-Bis(d im eth yleth ylsilyl)a llyllith iu m , TMEDA Com -
p lex, 18. n-Butyllithium-6Li in pentane (4.5 mL, 0.616 M, 2.77
mmol) was slowly added by syringe to a solution of TMEDA
(0.31 g, 0.41 mL, 2.7 mmol) and trans-1,3-bis(dimethylethyl-
silyl)propene (0.58 g, 2.7 mmol) in 2 mL of diethyl ether at 0
°C. The mixture was warmed to room temperature and stirred
for 3 h. A 0.5 M solution in diethyl ether-d10, degassed in a 5
mm OD NMR tube, was prepared for NMR studies, as
described above.
3-(Dim eth yl-ter t-bu tylsilyl)p r op en e, 20. Allyllithium19
(2.4 g, 0.05 mol) was placed in an addition funnel and dissolved
in 10 mL of dry, degassed THF. Under an argon atmosphere
and at room temperature, this solution was added dropwise
over 30 min to chloro-tert-butyldimethylsilane (7.53 g, 0.05
mol) dissolved in 30 mL of dry THF contained in a 250 mL
round-bottom Schlenk flask. After the addition was complete,
the reaction was allowed to continue for 2 h, after which it
was quenched by addition of 5 mL of 3% NaOH solution
saturated with NaCl. The organic phase was extracted with
diethyl ether and dried over Na2SO4. Solvents were removed
by rotary evaporation, and the residue was distilled at 132
°C/760 Torr to give 6.56 g of the title compound in 84% yield:
1H NMR (CDCl3, 200 MHz) δ 0.87 (s, 9H, C(CH3)3), -0.068 (s,
exo,exo-1-(Tr im eth ylsilyl)-3-(d im eth yleth ylsilyl)a llyl-
lith iu m , 25. n-Butyllithium-7Li (0.5 mL, 2.5 M, 1 mmol) in
pentane was slowly added by syringe to a solution of TMEDA
(0.168 mL, 1.12 mmol) and trans-1-(trimethylsilyl)-3-(dimeth-
ylethylsilyl)propene (0.223 g, 1.12 mmol) in 2 mL of diethyl
ether at 0 °C. The mixture was warmed to room temperature
over 3 h. An NMR sample tube of the title compound in diethyl
ether-d10 was prepared, as described above. This sample was
stored in dry ice prior to the NMR studies.
Ack n ow led gm en t. This research was generously
supported by the National Science Foundation Grant
No. CHE 9615116 as was, in part, acquisition of the
NMR equipment used in this work. We are grateful to
Dr. Charles Cottrell, Central Campus Instrument Cen-
ter, who provided invaluable advice on NMR technology.
3
6H, Si(CH3)2), 1.518 (d, 2H, CH2Si, J (CH2-CHdCH2) ) 8.1
3
Hz), 5.78 (m, 1H, CH2dCH, J (CH2dCH) ) 16.6, 10 Hz), 4.78
(19) Seyferth, D.; Weiner, M. A. J . Org. Chem. 1961, 26, 4797.
J O982196F