Bromine adducts of 9,10-diheteratriptycene derivatives

Article abstract of DOI:10.1246/bcsj.82.819

2,3,6,7,14,15-Hexamethyl-9,10-diphosphatriptycene (1), 2,3,6,7,14,15- hexamethyl-9-phospha-10-stibatriptycene (2), and 2,3,6,7,14,15-hexamethyl-9,10- distibatriptycene (3) were synthesized and their molecular structures were determined by X-ray crystallog

Full text of DOI:10.1246/bcsj.82.819

© 2009 The Chemical Society of Japan
Bull. Chem. Soc. Jpn. Vol. 82, No. 7, 819–828 (2009)
819
Bromine Adducts of 9,10-Diheteratriptycene Derivatives
Yosuke Uchiyama, Jun Sugimoto, Munenori Shibata, Gaku Yamamoto, and Yasuhiro Mazaki*
Department of Chemistry, School of Science, Kitasato University, 1-15-1 Kitasato, Sagamihara 228-8555
Received November 14, 2008; E-mail: mazaki@kitasato-u.ac.jp
2,3,6,7,14,15-Hexamethyl-9,10-diphosphatriptycene (1), 2,3,6,7,14,15-hexamethyl-9-phospha-10-stibatriptycene
(2), and 2,3,6,7,14,15-hexamethyl-9,10-distibatriptycene (3) were synthesized and their molecular structures were
determined by X-ray crystallography. Reactions of 2 and 3 with bromine gave the corresponding adducts 8 and 9 with the
compositions 2¢2Br2 and 3¢2Br2, respectively. Both of the adducts 8 and 9 have a zwitterionic structure composed of a
¹
hexacoordinate stiborate anion, (R3SbBr3 ) and a tetracoordinate phosphonium/stibonium cation (R3MBr+: M = P or Sb)
1
in the crystalline state. H and 31P NMR spectra of the adduct 8 indicated that the structure is static in solution at room
temperature. On the other hand, 1H NMR spectra of the adduct 9 suggested fast topomerization at 27 °C, which becomes
slow on the NMR time scale at ¹90 °C. Recrystallization of the adduct 9 from THF-mesitylene gave crystals with the
composition of 3¢2Br2¢2THF, in which each antimony atom bonds to two bromine atoms and one THF oxygen to give an
octahedral geometry.
Diheteratriptycenes (=9,10-dihydro-9,10-dihetera-9,10[1¤,2¤]-
benzoanthracenes) with Group 15 elements (N, P, As, Sb, and
Bi) at the bridgeheads are an intriguing series of compounds
because of their highly symmetric structure and the possible
interaction between the bridgehead atoms.1 Hitherto, com-
pounds shown in Chart 1 are known. Recently, theoretical and
electron diffraction studies of perfluoro derivatives of 9,10-
distibatriptycene and 9,10-dibismatriptycene have been report-
ed to reveal the geometries around antimony and bismuth
atoms and their valence shells.13 These 9,10-diheteratriptycenes
are expected to show interesting reactions at the bridgehead
atoms including those with metal carbonyls, halogens, and
alkyl halides to give compounds possessing structurally
interesting properties.
Oxidation of 9,10-diphosphatriptycene gave the P,P¤-dioxide
quantitatively.3 The reaction of 9,10-diphosphatriptycene with
benzyl bromide gave a P-monobenzylphosphonium product,
while that with methyl triflate gave a mixture of P-monomethyl
and P,P¤-dimethyl derivatives.3,14 Complexes15 of 9,10-diphos-
phatriptycene derivatives with palladium, tungsten, and molyb-
denum carbonyls were easily obtained and were shown to have
similar properties as those of the corresponding triphenylphos-
phine-metal complexes. On the other hand, reactions9 of 9,10-
diheteratriptycenes with halogens have scarcely been inves-
tigated because the reaction products easily decompose under
atmospheric conditions and are insoluble in common organic
solvents. Perfluoro-9,10-distibatriptycene reacted with chlorine
to give an adduct containing two molecules of chlorine, but its
structure was not determined because it was easily hydrolyzed
by moisture to give the corresponding dioxide.9
We wanted to have deeper insight into the chemistry of
9,10-diheteratriptycenes and planned to introduce alkyl groups
into the triptycene skeleton in order to increase the solubility
in common solvents. Recently, we successfully synthesized
2,3,6,7,14,15-hexamethyl-9,10-distibatriptycene (3) under mild
conditions, and found that compound 3 could be used for our
purpose. We have therefore undertaken studies on a series of
2,3,6,7,14,15-hexamethyl-9,10-diheteratriptycenes.
In this article, we wish to report the synthesis and reactions
with bromine of the 2,3,6,7,14,15-hexamethyl derivatives
of 9,10-diphosphatriptycene 1, 9-phospha-10-stibatriptycene
2, and 9,10-distibatriptycene 3 (Chart 2), and discuss the X-ray
molecular structures in the crystalline state and NMR behavior
in solution of these compounds as well as their bromine
adducts. Some of the previous results have been published.16
Results and Discussion
Synthesis of the 9,10-Diheteratriptycenes. Compounds
1-3 were synthesized as shown in Scheme 1. Treatment of 4,5-
Me
X
E
N
P
E'
N
P
X
15
Me
14
X
H2
X
16
H,3 F8
As As H,4 F, 8,10,11 Cl6
13
12
1: E = E' = P
2: E = P, E' = Sb
3: E = E' = Sb
11
Sb Sb H,5 F, 8−11,13 Cl6,9
X
X
E'10
X
Bi
N
P
Bi
P
H,6 F, 8,11,13 Cl6
H7
E'
4
5
3
X
E
6
Me
E
As F12
Sb F8
X
2
Me
9
X
P
7
X
1
8
Me
X
X
As Sb F8,10
Me
Chart 2.
Chart 1.
Published on the web July 10, 2009; doi:10.1246/bcsj.82.819

820
Bull. Chem. Soc. Jpn. Vol. 82, No. 7 (2009)
9,10-Diheteratriptycenes
1 (7%)
1) t-BuLi
2) PCl3
1) n-BuLi
2) PCl3
−78 °C, Et2O/THF
Me
Me
Br
P
1) t-BuLi
2) SbCl3
−110 °C, Et2O/THF
3
2 (13%)
−78 °C, THF
Me
Me
Br
Br
4
1) t-BuLi
2) PCl3/AlCl3/TMEDA
2 (10%)
3 (9%)
1) n-BuLi
2) SbCl3
−78 °C, THF
Me
Me
Br
1) t-BuLi
2) SbBr3
−110 °C, Et2O/THF
Sb
3
5
−78 °C, THF
Scheme 1.
aromatic protons.
dibromo-o-xylene with n-BuLi at ¹110 °C15,17 and subsequent
reaction with PCl3 or SbCl3 gave tris(2-bromo-4,5-dimethyl-
phenyl)phosphine (4) or tris(2-bromo-4,5-dimethylphenyl)-
stibine (5) in 38% and 59% yields, respectively. Triarylphos-
phine 4 was reacted with t-BuLi and then with PCl3 to give
9,10-diphosphatriptycene 1 in 7% yield. 9-Phospha-10-stiba-
triptycene 2 was synthesized by the reaction of compound 4
with t-BuLi and then addition of SbCl3 in 13% yield.
Compound 2 could be obtained by the reaction of compound
5 with t-BuLi followed by the addition of PCl3 in the presence
of TMEDA and AlCl3 in 10% yield. Compound 5 was treated
with t-BuLi and then with SbBr3 to give 9,10-distibatriptycene
3 in 9% yield. These compounds 1-3 were obtained in very low
yields because these compounds had to be separated from
significant quantities of polymer-like side products which were
recognized by GPC and 1H NMR spectra to have large
molecular weight and dimethylphenyl groups bridged by
phosphorus and/or antimony. Suitable purifications of com-
pounds 1-3 are shown in the experimental section in detail.
The 1H NMR spectrum of 9,10-diphosphatriptycene 1 in
CDCl3 showed a methyl signal at ¤ 2.18 as a singlet and an
aromatic proton signal at ¤ 7.68 as a multiplet in an integral
ratio of 3:1, reflecting the D3h symmetry of the compound.
31P NMR showed a multiplet at ¤ ¹46.1.
Crystals of compounds 1-3 were obtained by recrystalliza-
tion from CH2Cl2, CHCl3, and hexafluorobenzene, respectively,
and were characterized by X-ray crystallography. The crystals
of 3 contained solvent molecules. The molecular structures of
these compounds are shown in Figure 1, and selected bond
lengths and angles are compiled in Tables 1 and 2.
Both compounds 1 and 3 have nearly D3h symmetry, while
compound 2 shows almost C3v structure. The average lengths
of the P-C bonds in 1 and the Sb-C bonds in 3 are 1.840 and
2.152 ¡, respectively, and are almost the same as those of Ph3P
(1.831 ¡)19 and Ph3Sb (2.155 ¡),20 indicating that incorpora-
tion into a rigid skeleton does not largely affect the bond
lengths. In contrast, the averaged C-P-C angles in 1, 96.9°, and
the C-Sb-C angles in 3, 94.2°, are both somewhat smaller than
the corresponding values in Ph3P (102.8°)19 and Ph3Sb
(96.3°)20 due to the skeletal constraints.
The average P-C and Sb-C bond lengths in 9-phospha-10-
stibatriptycene 2 are 1.846 and 2.150 ¡, respectively, which are
similar to those in 1 and 3. In contrast, the average C-P-C
angle in 2, 100.1°, is larger than that in 9,10-diphosphatripty-
cene 1 (96.9°), while the average C-Sb-C angle, 90.3°, is
smaller than that in 9,10-distibatriptycene 3 (94.2°). The
phosphorus pyramid in 2 is flatter than in 1, while the antimony
pyramid in 2 is sharper than that of 3, which is ascribed to
skeletal constraints.
The cyclic voltammograms of compounds 1, 2, and 3 are
depicted in Figure 2 together with that of Ph3P, and (p-Tol)3Sb
(p-Tol = p-tolyl) and the data are summarized in Table 3. In
compounds 1, 2, and 3 irreversible oxidation waves were
observed similar to those of Ph3P, and (p-Tol)3Sb. Only one
irreversible oxidation wave of 9,10-diphosphatriptycene 1
(E1/2 = 0.75 V vs. Fc/Fc+) was found at a slightly higher
potential than that of Ph3P (E1/2 = 0.66 V). On the other hand,
two irreversible oxidation waves of 9,10-distibatriptycene 3
were observed at 0.68 and 1.1 V, showing that the first
oxidation occurred at somewhat lower potential and the second
oxidation occurred at higher potential compared with that
of (p-Tol)3Sb (E1/2 = 0.79 V vs. Fc/Fc+). For 9-phospha-10-
stibatriptycene 2 the first potential was observed at 0.72 V
located between the first potentials of 1 and Ph3P and the
1
The H NMR spectrum of 9-phospha-10-stibatriptycene 2 in
CDCl3 showed two signals at ¤ 2.14 and 2.18 as methyl groups,
and two aromatic proton signals, a singlet at ¤ 7.68 and a
doublet (J = 12.1 Hz) at ¤ 7.90, which were assigned to the
4/5/16-H and 1/8/13-H, respectively. The 13C NMR spectrum
gave two aliphatic and six aromatic signals, reflecting the C3v
symmetry. The 31P NMR spectrum of 2 showed a quartet
(3JHP = 11.4 Hz) at ¤ ¹10.1, which was at lower field than that
of 9,10-diphosphatriptycene 1 (¤ ¹46.1) and was close to that
of triphenylphosphine (¤ ¹4.83). This may be explained as
follows: 31P chemical shifts are known to depend on the bond
angles of C-P-C,18 and the phosphorus pyramid becomes
flatter and closer to the tetrahedral geometry in the order of 1, 2,
and triphenylphosphine, the C-P-C angles being 96.9, 100.2,
and 102.8°, respectively, as described later.
The 1H NMR spectrum of 3 in CDCl3 showed only two
signals at ¤ 2.18 and 7.81 due to the methyl groups and

Y. Uchiyama et al.
Bull. Chem. Soc. Jpn. Vol. 82, No. 7 (2009)
821
Table 2. Selected Bond Angles (deg) of Compounds 1, 2,
and 3
(a)
1
2
3
(E1 = E2 = P) (E1 = P, E2 = Sb) (E1 = E2 = Sb)
C1
P1
C1-E1-C2
C1-E1-C3
C2-E1-C3
C4-E2-C5
C4-E2-C6
C5-E2-C6
96.8(1)
97.2(1)
96.8(1)
96.8(1)
97.2(1)
96.8(1)
100.2(2)
100.6(2)
99.4(2)
90.0(2)
90.0(2)
90.8(2)
93.7(1)
94.6(1)
94.0(1)
94.1(1)
93.6(1)
95.2(1)
C4
C3
C2
P2
C5
C6
(b)
C1
C4
P
C3
Ph3P
C2
Sb
C6
C5
1
(c)
C1
Sb1
2
3
C4
C3
C2
Sb2
C6
C5
Figure 1. Molecular structures of (a) 9,10-diphosphatripty-
cene 1, (b) 9-phospha-10-stibatriptycene 2, and (c) 9,10-
distibatriptycene 3 drawn with 50% probability.
Table 1. Selected Bond Lengths (¡) of Compounds 1, 2,
and 3
p-Tol3Sb
1
2
3
(E1 = E2 = P) (E1 = P, E2 = Sb) (E1 = E2 = Sb)
E1-C1
E1-C2
E1-C3
E2-C4
E2-C5
E2-C6
E1£E2
1.838(1)
1.839(1)
1.842(1)
1.842(1)
1.839(1)
1.838(1)
3.248
1.844(5)
1.844(5)
1.849(5)
2.149(4)
2.151(5)
2.151(4)
3.482
2.151(2)
2.150(2)
2.154(3)
2.156(3)
2.149(2)
2.151(2)
3.692
[V] 2.0
1.0
0.0 −1.0
−2.0
Figure 2. The cyclic voltammograms of Ph3P, 1, 2, 3, and
(p-Tol)3Sb. The data are reported vs. Fc/Fc+. Conditions:
1.0 mM solutions in 0.1 M [n-Bu4N¢ClO4 ]/CH2Cl2 as
¹
¹1
supporting electrolyte, 100 mV s
.
second irreversible oxidation wave appeared at 1.3 V was a
slightly higher than the second oxidation wave of compound 3
(1.1 V). These oxidation properties on phosphorus and anti-
mony atoms would depend on structural features, that is, inner
angles of Cipso-P-Cipso and Cipso-Sb-Cipso rather than the
electrolytic nature of these compounds, judging from consid-
eration of the following situations. As the angles of Cipso-P-
C
ipso became smaller in the order of Ph3P (102.8°), 9-phospha-

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Bull. Chem. Soc. Jpn. Vol. 82, No. 7 (2009)
9,10-Diheteratriptycenes
Table 3. Comparison of CV Data for Ph3P, Compounds 1, 2,
3, and (p-Tol)3Sb
solids with sufficient solubility in common organic solvents
and high stability toward air and moisture (Scheme 3).
The molecular structures of the bromine adducts 8 and 9
obtained by X-ray crystallography are shown in Figure 3, and
selected bond lengths and angles are compiled in Tables 4 and
5. In the bromine adduct 8, one bromine atom bonds to the
phosphorus atom and three bromine atoms bond to the
antimony atom. The average angles of Br-P-C and C-P-C
are 110.8 and 108.1°, respectively, indicating the tetrahedral
geometry around the phosphorus atom. On the other hand,
the averaged trans-Br-Sb-C angle is 176.8°, indicating the
octahedral geometry around the antimony atom. The bond
lengths of the P-Br bond and the P-C bonds on average are
2.137 and 1.795 ¡, the latter being ca. 0.05 ¡ shorter than that
of 2, while the average length of the Sb-Br and Sb-C bonds are
2.624 and 2.181 ¡, respectively, the latter being ca. 0.03 ¡
longer than that of 2. These results suggest that the bromine
adduct 8 is an intramolecular salt with a zwitterionic structure
composed of a tetracoordinate triarylbromophosphonium cation
and a hexacoordinate triaryltribromostiborate anion.
The C-P-C angles of 8 (108.1° on average) are typical for
the tetrahedral geometry, though significantly wider than those
of 2 (100.1° on average). The C-Sb-C angles in 8 (91.3° on
average) are also typical for the octahedral geometry, though
slightly larger than those of 2 (90.3° on average). The smaller
Sb£P non-bonded distance in 8 (3.267 ¡) than in 2 (3.482 ¡)
will mainly be ascribed to these changes rather than the
electrostatic attraction between the opposite charges in 8.
In the adduct 9, one antimony atom, Sb1, bonds to one Br
atom and is almost tetrahedral. The C-Sb1-C and C-Sb1-Br
angles are 103.7 and 114.5°, respectively, on average. The
other antimony atom, Sb2, bonds to three Br atoms constituting
hexacoordination. The C-Sb2-C and trans-C-Sb2-Br angles
Ph3P
1
2
3
(p-Tol)3Sb
E1/2(1)/V
1/2(2)/V
0.66
®
0.75
®
0.72
1.3
0.68
1.1
0.79
®
E
10-stibatriptycene 2 (100.1°), and 9,10-diphosphatriptycene 1
(96.9°), the first oxidation potentials of these became larger,
0.66, 0.72, and 0.75 V. In the antimony portion, the oxidation
potentials, 0.79, 1.1, and 1.3 V, except for the first one of 9,10-
distibatriptycene 3 became larger in the order (p-Tol)3Sb
(96.3°), 3 (94.2°), and 2 (90.3°).
Reaction with Bromine and Structures of the Adducts.
The reaction of 9,10-diphosphatriptycene 1 with bromine in
CHCl3 was complicated because of the instability of the
possible initial product, the bis(bromophosphonium) salt.
However, the isolated product was guessed to be the mono-
(bromophosphonium) P-oxide salt 6 on the basis of a MS peak
of m/z 470 as well as 1H and 31P NMR data (Scheme 2).
Compound 6 was presumably formed upon hydrolysis of the
initial product with a trace of water in the reaction mixture. The
compound 6 was easily hydrolyzed by atmospheric moisture to
give quantitatively the P,P¤-dioxide 7, which was a very stable
compound (Scheme 2). This change was also followed by
31P NMR: a mixture of 1 and bromine in CDCl3 initially gave
two signals at ¤ ¹4.05 and 22.8 assignable to 6, but after 10 h
only one signal at ¤ ¹3.77 ascribed to 7. The P,P¤-dioxide of
the parent 9,10-diphosphatriptycene was shown to have a high-
ly symmetric structure by X-ray crystallographic analysis.3c
The reaction of compounds 2 and 3 with molecular bromine
in CH2Cl2 or CHCl3 at 0 °C gave bromine adducts 8 and 9 with
the composition 2¢2Br2 and 3¢2Br2, respectively, as yellow
Me
Me
Me
Me
O
O
Br2 (excess)
Br
P
P
1
0 °C, CHCl3
Me
Me
P
Me
Me
P
Me
Me
Me
Me
Br
O
6
7
Scheme 2.
Me
Me
Me
Me
Br
Br
Br2 (excess)
E
Sb
E
Br
0 °C, CH2Cl2 or CHCl3
Me
Me
Me
Me
Sb
Br
Me
Me
Me
Me
2 (E = P)
3 (E = Sb)
8 (E = P, 99%)
9 (E = Sb, 71%)
Scheme 3.

Y. Uchiyama et al.
Bull. Chem. Soc. Jpn. Vol. 82, No. 7 (2009)
823
(a)
Table 4. Selected Bond Lengths (¡) of Compounds 8, 9,
and 10
8 (E = P)
9 (E = Sb1) 10 (E = Sb1)
E-C1
E-C2
E-C3
Sb2-C4
Sb2-C5
S2b-C6
E-Br1
E-Br2
E-O1
Sb2-Br3
Sb2-Br4
Sb2-Br5
Sb2-O2
E£Sb2
1.794(5)
1.790(5)
1.801(5)
2.192(5)
2.176(5)
2.174(5)
2.137(2)
®
2.086(3)
2.080(3)
2.096(3)
2.213(3)
2.200(3)
2.190(3)
2.407(1)
®
2.151(3)
2.133(3)
2.166(3)
2.159(3)
2.137(3)
2.160(3)
2.604(1)
2.615(1)
2.478(2)
2.640(1)
2.582(1)
®
C1
C4
Br1
P1
Br5
Br3
C2
C3
Sb2
C6
C5
Br4
®
®
2.637(1)
2.621(1)
2.615(1)
®
2.639(1)
2.669(1)
2.634(1)
®
(b)
2.458(2)
3.534
3.267
3.426
C1
Br1
C4
Table 5. Selected Bond Angles (deg) of Compounds 8, 9,
and 10
Sb1
Br3
C2
Br5
C3
8 (E = P)
9 (E = Sb1) 10 (E = Sb1)
Sb2
Br4
C6
C5
C1-E-C2
C1-E-C3
C2-E-C3
108.4(2)
109.4(2)
106.6(2)
92.3(2)
90.2(2)
91.5(2)
111.0(2)
111.5(2)
109.8(2)
®
105.7(1)
100.5(1)
105.0(1)
96.3(1)
92.9(1)
95.6(1)
116.8(1)
118.4(1)
108.4(1)
®
100.6(1)
94.2(1)
97.2(1)
100.8(1)
94.7(1)
96.4(1)
163.2(1)
®
C4-Sb2-C5
C4-Sb2-C6
C5-Sb2-C6
C1-E-Br1
C2-E-Br1
C3-E-Br1
C2-E-O1
C3-E-Br2
C4-Sb2-Br4
C5-Sb2-Br5
C6-Sb2-Br3
C5-Sb2-O2
(c)
®
177.2(1)
165.8(1)
161.8(1)
®
Br2
C1
Sb1
®
®
C4
O1
176.6(1)
176.4(1)
177.4(1)
®
173.6(1)
172.0(1)
174.6(1)
®
Br3
O2
C3
166.2(1)
177.1(1)
C2
Br1
Sb2
C5
C6
Me
Sb
Br4
Me
Figure 3. Molecular structures of (a) bromine adduct 8,
(b) bromine adduct 9, and (c) the THF complex 10 drawn
with 50% probability.
Br
Br
THF
THF
Me
Me
Sb
Br
are 94.9 and 173.4° on average, respectively, indicating that
Sb2 has a slightly distorted octahedral geometry. The Sb1-Br
bond (2.407 ¡) is considerably shorter than the Sb2-Br bonds
(2.647 ¡ in average), suggesting the cationic nature of the
tetracoordinate moiety. These data strongly indicate that the
adduct 9 is a zwitterion composed of a triarylbromostibonium
cation and a triaryltribromostiborate anion. The Sb2-Br bond
lengths are comparable with those in dibromotriphenylstibo-
rane (2.63-2.64 ¡), where the bromine atoms are in the apical
positions of a trigonal bipyramid (TBP) structure.21 The smaller
Sb£Sb distance in 9 (3.426 ¡) than in 3 (3.692 ¡) will again be
ascribed to these geometric features.
Me
Me
Br
10
Chart 3. The structue of 10 was obtained by recrystallization
of 9 from THF-mesitylene.
X-ray crystallographic analysis of 10 revealed that one THF
molecule and two bromine atoms are bonded to each antimony
atom, and therefore the compound is regarded as a THF com-
plex of a bis(dibromostiborane) (Figure 3c). Two THF mole-
cules are located in the same notch made of the two benzene
rings of the 9,10-distibatriptycene skeleton so that the molecule
Recrystallization of compound 9 from THF-mesitylene gave
crystals 10 with the composition of 3¢2Br2¢2THF (Chart 3).

824
Bull. Chem. Soc. Jpn. Vol. 82, No. 7 (2009)
9,10-Diheteratriptycenes
Me
Sb
Me
Me
Me
9, 11, or 12
9
Br
Br
Br
Sb Br
Br
Br
Me
Me
Me
Sb
Sb
Br
Me
Sb
Me
Me
Me
Me
Me
Br
Me
9
11
Br
or
Br
Me
Me
Me
Me
Me
Sb
Me
Me
Me
Br
Br
9, 11, or 12
9
Br
Sb Br
Sb
Br
Br
12
Scheme 4.
Br
9
Sb Br
Br
Me
Me
Me
Sb
Me
Me
Me
Me
Br
9
Me
has a near C2 (or C2v if conformations of the THF moieties are
neglected) symmetry (Figure 3). Selected bond lengths and
angles are given in Tables 4 and 5. The trans-C-Sb-O and
trans-C-Sb-Br angles are 177.2 and 164.3° on average,
respectively, showing a distorted octahedral geometry around
the antimony atoms. The Sb1-C2 and Sb2-C5 bonds (2.133
and 2.137 ¡) are shorter than the other Sb-C bonds (2.16 ¡ in
average) presumably because of the trans effect of THF oxygen
atoms locating against C2 and C5. The non-bonded Sb£Sb
distance in 10 (3.534 ¡) lies in between those in 3 and 9.
Highly coordinate compounds have been known to become
increasingly stable by increasing presence of electron-with-
drawing groups and elements because the Lewis acidity of the
center atom is increased.1c,22,23 According to a general rule of
the stabilization of hypervalent compounds, the THF complex
10 was constructed by antimony atom with two bromine atoms
and three aryl groups as Lewis acid and a THF molecule as
Lewis base. Hexacoordinate stiborate anions of 8 and 9 with
three bromine atoms and three aryl groups were also formed
because dibromotriarylstiborane and bromide ion behaved as
Lewis acid and base, respectively. Additionally, bromine
adducts 8 and 9 had phosphonium or stibonium cation as
counter ion toward antimony ate complex to be isolated as
intramolecular salts.
On the other hand, the 1H NMR spectrum of compound 9 in
CD2Cl2 at 27 °C showed only two singlets at ¤ 2.34 and 7.87
with an intensity ratio of 3:1 due to the methyl and the aromatic
protons, respectively, which are contradictory to the structure
obtained in the crystalline state. Upon lowering the temperature,
however, each singlet broadened and split into two equally
intense singlets. The aromatic signal decoalesced at ca. ¹20 °C
and gave two sharp singlets at ¤ 7.20 and 8.35 at ¹90 °C. The
methyl protons appeared as two singlets at ¤ 2.20 and 2.29 at
¹90 °C. The temperature dependence of the line shape could
be explained in terms of the interchange between the two
topomeric structures as shown in Scheme 4. This process takes
place fast at room temperature and the averaged spectrum is
observed in 1H NMR spectroscopy. At ¹90 °C, the interchange
is sufficiently slow on the NMR timescale. The lower-field
aromatic signal at ¤ 8.35 is ascribed to the peri-protons close to
the stiborate moiety as in the case of compound 8.
Although the detailed mechanism of the topomerization is
still uncertain, it seems to occur intermolecularly, because the
topomerization rate was shown to be dependent on the
concentration of 9. The rate constants, which were obtained
by line shape analysis using DNMR3,24 in CD2Cl2 at ¹83 °C,
are 52, 83, and 113 s¹1 for the 2.63, 5.72, and 10.8 M solutions,
respectively, which correspond to the free energies of activa-
1
¹1 16
NMR Studies of the Bromine Adducts. The H NMR
tion of 39.6, 38.9, and 38.4 kJ mol
.
This notion is further
spectrum of compound 8 in CD2Cl2 at room temperature
showed two methyl singlets at ¤ 2.29 and 2.37 and two
supported by the finding that addition of tetrabutylammonium
bromide in the sample increased the rate so that the signal
splitting could not be observed even at ¹90 °C. It is speculated
that two bromide ions move from the stiborate site to the
stibonium site stepwise by way of a bis(dibromostiborane)
intermediate 11, which would be unstable under the isolation
conditions but could be significantly stabilized in the presence
of Lewis bases such as THF to give compound 10.
aromatic doublets at
¤ 7.44 (JPH = 18.5 Hz) and 8.44
(JPH = 8.9 Hz). The signal at ¤ 8.44 was assigned to the peri-
protons close to the antimony atom based on the smaller
coupling with the phosphorus and the deshielding effect of the
nearby antimony atom. 31P NMR spectrum of 8 showed the
signal at ¤ 37.4 at a significantly lower field than that of 9-
phospha-10-stibatriptycene 2 (¤ ¹10.1) because of the cationic
nature of the P atom and the bromine substitution.
1H NMR spectrum of the THF complex 10 in CD2Cl2 gives
signals ascribed to 9 and THF, indicating that 10 dissociates in

Y. Uchiyama et al.
Bull. Chem. Soc. Jpn. Vol. 82, No. 7 (2009)
825
s), 7.36 (3H, s). 13C NMR (75 MHz, CDCl3): ¤ 19.4 (p), 19.5 (p),
129.4 (q), 132.8 (q), 136.5 (t), 138.2 (t), 139.8 (q), 139.9 (q). MS
(70 eV) m/z 670 (M+, 100%).
solution to give the bis(dibromostiborane) 12 and THF, and the
former immediately isomerizes to 9 because the intramolecular
salts 9 is the most stable species thermodynamically in these
equilibrium systems.
Studies of the reactions of 9,10-diheteratriptycenes 1-3
with other halogens, F2, Cl2, and I2, and also with organic
electrophiles such as alkyl halides are in progress.
2,3,6,7,14,15-Hexamethyl-9,10-diphosphatriptycene (1). To
a
solution of tris(2-bromo-4,5-dimethylphenyl)phosphine (4)
(3.42 g, 5.87 mmol) in THF-Et2O (7:5, 100 mL) was added
1.54 M t-BuLi in pentane (8.0 mL, 12.3 mmol) at ¹78 °C, and
then the reaction mixture was stirred for 1 h at ¹78 °C. To the
mixture was added PCl3 (0.60 mL, 6.88 mmol) at ¹78 °C, and the
mixture was stirred for 1.5 h at ¹78 °C. To the reaction mixture
was added water (100 mL) and the mixture was extracted with
CHCl3 (100 mL © 4). The organic extracts were washed with aq
NaCl (50 mL), dried over MgSO4, and evaporated to give crude
material. Column chromatography (silica gel, CHCl3) of the
residue gave the 9,10-diphosphatriptycene 1 (148 mg, 0.39 mmol,
7%) as white solid, mp >300 °C (dec.) (from hexane). Found:
C, 77.37; H, 6.73%. Calcd for C24H24P2: C, 76.99; H, 6.46%.
1H NMR (600 MHz, CDCl3): ¤ 2.18 (18H, s), 7.68 (6H, m).
13C NMR (151 MHz, CDCl3): ¤ 19.5 (p), 135.6 (t), 136.6 (q,
J = 5.6 Hz), 142.9 (q, J = 4.2 Hz). 31P NMR (243 MHz, CDCl3): ¤
¹46.1 (m). MS (70 eV) m/z 374 (M+, 100%).
2,3,6,7,14,15-Hexamethyl-9-phospha-10-stibatriptycene (2):
With Phosphine Compound 4. To a solution of tris(2-bromo-
4,5-dimethylphenyl)phosphine (4) (583 mg, 1.00 mmol) in THF
(20 mL) was added 1.59 M t-BuLi in pentane (3.8 mL, 6.04 mmol)
at ¹78 °C, and then the reaction mixture was stirred for 20 min at
¹78 °C. To the mixture was added SbCl3 (280 mg, 1.23 mmol) at
¹78 °C, and the mixture was stirred for 12 h at ¹78 °C. To the
reaction mixture was added aq NH4Cl (20 mL) and the mixture was
extracted with CHCl3 (20 mL © 4). The organic extracts were
washed with aq NaCl (20 mL), dried over MgSO4, and evaporated
to give 9-phospha-10-stibatriptycene 2 (62 mg, 0.13 mmol, 13%)
as white solid.
2,3,6,7,14,15-Hexamethyl-9-phospha-10-stibatriptycene (2):
With Stibine Compound 5. To a solution of tris(2-bromo-4,5-
dimethylphenyl)stibine (5) (2.09 g, 3.10 mmol) in THF (100 mL)
was added 1.54 M t-BuLi in pentane (13.4 mL, 20.6 mmol) at
¹78 °C, and then the reaction mixture was stirred for 30 min at
¹78 °C. To the mixture was added AlCl3 (620 mg, 4.65 mmol),
TMEDA (4.0 mL, 3.13 mmol), and PCl3 (0.19 mL, 2.18 mmol) at
¹78 °C, and the mixture was stirred for 12 h at ¹78 °C. To the
reaction mixture was added aq NH4Cl (100 mL) and the mixture
was extracted with CHCl3 (100 mL © 4). The organic extracts were
washed with aq NaCl (50 mL), dried over MgSO4, and evaporated
to give white material. Soxhlet extraction with hexane gave the 9-
phospha-10-stibatriptycene 2 (144 mg, 0.31 mmol, 10%) as white
solid, mp 257-258 °C (dec.) [from CH2Cl2-hexane (1:1)]. Found:
C, 61.99; H, 5.37%. Calcd for C24H24PSb: C, 61.97; H, 5.20%.
1H NMR (300 MHz, CDCl3): ¤ 2.14 (9H, s, 3/6/15-Me), 2.18
Experimental
General Procedure. All reactions were carried out under
argon atmosphere except for bromination reactions. Preparative gel
permeation chromatography (GPC) was performed on LC-908,
LC-918, or LC-9201 with JAIGEL 1H column (Japan Analytical
Industry) with chloroform as the eluent. 1H, 13C, and 31P NMR
spectra were recorded on a Bruker ARX300 (300/75/121 MHz) or
a Bruker Avance 600 spectrometer (600/151/243 MHz). Chemical
shifts are reported in ¤ using the residual proton signal of the
deuterated solvents [CD2Cl2 (¤H 5.32)] or the signal of tetra-
1
methylsilane [TMS (¤H 0.00)] as internal standards for H NMR
spectra, the central peak of the solvent signal [CDCl3 (¤C 77.0)] for
13C NMR spectra, and the signal of phosphoric acid [85% H3PO4
(¤P 0.00) in a sealed tube] as external standard for 31P NMR
spectra, respectively. Letters p, s, t, and q given with the 13C
chemical shifts denote primary, secondary, tertiary, and quaternary,
respectively. MS spectra were taken on a Hitachi-2500 mass
spectrometer. Melting points were determined by differential
scanning calorimetry using
a DSC-50 differential scanning
calorimeter. Elemental analysis was performed on a Perkin-Elmer
CHN/S 2400II analyzer. Cyclic voltammetry measurements were
carried out with a Hokuto Denko Corporation HZ-5000 analyzer.
Tris(2-bromo-4,5-dimethylphenyl)phosphine (4).
To a
solution of 4,5-dibromo-o-xylene (16.0 g, 60.6 mmol) in THF-
¹3
Et2O (9:8, 170 mL) at ¹110°C was added 1.54M (1M = 1moldm
)
n-BuLi in hexane (39.0 mL, 60.1 mmol), and the reaction mixture
was stirred for 1 h at ¹110 °C. To the mixture was added a solution
of PCl3 (1.3 mL, 14.9 mmol) in Et2O (20 mL) at ¹110 °C, and the
mixture was stirred for 1.5 h at ¹110 °C and gradually warmed to
rt. The mixture was quenched with H2O (200 mL) and was
extracted with CHCl3 (200 mL © 3). The organic extracts were
washed with aq NaCl (200 mL), dried over MgSO4, and evaporated
to give 4 as a white solid (3.32 g, 5.69 mmol, 38%), mp 249-
250 °C (dec.) (from CH2Cl2/hexane). Found: C, 49.63; H, 4.17%.
1
Calcd for C24H24Br3P: C, 49.43; H, 4.15%. H NMR (300 MHz,
CDCl3): ¤ 2.07 (9H, s), 2.25 (9H, s), 6.48 (3H, s), 7.39 (3H, s).
13C NMR (75 MHz, CDCl3): ¤ 19.4 (p), 19.5 (p), 127.0 (q,
J = 57.4 Hz), 133.5 (q, J = 10.5 Hz), 133.8 (t, J = 2.9 Hz), 135.8
(t), 136.1 (q), 139.6 (q). 31P NMR (121 MHz, CDCl3): ¤ ¹4.75 (s).
MS (70 eV) m/z 580 (M+, 100%).
Tris(2-bromo-4,5-dimethylphenyl)stibine (5). To a solution
of 4,5-dibromo-o-xylene (2.60 g, 9.85 mmol) in THF-Et2O (1:1,
100 mL) at ¹110 °C was added 1.54 M n-BuLi in hexane (6.2 mL,
9.55 mmol), and the reaction mixture was stirred for 30 min at
¹110 °C. To the mixture was added a solution of SbCl3 (758 mg,
3.3 mmol) in THF-Et2O (1:1, 50 mL) at ¹110 °C, and the mixture
was stirred for 12 h at ¹110 °C. The mixture was quenched with
aq NH4Cl (200 mL) and was extracted with CHCl3 (200 mL © 3).
The organic extracts were washed with aq NaCl (200 mL), dried
over MgSO4, and evaporated to give 5 as a white solid (1.32 g,
1.96 mmol, 59%), mp 251-252 °C (dec.) (from EtOAc). Found: C,
42.74; H, 3.80%. Calcd for C24H24Br3Sb: C, 42.77; H, 3.59%.
1H NMR (300 MHz, CDCl3): ¤ 2.05 (9H, s), 2.23 (9H, s), 6.77 (3H,
(9H, s, 2/7/14-Me), 7.68 (3H, s, 4/5/16-H), 7.90 (3H, d, JPH =
12.1 Hz, 1/8/13-H). 13C NMR (151 MHz, CDCl3): ¤ 19.3 (p, 3/6/
15-Me), 19.5 (p, 2/7/14-Me), 136.4 (t, J = 52.2 Hz, 1/8/13-C),
136.5 (t, J = 1.5 Hz, 4/5/16-C), 137.0 (q, J = 29.1 Hz, 2/7/14-C),
137.7 (q, J = 1.7 Hz, 3/6/15-C), 140.4 (q, J = 5.3 Hz, 4a/10a/
11-C), 146.3 (q, J = 3.5 Hz, 8a/9a/12-C). 31P NMR (121 MHz,
3
CDCl3): ¤ ¹10.1 (q, JHP = 11.4 Hz). MS (70 eV) m/z 464 (M+,
100%), 239 [P(Me2-C6H2)2, 15%], 225 [Sb(Me2-C6H2), 15%],
135 [P(Me2-C6H2), 3%].
2,3,6,7,14,15-Hexamethyl-9,10-distibatriptycene (3). To a
solution of tris(2-bromo-4,5-dimethylphenyl)stibine (5) (948 mg,
1.71 mmol) in THF (100 mL) was added 1.54 M t-BuLi in pentane
(5.35 mL, 8.24 mmol) at ¹78 °C, and the reaction mixture was

826
Bull. Chem. Soc. Jpn. Vol. 82, No. 7 (2009)
9,10-Diheteratriptycenes
Table 6. Crystal Data of Compounds 1, 2, and 3, and Parameters for Data Collection, Structure
Determination, and Refinement
1
2
3
Formula
MW
Crystal system
Space group
Z
a/¡
b/¡
c/¡
¡/deg
¢/deg
£/deg
V/¡3
C24H24P2
374.37
monoclinic
C2/c
C24H24PSb
465.15
C24H24Sb2¢0.5C6F6
648.96
monoclinic
C2/c
rhombohedral
ꢀ
R3
4
18
20.086(1)
20.086(1)
26.775(1)
90
90
120
9355.5(5)
1.486
4212
8
16.681(2)
9.620(1)
13.949(1)
90
108.506(1)
90
26.410(1)
10.113 (1)
20.503(1)
90
116.932(1)
90
4882.1(3)
1.766
2520
2122.7(3)
1.171
¹3
D
calcd/g cm
F(000)
792
®(Mo Kα)/¡
Temp/K
0.71070
103
0.71070
103
0.71070
113
2ªmax/°
20
20
20
No. of reflections measured
Total
Unique
5663
2397
17749
4886
16932
5283
No. of refinement variables
R1 (all data)
wR2 (all data)
GOF
122
242
295
0.0408
0.0909
1.048
0.0583
0.1342
1.089
0.0273
0.0660
1.081
stirred for 30 min at ¹78 °C. To the mixture was added a solution
of SbBr3 (444 mg, 1.23 mmol) in THF (20 mL) at ¹78 °C, and the
mixture was stirred for 12 h at ¹78 °C. To the reaction mixture was
added aq NH4Cl (50 mL) and the mixture was extracted with Et2O
(100 mL © 3). The organic extracts were washed with aq NaCl
(50 mL), dried over MgSO4, and evaporated to give white solid.
Column chromatography (silica gel, CHCl3) and subsequent
GPC of the residue gave the 9,10-distibatriptycene 3 (67 mg,
0.121 mmol, 9%) as white solid (from benzene), mp 285-290 °C
(dec.). Found: C, 52.00; H, 4.46%. Calcd for C24H24Sb2: C, 51.85;
H, 4.35%. 1H NMR (600 MHz, CDCl3): ¤ 2.18 (18H, s), 7.81 (6H,
s). 13C NMR (151 MHz, CDCl3): ¤ 19.4 (p), 136.9 (q), 137.6 (t),
146.1 (q). MS (70 eV) m/z 554 (M+, 13%), 226 [Sb(Me2-C6H3),
100%].
Reaction of Compound 1 with Bromine. To a solution of the
9,10-diphosphatriptycene 1 (10 mg, 0.027 mmol) in CHCl3 (3 mL)
was added bromine (10 ¯L, 0.195 mmol) at 0 °C. The reaction
mixture was stirred for 0.5 h at 0 °C. The reaction solvent was
removed under reduced pressure and the residue was washed with
hexane to give the mono(bromophosphonium) P-oxide salt 6
quantitatively as an easily hydrolysable compound. 1H NMR
(600 MHz, CDCl3): ¤ 2.41 (9H, s), 2.47 (9H, s), 8.02 (3H, m),
8.10 (3H, m). 13C NMR (151 MHz, CDCl3): ¤ 20.2 (p), 20.4 (p),
124.2 (q), 131.8 (t), 131.9 (t), 134.0 (q), 142.2 (q, J = 14.5 Hz),
144.0 (q, J = 8.8 Hz). 31P NMR (121 MHz, CDCl3): ¤ ¹4.05 (d,
J = 55.1 Hz), 22.8 (d, J = 62.4 Hz). SIMS m/z 470 (M+, 12%),
390 (M ¹ Br, 100%). When the reaction mixture was left standing
overnight, the P,P¤-dioxide 7 was obtained as white solid (10 mg,
0.025 mmol, 93%), mp 270-275 °C (dec.). Found: C, 70.88; H,
6.20%. Calcd for C24H24P2O2: C, 70.93; H, 5.95%. 1H NMR
(600 MHz, CDCl3): ¤ 2.29 (18H, s), 7.92 (6H, m). 13C NMR
(151 MHz, CDCl3): ¤ 19.7 (p), 130.2 (t, J = 7.7 Hz), 135.6 (q,
J = 52.7 Hz), 139.2 (q, J = 4.4 Hz). 31P NMR (121 MHz, CDCl3):
¤ ¹3.77 (m). MS (70 eV) m/z 406 (M+, 100%).
Bromine Adduct 8.
To a solution of the 9-phospha-10-
stibatriptycene 2 (15 mg, 0.032 mmol) in CHCl3 (3 mL) was added
bromine (20 ¯L, 0.390 mmol) at 0 °C. The reaction mixture was
stirred for 0.5 h at 0 °C. The reaction solvent was removed under
reduced pressure and the residue was washed with hexane to give
the adduct 8 as yellow solid (25 mg, 0.032 mmol, 99%), mp 227-
230 °C (dec.). Found: C, 36.49; H, 3.33%. Calcd for C24H24Br4PSb:
1
C, 36.73; H, 3.08%. H NMR (300 MHz, CD2Cl2): ¤ 2.29 (9H, s,
3/6/15-Me), 2.37 (9H, s, 2/7/14-Me), 7.44 (3H, d, JPH = 18.5
Hz, 1/8/13-H), 8.44 (3H, d, JPH = 8.9 Hz, 4/5/16-H). 13C NMR
(151 MHz, CD2Cl2, 27 °C): ¤ 19.5 (p, CH3), 20.0 (p, CH3), 123.4
(q, J = 82.4 Hz), 126.6 (q, J = 9.2 Hz), 137.6 (t, J = 14.0 Hz),
138.0 (t, J = 14.1Hz), 144.1 (q, J = 3.7Hz), 158.1 (q, J = 13.4Hz).
31P NMR (121 MHz, CDCl3): ¤ 37.4 (m). SIMS m/z 705 (M ¹
Br + H, 0.2%), 545 (M ¹ 3Br, 20%), 464 (M ¹ 4Br, 0.1%).
Bromine Adduct 9. To a solution of the 9,10-distibatriptycene
3 (64 mg, 0.116 mmol) in CH2Cl2 (10 mL) was added bromine
(20 ¯L, 0.390 mmol) at 0 °C. The reaction mixture was stirred for
1 h at 0 °C. The solvent was removed under reduced pressure and
the residue was washed with hexane to give the adduct 9 as yellow
solid (64 mg, 0.082 mmol, 71%), mp 203-204 °C (dec.). Found:
C, 33.20; H, 3.02%. Calcd for C24H24Br4Sb2: C, 32.92; H,
1
2.76%. H NMR (600 MHz, CD2Cl2, 27 °C): ¤ 2.34 (18H, s), 7.87
(6H, s); 13C NMR (151 MHz, CD2Cl2, 27 °C): ¤ 20.0 (p), 134.5 (q),
138.1 (t), 142.3 (q). SIMS m/z 795 (M ¹ Br + H, 80%), 312
((C6H2(CH3)2)3, 100%).
Bis(dibromostiborane)-THF Complex 10. Recrystallization
of compound 9 from THF-mesitylene gave yellow solid of 10, mp
1
204-205 °C (dec.). H NMR (300 MHz, CD2Cl2): ¤ 1.82 (4H, m,
THF), 2.34 (18H, s, 9), 3.68 (4H, m, THF), 7.87 (6H, s, 9).

Y. Uchiyama et al.
Bull. Chem. Soc. Jpn. Vol. 82, No. 7 (2009)
827
Table 7. Crystal Data of Compounds 8, 9, and 10, and Parameters for Data Collection, Structure
Determination, and Refinement
8
9
10
Formula
MW
Crystal system
Space group
Z
C24H24Br4PSb¢CHCl3
904.16
monoclinic
P21/n
C24H24Br4Sb2¢CHCl3
994.94
monoclinic
P21/n
C24H24Br4Sb2¢2THF
1019.78
monoclinic
C2/c
4
4
8
a/¡
b/¡
c/¡
¡/deg
¢/deg
£/deg
V/¡3
11.092(2)
18.733(4)
14.192(3)
90
98.842(1)
90
11.080(1)
18.922(1)
14.346(1)
90
100.184(1)
90
21.246(1)
19.999(1)
17.183(1)
90
111.337(1)
90
2913.6(11)
2.061
2960.2(2)
2.232
6800.4(4)
1.992
¹3
Dcalcd/g cm
F(000)
1728
1872
3920
®(Mo Kα)/¡
Temp/K
0.71070
113
0.71070
113
0.71070
113
2ªmax/°
20
20
20
No. of reflections measured
Total
Unique
26063
8247
19685
5973
22747
6788
No. of refinement variables
R1 (all data)
wR2 (all data)
GOF
313
313
367
0.0592
0.1231
1.029
0.0271
0.0561
1.063
0.0295
0.0622
1.070
Cyclic Voltammetry. The three-electrode systems consisted
of Glass Carbon, a Pt wire as secondary electrode, and an Ag
wire as the pseudo-reference electrode. The cyclic voltammograms
were recorded 1.0 mM in CH2Cl2 solution with 0.1 M [TBAP;
ogy of Japan and Kitasato University Research Grant for
Young Researchers. We thank Dr. Mao Minoura at the
Department of Chemistry, School of Science, Kitasato Uni-
versity for his advice on X-ray crystallographic analysis.
¹
n-Bu4N+¢ClO4 ] as the supporting electrolyte and data were
reported relative to the ferrocene/ferrocenium couple (+0.31 V)
References
¹
with 0.1 M [n-Bu4N+¢ClO4 ] in CH2Cl2.
1
a) A. G. Massey, Adv. Inorg. Chem. 1989, 33, 1. b) A. Ishii,
X-ray Crystallography. Single crystals of 1, 2, 3, 8, 9, and 10
were grown by the slow evaporation of suitable saturated solutions
at room temperature. A colorless block crystal for each of 1, 2, 3,
8, 9, and 10 having approximate dimensions of 0.20 © 0.20 ©
0.20, 0.20 © 0.20 © 0.20, 0.60 © 0.40 © 0.25, 0.20 © 0.20 © 0.15,
0.20 © 0.20 © 0.15, and 0.15 © 0.10 © 0.05 mm3, respectively,
was mounted on a glass fiber. All measurements were made on a
Rigaku Mercury-CCD and Bruker AXS Inc. SMART APEXII with
graphite monochromated Mo K¡ radiation (- = 0.71070 ¡). The
structure was solved by direct methods and expanded using Fourier
techniques. All non-hydrogen atoms were refined anisotropically,
while hydrogen atoms were refined isotropically. Crystallographic
data are summarized in Tables 6 and 7.
J. Nakayama, Rev. Heteroat. Chem. 1994, 11, 1. c) H. Suzuki, Y.
Matano, Organobismuth Chemistry, Elsevier, Amsterdam, 2001.
d) N. P. McCleland, J. B. Whitworth, J. Chem. Soc. 1927, 2753.
e) R. Kasemann, D. Naumann, J. Fluorine Chem. 1988, 41, 321.
2
F. von Dechend, H. Wichelhaus, Ber. Dtsch. Chem. Ges.
1875, 8, 1609.
3
a) K. G. Weinberg, E. B. Whipple, J. Am. Chem. Soc. 1971,
93, 1801. b) K. G. Weinberg, J. Org. Chem. 1975, 40, 3586. c) D.
Schomburg, W. S. Sheldrick, Acta Crystallogr., Sect. B 1975, 31,
2427. d) S. Sørensen, H. J. Jakobsen, Org. Magn. Reson. 1977, 9,
101.
4
a) N. P. McCleland, J. B. Whitworth, J. Chem. Soc. 1927,
2753. b) N. Rot, W.-J. A. Wijs, F. J. J. de Kanter, M. A. Dam, F.
Bickelhaupt, M. Lutz, A. L. Spek, Main Group Met. Chem. 1999,
22, 519.
Crystallographic data of 1-3 and 8-10 have been deposited
with Cambridge Crystallographic Data Centre: Deposition num-
bers CCDC-725596, -725597, -269390, -725594, -269391, and
-725595 for compound Nos. 1-3 and 8-10. Copies of the data can
be obtained free of charge via http://www.ccdc.cam.ac.uk/conts/
retrieving.html (or from the Cambridge Crystallographic Data
Centre, 12, Union Road, Cambridge, CB2 1EZ, U.K.; Fax: +44
1223 336033; e-mail: deposit@ccdc.cam.ac.uk).
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