One-step syntheses of styryl germatranes via rhodium- or palladium-catalyzed hydrogermylation of arylacetylenes by HGe(OCH2CH2)3N

Article abstract of DOI:10.1021/om020714d

The addition of germatrane, HGe(OCH₂CH₂)₃N (1), to terminal acetylenes is catalyzed by [Cp*RhCl₂]₂ and yields styrylgermatranes. The stereochemistry of the double bond can be controlled by the choice

Full text of DOI:10.1021/om020714d

Organometallics 2003, 22, 199-202
199
On e-Step Syn th eses of Styr yl Ger m a tr a n es via Rh od iu m -
or P a lla d iu m -Ca ta lyzed Hyd r oger m yla tion of
Ar yla cetylen es by HGe(OCH2CH2)3N
J . W. Faller* and Roman G. Kultyshev
Department of Chemistry, Yale University, New Haven, Connecticut 06520
Received August 30, 2002
Summary: The addition of germatrane, HGe(OCH2-
CH2)3N (1), to terminal acetylenes is catalyzed by
[Cp*RhCl2]2 and yields styrylgermatranes The stereo-
chemistry of the double bond can be controlled by the
choice of solvent. In methylene chloride, (E)-â-styrylger-
matranes are the major products, whereas in toluene (Z)-
â-styrylgermatranes are the major products. The addi-
tion is also catalyzed by Pd(PPh3)4, giving (E)-â-
styrylgermatranes regardless of solvent.
occurs in a highly regio- and stereoselective manner, but
with the opposite stereochemistry (Table 1, entry 1). The
1H NMR spectrum of the main product agrees with that
reported by Lukevics and co-workers6,7 for (E)-â-
styrylgermatrane (E-4a ) prepared by a different route.
The rhodium-catalyzed hydrogermylation reactions of
p-tolylacetylene (3b) and p-chlorophenylacetylene (3c)
were less rapid than in the case of phenylacetylene;
nevertheless, no germanium hydride remained after 3
days of stirring at room temperature (entries 2, 3). Small
amounts of the corresponding stereoisomer Z-4 and
regioisomer 5 were also produced. The stereochemistry
of (E)-â-(4-methyl)styrylgermatrane, E-4b, was con-
firmed by single-crystal X-ray diffraction analysis.
In tr od u ction
The transition metal-catalyzed addition of germanium
hydrides to carbon-carbon multiple bonds is an efficient
way to synthesize functionalized germanes. Previously,
Oshima and co-workers1 showed that in the presence
of Pd(PPh3)4 triphenylgermane stereoselectively adds to
terminal acetylenes, providing (E)-alkenyltriphenylger-
manes in good yields. Hydrogermylation of isoprene by
tri(2-furyl)germane in water in the presence of allylpal-
ladium chloride dimer resulted in an allylic compound,
(E)-â-methylcrotyltri(2-furyl)germane.2
Germatrane, HGe(OCH2CH2)3N (1), was first synthe-
sized in 1981 by Mironov and co-workers.3a Although
they investigated the possibility of using 1 for the
preparation of other germatranes, in particular via its
reactions with alkyl halides,3b to the best of our knowl-
edge the addition of 1 to the triple bonds of alkynes has
not been investigated. Our interest in the synthesis of
alkenyl and styryl germatranes resulted from their
potential application in palladium-catalyzed cross-
coupling reactions and prompted us to explore 1 as a
hydrogermylating reagent for alkynes.4,5
We observed that the stereochemical outcome of the
rhodium-catalyzed addition of germatrane, 1, to ary-
lacetylenes, was solvent dependent. Thus, when instead
of using CH2Cl2 as solvent, the reaction of 1 with
phenylacetylene was performed in toluene under reflux,
Z-4a was the major product (entry 4). The cis-stereo-
chemistry was indicated by a smaller coupling between
3
the olefinic protons (3J ) 14 Hz, whereas J ) 18 Hz
for E-4a ) and was confirmed by single-crystal X-ray
diffraction. Similarly, hydrogermylation of 4-methyl and
4-chloro analogues, 3b and 3c, in toluene produced
predominantly Z-4b and Z-4c, with Z:E ratios of 5.5:1
and 4.7:1, respectively (entries 5, 6). Traces of R-prod-
ucts 5b and 5c were also observed.
Having established that the stereochemical outcomes
of the hydrogermylation reaction in dichloromethane
and toluene were different, we investigated some other
solvents. Addition of 1 to phenylacetylene in acetonitrile
at room temperature was significantly slower than that
in dichloromethane and resulted in only one-third
conversion after the same reaction time, yet it also
yielded predominantly the trans-styrylgermatrane, E-4a.
Upon heating under reflux in acetonitrile 1 was com-
pletely consumed, yielding E-4a and the R-product, 5a ,
in a ratio of 95:5. The latter was identified by a distinct
AB pattern of its diastereotopic methylene protons at δ
5.97 and 5.90 (CDCl3). Reaction in THF at room tem-
perature was more sluggish (20% conversion) and less
stereoselective, yielding both E- and Z-4a . Overnight
reflux resulted in 42% conversion with an observed Z/ E
ratio of 1:1.4. Apparently, in toluene at reflux the
reaction follows a pathway different from that in more
polar solvents, such as dichloromethane and acetoni-
trile, whereas in THF, a solvent of an intermediate
Resu lts a n d Discu ssion
[Cp *Rh Cl2]2- or P d (P P h 3)4-Ca ta lyzed Hyd r oger -
m yla t ion of Ar yla cet ylen es. Recently our group
reported the highly regio- and stereoselective hydrosi-
lylation of phenylacetylene by triorganosilanes, HSiR3
(R ) Ph, Et, OEt), in the presence of catalytic amounts
of [Cp*RhCl2]2 (2a ) that yielded (Z)-â-styrylsilanes.4
Similarly, addition of germatrane 1 to phenylacetylene
(3a ) in dichloromethane in the presence of [Cp*RhCl2]2
(1) Ichinose, Y.; Oda, H.; Oshima, K.; Utimoto, K. Bull. Chem. Soc.
J pn. 1987, 60, 3468-3470.
(2) Kinoshita, H.; Nakamura, T.; Kakiya, H.; Shinokubo, H.; Mat-
subara, S.; Oshima, K. Org. Lett. 2001, 3, 2521-2524.
(3) (a) Mironov, V. F.; Khromova, N. Yu.; Gar, T. K. Zh. Obshch.
Khim. 1981, 51, 954-955. (b) Gar, T. K.; Khromova, N. Yu.; Tandura,
S. N.; Mironov, V. F. Zh. Obshch. Khim. 1983, 53, 1800-1807.
(4) Faller, J . W.; D’Alliessi, D. G. Organometallics 2002, 21, 1743-
1746.
(5) Faller, J . W.; Kultyshev, R. G. Organometallics 2002, 21, in press.
10.1021/om020714d CCC: $25.00 © 2003 American Chemical Society
Publication on Web 12/05/2002

200 Organometallics, Vol. 22, No. 1, 2003
Notes
Ta ble 1. Tr a n sition Meta l-Ca ta lyzed Hyd r oger m yla tion of Ar yla cetylen es by Ger m a tr a n e, 1
entry
acetylene
R
catalysta
reaction conditions
time, hb
E-4:Z-4:5c
1
2
3
4
5
6
7
8
3a
3b
3c
3a
3b
3c
3a
3a
3a
3b
3c
H
CH3
Cl
H
CH3
Cl
H
H
H
CH3
Cl
2a
2a
2a
2a
2a
2a
2a
2b
2b
2b
2b
CH2Cl2, r.t.
CH2Cl2, r.t.
CH2Cl2, r.t.
toluene, reflux
toluene, reflux
toluene, reflux
acetonitrile, reflux
THF, r.t.
20
84
70
12
12
12
25
51
18
91
48
27.5:1.2:1
18.7:1.8:1
22.9:1d
7.5:26.5:1
5.4:29.7:1
6.2:29.4:1
15.8:0e:1
62:2.3:1
f
9
10
11
toluene, reflux
THF, r.t.
THF, r.t.
24.2:0e:1
12.6:0e:1
2a ) [Cp*RhCl2]2; 2b ) Pd(PPh3)4. b Not optimized. c Determined by integration of olefinic protons in 1H NMR spectra of crude products.
E-4:5 ratio, signals of Z-4 could not be integrated accurately. e Not observed by 1H NMR. f Not determined.
a
d
polarity, both pathways are accessible.8 Pure E-4a and
Z-4a did not isomerize upon heating in toluene either
in the presence or in the absence of [Cp*RhCl2]2.
Initial attempts to use aliphatic alkynes such as
1-hexyne and trimethylsilylacetylene in the rhodium-
catalyzed hydrogermylation reaction were not promis-
ing. In the former case only 20% conversion was
achieved after 24 h of stirring in CH2Cl2. In the latter
case no addition to the triple bond was observed after
25 h. Contrary to observations on related hydrosilyla-
tions,4 [Cp*Rh(BINAP)](SbF6)2 prepared in situ from
[Cp*Rh(BINAP)Cl]Cl and AgSbF6 did not catalyze the
hydrogermylation of phenylacetylene by 1.
rhodium-catalyzed reaction, the palladium-catalyzed
addition to 3a resulted in the (E)-olefin as the major
product regardless of solvent used (Table 1, entries 8,
9). Using toluene as solvent under reflux conditions not
only shortened the reaction time but also improved the
yield in the case of the 4-methyl analogue, 3b (75% vs
42%).
Con clu sion
We have shown that the addition of germatrane, HGe-
(OCH2CH2)3N, to terminal aryl acetylenes is catalyzed
by [Cp*RhCl2]2 and yields styrylgermatranes. The ster-
eochemistry of the double bond in the product can be
controlled by the choice of solvent. In methylene chlo-
ride, (E)-â-styrylgermatranes are the major products,
whereas in toluene (Z)-â-styrylgermatranes are the
major products. The same addition is also catalyzed by
Pd(PPh3)4; however (E)-â-styrylgermatranes are pro-
duced regardless of solvent. The rhodium catalyst is
more efficient, offers the ability to select the stereo-
chemistry of the product, and avoids contamination of
the product with triphenylphosphine oxide.
The addition of germanium hydride 1 to aryl acety-
lenes proceeds also in the presence of Pd(PPh3)4 (2b).
Although the palladium-catalyzed hydrogermylation of
3a in THF is faster than in CH2Cl2, it is still slower
than the corresponding rhodium-catalyzed reaction. The
addition products were contaminated with triphenylphos-
phine oxide (TPPO) resulting from oxidation of triph-
enylphosphine [derived from Pd(PPh3)4]. Owing to dif-
ficulties encountered with TPPO removal, the yields
1
were determined from H NMR spectra by the integra-
These methods provide routes to styryl germatranes
that can be used as reagents in environmentally friendly
“tin-free” Stille-type cross-coupling reactions.5
tion of the CH2O signals of germatranes and 1,2-
diphenoxyethane used as a standard (86, 42, and 81%
for 3a , 3b, and 3c, respectively). In contrast to the
Exp er im en ta l Section
(6) Ignatovich, L.; Belyakov, S.; Popelis, Yu; Lukevics, E. Chem.
Heterocycl. Compd. 2000, 36, 603-606.
(7) These authors reported two doublets due to vinyl protons at δ
6.38 and 6.44 in CDCl3. In fact, one doublet is at δ 6.41 while another
one overlaps with phenyl signals in the range δ 7.19-7.28, which is
clear from the integration data as well as from the 13C-1H correlation
spectrum (HMQC). In addition, in d4-MeOH the second vinyl signal
can be observed displaced from the aromatic protons. Our 13C{1H}
NMR data do not agree with those authors. The biggest discrepancy
is for the vinyl carbon bound to germanium, which was reported to
have a chemical shift of δ 88.1 in CDCl3. Our results show that both
olefinic carbon atoms have chemical shifts in the expected range (δ
120-150) at δ 125.3 and 144.9.
Gen er a l Da ta . Most synthetic manipulations were carried
out using standard Schlenk techniques under an inert atmo-
sphere. Dry solvents were used unless noted otherwise. 1H
NMR spectra were recorded on either a Bruker 500 MHz or
Bruker 400 MHz spectrometer, and chemical shifts are re-
ported in ppm relative to TMS by calibration from residual
protons in the deuterated solvent signals. Methylene reso-
nances of the germatranes are reported as triplets, but these
are apparent triplets arising from an AA′BB′ system. 13C{1H}

Notes
Organometallics, Vol. 22, No. 1, 2003 201
NMR spectra were recorded on either a Bruker 500 MHz or
Bruker 400 MHz spectrometer operating at 125.8 and 100.6
MHz, respectively, and referenced using carbon in the solvent.
Ger m a tr a n e 1. Compound 1 was prepared using a modi-
fication of the procedure of Mironov et al.3a A 100 mL Schlenk
flask equipped with a stirring bar and rubber septum was
charged with 3.00 mL of GeCl4 (26.3 mmol) and 30 mL of dry
hexane under nitrogen atmosphere and placed in an ice-water
bath. Trichlorosilane (2.70 mL, 26.7 mmol) was added by
syringe. After stirring for 30 min, 3.70 mL of dry Et3N (26.5
mmol) was added dropwise within 2 min, and the cold bath
was removed. Two phases formed, which initially were red
(bottom) and colorless and cloudy (top). The red color changed
to yellow within minutes. After stirring for 1 h the lower phase
was separated, washed with dry hexane (3 × 10 mL), and
returned to the 100 mL Schlenk flask. Dry toluene (35 mL)
was added under nitrogen followed by 4.6 mL of EtOH (78.4
mmol) and 11.0 mL of dry Et3N (78.9 mmol). After stirring
for 1 h, the white precipitate that formed was filtered off and
washed with 80 mL of dry toluene. The filtrate and washings
were combined and added to a 250 mL round-bottomed flask
containing 3.929 g of triethanolamine (25.81 mmol) in 10 mL
of toluene and a stirring bar. The resulting solution was stirred
at room temperature for 16 h. The yellow-orange precipitate
that formed was filtered off and washed with toluene. The
yellow-orange precipitate was washed on the frit with 60 mL
of dichloromethane, yielding a colorless filtrate, from which 1
(3.12 g, 55% yield) was obtained after solvent removal in vacuo.
Pentane was added to the toluene filtrate until the combined
volume was 300 mL, and the resulting white precipitate was
filtered off and washed with pentane. The white precipitate
was redissolved in 40 mL of dichloromethane and passed
through a 0.9 mm pad of silica gel on a 30 mL frit. The pad
was washed with dichloromethane (15 mL), the filtrates were
combined, and the solvent was removed in vacuo. This
provided an additional 0.83 g of 1 (70% combined yield) melting
evaporation of toluene was dissolved in dichloromethane and
passed through a pad of silica gel on a 15 mL frit (0.7 mm).
After washing with dichloromethane the filtrate and washings
were combined, and the volatiles were removed under reduced
pressure. The residue was crystallized from diethyl ether
followed by slow evaporation to yield pale yellow crystals.
Colorless crystals of Z-4a suitable for X-ray analysis were
grown by slow evaporation of CHCl3 from a chloroform-decalin
1
solution. H NMR (CD3OD, 400 MHz): δ 7.62 (d, 2H, J ) 7.1,
C6H5), 7.33-7.21 (m, 4H, C6H5 and CHd), 5.83 (d, 1H, J )
14.2, CHd), 3.76 (t, 6H, J ) 5.6, CH2O), 2.84 (t, 6H, J ) 5.6,
CH2N). 13C{1H} NMR (CDCl3, 100.6 MHz): δ 145.8, 139.2,
128.6, 127.8, 127.71, 127.68, 57.0, 52.4.
E-â-(4-Met h yl)st yr ylger m a t r a n e (E-4b ).
A 100 mL
Schlenk flask equipped with a stirring bar and a rubber
septum was charged with 0.2203 g of 1 (1.002 mmol) and
0.0314 g of 2a (0.051 mmol). Dichloromethane (10 mL) was
added under nitrogen followed by 0.20 mL of 3b (1.53 mmol).
The resulting solution was stirred at room temperature for
84 h. The reaction mixture was filtered through a pad of Celite
and washed with dichloromethane followed by solvent removal
in vacuo. The crude product was dissolved in acetonitrile and
chromatographed on reversed-phase silica gel (C8) using
acetonitrile as the eluent. The title compound was obtained
as a colorless solid (0.100 g, 30%). 1H NMR (CDCl3, 500
MHz): δ 7.32 (d, 2H, J ) 7.9, C6H4), 7.17 (d, 1H, J ) 18.6,
CHd), 7.07 (d, 2H, J ) 7.9, C6H4), 6.34 (d, 1H, J ) 18.6, CHd
), 3.83 (t, 6H, J ) 5.6, CH2O), 2.86 (t, 6H, J ) 5.6, CH2N),
2.30 (s, 3H, CH3). 13C{1H} NMR (CDCl3, 100.6 MHz): δ 144.8,
137.8, 135.5, 129.1, 126.8, 123.9, 56.9, 51.8, 21.4. Anal. Calcd
for C15H21O3NGe: C, 53.63; H, 6.30; N, 4.17. Found: C, 53.82;
H, 6.42; N, 4.30.
Z-â-(4-Meth yl)styr ylger m a tr a n e (Z-4b) (con ta in s 12%
of E-isom er ). A 25 mL three-necked round-bottomed flask
equipped with a stirring bar, reflux condenser, and a rubber
septum was charged with 0.2195 g of 1 (1.00 mmol) and 0.0291
g of 2a . Dry toluene (10 mL) was added under nitrogen
followed by 0.20 mL of 97% 3b (1.53 mmol). The resulting
solution was heated under reflux for 12 h and filtered through
a pad of Celite. After washing with dichloromethane and
solvent removal the residue was dissolved in 2 mL of aceto-
nitrile and chromatographed on reversed-phase silica gel (C8)
using acetonitrile as an eluent. The title compound was
obtained as a pale orange solid (0.2300 g, 68%). 1H NMR
(CDCl3, 400 MHz): δ 7.52 (d, 2H, J ) 7.8, C6H4), 7.26 (d, 1H,
J ) 14.2, CHd), 7.09 (d, 2H, J ) 7.8, C6H4), 5.76 (d, 1H, J )
14.2, CHd), 3.76 (t, 6H, J ) 5.6, CH2O), 2.83 (t, 6H, J ) 5.6,
CH2N), 2.32 (s, 3H, CH3). 13C{1H} NMR (CDCl3, 100.6 MHz):
δ 145.7, 137.4, 136.2, 128.56, 128.55, 126.4, 57.0, 52.4, 21.5.
Anal. Calcd for C15H21O3NGe: C, 53.63; H, 6.30; N, 4.17.
Found: C, 53.06; H, 6.30; N, 4.13.
1
at 162 °C (lit.3a 156-158 °C). H NMR (CDCl3, 400 MHz): δ
5.77 (s, 1H, GeH), 3.80 (apparent t, 6H, J ) 5.7, CH2O), 2.86
(apparent t, 6H, J ) 5.7, CH2N). 13C{1H} NMR (CDCl3, 125.8
MHz): δ 56.7, 51.8.
E-â-Styr ylger m a tr a n e (E-4a ). A 100 mL Schenk flask
equipped with a stirring bar was charged with 0.1108 g of 1
(0.504 mmol) and 0.0152 g of 2a (0.025 mmol). Dry dichlo-
romethane (10 mL) was added under nitrogen. After stirring
for 15 min 3a (0.055 mL, 0.50 mmol) was added via syringe.
The resulting solution was stirred at room temperature for
19 h and passed through a pad of silica gel (Natland Inter-
national, 200-400 mesh) on a 15 mL frit (0.7 mm). After
washing with 30 mL of dichloromethane the filtrate and
washings were combined, and the volatiles were removed
under reduced pressure. The residue was crystallized by
1
addition of ether followed by evaporation (0.0368 g, 23%). H
E-â-(4-Ch lor o)styr ylger m atr an e (E-4c). A 100 mL Schlenk
flask equipped with a stirring bar and a rubber septum was
charged with 0.2208 g of 1 (1.005 mmol), 0.0284 g of 2a (0.046
mmol), and 0.2048 g of 3c (1.500 mmol). Dichloromethane (10
mL) was added under nitrogen, and the resulting solution was
stirred at room temperature for 70 h. The reaction mixture
was filtered through a pad of Celite followed by washing with
dichloromethane (90 mL) and solvent removal in vacuo.
Acetonitrile (4-5 mL) was added to the residue, and the
resulting solution was chromatographed on reversed-phase
silica gel (C8) using acetonitrile as the eluent. The product after
chromatography was dissolved in 2-3 mL of dichloromethane
and precipitated by addition of 50 mL of petroleum ether (bp
35-60 °C). Compound E-4c was obtained as a pale yellow solid
NMR (CD3OD, 400 MHz): δ 7.42-7.20 (m, 5H, C6H5), 7.12 (d,
1H, J ) 18.7, CH ) ), 6.32 (d, 1H, J ) 18.7, CHd), 3.78 (t, 6H,
J ) 5.7, CH2O), 2.94 (t, 6H, J ) 5.7, CH2N). 13C{1H} NMR
(CDCl3, 100.6 MHz): δ 144.9, 138.2, 128.5, 128.0, 126.9, 125.3,
56.9, 51.9. Anal. Calcd for C14H19O3NGe: C, 52.24; H, 5.95;
N, 4.35. Found: C, 52.12; H, 5.85; N, 4.14. This compound was
previously prepared by a different route.6,7
Z-â-Styr ylger m a tr a n e (Z-4a , con ta in s 21% of E-4a ). A
25 mL three-necked round-bottomed flask equipped with a
stirring bar, reflux condenser, and a rubber septum was
charged with 0.2199 g of 1 (1.000 mmol) and 0.0283 g of 2a
(0.046 mmol). Toluene (10 mL) was added under nitrogen
followed by 0.17 mL of 3a (1.55 mmol). The resulting solution
was heated under reflux for 12 h and passed through a pad of
Celite. After washing with dichloromethane and removal of
solvents the residue was dissolved in 5 mL of acetonitrile and
chromatographed on reversed-phase silica gel (C8) using
acetonitrile as an eluent. The title compound was obtained as
a tan solid (0.2584 g, 80%). Alternatively the residue left after
1
(0.1925 g, 54%). H NMR (CDCl3, 500 MHz): δ 7.35 (d, 2H, J
) 8.5, C6H4), 7.23 (d, 2H, J ) 8.5, C6H4), 7.16 (d, 1H, J ) 18.6,
CHd), 6.39 (d, 1H, J ) 18.6, CHd), 3.85 (t, 6H, J ) 5.7, CH2O),
2.89 (t, 6H, J ) 5.7, CH2N). 13C{1H} NMR (CDCl3, 125.8
MHz): δ 143.5, 136.8, 133.7, 128.7, 128.1, 126.4, 56.9, 51.9.

202 Organometallics, Vol. 22, No. 1, 2003
Notes
Ta ble 2. Cr ysta llogr a p h ic Da ta for Z-4a
color, shape colorless plate
empirical formula
C
14H19GeNO3
fw
321.90
radiation /Å
T/K
Mo KR (monochr.) 0.71073
183
cryst syst
monoclinic
space group
P21/c (No. 14)
unit cell dimens
a/Å
b/Å
c/Å
9.7012(3)
11.2953(4)
13.3512(6)
107.081(2)
1398.47(9)
4
â/deg
V/Å3
Z
D
calc/g cm-3
1.529
21.93
µ/cm-1 (Mo KR)
cryst size/mm
0.048 × 0.169 × 0.169
11096, 3346; 2053
0.053
reflns tot., unique, useda
Rint
transmn range
params, restraints
R1,a wR2,b S
0.661-0.911
F igu r e 1. ORTEP diagram of (Z)-â-styrylgermatrane (Z-
4a ). Metrical data of interest: Ge1-C7 ) 1.950(3) Å; Ge1-
N1 ) 2.193(2) Å; C7-C8 ) 1.336(4) Å; Ge1-C7-C8 )
132.0(3)°; C7-C8-C9 ) 129.6(3)°.
172, 0
0.030, 0.033, 0.94
-0.39 < 0.34
resid density/e Å-3
a
b
2
R1 ) ∑||Fo| - |Fc||/∑|Fo|, for all I > 3σ(I). wR2 ) [∑[w(Fo
-
Fc2)2]/∑[w(Fo2)2]]1/2
.
Anal. Calcd for C14H18O3NClGe: C, 47.19; H, 5.09; N, 3.93.
Found: C, 46.37; H, 5.06; N, 3.87.
spectra of a crude product obtained after removal of solvent
indicated the presence of the corresponding styrylgermatrane
and TPPO. The spectra of styrylgermatranes were identical
to those obtained in rhodium-catalyzed reactions. The following
procedure was used for the synthesis of E-4a in toluene under
reflux. A 100 mL Schlenk flask equipped with a stirring bar
was charged with 0.2200 g of 1 (1.00 mmol) and 0.058 g of 2b
(0.050 mmol, 5 mol %). Toluene (10 mL) was added by syringe
via a septum followed by 0.22 mL of 3a (2.0 mmol), and the
resulting solution was brought to reflux. After 17.5 h the
reaction mixture was passed through a pad of Celite. Addition
of ether to a residue obtained after the solvent removal
resulted in precipitation of E-4a as a tan solid (0.2288 g, 71%)
Z-â-(4-Ch lor o)styr ylger m a tr a n e (Z-4c) (con ta in s 15%
of E-isom er ). A 25 mL three-necked round-bottomed flask
equipped with a stirbar, reflux condenser, and a rubber septum
was charged with 0.2205 g of 1 (1.003 mmol), 0.0291 g of 2a ,
and 0.1659 g of 3c (1.215 mmol). Dry toluene (10 mL) was
added under nitrogen. The resulting solution was heated under
reflux for 12 h and passed through a pad of Celite.8 After
washing with dichloromethane and removal of solvents the
residue was dissolved in 2 mL of acetonitrile and chromato-
graphed on reversed-phase silica gel (C8) using acetonitrile as
an eluent. The title compound, Z-4c, was obtained as a pale-
orange powder (0.2410 g, 67%). 1H NMR (CDCl3, 500 MHz):
δ 7.56 (d, 2H, J ) 8.3, C6H4), 7.25-7.22 (m, 3H, C6H4 and CHd
), 5.86 (d, 1H, J ) 14.2, CHd), 3.75 (t, 6H, J ) 5.6, CH2O),
2.84 (t, 6H, J ) 5.6, CH2N). 13C{1H} NMR (CDCl3, 125.8
MHz): δ 144.3, 137.8, 133.4, 130.0, 129.0, 127.9, 57.0, 52.4.
Anal. Calcd for C14H18O3NClGe: C, 47.19; H, 5.09; N, 3.93;
Found: C, 46.96; H, 5.17; N, 3.97.
1
free of TPPO by H NMR.
Str u ctu r e Deter m in a tion a n d Refin em en t of (Z)-â-
styr ylger m a tr a n e (Z-4a ). Crystals were grown by slow
evaporation of CHCl3 from a chloroform-decalin solution. Data
were collected on a Nonius KappaCCD (Mo KR radiation)
diffractometer and corrected for absorption (SORTAV9). The
structure was solved by direct methods (SIR9210) and refined
on F for all reflections. Non-hydrogen atoms were refined freely
with anisotropic displacement parameters. Hydrogen atoms
were included at calculated positions. Relevant crystal and
data parameters are presented in Table 2, and an ORTEP
diagram is shown in Figure 1.
Hyd r oger m yla tion of Ar yla cetylen es in th e P r esen ce
of P d (P P h 3)4 (2b). A 100 mL Schlenk flask equipped with a
stirring bar was charged with 0.5 mmol of 1 and 0.025 mmol
of 2b (5 mol %) under nitrogen. THF (5 mL) was added by
syringe via a septum followed by 0.6-0.8 mmol of arylacety-
lene 3 (1.2-1.6 equiv), and the resulting solution was stirred
at room temperature for 2-4 days. The 1H and 31P NMR
Ack n ow led gm en t. We thank the National Science
Foundation (Grant CHE0092222) for support of this
research. We also thank Dr. J onathan Parr for helpful
suggestions.
(8) At room temperature the reaction in toluene is very slow and
gives only a trace of the addition product after 21 h. Interestingly, 1H
NMR indicated that this trace amount was (E)-4a , not (Z)-4a , which
is the main product obtained after reflux. We have discussed the
possible mechanistic implications of solvent dependence previously.4
The relative ease of obtaining syn and anti addition products may be
determined by the ease of formation and stability of an η2-vinyl group
or the formation of organometallic dimers in different solvents. These
paths would provide a route for the initially formed (Z)-isomer to
convert to the (E)-isomer.
(9) (a) Blessing, R. H. Acta Crystallogr. 1995, A51, 33-38. (b)
Blessing, R. H. J . Appl. Crystallogr. 1997, 30, 421-426.
(10) Altomare, A.; Cascarano, G.; Giacovazzo, C.; Guagliardi, A. J .
Appl. Crystallogr. 1993, 26, 343-350.
Su p p or tin g In for m a tion Ava ila ble: Detailed crystal-
lographic data, atomic positional parameters, and bond lengths
and angles for Z-4a are available in CIF format. This material
is available free of charge via the Internet at http://pubs.acs.org.
OM020714D