Reactions of CpArCHCHArCp with Ru3(CO)12: An unexpected cleavage of a bridging C-C bond and coupling of the two cyclopentadienyl rings to fulvalene diruthenium complexes

Article abstract of DOI:10.1021/om050673w

Reactions of CpArCHCHArCp [Ar = Ph (1), p-MeOC₆H₄ (2)] with Ru₃(CO)₁₂ in refluxing xylene afforded the unexpected bridging C-C cleavage and cyclopentadienyl coupling products: the 2,2′-bisubstituted fulvalene diruthenium complexes (η⁵: η⁵-2,2′-ArCH₂C₅H₃C ₅H₃CH₂Ar)Ru₂(CO)₄ [Ar = Ph (5), p-MeOC₆H₄ (9)] and the partially hydrogenated products (η⁵:η³-ArCH₂C ₅H₃C₅H₆CHAr)Ru₂(CO) ₄ [Ar = Ph (4), p-MeOC₆H₄ (8)], in addition to the normal bridged bis(cyclopentadienyl) tetracarbonyl diruthenium complexes (ArCHCHAr)[(η⁵-C₅H₄)Ru(CO)] ₂(μ-CO)₂ [Ar = Ph (7), p-MeOC₆H₄, (10)]. When ligand (^tBuC₅H₄)PhCHCHPh( ^tBuC₅H₄) (3) reacted with Ru ₃(CO)₁₂, the tetrasubstituted fulvalene diruthenium complex (η⁵:η⁵-PhCH₂ ^tBuC₅H₂C₅H₂ ^tBuCH₂Ph)Ru₂(CO)₄ (11) and three normal bridged bis-(cyclopentadienyl) diruthenium complexes (PhCHCHPh) [(η⁵-^tBuC₅H₃)Ru(CO)] ₂(M-CO)₂ (12-14) were obtained. The molecular structures of 4, 5, 7-meso, 7-rac, 8, 10-meso, 11, 12, 13, and 14 were determined by X-ray diffraction. The stereochemistry of the reaction was also studied, and the possible mechanism was discussed.

Full text of DOI:10.1021/om050673w

1158
Organometallics 2006, 25, 1158-1166
Reactions of CpArCHCHArCp with Ru3(CO)12: An Unexpected
Cleavage of a Bridging C-C Bond and Coupling of the Two
Cyclopentadienyl Rings to Fulvalene Diruthenium Complexes
Bin Li, Baiquan Wang,* Shansheng Xu, Xiuzhong Zhou, and Haibin Song
State Key Laboratory of Elemento-Organic Chemistry, College of Chemistry, Nankai UniVersity,
Tianjin 300071, People’s Republic of China
ReceiVed August 4, 2005
Reactions of CpArCHCHArCp [Ar ) Ph (1), p-MeOC6H4 (2)] with Ru3(CO)12 in refluxing xylene
afforded the unexpected bridging C-C cleavage and cyclopentadienyl coupling products: the 2,2′-
bisubstituted fulvalene diruthenium complexes (η5:η5-2,2′-ArCH2C5H3C5H3CH2Ar)Ru2(CO)4 [Ar ) Ph
(5), p-MeOC6H4 (9)] and the partially hydrogenated products (η5:η3-ArCH2C5H3C5H6CHAr)Ru2(CO)4
[Ar ) Ph (4), p-MeOC6H4 (8)], in addition to the normal bridged bis(cyclopentadienyl) tetracarbonyl
diruthenium complexes (ArCHCHAr)[(η5-C5H4)Ru(CO)]2(µ-CO)2 [Ar ) Ph (7), p-MeOC6H4 (10)]. When
ligand (tBuC5H4)PhCHCHPh(tBuC5H4) (3) reacted with Ru3(CO)12, the tetrasubstituted fulvalene
t
t
diruthenium complex (η5:η5-PhCH2 BuC5H2C5H2 BuCH2Ph)Ru2(CO)4 (11) and three normal bridged bis-
(cyclopentadienyl) diruthenium complexes (PhCHCHPh)[(η5-tBuC5H3)Ru(CO)]2(µ-CO)2 (12-14) were
obtained. The molecular structures of 4, 5, 7-meso, 7-rac, 8, 10-meso, 11, 12, 13, and 14 were determined
by X-ray diffraction. The stereochemistry of the reaction was also studied, and the possible mechanism
was discussed.
Scheme 1
Introduction
Dinuclear metal complexes are often postulated as simple
models with which to study the interactions of organic molecules
with metal surfaces.1 Cyclopentadienyl metal carbonyl dimers
were reported to catalyze the allylic amination of olefins2a,b and
indolization of alkynes.2c,d The bridged bis(cyclopentadienyl)
ligands, including singly bridged ligand (η5-C5H4)2(Bridge) [S],
doubly bridged ligand (η5-C5H3)2(Bridge)2 [D], and fulvalene
ligand η5:η5-C5H4C5H4 [Fv] (Scheme 1), have been extensively
studied as frameworks for dinuclear metal complexes that are
resistant to fragmentation and maintain two metal centers in
close proximity even after the metal-metal bond cleavage.3
Among the group 6 and 8 metal carbonyl dimers with bridged
bis(cyclopentadienyl) ligands, diruthenium complexes received
attention for their special reactivity. The nature of the bridge
has a remarkable effect on the metal-metal bond and its
reactivity. Vollhardt and co-workers reported that in the FvRu2-
(CO)4 system reversible C-C, Ru-Ru, and Ru-C bond-
cleavage steps lead to a photochemical process that can be
thermally reversed.4 For the Me2Si-bridged bis(tetramethyl-
cyclopentadienyl) tetracarbonyl diruthenium complex (Me2Si)-
[C5Me4Ru(CO)]2(µ-CO)2, a photochemical albeit thermally
irreversible rearrangement by Si-C bond cleavage was also
observed.5 The Me2C-bridged bis(cyclopentadienyl) diruthenium
complex (Me2C)[(C5H4)Ru(CO)2]2 can be a fully reversible
organometallic thermooptical switch through reversible C-H,
Ru-H, Ru-C, and Ru-Ru bond-cleavage steps.6 The tetra-
methyldisilylene- or digermylene-bridged bis(cyclopentadienyl)
tetracarbonyl diruthenium complexes (Me2EEMe2)[Cp′Ru(CO)]2-
(µ-CO)2 (E ) Si, Ge; Cp′ ) C5H4, C5Me4) can thermally
rearrange with metathesis between the E-E and Ru-Ru bonds.7
Although many bridged bis(cyclopentadienyl) diruthenium
complexes were synthesized in the past few decades, to the best
of our knowledge, only two examples of complexes (CH2CH2)-
[Cp′Ru(CO)]2(µ-CO)2 (Cp′ ) C5H4, C9H7)8 are known for the
CR2-CR2 (R ) H, alkyl, aryl) bridge. In this paper, we will
* Corresponding author. Fax: 86-22-23504781. E-mail: bqwang@
nankai.edu.cn.
(1) (a) Muetterties, E. L.; Rhodin, T. N.; Band, E.; Brucker, C. F.; Pretzer,
W. R. Chem. ReV. 1979, 79, 91. (b) Bruce, M. I. J. Organomet. Chem.
1983, 242, 147. (c) Chifotides, H. T.; Dunbar, K. R. Acc. Chem. Res. 2005,
38, 146.
(4) (a) Boese, R.; Cammack, J. K.; Matzger, A. J.; Pflug, K.; Tolman,
W. B.; Vollhardt, K. P. C.; Weidman, T. W. J. Am. Chem. Soc. 1997, 119,
6757. (b) Vollhardt, K. P. C.; Weidman, T. W. J. Am. Chem. Soc. 1983,
105, 1676.
(5) Fox, T.; Burger, P. Eur. J. Inorg. Chem. 2001, 795.
(6) (a) Burger, P. Angew. Chem., Int. Ed. 2001, 40, 1917. (b) Bitterwolf,
T. E.; Leonard, M. B.; Horine, P. A.; Shade, J. E.; Rheingold, A. L.; Staley,
D. J.; Yap, G. P. A. J. Organomet. Chem. 1996, 512, 11.
(7) (a) Zhang, Y.; Xu, S.; Zhou, X. Organometallics 1997, 16, 6017.
(b) Zhang, Y.; Wang, B.; Xu, S.; Zhou, X. Organometallics 2001, 20, 3829.
(c) Zhang, Y.; Wang, B.; Xu, S.; Zhou, X.; Sun, J. J. Organomet. Chem.
1999, 584, 356.
(2) (a) Srivastava, R. S.; Nicholas, K. M. Chem. Commun. 1998, 2705.
(b) Kolel-Veetil, M.; Khan, M. A.; Nicholas, K. M. Organometallics 2000,
19, 3754. (c) Penoni, A.; Nicholas, K. M. Chem. Commun. 2002, 484. (d)
Penoni, A.; Volkmann, J.; Nicholas, K. M. Org. Lett. 2002, 4, 699.
(3) For general reviews of bridged bis(cyclopentadienyl) dinuclear metal
complexes, see: (a) Barlow, S.; O’Hare, D. Chem. ReV. 1997, 97, 637. (b)
Werner, H. Inorg. Chim. Acta 1992, 198-200, 715. (c) Bonifaci, C.; Ceccon,
A.; Gambaro, A.; Manoli, F.; Mantovani, L.; Ganis, P.; Santi, S.; Venzo,
A. J. Organomet. Chem. 1998, 557, 97. (d) Cuenca, T.; Royo, P. Coord.
Chem. ReV. 1999, 193-195, 447. (e) Ceccon, A.; Santi, S.; Orian, L.;
Bisello, A. Coord. Chem. ReV. 2004, 248, 683. (f) Royo, P. New J. Chem.
1997, 21, 791.
(8) (a) Nataro, C.; Thomas, L. M.; Angelici. R. J. Inorg. Chem. 1997,
36, 6000. (b) Khayatpoor, R.; Shapley, J. R. Organometallics 2002, 21,
4794.
10.1021/om050673w CCC: $33.50 © 2006 American Chemical Society
Publication on Web 01/24/2006

Reactions of CpArCHCHArCp with Ru3(CO)12
Organometallics, Vol. 25, No. 5, 2006 1159
Chart 1
δ 7.13-6.89 (m, 10H, C6H5), 5.58 (m, 4H, C5H4), 5.51 (m, 2H,
C5H4), 5.28 (m, 2H, C5H4), 3.86 (s, 2H, PhCH). IR (νCO, cm-1):
2002 (s), 1962 (s), 1791 (m), 1744 (s).
Reaction of rac-CpPhCHCHPhCp (1-rac) with Ru3(CO)12.
The pure racemic isomer 1-rac was obtained by hydrolysis of the
corresponding racemic calcium salt of ligand 1.9b Using a procedure
similar to that described above, reaction of 1-rac with Ru3(CO)12
1
gave 4 (2%), 5 (4%), 7-meso (7%), and 7-rac (7%). H NMR
(CDCl3, 300 MHz) of 1-rac: δ 7.10-6.90 (m, 10H, C6H5), 6.45
(m, 1H, C5H5), 6.40-6.29 (m, 3H, C5H5), 6.20 (m, 1H, C5H5), 6.11
(br s, 1H, C5H5), 4.44 (d, J ) 9.85 Hz, 1H, PhCH), 4.36 (d, J )
9.85 Hz, 1H, PhCH), 2.90 (br s, 2H, C5H5), 2.84 (br s, 2H, C5H5)
(see Supporting Information).
report the reactions of (ArCHCHAr)-bridged bis(cyclopenta-
diene) Cp′ArCHCHArCp′ (Cp′ ) C5H5, BuC5H4, Ar ) Ph,
t
Synthesis of Cp(p-MeOC6H4)CHCH(p-MeOC6H4)Cp (2). The
synthesis of ligand 2 was carried out by a method similar to that
for ligand 1.9 HgCl2 (210 mg, 75 mmol) was added to 2.0 g (50
mmol) of granulated calcium metal in 25 mL of THF. After the
mixture was stirred fiercely overnight, a grayish suspension was
obtained that contained small pieces of suspended calcium. THF
(80 mL) was added, and the mixture was cooled to 0 °C, then 6-(p-
methoxylphenyl)fulvene (7.0 g, 38 mmol) was added. During the
36 h of stirring, an exothermic reaction ensued and the red color
of the fulvene disappeared. After the mixture was poured into
saturated aqueous ammonium chloride solution, phases were
separated. The aqueous phase was extracted with ether (2 × 20
mL). The combined organic phase was washed with several small
portions of water and then dried over anhydrous magnesium sulfate.
After removal of the solvents, the crude product was recrystallized
from pentane/CH2Cl2 at -30 °C to afford 3.15 g (45%) of pure 2
as a white solid. Mp: 150-151 °C. Anal. Calcd for C26H26O2: C,
p-MeOC6H4) with Ru3(CO)12. The unexpected bridging C-C
bond cleavage and cyclopentadienyl coupling products were
obtained simultaneously.
Experimental Section
General Procedures. Schlenk and vacuum line techniques were
employed for all manipulations. All solvents were distilled from
appropriate drying agents under argon prior to use. 1H NMR spectra
were recorded on a Bruker AV300 or Bruker AC-P200 instrument.
2-D NMR experiments were carried out on a Varian Mercury
VX300 instrument. IR spectra were recorded as KBr disks on a
Nicolet 560 ESP FTIR spectrometer. Elemental analyses were
performed on a Perkin-Elmer 240C analyzer. ESI mass spectra were
obtained using a Thermo Finnigan LCQ Advantage instrument.
CpPhCHCHPhCp9 (1), 6-(p-methoxylphenyl)fulvene,10 and 2-tert-
butylphenylfulvene10 were prepared by literature procedures.
Reaction of CpPhCHCHPhCp (1) with Ru3(CO)12. The
solution of 350 mg (0.547 mmol) of Ru3(CO)12 and 280 mg (0.900
mmol) of CpPhCHCHPhCp (1) (as a mixture of racemic and meso
isomers with a ratio of about 1:0.9, see Supporting Information) in
40 mL of xylene was refluxed for 8 h. After removal of solvent
the residue was chromatographed on an alumina column using
petroleum ether/CH2Cl2 as eluent. Elution with petroleum ether/
CH2Cl2 gave two yellow bands and an orange band, which afforded
10 mg (2%) of 4, 20 mg (4%) of 5, and 136 mg (27%) of 7-meso
as yellow or orange crystals, respectively. Finally elution with CH2-
Cl2 developed a yellow band, which gave 19 mg (4%) of 7-rac as
orange crystals.
1
84.29; H, 7.07. Found: C, 84.56; H, 7.27. H NMR (CDCl3, 200
MHz, as a mixture of meso and rac isomers): δ 7.15-6.70 (m,
8H, C6H5), 6.62-5.78 (m, 6H, C5H5), 4.29 (s, 1H, PhCH), 4.26 (s,
1H, PhCH), 3.73 (s, 3H, OCH3), 3.67 (s, 3H, OCH3), 2.87-2.56
(m, 4H, C5H5).
Reaction of 2 with Ru3(CO)12. Using a procedure similar to
that described above, reaction of 2 with Ru3(CO)12 gave 8 (2%), 9
(4%), 10-meso (30%), and 10-rac (3%) as yellow or orange crystals.
8: mp 157 °C (dec). Anal. Calcd for C31H26O7Ru2: C, 52.14;
1
H, 3.67. Found: C, 51.98; H, 3.81. H NMR (CDCl3, 300 MHz,
see Chart 1 for key to assignments): δ 7.15 (d, J ) 8.70 Hz, 2H,
C6H4), 7.06 (d, J ) 8.70 Hz, 2H, C6H4), 6.84 (d, J ) 8.70 Hz, 2H,
C6H4), 6.79 (d, J ) 8.70 Hz, 2H, C6H4), 5.55 (t, 1H, C5H3), 5.16
(t, 1H, C5H3), 3.80 (s, 3H, OCH3), 3.79 (s, 3H, OCH3), 3.52 (s,
1H, Hb), 3.46 (d, J ) 16.20 Hz, 1H, Ha), 3.35 (t, 1H, C5H3), 3.17
(d, J ) 16.20 Hz, 1H, Ha), 2.98-2.62 (m, 4H, Hc + He), 2.24-
2.01 (m, 2H, Hd). IR (νCO, cm-1): 2038 (s), 1980 (s), 1965 (s),
1922 (s), 1887 (w).
4: mp 174 °C (dec). Anal. Calcd for C29H22O5Ru2: C, 53.37;
1
H, 3.40. Found: C, 53.23; H, 3.39. H NMR (CDCl3, 300 MHz,
see Chart 1 for key to assignments): δ 7.35-7.14 (m, 10H, C6H5),
5.58 (t, 1H, C5H3), 5.20 (m, 1H, C5H3), 3.55 (s, 1H, Hb), 3.52 (d,
J ) 16.2 Hz, 1H, Ha), 3.38 (t, 1H, C5H3), 3.24 (d, J ) 16.2 Hz,
1H, Ha), 3.00-2.59 (m, 4H, Hc + He), 2.23-2.00 (m, 2H, Hd).
IR (νCO, cm-1): 2050 (s), 1985 (s), 1962 (s), 1910 (s), 1870 (w).
5: mp 230 °C (dec). Anal. Calcd for C28H20O4Ru2: C, 54.02;
9: mp 199 °C (dec). Anal. Calcd for C30H24O6Ru2: C, 52.79;
1
H, 3.54. Found: C, 52.65; H, 3.59. H NMR (CDCl3, 200 MHz):
1
H, 3.24. Found: C, 53.97; H, 3.27. H NMR (CDCl3, 300 MHz):
δ 7.01 (d, J ) 8.47 Hz, 4H, C6H4), 6.83 (d, J ) 8.47 Hz, 4H,
C6H4), 5.63 (t, 2H, C5H3), 5.40 (t, 2H, C5H3), 4.26, (t, 2H, C5H3),
3.78 (s, 6H, OCH3), 2.96 (s, 2H, PhCH2), 2.92 (s, 2H, PhCH2). IR
(νCO, cm-1): 2010 (s), 1973 (s), 1958 (s), 1918 (s).
δ 7.35-7.24 (m, 6H, C6H5), 7.14-7.11 (m, 4H, C6H5), 5.66 (t,
2H, C5H3), 5.45 (t, 2H, C5H3), 4.28 (m, 2H, C5H3), 3.04 (s, 2H,
PhCH2), 3.02 (s, 2H, PhCH2). IR (νCO, cm-1): 1997 (s), 1958 (s),
1934 (s), 1918 (s).
10-meso: mp 189 °C (dec). Anal. Calcd for C30H24O6Ru2: C,
1
7-meso: mp 206 °C (dec). Anal. Calcd for C28H20O4Ru2: C,
52.79; H, 3.54. Found: C, 52.66; H, 3.50. H NMR (CDCl3, 200
1
54.02; H, 3.24. Found: C, 53.89; H, 3.24. H NMR (CDCl3, 300
MHz): δ 6.82-6.67 (m, 8H, C6H4), 5.61 (br s, 2H, C5H4), 5.51 (t,
4H, C5H4), 5.39 (br s, 2H, C5H4), 4.09 (s, 2H, PhCH), 3.75 (s, 6H,
OCH3). IR (νCO, cm-1): 1993 (s), 1966 (s), 1795 (m), 1759 (s).
10-rac: mp 222 °C (dec). Anal. Calcd for C30H24O6Ru2: C,
MHz): δ 7.16-7.10 (m, 6H, C6H5), 6.82-6.78 (m, 4H, C6H5),
5.59 (br s, 2H, C5H4), 5.49 (m, 4H, C5H4), 5.36 (br s, 2H, C5H4),
4.14 (s, 2H, PhCH). IR (νCO, cm-1): 1997 (s), 1962 (s), 1787 (sh,
w), 1759 (s).
1
52.79; H, 3.54. Found: C, 52.48; H, 3.49. H NMR (CDCl3, 200
7-rac: mp 208 °C (dec). Anal. Calcd for C28H20O4Ru2: C, 54.02;
MHz): δ 6.79 (d, J ) 8.55 Hz, 4H, C6H4) 6.51 (d, J ) 8.55 Hz,
4H, C6H4), 5.53-5.47 (m, 6H, C5H4), 5.22 (br s, 2H, C5H4), 3.76
(s, 2H, PhCH), 3.61 (s, 6H, OCH3). IR (νCO, cm-1): 1997 (s), 1954
(s), 1799 (sh, w), 1752 (s).
Synthesis of (tBuC5H4)PhCHCHPh(tBuC5H4) (3). Ligand 3 was
prepared similarly as described above for 2 from 7.0 g (33 mmol)
1
H, 3.24. Found: C, 54.02; H, 3.13. H NMR (CDCl3, 300 MHz):
(9) (a) Li, B.; Wang, B.; Xu, S.; Zhou, X. J. Organomet. Chem. 2005,
690, 5309. (b) Kane, K. M.; Shapiro, P. J.; Vij, A.; Cubbon, R.; Rheingold,
A. L. Organometallics 1997, 16, 4567.
(10) Stone, K. J.; Little, R. D. J. Org. Chem. 1984, 49, 1849.

1160 Organometallics, Vol. 25, No. 5, 2006
Table 1. Crystal Data and Summary of X-ray Data Collection for 4, 5, 7-meso, 7-rac, and 8
Li et al.
4
5
7-meso
7-rac
8
formula
fw
C29H22O5Ru2
652.61
C28H20O4Ru2
622.58
C29H22Cl2O4Ru2
707.51
C28.25H20.50Cl0.50O4Ru2
643.81
C31H26O7Ru2
712.66
cryst syst
space group
a (Å)
b (Å)
c (Å)
triclinic
P1h
monoclinic
C2/c
24.070(7)
7.290(2)
16.239(5)
90
124.083(4)
90
2359.7(12)
4
monoclinic
C2/c
22.024(6)
14.171(5)
16.957(6)
90
90.719(8)
90
5292(3)
8
monoclinic
C2/c
28.419(9)
12.792(4)
16.503(5)
90
118.054(4)
90
5294(3)
monoclinic
P2(1)/n
8.687(9)
11.673(12)
27.86(3)
90
97.826(16)
90
2799(5)
4
8.928(3)
10.143(4)
14.022(5)
98.909(6)
95.115(6)
93.640(6)
1245.6(7)
2
R (deg)
â (deg)
γ (deg)
V (Å3)
Z
8
D
calcd (g cm-3
)
1.740
1.251
648
1.752
1.313
1232
1.776
1.378
2800
1.615
1.222
2548
1.691
1.126
1424
µ (mm-1
F(000)
)
cryst size (mm)
max. 2θ (deg)
0.18 × 0.16 × 0.12
0.22 × 0.16 × 0.06
0.12 × 0.08 × 0.06
0.22 × 0.20 × 0.18
0.20 × 0.18 × 0.12
52.96
52.78
52.80
52.76
52.72
no. of reflns collected
no. of indep reflns/Rint
no. of params
7213
5071/0.0340
326
1.012
0.0439, 0.0783
0.0934, 0.0958
6688
2402/0.0342
154
1.056
0.0276, 0.0522
0.0453, 0.0568
15 035
5414/0.0835
335
0.956
0.0453, 0.0667
0.0992, 0.0794
14 877
5401/0.0305
349
1.150
0.0334, 0.0887
0.0557, 0.1051
15 583
5595/0.0340
363
1.075
0.0549, 0.1707
0.0770, 0.1890
goodness-of-fit on F2
R1, wR2 (I > 2σ(I))
R1, wR2 (all data)
of 2-tert-butylphenylfulvene in 31% yield as white solids. Mp:
123-124 °C. Anal. Calcd for C32H38: C, 90.94; H, 9.06. Found:
C, 90.90; H, 8.96. MS (ESI): m/z 423 (M + 1). 1H NMR (CDCl3,
200 MHz, as a mixture of meso and rac isomers): δ 7.23-7.11
(m, 10H, C6H5), 6.00-5.75 (m, 4H, C5H4), 4.27 (s, 1H, PhCH),
4.25 (s, 1H, PhCH), 2.68-2.35 (m, 4H, C5H4), 1.12-0.92 (m, 18H,
tBu-H).
Results and Discussion
Reactions of CpArCHCHArCp [Ar ) Ph (1), p-MeOC6H4
(2)] with Ru3(CO)12. The reaction of Ru3(CO)12 with the
PhCH-CHPh-bridged bis(cyclopentadiene) ligand 1 (as a
mixtures of racemic and meso isomers with a ratio of about
1:0.9) in refluxing xylene afforded not only the normal bridged
bis(cyclopentadienyl) diruthenium complexes 7 (27% for 7-meso
and 4% for 7-rac), but also the 2,2′-bisubstituted11 fulvalene
diruthenium complexes 5 (4%) and complexes 4 (2%), in which
one of the cyclopentadienyl rings was partially hydrogenated
(Scheme 2). The reactions can also be conducted in heptane,
benzene, and toluene, which demand longer reaction time, but
the amount of the C-C cleavage products seems to decrease.
To further examine the stereochemistry of the reaction, the pure
racemic isomer (1-rac) of ligand 1 was obtained by hydrolysis
of the corresponding racemic calcium salt9b and used to react
with Ru3(CO)12 instead of the mixture of racemic and meso
isomers. However, similar products, 7-meso (7%), 7-rac (7%),
5 (4%), and complexes 4 (2%), were obtained. This opens up
a possibility that the reaction itself has led to some sort of
equilibration between the two stereochemistries and would
suggest some equilibrium processes within the mechanism. To
further confirm the relationship between the products, a xylene
solution of 7-meso or 7-rac was heated alone or with Ru3(CO)12
under reflux for 8 h; no 4, 5, or any other product was observed
by TLC monitoring. This suggests that the racemic and meso
isomers of 7 cannot interconvert to each other; complexes 4
and 5 are formed during the reaction of Ru3(CO)12 with ligand
1 and not from complex 7.
Reaction of 3 with Ru3(CO)12. Using a procedure similar to
that described above, reaction of 3 with Ru3(CO)12 gave 11 (4%),
12 (5%), 13 (4%), and 14 (3%) as yellow or orange crystals.
11: mp 246 °C (dec). Anal. Calcd for C36H36O4Ru2: C, 58.84;
1
H, 4.94. Found: C, 59.09; H, 4.88. H NMR (CDCl3, 200 MHz):
δ 7.30-7.24 (m, 6H, C6H5), 7.06 (m, 4H, C6H5), 5.34 (s, 2H, C5H2),
4.17 (s, 2H, C5H2), 2.90 (s, 4H, PhCH2), 1.22 (s, 18H, tBu-H). IR
(νCO, cm-1): 1993 (s), 1950 (s), 1934 (s), 1910 (m).
12: mp 135 °C (dec). Anal. Calcd for C36H36O4Ru2: C, 58.84;
1
H, 4.94. Found: C, 59.00; H, 4.82. H NMR (CDCl3, 200 MHz):
δ 7.20-7.14 (m, 6H, C6H5), 6.86 (m, 4H, C6H5), 5.62-5.15 (m,
t
6H, C5H3), 4.11 (br s, 2H, PhCH), 1.29 (s, 9H, Bu-H), 1.27 (s,
t
9H, Bu-H). IR (νCO, cm-1): 1989 (s), 1962 (m), 1765 (s).
13: mp 235 °C (dec). Anal. Calcd for C36H36O4Ru2: C, 58.84;
1
H, 4.94. Found: C, 59.00; H, 4.87. H NMR (CDCl3, 200 MHz):
δ 7.20-7.14, (m, 6H, C6H5), 6.81 (m, 4H, C6H5), 5.56 (br s, 2H,
C5H3), 5.50 (br s, 2H, C5H3), 5.24 (m, 2H, C5H3), 4.12 (s, 2H,
t
PhCH), 1.26 (s, 18H, Bu-H). IR (νCO, cm-1): 1989 (s), 1954 (s),
1799 (m), 1759 (s).
14: mp: 229 °C (dec). Anal. Calcd for C36H36O4Ru2: C, 58.84;
1
H, 4.94. Found: C, 58.88; H, 4.72. H NMR (CDCl3, 200 MHz):
δ 6.94-6.78 (m, 10H, C6H5), 5.51-5.47 (m, 3H, C5H3), 5.40 (br
s, 1H, C5H3), 5.12 (s, 1H, C5H3), 5.08 (s, 1H, C5H3), 3.70 (s, 1H,
The reaction of Ru3(CO)12 with ligand 2 (as a mixture of
racemic and meso isomers) gave similar products, 10-meso
(30%), 10-rac (3%), 9 (4%), and 8 (2%).
t
PhCH), 3.67 (s, 1H, PhCH), 1.31 (s, 9H, Bu-H), 1.21 (s, 9H,
tBu-H). IR (νCO, cm-1): 1997 (s), 1942 (s), 1771 (s).
All the compounds are yellow to orange air-stable crystals
but slightly air-sensitive in solution. The IR spectrum of 4 shows
five terminal carbonyl absorption peaks at 2050, 1985, 1962,
Crystallographic Studies. Single crystals of complexes 4, 5,
7-meso, 7-rac, 8, 10-meso, 11, 12, 13, and 14 suitable for X-ray
diffraction were obtained from hexane/CH2Cl2 solution. Data
collection was performed on a Bruker SMART 1000, using
graphite-monochromated Mo KR radiation (ω-2θ scans, λ )
0.71073 Å). Semiempirical absorption corrections were applied for
all complexes. The structures were solved by direct methods and
refined by full-matrix least-squares. All calculations were using the
SHELXTL-97 program system. The crystal data and summary of
X-ray data collection are presented in Tables 1 and 2.
1
1910, and 1870 cm-1. The H NMR spectrum of 4 displays
(11) The sequence of the carbons in the parent fulvalene was labeled as
shown.

Reactions of CpArCHCHArCp with Ru3(CO)12
Organometallics, Vol. 25, No. 5, 2006 1161
Table 2. Crystal Data and Summary of X-ray Data Collection for 10-meso, 11, 12, 13, and 14
10-meso
11
12
13
14
formula
fw
C30H24O6Ru2
682.63
C36H36O4Ru2
734.79
C36H36O4Ru2
734.79
C37H38Cl2O4Ru2
819.71
C36H36O4Ru2
734.79
cryst syst
space group
a (Å)
b (Å)
c (Å)
triclinic
P1h
monoclinic
C2/c
22.262(5)
7.069(2)
22.290(5)
90
112.186(19)
90
3248.1(14)
4
triclinic
P1h
monoclinic
C2/c
18.902(6)
17.305(5)
21.960(7)
90
95.924(7)
90
7145(4)
8
triclinic
P1h
9.869(5)
10.941(6)
13.370(7)
84.886(8)
70.146(8)
64.953(8)
1227.6(12)
2
10.579(4)
11.980(4)
14.910(5)
76.461(5)
73.896(5)
66.281(4)
1645.9(10)
2
11.022(4)
11.305(4)
15.355(5)
98.781(6)
106.070(5)
112.801(5)
1620.2(10)
2
R (deg)
â (deg)
γ (deg)
V (Å3)
Z
D
calcd (g cm-3
)
1.847
1.276
680
1.503
0.966
1488
1.483
0.953
744
1.524
1.032
3312
1.506
0.969
744
µ (mm-1
F(000)
)
cryst size (mm)
max. 2θ (deg)
0.20 × 0.18 × 0.16
0.24 × 0.20 × 0.16
0.32 × 0.22 × 0.20
0.18 × 0.16 × 0.14
0.32 × 0.28 × 0.22
52.76
53.00
52.86
52.84
56.58
no. of reflns collected
no. of indep reflns/Rint
no. of params
7053
4918/0.0210
345
1.104
0.0292, 0.0712
0.0484, 0.0906
8467
3313/0.0491
193
1.020
0.0433, 0.0849
0.0801, 0.0961
10 049
6676/0.0222
385
1.034
0.0318, 0.0662
0.0572, 0.0757
20 453
7304/0.1148
440
0.973
0.0578, 0.1025
0.1599, 0.1522
10 408
7584/0.0201
385
1.045
0.0330, 0.0798
0.0613, 0.0902
goodness-of-fit on F2
R1, wR2 (I > 2σ(I))
R1, wR2 (all data)
Scheme 2
three multiplets for cyclopentadienyl protons at 5.58, 5.20, and
3.38 ppm,12 one singlet and two doublets for benzyl protons at
3.55, 3.52, and 3.24 ppm, and two multiplets for the allyl and
alkyl protons at 3.00-2.59 and 2.23-2.00 ppm, indicating the
unusual structure. Single-crystal X-ray diffraction analysis shows
that in complex 4 the two cyclopentadienyl rings were linked
together, with one of them being partially hydrogenated. It
contains a Ru-Ru bond, and one ruthenium atom is coordinated
with a cyclopentadienyl ligand in an η5 manner and the other
ruthenium atom is coordinated in an η3 manner with the allyl
group consisting of the benzyl carbon and the two linked or
substituted carbons of the partially hydrogenated cyclopenta-
of Ha (see Experimental Section), indicating a similar structure.
It was reported that reaction of the CH2 and Me2Si or Me2Ge
doubly bridged bis(cyclopentadiene) with Fe(CO)5 could also
give complexes with η5 and η3 coordination mode similar to
that of 4.13
Complexes 7 and 10 are the normal intramolecular diruthe-
nium complexes. All their IR spectra show two terminal and
two bridging carbonyl absorptions at around 1997, 1960 cm-1
,
1
and 1793, 1753 cm-1. Their IR and H NMR spectra are very
similar to that for PhCHCHPh-bridged iron analogues.9 An
interesting feature of this reaction is the relative yield of the
isomers of 7 and 10, which is much more in favor of the meso
1
8b
dienyl ring. Combining the H NMR spectrum and the crystal
form. Similarly, (CH2CH2)[(C9H6)Ru(CO)(µ-CO)]2
and
structure with the aid of the 1H-1H COSY analysis (Figure 1),
the signals at 2.23-2.00 (m, 2H), 3.00-2.59 (m, 4H), 3.55 (s,
1H), 3.52 (d, J ) 16.20 Hz, 1H), and 3.24 (d, J ) 16.20 Hz,
1H) ppm were assigned to Hd, Hc + He, Hb, and Ha (see Chart
1), respectively. Complex 8 has IR and 1H NMR spectra similar
to 4 except that in 8 the signal of Hb does not overlap with that
(MeHC)[(C9H6)Ru(CO)2]2 were obtained as 2:1 and 4:1
mixtures of the isomers, respectively, with the meso form
predominating.
14
The 1H NMR spectrum of 5 exhibits three triplets or
multiplets for cyclopentadienyl protons at 5.66, 5.45, and 4.28
ppm12 and two singlets for benzyl protons at 3.04 and 3.02 ppm.
(12) The chemical shift difference between the Cp-H protons of fulvalene
ligands in the 1H NMR spectra appears to correlate with the presence of
metal-metal bonding, as observed earlier: (a) Smart, J. C.; Curtis, C. J.
Inorg. Chem. 1977, 16, 1788. (b) See also ref 4.
(13) Wang, B.; Zhu, B.; Zhang, J.; Xu, S.; Zhou, X.; Weng, L.
Organometallics 2003, 22, 5543.
(14) Schiavo, S. L.; Renouard, C.; Simpson, M. C.; Adams, H.; Bailey,
N. A.; White, C. J. Chem. Soc., Dalton Trans. 1994, 1731.

1162 Organometallics, Vol. 25, No. 5, 2006
Li et al.
1
Figure 1. Partial H-1H COSY spectrum of complex 4 in CDCl3.
Its IR spectrum shows only four terminal carbonyl absorptions
at 1997, 1958, 1934, and 1918 cm-1. The elemental analysis
indicates that complexes 5 and 7 are isomers. Single-crystal
X-ray diffraction analysis shows that the complex 5 is a 2,2′-
bisubstituted fulvalene diruthenium complex, an analogue of
the known complex FvRu2(CO)4 (6).15 So the formation of 5
must be accompanied by the cleavage of the bridging C-C bond
of the ligand and the coupling of the two cyclopentadienyl rings.
absorptions at 1993, 1950, 1934, and 1910 cm-1, which is
similar to that for 5 and 9. The single-crystal X-ray diffraction
analysis further proves it to be a 2,2′,4,4′-tetrasubstituted
fulvalene diruthenium complex. Complexes 12, 13, and 14 have
1H NMR and IR spectra similar to complexes 7 and 10,
indicating the similar structures. There are 10 normal intramo-
lecular diruthenium complex isomers in theory for ligand 3
(Chart 2). When two phenyl groups lie in meso form, there are
four isomers, and among them 3 and 4 are enantiomers. When
two phenyl groups lie in racemic form, there are six isomers,
and among them 5 and 6, 7 and 8, and 9 and 0 are
enantiomers, respectively. In our case only three isomers (1,
2, and 5) of them were obtained, possibly due to the relative
amount of the isomers in ligand 3.
1
Complex 9 has IR and H NMR spectra and structure similar
to those of 5.
t
t
Reaction of BuC5H4PhCHCHPhC5H4 Bu (3) with Ru3-
(CO)12. To further examine the effect of the structure of the
ligand on the C-C cleavage reaction, a tert-butyl group was
introduced to the cyclopentadienyl rings. Reaction of ligand 3
(as a mixture of racemic and meso isomers) with Ru3(CO)12 in
refluxing xylene afforded the fulvalene diruthenium analogue
11 (4%) and three isomers of the normal bridged bis(cyclopen-
tadienyl) diruthenium complexes 12 (5%), 13 (4%), and 14 (3%)
in low yield (Scheme 3). The partially hydrogenated η5:η3-
analogue mentioned above was not obtained, possibly because
the bulky tert-butyl may be resistant to the hydrogenation.
Molecular Structures. The molecular structures of 4 and 8
are shown in Figure 2 and the Supporting Information,
respectively. The selected bond lengths and angles are listed in
Table 3. Complexes 4 and 8 have similar structures. One
ruthenium atom is coordinated with a cyclopentadienyl ligand
in an η5 manner, and the other ruthenium atom is coordinated
in an η3 manner with the allyl group consisting of the benzyl
carbon and the two linked or substituted carbons of the partially
hydrogenated cyclopentadienyl ring. The two benzyl groups
result from the cleavage of the bridging C-C bond of the ligand
and lie in ortho-positions of the new building C(17)-C(18) bond
on the opposite side and point away from each other. The five
carbonyls, three bound on η3-Ru(1) and the other two bound
1
The H NMR spectrum of 11 displays two singlets for the
cyclopentadienyl protons at 5.34 and 4.17 ppm and a singlet
for the benzyl and tert-butyl protons at 2.90 and 1.22 ppm,
respectively. Its IR spectrum shows only four terminal carbonyl
(15) Vollhardt, K. P. C.; Weidman, T. W. Organometallics 1984, 3, 82.

Reactions of CpArCHCHArCp with Ru3(CO)12
Organometallics, Vol. 25, No. 5, 2006 1163
Scheme 3
Table 3. Selected Bond Lengthes (Å) and Angles (deg) for 4
and 8
Chart 2
4
8
Ru(1)-Ru(2)
Ru(1)-C(12)
Ru(1)-C(13)
Ru(1)-C(17)
Ru(2)-C(Cp)(av)
C(12)-C(13)
C(13)-C(14)
C(14)-C(15)
C(15)-C(16)
C(16)-C(17)
C(13)-C(17)
C(17)-C(18)
2.8583(9)
2.256(5)
2.242(5)
2.302(5)
2.246
1.425(8)
1.515(8)
1.530(9)
1.519(9)
1.524(8)
1.414(7)
1.465(8)
2.867(2)
2.289(7)
2.261(7)
2.304(7)
2.2482
1.419(10)
1.526(9)
1.536(11)
1.522(11)
1.514(10)
1.427(10)
1.475(10)
C(11)-C(12)-C(13)
C(12)-C(13)-C(17)
C(13)-C(17)-C(18)
C(23)-C(22)-C(18)
C(22)-C(23)-C(24)
Ru(2)-Ru(1)-C(17)
Ru(2)-Ru(1)-C(13)
Ru(2)-Ru(1)-C(12)
126.0(5)
123.7(5)
125.0(5)
127.7(5)
114.8(5)
76.24(14)
96.58(15)
88.43(15)
123.3(6)
125.2(6)
124.6(6)
128.3(7)
115.9(6)
76.41(18)
96.73(18)
89.61(19)
on η5-Ru(2), are all terminal, which is consistent with their IR
spectra. It is interesting that C(1)-O(1), one of the carbonyls
bound on η3-Ru(1), almost lies in the same line with Ru(2)-
Ru(1) ( Ru(2)-Ru(1)-C(13): 174.8(2)° for 4 and 173.7(2)
for 8). In both complexes, Ru(1), Ru(2), C(17), and the centroid
of the cyclopentadienyl ring (CEN) are almost coplanar: the
torsion angle of Ru(2)-Ru(1)-C(17)-CEN is 3.1° for 4 and
2.7° for 8. The Ru(1)-C(η3-allyl) bond length (average for 4:
2.267 Å; 8: 2.285 Å) is very close to Ru(2)-C(Cp) (average
for 4: 2.246 Å; 8: 2.2482 Å). Similarly, the C-C(η3-allyl) bond
distances C(12)-C(13) and C(13)-C(17) [1.425(8), 1.414(7)
Å for 4, 1.419(10), 1.427(10) Å for 8] are also close to those
of C-C(Cp) (1.4236 Å for 4 and 1.4252 Å for 8), which are
much shorter than that of C(13)-C(14), C(14)-C(15), C(15)-
C(16), and C(16)-C(17), the latter belonging to C-C single
bonds. The five-membered ring C(13)-C(14)-C(15)-C(16)-
C(17), resulting from a partially hydrogenated cyclopentadienyl
ring, adopts a standard envelope conformation [C(13), C(14),
C(16), and C(17) atoms are completely coplanar, with C(15)
deviating from the plane by 0.4554 Å for 4 and 0.4571 Å for
8]. The Ru-Ru bond lengths of 2.8583(9) Å for 4 and 2.867-
(2) Å for 8 are quite comparable to the value of 2.845(1) Å for
the similar complex (η5-C5H4-η3-(CC6H5)C6H5)Ru(CO)2Ru-
(CO)316 and much longer than the normal bis(cyclopentadienyl)
diruthenium complexes due to the fact that the very strong (η3-
allyl)-Ru linkage stretches the relatively weak Ru-Ru bond
in order to maintain its own optimal geometry.17
As shown in Figures 3 and 4, complexes 5 and 11 contain a
pair of ruthenium atoms linked by a metal-metal bond and a
substituted fulvalene ligand, with four terminal carbonyls. The
4
selected bond lengths and angles for them and FvRu2(CO)4
(6) are listed in Table 4. Complex 5 has two benzyl groups at
the 2,2′-positions and complex 11 has two more tert-butyl
groups at the 4,4′-positions of the fulvalene ligand. Both the
molecules possess crystallographically C2 symmetry. Thus,
(16) Behrens, U.; Weiss, E. J. Organomet. Chem. 1975, 96, 435.
(17) Cotton, F. A.; DeBoer, B. G.; Marks, T. J. J. Am. Chem. Soc. 1971,
93, 5069.
Figure 2. ORTEP diagram of 4. Thermal ellipsoids are shown at
the 30% level. Hydrogen atoms have been omitted for clarity.

1164 Organometallics, Vol. 25, No. 5, 2006
Li et al.
Figure 3. ORTEP diagram of 5. Thermal ellipsoids are shown at
the 30% level. Hydrogen atoms have been omitted for clarity.
Figure 5. ORTEP diagram of 7-meso. Thermal ellipsoids are
shown at the 30% level. All hydrogen atoms except for the bridging-
carbon protons have been omitted for clarity.
Figure 4. ORTEP diagram of 11. Thermal ellipsoids are shown
at the 30% level. Hydrogen atoms have been omitted for clarity.
Table 4. Selected Bond Lengthes (Å) and Angles (deg) for 5,
11, and FvRu2(CO)4 (6)a
Figure 6. ORTEP diagram of 7-rac. Thermal ellipsoids are shown
at the 30% level. All hydrogen atoms except for the bridging-carbon
protons have been omitted for clarity.
5
11
6
Ru(1)-Ru(1A)
Ru(1)-C(1)
Ru(1)-C(2)
Ru(1)-CENb
C(3)-C(3A)
C-C(Cp)(av)
2.8309(8)
1.862(4)
1.861(4)
1.905
1.458(5)
1.425
2.8650(11)
1.852(5)
1.865(5)
1.902
1.459(8)
1.428
2.821(1)
1.860(3)
1.866(3)
1.894
1.457(3)
1.416
ruthenium complexes (Table 5). The Ru-Ru bond [2.8650(11)
Å] in 11 is the longest up to now for the bis(cyclopentadienyl)
diruthenium complexes. It is also worth noting that the torsion
angles of CEN-Ru(1)-Ru(1A)-CEN in 5 (17.3°) and 11
(17.5°) are much larger than that of 6 (4.3°), possibly attributed
to the effects of the benzyl and tert-butyl substituents.
Ru(1A)-Ru(1)-C(1)
Ru(1A)-Ru(1)-C(2)
Ru(1A)-Ru(1)-CEN
C(1)-Ru(1)-C(2)
93.66(11)
93.73(11)
104.6
95.87(18)
93.03(19)
104.3
94.40(8)
93.32(7)
105.4
Complexes 7-meso, 7-rac, 10-meso, 12, 13, and 14 are normal
intramolecular diruthenium complexes (Figures 5-9 and Sup-
porting Information). Complexes 12, 13, and 14 are three of 10
intramolecular diruthenium complex isomers of the reaction of
ligand 3 with Ru3(CO)12. It is difficult to differentiate them from
their 1H NMR and IR spectra. Fortunately all their crystals are
suitable for X-ray analysis. The orientation of the bridging-
carbon protons can easily differentiate the isomers. The Ru-
Ru bond distances in these complexes of around 2.70 Å are
quite comparable to those in related linked compounds, e.g.,
(CH2CH2)[(η5-C5H4)Ru(CO)(µ-CO)]2 [2.7037(10) Å]8a and
trans-(CH2CH2)[(C9H6)Ru(CO)(µ-CO)]2 [2.7185(7) Å].8b Their
torsion angles CEN-Ru(1)-Ru(2)-CEN vary from 1.7° to
8.3°, while the corresponding angle in (CH2CH2)[(η5-C5H4)-
Ru(CO)(µ-CO)]2 is only 0.9°. The difference may also be
attributed to the introduction of substituents to the bridging
carbons and the cyclopentadienyl rings.
88.93(16)
90.2(2)
91.49(11)
a See ref 4a; 6 deviates from C2V slightly, so half of its data was chosen
for comparison. b CEN, centroid of the cyclopentadienyl ring.
although substituents were introduced to the fulvalene ligand
in complexes 5 and 11, their bond lengths and angles vary little
compared with the mother complex 6 (Table 4). The dihedral
angles between the two cyclopentadienyl planes are still
relatively large (148.1° for 5 and 149.7° for 11), comparable to
that of 6 (151.5°). The normally planar fulvalene moiety is
strained and leads to the expectation of a longer than normal
Ru-Ru single-bond distance. Thus, the Ru-Ru bond distances
of 2.8309(8) Å for 5 and 2.8650(11) Å for 11 are longer than
those of 6 [2.821(1) Å] and the nonbridged18 and singly or
doubly bridged4-8,19 bis(cyclopentadienyl) tetracarbonyl di-
(18) Mills, O. S.; Nice, J. P. J. Organomet. Chem. 1967, 9, 339.
(19) (a) Zhou, X.; Zhang, Y.; Xu, S.; Tian, G.; Wang, B. Inorg. Chim.
Acta 1997, 262, 109. (b) Zhang, Y.; Wang, B.; Xu, S.; Zhou, X. Transition
Met. Chem. 1999, 24, 610. (c) Knox, S. A. R.; Macpherson, K. A.; Orpen,
A. G.; Rendle. M. C. J. Chem. Soc., Dalton Trans. 1989, 1807. (d)
Ovchinnikov, M. V.; Klein, D. P.; Guzei, I. A.; Choi, M. G.; Angelici, R.
J. Organometallics 2002, 21, 617.
Plausible Mechanism. The formation of the substituted
fulvalene diruthenium complexes 5, 9, and 11, and the partially
hydrogenated complexes 4 and 8, must be accompanied with
the cleavage of the bridging C-C bond of the ligand and the

Reactions of CpArCHCHArCp with Ru3(CO)12
Organometallics, Vol. 25, No. 5, 2006 1165
Table 5. Structural Parameter Comparison for Bis(cyclopentadienyl) Diruthenium Complexes
CEN-M-M-CEN
complex
M-M (Å)
PL-PLa (deg)
torsion angle (deg)
ref
18
trans-[(η5-C5H5)Ru(CO)(µ-CO)]2
(CH2)[C5H4Ru(CO)2]2
2.735(2)
2.766(1)
112.9
39.9
49
19c
(CMe2)[C5H4Ru(CO)2]2
2.7879(4)
2.706(1)
119.3
103.53
32.9
6a
6b, 19a
(SiMe2)[(η5-C5H4)Ru(CO)(µ-CO)]2
2.7042(4)
2.7036(6)
2.7037(10)
2.700(1)
(GeMe2)[(η5-C5H4)Ru(CO)(µ-CO)]2
101.98
19b
8a
7
(CH2CH2)[(η5-C5H4)Ru(CO)(µ-CO)]2
0.9
4.3
(Me2SiSiMe2)[(η5-C5H4)Ru(CO)(µ-CO)]2
FvRu2(CO)4
91.9
151.5
2.821(1)
4
4
8
5
11
7-meso
7-rac
10-meso
12
2.8583(9)
2.867(2)
twb
tw
tw
tw
tw
tw
tw
tw
tw
tw
19d
8b
2.8309(8)
2.8650(11)
2.7031(10)
2.6988(8)
2.6548(14)
2.7102(10)
2.7105(9)
2.7052(6)
2.8180(3)
2.7185(7)
148.1
149.7
99.1
100.4
82.1
80.2
98.3
101.3
122.86
17.3
17.5
1.7
4.7
4.0
6.2
8.3
2.9
24.2
4.7
13
14
(Me2Si)2[(η5-C5H3)Ru(CO)2]2
rac-(CH2CH2)[(C9H6)Ru(CO)(µ-CO)]2
a PL, plane of the cyclopentadienyl ring. b tw, this work.
Figure 9. ORTEP diagram of 14. Thermal ellipsoids are shown
at the 30% level. All hydrogen atoms except for the bridging-carbon
protons have been omitted for clarity.
Figure 7. ORTEP diagram of 12. Thermal ellipsoids are shown
at the 30% level. All hydrogen atoms except for the bridging-carbon
protons have been omitted for clarity.
Scheme 4
rearrangement) may take place. Indeed, the analogous compound
2,3-dimethyl-2,3-di(cyclopentadienyl)butane (15) was reported
to be quite unstable even in dilute solution at room temperature
and nearly quantitatively isomerizes to 1,1′-bi(2-isopropyli-
denecyclopent-3-enyl) (16) by Cope rearrangement (Scheme
4).20 However, when ligand 1 was heated in refluxing CDCl3
for 50 h or in refluxing xylene for 12 h, no new compound was
monitored. So the easy rearrangement of 15 may come from
the crowded substituents at the 2- and 3-carbons. Both kinetics
and thermodynamics apparently favor this reaction. In contrast,
the Cope rearrangement is not observed for 1 alone, but with
Ru3(CO)12 present this does occur. This indicates that the less
crowded nature of ligand 1 does not favor the thermal rear-
Figure 8. ORTEP diagram of 13. Thermal ellipsoids are shown
at the 30% level. All hydrogen atoms except for the bridging-carbon
protons have been omitted for clarity.
coupling of the two cyclopentadienyl rings. Introduction of a
methoxyl to the 4-position of the phenyl or a tert-butyl to the
cyclopentadienyl ring does not seem to affect the bridging C-C
cleavage and cyclopentadienyl coupling. The coupling positions
are at the ortho positions of the bridgehead carbons. It easily
led us to consider that a [3, 3] sigmatropic shift (Cope
(20) You, S.; Gubler, M.; Neuenschwander, M. HelV. Chim. Acta 1994,
77, 1346.

1166 Organometallics, Vol. 25, No. 5, 2006
Li et al.
Scheme 5
rangement, but Ru3(CO)12 in some way catalyzes the reaction.
The conversion of 1-rac to 7-meso opens up the possibility that
the reaction itself has led to some sort of equilibration between
the two stereochemistries and would suggest some equilibrium
processes within the mechanism. So the reaction may be through
a reversible nonconcerted Cope rearrangement, involving either
a biradical intermediate or a spectrum of transition states ranging
from a six-center structure, representing interacting allyl radicals,
to the biradical.21
substituents at the 2- and 3-positions of the ligand may be
necessary for both the Cope rearrangement and the further
isomerization from 17 to 18. The new double bonds in 17
conjugate with the aromatic rings, which makes the rearrange-
ment product higher in energy. On the contrary, reactions of
the CH2CH2-bridged bis(cyclopentadiene or indene) with
Ru3(CO)12 gave only the normal bridged bis(cyclopentadienyl
or indenyl) diruthenium complexes.8
Conclusions
The rearrangement of 1-meso (we cannot separate enough of
pure 1-meso for the reaction) may vary from that of the racemic
isomer, as the meso and racemic isomers of 3,4-diphenylhexa-
1,5-diene rearrange to give different products through different
transition states.22 However, from the reaction results of the pure
1-rac and the mixture of racemic and meso isomers of ligand
1, it can be concluded that the reactions are similar, and the
reactivity of the meso isomer of ligand 1 with Ru3(CO)12 is
much better than that of the racemic isomer. The poorer
reactivity of the racemic isomer than that of the meso isomer
of the ligand was also observed for ligand 2 and some bridged
indenyl ligands.8b,14 On the basis of these results, the possible
mechanism of the reaction may be as shown in Scheme 5.
The Cope rearrangement of ligand 1 to the intermediate 17
is promoted by coordination of the double bonds of the ligand
to Ru3(CO)12 instead of carbonyls. Then 17 can further isomerize
to the benzyl-substituted dihydrofulvalene 18 and react with Ru3-
(CO)12 to form complexes 4 and 5. The rearrangement is
reversible and nonconcerted. So 1-rac can rearrange to 17, and
the meso isomer 1-meso can be formed from 17 by the reverse
rearrangement.
Reaction of CpPhCHCHPhCp with Ru3(CO)12 in refluxing
xylene afforded the unexpected bridging C-C cleavage and
cyclopentadienyl coupling products: the 2,2′-bisubstituted ful-
valene diruthenium complex 5 and the partially hydrogenated
product 4, in addition to the normal bridged bis(cyclopentadi-
enyl) tetracarbonyl diruthenium 7. Introduction of a methoxyl
to the 4-position of the phenyl or a tert-butyl to the cyclopen-
tadienyl ring did not affect the bridging C-C cleavage and
cyclopentadienyl coupling. This provides a new method to
synthesize the ortho-benzyl-substituted fulvalene diruthenium
complexes. The mechanism may involve the Ru3(CO)12-
promoted nonconcerted reversible Cope rearrangement.
Acknowledgment. We are grateful to the National Natural
Science Foundation of China (20421202, 20472034), the
Specialized Research Fund for the Doctoral Program of Higher
Education of China (20030055001), and the Program for New
Century Excellent Talents in University for financial support.
Supporting Information Available: X-ray structural informa-
tion for complexes 4, 5, 7-meso, 7-rac, 8, 10-meso, 11, 12, 13, and
The reaction of 15 with Ru3(CO)12 gave only a trace of
complex, which was too small to identify, and the rearrangement
product 16 did not react with Ru3(CO)12 at all. So the aromatic
1
14, including the ORTEP figures of 8 and 10-meso, the full H-
1
1H COSY spectrum of complex 4, the H NMR spectra of ligand
1 as a mixture of racemic and meso isomers with a ratio of about
1:0.9 and as a pure racemic isomer. This material is available free
of charge via the Internet at http://pubs.acs.org.
(21) (a) Lutz, R. P. Chem. ReV. 1984, 84, 205. (b) Gajewski, J. J. Acc.
Chem. Res. 1980, 13, 142.
(22) Lutz, R. P.; Bernal, S.; Boggio, R. J.; Harris, R. O.; McNicholas,
M. W. J. Am. Chem. Soc. 1971, 93, 3985.
OM050673W