Synthesis and thermal stability of 3-substituted 3-benzostibepines

Article abstract of DOI:10.3987/COM-08-S(D)33

Fully unsaturated 3-benzostibepines having various aryl groups on antimony have been prepared by a ring closure reaction of an appropriate antimony dihalide (ArSbBr₂) with (Z,Z)-1,2-bis(2-lithiovinyl)benzene generated by treatment of (Z,Z)-1,2-

Full text of DOI:10.3987/COM-08-S(D)33

HETEROCYCLES, Vol. 79, 2009
659
HETEROCYCLES, Vol. 79, 2009, pp. 659 - 667. © The Japan Institute of Heterocyclic Chemistry
Received, 26th September, 2008, Accepted, 10th November, 2008, Published online, 13th November, 2008.
DOI: 10.3987/COM-08-S(D)33
SYNTHESIS AND THERMAL STABILITY OF 3-SUBSTITUTED
3
-BENZOSTIBEPINES
1
,2
1
1
1
Shuji Yasuike, Masaaki Ikoma, Naoki Kakusawa, Takashi Tsuchiya, and
*
1
Jyoji Kurita
1
Faculty of Pharmaceutical Sciences, Hokuriku University, Kanagawa-machi,
Kanazawa 920-1181, Japan. E-mail: j-kurita@hokuriku-u.ac.jp
2
Organization for Frontier Research in Preventive Pharmaceutical Sciences,
Hokuriku University, Kanagawa-machi, Kanazawa 920-1181, Japan
Abstract – Fully unsaturated 3-benzostibepines having various aryl groups on
antimony have been prepared by a ring closure reaction of an appropriate
2
antimony dihalide (ArSbBr ) with (Z,Z)-1,2-bis(2-lithiovinyl)benzene generated
by treatment of (Z,Z)-1,2-bis(2-bromovinyl)benzene with t-BuLi. All the
stibepines obtained here are thermolabile in solution toward heteroatom extrusion.
1
The half-lives of the stibepines estimated from H NMR spectral analysis revealed
that the thermal stabilities of the stibepines bearing a heteroatom moiety (N, O) in
the vicinity of the antimony are far less stable than others.
INTRODUCTION
Considerable attention has recently been focused on the chemistry of fully unsaturated seven-membered
rings (heteroepines) containing group 15 (P, As, Sb, and Bi) and 16 (S, Se, and Te) elements. In general,
simple heteroepines (monocyclic or mono aromatic ring-fused) are know to be thermally unstable owing
1
to ready extrusion of heteroatom moiety via electrocyclic reaction. With regard to benzostibepines,
several reports for the synthesis have been reported in recent years, in that the 7-membered ring was
2
,3
mainly constructed with tin-antimony metal exchange reaction of stannepines and with ring closure
4
-6
reaction of 1,6-dilithium compounds with antimony dihalides. Furthermore, the thermal stability of
these compounds is of remarkable interest and is well documented; e.g. i) 3- (1) and 1-benzostibepines (2)
2
,4
are thermally unstable and decompose to naphthalene with elimination of heteroatom moiety, ii)
2
3
3
-chloro- and 3-alkyl-3-benzostibepines are thermolabile and can be isolated only at low temperature, iii)
4
-benzostibepines (1) are less stable than the corresponding 1-benzostibepines (2), iv) the

660
HETEROCYCLES, Vol. 79, 2009
3
-benzostibepine (3) having bulky trimethylsilyl group on both 2- and 4-positions is much more stable
6
than C-unsubstituted compounds, v) the dibenzostibepine (4) is thermally stable and remains unchanged
5
a
even when it is heated over 60 °C. However, little is known about the influence of antimony ligand
upon their thermal stability. This paper describes a versatile synthesis of various 3-substituted
3
-benzostibepine derivatives and their thermal stabilities in detail.
SiMe3
Sb R
Sb Ph
Sb
Ph
Sb
SiMe3
Ph
1
: R = Cl, Me, nBu, Ph
2
3
4
Scheme 1
RESULTS AND DISCUSSION
The synthesis of 3-benzostibepines (1a-e) from (Z,Z)-1,2-bis(2-bromovinyl)benzene (5) is shown in
Scheme 2. The route for the synthesis of 3-aryl-3-benzostibepines (1a-e) from 5 is essentially the same as
that for the preparation of 3-benzoheteroepines containing group 15 (P, As, Sb, Bi) and 16 (S, Se, Te)
4
,6
heavier elements in our previous paper. The key starting bromide (5) was prepared stereoselectively in
high yield (90%) by a double Wittig reaction of o-phthalaldehyde with bromomethyltriphenyl-
4
,7
phosphonium ylide, generated in situ by treatment of bromomethyltriphenylphosphonium bromide with
potassium tert-butoxide in tetrahydrofuran at low temperature (–80 °C). The bromide (5) was treated with
a large excess of tert-butyllithium (7.5 eq) in anhydrous Et
then with dibromoarylstibanes (8a-e) to undergo ring closure giving rise to the expected
-aryl-3-benzostibepines (1a-e) in 10-36% yield, via 1,6-dilithium intermediate (6). All
2
O at –80 °C under an argon atmosphere, and
3
dibromoarylstibanes (8a-e) employed in the present reactions were prepared by treatment of a 1:2 mixture
Ar Sb / SbBr (1 : 2)
3
3
7a-e
heat 110 °C
ArSbBr2
Br
Br
tert-BuLi
80 °C
Et O
Li
Li
8a-e
Sb Ar
-
-
80 to -10°C
2
6
1a-e
5
Me N
MeO
2
Ar = a:
b:
c:
d:
OMe
e:
F
Scheme 2

HETEROCYCLES, Vol. 79, 2009
661
of triarylstibanes (7a-e) and tribromostibane at 90 °C for 1-3 h, and were used directly without
purification.
We have recently reported that the reaction of organoantimony (III) compounds with Grignard or
organolithium reagents resulted in nucleophilic displacement of the substituents on the antimony to give
8
various new antimony (III) compounds. Especially, the displacement of the phenyl substituent on group
1
5 atoms in 1-phenyl-1-benzoheteroles (As, Sb, Bi) to methyl group occurred easily by treatment with
8
a
methyllithium. Taking these results into consideration, we next examined the behavior of
-benzostibepine toward organolithium reagent. The reaction of 3-phenyl-3-benzostibepine (1a) with 1.2
3
equivalent of methyllithium in tetrahydrofuran at –80 °C underwent the expected substitution on the
antimony to give 3-methyl-3-benzostibepine (1f) in low yield (12%), which is the first example of
nucleophilic displacement of the substituent on antimony of heteroepine (Scheme 3).
MeLi
Sb
Sb Me
-
80 °C
THF
1a
1f
Scheme 3
1
Table 1. Selected H NMR spectral data for 3-benzoheteroepines (1) δ (CDCl
3
, 400 MHz)
Compd.
1- and 5-H
7.57
7.56
7.56
7.54
2- and 4-H
6.52
6.64
6.57
6.48
J
1,2 (J4,5) / Hz
-ArCH
---
3.49
4.56
---
2
XR
XR
1a
1b
1c
1d
1e
1f
12.1
12.5
12.5
12.5
12.1
12.1
---
2
2.18 (NMe )
3.37 (OMe)
---
---
---
7.56
7.46
6.46
6.50
---
---
2
4
Although 3-methyl- (1f) and 3-phenylstibepines (1a) are known, the other heteroepines (1b-e) obtained
1
here are new compounds. The structures of 1a-f were mainly established by their HRMS and H NMR
1
spectra. The H NMR spectroscopic data of the seven-membered ring in 1 are given in Table 1. The
values of the chemical shift and coupling constant of J1,2 (4,5) of the protons are not so affected by the
difference of the substituent on antimony. On the other hand, the methyl protons on the hetero atoms for
1
b (N-CH , δ 2.18) and 1c (O-CH , δ 3.37) appeared at a relatively higher field. These results would be
3
3
interpreted by the shielding effect of the C=C bonds on the seven-membered ring, in that an
intramolecular coordination would form between antimony and the hetero atoms (N and O) referred below.

662
HETEROCYCLES, Vol. 79, 2009
heat
Sb
R
1a-f
9
Scheme 4
Table 2. Half-lives and activation energies of 1
Compound 1/2 min at 40 ˚C (d -toluene)
-1
t
8
Ea / Kcal mol
25.8
26.6
24.4
22.8
1a
1b
1c
1d
1e
1f
149
29
100
131
157
72
28.2
24.6
All the 3-benzostibepines (1) obtained here were thermolabile in solution toward elimination of the
antimony moiety (R-Sb) and gradually decompose to naphthalene even during isolation by column
chromatography (Scheme 4). Thus, thermolysis (50 ºC, 2.5 h, in d
8
-toluene) of 1a gave naphthalene
1
almost quantitatively along with black precipitates with metallic glint, biphenyl, and triphenylstibane ( H
1
NMR and TLC analyses). The half-lives (t1/2) and activation energies (Ea) of 1a-f calculated from H
NMR spectral data are listed in Table 2. In 3-aryl-3-benzostibepines (1a-e), the stabilities estimated by
their half-lives decrease in the order 1e > 1a > 1d > 1c > 1b at 40 °C. The stibepines (1b, c) having
heteroatom (N, O) substituent at 2-position on the aryl group are far less stable than others, and
3
3
4
-[2-(N,N-dimethylaminomethyl)phenyl]-3-benzostibepine (1b) is the most unstable in this series of
-benzostibepines. A little difference of the thermal stability was observed between the stibepines bearing
-methoxyphenyl (1d) and 4-fluorophenyl groups (1e), and 1e having electron-withdrawing group (-F) is
3
slightly more stable than unsubstituted 1a and 1d having electron-donating group (-OCH ). These results
indicate that the electronic nature of the aryl group on the antimony affects the stability of the stibepines.
The widely accepted mechanism of heteroatom extrusion involves isomerization of the heteroepine to the
1
, 4, 5
corresponding hetero-norcaradiene isomer, followed by irreversible loss of heteroatom moiety.
The
same route would be applicable in the present extrusive decomposition of the stibepines (1a-f). It is also
known that the stability of 1H-azepine is enhanced by electron-withdrawing substituents on nitrogen,
9
whereas electron-donating substituents suppress the stability. The difference of the stability in 1e
[
3-(4-fluorophenyl): half life, 157 min] > 1a (3-phenyl: 149 min) > 1d [3-(4-methoxyphenyl): 131 min]
would be understood by this interpretation. Also apparent was that the stibepines (1b, c) having

HETEROCYCLES, Vol. 79, 2009
663
heteroatom (N, O) moiety at the phenyl group on antimony were apparently far less stable than the other
-aryl-3-stibepines (1a, 1d, and 1e). This fact implies that an intramolecular interaction between
3
antimony and hetero atoms (N and O) promotes electrocyclic isomerization of A to C via B and the
formation of naphthalene (9) as shown in Scheme 5. A similar non-bonding interaction between antimony
and hetero atoms such as nitrogen, oxygen, and sulfur has been observed in many antimony compounds,
10
and has been characterized by NMR and X-ray analyses. As noted above, the methyl groups on the
Sb
Sb
X
A
X
B
X = NMe , OMe
2
Sb
X
9
C
Scheme 5
space
heteroatom moiety for 1b and 1c were observed at a higher field, indicating the presence of
intramolecular coordination between the antimony and hetero atoms in solution.
In conclusion, the general synthesis of 3-substituented 3-benzostibepines was attained by the ring closure
reaction between antimony dihalides (8a-e) and 1,6-dilithium intermediate (6) generated from easily
available (Z,Z)-1,2-bis(2-bromovinyl)benzene (5). The benzostibepines prepared here were thermolabile
in solution and decomposed to naphthalene accompanied by extrusion of antimony moiety with ease. In
particular, the stibepines bearing heteroatom substituents in the vicinity of antimony were far less stable
than others. Further studies including trapping of antimony moiety formed during the present heteroatom
extrusion with diene are now in progress.
EXPERIMENTAL
Melting points were measured on a Yanagimoto micro melting point hot stage apparatus and are
uncorrected. Mass spectra (MS) and high-resolution mass spectra (HRMS) were recorded on a JEOL
JMP-DX300 instrument. NMR spectra were determined with a JEOL JNM-GSX-400 (400 MHz)
3
spectrometer in CDCl using tetramethylsilane as an internal standard unless otherwise stated, and
spectral assignments were confirmed by spin-decoupling experiments. Column chromatography was
performed on silica gel (BW-127ZH, Fuji Silysia) or activated alumina (Aluminium oxide 90, Merck).

664
HETEROCYCLES, Vol. 79, 2009
1
0c
11
Tris[2-(N,N-dimethylaminomethyl)phenyl]stibane (7b),
tris(4-methoxyphenyl)stibane (7d)
and
1
2
tris(4-fluorophenyl)stibane (7e) were prepared according to the reported procedure. Microanalyses were
performed in the Microanalytical Laboratory of this Faculty by Ms. C. Kuroda and Ms. M. Kashihara.
Synthesis of tris[2-(methoxymethyl)phenyl]stibane (7c)
2
To a solution of 2-(methoxymethyl)bromobenzene (20.1 g, 0.1 mol) in Et O (100 mL) was added
n-butyllithium (1.56 M in hexane, 71 mL, 0.11 mol) at -20 °C under an argon atmosphere, and the
solution was stirred for 1.6 h. To this was added a solution of antimony trichloride (7.62 g, 33.4 mmol) in
Et
2
O (70 mL) over 40 min at -15 °C, and the mixture was stirred for 1 h at the same temperature. The
mixture was quenched with water (150 mL) and diluted with Et O (300 mL). The organic layer was
2
2
separated and the aqueous layer was extracted with Et O (50 mL x 2). The combined organic layer was
washed with brine, dried, and evaporated in vacuo. The residue was chromatographed on silica gel with
1
hexane/EtOAc (20:1) to give 7c. Colorless prisms (11.6 g, 71%), mp 60.5-61 °C (from MeOH-Et
2
O); H
NMR(400 MHz) δ : 3.14 (9H, s, OMe), 4.58 (6H, s, benzyl-H), 7.11-7.35 (12H, m, Ar-H); MS m/z (EI)
+
4
84 (M ). Anal. Calcd for C24
H
27
3
O Sb: C, 59.41; H, 5.61. Found: C, 59.36; H, 5.53.
General procedure for the preparation of 3-aryl-3-benzostibepines (1a-e)
2
A solution of (Z,Z)-1,2-bis(2-bromovinyl)benzene (5: 576 mg, 2 mmol) in anhydrous Et O (20 mL) was
added dropwise over a 10 min period to a solution of tert-buthyllithium (1.5 M pentane solution, 10 mL,
5 mmol) in anhydrous Et O (20 mL) with stirring at –80 °C under an argon atmosphere, then the mixture
was stirred for an additional 10 min at the same temperature. Dibromoarylstibanes (8a-e: 4 mmol)
prepared from redistribution reaction on heating a 1:2 mixture of triarylstibane (7a-e) and
tribromostibane (SbBr ) for 1-3 h at 90 °C] were added in small portions over a 10 min period to the
1
2
[
3
above mixture with stirring at –80 °C. The mixture was allowed to warm to –10 °C and stirred for 3 h,
and then warmed to rt. Et O (100 mL) and water (100 mL) were added to the mixture with stirring. The
2
solution was separated and the aqueous layer was extracted with Et
organic layer was washed with brine, dried, and evaporated in vacuo. The resulting residue was
chromatographed on silica gel or aluminum oxide with pentane/Et O to give 1a-e.
2
O (100 mL x 2). The combined
2
3
-Phenyl-3-benzostibepine (1a)
Colorless needles (163 mg, 25%), mp 76-78 °C (from MeOH). The compound (1a) was identical with the
4
authentic sample prepared in our previous paper.
3-[2-(N, N-Dimethylaminomethyl)phenyl]-3-benzostibepine (1b)

HETEROCYCLES, Vol. 79, 2009
665
The compound (1b) was purified by aluminum oxide using pentane as an eluent. Colorless oil (76 mg,
1
1
0%); H NMR (400 MHz) δ: 2.18 (6H, s, NMe
2
), 3.49 (2H, s, benzyl-H), 6.64 (2H, d, J = 12.5 Hz, 2-
+
and 4-H), 7.56 (2H, d, J = 12.5 Hz, 1- and 5-H), 7.11-7.81 (8H, m, Ar-H); MS m/z (EI) 255 (M -C10
H
8
).
9
HRMS Calcd for C H12NSb: 255.0008. Found: 255.0012.
3
-[2-(Methoxymethyl)phenyl]-3-benzostibepine (1c)
2
The compound (1c) was purified by silica gel using pentane-Et O (20:1) as an eluent. Colorless oil (74
1
mg, 11%); H NMR (400 MHz) δ: 3.37 (3H, s, OMe), 4.56 (2H, s, benzyl-H), 6.57 (2H, d, J = 12.5 Hz, 2-
+
and 4-H), 7.56 (2H, d, J = 12.5 Hz, 1- and 5-H), 7.19-7.82 (8H, m, Ar-H); MS m/z (EI) 242 (M -C10
H
8
).
8 9
HRMS Calcd for C H OSb: 241.9690. Found: 241.9697.
3
-(4-Methoxyphenyl)-3-benzostibepine (1d)
The compound (1d) was purified by silica gel using pentane as an eluent. Yellow prisms (185 mg, 26%),
1
mp 80-85 °C (decomp.) (from MeOH); H NMR (400 MHz) δ: 3.83 (3H, s, OMe), 6.48 (2H, d, J = 12.1
Hz, 2- and 4-H), 7.54 (2H, d, J = 12.1 Hz, 1- and 5-H), 6.90-7.64 (8H, m, Ar-H); MS m/z (EI) 228
+
(
M -C10
H
8
). Anal. Calcd for C17
H15OSb: C, 57.19; H, 4.23. Found: C, 57.06; H, 4.14.
3
-(4-Fluorophenyl)-3-benzostibepine (1e)
The compound (1e) was purified by silica gel using pentane as an eluent. Colorless prisms (144 mg, 21%),
1
mp 63-68 °C (decomp.) (from MeOH); H NMR (400 MHz) δ: 6.46 (2H, d, J = 12.1 Hz, 2- and 4-H),
+
7
.56 (2H, d, J = 12.1 Hz, 1- and 5-H), 7.22-7.69 (8H, m, Ar-H); MS m/z (EI) 216 (M -C H ). Anal.
1
0
8
Calcd for C16H12FSb: C, 55.70; H, 3.51. Found: C, 55.87; H, 3.69.
Synthesis of 3-methyl-3-benzostibepine (1f)
Methyllithium (1.14 M in pentane, 0.2 mL, 0.23 mmol) was added dropwise to a solution of 1a (62 mg,
.19 mmol) in THF (2 mL) with stirring at -78 °C and the solution was stirred for an additional 20 min.
After addition of pentane (10 mL) and water (10 mL), the reaction mixture was stirred for 10 min at
0
-
10 °C. The organic layer was separated, washed with brine, dried, and evaporated in vacuo. The residue
1
was chromatographed on silica gel using pentane as an eluent to give 1f. Pale yellow oil (6 mg, 12%); H
NMR (400 MHz) δ: 0.96 (3H, s, Me), 6.50 (2H, d, J = 12.1 Hz, 2- and 4-H), 7.46 (2H, d, J = 12.1 Hz, 1-
+
and 5-H), 7.19-7.48 (4H, m, Ph-H); MS m/z (EI) 264 (M ); HRMS Calcd for C11
H11Sb 263.9900. Found
2
63.9902.

666
HETEROCYCLES, Vol. 79, 2009
General procedure for thermal conversion of 3-benzostibepines (1a-f) to naphthalene (9)
A solution of stibepine 1a-f (6-20 mg, 0.02-0.06 mmol) in d -toluene (0.7 mL) was heated at each
temperature. The disappearance of 1 and appearance of 9 were monitored by NMR integration. The first
8
313
-5 -1 323
-4 -1 333
-4 -1
order rate constants are shown below; 1a: k = 7.73x 10 s , k = 2.56 x 10 s , k = 9.09 x 10 s ,
2
97
-5 -1 303
-5 -1 313
-4 -1
303
-5 -1 313
1
b: k = 3.85 x 10 s , k = 8.75 x 10 s , k = 3.97 x 10 s , 1c: k = 3.57 x 10 s , k = 1.13 x
-4
-1 323
-4 -1
313
-5 -1 323
-4 -1 333
-4 -1
313
1
0 s , k = 4.23 x 10 s , 1d: k = 8.75 x 10 s , k = 2.21 x 10 s , k = 7.81 x 10 s , 1e: k
-
5
-1 323
-4 -1 333
-3 -1
303
-5 -1 313
-4
=
7.40 x 10 s , k = 2.04 x 10 s , k = 1.09 x 10 s , and 1f: k = 4.51 x 10 s , k = 1.60 x 10
-1
323
-4 -1
s , k = 5.35 x 10 s .
ACKNOWLEDGEMENTS
This work was supported by a Grant-in Aid for Scientific Research (C) (to J. K.), and the “Academic
Frontier” Project for Private Universities from the Ministry of Education, Culture, Sports, Science and
Technology of Japan (to S. Y.). Financial support by the Special Research Fund from Hokuriku
University is also gratefully acknowledged.
REFERENCES
1
.
(a) G. Märkl and W. Burger, Angew. Chem., Int. Ed. Engl., 1984, 23, 894; (b) Idem, Tetrahedron
Lett., 1983, 24, 2545; (c) S. Shiratori, S. Yasuike, J. Kurita, and T. Tsuchiya, Chem. Pharm. Bull.,
1
994, 42, 2441; (d) I. Murata and K. Nakatsuji, Top. Curr. Chem., 1981, 97, 33; (e) K. Yamamoto
and S. Yamazaki, “Comprehensive Heterocyclic Chemistry II,” Vol. 9, ed. by A. R. Katritzky, C. W.
Rees, and E. F. V. Scriven, Pergamon, Oxford, 1996, pp. 67-111; (f) H. Hori, S. Yamazaki, K.
Yamamoto, and I. Murata, Angew. Chem., Int. Ed. Engl., 1990, 29, 424; (g) H. Sashida, H.
Kurahashi, and T. Tsuchiya, J. Chem. Soc., Chem. Commun., 1991, 802.
2
.
.
A. J. Ashe III, L. Goossen, J. W. Kampf, and H. Konishi, Angew. Chem., Int. Ed. Engl., 1992, 31,
1
642.
3
(a) H. Sashida, Heterocycles, 2000, 53, 49; (b) H. Sashida and A. Kuroda, J. Chem. Soc., Perkin
Trans. 1, 2000, 1965.
4
.
.
S. Yasuike, T. Kiharada, J. Kurita, and T. Tsuchiya, Chem. Commun., 1996, 2183.
(a) S. Yasuike, H. Ohta, S. Shiratori, J. Kurita, and T. Tsuchiya, J. Chem. Soc., Chem. Commun.,
5
1
1
993, 1817; (b) S. Yasuike, S. Shiratori, J. Kurita, and T. Tsuchiya, Chem. Pharm. Bull., 1999, 47,
108.
6
.
.
S. Yasuike, S. Shiratori, T. Tsuchiya, and J. Kurita, Chem. Pharm. Bull., 2003, 51, 1283.
(a) M. Matsumoto and K. Kuroda, Tetrahedron Lett., 1980, 21, 4021; (b) M. A. Romero and A. G.
Fallis, Tetrahedron Lett., 1994, 35, 4711.
7

HETEROCYCLES, Vol. 79, 2009
667
8
9
1
.
(a) J. Kurita, M. Ishii, S. Yasuike, and T. Tsuchiya, Chem. Pharm. Bull., 1994, 42, 1437; (b) N.
Kakusawa, T. Ikeda, A. Osada, J. Kurita, and T. Tsuchiya, Synlett, 2000, 1503.
R. K. Smalley, “Comprehensive Heterocyclic Chemistry ,” Vol. 7, ed. by A. R. Katritzky and C. W.
Rees, Pergamon, Oxford, 1984, pp. 491-546.
.
0. For examples; (a) K. Ohkata, S. Takemoto, M. Ohnishi, and K. –y. Akiba, Tetrahedron Lett., 1989,
0, 4841; (b) Y. Yamamoto, X. Chen, S. Kojima, K. Ohdoi, M. Kitano, Y. Doi, and K. –y. Akiba, J.
3
Am. Chem. Soc., 1995, 117, 3922; (c) S. Kamepalli, C. J. Carmalt, R. D. Culp, A. H. Cowley, R. A.
Jones, and N. C. Norman, Inorg. Chem., 1996, 35, 6179; (d) E. Bräu, A. Zickgraf, M. Dräger, E.
Mocellin, M. Maeda, M. Takahashi, M. Takeda, and C. Mealli, Polyhedron, 1998, 17, 2655; (e) S.
Yasuike, S. Tsukada, J. Kurita, T. Tsuchiya, Y. Tsuda, H. Kiuchi, and S. Hosoi, Heterocycles, 2000,
5
3, 525; (f) T. Tokunaga, H. Seki, S. Yasuike, M. Ikoma, J. Kurita, and K. Yamaguchi, Tetrahedron,
000, 56, 8833; (g) S. Okajima, S. Yasuike, N. Kakusawa, A. Osada, K. Yamagichi, H. Seki, and J.
2
Kurita, J. Organomet. Chem., 2002, 656, 234; (h) K. Hoshino, T. Ogawa, S. Yasuike, H. Seki, J.
Kurita, T. Tokunaga, and K. Yamagichi, J. Phys. Chem. B, 2004, 108, 18698; (i) P. Sharma, J. G.
Lopez, C. Ortega, N. Rosas, A. Cabrera, C. Alvarez, A. Toscano, and E. Reyes, Inorg. Chem.
Commun., 2006, 9, 82; (j) S. Yasuike, Y. Kishi, S. Kawara, K. Yamagichi, and J. Kurita, J.
Organomet. Chem., 2006, 691, 2213; (k) P. Sharma, D. Pérez, J. Vázquez, A. Toscano, and R.
Gutiérrez, Inorg. Chem. Commun., 2007, 10, 389; (l) L. Dostál, L. Jambor, A. Růžička, R. Jirásko, I.
Císařová, and J. Holeček, J. Fluorine Chem., 2008, 129, 167, and references cited therein.
1
1. A. F. M. M. Rahman, T. Murafuji, M. Ishibashi, Y. Miyoshi, and Y. Sugihara, J. Organomet. Chem.,
2
005, 690, 4280.
1
2. R. F. Ketelaere, F. T. Delbeke, and G. P. Kelen, J. Organomet. Chem., 1971, 30, 365.