Synthesis and structures of novel zerovalent ruthenium p-quinone complexes and a bimetallic p-biquinone complex

Article abstract of DOI:10.1021/om020730a

Ru(η⁶-cot)(η²-dmfm)₂ (1; cot = 1,3,5-cyclooctatriene, dmfm = dimethyl fumarate) reacted with p-quinones to give novel p-quinone-coordinated ruthenium(0) complexes, Ru(η⁶-cot)(p-quinone) (2), in good to high yields via the replacement of two dimethyl fumarates by p-quinones. The reaction of 1 with p-biquinone gave a novel bimetallic zerovalent complex {Ru(η⁶-cot)}₂(p-biquinone) (3), in which p-biquinone coordinates to two isolated Ru(cot) moieties with a unique mode and the two Ru(cot) groups are located at endo positions. Complexes 2 and 3 have either p-quinone or p-biquinone as π-acceptor ligands. The structures of complexes Ru(η⁶-cot)(2,6-dimethoxy-p-quinone) (2f) and 3 were determined by X-ray crystallography.

Full text of DOI:10.1021/om020730a

Organometallics 2003, 22, 77-82
77
Syn th esis a n d Str u ctu r es of Novel Zer ova len t
Ru th en iu m p-Qu in on e Com p lexes a n d a Bim eta llic
p-Biqu in on e Com p lex
Yasuyuki Ura, Yoshitaka Sato, Masashi Shiotsuki, Toshiaki Suzuki, Kenji Wada,
Teruyuki Kondo, and Take-aki Mitsudo*
Department of Energy and Hydrocarbon Chemistry, Graduate School of Engineering,
Kyoto University, Sakyo-ku, Kyoto 606-8501, J apan
Received September 4, 2002
Ru(η6-cot)(η2-dmfm)2 (1; cot ) 1,3,5-cyclooctatriene, dmfm ) dimethyl fumarate) reacted
with p-quinones to give novel p-quinone-coordinated ruthenium(0) complexes, Ru(η6-cot)-
(p-quinone) (2), in good to high yields via the replacement of two dimethyl fumarates by
p-quinones. The reaction of 1 with p-biquinone gave a novel bimetallic zerovalent complex
{Ru(η6-cot)}2(p-biquinone) (3), in which p-biquinone coordinates to two isolated “Ru(cot)”
moieties with a unique mode and the two Ru(cot) groups are located at endo positions.
Complexes 2 and 3 have either p-quinone or p-biquinone as π-acceptor ligands. The structures
of complexes Ru(η6-cot)(2,6-dimethoxy-p-quinone) (2f) and 3 were determined by X-ray
crystallography.
In tr od u ction
in proton/electron transfer but also in view of their
strong electron-accepting ability through π-back-dona-
tion. Since the degree of π-acidity can be controlled by
changing the substituents on quinone, the electron
density on the metal center is easily adjusted, which is
important from the viewpoint of catalytic activity. The
first synthesis of a transition-metal p-quinone complex,
Fe(CO)3(duroquinone), was accomplished by Sternberg,
Markby, and Wender in 1958.1 Several group 9 and 10
metal p-quinone complexes have been reported so
far.2-16 In contrast, there are very few examples of other
metal complexes such as iron(0),1,17 ruthenium(II),18
manganese(-I),19 and molybdenum(II).20
The methods used to prepare p-quinone complexes
can be divided into four classes: (1) direct ligand
exchange of appropriate complexes with p-quinones
(method A), (2) coupling of alkynes with carbon mon-
oxides on the transition-metal (method B), (3) reaction
of maleoyl/phthaloylmetal species with an alkyne (method
C), and (4) deprotonation of hydroquinone complexes
(method D). In the synthesis of p-quinone complexes by
method A, duroquinone has been frequently used,2-5,7,9,11
whereas few examples of other p-quinone complexes
have been reported.10,12,13,16 Fe(CO)3(duroquinone),1 Cp-
Co(p-quinone),8 and CpMoCl(CO)(duroquinone)20 have
been prepared by method B. Liebeskind and co-workers
reported a high-yield synthesis of p-quinone cobalt
complexes through method C, in which maleoyl/phtha-
loylmetal species were generated by oxidative addition
Among low-valent transition-metal complexes bearing
an olefinic π-acceptor ligand, p-quinone complexes have
been intensively investigated.1-22 The study of p-quino-
ne ligands is intriguing not only because of their role
(1) Sternberg, H. W.; Markby, R.; Wender, I. J . Am. Chem. Soc.
1958, 80, 1009.
(2) (a) Schrauzer, G. N.; Thyret, H. J . Am. Chem. Soc. 1960, 82,
6420. (b) Schrauzer, G. N.; Thyret, H. Z. Naturforsch. 1961, 16b, 353.
(c) Schrauzer, G. N.; Thyret, H. Z. Naturforsch. 1962, 17b, 73. (d)
Schrauzer, G. N.; Thyret, H. Angew. Chem., Int. Ed. Engl. 1963, 2,
478.
(3) Schrauzer, G. N.; Dewhirst, K. C. J . Am. Chem. Soc. 1964, 86,
3265.
(4) Glick, M. D.; Dahl, L. F. J . Organomet. Chem. 1965, 3, 200.
(5) (a) Aleksandrov, G. G.; Gusev, A. I.; Khandkarova, V. S.;
Struchkov, Yu. T.; Gubin, S. P. Chem. Commun. 1969, 748. (b)
Aleksandrov, G. G.; Struchkov, Yu. T.; Khandkarova, V. S.; Gubin, S.
P. J . Organomet. Chem. 1970, 25, 243.
(6) Uchtman, V. A.; Dahl, L. F. J . Organomet. Chem. 1972, 40, 403.
(7) Slocum, D. W.; Engelmann, T. R. J . Am. Chem. Soc. 1972, 94,
8596.
(8) (a) Dickson, R. S.; Kirsch, H. P. Aust. J . Chem. 1974, 27, 61. (b)
Dickson, R. S.; J ohnson, S. H. Aust. J . Chem. 1976, 29, 2189. (c)
Corrigan, P. A.; Dickson, R. S. Aust. J . Chem. 1981, 34, 1401.
(9) Bodner, G. M.; Engelmann, T. R. J . Organomet. Chem. 1975,
88, 391.
(10) Minematsu, H.; Takahashi, S.; Hagihara, N. J . Organomet.
Chem. 1975, 91, 389.
(11) (a) Fairhurst, G.; White, C. J . Organomet. Chem. 1978, 160,
C17. (b) Fairhurst, G.; White, C. J . Chem. Soc., Dalton Trans. 1979,
1531.
(12) (a) Chetcuti, M. J .; Howard, J . A. K.; Pfeffer, M.; Spencer, J .
L.; Stone, F. G. A. J . Chem. Soc., Dalton Trans. 1981, 276. (b) Chetcuti,
M. J .; Herbert, J . A.; Howard, J . A. K.; Pfeffer, M.; Spencer, J . L.; Stone,
F. G. A.; Woodward, P. J . Chem. Soc., Dalton Trans. 1981, 284.
(13) Hiramatsu, M.; Shiozaki, K.; Fujinami, T.; Sakai, S. J . Orga-
nomet. Chem. 1983, 246, 203.
(14) (a) J ewell, C. F., J r.; Liebeskind, L. S.; Williamson, M. J . Am.
Chem. Soc. 1985, 107, 6715. (b) Liebeskind, L. S.; J ewell, C. F., J r. J .
Organomet. Chem. 1985, 285, 305. (c) Cho, S. H.; Wirtz, K. R.;
Liebeskind, L. S. Organometallics 1990, 9, 3067.
(15) Le Bras, J .; Amouri, H.; Vaissermann, J . Organometallics 1998,
17, 1116.
(18) Rosete, R. O.; Cole-Hamilton, D. J .; Wilkinson, G. J . Chem. Soc.,
Dalton Trans. 1979, 1618.
(19) (a) Oh, M.; Carpenter, G. B.; Sweigart, D. A. Angew. Chem.,
Int. Ed. 2001, 40, 3191. (b) Oh, M.; Carpenter, G. B.; Sweigart, D. A.
Organometallics 2002, 21, 1290.
(20) Davidson, J . L.; Green, M.; Stone, F. G. A.; Welch, A. J . J . Chem.
Soc., Dalton Trans. 1976, 738.
(16) Klein, H.-F.; Auer, E.; Dal, A.; Lemke, U.; Lemke, M.; J ung,
T.; Rohr, C.; Florke, U.; Haupt, H.-J . Inorg. Chim. Acta 1999, 287,
167.
(21) Le Bras, J .; Amouri, H.; Vaissermann, J . J . Organomet. Chem.
1998, 553, 483.
(22) Sun, S.; Carpenter, G. B.; Sweigart, D. A. J . Organomet. Chem.
1996, 512, 257.
(17) Cooke, J .; Takats, J . J . Am. Chem. Soc. 1997, 119, 11088.
10.1021/om020730a CCC: $25.00 © 2003 American Chemical Society
Publication on Web 12/02/2002

78 Organometallics, Vol. 22, No. 1, 2003
Ta ble 1. Rea ction s of 1 w ith p-Qu in on es
Ura et al.
a p-biquinone under mild conditions give novel com-
plexes Ru(η6-cot)(p-quinone) (2) and {Ru(η6-cot)}2(p-
biquinone) (3) in high yields via simple and selective
ligand exchange (method A) between π-acceptors. We
report here the synthesis and structures of a series of
novel p-quinone ruthenium(0) complexes 2 and a unique
p-biquinone bimetallic complex 3.
Resu lts a n d Discu ssion
Ru (η6-cot)(p-qu in on e) (2). As shown in Table 1, the
reactions of 1 with p-quinones were performed in Et2O
at room temperature for 2 h (entry 1), under reflux for
4 h (entries 2-5, 7), and in toluene at 80 °C for 2 h
(entry 6), respectively. The selective ligand exchange
between π-acceptors, dimethyl fumarate and p-quinone,
proceeded smoothly to afford 2 in good to high yield.
Several kinds of p-quinones with an electron-donating
group (entries 2, 3, 6) or an electron-withdrawing group
(entries 4, 5) were found to be suitable for this substitu-
tion reaction, including p-naphthoquinone (entry 7). The
reaction with chloranil (tetrachloro-p-benzoquinone)
also proceeded to give a precipitate; however, spectro-
scopic characterization was impossible because of the
low solubility of the product. The use of DDQ (2,3-
dichloro-5,6-dicyano-p-benzoquinone) gave a complex
mixture of products.
amount of
quinone
reaction pro- yield
entry
R1
R2 R3 R4
(equiv) solvent condition duct (%)a
1
2
3
4
5
6
7
H
H
H
H
H
H
H
H
H
H
Ph H
Cl H
H
H
Me
1.1
1.1
2.2
1.2
1.1
1.1
3.0
Et2O
Et2O
Et2O
Et2O
Et2O
rt, 2 h
2a 98
Me
Me
Ph
Cl
OMe
reflux, 4 h 2b 87
reflux, 4 h 2c 94
reflux, 4 h 2d 64
reflux, 4 h 2e 65
H
H
OMe
toluene 80 °C, 2 h 2f
60
-CHdCH-
CHdCH-
H
Et2O reflux, 4 h 2g 89
a
Isolated yield.
The structures of 2a -2g were deduced on the basis
of cyclobutenedione or benzocyclobutenedione to a low-
valent cobalt complex.14 Iridium and manganese η6-
hydroquinone complexes have been prepared by Amouri
and co-workers15,21 and Sweigart and co-workers,19,22
respectively, taking advantage of method D; η5-semi-
quinone and η4-p-quinone complexes are synthesized.
Recently, we reported a novel zerovalent ruthenium
complex Ru(η6-cot)(dmfm)2 (1; η6-cot ) 1-6-η-cyclooc-
tatriene, dmfm ) dimethyl fumarate).23 Complex 1 was
found to be an excellent catalyst for a unique dimer-
ization of 2,5-norbornadiene to afford a novel half-cage
compound.23 In this catalyst, the coordinated dimethyl
fumarate was found to be crucial as a π-acceptor ligand.
Complex 1 is also a versatile precursor for novel Ru(0)
complexes, as we demonstrated previously.24 In the
course of our further investigation of the reactivity of
1, we found that reactions with various p-quinones and
of H and 13C NMR, IR, and mass spectra. The H and
13C NMR data for 2a -2g are summarized in Tables 2
and 3, respectively. In the 1H NMR spectra of 2, the
signals for the olefinic protons of the 1,3,5-cyclooc-
tatriene moiety appear at 6.6-4.1 ppm, and those for
the methylene protons appear at 2.8-0.1 ppm. The
signals for the olefinic protons of p-quinone ligands in
2 appear at 5.0-5.8 ppm, which are shifted to a higher
magnetic field than those of the corresponding free
p-quinones by 1.5-1.8 ppm. The appearance of these
signals as singlet peaks, except in 2b, suggests that
cyclooctatriene rotates freely on ruthenium at room
temperature in solution. In the 13C NMR spectra of 2,
the carbonyl carbons of the coordinated p-quinones are
observed at 153-159 ppm, which are shifted upfield by
ca. 30 ppm compared with free p-quinones, whereas one
1
1
Ta ble 2. 1H NMR Da ta of 2a -2g (δ, p p m )a
p-quinone
complex
dCH
5.02 (s, 4H)
others
1,3,5-cyclooctatriene
2a
6.33 (m, 2H), 5.56 (br t, 6.8, 2H), 5.04 (m, 2H), 2.22
(m, 2H), 1.00 (m, 2H)
2b
2c
2d
5.16 (s, 1H), 5.00 (m, 2H)
5.09 (s, 2H)
1.82 (s, 3H)
6.20 (m, 2H), 5.42 (br t, 7.4, 1H), 5.38 (br t, 7.4, 1H),
4.90 (m, 2H), 2.19 (m, 2H), 0.95 (m, 2H)
6.04 (dd, 4.9, 2.0, 2H), 5.22 (ddd, 8.3, 4.9, 2.0, 2H), 4.74
(m, 2H), 2.14 (m, 2H), 0.90 (m, 2H)
5.96 (t, 7.3, 1H), 5.61 (m, 1H), 5.50 (t, 8.0, 1H), 5.35
(t, 8.5, 1H), 5.03 (m, 1H), 4.12 (dd, 13.6, 7.4, 1H), 2.29
(m, 1H), 1.53 (m, 2H), 0.09 (m, 1H)
1.82 (s, 6H)
5.59 (s, 2H)
7.36-7.84 (m, 10H)
2e
5.76 (s, 2H)
6.58 (t, 7.4, 1H), 6.19 (t, 8.3, 1H), 5.31 (t, 7.1, 2H),
4.90 (t, 8.8, 1H), 4.80 (dd, 8.0, 14.4, 1H), 2.75 (m, 1H),
1.91 (m, 2H), 0.20 (m, 1H)
2f
5.24 (s, 2H)
5.20 (s, 2H)
3.68 (s, 6H)
6.13 (m, 2H), 5.27 (m, 2H), 4.91 (m, 2H), 2.17 (m, 2H),
0.89 (m, 2H)
5.39 (m, 2H), 4.92 (m, 2H), 4.79 (m, 2H), 1.97 (m, 2H),
0.57 (m, 2H)
2g
8.01 (m, 2H), 7.40 (m, 2H)
a
Measured in CDCl3 at room temperature and 400 MHz. s ) singlet, d ) doublet, t ) triplet, m ) multiplet, br ) broad. Figures in
parentheses are the values of the coupling constants, J H-H (in Hz).

Zerovalent Ruthenium p-Quinone Complexes
Organometallics, Vol. 22, No. 1, 2003 79
Ta ble 3. 13C NMR Da ta of 2a -2g (δ, p p m )a
p-quinone
CdO
complex
CdC (coordinated)
others
1,3,5-cyclooctatriene
99.8, 92.6, 91.1, 32.9
99.9, 99.7, 94.3, 93.2, 91.8, 90.6, 32.9, 32.6
99.9, 94.8, 90.8, 32.6
102.4, 101.9, 97.7, 95.8, 93.2, 87.7, 34.4, 29.7
101.5, 101.4, 100.9, 100.8, 98.3, 90.8, 37.6, 28.6
99.1, 94.7, 91.0, 32.8
2a
2b
2c
2d
2e
2f
83.7
158.6
99.7, 87.2, 82.4, 82.3
97.8, 85.7
97.7, 81.8
103.1, 82.7
132.3, 68.6
109.9, 74.3
158.1, 157.6
158.0, 156.8
158.6
154.2
153.4, 141.3
157.0
15.7
15.7
133.0, 128.8, 128.6, 128.3
56.4
2g
130.2, 125.2
101.8, 95.5, 87.4, 32.0
a
Measured in CDCl3 at room temperature and 100 MHz.
F igu r e 2. Simplified side view of 2f. Hydrogen atoms,
cyclooctatriene, and two methoxy groups are omitted for
clarity. R ) 3.2°, R′ ) 19.0°.
(C9-C10) and an olefinic moiety of 2,5-dimethoxy-p-
benzoquinone (C2-C3), which are located diagonally
from each other, and other olefinic parts of either
cyclooctatriene (C11-C12, C13-C14) or p-quinone (C5-
C6) are located at the three equatorial positions. The
average bond distance between Ru and the four olefinic
carbons of p-quinone is 2.24 Å. On the other hand, the
bond lengths between Ru and the carbonyl carbons of
quinone, i.e., Ru-C1 (2.410(4) Å) and Ru-C4 (2.438(4)
Å), are longer than the average distance by ca. 0.2 Å.
The bond distances of C1-O1 and C4-O2 are 1.258(5)
and 1.251(5) Å, respectively, which are typical lengths
F igu r e 1. ORTEP drawing of 2f. Thermal ellipsoids are
shown at the 30% probability level. Hydrogen atoms are
omitted for clarity. Selected bond distances (Å) and angles
(deg): Ru1-C1 ) 2.410(4), Ru1-C2 ) 2.305(5), Ru1-C3
) 2.238(4), Ru1-C4 ) 2.438(4), Ru1-C5 ) 2.189(4), Ru1-
C6 ) 2.246(4), Ru1-C9 ) 2.210(6), Ru1-C10 ) 2.134(6),
Ru1-C11 ) 2.185(7), Ru1-C12 ) 2.188(6), Ru1-C13 )
2.165(5), Ru1-C14 ) 2.227(6), C2-C3 ) 1.400(6), C5-C6
) 1.416(6), C1-O1 ) 1.258(5), C4-O2 ) 1.251(5), C1-C2-
C3 ) 123.3(4), C2-C3-C4 ) 121.9(4), C3-C4-C5 ) 112.4-
(4), C4-C5-C6 ) 121.6(4), C5-C6-C1 ) 123.8(4), C6-
C1-C2 ) 112.8(4).
in transition-metal p-quinone complexes.5b,14c,15,16,21
A
simplified side view of 2f is shown in Figure 2, where
the boat shape of the p-quinone ligand can be recognized
clearly. The dihedral angles between the plane of four
olefinic carbons C2-C3, C5-C6 and the planes that
include C1, C2, C6 (R) and C3, C4, C5 (R′) are 3.2° and
19.0°, respectively. These angles in transition-metal
p-quinone complexes are normally ∼20°: for example,
CpRh(η4-duroquinone) (23°),5b (π-C9H7)Rh(η4-duroquino-
ne) (25°),5b CpCo(η4-duroquinone) (21°),6 and Cp*Ir(η4-
p-benzoquinone) (16°).15 Since the smallest reported
value is 6.0° in Ni(cod)(duroquinone),4 the 3.2° in
complex 2f is quite unusual. Surprisingly, this dihedral
angle is even smaller than those of semiquinone com-
plexes such as Ru(η6-p-MeC6H4SO3-H2O)(η6-p-OdC6-
Me4OH) (8.7°, 10°)25 and Mn(η5-p-OdC6H4OH)(CO)3
(6.7°, 11.3°).19b
The ambiguity of hapticity is often discussed in
transition-metal p-quinone complexes.11b,19b Scheme 1
shows possible resonance structures 2f-2f ′′. The η4-p-
quinone form (2f) basically gives a large contribution
because the bond lengths of Ru-C2, C3, C5, C6 are ca.
0.2 Å shorter than those of Ru-C1 and C4. However,
the quite small exo-bending (R ) 3.2°) of the plane that
includes C1, C2, and C6 compared to the plane of four
of the two carbonyl carbons in 2f appeared at a higher
field (141.3 ppm). The signals for the olefinic carbons
of p-quinones vary from 68 to 132 ppm depending on
their magnetic environment, and most of them are also
shifted to higher fields because of π-back-bonding from
ruthenium.
The molecular structure of Ru(η6-cot)(2,6-dimethoxy-
p-benzoquinone) (2f) was confirmed by X-ray crystal-
lography, and the ORTEP drawing is shown in Figure
1.
This structure is represented by a highly distorted
trigonal bipyramid and is quite similar to that of 1.23
Figure 1 shows the η4-coordination of the p-quinone
ligand with olefinic carbons. The axial positions are
occupied by an olefinic moiety of 1,3,5-cyclooctatriene
(23) Mitsudo, T.; Suzuki, T.; Zhang, S.-W.; Imai, D.; Fujita, K.;
Manabe, T.; Shiotsuki, M.; Watanabe, Y.; Wada, K.; Kondo, T. J . Am.
Chem. Soc. 1999, 121, 1839.
(24) (a) Suzuki, T.; Shiotsuki, M.; Wada, K.; Kondo, T.; Mitsudo, T.
Organometallics 1999, 18, 3671. (b) Suzuki, T.; Shiotsuki, M.; Wada,
K.; Kondo, T.; Mitsudo, T. J . Chem. Soc., Dalton Trans. 1999, 4231.
(c) Shiotsuki, M.; Suzuki, T.; Kondo, T.; Wada, K.; Mitsudo, T.
Organometallics 2000, 19, 5733.
(25) Koelle, U.; Weisschadel, Chr.; Englert, U. J . Organomet. Chem.
1995, 490, 101.

80 Organometallics, Vol. 22, No. 1, 2003
Ura et al.
Sch em e 1. P ossible Reson a n ces in 2f
olefinic carbons C2, C3, C5, and C6, as described above,
indicates a considerable contribution by an η5-p-semi-
quinone coordination mode (2f ′). The resonance struc-
ture of the hydroquinone dianion (2f ′′) also cannot be
ruled out, since the carbonyl carbons of p-quinones were
shifted upfield by ∼30 ppm in the 13C NMR spectrum
in 2, as reported for p-quinone complexes.9,11a,12a,19b In
the infrared spectra of 2, the ν(CdO) bands of the
quinone ligands appeared at 1550-1610 cm-1, which
are shifted to a lower wavenumber by 50-100 cm-1
compared with those of the corresponding free quinones.
This shift is attributable to π-back-donation from ru-
thenium to quinone and also supports some contribution
from the structure 2f ′′.
Complexes 2 are the first example of zerovalent
ruthenium p-quinone complexes, whereas Wilkinson
and co-workers reported a hydroquinone-bridged diva-
lent ruthenium p-quinone complex by reacting RuH2-
(PPh3)4 with hydroquinone.18 Complexes 2 are generally
moisture-sensitive due to the highly oxophilic ruthe-
nium center caused by the coordinated p-quinones. The
reactivity of 2 toward H2O is dramatically affected by
the substituent on the p-quinone ligand. For example,
complex 2a was readily decomposed by H2O in air. On
the other hand, complex 2f, which has two methoxy
groups at the 2- and 6-positions, does not react with
excess H2O in dioxane even at a high temperature such
as 100 °C.
F igu r e 3. ORTEP drawing of 3. Thermal ellipsoids are
shown at the 30% probability level. Hydrogen atoms are
omitted for clarity. Selected bond distances (Å) and angles
(deg): Ru1-C2 ) 2.152(8), Ru1-C3 ) 2.146(7), Ru1-C8
) 2.20(1), Ru1-C9 ) 2.12(1), Ru1-C10 ) 2.236(9), Ru1-
C11 ) 2.248(9), Ru1-C12 ) 2.18(1), Ru1-C13 ) 2.20(1),
Ru1-O4 ) 2.172(6), C1-C2 ) 1.41(1), C2-C3 ) 1.46(1),
C3-C4 ) 1.45(1), C1-O1 ) 1.278(9), C2-Ru1-C3 )
39.6(3), C2-Ru1-O4 ) 78.3(3), C3-Ru1-O4 ) 84.1(3),
Ru1-C2-C17 ) 105.8(5), Ru1-O4-C16 ) 113.6(5), O1-
C1-C2 ) 120.2(7), C1-C2-C3 ) 120.6(7), C2-C3-C4 )
119.6(7), C6-C1-C2 ) 120.1(7).
{Ru (η6-cot)}2(p-biqu in on e) (3). The reaction of 1
with 0.5 equiv of p-biquinone26 in place of p-quinone
gave a novel Ru(0) bimetallic complex 3 under very mild
conditions, as illustrated in eq 1. η4-Coordinated mono-
metallic or bimetallic complexes that are similar to
complexes 2 did not form at all in this reaction. X-ray
crystallography of 3 was successfully performed, and the
ORTEP drawing is shown in Figure 3. Symmetrical
patterns can be recognized from the top and side views
of 3 (Figure 4).
F igu r e 4. Top and side views of 3.
In complex 3, the coordination mode of the p-quinone
moiety is different from that in 2. One of the two olefinic
parts and an oxygen atom of a carbonyl group of each
p-quinone moiety coordinate to each ruthenium atom
to form stable chelate rings. Two ruthenium atoms are
located on the same side of the twisted p-biquinone
framework. Thus, 3 is a C2-symmetric compound and
the symmetry axis penetrates the center of p-biquinone
vertically. The distance between the two ruthenium

Zerovalent Ruthenium p-Quinone Complexes
Organometallics, Vol. 22, No. 1, 2003 81
atoms is 4.12 Å, and no metal-metal bond exists. The
shorter lengths of Ru1-C2 (2.152(8) Å) and Ru1-C3
(2.146(7) Å) and the greater length of C2-C3 (1.46(1)
Å) in 3 compared to those in 2f reveal that the degree
of π-back-donation in 3 is much greater than that in
2f. The C1-O1 bond length in 3 is 1.278(9) Å, which is
a little longer than that in 2f, mainly due to σ-donation
from O1 to Ru2. The dihedral angle between a p-quinone
plane (C1-C6) and a plane containing Ru1, C2, and C3
is 107.7°. Similarly, the dihedral angle between another
p-quinone plane (C16-C21) and a plane containing Ru2,
C17, and C18 is 108.5°. Thus, ruthenium atoms are not
located over the hexagonal face of quinones. These
quinone planes are twisted relative to each other by
119.1°.
Exp er im en ta l Section
Ma ter ia ls a n d Meth od s. All manipulations were per-
formed under an argon atmosphere using standard Schlenk
techniques. Ru(η6-cot)(dmfm)2 (1) was synthesized as we
reported previously.23 All solvents were distilled under argon
over appropriate drying reagents (sodium, calcium hydride,
sodium-benzophenone, or calcium chloride). 5,5′-Dimethoxy-
2,2′-p-biquinone was prepared as reported in the literature.26
P h ysica l a n d An a lytica l Mea su r em en ts. NMR spectra
were recorded on J EOL EX-400 (FT, 400 MHz (1H), 100 MHz
(13C)) and AL-300 (FT, 300 MHz (1H), 75 MHz (13C)) spectrom-
eters. Chemical shift values (δ) for 1H and 13C are referenced
to internal solvent resonances and reported relative to SiMe4.
NMR data for 2a -2g are summarized in Table 2 (1H) and
Table 3 (13C). IR spectra were recorded on a Nicolet Impact
410 FT-IR spectrometer. Melting points were determined
under argon on a Yanagimoto micro melting point apparatus.
HR-MS spectra were recorded on J EOL SX102A spectrometers
with m-nitrobenzyl alcohol (m-NBA) as a matrix.
Syn th esis of Ru (η6-cot)(p-qu in on e), 2a -2g. All of the
p-quinone complexes 2a -2g were synthesized in a similar
manner. The following procedure for 2a is representative.
Ru (η6-cot)(p-ben zoqu in on e), 2a . A mixture of 100 mg
(0.20 mmol) of Ru(η6-cot)(dmfm)2 (1), 24 mg (0.22 mmol) of
p-benzoquinone, and 5 mL of Et2O was stirred at room
temperature for 2 h. The resulting pale yellow precipitate was
filtered, rinsed with Et2O (5 mL × 5), and dried under vacuum
to give the title complex (67 mg, 98%), mp 122 °C (dec). IR
(CHCl3): 1600, 1573 cm-1. HR-MS(FAB-mNBA): m/z 317.0114
(M + H)+, calcd for C14H15O2Ru 317.0116.
1
In the H NMR spectrum of 3, the olefinic protons on
C3 and C18 appear at 3.68 ppm, which are considerably
shifted to a higher field. A characteristic downfield
signal was observed at 202.2 ppm in the 13C NMR,
which was assignable to carbonyl carbons C1 and C16.
The olefinic carbons of the p-biquinone ligand attached
to the ruthenium, C2, C17 and C3, C18, appeared at
69.3 and 53.6 ppm, respectively.
A couple of chelations in complex 3 cooperate to
strengthen the binding of the p-biquinone ligand to each
ruthenium atom. An attempt to form a monometallic
p-biquione complex by reacting 1 with 1 equiv of
p-biquinone resulted in failure and gave only the
bimetallic complex 3. This is because the monometallic
p-biquinone complex can easily capture a second ruthe-
nium by an appropriately located chelation system
which was fixed by the first chelation, and as a result,
a more stable bimetallic species 3 is formed. Although
several transition-metal p-quinone complexes have been
synthesized so far, such a p-biquinone-coordinated
bimetallic complex is unprecedented, to the best of our
knowledge.
In contrast to the case of complex 1, reactions of Ru-
(η4-cod)(η6-cot) (η4-cod ) η4-1,5-cyclooctadiene), which
is a precursor of 1, with p-quinones and p-biquinone
gave only insoluble materials and did not afford 2 or 3
at all, respectively. This suggests that a π-acidic di-
methyl fumarate ligand in 1 is required to control the
electron density of ruthenium during substitution by
p-quinones or p-biquinone. In the case of Ru(η4-cod)(η6-
cot), the relatively electron-rich ruthenium center may
donate the d-electrons and reduce the coordinated
p-quinone to a semiquinone anion or a hydroquinone
dianion species.
Ru (η6-cot)(p-tolu qu in on e), 2b: pale yellow solid, mp 117
°C (dec). IR (CHCl3): 1597, 1568 cm-1. HR-MS(FAB-mNBA):
m/z 331.0246 (M + H)+, calcd for C15H17O2Ru 331.0272.
Ru (η6-cot)(2,6-d im eth yl-p-ben zoqu in on e), 2c: pale yel-
low solid, mp 144 °C (dec). IR (KBr disk): 1583, 1558, 1551
cm-1. HR-MS(FAB-mNBA): m/z 345.0457 (M + H)+, calcd for
C
16H19O2Ru 345.0429.
Ru (η6-cot)(2,5-d ip h en yl-p-ben zoqu in on e), 2d : pale yel-
low solid, mp 233 °C (dec). IR (KBr disk): 1606, 1584 cm-1
.
HR-MS(FAB-mNBA): m/z 469.0766 (M + H)+, calcd for
C
26H23O2Ru 469.0742.
Ru (η6-cot)(2,5-dich lor o-p-ben zoqu in on e), 2e: brown solid,
mp 221 °C (dec). IR (KBr disk): 1604 cm-1. HR-MS(FAB-
mNBA): m/z 384.9356 (M + H)+, calcd for C14H13Cl2O2Ru
384.9336.
Ru (η6-cot)(2,6-dim eth oxy-p-ben zoqu in on e), 2f: pale yel-
low solid, mp 172 °C (dec). IR (KBr disk): 1579, 1545 cm-1
.
HR-MS(FAB-mNBA): m/z 377.0312 (M + H)+, calcd for
C
16H19O4Ru 377.0327.
Ru (η6-cot)(p-n a p h th oqu in on e), 2g: brown solid, mp 300
°C (dec). IR (Nujol): 1567 cm-1. HR-MS(FAB-mNBA): m/z
367.0291 (M + H)+, calcd for C18H17O2Ru 367.0272.
Syn th esis of {Ru (η6-cot)}2(5,5′-dim eth oxy-2,2′-p-biqu in o-
n e), 3. To an Et2O suspension (5 mL) of 5,5′-dimethoxy-2,2′-
p-biquinone (69 mg, 0.25 mmol) was added a CH2Cl2 solution
(5 mL) of 1 (248 mg, 0.50 mmol) dropwise at 0 °C. The reaction
mixture immediately turned black and was warmed to room
temperature. After stirring for 1 h, the solvent was removed,
and then CH2Cl2 (1.5 mL) and Et2O (18 mL) were added for
recrystallization. The resulting black powder was filtered,
washed with Et2O (3 mL × 2), and dried under vacuum to give
complex 3 (109 mg, 63%), mp 225-227 °C (dec). IR (CHCl3):
Con clu sion
Novel zerovalent ruthenium complexes 2 and 3,
bearing either p-quinone or p-biquinone as π-acceptors,
were synthesized by simple and selective ligand ex-
change of 1. Since complexes 2 and 3 are a potentially
electron-rich species and also have electron-accepting
systems, versatile catalytic activities are expected.
Complex 3 has two electron-rich reaction sites located
close together without a metal-metal bond, and this
unique structure should provide novel catalytic reac-
tions.
1
1672, 1621 cm-1. H NMR (400 MHz, CDCl3): δ 6.66 (dd, J )
8.8 and 5.3 Hz, CH of cot, 2H), 6.17 (t, J ) 8.8 Hz, CH of cot,
2H), 5.52 (m, CH of cot, 2H), 5.25 (s, CH at 6 and 6′-positions
of biquinone, 2H), 4.74 (t, J ) 9.3 Hz, CH of cot, 2H), 4.33 (t,
J ) 6.6 Hz, CH of cot, 2H), 3.68 (s, CH at 3 and 3′-positions of
biquinone, 2H), 3.60 (s, OCH3, 6H), 2.70 (q, J ) 7.3 Hz, CH of
cot, 2H), 2.17 (m, CHH of cot, 2H), 1.64 (m, CHH of cot, 2H),
1.02 (m, CHH of cot, 2H), -0.64 (m, CHH of cot, 2H). 13C NMR
(26) J acob, P., III; Callery, P. S.; Shulgin, A. T.; Castagnoli, N., J r.
J . Org. Chem. 1976, 41, 3627.

82 Organometallics, Vol. 22, No. 1, 2003
Ura et al.
Ta ble 4. Su m m a r y of Cr ysta l Da ta , Collection
Da ta , a n d Refin em en t of 2f a n d 3
radiation (λ ) 0.71069 Å). The structures were solved by direct
methods using SIR9227 and expanded using Fourier tech-
niques, DIRDIF99.28 The non-hydrogen atoms were refined
anisotropically, except for an oxygen atom of a lattice water
in 2f, which was refined isotropically. Hydrogen atoms were
refined using the riding model. Neutral atom-scattering factors
were taken from Cromer and Waber.29 Anomalous dispersion
2f
3
formula
fw
C
16H18O4Ru‚H2O
C30H30O6Ru2‚CH2Cl2
773.64
393.40
cryst color
habit
yellow
prismatic
black
platelet
effects were included in Fcalc;
30 the values for ∆f ′ and ∆f′′ were
cryst size, mm
cryst syst
space group
a, Å
b, Å
c, Å
0.20 × 0.10 × 0.10 0.35 × 0.20 × 0.10
those of Creagh and McAuley.31 The values for the mass
attenuation coefficients were those of Creagh and Hubbell.32
All calculations were performed using the CrystalStructure33,34
crystallographic software package.
orthorhombic
Pbca
monoclinic
P21/n
10.5230(3)
13.5805(3)
20.7004(5)
10.7583(5)
23.2869(9)
11.4630(7)
103.372(2)
2793.9(2)
4
â, deg
Ack n ow led gm en t. This work was supported in part
by Grants-in-Aid for Scientific Research from the Min-
istry of Education, Science, Sports and Culture, J apan.
V, Å3
2958.2(1)
8
Z
D(calcd), g cm-3
data collection
temp, °C
µ (Mo KR), cm-1
2θ max, deg
1.766
-50
1.839
-130
Su p p or tin g In for m a tion Ava ila ble: Description of the
X-ray procedures, tables of X-ray data, positional and thermal
parameters, and bond lengths and angles, and an ORTEP
diagram for compounds 2f and 3. This material is available
free of charge via the Internet at http://pubs.acs.org.
10.82
54.9
13.18
54.9
24 764
no. of measd reflns 28 298
no. of unique reflns 3371 (Rint ) 0.057) 6377 (Rint ) 0.042)
no. of obsd reflns
(I > 3.00σ(I))
no. of variables
Ra
1948
5076
OM020730A
212
403
0.026
0.030
0.43
0.056
0.073
1.61
(27) Altomare, A.; Cascarano, G.; Giacovazzo, C.; Guagliardi, A.;
Burla, M.; Polidori, G.; Camalli, M. J . Appl. Crystallogr. 1994, 27, 435.
(28) Beurskens, P. T.; Admiraal, G.; Beurskens, G.; Bosman, W. P.;
de Gelder, R.; Israel, R.; Smits, J . M. M. The DIRDIF-99 program
system; Technical Report of the Crystallography Laboratory: Univer-
sity of Nijmegen, Netherlands, 1999.
a
Rw
GOF
a
2 1/2
R ) ∑||Fo| - |Fc||/∑|Fo|; Rw ) [∑w(|Fo| - |Fc|)2/∑wFo
] .
(29) Cromer, D. T.; Waber, J . T. International Tables for X-ray
Crystallography; The Kynoch Press: Birmingham, England, Vol. IV,
1974.
(30) Ibers, J . A.; Hamilton, W. C. Acta Crystallogr. 1964, 17, 781.
(31) Creagh, D. C.; McAuley, W. J . International Tables for X-ray
Crystallography; Kluwer Academic Publishers: Boston, Vol. C, 1992.
(32) Creagh, D. C.; Hubbell, J . H. International Tables for X-ray
Crystallography; Kluwer Academic Publishers: Boston, Vol. C, 1992.
(33) CrystalStructure 2.00, Crystal Structure Analysis Package;
Rigaku and MSC, 2001.
(100 MHz, CDCl3): δ 202.2, 191.4, 161.9, 105.9, 105.0, 101.6,
92.2, 87.0, 86.2, 69.3, 66.0, 56.4, 53.6, 33.2, 25.3. HR-MS(FAB-
mNBA): m/z 690.0134 (M)+, calcd for C30H30O6Ru2 690.0129.
Cr ysta llogr a p h ic Stu d y of Com p lexes 2f a n d 3. Single
crystals of complexes 2f and 3 obtained by recrystallization
from CHCl3/pentane (2f) or CH2Cl2/pentane (3) were subjected
to X-ray crystallographic analysis. The crystal data and
experimental details for 2f and 3 are summarized in Table 4.
All measurements were made on a Rigaku RAXIS imaging
plate area detector with graphite-monochromated Mo KR
(34) Watkin, D. J .; Prout, C. K.; Carruthers, J . R.; Betteridge, P.
W. CRYSTALS Issue 10; Chemical Crystallography Laboratory: Ox-
ford, UK.