Preparation of Di-μ-chlorobis[π-1-chloro-1-aryl-2-(2′,2′- diarylvinyl)allyl]palladium(II) complexes and a novel dehydrogenative rearrangement of arylvinylcyclopropenes for the synthesis of 7 H-benzo[ c ]fluorene derivatives

Article abstract of DOI:10.1021/om1009846

A new synthetic method for the preparation of di-μ-chlorobis[π-1- chloro-1-aryl-2-(2′,2′-diarylvinyl)allyl]palladium(II) complexes has been developed from the reaction of arylvinylcyclopropenes with a Pd(II) complex along with a novel dehydrogenative rearrangement of arylvinylcyclopropenes via di-μ-chlorobis[π-1-chloro-1-aryl-2-(2′, 2′-diarylvinyl)allyl]palladium(II) complexes to produce 7H-benzo[c]fluorene derivatives in good yields under mild conditions. A stoichiometric amount of silver salts or a catalytic amount of strong Bronsted acid HOTf can be the promoter or the catalyst for this interesting dehydrogenative rearrangement.

Full text of DOI:10.1021/om1009846

Organometallics 2011, 30, 627–632 627
DOI: 10.1021/om1009846
Preparation of Di-μ-chlorobis[π-1-chloro-1-aryl-2-
(20,20-diarylvinyl)allyl]palladium(II) Complexes and a Novel
Dehydrogenative Rearrangement of Arylvinylcyclopropenes for the
Synthesis of 7H-Benzo[c]fluorene Derivatives
Zhi-Bin Zhu,† Kai Chen,† Yin Wei,‡ and Min Shi*,†,‡
†Laboratory for Advanced Materials and Institute of Fine Chemicals, School of Chemistry & Molecular
Engineering, East China University of Science and Technology, 130 Mei-Long Road, Shanghai 200237,
People’s Republic of China, and ‡State Key Laboratory of Organometallic Chemistry, Shanghai Institute of Organic
Chemistry, Chinese Academy of Sciences, 354 Fenglin Road, Shanghai 200032, People’s Republic of China.
Received October 14, 2010
A new synthetic method for the preparation of di-μ-chlorobis[π-1-chloro-1-aryl-2-(20,20-diarylvinyl)-
allyl]palladium(II) complexes has been developed from the reaction of arylvinylcyclopropenes with a Pd(II)
complex along with a novel dehydrogenative rearrangement of arylvinylcyclopropenes via di-μ-chlorobis-
[π-1-chloro-1-aryl-2-(20,20-diarylvinyl)allyl]palladium(II) complexes to produce 7H-benzo[c]fluorene deriv-
atives in good yields under mild conditions. A stoichiometric amount of silver salts or a catalytic amount of
strong Brønsted acid HOTf can be the promoter or the catalyst for this interesting dehydrogenative
rearrangement.
Introduction
ring-opening/ring-expanding of cyclopropenes, such as
3-vinylcyclopropenes.6 For example, complexation of
transition metals with cyclopropenes along with the C-C
bond cleavage of ring structure including transformation
of cyclopropenes into vinylcarbene metal complexes7 and
Cyclopropenes1 are well known as a large class of excellent
ligands for various π-philic transition metals.2 The driving
force of coordination between cyclopropenes and metal centers
is the relief of ring strain3 via donation of filled π-orbital
electrons from cyclopropene moieties to the hybrid spd-orbital
of the metals along with the formation of π-back-bonding.4
Since the first Pd-promoted ring-opening reaction of cyclopro-
penes reported by Battiste and co-workers,5 numerous inves-
tigations have been focused on the transition-metal-mediated
(6) For selected examples of the synthesis of transition metal com-
plexes via ring-opening/expanding of 3-vinylcyclopropenes promoted
by Ir, see: (a) Hughes, R. P.; Trujillo, H. A.; Egan, J. W.n., Jr. J. Am.
Chem. Soc. 2000, 122, 2261. (b) Hughes, R. P.; Trujillo, H. A.; Rheingold,
A. L. J. Am. Chem. Soc. 1993, 115, 1583. For Rh, see: (c) Donovan-
Merkert, B. T.; Tjiong, H. I.; Rhinehart, L. M.; Russel, R. A.; Malik, J.
Organometallics 1997, 16, 819. (d) Donovan, B. T.; Hughes, R. P.; Kowalski,
A. S.; Trujillo, H. A.; Rheingold, A. L. Organometallics 1993, 12, 1038. (e)
Donovan, B. T.; Hughes, R. P.; Trujillo, H. A.; Rheingold, A. L. Organome-
tallics 1992, 11, 64. (f) Donovan, B. T.; Hughes, R. P.; Trujillo, H. A. J. Am.
Chem. Soc. 1990, 112, 7076. (g) Donovan, B. T.; Egan, J. W., Jr.; Spara, P. P.;
Trujillo, H. A.; Rheingold, A. L. Isr. J. Chem. 1990, 30, 351. (h) Egan, J. W.;
Hughes, R.P.;Rheingold, A. L.Organometallics1987, 6, 1578. ForPd, see:(i)
Hughes, R. P.; Trujillo, H. A.; Egan, J. W.; Rheingold, A. L. Organometallics
1999, 18, 2766. (j) Donovan, B. T.; Hughes, R. P.; Spara, P. P.; Rheingold, A. L.
Organometallics1995, 14, 489. For Ru and Fe, see: (k) Hughes, R. P.; Trujillo,
H. A.; Gauri, A. J. Organometallics 1995, 14, 4319. (l) Hughes, R. P.;
Robinson, D. J. Organometallics 1989, 8, 1015. (m) Hemond, R. C.; Hughes,
R. P. J. Chem. Soc., Chem. Commun. 1988, 319. (n) Grabowski, N. A.;
Hughes, R. P.; Jaynes, B. S.; Rheingold, A. L. J. Chem. Soc., Chem. Commun.
1986, 1694.
*To whom correspondence should be addressed. E-mail: Mshi@mail.
sioc.ac.cn. Fax: 86-21-64166128.
(1) Baird, M. S. In Cyclopropenes: Synthesis: By Construction of the
System; Houben-Weyl Thieme: Stuttgart, Germany, 1997; Vol. E17d/2, p
2695.
(2) For reviews on coordination chemistry of cyclopropenes, see: (a)
Baird, M. S. In Cyclopropenes: Transformations; de Meijere, A., Ed.;
Houben-Weyl Thieme: Stuttgart, Germany, 1997; Vol. E17d/2, p 2949. (b)
Goldschmidt, Z. In The Chemistry of the Cyclopropyl Group; Rappoport,
Z., Ed.; Wiley: New York, 1995; Vol. 2, p 495.
(3) For studies on strain energy of cyclopropenes, see: (a) Bach,
R. D.; Dmitrenko, O. J. Am. Chem. Soc. 2004, 126, 4444. (b) Johnson,
W. T. G.; Borden, W. T. J. Am. Chem. Soc. 1997, 119, 5930. (c) Wiberg,
K. B.; Fenoglio, R. A. J. Am. Chem. Soc. 1968, 90, 3395. (d) Sonoda, N.;
Tsutsumi, S. Bull. Chem. Soc. Jpn. 1961, 34, 1006.
(7) For selected examples of transformation of cyclopropenes into
€
vinylcarbene metal complexes, see: (a) Forstner, J.; Kakoschke, A.;
(4) For recent reviews of cyclopropenes, see: (a) Rubin, M.; Rubina,
M.; Gevorgyan, V. Chem. Rev. 2007, 107, 3117. (b) Rubin, M.; Rubina, M.;
Gevorgyan, V. Synthesis 2006, 1221. (c) Fox, J. M.; Yan, N. Curr. Org.
Chem. 2005, 9, 719. (d) Walsh, R. Chem. Soc. Rev. 2005, 34, 714. (e)
Dolbier, W. R., Jr.; Battiste, M. A. Chem. Rev. 2003, 103, 1071. (f)
Sekiguchi, A.; Lee, V. Y. Chem. Rev. 2003, 103, 1429. (g) Chen, K.-C.;
Lee, G.-A. Huaxue 2006, 64, 73. (h) Baird, M. S. Chem. Rev. 2003, 103,
1271.
(5) For the first example of a metal-promoted ring-opening reaction
in the cyclopropropene series, see: (a) Mushak, P.; Battiste, M. A. J.
Organomet. Chem. 1969, 17, 46. For studies on Pd-promoted ring-
opening reaction of cyclopropenes, see: (b) Battiste, M. A.; Friedrich,
L. E.; Fiato, R. A. Tetrahedron Lett. 1975, 45. (c) Fiato, R. A.; Mushak, P.;
Battiste, M. A. J. Chem. Soc., Chem. Commun. 1975, 869.
Stellfeldt, B.; Butenschon, H.; Wartchow, R. Organometallics 1998, 17,
893. (b) Forstner, J.; Kakoscke, A.; Wartchow, R.; Butenschon, H. Organo-
€
metallics 2000, 19, 2108. (c) Johnson, L. K.; Grubbs, R. H.; Ziller, J. W. J.
Am. Chem. Soc. 1993, 115, 8130. (d) de la Mata, F. J.; Grubbs, R. H.
Organometallics 1996, 15, 577. (e) Binger, P.; M€uller, P.; Hermann, A. T.;
Phillips, P.; Gabor, B.; Langhau, F. Chem. Ber. 1991, 124, 2165. (f) Flatt,
B. T.; Grubbs, R. H.; Blanski, R. L.; Calabrese, J. C.; Feldman, J. Organo-
metallics 1994, 13, 2728. (g) Huang, J. H.; Lee, T. Y.; Swenson, D. C.;
Messerle, L. Inorg. Chim. Acta 2003, 345, 209. (h) Green, M.; Orpen, A. G.;
Schaverien, C. J. J. Chem. Soc., Dalton Trans. 1989, 1333. (i) Nguyen,
S. T.; Johnson, L. K.; Grubbs, R. H.; Ziller, J. W. J. Am. Chem. Soc. 1992,
114, 3974. (j) Nguyen, S. T.; Grubbs, R. H.; Ziller, J. W. J. Am. Chem. Soc.
1993, 115, 9858. (k) Sanford, M. S.; Valdez, M. R.; Grubbs, R. H. Organo-
metallics 2001, 20, 5455.
r
2011 American Chemical Society
Published on Web 01/10/2011
pubs.acs.org/Organometallics

628 Organometallics, Vol. 30, No. 3, 2011
Zhu et al.
Table 1. Chloropalladation of Arylvinylcyclopropene 1a
metallabenzenes8 has been realized during the last several
decades. On the other hand, isolable η2-cyclopropenylmetal
complexes containing transition metals Ni,9 Ir,10 Pt,11 Mo,12
W,13 Ti, and Zr,14 which involve complexation with cyclopro-
penes along with the retention of ring structure, have also been
characterized by NMR spectroscopic analyses and X-ray dif-
fraction. To the best of our knowledge, transition-metal-pro-
moted reactions of 1-vinylcyclopropenes are rarely reported.15
On the basis of the previous studies on PdCl2-promoted ring-
opening reactions of methylenecyclopropanes/vinylidenecyclo-
propanes (MCPs/VDCPs)16 as well as transformation of vinyl-
idenecyclopropanes to 1-vinylcyclopropenes,17 we attempted to
examine the reaction of arylvinylcyclopropenes 1 with palla-
dium dichloride. Herein we wish to report the synthesis of di-μ-
chlorobis[π-1-chloro-1-aryl-2-(20,20-diarylvinyl)allyl]palladium-
(II) complexes from the reaction of 1 with PdCl2 as well as
dehydrogenative rearrangement of arylvinylcyclopropenes to
construct 7H-benzo[c]fluorene skeletons18 via palladium-pro-
moted ring-opening of 1 under mild conditions.
entrya
Pd source
PdCl2
PdCl2
PdCl2
PdCl2
PdCl2(PhCN)2
PdCl2(PhCN)2
PdCl2(PhCN)2
PdCl2(PhCN)2
solvent
T (°C)
time (h)
yield (%)b
1
2
3
4
5
6
7
8
THF
THF
THF
THF
THF
DCM
toluene
toluene
50
20
0
-10
20
20
20
5
3
24
48
48
12
12
12
12
40
51
33
31
84
68
90 (77)
70
a All reactions were carried out using 1 (0.2 mmol) in the presence of
Pd sources (0.24 mmol) and solvents (2.0 mL). b Isolated yield. Value in
parentheses: isolated yield after second time flash column chromatog-
raphy using toluene as eluent.
Results and Discussion
Our initial experiments were carried out to investigate the reac-
tion of 1-(20,20-diphenylvinyl)-2-phenyl-3,3-dimethylcyclopropene
(8) For selected examples of transformation of cyclopropenes into
metallabenzenes, see: (a) Gilbertson, R. D.; Weakley, T. J. R.; Haley,
M. M. Chem.;Eur. J. 2000, 6, 437. (b) Wu, H. P.; Weakley, T. J. R.; Haley,
M. M. Organometallics 2002, 21, 4320. (c) Wu, H. P.; Weakley, T. J. R.;
Haley, M. M. Chem.;Eur. J. 2005, 11, 1191. (d) Iron, M. A.; Lucassen,
A. C. B.; Cohen, H.; van der Boom, M. E.; Martin, J. M. L. J. Am. Chem.
Soc. 2004, 126, 11699. (e) Gilbertson, R. D.; Lau, T. L. S.; Lanza, S.; Wu,
H. P.; Weakley, T. J. R.; Haley, M. M. Organometallics 2003, 22, 3279. (f)
Jacob, V.; Weakley, T. J. R.; Haley, M. M. Organometallics 2002, 21, 5394.
(g) Gilbertson, R. D.; Weakley, T. J. R.; Haley, M. M. J. Am. Chem. Soc.
1999, 121, 2597. (h) Landorf, C. W.; Jacob, V.; Weakley, T. J. R.; Haley,
M. M. Organometallics 2004, 23, 1174. (i) Jacob, V.; Weakley, T. J. R.;
Haley, M. M. Angew. Chem., Int. Ed. 2002, 41, 3470. (j) Elliot, G. P.;
McAuley, N. M.; Roper, W. R. Inorg. Synth. 1989, 26, 184.
(9) (a) Isaeva, L. S.; Peganova, T. A.; Petrovskii, P. V.; Bolesov, I. G.;
Kravtsov, D. N. Bull. Acad. Sci. USSR, Div. Chem. Sci. (Engl. Transl.)
1987, 36, 1904. (b) Isaeva, L. S.; Peganova, T. A.; Petrovskii, P. V.; Kravtsov,
D. N. J. Organomet. Chem. 1989, 376, 141. (c) Weiss, H.; Hampel, F.;
Donaubauer, W.; Grundl, M. A.; Bats, J. W.; Hashmi, A. S. K.; Schindler, S.
Organometallics 2001, 20, 1713.
Figure 1. ORTEP drawing of Pd complex 2a.
(1a) with PdCl2 (1.2 equiv) at 50 °C in THF for 3 h, which
were the best reaction conditions for the complexation
of VDCPs with palladium dichloride.16b The reaction proceeded
smoothly to produce di-μ-chlorobis[π-1-chloro-1-phenyl-
2-(20,20-diphenylvinyl)-3,3-dimethylallyl]palladium(II) com-
plex 2a in 40% isolated yield, which is an air- and moisture-
stable solid (Table 1, entry 1). The structure of trans-anti-2a was
unambiguously determined by X-ray diffraction. Its ORTEP
drawing having two toluene molecules is shown in Figure 1, and
its CIF data are presented in the Supporting Information.19 The
formation of anti-2a, having a configuration opposite the similar
π-1-chloro-3-arylallylpalladium(II) complexes that have been
previously reported by Battiste and co-workers,5 is presumably
due to the steric interaction between the R2 ring and 2,2-diphe-
nylvinyl substitution in the syn-configuration of 2a (Figure 2).
A slightly higher isolated yield was obtained by reducing the
temperature to 20 °C with lengthening of the reaction time
(10) Li, R. T.; Nguyen, S. T.; Grubbs, R. H.; Ziller, J. W. J. Am.
Chem. Soc. 1994, 116, 10032.
(11) Hughes, D. L.; Leigh, G. J.; McMahon, C. N. J. Chem. Soc.,
Dalton Trans. 1997, 1301.
(12) Huges, R. P.; Reisch, J. W.; Rheingold, A. L. Organometallics
1985, 4, 241.
(13) Fischer, H.; Hofmann, J.; Mauz, E. Angew. Chem., Int. Ed. Engl.
1991, 30, 998.
(14) Binger, P.; Muller, P.; Benn, R.; Mynott, R. Angew. Chem., Int.
Ed. Engl. 1989, 28, 610.
(15) Shapiro, E. A.; Kalinin, A. V.; Nefedov, O. M. Mendeleev
Commun. 1992, 116.
(16) (a) Qi, M.-H.; Shao, L.-X.; Shi, M. Dalton Trans. 2010, 39, 8829.
(b) Gu, X.; Wang, F.; Qi, M.-h.; Shao, L.-x.; Shi, M. Organometallics 2009,
28, 1569. For a review on vinylidenecyclopropanes, see: (c) Shi, M.; Shao,
L.-X.; Lu, J.-M.; Wei, Y.; Mizuno, K.; Maeda, H. Chem. Rev. 2010, DOI:
10.1021/cr900381k.
(17) For the preparation of 1-vinylcyclopropenes from vinylidenecy-
clopropanes, see: (a) Shao, L. X.; Zhang, Y. P.; Qi, M. H.; Shi, M. Org.
Lett. 2007, 9, 117. For reactions of arylvinylcyclopropenes, see: (b) Zhu,
Z. B.; Shi, M. Chem.;Eur. J. 2008, 14, 10219. (c) Yu, F. F.; Yang, W. G.;
Shi, M. Chem. Commun. 2009, 1392. (d) Zhu, Z. B.; Shi, M. J. Org. Chem.
2009, 74, 2481. (e) Zhu, Z. B.; Shi, M. Org. Lett. 2009, 11, 5278. (f) Zhu,
Z. B.; Wei, Y.; Shi, M. Chem.;Eur. J. 2009, 15, 7543. (g) Zhu, Z.-B.; Shi,
M. Org. Lett. 2010, 12, 4462.
(19) The crystal data of 2a have been deposited in the CCDC with
number 759635. Empirical formula: C64H60Cl4Pd2 (C50H44Cl4Pd2
toluene*2); formula weight: 1183.72; crystal color, habit: colorless,
þ
(18) For recent examples of synthesis of 7H-benzo[c]fluorenes, see:
(a) Su, C. L.; Huang, X.; Liu, Q. Y. J. Org. Chem. 2009, 74, 8272. (b) Su,
C. L.; Huang, X. Adv. Synth. Catal. 2009, 351, 135. (c) Su, C.; Huang, X.;
Liu, Q.; Huang, X. J. Org. Chem. 2009, 74, 8272. (d) Wang, J. Q.; Weyand,
E. H.; Harvey, R. G. J. Org. Chem. 2002, 67, 6216.
prismatic; crystal dimensions: 0.265 ꢀ 0.123 ꢀ 0.069 mm; crystal system:
˚
monoclinic; lattice type: primitive; lattice parameters: a = 19.611(5) A,
o
˚
˚
b=11.893(3) A, c=25.775(7) A, R=90°, β = 108.957(6) , γ = 90°, V =
=
2416; diffractometer: Rigaku AFC7R; residuals: R; Rw: 0.0669, 0.1152.
3
5686(3) A ; space group: P2(1)/n; Z = 4; Dcalc = 1.383 g/cm3; F000
˚

Article
Organometallics, Vol. 30, No. 3, 2011 629
and 8). 3-Monosubstituted arylvinylcyclopropene 1j produced
the corresponding palladium(II) complex 2j in lower yield, and
when 3-nonsubstituted arylvinylcyclopropene 1k was employed
as the substrate, the isolation of the corresponding Pd complex
was not observed under the standard conditions (Table 2, entries
9 and 10).
We have previously reported a stepwise dehydrogenative
rearrangement of arylvinylcyclopropenes 1 to produce ben-
zofulvene derivatives in good yields in the presence of Pd-
(OAc)2 (Scheme 1).17e In the present case, we assumed that
abstraction of a Cl- in the produced π-allylpalladium chlo-
ride complex 2 to generate a cationic palladium species
followed by intramolecular electrophilic addition would also
possibly produce a dehydrogenative rearrangement product
in good yield. Therefore, we next employed a variety of
silver(I) salts to generate cationic palladium species for the
dehydrogenative rearrangement reaction. It was found that
the reaction of 2a with stoichiometric amounts of AgOTf,
AgSbF6, and AgBF4 indeed produced 7,7-dimethyl-5-
phenyl-7H-benzo[c]fluorene 3a in excellent isolated yields in
toluene at 80 °C within 8 h (Table 3, entries 1-3). The structure
of 3a was determined by X-ray diffraction. Its ORTEP drawing
is shown in Figure 3, and its CIF data are presented in the
Supporting Information.20 Silver nitrate did not promote the
transformation, leading to decomposition of 2a rapidly
(Table 3, entry 4). We also observed that a trace of 3a was
formed along with the decomposition of 2a when a catalytic
amount of AgSbF6 was used (Table 3, entry 5). Upon heating
and without addition of silver(I) salt, 2a decomposed to produce
complex product mixtures (Table 3, entry 6). Product 3a was
also isolated in 99% yield when the reaction was carried out in
the presence of inorganic base Na2CO3 (2.0 equiv) and 2.0 equiv
of AgSbF6 (Table 3, entry 7).
Figure 2. Steric hindrance in trans-syn-2a.
Table 2. Substrate Scope of the Palladium Complex Promoted
Ring-Opening of Arylvinylcyclopropenes 1
entrya
1 (R1/R2/R3/R4)
yield (%)b
1
2
3
4
5
6
7
8
9
10
1b (C6H5/4-CH3C6H4/CH3/CH3)
1c (C6H5/4-ClC6H4/CH3/CH3)
1d (C6H5/3-ClC6H4/CH3/CH3)
1e (C6H5/4-BrC6H4/CH3/CH3)
1f (4-CH3C6H4/C6H5/CH3/CH3)
1g (4-ClC6H4/C6H5/CH3/CH3)
1h (C6H5/C6H5/-(CH2)5-)
1i (C6H5/C6H5/-(CH2)4-)
1j (C6H5/C6H5/CH3/H)
2b, 92 (71)
2c, 87 (74)
2d, 68 (61)
2e, 83 (71)
2f, 86 (74)
2g, 73 (63)
2h, 81 (70)
2i, 68 (60)
2j, 76 (55)
1k (C6H5/C6H5/H/H)
a All reactions were carried out using 1 (0.40 mmol) and PdCl2-
(PhCN)2 (0.48 mmol) in toluene (2.0 mL) at room temperature for 12
h. b Isolated yields. Value in parentheses: isolated yields after second
time flash column chromatography using toluene as eluent.
(Table 1, entry 2). When the reaction was carried out at 0 or -10
°C, the complexation proceeded much slower, affording 2a in
lower yields (Table 1, entries 3 and 4). Using PdCl2(PhCN)2 as
the palladium precursor, the reaction completed within 12 h to
produce 2a in 84% isolated yield (Table 1, entry 5). Further
examination of the solvent effects revealed that toluene is the
solvent of choice for this transformation (Table 1, entries 6-8).
Moreover, it should also be noted that when 2a was purified by
flash column chromatography [petroleum ether (PE)/ethyl
acetate (EA) = 10:1 as the eluent], small amounts of PE could
not be removed from the product, even with high-vacuum
pumping. Therefore, we carried out a second time flash column
chromatography by employing toluene as the eluent and calcu-
lated a more accurate yield by 1H NMR spectroscopic data of
the isolated product (toluene cannot be removed by high-
vacuum pumping either, Table 1, entry 7).
With these optimized conditions in hand, we next exam-
ined a variety of arylvinylcyclopropenes 1 in this reaction,
and the results of these experiments are shown in Table 2. A
variety of π-allylpalladium chloride complexes 2 were at-
tained in moderate to good yields (Table 2, entries 1-10).
The reaction of arylvinylcyclopropenes 1b and 1f, bearing
electron-donating methyl group(s) on the benzene ring of R1
or R2, produced the corresponding π-allylpalladium chloride
complexes 2b and 2f in relatively higher yields than those of
arylvinylcyclopropenes 1c, 1d, 1e, and 1g, which have electron-
withdrawing groups on the benzene ring presumably due to the
electronic property (Table 2, entries 1-6). The reaction also
proceeded smoothly to produce π-allylpalladium chloride com-
plexes 2h and 2i in good yields when substituted spiro[2.5]oct-1-
ene 1h and spiro[2.4]hept-1-ene 1i were used (Table 2, entries 7
Hereafter, we examined the substrate scope of this trans-
formation. Substrates 2, bearing electron-donating groups
on the benzene ring, underwent the reactions smoothly to
provide the corresponding 7H-benzo[c]fluorene derivatives 3
in excellent yields (Table 4, entries 1 and 5). Using AgOTf as
the promoter, the rearrangement reactions of π-allylpalla-
dium chloride complexes 2, bearing electron-withdrawing
groups on the benzene ring, proceeded smoothly to give the
corresponding products 3 in moderate to good isolated yields
at 100 °C (Table 4, entries 2-4 and 6). We also isolated
formal rearrangement product 7-chloro-4-(4-chlorophenyl)-
2-isopropyl-1-phenylnaphthalene 417a in 34% yield in addi-
tion to 3g in 45% yield when Pd(II) complex 2g was used as
the substrate (Table 4, entry 6). The reaction of palladium(II)
complex 2h, bearing a six-membered ring, produced 5-phenyl-
spiro[benzo[c]fluorene-7,10-cyclohexane] 3h in 83% yield under
the standard conditions (Table 4, entry 7). However, the reac-
tion of 2i under various conditions produced only unidentified
complex product mixtures (Table 4, entry 8), presumably due
to the steric difference between the five-membered ring and
six-membered ring. The reaction of 2j produced the correspond-
ing product 3i in 72% isolated yield in the presence of AgOTf
(1.0 equiv) at 100 °C (Table 4, entry 9).
(20) The crystal data of 3a have been deposited in the CCDC with
number 759636. Empirical formula: C25H20; formula weight: 320.41;
crystal color, habit: colorless, prismatic; crystal dimensions: 0.408 ꢀ
0.322 ꢀ 0.074 mm; crystal system: orthorhombic; lattice type: primitive;
˚
˚
˚
lattice parameters: a = 8.1602(14) A, b = 13.070(2) A, c = 16.940(3) A,
3
˚
R = 90°, β = 90°, γ = 90°, V = 1806.6(5) A ; space group: P2(1)2-
(1)2(1); Z = 4; Dcalc = 1.178 g/cm3; F000 = 680; diffractometer: Rigaku
AFC7R; residuals: R; Rw: 0.0475, 0.1060.

630 Organometallics, Vol. 30, No. 3, 2011
Zhu et al.
Scheme 1. Dehydrogenative Rearrangement of Arylvinylcyclopropene 1 Promoted by Pd(OAc)2/p-BQ
examination of the dehydrogenative rearrangement of 2 using
a 0.1 equiv amount of HOTf as the catalyst was carried out,
and we found that the reaction proceeded smoothly to pro-
duce3ain99% isolated yieldwithin1 h (Table5, entry 1). This
result is totally different from our previous report on the direct
treatment of arylvinylcyclopropenes 1 with catalytic Lewis
acid or Brønsted acid in which different naphthalene deriva-
tives could be obtained in good yields under mild conditions
(Scheme 2).17a We also examined the reactions of 2c and 2g
using a catalytic amount of HOTf instead of a stoichiometric
amount of AgOTf and found that the reaction proceeded
smoothly, producing the corresponding products 3c and 3g in
excellent yields within 1 h (Table 5, entries 2 and 3). Unfortu-
nately, transformation of 2i in the presence of a catalytic
amount of HOTf still failed (Table 5, entry 4). Furthermore,
when a catalytic amount of AgOTf (0.1 equiv) was used
instead of HOTf, the reaction of 2a produced 3a in 90%
isolated yield under the standard conditions. Compared to a
catalytic amount of AgSbF6 in the reaction (Table 3, entry 5),
the in situ generated strong Brønsted acid HOTf may be the
real catalytic species in this case, driving the transformation
more efficiently than the in situ generated HSbF6. It should be
emphasized here that the catalytic amount of AgOTf (0.1
equiv) cannot catalyze the reaction in the presence of inor-
ganic base Na2CO3 (2.0 equiv) presumably because the in situ
generated HOTf was quenched under basic conditions. Fi-
nally, the one-pot dehydrogenative rearrangement of 1a has
been carried out without isolation of palladium(II) complex
2a using HOTf (0.1 equiv) as the catalyst, affording 3a in 75%
overall yield (Scheme 3).
Table 3. Dehydrogenative Rearrangement to Produce 7H-
Benzo[c]fluorene Derivative 3a
entrya
Ag source
solvent
T (°C)
time (h)
yield (%)b
1
2
3
4
5
6
7
AgOTf
AgSbF6
AgBF4
AgNO3
AgSbF6
toluene
toluene
toluene
toluene
toluene
toluene
toluene
80
80
80
80
80
80
80
8
8
8
12
12
12
8
95
99
95
complex
tracec
complex
99d
AgSbF6
a All reaction were carried out using 1 (0.1 mmol, as monomer) in the
presence of Ag sources (0.1 mmol) and solvents (1.0 mL). b Isolated yield.
c AgSbF6 (0.1 equiv) was used. d AgSbF6 (2.0 equiv) was used in the
presence of Na2CO3 (2.0 equiv).
A plausible mechanism for the formation of these 7H-benzo-
[c]fluorene derivatives 3 is outlined in Scheme 4. Abstraction of
Cl- in π-allylpalladium chloride complexe 2by strong Brønsted
acid HOTf or silver(I) salt generates cationic palladium specie
A,21 which undergoes intramolecular electrophilic addition22
to the phenyl ring of R1 to afford intermediate B. Reductive
elimination and oxidative addition23 of intermediate C, whichis
generated from intermediate B via deprotonation, produce a
Figure 3. ORTEP drawing of compound 3a.
(21) Chloride ligands can be converted to the corresponding triflates
in the presence of HOTf; see: Dixon, N. E.; Lawrance, G. A.; Lay, P. A.;
Sargeson, A. M.; Taube, H. Trifluoromethanesulfonates and Trifluoro-
methanesulfonato-O Complexes; John Wiley & Sons, Inc.: New York, 2007;
p 70.
(22) For enhancement of the aromatic C-H bonds’ metalation
via electrophilic C-H activation with cationic Pd(II) species, see:
(a) Nishikata, T.; Abela, A. R.; Huang, S.; Lipshutz, B. H. J. Am. Chem.
Soc. 2010, 132, 4978. (b) Jia, C.; Piao, D.; Kitamura, T.; Fujiwara, Y. J. Org.
Chem. 2000, 65, 7516.
(23) For recent studies on oxidative addition of Pd(0) to allyl/benzylic
chlorides, see: (a) Lu, S.; Xu, Z.; Bao, M.; Yamamoto, Y. Angew. Chem.,
Int. Ed. 2008, 47, 4366. (b) Kabalka, G. W.; Dadush, E.; Al-Masum, M.
Tetrahedron Lett. 2006, 47, 7459. (c) Carvajal, M. A.; Miscione, G. P.; Novoa,
J. J.; Bottoni, A. Organometallics 2005, 24, 2086. (d) Bao, M.; Nakamura, H.;
Yamamoto, Y. J. Am. Chem. Soc. 2001, 123, 759. (e) Nakamura, H.; Shibata, H.;
Yamamoto, Y. Tetrahedron Lett. 2000, 41, 2911.
According to the above silver(I) salt promoted reactions of
π-allylpalladium chloride complexes 2 to produce 7H-benzo-
[c]fluorene derivatives 3, it is worth noting that the addition
of 1.0 equiv of silver(I) salt (relative to the monomer of 2) has
the capability to abstract only 1.0 equiv of Cl- in the absence
of a base (Table 3, entry 7). However, both chloride atoms
have been abstracted from starting material 2 to produce
product 3. Thus, we considered the possibility of a second
abstraction of Cl- by the in situ generated trifluoromethane-
sulfonic acid CF3SO3H (HOTf) to give a new cationic palla-
dium species and HCl. In this case, using a catalytic amount of
strong Brønsted acid to abstract Cl- instead of stoichiometric
silver(I) salt would also promote the transformation. Further

Article
Organometallics, Vol. 30, No. 3, 2011 631
Table 4. Substrate Scope of Stoichiometric Silver(I)-Promoted Transformation of π-Allylpalladium Chloride Complexes 2 to 7H-
Benzo[c]fluorene Derivatives 3
entrya
2 (R1/R2/R3/R4)b
Ag source
AgSbF6
AgOTf
AgOTf
AgOTf
AgSbF6
AgOTf
T (°C)
yield (%)c
1
2
3
4
5
6
2b (C6H5/4-CH3C6H4/CH3/CH3)
2c (C6H5/4-ClC6H4/CH3/CH3)
2d (C6H5/3-ClC6H4/CH3/CH3)
2e (C6H5/4-BrC6H4/CH3/CH3)
2f (4-CH3C6H4/C6H5/CH3/CH3)
2g (4-ClC6H4/C6H5/CH3/CH3)
80
3b, 99
3c, 68
3d, 86d
3e, 88
3f, 99
3g, 45e
4f
100
100
100
80
100
7
8
9
2h (C6H5/C6H5/-(CH2)5-)
2i (C6H5/C6H5/-(CH2)4-)
2j (C6H5/C6H5/CH3/H)
AgSbF6
AgOTf/AgSbF6
AgOTf
80
80/100
100
3h, 83
complex
3i, 72
1
2
a All reactions were carried out using 2 (0.1 mmol, as monomer) and Ag source (0.1 mmol) in toluene (1.0 mL) for 8 h. b R /R 0 are the substituent on
the aromatic rings R1/R2. c Isolated yields. d 1.2:1 mixture of regioisomers. e 7-Chloro-4-(4-chlorophenyl)-2-isopropyl-1-phenylnaphthalene 4 was
isolated in 34% yield. f
0
Table 5. Substrate Scope of HOTf-Catalyzed Transformation of
π-Allylpalladium Chloride Complexes 2 to 7H-Benzo[c]fluorene
Derivatives 3
Scheme 2. Acid-Catalyzed Rearrangement of Arylvinylcyclo-
propene 1
Scheme 3. One-Pot Dehydrogenative Rearrangement of Arylvi-
nylcyclopropene 1a
entrya
2 (R1/R2/R3/R4)b
yield (%)c
1
2
3
4
2a (C6H5/C6H5/CH3/CH3)
2c (C6H5/4-ClC6H4/CH3/CH3)
2g (4-ClC6H4/C6H5/CH3/CH3)
2i (C6H5/C6H5/-(CH2)4-)
3a, 99
3c, 99
3g, 99
complex
a All reactions were carried out using 2 (0.1 mmol, as monomer) and
1
2
HOTf (0.01 mmol) in toluene (1.0 mL) at 80 °C for 1 h. b R /R 0 are the
0
substituents on the aromatic rings R1/R2. c Isolated yields.
one,24h direct protonolysis24 of intermediate E would also
produce the corresponding formal rearrangement product 4
new π-allyl-palladium(II) complex D. Aromatization followed
by an allylic rearrangement affords intermediate E, which
undergoes abstraction of Cl- by silver(I) salts or the in situ
generated Brønsted acid along with an intramolecular electro-
philic addition to the phenyl ring of R2 to give cyclic-palladium
intermediate F. Further deprotonation of F along with reduc-
tive elimination produces the final product 3 and regenerates
Hþ. Alternatively, since the protonolysis of an electron-defi-
cient palladium complex is easier than that of an electron-rich
(24) For recent studies on protonolysis of the Pd-C bond, see: (a) Yang,
S.-R.; Jiang, H.-F.; Li, Y.-Q.; Chen, H.-J.; Luo, W.; Xu, Y.-B. Tetrahedron
2008, 64, 2930. (b) Cochran, B. M.; Michael, F. E. J. Am. Chem. Soc. 2008, 130,
2786. (c) Bercaw, J. E.; Chen, G. S.; Labinger, J. A.; Lin, B.-L. J. Am. Chem. Soc.
2008, 130, 17654. (d) Shen, Z.; Lu, X. Tetrahedron 2006, 62, 10896. (e) Feducia,
J. A.; Campbell, A. N.; Anthis, J. W.; Gagne, M. R. Organometallics 2006, 25,
3114. (f) Zhao, L. G.; Lu, X. Y.; Xu, W. J. Org. Chem. 2005, 70, 4059. (g) Wang,
Z.; Zhang, Z.; Lu, X. Organometallics 2000, 19, 775. (h) Liu, H.; Yu, J.; Wang, L.;
Tong, X. Tetrahedron Lett. 2008, 49, 6924.

632 Organometallics, Vol. 30, No. 3, 2011
Zhu et al.
Scheme 4. Plausible Mechanism of Dehydrogenative Rearrange-
ment Promoted by Stoichiometric Amount of Silver(I) Salt and
Catalytic Amount of HOTf
Experimental Section
General Procedure for the Synthesis of Di-μ-Chlorobis[π-1-
chloro-1-phenyl-2-(20,20-diphenylvinyl)-3,3-dimethylallyl]palla-
dium(II) Complex 2a. Under an argon atmosphere, 1-(20,20-diphenyl-
vinyl)-2-phenyl-3,3-dimethylcyclopropene 1a (64.0 mg, 0.2 mmol),
PdCl2(PhCN)2 (92.0 mg, 0.24 mmol), and toluene (2.0 mL) were
added into a flame-dried Schlenk tube. The reaction mixture was
stirred at rt for 8 h. Then, the solvent was removed under reduced
pressure, and the residue was purified by flash chromatogra-
phy on a silica gel column (PE/EA = 10:1) to provide 2a (90
mg, 90%). A second purification by flash chromatography on
a silica gel column (toluene as eluent) was required to deter-
mine the yield (2a/toluene = 1:2, determined by X-ray diffrac-
tion and 1H NMR spectroscopic data). We found that recrys-
tallization of these complexes from toluene for the elementary
analysis was very difficult because only a small amount of the
complex could be isolated. However, recrystallization of these
complexes in hexane with addition of a very small amount of
CH2Cl2 was successful, affording an acceptable amount of
complexes for the elementary analyses. After filtration and
€
drying under reduced pressure via a Buchi B-585 Kugelrohr at
50 °C for 2 h, these samples could pass the elementary
analyses. We have calculated the corresponding components
of hexane and palladium complex according to the analytical
data, and these elemental analysis data are shown in the
Experimental Section.
General Procedure for the Synthesis of 7H-Benzo[c]fluorene
Derivative 3a. Di-μ-chlorobis[π-1-chloro-1-phenyl-2-(20,20-
diphenylvinyl)-3,3-dimethylallyl]palladium(II) complex 2a (59.0
mg, 0.1 mmol as monomer containing 0.1 mmol of toluene),
AgSbF6 (34.4 mg, 0.1 mmol) or HOTf (1.0 μL, 0.01 mmol), and
toluene (1.0 mL) were added into a Schlenk tube. The reaction
mixture was stirred at 80 °C until the reaction was complete. Then,
the solvent was removed under reduced pressure and the residue
was purified by flash chromatography on a silica gel column (PE as
eluent) to provide pure 3a (32 mg, 99%).
when 2g was used as the substrate with a stoichiometric amount
of AgOTf as the promoter.
Conclusion
In summary, we have developed a new synthetic protocol
for the preparation of di-μ-chlorobis[π-1-chloro-1-aryl-2-(20,20-
diarylvinyl)allyl]palladium(II) complexes from arylvinylcyclo-
propenes with a Pd(II) complex as well as an unusual dehydro-
genative rearrangement of arylvinylcyclopropenes promoted by
a palladium(II) complex in the presence of silver(I) salts or
HOTf to produce 7H-benzo[c]fluorene derivatives in good to
excellent yields. This synthetic protocol furnishes 7H-benzo-
[c]fluorene derivatives straightforwardly from simple starting
materials under mild conditions. A plausible mechanism that is
based on an intramolecular electrophilic addition pathway has
been also proposed. Clarification of the reaction mechanism and
further application of this chemistry are currently in progress.
Acknowledgment. We thank the Shanghai Municipal
Committee of Science and Technology (08dj1400100-2),
National Basic Research Program of China (973)-
2009CB825300, the Fundamental Research Funds for the
Central Universities, and the National Natural Science
Foundation of China for financial support (20472096,
20872162, 20672127, 20821002, and 20732008).
Supporting Information Available: Detailed description of
experimental procedures, full characterization of new com-
pounds shown in tables and figures, along with the X-ray data
of 2a and 3a. This material is available free of charge via the
Internet at http://pubs.acs.org or from the authors.