Bromination of Silatranyl-, Germatranyl-, Silyl-, and Germyl-phenylacetylenes

Article abstract of DOI:10.1002/hc.10211

Reactions of element-substituted alkynes R₃MC≡CPh (R ₃M = Me₃Si, Et₃Si, Ph₃Si, Et ₃Ge, n-Bu₃Sn, N(CH₂CH₂O) ₃Si, N(CH₂CH₂O)<

Full text of DOI:10.1002/hc.10211

Heteroatom Chemistry
Volume 15, Number 1, 2004
Bromination of Silatranyl-, Germatranyl-,
Silyl-, and Germyl-phenylacetylenes
Anastasia A. Selina,1 Sergey S. Karlov,1 Ekaterina V. Gauchenova,1
Andrei V. Churakov,2 Lyudmila G. Kuz’mina,2 Judith A. K. Howard,3
Jo¨rg Lorberth,4 and Galina S. Zaitseva1
1Chemistry Department, Moscow State University, Moscow, Russia
2Institute of General and Inorganic Chemistry, Russian Academy of Science, Moscow, Russia
3Department of Chemistry, Science Laboratories, University of Durham, Durham, England
4Fachbereich Chemie, Philipps-Universita¨t Marburg, Marburg, Germany
Received 25 June 2003
metallatranes of the group 14 elements have been
ABSTRACT: Reactions of element-substituted alky-
investigated rather in detail by the present time
nes R3MC CPh (R3M = Me3Si, Et3Si, Ph3Si, Et3Ge,
[1–5].
n-Bu3Sn, N(CH2CH2O)3Si, N(CH2CH2O)3Ge, N(CH2-
Hypercoordination in these compounds arises
CHMeO)3Ge, and N(CH2CH2O)2(CH2CHPhO)Ge)
from the existence of a transannular interaction be-
with bromine, tetra-n-butylammonium tribromide
tween nitrogen and the element atoms. This results
(TBAT), and N-bromosuccinimide (NBS)/DMSO were
in approximately trigonal bipyramidal coordination
investigated. The Z,E-ratio of isomeric dibromoal-
of the element and also in formal quarternization
kenes formed in bromination reaction with Br2 and
of nitrogen. Extended coordination explains speci-
TBAT are discussed. The crystal structures of N(CH2-
ficity of metallatrane properties that differ in many
CH2O)3SiC CPh and N(CH2CHMeO)3GeX (X = C
respects from the characteristics of tetracoordinated
CPh, C(Br) C(Br)Ph, C(Br2)C(O)Ph), and Ph3SiC-
derivatives with the similar structure. Investigation
ꢀ
C
(Br) C(Br)Ph are reported.
2003 Wiley Periodicals,
of metallatranes by using different spectroscopic and
other physical methods permits to form a general
idea about their electronic nature and bonding [1]. It
should be noted that the observed changes in phys-
ical properties and reactivity successfully correlate
with those in the transannular M ← N bond length
[2,6]. The latter and a number of other reasons cause
metallatranes to make a significant contribution to
the theoretic organometallic chemistry.
However, the main efforts in the area dis-
cussed were directed toward development of syn-
thetic routes for the preparation of metallatranes
with various structures. The chemistry of function-
ally substituted metallatranes is practically undevel-
oped. Studies concerning transformations of sub-
stituent at the element atom have so far been very
limited.
Inc. Heteroatom Chem 15:43–56, 2004; Published online
in Wiley InterScience (www.interscience.wiley.com). DOI
10.1002/hc.10211
INTRODUCTION
The chemistry of metallatranes has attracted con-
siderable interest in recent years [1]. Among them
Correspondence to: Jo¨rg Lorberth and Sergey S. Karlov; e-mail:
lorberth@chemie.uni-marburg.de, sergej@org.chem.msu.su.
Contract grant sponsor: Russian Foundation for Basic
Research.
Contract grant numbers: 01-03-32474 and 02-03-06347.
Contract grant sponsor: Royal Society of Chemistry.
c
ꢀ
2003 Wiley Periodicals, Inc.
43

44 Selina et al.
Earlier we reported that the treatment of
The triple bond of (trialkylsilyl)alkynes R3SiC
CH (R = Me, Et) vigorously adds Br2 without solvent,
one molecule of bromine adding at 20–50◦C and two
molecules at 70–90◦C [13]. The reaction was found
to proceed somewhat slower and with less heat ef-
ficiency in the dark and in the presence of inhibitor
(hydroquinone), although the yield of the products
does not change considerably. Evidently, free-radical
addition of bromine takes place along with the elec-
trophilic process of bromination. The presence of
alkoxy groups at the silicon atom was determined to
reduce the activity of the triple bond in the bromina-
tion reaction [14]. As to stereochemistry of the prod-
ucts, it has not been discussed in the papers cited
above.
N(CH2CH2O)3GeC CPh (1) with NBS/DMSO system
affords N(CH2CH2O)3GeCBr2C(O)Ph and the reac-
tion with bromine leads to the formation of cis-
N(CH2CH2O)3GeC(Br) C(Br)Ph [7]. In contrast to
this most of alkylatylacetylenes react with bromine
in chloroalkanes under conditions of kinetic control
to give a mixture of cis- and trans-dibromoalkenes,
the latter considerably prevailing [8,9]. The addi-
tion of bromine to alkylphenylacetylenes contain-
ing strong electron-withdrawing para-substituents
in the phenyl group is stereoselective and yields only
the trans-dibromo adducts. As an exception, stere-
oselective cis-addition to tert-butylphenylacetylene
gives rise to the Z-isomer as the main or single re-
action product. Such stereochemical outcome of the
reaction may likely be attributed to the considerable
steric crowding of the tert-butyl substituent [10].
Bromination of element-substituted acetylenes
has hitherto been explored insufficiently. Thus, it was
shown [11] that bromination of bis(trimethylsilyl)-
acetylene with bromine in CCl4 affords the cor-
responding dibromo derivative in 56% yield. The
product is the single one even if an excess of
bromine is used with prolonged heating of the reac-
tion mixture. Lower temperature during the trans-
formation and utilization of pentane as a solvent
improve appreciably the yield of 1,2-dibromo-1,2-
bis(trimethylsilyl)ethene (82%) [12]. The product ob-
tained was assigned a trans-configuration [11,12];
however, the authors have not adduced any data pro-
viding the grounds of such attribution.
In the present study we report the results of
our investigation concerning the bromination of
silatranyl- and germatranylphenylacetylenes as well
as tetracoordinate silicon-, germanium-, and tin-
substituted phenylacetylenes with Br2, n-Bu4NBr3
(TBAT), and NBS/DMSO.
RESULTS AND DISCUSSION
Synthesis of 1-(Phenylethynyl)metallatranes
In the present study synthesis of 1-(phenylethynyl)-
germatrane (1) as well as 1-(phenylethynyl)-3,7,
10-trimethylgermatrane (2) required for the further
investigation of bromination reactions as more ster-
ically hindered substance was carried out by three
ways (Eqs. 1 and 2) [7,15,16].
(1)
(2)

Bromination of Silatranyl-, Germatranyl-, Silyl-, and Germyl-phenylacetylenes 45
1-(Phenylethynyl)silatrane (5) has been prepared
Bromination of Element-Substituted
Phenylacetylenes
with 44% yield when lithium phenylacetylide was
employed (Eq. 2). Thus, we have found the first ex-
ample of synthesis of functionally substituted sila-
trane with use of an organolithium reagent. In the
reaction of 1-bromosilatrane (8) with n-BuLi only
substitution, including cleavage of equatorial Si O
bonds, was observed [17].
To obtain 1-(phenylethynyl)-3-phenylgermatrane
(9) we used the transalkoxylation reaction (Eq. 3)
[18].
As mentioned above bromination of 1 with bromine
proceeds smoothly and leads to Z-isomer as the only
product. It seemed to be interesting for us to exam-
ine tetra-n-butylammonium tribromide (TBAT) as
a brominating reagent. Literature data review re-
veals wide range of acetylenes being treated with
this reagent give trans-1,2-dibromalkenes as the only
products, result of the reaction being independent of
its conditions and ratio of reagents [9].
It was found, however, that the reaction between
1 and TBAT affords only cis-dibromide 14 in 58%
yield (Eq. 5). The behavior of the more bulky 3,7,10-
trimethyl-substituted germatrane 2 and 3-phenyl-
subsituted germatrane 9 is analogous to that of 1.
Bromination with Br2 leads to the formation of cis-
dibromalkenes 15 and 16 as the only reaction prod-
ucts. Similar product was obtained from reaction of
2 with TBAT (Eq. 5).
(3)
Synthesis of R3MC CPh
To synthesize element-substituted acetylenes 10–
13 we used the method based on the reaction be-
tween lithium phenylacetylide and corresponding
trialkylhalosilanes and -germanes as well as triph-
enylchlorosilane. We chose this way as the most suit-
able one according to the literature data (Eq. 4 also
see the Experimental section).
(5)
(4)
The absence of trans-N(CH2CH2O)3GeC(Br)
C(Br)Ph (E-14) in the reaction between 1 and TBAT
was established by NMR spectroscopy. Very recently
this trans-dibromide was obtained from reaction
mixture yielded by the treatment of a mixture Z- and
E-(EtO)3GeC(Br) C(Br)Ph (17) with N(CH2CH2-
OH)3 (TEA) (Eq. 6) [19].
Compounds 10–13 were prepared in 64–95% yields;
1
their structures were confirmed by IR, H, and 13C
NMR data.
(6)

46 Selina et al.
Essentially different results have been obtained
in the bromination of 5 with Br2. The main course of
the ratio Z/E = 3/1 (NMR data) (Eq. 9) [19].
this reaction is the cleavage of the Si C bond (Eq. 7).
(9)
The presence of both isomers in this reaction
can be attributed to less steric hindrances in the
case of triethoxy derivative 4 in comparison with
germatrane 1. No reaction of 4 with TBAT was ob-
served. The reactions of 13 with bromine and TBAT
are more complicated. The reaction mixtures con-
tained dibromo adduct Z-19 as well as the Ge C
bond cleavage products. In contrast to the above, 10
and 11 react with bromine and TBAT smoothly giv-
ing mixtures of Z,E-20 and Z,E-21, respectively. The
ratios of cis-, trans-dibromides 20 and 21 from the
reaction of 10 and 11 with bromine are Z/E = 9/1
in both cases (Eq. 10).
(7)
It should be noted, however, that the dibromod-
erivative cis-N(CH2CH2O)3Si C(Br) C(Br)Ph (18)
is also formed in small amounts. Analogously, sila-
trane 8 was obtained from reaction of 5 with TBAT
(Eq. 8). However, cis-adduct 18 is the concomitant
product in this case. The yield of Z-18 is about
30% (1H NMR data). Unfortunately, Z-18 was not
isolated from the reaction mixture as a pure sub-
stance because of the presence of starting silatrane
5.
(10)
(8)
Perhaps, the more electrophilic nature of
bromine in comparison with TBAT leads to the
difference of the compound 5 bromination path-
ways. Thus, the electophilic-substitution reaction is
more preferable when 5 was treated with bromine.
The easy cleavage of Si R bond (R = Alk, Ar)
in 1-organylsilatranes has been described earlier
[20].
An opposite ratio of 20 and 21 (Z/E = 1/9) was
found when 10 and 11 were treated with TBAT
(Eq. 11).
Compound 4 is a close tetracoordinated counter-
part of germatrane 1. Recently we have showed that
when affected by bromine this compound yields a
mixture of Z- and E-isomers of dibromoalkene 17 in
(11)

Bromination of Silatranyl-, Germatranyl-, Silyl-, and Germyl-phenylacetylenes 47
The treatment of acetylene 12 containing
very bulky triphenylsilyl group at triple bond
with bromine led to the only stereoisomer 22
(Eq. 12).
(12)
According to X-ray diffraction data this deri-
vative possesses cis-structure (see below). The reac-
tion of compound 12 with TBAT was not observed.
In general, the 1H NMR spectroscopy data
were used for the determination of product steric
configuration. Recently we have shown that δ1H
values of R3M protons in cis-R3GeC(Br) C(Br)Ph
(R3Ge = N(CH2CH2CO)3Ge (14), (EtO)3Ge (17)) shift
1
to high field as compared with H NMR data of re-
lated trans-dibromoalkene because of the influence
of steric proximity of Ph group in cis-isomers [19].
So, δ1H (CDCl3) of CH2O and NCH2 protons of atrane
skeleton in Z-14 are 3.55 and 2.72 ppm [7], respec-
tively, while “usual” δ1H for sila- and germatranes are
3.9–4.0 and 2.9–3.0 ppm [2]. Granting this we were
able to define the structure of dibromoalkenes 15,
16, and 18.
SCHEME 1
as well as in the reaction of 1, 2, and 5 with TBAT
might be attributed to the possible steric hindrances
due to the presence of bulky groups at triple bond in
these alkynes. This steric crowding is probably less
in the case of 4, 10, 11, and 13 during bromine addi-
tion when E-adducts are also formed together with
Z-dibromides. The results of alkyne bromination re-
actions are summarized in Table 1.
Alk3SnC CPh undergoes the bromodestannyla-
tion by bromine in DMSO or DMF/CCl4 [21]. We have
shown that the treatment of tin derivative 23 with
the softer brominating reagent TBAT, as well as with
NBS/DMSO system, and Br2 in CHCl3/CCl4 leads to
the cleavage of Sn C bond (Eq. 13).
The Z/E ratios for cis-, trans-isomer pairs of
19–21 were also found from 1H NMR data. In
present study the assignments of the R3M protons
signals in 19–21 have also been made on the basis
1
of 2D H NOESY correlations. We have confirmed
that the signals of Me groups (20) and CH2 groups
(19 and 21) for cis-dibromides can unequivocally
be assigned by the strong NOEs from H (Me or
CH2 groups) to the ortho-protons of phenyl group
(Scheme 1).
After heating the mixture of cis-, trans-
dibromides 20 (Z/E = 9/1) at 180◦C for 3 h,
the amount of trans-isomer has slightly increased
(Z/E = 7/3). No cleavage products were detected in
this reaction. On the contrary, 1-bromogermatrane 6
was the main product of the heating of cis-dibromide
Z-14 in the same conditions.
(13)
It should be noted that the heating of trans-
dibromide E-14 also led to germatrane 6 but in
notably smaller extent. Obviously, only Z-isomer
(Z-14) may undergo ꢀ-elimination with the forma-
tion of germatrane 6. The presence of compound 6
in heating products of E-14 may be attributed to
E → Z isomerization with further ꢀ-elimination of
Z-14.
Recently we have shown that the reaction be-
tween germatrane 1 and 2 equivalents of NBS in
DMSO yielded dibromoketone 24 [7]. Analogous
behavior was observed for 3,7,10-trimethyl- and 3-
phenyl-substituted germatranes 2 and 9. It should
be noted that we have not detected either diketo-
derivatives (R3GeC(O)C(O)Ph) or dibromo adducts
(R3GeC(Br) C(Br)Ph) among the products of the re-
action (14), whereas they are formed under the same
To all appearance, the formation of only cis-
adducts in the reaction of 1, 2, 9 and 12 with bromine

48 Selina et al.
TABLE 1 Yields and Product Distribution (Ratio of E- and Z-Isomers) of R3MC(Br) C(Br)Ph for the Reaction of Alkynes With
Br2 and TBAT
Yield (%)a
R3M
Br2
TBAT
14
15
16
17
18
19
20
21
22
N(CH2CH2O)3Ge
N(CH2CHMeO)3Ge
N(CH2CH2O)2(CH2CHPhO)2Ge
(EtO)3Ge
N(CH2CH2O)3Si
Et3Ge
Me3Si
Et3Si
55 (100/0) [7]
73 (100/0)
43 (100/0)
72 (75/25) [19]
17 (100/0)
38 (100/0)
95 (90/10)
92 (90/10)
83 (100/0)
58 (100/0)
52 (100/0)
–
No reaction
30 (100/0)
Trace
59 (10/90)
39(10/90)
No reaction
Ph3Si
aValues given in parentheses indicate Z/E ratio.
conditions in the case of alkylphenylacetylenes [22].
The N Si distance in compound 5 is one of
the shortest (2.094(2) A) among those observed
˚
in the structures of silatranes with Si C bond
˚
(2.02–2.23 A) [25,26]. It should be noted that the
N Si distance in compound 5 is shorter than the
N Ge distance found previously in closely related
˚
N(CH2CH2O)3Ge C C Ph (2.178(6) A) [7]. This fact
is in accordance with data reported for absolute ma-
jority of sila- and germatrane pairs studied earlier
(Table 2). However, there is a study giving the struc-
ture of N(CH2CH2O)3Ge F where the Ge N distance
˚
(2.011(9) A [46]) is shorter than the Si N distance
in corresponding silatrane. At the same time Eujen
et al. [30] have prejudiced the results of mentioned
X-ray analysis [46].
The coordination polyhedron of the germanium
atoms in 3,7,10-trimethyl-substituted germatranes
2, Z-15, and 25 represents a distorted trigonal
bipyramid with N and C atoms in the apical positions
and the three oxygen atoms in equatorial sites. The
(14)
The treatment of tetracoordinated Si- and Ge-
substituted alkynes 10–13 with NBS/DMSO resulted
in complicated mixtures of unidentifiable products
(see the Experimental section).
Crystal Structures of 2, 5, Z-15, Z-22, and 25
TABLE 2 Transannular N → M Distances in Closely Related
The molecular structures of 2, 5, Z-15, Z-22, and
25 are shown in Figs. 1–5. The coordination poly-
hedron of the silicon atom in 5 is the common one
for silatrane derivatives [23–25] and represents a dis-
torted trigonal bipyramid with N and C(1) atoms in
the apical positions and the three oxygen atoms in
equatorial positions. The silicon atom is displaced
Sila- and Germatrances, N(CH2CH2O)3M X
˚
N → M Distance (A)
X
M = Si
M = Ge
NCS
F
Cl
CHCl2
2-Furyl
CH2Cl
2.007(3) [27]
2.042(1) [29]
2.023 [31]
2.062 [32]
2.112 [34]
2.120 [36]
2.081(5) [28]
2.104(2) [30]
2.096(3) [30]
2.145(5) [33]
2.158(5) [35]
2.167(2) [37]
2.223(5) [39]
2.212(5) [40]
˚
by 0.14 A toward the phenylethynyl substituent from
the equatorial plane defined by three oxygen atoms.
The N Si C(1) fragment is almost linear (178.0(1)◦).
All five-membered rings of the silatrane skeleton in
5 adopt an envelope-like conformation. The carbon
atoms in the ꢁ-positions to the N atom occupy flap
sites, while the C-ꢀ atoms are part of the base of the
envelope planes. No disordered atoms in the atrane
cage were found in the structure of 5.
2-Pyrrolidonyl-CH(CH3) 2.126(9) [38]
Ph
2.132(4),
2.156(4),
2.193(5)a [41–43]
2.171(1) [44]
4-Me-C6H4
2.217(4) [45]
aDifferent crystalline modifications.

Bromination of Silatranyl-, Germatranyl-, Silyl-, and Germyl-phenylacetylenes 49
FIGURE 3 Molecular structure of Z-15. Displacement ellip-
soids are shown at 50% probability level. Hydrogen atoms
are omitted for clarity. Minor components of disordered
groups are shown ◦using open lines. Selected bond lengths
˚
(A) and angles ( ): Ge N 2.196(7), Ge C(1) 1.977(8),
C(1) C(2) 1.31(1), Br(1) C(1) 1.898(8), Br(2) C(2) 1.946(8),
N Ge C(1) 173.7(3), angles around C(1) and C(2) range
within 111.6(6) 126.2(7).
FIGURE 1 Molecular structure of 2. Displacement ellipsoids
are shown at 30% probability level. Hydrogen atoms are
omitted for clarity. Minor components of disordered groups
˚
are shown using open lines. Selected bond lengths (A)
and angles (◦): Ge(1) N 2.199(4), Ge(1) C(1) 1.919(6),
C(1) C(2) 1.181(7), N(1) Ge(1) C(1) 179.2(2), C(2) C(1)
Ge(1) 176.2(5).
FIGURE 4 Molecular structure of Z-22 (one independent
molecule). Displacement ellipsoids are shown at 50% prob-
ability level. Hydrogen atoms are omitted for clarity. Selected
bond lengths (A) and angles ( ): Si(1) C(2) 1.91(1), Br(11)
C(1) 1.933(9), Br(12) C(2) 1.956(9), C(1) C(2) 1.27(1), an-
gles around C(1) and C(2) range within 109.1(5) 131.8(8)
and angles around Si(1) range within 106.3(5) 112.5(4).
◦
˚
FIGURE 2 Molecular structure of 5. Displacement ellipsoids
˚
are shown at 50% probability level. Selected bond lengths (A)
and angles (◦): Si N 2.094(2), Si C(1) 1.884(3), C(1) C(2)
1.211(4), N Si C(1) 178.0(1), C(2) C(1) Si 171.0(2).

50 Selina et al.
TABLE 3 Transannular N → M Distances in Sila- and
Germatranes, N(CH2CHRO)3M X
˚
N → M Distance (A)
M
X
R = H
M = Me
Si
4-Me C6H4,
2.171(1) [44] 2.236(3) [44]
2.166(2) [15] 2.194(5) [47]
2.206(6) [50] 2.247(9) [49]
Ge 9-Fluorenyl
Ge 9-(9-Me3Sn)-fluorenyl
transannular distance N Ge in germatranes by the
formal substitution of hydrogen atoms by methyl
groups at positions 3,7,10 of atrane framework.
Only one analogous example was previously found
˚
among silatranes: N(CH2CHRO)3Si Ph, 2.193(5) A
˚
for R = H (ꢁ-modification) [41] and 2.175(6) A for
R = Me [45].
FIGURE 5 Molecular structure of 25. Displacement ellip-
soids are shown at 30% probability level. Hydrogen atoms are
omitted for clarity. Minor components of disordered groups
On the contrary the Ge Capical bond lengths
˚
˚
(1.919(6) A in 2 and 1.977(8) A in Z-15) are similar to
that observed in the structures of corresponding ger-
matranes N(CH2CH2O)3Ge X (1.920(8) and 1.98(2)
˚
are shown using open lines. Selected bond lengths (A)
and angles (◦): Ge(1) N(1) 2.169(6), Ge(1) C(16) 2.028(7),
Br(1) C(16) 1.952(7), Br(2) C(16) 1.954(7), O(4) C(17)
1.193(8), N(1) Ge(1) C(16) 174.7(3).
˚
A, respectively [7]). Of interest, the Ge C distance in
2 is the shortest one among the previously found in
germatranes containing N Ge C moiety (1.92–2.01
˚
A) [7,51,52].
germanium atom is displaced by 0.21 (for 2), 0.22
The N Ge distance in compound 25 (2.169(6)
A) is the shortest among those known by the present
˚
˚
(for Z-15), and 0.20 A (for 25) toward an apical sub-
stituent from the equatorial plane defined by three
oxygen atoms. The N Ge C fragment is almost lin-
ear (173.7(3)–179.2(2)◦) in all these compounds.
All five-membered rings of the germatrane skele-
ton in 2, Z-15, and 25 adopt an envelope-like con-
formation. In contrast to compound 5, the carbon
atoms lying in the ꢀ-positions to the N atom occupy
flap sites, while the C-ꢁ atoms are part of the base
of the envelope planes. This seems to be characteris-
tic for the structures of 3,7,10-trimethyl-substituted
atranes [44,45,47–49]. The carbon atoms of atrane
cage in the ꢀ-positions to the N atom are disordered
between two opposite flap sites in the structures of
2, Z-15, and 25. It should be noted that the bromine
atoms in compound Z-15 occupy cis-positions at
double carbon–carbon bond as they do in germa-
trane Z-14 [7].
time in 3,7,10-trimethyl-substituted germatranes. At
the same time the Ge Capical distance in compound
25 is the longest one among the previously found
in germatranes containing N Ge C fragment (1.92–
2.01 A). This may be due to the electronegative char-
acter of the PhC(O)CBr2 substituent.
˚
The asymmetric unit of Z-22 contains two in-
dependent molecules with very close geometric pa-
rameters. Unfortunately, the structure of Z-22 is not
of satisfactory quality because of poor crystallinity.
Thus, although the atom connectivity is undoubtedly
correct, the metrical parameters for Z-22 (Fig. 4,
Table 4) should be viewed with due caution. Nev-
ertheless, it is clear that bromine atoms occupy cis-
positions such as that found in Z-14 [7] and Z-15.
In conclusion, we have found that the addi-
tion of bromine to triple bond of studied element-
substituted acetylenes in CHCl3/CCl4 leads to form-
ing of cis-dibromo adducts as a preferred or single
isomer. Obviously, this fact may be attributed to the
presence of steric hindrances for E-isomer forma-
tion. Trialkylsilyl-substituted phenylacetylenes re-
acting with TBAT preferably gave trans-dibromide
as a major product of addition reaction. The incli-
nation of the M C bond in phenylacetylenyl deriva-
tives of the tetracoordinated group 14 elements to
˚
The N Ge distance in compound 2 (2.199(4) A) is
slightly longer than that observed in the structure of
˚
germatrane 1 (2.178(6) A) [7]. The same lengthening
of the N M distance has been found previously in
three pairs (Table 3).
However, the N Ge distance in compound Z-15
˚
(2.196(7) A) is slightly shorter than that observed in
˚
the structure of Z-14 (2.23(1) A) [7]. According to
our knowledge this is the first case of shortening of

Bromination of Silatranyl-, Germatranyl-, Silyl-, and Germyl-phenylacetylenes 51

52 Selina et al.
be broken under the influence of bromine increases
in Si < Ge < Sn series. Opposite order is observed for
derivatives of pentacoordinated Si (silatrane 5) and
Ge (germatranes 1, 2, and 9), namely, the cleavage of
Si C bond proceeds much easier than that of Ge C
bond.
were made with reference to the most abundant
isotopes.
Synthesis of 1-(Phenylethynyl)silatrane (5)
The reaction was carried out under an argon at-
mosphere. A 1.6 M solution of n-BuLi in hexane
(5.1 ml, 8.1 mmol) was added dropwise to a stirred
solution of phenylacetylene (0.86 ml, 7.9 mmol) in
Et2O (30 ml). The reaction mixture was refluxed for
15 min. The solution of PhC CLi in Et2O thus ob-
tained was then added with stirring to a suspension
of 1-bromosilatrane (2.0 g, 7.9 mmol) in Et2O (15 ml).
After refluxing for 8 h the volatiles were removed
entirely and chloroform (30 ml) was added to the
residue. The undissolved precipitate was filtered off
and the filtrate was evaporated in vacuo. Recrystal-
lization of a solid residue from chloroforom/hexane
gave 0.96 g (44%) of 5, m.p. 259–261◦C; [58]: m.p.
275◦C (from chloroform).
EXPERIMENTAL
General Comments
Trimethylsilyl-, triethylsilyl-, triphenylsilyl-, and trie-
thylgermyl-phenylacetylenes 10–13 were prepared
by literature methods [55,56]. Triethylbromoger-
mane was synthesized according to the literature
[57]. NMR spectra of these compounds are given
below.
1
10: H NMR (CDCl3) δ = −0.25 (s, 9H, SiMe3);
7.26–7.33 (m, 3H, C6H5); 7.44–7.49 (m, 2H, C6H5).
13C NMR (CDCl3) δ = −0.03 (SiMe3); 94.02 ( CSi);
105.13 (PhC ); 123.11, 128.16, 128.44, 131.92 (aro-
matic C).
1
IR (Nujol): ν(C C) 2165 cm−1. H NMR data in
CDCl3 are consistent with those reported in litera-
ture [53]. 13C NMR (CDCl3) δ = 50.87 (NCH2); 57.44
(OCH2); 96.86 ( CSi); 101.62 (PhC ); 124.03, 127.48,
127.60, 132.32 (aromatic C).
11: 1H NMR (CDCl3) δ = 0.62 (q, 6H, SiCH2); 0.99
(t, 9H, CH3); 7.20–7.24 (m, 3H, C6H5); 7.38–7.42 (m,
2H, C6H5). 13C NMR (CDCl3) δ = 4.42 (SiCH2); 7.47
(CH3); 91.45 ( CSi); 106.37 (PhC ); 123.33, 128.13,
128.33, 132.00 (aromatic C).
Reactions of Studied Phenylacetylenes
With Bromine
12: 1H NMR (CDCl3) δ = 7.29–7.74 (m, 20H,
C6H5). 13C NMR (CDCl3) δ = 89.00 ( CSi); 109.56
(PhC ); 122.70, 127.98, 128.27, 129.03, 129.92,
132.23, 133.55, 135.59 (aromatic C).
A solution of bromine (0.05 mol) in 30 ml of CCl4
was added dropwise to a solution of phenylacetylene
(0.05 mol) in 30 ml of chloroform. Stirring of the
reaction mixture for 3–6 h at room temperature was
accompanied with gradual disappearance of the red
color of bromine. The solvents then were removed
in vacuo. Resulting product was isolated by further
distillation or recrystallization of the residue.
1
13: H NMR (CDCl3) δ = 0.91 (q, 6H, GeCH2);
1.13 (t, 9H, CH3); 7.23–7.27 (m, 3H, C6H5); 7.42–7.45
(m, 2H, C6H5). 13C NMR (CDCl3) δ = 5.77 (GeCH2);
9.00 (CH3); 91.94 ( CGe); 105.96 (PhC ); 123.70,
127.96, 128.08, 131.91 (aromatic C).
Et3GeBr: 1H NMR (CDCl3) δ = 1.12 (t, 9H, CH3);
1.21 (q, 6H, GeCH2). 13C NMR (CDCl3) δ = 8.51
(CH3); 10.76 (GeCH2).
10: Fractionation of the liquid residue yielded
l,2-dibromo-l-(trimethylsilyl)-2-phenylethene (20)
as a mixture of Z- and E-isomers. b.p. 102–103◦C
(2 Torr). Calcd. for C11H14Br2Si (334.13): C, 39.54;
H, 4.22. Found: C, 39.13; H, 4.17%. IR (thin film):
1, 2, and 4 were prepared as previously described
[7,19]. Tributylstannyl-phenylacetylene, bromine,
TBAT, and NBS were commercial products and were
used without further purification. All solvents were
dried by standard procedures and distilled before
use. NMR spectra were recorded at 25◦C on Bruker
AC 300 and Varian VXR 400 spectrometers; CDCl3
was used as the solvent and for internal deuterium
1
ν(C C) 1553 cm−1. H NMR (CDCl3) δ = −0.05 (s,
9H, SiMe3, Z-isomer); 0.44 (s, 9H, SiMe3, E-isomer);
7.28–7.36 (m, 5H, C6H5). 13C NMR (CDCl3) for
Z-isomer δ = 0.11 (SiMe3); 128.20, 128.81, 129.14,
141.32 (aromatic C); 131.27, 133.52 (C C). 13C
NMR (CDCl3) for E-isomer δ = 0.49 (SiMe3); 128.14,
128.25, 128.51, 142.12 (aromatic C), 131.92, 133.52
1
lock. The chemical shifts in the H and 13C NMR
spectra are given in ppm relative to internal TMS.
The IR spectra were recorded on Zeiss UR-20. El-
emental analyses were carried out by the Micro-
analytical Laboratory of the Chemistry Department
of the Moscow State University. Mass spectra (EI-
MS) were obtained on a VARIAN CH-7a device using
electron impact ionization at 70 eV; all assignments
(C C). EI MS (70 eV): m/z = 334 (M+, 12%), 319
+
(M+ − Me, 7%), 253 (M+ − Br, 20%), 73 (SiMe3
,
100%).
11: Fractionation of the liquid residue gave 1,2-
dibromo-1-(triethylsilyl)-2-phenylethene (21) as a
mixture of Z- and E-isomers. b.p. 118–120◦C (1 Torr).

Bromination of Silatranyl-, Germatranyl-, Silyl-, and Germyl-phenylacetylenes 53
Calcd. for C14H20Br2Si (376.21): C, 44.70; H, 5.36.
2: Removal of the solvent left very viscous
brown oil. NMR spectra analysis showed this oil
to be practically pure Z-1,2-dibromo-1-[1-(3,7,10-
trimethyl)germatranyl]-2-phenylethene (15) (chem-
ical shifts are consisted with those described below
in the reaction with TBAT). The crude product was
dissolved in minimum quantity of CHCl3, then 10 ml
of hexane was added, and the resulting mixture was
stored at −10◦C. The compound turned into a crys-
talline material only after 3 months at this tempera-
ture. It was collected by filtration, washed with hex-
ane, and dried in vacuo to yield 0.79 g (73%) of
Z-15.
Found: C, 44.26; H, 5.58%. IR (thin film): ν(C C)
1556 cm−1. 1H NMR (CDCl3) δ = 0.39 (q, 6H, SiCH2,
Z-isomer); 0.68 (q, 6H, SiCH2, E-isomer); 0.82 (t, 9H,
CH3, Z-isomer); 1.06 (t, 9H, CH3, E-isomer); 7.26–
7.36 (m, C6H5, 5H). 13C NMR (CDCl3) for Z-isomer
δ = 4.11 (SiCH2); 7.28 (CH3); 128.07, 128.86, 129.10,
141.28 (aromatic C); 129.37, 134.34 (C C). 13C NMR
(CDCl3) for E-isomer: δ 4.58 (SiCH2); 7.45 (CH3);
121.68, 128.19, 128.46, 142.48 (aromatic C); signals
of double bond carbons were not found due to the
small concentration of E-21. EI MS (70 eV): m/z =
376 (M+, 6%), 347 (M+ − Et, 16%), 319 (M+ − 2Et,
9%), 291 (M+ − 3Et, 53%).
9: Removal of the solvent left a yellow solid.
Crude product was recrystallized from CHCl3/ hex-
ane gave 0.34 g (43%) of Z-22. Calcd. for C20H21Br2-
GeNO3 (555.78): C, 43.22; H, 3.81; N, 2.52. Found: C,
43.32; H, 3.81; N, 2.52%.
12: Removal of the solvents afforded a brown oil.
Addition of hexane (20 ml) precipitated a beige solid,
which was collected by filtration, washed with hex-
ane, and dried in vacuo. The solid was found to be
Z-1,2-dibromo-1-(triphenylsilyl)-2-phenylethene (Z-
22). m.p. 125–126◦C. Calcd. for C26H20Br2Si (520.34):
C, 60.62; H, 3.87. Found: C, 60.15; H, 3.79%.
IR (Nujol): ν(C C) 1533 cm−1. 1H NMR
(CDCl3) δ = 2.32, 2.81, 3.38, 3.52, 3.82, 4.42 [6 m,
11H, (AAꢁXXꢁ)2 and ABX systems of NCH2CH2O and
NCH2CHPhO groups protons], 7.09–7.51 (m, 10H,
aromatic protons). 13C NMR (CDCl3) δ (atrane C)
52.80, 53.33, 56.90, 57.08, 59.32, 68.66 (CH Ph);
126.51 (GeCBr); 134.75 (BrCPh); δ (aromatic C)
125.58, 127.19, 127.72, 128.21, 128.27, 129.21,
140.83, 142.73. EI MS (70 eV): m/z = 555 (M+, 0.5%),
449 (M+ − C6H5CHO, 22%), 296 (M+ − CBr CBrC6-
H5, 10%), 266 (M+ − CBr CBrC6H5 CH2O, 10%),
190 (M+ − CBr CBrC6H5 C6H5CHO, 40%): 146
(M+ − CBr CBrC6H5 C6H5CHO CH2CH2O, 63%).
5: The solid residue obtained after the removal
of the solvents contained 1-bromosilatrane 8 as well
as the trace amounts of 5 and Z-1,2-dibromo-1-
1
IR (Nujol): ν(C C) 1550 cm−1. H NMR (CDCl3):
δ 6.73–6.77, 6.85–6.88, 6.99–7.01, 7.22–7.26, 7.30–
7.34, 7.47–7.50 (6m, aromatic H). 13C NMR (CDCl3):
δ 127.61, 127.69, 128.89, 128.53, 132.86, 135.96,
136.23, 140.04 (aromatic C); 137.34, 139.74 (C C).
EI MS (70 eV): m/z = 520 (M+, 1%), 441 (M+ − Br,
21%), 361 (M+ − 2Br, 44%), 259 (Si(C6H5)3+, 100%).
13: 1H and 13C NMR spectra of the liquid
residue revealed the presence of bromophenylacety-
lene, triethylbromogermane, and dibromoalkene Z-
19. Distillation of the mixture gave two fractions
with b.p. 35–40◦C and 135–136◦C (∼1 Torr). Ac-
cording to NMR spectra the former contains bro-
mophenylacetylene and triethylbromogermane. 13C
NMR (CDCl3) for PhC CBr δ = 49.69 ( CBr); 79.99
(PhC ); 122.64, 128.28, 128.63, 131.92 (aromatic C).
The second fraction was Z-1,2-dibromo-1-
(triethylgermyl)-2-phenylethene (Z-19). Calcd. for
C14H20Br2Ge (420.71): C, 39.97; H, 4.79. Found: C,
1
(1-silatranyl)-2-phenylethene Z-18 (according to H
1
NMR). H NMR (CDCl3) for Z-18: δ 2.71 (t, NCH2,
6H); 3.54 (t, OCH2, 6H); signals of the phenyl group
are in the standard area.
Reactions of Studied Phenylacetylenes
With TBAT
1
39.63; H, 4.57%. H NMR (CDCl3) δ = 0.62 (q, 6H,
GeCH2); 0.91 (t, 9H, CH3); 7.25–7.28, 7.31–7.33 (m,
5H, C6H5). 13C NMR (CDCl3) δ = 6.28 (GeCH2); 8.69
(CH3); 128.16, 128.98, 129.01, 141.28 (aromatic C);
129.39, 131.07 (C C).
Under an argon atmosphere [8], solid TBAT (0.01
mol) was added in small portions to a solution of
phenylacetylene (0.01 mol) in 45 ml of chloroform.
When the addition was complete, the resulting bright
orange solution was stirred at room temperature for
7 days; the color of the solution slowly faded during
this period. The reaction mixture was then washed
with 5% aqueous Na2S2O3 (2 × 50 ml) and water
(7 × 50 ml), dried (Na2SO4), and evaporated. Further
distillation or recrystallization of a residue yielded fi-
nal reaction product.
23: In the course of the reaction, immediate de-
coloration of bromine drops and warming-up of a
reaction mixture was observed. Evaporation of the
solvents left yellow oil, which contained only bro-
mophenylacetylene and tributylbromostannane (by
1
13C NMR). Bu3SnBr: H NMR (CDCl3) δ = 0.90 (t,
9H, CH3); 1.28, 1.33 (m, 12H, SnCH2CH2, CH2CH3);
1.62 (m, 6H, SnCH2CH2). 13C NMR (CDCl3) δ =
14.01 (CH3); 17.92 (SnCH2); 27.24 (CH2CH3), 28.27
(SnCH2CH2).
10: Distillation of a pale yellow liquid afforded a
mixture of Z- and E-isomers of 20. 1H and 13C NMR

54 Selina et al.
spectra for Z- and E-isomers are identical to those
described with Br2.
Reactions of Studied Phenylacetylenes
With NBS in DMSO Solution
11: A liquid residue was distilled in vacuo to give
21 as a mixture of Z- and E-isomers. 1H and 13C NMR
data are consistent with those depicted with Br2.
12: After 7 days at room temperature no change
in color of the reaction mixture was detected. Usual
work-up of the solution and removal of the solvent
led to a solid material that was found to be unreacted
12 (according to 13C NMR spectrum).
13: Evaporation of the solvent left an oil com-
position of which was established without further
isolation. According to 1H and 13C NMR spectra
bromophenylacetylene, triethylbromogermane, and
C Br bond hydrolysis products of the latter are
the greater part of the mixture. Besides this, the
residue contains small amount of 1,2-dibromo-1-
(triethylgermyl)-2-phenylethene (19).
Under an argon atmosphere [22], NBS (0.02 mol)
was added in one portion with stirring to a solution
of phenylacetylene (0.01 mol) in DMSO (30 ml). As
a result, a transparent bright orange solution was
obtained and in general noticeable amount of heat
was produced. The reaction mixture was stirred at
ambient temperature for 48 h, the color intensity
gradually diminishing during this period. The reac-
tion mixture was then diluted with water (240 ml).
Yellowish solid precipitated immediately. The result-
ing mixture was extracted with chloroform (120 ml).
Combined chloroform extracts were washed succes-
sively with water (3 × 40 ml) and brine (2 × 40 ml).
After drying over MgSO4, the solvent was removed
under reduced pressure, and the residue was ana-
lyzed by 1H and 13C NMR spectroscopy.
23: 1H and 13C NMR spectra of a dark yellow liq-
uid residue revealed the presence of two compounds:
bromophenylacetylene and tributylbromostannane.
4: No exterior changes of the reaction mixture
have been observed. The course of the reaction was
monitored by means of 13C NMR. Analysis of spectra
obtained after stirring the reaction mixture for 7 and
20 days showed the presence of only starting pheny-
lacetylene 4 and ammonium salt in the solution.
1: Removing the solvent afforded a foam look-
ing solid. It was recrystallized from hexane/CH2Cl2
mixture to give 0.82 g (58%) of Z-1,2-dibromo-1-(1-
germatranyl)-2-phenylethene (14). 1H and 13C NMR
data are consistent with those already published [7].
2: After the solvent was removed under re-
duced pressure, hexane (5 ml) was added to the
oily residue. The solid precipitated after a while
was filtered off, washed with hexane, and dried in
vacuo. As a result, 0.57 g (52%) of Z-15 was obtained
as a yellowish solid. m.p. 123–125◦C. Calcd. for
C17H23Br2GeNO3 (521.77): C, 39.13; H, 4.44. Found:
C, 38.87; H, 4.28%. IR (Nujol): ν(C C) 1533 cm−1. 1H
NMR (CDCl3) δ = 0.93–3.94 (18 H, ABXM3 system of
NCH2CHMeO group protons); 7.23–7.25, 7.48–7.51
(2m, 5H, C6H5). 13C NMR (CDCl3): δ 20.06, 20.27,
20.51, 22.93 (CH3); 59.79, 62.31, 62.68, 62.81, 63.75,
64.13, 65.68, 66.17 (OCH2, NCH2); 121.64, 127.08,
128.05, 129.37, 129.77, 130.07, 132.51, 133.96,
134.23, 135.37, 139.16, 142.95 (C C, aromatic C).
EI MS (70 eV); m/z = 477 (M+ − CH3CHO, 3%), 442
(M+ − Br, 9%); 262 (M+ − C6H5CBr CBr, 27%).
5: After the standard work-up the reaction
mixture contained starting 5, 1-bromosilatrane
(8), bromophenylacetylene, and Z-1,2-dibromo-1(1-
silatranyl)-2-phenylethene (Z-18) in ca. ratio 1:2:1
(according to 1H NMR).
10: NMR spectra revealed the presence of com-
plicated mixture of compounds. The major part of
this mixture is unreacted 10. Besides, we could estab-
lish the presence of small amounts of bromopheny-
lacetyelene and Z-20, as well as trace amounts of E-
20. Other components of the resulting mixture were
not identified.
11: The main reaction products are bro-
mophenylacetylene and hexaethyldisiloxane; and
latter results from the treatment of the reaction mix-
ture with water.
12: The solid residue contains complicated mix-
ture of compounds, which are difficult to be identi-
fied.
13: The dominant reaction pathway is the
cleavage of the Ge C bond with the formation
of bromophenylacetylene, triethylhydroxygermane,
and hexaethyldisiloxane. Et3GeOH and (Et3Ge)2O
arise from the treatment of the reaction mixture with
water and are evidently products of Ge Br linkage
hydrolysis in triethylbromogermane.
23: The reaction results in the formation of a
mixture of bromophenylacetylene and tributylbro-
mostannane (according NMR and mass spectra).
5: A mixture of compounds difficult to be iden-
1
tified was obtained. H NMR spectrum showed the
absence of compounds containing atrane fragment
among the reaction products.
2: Removal of the solvent gave 1.74 g (59%)
of 2,2-dibromo-2-[1-(3,7,10-trimethyl)germatranyl]-
1-phenyl-1-ethanone (25) as a yellow oil. It solidi-
fied from CHCl3/hexane mixture when left to stand
at −10◦C for 1 month. Calcd. for C17H23Br2GeNO4
(537.77): C, 37.97; H, 4.31. Found: C, 37.62: H,
4.20%. 1H NMR (CDCl3) δ = 1.15–4.21 (18H, ABXM3

Bromination of Silatranyl-, Germatranyl-, Silyl-, and Germyl-phenylacetylenes 55
system of NCH2CHMeO group protons); 7.33–7.47,
ACKNOWLEDGMENTS
8.29–8.34 (2m, 5H, C6H5). 13C NMR (CDCl3) δ =
20.18, 20.57, 20.62, 22.82, (CH3); 40.94, 41.00 (CBr2);
59.35, 60.34, 62.87, 63.31, 64.33, 64.53, 65.77,
66.47 (OCH2, NCH2); 127.28, 127.37, 130.91, 131.01,
131.95, 132.17, 133.85, 134.26 (aromatic C); 190.91,
191.23 (C O). EI MS (70 eV); m/z = 537 (M+, 5%),
262 (M+ − C6H5COCBr2, 100%).
We thank Dr. A. V. Yatsenko for the X-ray crystal
structure determination of 5, Z-15, and 25.
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1
ν(C O) 1661 cm−1. H NMR (CDCl3) δ = 2.85–3.18,
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X-Ray Crystallography Study of 2, 5, Z-15,
Z-22, and 25
Table 4 summarizes the crystal data as well as de-
tails of data collection and structure determina-
tion. For all compounds non-hydrogen atoms (in-
cluding disorder components) were refined with
anisotropic thermal parameters. In the structure of
5, all hydrogen atoms were found from difference
Fourier map and refined isotropically. As for the
structures of 2, Z-15, Z-22, and 25, all hydrogen
atoms were placed in calculated positions and re-
fined using a riding model. Atrane frameworks in
the structures of 2, Z-15, and 25 were found to
be disordered with approximate occupancies ratios
0.5/0.5.
Crystallographic data (excluding structure fac-
tors) for the structures reported in this paper
have been deposited with the Cambridge Crys-
tallographic Data Centre as supplementary pub-
lications no. CCD-191695 for 5, 191696 for 2,
191697 for Z-15, 191698 for 25, and 191699 for
Z-22. Copies of the data can be obtained free of
charge on application to CCDC, 12 Union Road,
Cambridge CB2 1EZ, UK (fax: +44(1223)336-033;
e-mail: deposit@ccdc.cam.ac.uk).

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