Synthesis and property of diruthenium complexes containing bridging cyclic diene ligands and the reaction of diruthenium tetrahydrido complex with benzene forming a μ-η2:η2-cyclohexadiene complex via partial hydrogenation on a Ru2 center

Article abstract of DOI:10.1021/om200728e

The syntheses, structures, and reactivities of diruthenium complexes having a five-, six-, and seven-membered cyclic diene ligands are discussed in this paper. While the μ-η²:η²-cyclohexadiene complex 3 was readily prepared by the reaction of the diruthenium tetrahydrido complex 1 with 1,3-cyclohexadiene, 3 was alternatively synthesized by the reaction of 1 with benzene via partial hydrogenation of benzene on a diruthenium plane. While the μ-η²:η²-cyclohexadiene ligand was liberated as benzene upon mild heating, the treatment of 3 with ^tBuNC and CO caused further migration of hydrido ligand to the C₆ moiety to yield the μ-η²-cyclohexenyl complex 6 and the μ-cyclohexylidene complex 8, respectively. The reactions of 1 with cyclopentadiene and cycloheptatriene also afforded the bridging cyclic diene complexes 10 and 11. While the thermolysis of the μ-η²:η²- cyclopentadiene complex 10 resulted in the degradation of the cluster skeleton forming Cp*RuCp (12), the μ-η²:η²- cycloheptadiene complex 11 was stable upon heating. These differences can be attributed to the aromatization of the cyclic diene moiety.

Full text of DOI:10.1021/om200728e

ARTICLE
pubs.acs.org/Organometallics
Synthesis and Property of Diruthenium Complexes Containing
Bridging Cyclic Diene Ligands and the Reaction of Diruthenium
Tetrahydrido Complex with Benzene Forming a μ-η2:η2-
Cyclohexadiene Complex via Partial Hydrogenation on a Ru2 Center
Toshiro Takao, Nozomi Obayashi, Bo Zhao, Kazunori Akiyoshi, Hideki Omori, and Hiroharu Suzuki*
Department of Applied Chemistry, Graduate School of Science and Engineering, Tokyo Institute of Technology, 2-12-1 O-okayama,
Meguro-ku, Tokyo 152-8552, Japan
S Supporting Information
b
ABSTRACT: The syntheses, structures, and reactivities of diruthe-
nium complexes having a five-, six-, and seven-membered cyclic
diene ligands are discussed in this paper. While the μ-η2:η2-
cyclohexadiene complex 3 was readily prepared by the reaction of the
diruthenium tetrahydrido complex 1 with 1,3-cyclohexadiene, 3 was
alternatively synthesized by the reaction of 1 with benzene via partial
hydrogenation of benzene on a diruthenium plane. While the μ-
η2:η2-cyclohexadiene ligand was liberated as benzene upon mild
t
heating, the treatment of 3 with BuNC and CO caused further
migration of hydrido ligand to the C6 moiety to yield the μ-η2-
cyclohexenyl complex 6 and the μ-cyclohexylidene complex 8,
respectively. The reactions of 1 with cyclopentadiene and cyclohep-
tatriene also afforded the bridging cyclic diene complexes 10 and 11.
While the thermolysis of the μ-η2:η2-cyclopentadiene complex 10 resulted in the degradation of the cluster skeleton forming
Cp*RuCp (12), the μ-η2:η2-cycloheptadiene complex 11 was stable upon heating. These differences can be attributed to the
aromatization of the cyclic diene moiety.
Scheme 1. Formation and Reactivity of μ-Phosphido:
μ-η2:η2-benzene Complex 2
’ INTRODUCTION
The properties of aromatic molecules coordinated to a multi-
metallic center have attracted considerable attention in relation
to catalytic reactions performed on a metal surface.1 Many
bimetallic2 and trimetallic complexes2d,3 having arene ligands
have been synthesized thus far, and studies on these complexes
provide important information about the structures and reactiv-
ities of adsorbed aromatic molecules in addition to the recent
developments in surface chemistry; these studies afford high-
resolution images of aromatic molecules adsorbed on a metal
surface.4
Previously, we reported a reaction of a diruthenium tetrahy-
drido complex, Cp*Ru(μ-H)4RuCp* (Cp* = η5-C5Me5) (1),
with triphenylphosphine to yield a diruthenium μ-phosphido
complex, (Cp*Ru)2(μ-PPh2)(μ-H)(μ-η2:η2-C6H6) (2), as a
result of a PꢀC bond cleavage (Scheme 1).5 Complex 2 has a
bridging benzene ligand, which adopts a μ-η2:η2-coordination
mode. The bridging benzene ligand of 2 is readily substituted by
other aromatic molecules such as toluene, which is used as a
solvent. Similarly, 2 reacts with 2,20-bipyridine to form a μ-η2:η2-
bipyridine complex.6 This μ-bipyridine complex would be
present in the catalytic cycle of the dehydrogenative coupling
of pyridines. A facile exchange of the μ-η2:η2-arene probably
occurs because of the recovery of aromaticity of the coordinated
arene molecule, and this arene exchange is a crucial step of the
catalytic cycle.
While the reaction of the triruthenium pentahydrido complex
{Cp*Ru(μ-H)}3(μ3-H)2 with benzene and pyridine affords a
face-capping arene complex,3d,7 reactivities of 1 with benzene
Received: August 4, 2011
Published: August 26, 2011
r
2011 American Chemical Society
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have not been studied in detail thus far. Since 1 catalyzes the
dehydrogenative coupling of 4-substituted pyridines,6 complex 1
is expected to be able to activate aromatic molecules as the
triruthenium complex does. In this article, we report the reaction
of 1 with benzene. The treatment of 1 with benzene resulted in
the formation of a μ-η2:η2-cyclohexadiene complex, {Cp*Ru(μ-
H)}2(μ-η2:η2-C6H8) (3), instead of a μ-benzene complex due to
the partial hydrogenation of benzene on a bimetallic center.
Complex 3 is alternatively synthesized by the reaction of 1 with
cyclohexadiene. This method is applied to the synthesis of other
cyclic diene complexes, and the properties of the μ-η2:η2-diene
complexes having a five-, six-, or seven-membered ring are also
mentioned in this article.
Figure 1. Molecular structure of 3 with thermal ellipsoids at the 30%
level of probability.
’ RESULTS AND DISCUSSION
similar structural properties in the unit cell, only one molecule is
shown in Figure 1. Selected bond distances and angles are listed
in Table 1. Multimetallic complexes containing a μ-η2:η2-cyclo-
hexadiene ligand have been known to exist; however, their
examples are still limited.10
While a μ-arene ligand was formed on the bimetallic center of
2, μ-cyclohexadiene complex 3 was formed upon treatment of 1
with benzene at 70 °C (eq 1). Complex 3 was formed via partial
hydrogenation of an aromatic ring on the bimetallic center of 1.
Such a facile hydrogenation of benzene was unexpected. This is
probably due to the electron-rich nature of the metal centers
composed of [Cp*Ru] units. Upon coordination, the C6 moiety
would effectively stabilize the bimetallic system as diene rather
than benzene due to a strong back-donation. However, this
stabilization is in competition with the recovery of aromatization.
When 3 was heated in tetrahydrofuran (THF), complex 1 was
completely regenerated with the elimination of benzene. This
implies that complex 3 was equilibrated with 1 via the elimination
of benzene. This equilibrium was also confirmed by the H/D
exchange of the C6 fragment upon mild thermolysis of 3 in C6D6.
Upon heating at 70 °C, the benzene solution of 1 equilibrated
with 3 in 72 h. At that point, the ratio of 1 to 3 was estimated at ca.
1:17. Because of the thermal instability of 1, the formation of a
small number of polymetallic hydrido clusters, {Cp*Ru(μ-H)}3-
(μ3-H)2 (7%)8 and (Cp*Ru)4(H)6 (10%),9 was also observed
during the reaction. Complex 3 was isolated in 61% yield from
the mixture by using column chromatography. Complex 3 was
fully characterized by the 1H and 13C NMR spectroscopy.
The two Cp* groups are attached to the metal centers in a cis
geometry with respect to the RuꢀRu vector similar to a
precedent μ-η2:η2-cyclohexadiene complex having indenyl
groups.10a Complex 3 adopts a coordinatively unsaturated
32-electron configuration; thus, a RudRu double bond is
anticipated according to the EAN rule. The value of the dis-
tance between the two ruthenium atoms (2.7391(15) Å) is in
the upper limit of the reported values for a RudRu bond
(2.257ꢀ2.767 Å).11 The elongation of the RudRu distance is
ascribed to the ring size of the bridging diene moiety. As will
be mentioned later, the RudRu distance is increased to
2.7833(4) Å upon the bridging coordination of a seven-
membered ring in 11, while that of μ-cyclopentadiene com-
plex 10 is reduced to 2.692(6) Å.
Upon the η2:η2-coordination of the cyclohexadiene ligand,
the six-membered ring is folded around the C(1)ꢀC(4) vector
and the dihedral angle between the C(1)ꢀC(2)ꢀC(3)ꢀC(4)
and C(1)ꢀC(4)ꢀC(5)ꢀC(6) planes is estimated at ca. 10°.
The length of the coordinated CdC bond is on average 1.44 Å,
which is less than the inner C(2)ꢀC(3) distance by ca. 0.03 Å.
These results suggest a localization of the π-electrons at
C(1)ꢀC(2) and C(3)ꢀC(4) bonds as seen in the precedent
μ-η2:η2-diene complexes.10,12
In the 1H NMR spectrum of 3, a signal derived from the Cp*
groups was observed at δ 1.77 ppm. This shows that complex 3
has a time-averaged structure containing a pseudo mirror plane
bisecting the RudRu bond as well as the μ-cyclohexadiene
ligand. Two sharp signals assignable with the hydrido ligands
were observed at δ ꢀ9.00 (Ha) and ꢀ22.88 (Hb) ppm with 4.8
Hz spinꢀspin coupling between each other. The shapes of these
signals did not change and were still sharp up to 80 °C, which
indicates that the site exchange between the hydrido ligands
within the NMR time scale was unimportant.
Four signals for the cyclohexadiene moiety were observed in
the 1H NMR spectrum, as shown in Chart 1. Among them, the
protons derived from the diene moiety resonated at δ 4.98 and
3.43 ppm. These resonances considerably shifted toward a higher
magnetic field than those of the free 1,3-cyclohexadiene, and the
chemical shifts are comparable to those of the precedent μ-1,
3-cyclohexadine complexes.10 Signals for the methylene moieties
Complex 3 is alternatively synthesized by the reaction of 1
with a slightly excess amount of 1,3-cyclohexadiene at an ambient
temperature with the elimination of dihydrogen. In this case, the
reaction proceeded quantitatively, and 3 was isolated in 82%
yield (eq 2). The reaction of 1 with 1,4-cyclohexadiene also
afforded the μ-1,3-cyclohexadiene complex 3 via the isomeriza-
tion of 1,4-cyclohexadiene (vide infra).
The formation of a 1,3-cyclohexadiene ligand, which adopts a
μ-η2:η2-coordination mode, was confirmed by an X-ray diffraction
study. Because there were two independent molecules having
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Table 1. Selected Bond Distances (Å) and Angles (deg) for 3
Ru(1)ꢀRu(2)
Ru(2)ꢀC(3)
C(1)ꢀC(6)
2.7391(15)
2.257(16)
1.534(19)
1.560(19)
2.7406(17)
2.221(15)
1.54(2)
Ru(1)ꢀC(1)
Ru(2)ꢀC(4)
C(2)ꢀC(3)
2.194(15)
2.202(14)
1.463(18)
1.550(19)
2.217(13)
2.234(15)
1.47(2)
Ru(1)ꢀC(2)
C(1)ꢀC(2)
C(3)ꢀC(4)
2.241(15)
1.48(2)
1.421(19)
C(4)ꢀC(5)
C(5)ꢀC(6)
Ru(3)ꢀRu(4)
Ru(4)ꢀC(29)
C(27)ꢀC(32)
C(30)ꢀC(31)
Ru(3)ꢀC(27)
Ru(4)ꢀC(30)
C(28)ꢀC(29)
C(31)ꢀC(32)
Ru(3)ꢀC(28)
C(27)ꢀC(28)
C(29)ꢀC(30)
2.245(16)
1.42(2)
1.42(2)
1.53(2)
1.57(2)
C(1)ꢀRu(1)ꢀC(2)
C(2)ꢀC(1)ꢀC(6)
38.9(5)
122.2(12)
120.5(14)
115.4(11)
37.2(5)
C(3)ꢀRu(2)ꢀC(4)
C(1)ꢀC(2)ꢀC(3)
37.2(5)
119.1(14)
123.6(12)
116.4(12)
37.2(5)
C(2)ꢀC(3)ꢀC(4)
C(3)ꢀC(4)ꢀC(5)
C(4)ꢀC(5)ꢀC(6)
C(1)ꢀC(6)ꢀC(5)
C(27)ꢀRu(3)ꢀC(28)
C(28)ꢀC(27)ꢀC(32)
C(28)ꢀC(29)ꢀC(30)
C(30)ꢀC(31)ꢀC(32)
C(29)ꢀRu(4)ꢀC(30)
C(27)ꢀC(28)ꢀC(29)
C(29)ꢀC(30)ꢀC(31)
C(27)ꢀC(32)ꢀC(31)
124.5(14)
120.2(15)
117.1(13)
119.2(14)
123.4(14)
113.5(13)
Chart 1. Selected 1H NMR Data of 3
Figure 2. 1H NMRspectraof3measured at 80 °C showing the methylene
region: (a) without irradiation, (b) irradiation at δ ꢀ22.92 ppm.
appeared at δ 2.14 and 1.22 ppm, which are assignable to the exo-
and endo-H, respectively.
Because of the magnetic inequivalence, the 1H signals of the
bridging cyclohexadiene moiety showed complicated coupling
patterns. By the computer simulation, we evaluated the coupling
constants among these protons (complete details of the simula-
tion are summarized in the Supporting Information). The value
of the geminal coupling constant between the exo-H (δ 2.14) and
the endo-H (δ 1.22) was evaluated at ꢀ14.6 Hz. As will be
mentioned later, a spinꢀsaturationꢀtransfer phenomenon was
observed only between the methylene signal at δ 1.22 and the
hydrido signal at δ ꢀ22.88. This enables us to assign the signal at
δ 1.22 to endo-H, and the position of Hb is found to be below
the methylene carbons. As seen in Figure 2a, the signal for the
exo-H exhibited a more complicated coupling pattern than
that for the endo-H because of the long-range coupling with Hb
(4J = 1.35 Hz). A similar long-range coupling with a hydrido
ligand was also observed for the μ3-dimetalloallyl complex: a
Scheme 2. Plausible Mechanism of the Site-Exchange be-
tween endo-H and Hb in 3
complex 10 and its iron analogue,14 in which the magnitude of
4JHꢀH was estimated to be 7.8 and 6.3 Hz, respectively.
Although the site exchange between the hydrido ligands was
negligible within the NMR time scale, another fluxional process
arising from the motion of Hb was observed. Upon irradiation
of Hb at 80 °C, the intensity of the endo-H signal decreased by
ca. 80%, while those of the exo-H and Ha remained unchanged.
methine proton at the 2-position of the dimetalloallyl group
4
exhibited J coupling with a hydrido ligand (0.5ꢀ3.5 Hz).13
A
similar but considerably large long-range coupling between the
endo-H and the hydride was observed in μ-η2:η2-cyclopentadiene
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Scheme 3. Plausible Mechanism for the Formation of μ-η2:η2-Cyclohexadiene Complex 3
(Figure 2b). This clearly proves that the site exchange occurred
only between Hb and the endo-H.
center would afford the μ-cyclohexadienyl complex 4, which
would easily isomerize to the μ-1,3-cyclohexadiene complex 3.
This site exchange can be rationalized by the formation of a μ-
η3:η2-cyclohexadienyl intermediate 4; this formation involves
oxidative addition of one of the endo-CꢀH bonds (Scheme 2).
Whereas complex 3 adopted a coordinatively unsaturated 32-
electron configuration, intermediate 4 formally adopted a co-
ordinatively saturated 34-electron configuration. A related bime-
tallic complex, which possesses a μ-η3:η2-cyclohexadienyl ligand,
was known and structurally characterized.15
The facile elimination of benzene from 3 suggests the possi-
bility of catalytic dehydrogenation of cyclohexadiene using 1 as
a catalyst. The reaction of 1 with 16 equiv amounts of 1,
3-cyclohexadiene was then examined; the reaction carried out at
70 °C for 8 h resulted in the formation of benzene in 26% yield
(eq 3). The yields of cyclohexene and cyclohexane that were
formed in the reaction were as low as 0.8% and less than 0.1%,
respectively. These facts clearly indicate that cyclohexadiene did
not act as a hydrogen acceptor. The formation of dihydrogen was
confirmed by the GLC analysis of the gas phase.
If the μ-cyclohexadiene ligand in 3 was liberated as cyclohex-
adiene or cyclohexene, complex 1 could have catalyzed the partial
hydrogenation of benzene upon treatment with dihydrogen. The
liberation of 1,3-cyclohexadiene from a bimetallic center was
observed for {CpV(μ-H)}2(μ-η4:η4-C6H6) (Cp = C5H5) upon
treatment with CO as a result of the migration of hydrido ligands
onto the C6 fragments.2b However, the liberation of cyclohex-
adiene or cyclohexene from 3 was not observed during the
hydrogenation of 3; the treatment of 3 with pressurized dihydro-
gen (10 atm) resulted in the quantitative regeneration of
the tetrahydrido complex 1 with a concomitant formation of
benzene caused probably by the equilibrium between 1 and 3 as
shown in eq 1.
A partially deuterated μ-cyclohexadiene complex, 3-d2, was
prepared by the reaction of 1-d416 with 1,3-cyclohexadiene. The
1
1H NMR spectrum of 3-d2 showed the incorporation of H
atoms into both the hydrido positions, Ha and Hb, with the same
amount (0.25 H) and a decrease in the intensity of the endo-H
signal by 25%. The incorporation of deuterium atoms into other
positions, especially the exo-H position, was not observed. This
result also strongly supports the formation of the μ-η3:η2-
cyclohexadienyl intermediate 4. The slower site exchange pro-
cess between Ha and Hb would cause the incorporation of
protons at the both hydrido positions.
The elimination of the μ-η2:η2-cyclohexadiene ligand in 3 as
benzene is possibly due to the stabilization arising from aroma-
tization. Further migration of the allylic proton of the μ-
cyclohexadienyl intermediate 4 onto the metal center led to
the formation of a benzene ligand, which would readily eliminate
from the metal center and regenerate the tetrahydrido complex 1.
This process is the reverse of the formation of 3 by the reaction of
1 with benzene via the formation of the μ-η3:η2-cyclohexadienyl
intermediate 4 (Scheme 3).
The intermediate 4 can also be formed by the reaction of 1
with 1,4-cyclohexadiene. A 1,4-diene coordination to a bimetallic
center was found in a μ-η2:η2-1,4-benzoquinone complex, which
was obtained by the reaction of 1 with benzoquinone.17 There-
fore, it is reasonable to assume that 1,4-diene complex 5 is
produced by the reaction of 1 with 1,4-cyclohexadiene at first.
The subsequent migration of an allylic proton onto the metal
We, then, examined the reaction of 3 with tert-butylisocyanide.
In this case, the elimination of the C6 moiety was suppressed, and
the μ-η2-cyclohexenyl complex 6 was obtained in 88% yield
(eq 4). The formation of 6 was rationalized by the insertion of
one of the CdC bonds into a RuꢀH bond. During this reaction,
the tetraisocyanido complex 7 was also formed as a consequence
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center. Since the cyclohexenyl moiety is π-bonded to Ru(1), the
back-donation to the isocyanido group on Ru(1) is considerably
reduced. The difference in the magnitude of back-donation is
also reflected in the bond distances around CꢀN and RuꢀC
bonds; the N(2)ꢀC(12) bond is longer than N(1)ꢀC(7) by
0.04 Å, and Ru(2)ꢀC(12) is shorter than Ru(1)ꢀC(7) by 0.05
Å. These data are consistent with the enhanced back-donation
from Ru(2) to the π*(CN) orbital. These isocyanido groups are
also distinguished from each other by IR spectroscopy. In the IR
spectrum of 6, two sharp adsorptions are seen at 2045 and
1838 cmꢀ1, which are assignable to ν(CN) of the linear and the
bent isocyanido groups, respectively.
Figure 3. Molecular structure of 6 with thermal ellipsoids at the 30%
level of probability.
of the elimination of the cyclohexadiene ligand; however, the
amount of 7 was considerably low.18
The reaction of 3 with the isoelectronic CO was also inves-
tigated. Because of its small size, three molecules of CO were
incorporated into the bimetallic center, which caused further
migration of the hydrido ligand onto the C6 moiety. The
treatment of 3 with 1 atm of CO resulted in the formation of a
μ-cyclohexylidene complex, {Cp*Ru(CO)}2(μ-C6H10)(μ-CO)
(8), in 47% yield (eq 5). The formation of a considerable amount
of {Cp*Ru(CO)(μ-CO)}2 (9) was also observed. Complex 8 did
not react with CO even under forced conditions. This shows that
these complexes are formed independently, and the formation of
9 was rationalized by the reaction of the regenerated complex 1
with CO.
The molecular structure of 8 was confirmed by an X-ray
diffraction study as shown in Figure 4, which clearly shows the
formation of a μ-cyclohexylidene ligand. Two of the three CO
ligands are coordinated as terminal ligands in a trans geometry
with respect to the RuꢀRu vector, and the third CO molecule
bridges the two ruthenium centers. The Ru(1)ꢀRu(2) distance
(2.7569(6) Å) is typical for a RuꢀRu single bond, which
makes each ruthenium center coordinatively saturated accord-
ing to the EAN rule. The sum of the interior angles of the
Ru2C2 core is 359.9°, and the Ru(1), Ru(2) C(1), and C(7)
atoms are coplanar.
The formation of a μ-cyclohexylidene ligand was rationalized
as shown in Scheme 4. Because CO closely resembles tBuNC, it is
reasonable to consider the μ-cyclohexenyl intermediate A. The
intermediate A equilibrates with isomeric vinyl intermediate B,
which would be formed via the oxidative addition of an olefinic
CꢀH bond and the consecutive reductive CꢀH bond formation.
The insertion of the CdC bond into a RuꢀH bond afforded a
coordinatively unsaturated μ-cyclohexylidene intermediate,
which captured the third CO molecule to form 7.
In the 1H NMR spectrum of 6, the two signals derived from
the Cp* groups resonated at δ 1.84 and 2.05 ppm, respectively;
this shows that the two ruthenium centers have inequivalent
environments. The signal for the hydrido ligand was observed at
δ ꢀ13.57 ppm with the intensity of 1 H. These results indicate
that one of the two hydrido ligands in 3 migrates to the
cyclohexadiene ligand to form a μ-cyclohexenyl ligand. The signal
for the σ-bonded carbon of the cyclohexenyl moiety appeared in
a significantly higher magnetic field and resonated at δ 4.3 ppm
(d, JCꢀH = 138 Hz). The formation of a μ-cyclohexenyl ligand
was also unambiguously confirmed by an X-ray diffraction study
using the orange single crystal obtained from the cold pentane
solution.
The molecular structure of 6 is shown in Figure 3, and selected
bond distances and angles are listed in Table 2. The C(2)
and C(3) atoms are π-bonded to Ru(1), and the C(1) atom is
σ-bonded to Ru(2). Each ruthenium atom adopts a three-legged
piano stool structure with the hydrido, isocyanide, and cyclohex-
enyl group. The two tert-butylisocyanido ligands are coordinated
in a trans geometry with respect to the RuꢀRu vector.
The relevant cyclic diene complexes were also synthesized by
the reaction of 1 with cyclopentadiene and cycloheptatriene
(eqs 6 and 7). In the reaction of 1 with cycloheptatriene, the
μ-cycloheptadiene complex 11 was obtained as a consequence
of hydrogenation. Complexes 10 and 11 were characterized
While the isocyanido group on Ru(1) is linear, that on Ru(2)
adopts a bent structure; the angles C(7)ꢀN(1)ꢀC(8) and
C(12)ꢀN(2)ꢀC(13) are estimated at 170.61(18)° and
135.12(16)°, respectively. This indicates that the isocyanido
group on Ru(2) underwent strong back-donation from the metal
1
by H and 13C NMR spectra; their molecular structures were
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Table 2. Selected Bond Distances (Å) and Angles (deg) for 6
Ru(1)ꢀRu(2)
Ru(1)ꢀC(7)
N(1)ꢀC(7)
N(2)ꢀC(13)
C(2)ꢀC(3)
C(5)ꢀC(6)
C(8) ꢀC(11)
C(13)ꢀC(16)
3.07636(18)
1.9050(17)
1.166(2)
1.472(2)
1.413(2)
1.523(2)
1.529(3)
1.522(3)
Ru(1)ꢀC(2)
Ru(2)ꢀC(1)
N(1)ꢀC(8)
C(1)ꢀC(2)
C(3)ꢀC(4)
C(8) ꢀC(9)
C(13)ꢀC(14)
2.3125(16)
2.1799(16)
1.448(2)
1.471(2)
1.516(2)
1.518(3)
1.511(3)
Ru(1)ꢀC(3)
Ru(2)ꢀC(12)
N(2)ꢀC(12)
C(1)ꢀC(6)
2.2107(16)
1.8473(17)
1.208(2)
1.529(2)
1.528(2)
1.505(3)
1.525(3)
C(4)ꢀC(5)
C(8) ꢀC(10)
C(13)ꢀC(15)
C(2)ꢀRu(1)ꢀC(3)
C(7)ꢀN(1)ꢀC(8)
C(2)ꢀC(1)ꢀC(6)
C(2)ꢀC(3)ꢀC(4)
C(4)ꢀC(5)ꢀC(6)
36.31(6)
170.61(18)
113.17(14)
119.47(15)
110.48(15)
Ru(1)ꢀRu(2)ꢀC(1)
C(12)ꢀN(2)ꢀC(13)
C(1)ꢀC(2)ꢀC(3)
C(3)ꢀC(4)ꢀC(5)
C(1)ꢀC(6)ꢀC(5)
74.90(4)
135.12(16)
124.18(15)
112.77(14)
112.77(14)
Table 3. Selected Bond Distances (Å) and Angles (deg) for 8
Ru(1)ꢀRu(2) 2.7569(6) Ru(1)ꢀC(1) 2.138(4) Ru(1)ꢀC(7) 2.035(4)
Ru(1)ꢀC(8) 1.830(4) Ru(2)ꢀC(1) 2.121(3) Ru(2)ꢀC(7) 2.021(4)
Ru(2)ꢀC(9) 1.843(4) C(1)ꢀC(2) 1.517(5) C(1)ꢀC(6) 1.534(5)
C(2)ꢀC(3)
C(5)ꢀC(6)
C(9)ꢀO(3)
1.537(5) C(3)ꢀC(4) 1.511(6) C(4)ꢀC(5) 1.523(6)
1.535(5) C(7)ꢀO(1) 1.185(5) C(8)ꢀO(2) 1.160(5)
1.155(5)
C(1)ꢀRu(1)ꢀC(7)
C(1)ꢀRu(2)ꢀC(7)
Ru(1)ꢀC(1)ꢀRu(2)
Ru1ꢀC(1)ꢀC(2)
Ru2ꢀC(1)ꢀC(2)
C(2)ꢀC(1)ꢀC(6)
C(2)ꢀC(3)ꢀC(4)
C(4)ꢀC(5)ꢀC(6)
Ru(1)ꢀC(7)ꢀO(1)
96.32(14) Ru(2)ꢀRu(1)ꢀC(8)
97.29(15) Ru(1)ꢀRu(2)ꢀC(9)
80.67(12) Ru(1)ꢀC(7)ꢀRu(2)
92.59(12)
90.80(12)
85.64(15)
118.1(3)
114.6(2)
115.8(3)
109.9(3)
112.0(3)
136.6(3)
119.4(3)
115.4(2)
107.0(3)
112.0(3)
110.6(3)
137.8(3)
Ru1ꢀC(1)ꢀC(6)
Ru2ꢀC(1)ꢀC(6)
C(1)ꢀC(2)ꢀC(3)
C(3)ꢀC(4)ꢀC(5)
C(1)ꢀC(6)ꢀC(5)
Ru(2)ꢀC(7)ꢀO(1)
diruthenium complex {CpRu(μ-CH2)}2(μ-η2:η2-C5H6).12b The
RuꢀRu distance of 10 is less than those of μ-cyclohexadiene
complex 3 (2.7391(15) Å) and μ-cycloheptadiene complex 11
(2.7833(4) Å), because of the small ring-size of the coordinated
cyclic diene ligand in 10. On the other hand, the RuꢀRu distance is
significantly greater than the FeꢀFe distance of the iron analogue,
{Cp*Fe(μ-H)}2(μ-η2:η2-C5H6) (2.483(1) Å), which clearly re-
flects the difference between the ionic radii of iron and ruthenium.14
The cyclopentadiene ligand in 10 bridges the two ruthenium
centers in a μ-η2:η2-fashion. The methylene carbon of the
cyclopentadiene ligand, C(1), is located above the plane com-
posed of the four carbon atoms of the diene moiety by ca. 0.25 Å.
The lengths of the coordinated CdC bond were 1.375(8) and
1.380(8) Å, which were less than that of the inner CꢀC single
bond by ca. 0.10 Å. While the lengths of the CdC bond of the
diene moiety were similar to those of the iron analogue, the
length of the inner CꢀC single bond was significantly greater by
0.07 Å.14 This further shows the difference between the MꢀM
bond length of RuꢀRu and FeꢀFe.
Figure 4. Molecular structure of 8 with thermal ellipsoids at the 30%
level of probability.
determined by the X-ray diffraction studies, which are shown in
Figures 5 and 6, and selected bond distances and angles of the
complexes are listed in Table 4.
In the 1H NMR spectrum of 10, four signals assignable to the
cyclopentadiene moiety were observed at δ 2.45 (endo-H), 3.75
(exo-H), 4.19, and 5.13 ppm (Chart 2). Similar to the 1H NMR
spectrum of 3, these signals showed complicated coupling
patterns arising from the magnetically inequivalent circumstance.
By using simulation, the coupling constants of these protons
were evaluated (see Supporting Information). A significantly large
The two Cp* groups adopted a cis geometry with respect to
the RuꢀRu vector as seen in 3. The Ru(1)ꢀRu(2) distance of
2.6922(4) Å in 10 corresponds to the RudRu double bond,
which is anticipated according to the EAN rule. The RuꢀRu
distance of 2.692(6) Å was reported for the closely related
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Scheme 4. Plausible Mechanism of the Reaction of 3 with CO
Table 4. Selected Bond Distances (Å) and Angles (deg) for
10 and 11
10
11
Ru(1)ꢀRu(2)
Ru(1)ꢀC(2)
Ru(1)ꢀC(3)
Ru(2)ꢀC(4)
Ru(2)ꢀC(5)
2.6922(4)
2.179(4)
2.250(5)
2.210(4)
2.178(5)
Ru(1)ꢀRu(2)
Ru(1)ꢀC(3)
Ru(1)ꢀC(4)
Ru(2)ꢀC(5)
Ru(2)ꢀC(6)
C(1)ꢀC(2)
C(2)ꢀC(3)
C(3)ꢀC(4)
C(4)ꢀC(5)
C(5)ꢀC(6)
C(6)ꢀC(7)
C(7)ꢀC(1)
2.7834(4)
2.209(4)
2.248(4)
2.189(4)
2.199(5)
1.512(7)
1.492(7)
1.384(6)
1.452(6)
1.402(6)
1.504(7)
1.512(8)
C(1)ꢀC(2)
C(2)ꢀC(3)
C(3)ꢀC(4)
C(4)ꢀC(5)
C(5)ꢀC(1)
1.523(8)
1.375(8)
1.477(7)
1.380(8)
1.483(9)
Figure 5. Molecular structure of 10 with thermal ellipsoids at the 30%
level of probability.
C(2)ꢀRu(1)ꢀC(3)
C(4)ꢀRu(2)ꢀC(5)
36.1(2)
36.6(2)
C(3)ꢀRu(1)ꢀC(4)
C(5)ꢀRu(2)ꢀC(6)
C(2)ꢀC(1)ꢀC(7)
C(1)ꢀC(2)ꢀC(3)
C(2)ꢀC(3)ꢀC(4)
C(3)ꢀC(4)ꢀC(5)
C(4)ꢀC(5)ꢀC(6)
C(5)ꢀC(6)ꢀC(7)
C(6)ꢀC(7)ꢀC(1)
36.18(16)
37.27(16)
114.4(5)
119.0(4)
128.6(4)
128.0(4)
127.3(4)
129.2(4)
120.7(4)
C(2)ꢀC(1)ꢀC(5)
C(1)ꢀC(2)ꢀC(3)
C(2)ꢀC(3)ꢀC(4)
C(3)ꢀC(4)ꢀC(5)
C(4)ꢀC(5)ꢀC(1)
101.7(5)
108.5(5)
109.0(5)
107.2(5)
110.7(5)
Chart 2. Selected 1H NMR Data of 10
Figure 6. Molecular structure of 11 with thermal ellipsoids at the 30%
level of probability.
spinꢀspin coupling of 4JHꢀH (7.75 Hz) was observed between
the exo-H and Hb in the simulation. Unlike complex 3, 10 does
not show any fluxional behavior within the NMR time scale.
The thermolysis of 10 in C6D6 at 70 °C resulted in the
fragmentation of the Ru2 core, and a pentamethytlruthenocene,
Cp*RuCp (12), was formed in 45% yield (eq 8). The driving
force for this reaction could be the stabilization due to the
formation of the aromatic C5H5ꢀ. The fate of the rest of the
[Cp*Ru] fragment is unknown at present.19 The formation of 12
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Table 5. Crystallographic Data for 3, 6, 8, 10, and 11
3
6
8
10
11
(a) Crystal Data
empirical formula
fw
C
26 H40Ru2
C36 H58N2Ru2
C29 H40 O3 Ru2
638.75
C25 H38 Ru2
540.69
C27 H42 Ru2
568.75
554.72
720.98
cryst description
cryst color
block
platelet
block
needle
needle
red
orange
yellow
orange
red
cryst size (mm)
crystallizing solution
cryst syst
0.08 ꢁ 0.07 ꢁ 0.05
pentane (ꢀ30 °C)
monoclinic
0.16 ꢁ 0.11 ꢁ 0.04
pentane (ꢀ30 °C)
monoclinic
0.14 ꢁ 0.08 ꢁ 0.07
THF (25 °C)
triclinic
0.19 ꢁ 0.08 ꢁ 0.02
pentane (ꢀ30 °C)
monoclinic
0.12 ꢁ 0.08 ꢁ 0.04
pentane (25 °C)
monoclinic
space group
lattice params
P21/c (#14)
P21/c (#14)
a = 11.6809(3)
b = 8.8655(2)
c = 33.7174(7)
P1 (#2)
P21/n (#1014)
a = 8.3926(4) Å
b = 26.2462(11) Å
c = 10.9157(4) Å
P21/c (#14)
a = 8.0533(8) Å
b = 36.216(3)Å
c = 9.1233(10) Å
a = 14.9607(10) Å
b = 19.8883(12) Å
c = 17.2271(12) Å
a = 9.7930(15) Å
b = 9.8397(18) Å
c = 15.993(2) Å
α = 100.994(5)°
β = 100.953(5)°
γ = 112.116(5)°
1342.2(4)
β = 109.262(2)°
β = 98.3910(7)°
β = 104.1550(14)°
β = 109.657(3)°
V (Å3)
4838.9(6)
8
3454.30(15)
4
2331.44(17)
4
2505.8(4)
4
Z value
2
Dcalc (g/cm3)
1.523
ꢀ120
1.257
1.386
1.581
1.540
1.508
ꢀ100
1.216
measurement temp (°C)
μ(Mo Kα) (mmꢀ1
ꢀ150
0.900
ꢀ100
1.153
ꢀ100
1.302
)
(b) Intensity Measurements
diffractometer
radiation
RAXIS-RAPID
Mo Kα
RAXIS-RAPID
Mo Kα
RAXIS-RAPID
RAXIS-RAPID
Mo Kα
RAXIS-RAPID
Mo Kα
Mo Kα
monochromator
2θmax
graphite
graphite
graphite
graphite
graphite
50°
55°
55°
55°
55°
reflns collected
indep reflns
reflns obsd (>2σ)
abs corr type
abs transmn
30 116
49 966
13 243
23 098
22 008
8997 (Rint = 0.1938)
3569
7886 (Rint = 0.0374)
7072
6102 (Rint = 0.0422)
4915
5445 (Rint = 0.0571)
4233
5826 (Rint = 0.0722)
4045
empirical
empirical
empirical
0.7017 (min.),
1.0000 (max.)
empirical
empirical
0.2198 (min.),
1.0000 (max.)
0.8657 (min.),
0.9623 (max.)
0.7129 (min.),
1.0000 (max.)
0.5840 (min.),
1.0000 (max.)
(c) Refinement (Shelxl-97-2)
R1 (I > 2σ(I))
wR2 (I > 2σ(I))
R1 (all data)
0.0777
0.0204
0.0395
0.0384
0.0354
0.1687
0.0472
0.0868
0.0925
0.0660
0.1974
0.0250
0.0535
0.0533
0.06489
wR2 (all data)
0.2318
0.0489
0.0939
0.1012
0.0843
data/restraints/params
8709/0/526
0.927
7886/0/581
1.056
6087/0/415
1.027
5301/0/272
1.042
5696/0/320
1.081
GOF
largest diff peak and hole (e Åꢀ3
)
1.021 and ꢀ1.807
0.484 and ꢀ0.347
3.275 and ꢀ1.401
0.869 and ꢀ0.749
0.866 and ꢀ0.786
1
was confirmed by comparing its H NMR spectrum with the
very slow. The treatment of a trimetallic closo-ruthenacyclo-
pentadiene complex, (Cp*Ru)2{Cp*Ru(μ3-C6H4-C(H)dC-
(C3H8)ꢀ)}(μ-H), with 7 atm of dihydrogen at 180 °C afforded
a triruthenium pentahydrido complex, {Cp*Ru(μ-H)}3(μ3-H)2,
with the elimination of n-pentylbenzene in a low yield of 10%
in 3 days.21
reported data.20
Unlike the μ-cyclohexadiene ligand in 3, the μ-cyclohepta-
diene ligand in 11 was not substituted by benzene, and 11 was
stable for at least 3 days in benzene at 70 °C. This stability
possibly arose from the difficulty in the aromatization of the
seven-membered ring.
The hydrocarbyl moieties were tightly bound to the multi-
metallic center of an electron-rich cluster composed of the
[Cp*Ru] units. This stabilizes the cluster compound; thus, the
bonds in such complexes are very strong and cannot release a
hydrocarbyl moiety from a multimetallic center as seen in
complex 11. Under forced conditions, a hydrocarbyl ligand was
eliminated as an organic molecule; however, the reaction rate was
’ CONCLUSIONS
We synthesized novel bimetallic complexes having cyclic
diene ligands by the reactions of the diruthenium tetrahydrido
complex 1 with several cyclic dienes. All the cyclic diene ligands
adopted an s-cis coordination mode and bridged two metal
nuclei in a μ-η2:η2-fashion. The μ-cyclohexadiene complex 3
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was alternatively synthesized by the reaction of 1 with benzene
via partial hydrogenation of benzene on the bimetallic center.
The facile hydrogenation of aromatic molecules was possibly
directed by the electron-rich metal center composed of the
[Cp*Ru] units, and the formation of 3 can be attributed to the
partial hydrogenation of benzene. However, the cyclohexadiene
ligand formed in 3 was readily eliminated as benzene upon mild
heating.
In contrast to the μ-cyclohexadiene ligand in 3, the μ-cyclo-
heptadiene ligand in 11 was sufficiently robust against elimina-
tion. This distinct contrast was possibly due to the absence of the
aromatization process for the hydrocarbyl ligand. This fact indi-
cates the construction of novel catalytic systems on a multi-
metallic site. These results imply that the aromatization of the
coordinated hydrocarbyl group can overcome the gravity of the
multimetallic center.
Although cyclohexene or cyclohexadiene did not eliminate
from the bimetallic center at present, the treatment of 3 with 2e-
donors suppresses the elimination of benzene and promotes
further migration of hydrido onto the C6 moiety. The introduc-
tion of an appropriate ligand can functionalize the C6 moiety.
Particularly, the μ-cyclohexenyl ligand in 6 can be assumed to be
an allyl group. We continued the research of the reactivity of 3
with various substrates in order to introduce a functional group in
the C6 moiety and eliminate the C6 moiety as cyclohexene.
NMR Simulations. NMR simulations for 3 and 10 were performed
using gNMR v4.1.0. (1995ꢀ1999 Ivory Soft). Final simulated line
shapes were obtained via an iterative parameter search upon the
coupling constants among the hydride ligands and the protons on the
diene moiety. Complete details of the fitting procedure and results are
shown in Supporting Information.
Preparation of μ-η2:η2-Cyclohexadiene Complex {Cp*Ru-
(μ-H)}2(μ-η2:η2-C6H8) (3). Pentane (10 mL) and diruthenium
tetrahydrido complex 1 (0.208 g, 0.44 mmol) were charged in a reaction
flask. After 1,3-cyclohexadiene (320 mg, 4.0 mmol) was added to the
solution, the solution was vigorously stirred for 4 h at 70 °C. The color of
the solution changed from red to purple. After the solvent and remaining
1,3-cyclohexadiene were removed under reduced pressure, the residual
solid was dissolved in 2 mL of pentane. The residual solid was then
purified by column chromatography on alumina (Merck, Art. No. 1097)
with pentane. Removal of the solvent under reduced pressure afforded a
0.199 g amount of 3 as a purple crystalline solid (82% yield). A thin plate-
like crystal used for the diffraction studies was prepared from the cold
1
pentane solution of 3 stored at ꢀ30 °C. H NMR (400 MHz, 23 °C,
benzene-d6): δ ꢀ22.88 (m, 1H, RuH), ꢀ9.00 (d, JHꢀH = 4.8 Hz, 1H,
RuH), 1.22 (m, 2H, ꢀCHHendoꢀ), 1.77 (s, 30H, C5Me5), 2.14 (m, 2H,
ꢀCHexoHꢀ), 3.43 (m, 2H, ꢀCHdCHꢀCH2ꢀ), 4.98 (m, 2H, ꢀCHd
CHꢀCH2ꢀ). 13C NMR (100 MHz, 23 °C, benzene-d6): δ 12.0
(q, JCꢀH = 127 Hz, C5Me5), 24.4 (t, JCꢀH = 126 Hz, ꢀCHdCHꢀ
CH2ꢀ), 62.9 (d, JCꢀH = 159 Hz, ꢀCHdCHꢀCH2ꢀ), 65.7 (d, JCꢀH
=
154 Hz, ꢀCHdCHꢀCH2ꢀ), 86.1 (s, C5Me5). IR (KBr): 893, 1020,
1112, 1163, 1193, 1370, 1443, 1460, 1480, 2820, 2890, 2942, 2960,
3013 (cmꢀ1). Anal. Calcd for C26H40Ru2: C, 56.26; H, 7.27. Found: C,
56.20; H, 7.22.
’ EXPERIMENTAL SECTION
Reaction of Cp*Ru(μ-H)4RuCp* (1) with Benzene. Benzene
(2 mL) and diruthenium tetrahydrido complex 1 (37.8 mg, 79.3 μmol)
were charged in a reaction flask. The solution was vigorously stirred for
3 days at 70 °C. After the solvent was removed under reduced pressure,
the residual solid was dissolved in 1 mL of pentane. The residual solid
was then purified by column chromatography on alumina (Merck, Art.
No. 1097) with pentane. After the first purple band was collected, the
solvent was removed under reduced pressure. A 26.9 mg amount of 3
was obtained as a purple crystalline solid (61% yield).
General Procedures. All air- and moisture-sensitive compounds
were manipulated using standard Schlenk and high-vacuum line tech-
niques under an argon atmosphere. Dehydrated benzene, toluene,
pentane, and THF used in this study were purchased from Kanto
Chemicals and stored under an argon atmosphere. Benzene-d6 and
THF-d8 were distilled from sodium benzophenone ketyl and stored
under an argon atmosphere. Cyclopentadiene was prepared by the
cracking of dicyclopentadiene before use. Other materials were used as
purchased. 1H and 13C NMR spectra were recorded on a Varian
1
Reaction of Cp*Ru(μ-H)4RuCp* (1) with Benzene-d6. Ben-
zene-d6 (0.5 mL), diruthenium tetrahydrido complex 1(8.7 mg, 18.2 μmol),
and cyclooctane (0.5 μL) as an internal standard were charged in an
NMR tube equipped with a Teflon valve. The solution was heated at
70 °C in an NMR probe. Due to rapid scrambling of deuterium of
benzene-d6 into the hydrido position, all of the signal except for the Cp*
signal was gradually diminished. Concentrations of 1-d4 and 3-d10 were
evaluated by the intensity of the Cp* signals. The ratio between 1-d4 and
3-d10 reached ca. 1:17 after 72 h heating and became steady. At the same
time, other signals for Cp* groups were found at δ 2.03 and 1.90 ppm,
which were assignable to triruthenium pentahydrido complex {Cp*Ru-
(μ-H)}3(μ3-H)2 and tetraruthenium hexahydrido complex (Cp*Ru)4(H)6,
respectively. On the basis of intensities of the Cp* signals, the yields of 1, 3,
[Ru3], and [Ru4] were estimated at 4.5, 75.8, 7.1, and 10.1%, respectively.
Thermolysis of {Cp*Ru(μ-H)}2(μ-η2:η2-C6H8) (3) under 1
atm of Dihydrogen Atmosphere. THF-d8 (0.4 mL), μ-cyclohex-
adiene complex 3 (9.0 mg, 13.6 μmol), and cyclooctane (0.5 μL) as an
internal standard were charged in an NMR tube equipped with a Teflon
valve. After the NMR tube was degassed, the tube was filled with 1 atm of
dihydrogen. The solution was heated at 40 °C for 30 h. The 1H NMR
spectrum of this solution showed the formation of diruthenium tetra-
hydrido complex 1 (92%) as well as benzene (90%).
INOVA-400 spectrometer. H NMR spectra were referenced to tetra-
methylsilane as an internal standard. 13C NMR spectra were referenced
to the natural-abundance carbon signal of the solvent employed. IR
spectra were recorded on a Jasco FTIR4200 spectrophotometer. GLC
analyses were performed on Shimadzu GC-17A and Shimadzu GC-14B
with helium gas as a carrier. Elemental analysis was performed on a
Perkin-Elmer 2400II series CHN analyzer. Complex 1 was prepared
according to a previously published method.22
X-ray Diffraction Studies. Single crystals of 3, 6, 8, 10, and 11 for
an X-ray analysis were obtained directly from the preparations described
below and mounted on nylon Cryoloops with Paratone-N (Hampton
Research Corp.). Diffraction experiments were performed on a Rigaku
R-AXIS RAPID imaging plate diffractometer with graphite-monochro-
mated Mo Kα radiation (λ = 0.71069 Å). In all samples, cell refinement
and data reduction were performed using the PROCESS-AUTO
program.23 Intensity data were corrected for Lorentzꢀpolarization
effects and for empirical absorption. The structures were solved by the
direct method using the SHELX-97 program package.24 The structures
were refined anisotropically for all non-hydrogen atoms by full-matrix
least-squares calculation on F2 using the SHELX-97 program package
except for the disordered Cp* group in 10. All hydrogen atoms were
refined isotropically. Neutral atom scattering factors were obtained from
the standard sources.25 The metal-bound hydrogen atoms in 6, 10, and
11 were located in the difference Fourier map and refined isotropically,
while the positions of the metal-bound hydrogen atoms of 3 were not
determined. Crystal data and results of the analysis are listed in Table 5.
Preparation of μ-η2-Cyclohexenyl Complexes {Cp*Ru-
(CNtBu)}2(μ-H)(μ-η2-C6H9) (6). Pentane (10 mL) and μ-cyclohex-
adiene complex 3 (26.9 mg, 0.049 mmol) were charged in a reaction
flask. After tert-butylisocyanide (0.15 mL, 1.5 mmol) was added to the
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solution, the solution was vigorously stirred for 8 h at 40 °C. The color of
the solution changed from purple to orange. The solvent was then
removed under reduced pressure. The residual solid was dissolved in
2 mL of pentane. The residual solid was then purified by column
chromatography on alumina (Merck, Art. No. 1097) with pentane.
Removal of the solvent under reduced pressure afforded an orange
residual solid including 6 with a small amount of 7. Recrystallization
from the pentane solution of the solid stored at ꢀ30 °C gave 6 as an
orange crystal (30.7 mg, 88% yield) and small amount of 7 as a red
crystal. 1H NMR of 6 (400 MHz, 23 °C, benzene-d6): δ ꢀ13.57 (s, 1H,
tBuNC), 1.36ꢀ1.54 (m, 2H, μ-η2-C6H9), 1.84 (s, 15H, C5Me5), 2.05
(s, 15H, C5Me5), 2.34 (m, 1H, μ-η2-C6H9), 2.53 (m, 1H, μ-η2-C6H9),
2.70ꢀ2.80 (m, 2H, μ-η2-C6H9), 3.87 (m, 1H, μ-η2-C6H9), the signal
derived from one of the methylene proton of the μ-cyclohexenyl ligand
is obscured by the Cp* signal appearing at δ 2.05 ppm. 13C NMR
(100 MHz, 23 °C, benzene-d6): δ 4.3 (d, JCꢀH = 138 Hz, RuꢀCHꢀ),
11.0 (q, JCꢀH = 126 Hz, C5Me5), 12.0 (q, JCꢀH = 125 Hz, C5Me5), 23.2
(t, JCꢀH = 128 Hz, ꢀCH2ꢀ), 30.6 (t, JCꢀH = 128 Hz, ꢀCH2ꢀ), 31.9 (q,
was dissolved in 2 mL of toluene. The residual solid was then purified by
columnchromatography onalumina(Merck, Art. No. 1097) withtoluene,
and the brown band was collected. After removal of the solvent under
reduced pressure, complex 10 was obtained as a brownish solid (0.065 g,
60%yield). A needle-likeorange crystalusedfor the diffractionstudieswas
preparedfromthe coldpentane solutionof10storedatꢀ30 °C. 1H NMR
(400 MHz, 23°C, benzene-d6): δ ꢀ22.32 (m, 1H, RuH), ꢀ9.91 (d, JHH
=
4.0 Hz, 1H, RuH), 1.69(s, 30H, C5Me5), 2.45 (m, 1H, ꢀCHendoHꢀ), 3.75
(m, 1H, ꢀCHHexoꢀ), 4.19 (m, 2H, ꢀCHdCHꢀCH2ꢀ), 5.13 (m, 2H,
ꢀCHdCHꢀCH2ꢀ). 13C NMR (100 MHz, 23 °C, benzene-d6): δ 11.3
(q, JCꢀH = 127 Hz, C5Me5), 52.6 (dd, JCꢀH = 137, 115 Hz ꢀCHdCHꢀ
t
RuH), 0.98 (m, 1H, μ-η2-C6H9), 1.10 (s, 9H, BuNC), 1.27 (s, 9H,
CHH0ꢀ), 70.4 (d, JCꢀH = 162 Hz, ꢀCHdCHꢀCH H0ꢀ), 71.4(d, JCꢀH
=
165 Hz, ꢀCHdCHꢀCH H0ꢀ), 86.7 (s, C5Me5). IR (KBr): 869, 903, 985,
1022, 1098, 1135, 1159, 1260, 1317, 1422, 1449, 2777, 2893 (cmꢀ1). Anal.
Calcd for C25H38Ru2: C, 55.53; H, 7.08. Found: C, 55.36; H, 7.17.
Preparation of μ-η2:η2-Cycloheptadiene Complex {Cp*Ru-
(μ-H)}2(μ-η2:η2-C7H10) (11). Toluene (5 mL) and diruthenium
tetrahydrido complex 1 (0.081 g, 0.17 mmol) were charged in a reaction
flask. Cycloheptatriene (0.1 mL, 0.88 mmol) was added to the solution at
25 °C. The solution was vigorously stirred for 18 h at 70 °C. The color of
the solution changed from red to purple. After the solvent and remaining
cyclopentadiene were removed under reduced pressure, the residual solid
was dissolved in 2 mL of toluene. The residual solid was then purified by
column chromatography on alumina (Merck, Art. No. 1097) with toluene,
and a purple band was collected. After removal of the solvent under
reduced pressure, complex 11 was obtained as a purple solid (0.067 g, 70%
yield). Aneedle-like redcrystalusedforthediffraction studies was prepared
J
CꢀH = 128 Hz, (CH3)3CNC), 32.4 (t, ꢀCH2ꢀ), 33.3 (q, JCꢀH = 129
Hz, (CH3)3CNC), 43.4 (d, JCꢀH = 156 Hz, ꢀCHdCHꢀ), 55.0
((CH3)3CNC), 59.3 (d, JCꢀH = 152 Hz, ꢀCHdCHꢀ), 92.1 (s, C5Me5),
92.9 (s, C5Me5), 172.3 ((CH3)3CNC), 203.3 ((CH3)3CNC), only one
signal for the quaternary carbon of the tert-butyl groups was observed at
δ 55.0 ppm. This was probably due to the coincidence of the chemical
shifts of the two signals. IR (KBr disk): 747, 813, 888, 1027, 1202, 1363,
1455, 1838 (ν(CN)), 2045 (ν(CN)), 2817, 2897, 2974 (cmꢀ1). Anal.
Calcd for C36H58N2Ru2: C, 59.97; H, 8.11; N, 3.88. Found: C, 59.63; H,
1
from the pentane solution of 11 stored at 20 °C. H NMR (400 MHz,
1
23 °C, benzene-d6): δ ꢀ22.84 (m, 1H, RuH), ꢀ8.39 (d, JHH = 4.8 Hz, 1H,
RuH), 0.06 (m, 1H, ꢀCHH0ꢀ), 1.25 (m, 1H, ꢀCHH0ꢀ), 1.70 (m, 2H,
ꢀCHH0ꢀ), 1.72 (s, 30H, C5Me5), 1.94 (m, 2H, ꢀCHH0ꢀ), 2.45 (m, 1H,
ꢀCHendoHꢀ), 3.75 (m, 1H, ꢀCHHexoꢀ), 3.11 (m, 2H, ꢀCHdCHꢀ
CH2ꢀ), 5.09 (m, 2H, ꢀCHdCHꢀCH2ꢀ). 13CNMR(100 MHz, 23°C,
benzene-d6): δ 12.0 (q, JCꢀH = 126 Hz, C5Me5), 30.1 (t, JCꢀH = 124
Hz, ꢀCH2ꢀ), 30.5 (t, JCꢀH = 124 Hz, ꢀCH2ꢀ), 68.3 (d, JCꢀH = 154
Hz, ꢀCHdCHꢀCH2ꢀ), 74.8 (d, JCꢀH = 148 Hz, ꢀCH=CHꢀCH2ꢀ),
85.3 (s, C5Me5).
8.11; N, 3.89. H NMR of 7 (400 MHz, 23 °C, benzene-d6): δ 1.13
(s, 18H, tBuNC), 1.16 (s, 18H, tBuNC), 1.79 (s, C5Me5).
Preparation of μ-Cyclohexylidene Complex {Cp*Ru(CO)}2-
(μ-C6H10)(μ-CO) (8). THF (5 mL) and μ-cyclohexadiene complex 3
(80.8 mg, 0.15 mmol) were charged in a reaction flask. After the flask was
degassed, 1 atm of CO was introduced into the flask. The solution was
heated at 50 °C for 15 h. The color of the solution changed from purple to
yellow. The solvent was then removed under reduced pressure. The 1H
NMR spectrum of the residual solid showed that complexes 8 and
{Cp*Ru(CO)(μ-CO)}2 (9) were formed in a 47:53 ratio. Characteriza-
tion of 9 was carried out by comparing its 1H NMR and IR spectra with
that of authentic samples (δ 1.71 (s, 30H, C5Me5), ν(CO) = 1748 and
1934 cmꢀ1). The residue was extracted three times with 5 mL of pentane
to remove 9. After the combined solution was condensed to 2 mL, the
solution was purifiedby column chromatography on alumina (Merck, Art.
No. 1097) with pentane. The first yellow band including 8 was collected,
and removal of the solvent under reduced pressure afforded a 23.0 mg
amount of 8 as a yellow crystalline solid (24% yield). A yellow single
crystal used for the diffraction studies was prepared by the slow evapora-
tion of the THF solution of 8 stored at 25 °C. 1H NMR (400 MHz, 23 °C,
benzene-d6): δ 1.75 (s, 30H, C5Me5), 1.85ꢀ2.00 (m, 4H, μ-C6H10),
2.02ꢀ2.12 (m, 2H, μ-C6H10), 3.17 (m, 2H, μ-C6H10), 3.25 (m, 2H, μ-
C6H10) ppm. 13C NMR (100 MHz, 23 °C, benzene-d6): δ 10.3 (q, JCꢀH
= 127 Hz, C5Me5), 28.1 (t, JCꢀH = 136 Hz, ꢀCH2ꢀ), 30.5 (t, JCꢀH = 126
Hz, ꢀCH2ꢀ), 60.0 (t, JCꢀH = 115 Hz, ꢀCH2ꢀ), 102.1 (s, C5Me5), 181.3
(s, μ-C), 204.0 (s, CO), 254.7 (μ-CO) ppm. IR (KBr): 800, 857, 1007,
1025, 1111, 1257, 1381, 1442, 1473, 1769 (ν(CO)), 1911(ν(CO)), 2855,
2913, 2961, 2989 (cmꢀ1). Anal. Calcd for C29H40O3Ru2: C, 54.53; H,
6.31. Found: C, 54.17; H, 6.28.
Thermolysis of μ-η2:η2-Cyclopentadiene Complex 10 in
Benzene-d6. Benzene-d6 (0.4 mL) and μ-η2:η2-cyclopentadiene
complex 10 (6.5 mg, 12 μmol) were charged in an NMR tube with
hexamethyldisiloxane as an internal standard. The NMR tube was heated
at 70 °C for 2 h. The 1H NMR spectrum of the solution showed that 94%
of 10 was consumed and Cp*RuCp (12) was formed in 45% yield.
The yield was estimated from the signal intensity of the Cp* group
compared with that of the internal standard. 1H NMR (400 MHz, 23 °C,
benzene-d6): δ 1.92 (s, 15H, C5Me5), 4.18 (s, 5H, C5H5) ppm.
13C NMR (100 MHz, 23 °C, benzene-d6): δ 12.4 (q, JCꢀH = 127 Hz,
C5Me5), 72.4 (doublets of quintet, JCꢀH = 174, 7 Hz, C5H5), 84.9
(s, C5Me5) ppm. 1H NMR (400 MHz, 23 °C, CD3Cl): δ 1.96 (s, 15H,
C5Me5), 4.17 (s, 5H, C5H5) ppm.
’ ASSOCIATED CONTENT
S
Supporting Information. Results of NMR simulations
b
on 3 and 10, results of X-ray diffraction studies of 7, as well as
crystallographic files including CIF files of 3, 6, 7, 8, 10, and 11
are available free of charge via the Internet at http://pubs.acs.org.
Preparation of μ-η2:η2-Cyclopentadiene Complex {Cp*Ru-
(μ-H)}2(μ-η2:η2-C5H6) (10). Toluene (5 mL) and diruthenium tetra-
hydrido complex 1 (0.094 g, 0.20 mmol) were charged in a reaction flask.
Cyclopentadiene (0.1 mL, 1.27 mmol) was added to the solution at 25 °C.
The solution was vigorously stirred for 4 h at 70 °C. The color of the
solution changed from red to brown. After the solvent and remaining
cyclopentadiene were removed under reduced pressure, the residual solid
’ ACKNOWLEDGMENT
This work was supported by a Grant-in-Aid for Scientific
Research in Innovative Areas “Molecular Activation Directed
toward Straightforward Synthesis” from NEXT, Japan.
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dx.doi.org/10.1021/om200728e |Organometallics 2011, 30, 5057–5067

Organometallics
ARTICLE
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