Arylation of styrenes with aryliron complexes [CpFe(CO)2Ar]

Article abstract of DOI:10.1021/om1001952

Treatment of aryliron complexes [CpFe(CO)₂Ar] with styrenes in boiling xylene affords the corresponding stilbenes. The aryliron complexes, which become active upon heating, serve as arylating agents in the reaction.

Full text of DOI:10.1021/om1001952

2634 Organometallics 2010, 29, 2634–2636
DOI: 10.1021/om1001952
Arylation of Styrenes with Aryliron Complexes [CpFe(CO)2Ar]
Shigeo Yasuda,† Hideki Yorimitsu,*,†,‡ and Koichiro Oshima*,†
†Department of Material Chemistry, Graduate School of Engineering, Kyoto University, Kyoto-daigaku
Katsura, Nishikyo-ku, Kyoto 615-8510, Japan, and Department of Chemistry, Graduate School of Science,
‡
Kyoto University, Sakyo-ku, Kyoto 606-8502, Japan
Received March 12, 2010
Summary: Treatment of aryliron complexes [CpFe(CO)2Ar]
with styrenes in boiling xylene affords the corresponding
stilbenes. The aryliron complexes, which become active upon
heating, serve as arylating agents in the reaction.
course of these studies, we now report that [CpFe(CO)2Ar]
react with styrenes to yield the corresponding stilbenes.11,12
The reaction begins with insertion of the CdC bond of
styrene into the aryl-iron bond. Insertion of unsaturated
bonds into aryl-iron bonds of [CpFe(CO)2Ar] is well
known.2,3 However, there has been only one report on appli-
cation of such insertion to useful organic transformation.2
Treatment of [CpFe(CO)2(4-tolyl)] (1a) with 2 equiv of
styrene in refluxing xylene afforded 4-methylstilbene (3a)
in 79% yield (Table 1, entry 1). The high temperature is
essential. The yield of 3a was much lower when a similar
reaction was performed at a lower temperature (entry 2).
Electron-rich styrene 2b and electron-deficient ones 2c and
2d reacted with 1a, although the yields of the corresponding
products were modest (entries 3-5). The reactions with
styrenes having a bromo and acetoxy group proceeded to
afford 3e and 3g in modest yields, leaving the functional
groups untouched (entries 6 and 8). The reaction with
4-iodostyrene (2f) afforded the corresponding stilbene 3f,
having an iodo group, although the yield of 3f was low (entry
7). Unfortunately, alkenes other than styrenes were much
less reactive in the reactions. For example, the reactions with
ethyl acrylate (2h) and vinyl boronate 2i were sluggish
(entries 9 and 10). In all cases, some amount of hydridoiron
complex [CpFe(CO)2H] was formed as a byproduct.
Organoiron complexes bearing a dicarbonylcyclopenta-
dienylironmoiety[CpFe(CO)2R] are utilizedas useful organo-
metallic reagents in organic synthesis.1 Among them, the
reactions of the corresponding aryliron complexes [CpFe-
(CO)2Ar] are still unexplored.2-8 Studies on chemical reac-
tivity of [CpFe(CO)2Ar] provide useful organic reactions
because they are expected to show different reactivity from
other arylmetal reagents. Recently, we have developed the
efficient synthesis of [CpFe(CO)2Ar] and have been pursuing
their synthetic utility as useful arylmetal reagents.9,10 In the
*To whom correspondence should be addressed. E-mail: yori@
kuchem.kyoto-u.ac.jp; oshima@orgrxn.mbox.media.kyoto-u.ac.jp
(1) (a) Pearson, A. J. Iron Compounds in Organic Synthesis; Academic
Press: London, 1994. (b) Pearson, A. J. Pure Appl. Chem. 1983, 55, 1767–
1779. The coordination chemistry of [CpFe(CO)2R] has been summarized:
(c) Kerber, R. C. In Comprehensive Organometallic Chemistry II; Abel,
E. W., Stone, F. G. A., Wilkinson, G., Eds.; Elsevier: Oxford, U.K., 1995;
Vol. 7, Chapter 2.
(2) Reaction with diphenylacetylene yielding indenone derivatives:
Butler, I. R.; Cullen, W. R.; Lindsell, W. E.; Preston, P. N.; Rettig, S. J.
J. Chem. Soc., Chem. Commun. 1987, 439–441.
(3) Insertion of unsaturated bonds into aryl-iron bonds: (a) Severson,
R. G.; Leung, T. W.; Wojcicki, A. Inorg. Chem. 1980, 19, 915–923. (b) Su,
S. R.; Wojcicki, A. Inorg. Chem. 1975, 14, 89–98. (c) Jacobson, S. E.; Wojcicki,
A. J. Am. Chem. Soc. 1973, 95, 6962–6970.
This arylation reaction with [CpFe(CO)2Ar] was much
affected by steric effects. Unfortunately, the reactions of
1a with sterically demanding R-methylstyrene (2j) and
β-methylstyrene (2k) failed to afford the corresponding stil-
bene derivatives 3j and 3k in reasonable yields (eqs 1 and 2).
(4) Iron-carbon bond cleavage in strong carboxylic acids: De Luca,
N.; Wojcicki, A. J. Organomet. Chem. 1980, 193, 359–378.
(5) Reaction with HgX2 affording ArHgX: Dizikes, L. J.; Wojcicki,
A. J. Am. Chem. Soc. 1977, 99, 5295–5303.
(6) Electrochemical behavior: Magdesieva, T. V.; Kukhareva, I. I.;
Artamkina, G. A.; Beletskaya, I. P.; Butin, K. P. Izv. Akad. Nauk, SSSR
Ser. Khim. 1996, 1812–1821.
(7) Photochemical behavior: (a) Nesmeyanov, A. N.; Chapovskii,
Y. A.; Polovyanyuk, I. V.; Makarova, L. G. Izv. Akad. Nauk, SSSR Ser.
Khim. 1968, 1628–1629. (b) Nesmeyanov, A. N.; Chapovskii, Y. A.;
Lokshin, B. V.; Polovyanyuk, I. V.; Makarova, L. G. Dok. Akad. Nauk,
SSSR 1966, 166, 1125–1128.
(8) Cp ring lithiation reaction: Orlova, T. Y.; Setkina, V. N.; Sizoi,
V. F.; Kursanov, D. N. J. Organomet. Chem. 1983, 252, 201–204.
(9) (a) Yasuda, S.; Yorimitsu, H.; Oshima, K. Organometallics 2008,
27, 4025–4027. (b) Asada, Y.; Yasuda, S.; Yorimitsu, H.; Oshima, K.
Organometallics 2008, 27, 6050–6052. (c) Yasuda, S.; Asada, Y.; Yorimitsu,
H.; Oshima, K. Materials 2009, 2, 978–991. (d) Yasuda, S.; Yorimitsu, H.;
Oshima, K. Organometallics 2009, 28, 4872–4875. (e) Yasuda, S.; Yorimitsu,
H.; Oshima, K. Organometallics 2010, 29, 273–274.
(10) Other methods for the synthesis of [CpFe(CO)2Ar]: (a) Butler,
I. R.; Lindsell, W. E.; Preston, P. N. J. Chem. Res. Synop. 1981, 185.
(b) Artamkina, G. A.; Mil'chenko, A. Y.; Bumagin, N. A.; Beletskaya, I. P.;
Reutov, O. A. Organomet. Chem., USSR 1988, 1, 17–20. (c) Nesmeyanov,
A. N.; Chapovsky, Y. A.; Polovyanyuk, I. V.; Makarova, L. G. J. Organomet.
Chem. 1967, 7, 329–337. (d) Hunter, A. D.; Szigety, A. B. Organometallics
1989, 8, 2670-2679, and references therein.
The reactions of various aryliron complexes with styrene
were investigated (Table 2). The reaction of 2-naphthyliron
1c afforded 3l in slightly lower yield than the case of 1a
(11) Recent examples of methods for the preparation of unsymme-
trical stilbenes. (a) Kormos, C. M.; Leadbeater, N. E. J. Org. Chem.
2008, 73, 3854–3858. (b) Kabir, M. S.; Monte, A.; Cook, J. M. Tetrahedron
Lett. 2007, 48, 7269–7273.
(12) The reaction of [CpFe(CO)2H] with R-cyclopropylstyrene has
been reported: Bullock, R. M.; Samsel, E. G. J. Am. Chem. Soc. 1990,
112, 6886–6898.
r
pubs.acs.org/Organometallics
Published on Web 05/12/2010
2010 American Chemical Society

Note
Organometallics, Vol. 29, No. 11, 2010 2635
Table 1. Reactions of [CpFe(CO)2(4-tolyl)] with Various Styrenes
Scheme 1
entry
Ar
2
3
yield/%
1
Ph
Ph
2a
2a
2b
2c
2d
2e
2f
2g
2h
2i
3a
3a
3b
3c
3d
3e
3f
3g
3h
3i
79
23
59
71
58
53
23
50
15
10
2a
3
4-MeOC6H4
4-FC6H4
4-ClC6H4
4-BrC6H4
4-IC6H4
4-AcOC6H4
(CO2Et)
(B(pin))
4
5
reactions of 1a with 2l and 1k with 2l afforded gem-difluoro-
alkenes 4a and 4b, respectively, although the yields were
low (eq 3).14 In the reactions, the stilbene derivatives were
not obtained. We assume that β-fluoride elimination, not
β-hydride elimination, occurred selectively from the benzylic
iron complex generated in situ.
6
7b
8
9
10
a Performed in refluxing toluene. b [CpFe(CO)2Ph] (1b) was used
instead of 1a.
Table 2. Scope of Aryliron Complexes
Aryliron complexes [CpFe(CO)2Ar] have emerged as
arylating agents in the reaction with styrenes. This reaction
utilizes insertion of the CdC bond of styrene into the
aryl-iron bond, representing a new chemical reactivity of
[CpFe(CO)2Ar] toward carbon-carbon multiple bonds.
entry
Ar
1
3
yield/%
1
2-naphthyl
2-MeC6H4
4-MeOC6H4
4-FC6H4
4-ClC6H4
1c
1d
1e
1f
1g
1h
1i
3l
69
32
53
57
58
58
58
70
84
2
3m
3n
3o
3p
3q
3r
3s
3t
3a
4
Experimental Section
5
6
4-BrC6H4
1
General Procedures. H NMR (500 and 300 MHz) and 13C
7a
8
3-CF3C6H4
4-EtOC(dO)C6H4
4-(pin)BC6H4
NMR (125.7 and 75.3 MHz) spectra were taken on a Varian
UNITY INOVA 500 spectrometer and a Varian GEMINI 300
spectrometer. 1H NMR and 13C NMR spectra were obtained
in CDCl3 with tetramethylsilane as an internal standard.
Chemical shifts (δ) are in parts per million relative to tetra-
methylsilane at 0.00 ppm for 1H and relative to CDCl3 at
77.2 ppm for 13C unless otherwise noted. IR spectra were
determined on a JASCO IR-810 spectrometer. The elemental
analyses were carried out at the Elemental Analysis Center of
Kyoto University.
Unless otherwise noted, materials obtained from commercial
suppliers were used without further purification. THF was
purchased from Kanto Chemical Co., stored under nitrogen,
and used as is. [CpFe(CO)2Ar] were synthesized by palladium-
catalyzed transmetalation between [CpFe(CO)2I] and arylmetal
reagents according to the methods reported previously.9a-c,e
Xylene was purchased from Nacalai Tesque and stored over
slices of sodium. Silica gel (Wakogel 200 mesh) was used for
column chromatography.
1j
1k
9a
a Performed for 24 h.
(entry 1). The reaction of sterically demanding aryliron 1d
was sluggish (entry 2). Electron-rich aryliron 1e, halophenyl-
irons 1f-1h, and electron-deficient aryliron 1i underwent the
reaction to afford the corresponding stilbene derivatives in
modest yields (entries 3-7). The reaction of arylirons having
an ester (1j) and a boron (1k) moiety occurred selectively at
the iron-carbon bond without affecting the functional
groups (entries 8 and 9).
The reaction would proceed as shown in Scheme 1. Dis-
sociation of a carbonyl ligand by heating and subsequent
insertion of the CdC bond of styrene into the aryl-iron
bond generates the corresponding benzylic iron com-
plex. Subsequent β-hydride elimination affords the stilbene
derivative.13
Experimental Procedure. Typical Procedure for Reactions of
[CpFe(CO)2Ar] with Styrenes (Table 1, entry 1). Dicarbonyl-
cyclopentadienyl(4-methylphenyl)iron (1a, 80 mg, 0.30 mmol),
styrene (2a, 62 mg, 0.60 mmol), and xylene (1.5 mL) were
sequentially added in a 30 mL reaction flask under argon. The
mixture was heated at reflux for 12 h. Then the reaction mixture
was cooled to room temperature and filtered through a pad of
silica gel. After evaporation, silica gel column purification
(eluent: hexane) of the crude product provided 4-methylstilbene
(3a, 46 mg, 0.24 mmol, 79% yield).
We could assume another mechanism where the Ar radical
generated in situ would participate in the reaction. There-
fore, we carried out the reaction of 1a with 2a in the presence
of a radical inhibitor, TEMPO. The reaction proceeded to
afford 3a in 45% yield, although the yield was lower than
that in the absence of TEMPO (vs Table 1, entry 1). This
result rules out the mechanism in which an Ar radical
addition to styrene is involved.
In the reactions with R-trifluoromethylstyrene (2l), we
obtained an outcome different from the case with 2a. The
(14) It was reported that similar gem-difluoroalkenes were obtained
in rhodium-catalyzed addition reactions of arylboron reagents to R-
trifluoromethylstyrene through β-fluoride elimination: Miura, T.; Ito,
Y.; Murakami, M. Chem. Lett. 2008, 37, 1006–1007.
(13) Photoinduced β-hydride elimination of [CpFe(CO)2(alkyl)]:
(a) Alt, H. G. Angew. Chem., Int. Ed. Engl. 1984, 23, 766–782. (b) Waltz,
K. M.; Muhoro, C. N.; Hartwig, J. F. Organometallics 1999, 18, 3383–3393.

2636 Organometallics, Vol. 29, No. 11, 2010
Yasuda et al.
Characterization Data. The spectral data of the products 3a,15
3b,16 3d,15 3e,17 3f,18 3h,19 3i,20 3j,21 3k,22 3l,23 3m,15 3n,18 3p,15
3q,18 3r,24 3s,25 3t,26 and 4a14 can be found in the literature.
(E)-4-Fluoro-40-methylstilbene (3c). IR (Nujol): 1507, 1233,
1210, 972, 829, 719 cm-1. 1H NMR (CDCl3): δ 2.36 (s, 3H), 7.00
(d, J = 4.0 Hz, 2H), 7.02-7.05 (m, 2H), 7.16 (d, J = 8.0 Hz, 2H),
7.39 (d, J = 8.0 Hz, 2H), 7.44-7.47 (m, 2H). 13C NMR (CDCl3):
δ 21.46, 115.78 (d, JC-F = 21.5 Hz), 126.57, 126.71, 128.04 (d,
(s, 2H), 7.07 (d, J = 9.0 Hz, 2H), 7.16 (d, J = 8.5 Hz, 2H),
7.40 (d, J = 8.5 Hz, 2H), 7.49 (d, J = 9.0 Hz, 2H). 13C NMR
(CDCl3): δ 21.35, 21.46, 121.96, 126.63, 126.87, 127.49, 129.09,
129.62, 134.60, 135.57, 137.83, 150.10, 169.67. Anal. Calcd
for C17H16O2: C, 80.93; H, 6.39. Found: C, 80.69; H, 6.46. Mp:
157-159 °C.
(E)-4-Fluorostilbene (3o). IR (Nujol): 1030, 964, 824, 690
1
cm-1. H NMR (CDCl3): δ 6.99-7.08 (m, 4H), 7.25 (t, J =
JC-F = 8.1 Hz), 128.64 (d, JC-F = 2.4 Hz), 129.63, 133.92 (d,
7.5 Hz, 1H), 7.35 (dd, J = 7.5, 7.5 Hz, 2H), 7.45-7.50 (m, 4H).
13C NMR (CDCl3): δ 115.82 (d, JC-F = 22.0 Hz), 126.65,
127.70, 127.87, 128.19 (d, JC-F = 7.8 Hz), 128.71 (d, JC-F = 2.4
Hz), 128.92, 133.74 (d, JC-F = 3.4 Hz), 137.39, 162.55 (d,
JC-F = 3.4 Hz), 134.61, 137.79, 162.43 (d, JC-F = 245.4 Hz).
Anal. Calcd for C15H13F: C, 84.88; H, 6.17. Found: C, 84.63; H,
6.28. Mp: 125-126 °C.
(E)-4-[2-(4-Methylphenyl)ethenyl]phenyl Acetate (3g). IR
(Nujol): 1752, 1701, 1685, 1507, 1223, 1196, 1013, 972, 915
JC-F =245.8 Hz). Anal. Calcd for C14H11F: C, 84.82; H, 5.59.
Found: C, 84.82; H, 5.55. Mp: 118-119 °C.
cm-1
.
1H NMR (CDCl3): δ 2.30 (s, 3H), 2.36 (s, 3H), 7.03
1-(3,3-Difluoro-2-phenyl-2-propen-1-yl)-4-(4,4,5,5-tetramethyl-
1,3,2-dioxaborolan-2-yl)benzene (4b). IR (neat): 2978, 2932,
1
1728, 1612, 1366, 1319, 1242, 1150, 1088, 955, 856 cm-1. H
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Angew. Chem., Int. Ed. 2006, 45, 2404–2409.
NMR (CDCl3): δ 1.32 (s, 12H), 3.74 (dd, J = 2.5, 2.0 Hz, 2H),
7.17 (d, J = 8.0 Hz, 2H), 7.18-7.28 (m, 5H), 7.69 (d, J = 8.0
Hz, 2H). 13C NMR (CDCl3): δ 25.07, 34.37, 83.92, 91.74 (dd,
J
C-F = 21.0, 13.9 Hz), 127.51, 127.96, 128.49 (dd, JC-F = 3.4,
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3.3 Hz), 128.57, 133.66 (dd, JC-F = 3.9, 3.8 Hz), 135.22, 141.95
(dd, JC-F = 2.9, 2.4 Hz), 154.64 (dd, JC-F = 290.1, 285.9 Hz).
The borylated carbon could not be observed. Anal. Calcd for
˚
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Acknowledgment. This work was supported by Grants-
in-Aid for Scientific Research and for GCOE Research
from MEXT and JSPS. S.Y. acknowledges JSPS for
financial support. H.Y. thanks The Kurata Memorial
Hitachi Science and Technology Foundation and Mizuho
Foundation for the Promotion of Sciences for financial
support.
€
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