Intramolecular C-H bond activation in bridged dicyclopentadienyl dimethyl dinuclear complexes

Article abstract of DOI:10.1021/om400986a

Photolysis of the doubly bridged dicyclopentadienyl dimethyl dinuclear complexes [(η⁵-C₅H₂R)₂(SiMe ₂)₂]M₂(CO)₄Me₂ (M = Ru, R = H (2a), ^tBu (2b); M = Fe, R = H (2c)) in benzene yields the corresponding methylene-bridged complexes [(η⁵-C ₅H₂R)₂(SiMe₂)₂]M ₂(CO)₂(μ-CO)(μ-CH₂) (3a-c) and the M-M-bonded complexes [(η⁵-C₅H₂R) ₂(SiMe₂)₂]M₂(CO)₄ (1a-c). Irradiation of the analogous diethyl complex [(η⁵-C ₅H₂R)₂(SiMe₂)₂]Ru ₂(CO)₄Et₂ (4) affords only 1a. Unlike the case for the doubly bridged complexes, photolysis of the singly bridged dicyclopentadienyl dimethyl diruthenium complexes [(η⁵-C ₅H₄)₂(EMe₂)]Ru₂(CO) ₄Me₂ (E = C (5a); E = Si (5b)) in benzene yields the corresponding twisted ruthenium methyl complexes with a cyclopentadienyl-Ru σ bond (η⁵,η⁵: η¹-C₅H₄(EMe₂)C₅H ₃)[Ru(CO)₂][Ru(CO)₂Me] (6a,b) and the similar phenyl complexes (η⁵,η⁵:η¹-C ₅H₄(EMe₂)C₅H₃)[Ru(CO) ₂][Ru(CO)₂Ph] (7a,b), from reaction with the benzene solvent. Plausible mechanisms for the formation of the different types of products are proposed involving intramolecular C-H bond activation. The molecular structures of 2a,c, 3a,c, 4, 5a, 6a, and 7b, determined by X-ray diffraction, are also presented.

Full text of DOI:10.1021/om400986a

Article
pubs.acs.org/Organometallics
Intramolecular C−H Bond Activation in Bridged Dicyclopentadienyl
Dimethyl Dinuclear Complexes
Bolin Zhu,* Xiaoting Hao, and Yunfei Chen
Tianjin Key Laboratory of Structure and Performance for Functional Molecules, Key Laboratory of Inorganic−Organic Hybrid
Functional Material Chemistry, Ministry of Education, College of Chemistry, Tianjin Normal University, Tianjin 300387, People’s
Republic of China
S
* Supporting Information
ABSTRACT: Photolysis of the doubly bridged dicyclopenta-
dienyl dimethyl dinuclear complexes [(η5-C5H2R)2(SiMe2)2]-
M2(CO)4Me2 (M = Ru, R = H (2a), tBu (2b); M = Fe, R = H
(2c)) in benzene yields the corresponding methylene-bridged
complexes [(η5-C5H2R)2(SiMe2)2]M2(CO)2(μ-CO)(μ-CH2)
(3a−c) and the M−M-bonded complexes [(η5-
C5H2R)2(SiMe2)2]M2(CO)4 (1a−c). Irradiation of the analo-
gous diethyl complex [(η5-C5H2R)2(SiMe2)2]Ru2(CO)4Et2
(4) affords only 1a. Unlike the case for the doubly bridged
complexes, photolysis of the singly bridged dicyclopentadienyl
dimethyl diruthenium complexes [(η5-C5H4)2(EMe2)]-
Ru2(CO)4Me2 (E = C (5a); E = Si (5b)) in benzene yields the corresponding “twisted” ruthenium methyl complexes with a
cyclopentadienyl−Ru σ bond (η5,η5:η1-C5H4(EMe2)C5H3)[Ru(CO)2][Ru(CO)2Me] (6a,b) and the similar phenyl complexes
(η5,η5:η1-C5H4(EMe2)C5H3)[Ru(CO)2][Ru(CO)2Ph] (7a,b), from reaction with the benzene solvent. Plausible mechanisms for
the formation of the different types of products are proposed involving intramolecular C−H bond activation. The molecular
structures of 2a,c, 3a,c, 4, 5a, 6a, and 7b, determined by X-ray diffraction, are also presented.
C5H2R)2(SiMe2)2)M2(CO)4]2−·2Na+ (synthesized from the
corresponding M−M bond complexes 1a−c with an excess of
INTRODUCTION
■
Although “classic” transition-metal methyl complexes CpM-
Na−Hg alloy) with iodomethane in 38−52% yield (Scheme 1);
they were isolated as colorless (2a,b) or yellow (2c) air-stable
crystals. Their IR spectra (KBr film) indicate the expected three
strong ν(CO) absorptions in the range 2020−1936 cm−1. In
(CO)2Me (M = Fe, Ru) (type A in Chart 1) were synthesized
half a century ago,1,2 their catalytic applications to the activation
of relatively inert bonds in organic molecules were discovered
only in recent years, especially for the iron complex.3
Nakazawa’s group4 and Pannell’s group5 reported a series of
studies of organic reactions catalyzed by CpFe(CO)2Me, like
the dehydrocoupling dimerization of RnEH4−n (E = Si, Ge, Sn;
n = 2, 3), which mostly involve the activation of an E−H bond
by the 16e species CpFe(CO)Me generated by the photo-
irradiation of the iron complex CpFe(CO)2Me. To the best of
our knowledge, no similar organic reaction catalyzed by the
ruthenium analogue has been reported except a C−H bond
activation reaction of benzene with Cp*Ru(CO)2Me reported
by Moss et al.6 We considered that bridged dicyclopentadienyl
dinuclear methyl analogues in which the bridging ligand locks
the two reactive metal centers in close proximity may promote
C−H activation. However, this type of chemistry has never
been reported. Herein, we report our findings on the
photochemical reactivity of a family of bridged dicyclopenta-
dienyl dinuclear dimethyl complexes (types B and C in Chart
1).
1
the H NMR spectra of 2a,c, the cyclopentadienyl hydrogens
occur as a doublet (5.33 ppm for 2a, 4.90 ppm for 2c) and a
triplet (5.42 ppm for 2a, 4.95 ppm for 2c), consistent with an
AB2 spin system. For 2b, the spectrum shows a singlet (5.38
ppm) for the four equal cyclopentadienyl hydrogens. X-ray
structural determinations of 2a,c (Figures 1 and 2) show their
structures to be very similar to each other, both of which have a
perfect crystallographic mirror plane passing through two metal
atoms and the centroids of the two cyclopentadienyl rings. The
metal atoms exhibit a three-legged piano-stool geometry. The
configurations of the (η5-C5H3)2(SiMe2)2 ligand are almost flat
in 2a,c, which is reflected in the fold angles between the two
cyclopentadienyl rings (170.6° in 2a, 170.2° in 2c). As
expected, the M−M nonbonding distances (5.317 Å in 2a,
5.292 Å in 2c) are long. The structural features of 2a,c are very
close to those of the diiodo complex [(η5-C5H3)2(SiMe2)2]-
Ru2(CO)4I2 reported by Angelici’s group.7
RESULTS AND DISCUSSION
■
Syntheses of [(η5-C5H2R)2(SiMe2)2]M2(CO)4Me2 (2a−c).
Received: October 8, 2013
Complexes 2a−c were prepared from the reaction of [((η5-
© XXXX American Chemical Society
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Chart 1
Scheme 1
Figure 2. Thermal ellipsoid drawing of [(η5-C5H3)2(SiMe2)2]-
Fe2(CO)4Me2 (2c) showing the labeling scheme and 30% probability
ellipsoids. Hydrogens are omitted for clarity. Selected bond lengths
(Å) and angles (deg): Fe(1)- - Fe(2) 5.292(11), Fe(1)−C(4A)
1.999(14), Fe(1)−C(4′) 1.803(12), Fe(1)−C(5) 1.759(5), Fe(1)−
Cp(centroid) 1.729, Fe(2)−Cp(centroid) 1.733; ∠C(4′)−Fe(1)−
C(5) 90.8(10), ∠C(4′)−Fe(1)−C(4A) 89.7(4), ∠C(4A)−Fe(1)−
C(5) 86.1(8), ∠Cp(centroid)−Fe(1)−Fe(2)−Cp(centroid) 0, ∠Cp-
Cp fold angle 170.2.
Figure 1. Thermal ellipsoid drawing of [(η5-C5H3)2(SiMe2)2]-
Ru2(CO)4Me2 (2a) showing the labeling scheme and 30% probability
ellipsoids. Hydrogens are omitted for clarity. Selected bond lengths
(Å) and angles (deg): Ru(1)- - Ru(2) 5.317(9), Ru(1)−C(4A)
2.082(13), Ru(1)−C(4′) 1.895(13), Ru(1)−C(5) 1.870(5), Ru(1)−
Cp(centroid) 1.914, Ru(2)−Cp(centroid) 1.920; ∠C(4′)−Ru(1)−
C(5) 90.1(8), ∠C(4′)−Ru(1)−C(4A) 88.3(4), ∠C(4A)−Ru(1)−
C(5) 84.8(7), ∠Cp(centroid)−Ru(1)−Ru(2)−Cp(centroid) 0, ∠Cp-
Cp fold angle 170.6.
reaction of 2a was also carried out in toluene and provided the
same products (3a and 1a) as those in benzene, which indicates
that the different aromatic solvents have no effect on the
reaction. Thermal treatment of 2a in refluxing toluene for 24 h
gave none of these products, which shows that UV irradiation is
necessary for this reaction.
Photolysis of 2a−c. It has been reported that irradiation of
Cp*Ru(CO)2Me in benzene yields Cp*Ru(CO)2Ph via C−H
bond activation.6 With 2a−c in hand, our initial objective was
to focus on a double C−H bond activation of benzene.
Surprisingly, UV irradiation of a solution of 2a−c in benzene
under an N2 or Ar atmosphere results in formation of the
corresponding bridging methylene complexes [(η5-
C5H2R)2(SiMe2)2]M2(CO)2(μ-CO)(μ-CH2) (3a−c, 11−43%
yield) and the M−M-bonded complexes [(η5 -
C5H2R)2(SiMe2)2]M2(CO)4 (1a−c, 21−37% yield) (Scheme
1), both of which do not involve C−H bond activation of
benzene. Obviously, the photochemical behaviors of 2a−c and
Cp*Ru(CO)2Me toward benzene were different. The photo-
Complexes 3a,b were isolated as yellow crystals, while 3c was
1
obtained as brown crystals. In the H NMR spectra of 3a−c,
the most notable and characteristic chemical shifts are two
doublets at low field which are assigned to the bridging
methylene protons (8.77, 6.64 ppm in 3a, 8.67, 6.56 ppm in 3b,
10.05, 6.68 ppm in 3c). In the IR spectra (KBr film) of 3a−c,
ν(CO) absorptions in the ranges 1980−1936 and 1769−1796
cm−1 indicate the presence of both terminal and bridging
B
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carbonyl ligands. The X-ray structural determinations of 3a,c
(Figures 3 and 4) reveal that they have similar structures, both
Figure 4. Thermal ellipsoid drawing of [(η5-C5H3)2(SiMe2)2]-
Fe2(CO)2(μ-CO)(μ-CH2) (3c) showing the labeling scheme and
30% probability ellipsoids. Hydrogens are partially omitted for clarity.
Selected bond lengths (Å) and angles (deg): Fe(1)−Fe(1A)
2.4898(5), Fe(1)−C(8) 1.743(2), Fe(1)−C(9) 1.84(3), Fe(1)−
C(10A) 2.04(3), C(9)−O(2) 1.19(3), Fe(1)−Cp(centroid) 1.757;
∠Fe(1A)−Fe(1)−C(9) 48.4(9), ∠Fe(1A)−Fe(1)−C(10A) 53.4(8),
∠C(9)−Fe(1)−C(10A) 92.1(12), ∠Fe(1)−C(10A)−Fe(1A) 74.5(9),
∠C(8)−Fe(1)−Fe(1A)−C(8A) 0.8, ∠Cp(centroid)−Fe(1)−Fe(2)−
Cp(centroid) 1.0, ∠Cp-Cp fold angle 110.9.
Figure 3. Thermal ellipsoid drawing of [(η5-C5H3)2(SiMe2)2]-
Ru2(CO)2(μ-CO)(μ-CH2) (3a) showing the labeling scheme and
30% probability ellipsoids. Hydrogens are partially omitted for clarity.
Selected bond lengths (Å) and angles (deg): Ru(1)−Ru(1A)
2.6557(5), Ru(1)−C(8) 1.854(3), Ru(1)−C(9) 1.99(2), Ru(1)−
C(10A) 2.14(2), C(9)−O(2) 1.17(2), Ru(1)−Cp(centroid) 1.923;
∠Ru(1A)−Ru(1)−C(9) 48.1(7), ∠Ru(1A)−Ru(1)−C(10A) 52.1(6),
∠C(9)−Ru(1)−C(10A) 89.2(8), ∠Ru(1)−C(10A)−Ru(1A) 76.4(8),
∠C(8)−Ru(1)−Ru(1A)−C(8A) 1.8, ∠Cp(centroid)−Ru(1)−
Ru(2)−Cp(centroid) 2.2, ∠Cp-Cp fold angle 119.3.
drosilanes HnSiR′4−n (n = 2, 3) for 1 week.13 This paper reports
for the first time that compounds 3a−c with bridging carbonyl
and methylene ligands can be synthesized directly by the
photolysis of the corresponding dimethyl dinuclear complexes
in aromatic solvents. In order to gain insight into the reaction
mechanism, a labeling experiment was carried out in order to
investigate the source of the bridging CH2 moieties. Photolysis
of 2a-d6 (synthesized from [((η5-C5H3)2(SiMe2)2)-
Ru2(CO)4]2−·2Na+ with CD3I) in benzene afforded 1a and
the bridging CD2 complex [(η5-C5H3)2(SiMe2)2]Ru2(CO)2(μ-
CO)(μ-CD2) (3a-d2) (Scheme 2), which is evident in the
presence of the same peaks as for 3a in the 1H NMR spectrum,
except for the two peaks at low field assigned to methylene
protons. This experiment confirms that the μ-CH2 moiety in 2a
comes from methyl groups attached to ruthenium. In addition,
to examine whether this reaction takes place via an intra-
of which show approximate C2v symmetry with the C2 axis
passing through the midpoints of the M−M bonds and the
Si(1) and Si(1A) atoms. The metal atoms are bridged
symmetrically by a carbonyl and a methylene ligand, and
each metal atom also carries a terminal carbonyl. The two
terminal carbonyls are highly eclipsed, which is evident in the
very small ∠C(8)−M(1)−M(1A)−C(8A) torsion angle (1.8°
in 3a, 0.8° in 3c). The M−M bond distances (2.6557(5) Å in
3a, 2.4898(5) Å in 3c) are slightly shorter than those found for
their respective nonbridged parents (η5-C5H5)2M2(μ-CO)(μ-
CH2)(CO)2 (M = Ru, 2.707(1) Å; M = Fe, 2.5196(6) Å).8,9
The presence of the bridging carbonyl and methylene in 3a
leads to a distinctly shortened Ru−Ru bond distance, in
comparison to that found in the all terminal carbonyl analogue
1a (2.8180(3) Å).7 The short Ru−Ru distance causes severe
bending of the doubly bridged (η5-C5H3)2(SiMe2)2 ligand,
which is evident in a smaller ∠Cp-Cp fold angle (119.3°).
In contrast to the method (Scheme 1) used to prepare the
methylene-bridged 3a−c, the nonbridged and singly bridged
dicyclopentadienyl ruthenium analogues are synthesized by the
reactions of the corresponding dinuclear tetracarbonyl
complexes with LiBHEt3 in aromatic solvents10−12 or in a
rare case from the thermolysis of diruthenium carbonyl
complexes (η5-C5H4R)2Ru2(μ-CO)2(CO)2 with di- or trihy-
Scheme 2
C
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molecular or intermolecular pathway, we carried out the
photolysis of 2a-d6 and 2c in C6D6, which was followed by H
1.55 and 0.80 ppm corresponding to acetone and ethane
protons, which further supports the above mechanism.
1
NMR. Only the corresponding 3a-d2 and 3c were observed,
and no crossover products 3a and 3c-d2 were detected. This
indicated that the photolysis of 2a−c in C6H6 proceeds via an
intramolecular rather than an intermolecular pathway.
On the basis of our results and those in previous related
reports,14,15 a plausible mechanism for the formation of 3a is
tentatively proposed in Scheme 3. First, a CO is lost from 2a
On the basis of the mechanism proposed above, it seems that
the ratio of the two products 3a and 1a depends on the
competition between two processes: loss of CO and homolysis
of the Ru−CH3 bond in 2a. To test this hypothesis, another
control experiment was carried out. Before irradiation, carbon
monoxide was bubbled into a benzene solution of 2a for 5 min.
Photolysis of this solution afforded only 1a; no 3c was observed
by TLC monitoring and column chromatography (eq 1). On
the basis of experimental evidence, we suggest that the added
carbon monoxide inhibits the loss of CO step which gives the
bridging methylene product 3a via intramolecular C−H bond
activation. However, another possibility could not be ruled out:
that the reaction of the methyl radicals with CO is faster, which
facilitates the process of homolysis of the Ru−CH3 bond.
Scheme 3
2a ⎯⎯C⎯⎯6⎯H⎯⎯6⎯,⎯h⎯→ν⎯ 1a
(1)
CO (1 atm)
Photolysis of [(η5-C5H3)2(SiMe2)2]Ru2(CO)4Et2 (4). The
diethyl analogues of 2a−c, which were synthesized by a method
similar to that in Scheme 1, show spectroscopic (NMR, IR)
characteristics similar to those of 2a. The molecular structure of
4, determined by X-ray single-crystal diffraction (Figure 5),
under UV radiation to give a 16e unsaturated ruthenium
species (A); this is followed by oxidative addition of a C−H
bond on methyl group attached to the other ruthenium atom to
form B. In the next step, elimination of CH4 from B results in
intermediate C. Finally, a terminal CO ligand in C moves into a
bridging position to give the final product 3a. When photolysis
1
of 2a in C6D6 was followed by H NMR, the presence of a
singlet at δ 0.16 ppm corresponding to CH4 further supported
the above mechanism. We also attempted to use CCl4 to trap
intermediate B by a halogen−hydrogen exchange reaction;
unfortunately, we did not succeed in isolating the correspond-
ing chloride.
The mechanism for the formation of 1a seems more
straightforward (Scheme 4): UV irradiation causes homolysis
of the Ru−CH3 bond in 2a, the resulting intramolecular
diruthenium radicals form a Ru−Ru bond to give the final
product 1a, and two methyl radicals combine to generate
ethane or react with free CO released in the formation of 3a to
afford acetone. Similarly, following the photolysis of 2a in
C6D6, the 1H NMR spectrum exhibits two distinct singlets at δ
Figure 5. Thermal ellipsoid drawing of [(η5-C5H3)2(SiMe2)2]-
Ru2(CO)4Et2 (4) showing the labeling scheme and 30% probability
ellipsoids. Hydrogens are omitted for clarity. Selected bond lengths
(Å) and angles (deg): Ru(1)- - -Ru(2) 4.788(5), Ru(1)−C(8)
1.867(2), Ru(1)−C(9) 1.864(2), Ru(1)−C(10) 2.164(2), C(10)−
C(11) 1.514(4), Ru(1)−Cp(centroid) 1.925; ∠C(8)−Ru(1)−C(9)
88.96(9), ∠C(8)−Ru(1)−C(10) 86.56(9), ∠C(9)−Ru(1)−C(10)
86.4(1), ∠Ru(1)−C(10)−C(11) 113.8(2), ∠Cp(centroid)−Ru(1)−
Ru(2)−Cp(centroid) 4.4, ∠Cp-Cp fold angle 172.0.
Scheme 4
shows approximate C2v symmetry with the C2 axis passing
through the midpoints of the Ru(1), Ru(1A) atoms and Si(1),
Si(1A) atoms. The Ru(1)- - -Ru(1A) nonbonding distance
(4.788 Å) is much shorter than that (5.317 Å) in 2a, which is
attributed to coordination of two Ru(CO)2Et fragments on the
concave surface of the slightly bent, doubly bridged (η5-
C5H3)2(SiMe2)2 ligand, in comparison to that on the convex
surface in 2a.
Similarly, a solution of 4 in C6D6 was sealed in the NMR
tube, which was photolyzed for 30 min. Unlike 2a−c, the
reaction gave clean 1a, ethane (0.80 ppm), and ethylene (5.25
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1
ppm) by following the reaction with the H NMR spectra.
Unfortunately, we did not see a peak for hydrogen (4.47 ppm)
(Scheme 5). This indicates that β-hydride elimination
different method: namely, by the reaction of the corresponding
diiodo compound with Li[CuMe2].12
With 5a,b in hand, our original objective was to compare
their photochemistry with that of the doubly bridged complexes
2a−c, which resulted in intramolecular C−H bond activation
(Scheme 1). Surprisingly, UV irradiation of solutions of 5a,b in
benzene under a N2 atmosphere results in the formation of
“twisted” ruthenium methyl complexes with a cyclopentadien-
yl−Ru σ bond, (η5,η5:η1-C5H4(EMe2)C5H3)[Ru(CO)2][Ru-
(CO)2Me] (6a,b) and the phenyl complexes (η5,η5:η1-
C5H4(EMe2)C5H3)[Ru(CO)2][Ru(CO)2Ph] (7a,b) (Scheme
6), the latter product resulting from C−H bond activation of
benzene. Obviously, the photochemical behavior of 5a,b is very
different than that of doubly bridged analogues 2a−c.
Scheme 5
Complexes 6a,b were isolated as air-stable colorless crystals.
The IR spectra of 6a,b indicate the expected four strong ν(CO)
dominates the photoreaction chemistry rather than intra-
molecular C−H bond activation. The same products (ethane
and ethylene) have been observed from the photolysis of the
mononuclear iron analogue (η5-C5H5)Fe(CO)2Et.14
1
absorptions in the range 2038−1924 cm−1. The H NMR
spectra of 6a,b show seven sets of peaks for protons in the two
different cyclopentadienyl rings, two singlets for the different
CH3 protons in the CMe2 or SiMe2 group, and one singlet for
the Ru−CH3 protons. An X-ray structural determination of 6a
(Figure 7) shows an asymmetrical structure: the ruthenium
atom in the Ru(CO)2Me fragment is coordinated with a Cp
ligand in an η5 mode, and the other ruthenium atom is
coordinated with two Cp rings in an η1 and η5 manner. The
Ru(1)−C(10) bond distance (2.079(4) Å) in 6a is very close to
those values in its analogues (2.08 Å in (η5,η5:η1-
C5H4CMe2C5H3)[Ru(CO)2][Ru(CO)2H],16 2.054(3) Å in
(η5,η5:η1-C5H4CMe2C5H3)[Ru(CO)2][Ru(CO)2Cl],17 and
2.070(5) Å (the mean value) in (η5,η5:η1-C5H4CH2C5H3)[Ru-
(CO)2][Ru(CO)2Cl]18). The five-membered ring Ru(1)−
C(1)−C(6)−C(9)−C(10) adopts an envelope form, in which
C(6) lies 0.12 Å out of the plane defined by the other four
atoms away from Ru(2).
Photolysis of [(η5-C5H4)2(EMe2)]Ru2(CO)4Me2 (5a, E = C;
5b, E= Si). To examine the importance of the double bridge in
the photochemistry of 2a−c (Scheme 1), we studied the
reactions of the singly bridged dicyclopentadienyl dimethyl
diruthenium compounds 5a,b, which were prepared by similar
methods. The IR spectrum of 5a contains the expected strong
ν(CO) absorptions (2014, 1952 cm−1) for terminal carbonyls.
In the 1H NMR spectrum of 5a, the cyclopentadienyl
hydrogens occur as two sets of pseudotriplets (5.24 and 5.04
ppm), consistent with an AA′BB′ spin system. The Ru−Me
hydrogens occur as one singlet at 0.31 ppm. Since the
spectroscopic data do not provide information on the relative
orientation of both metal moieties, a single-crystal X-ray
structural determination of 5a was carried out (Figure 6). The
crystal structure of 5a shows a three-legged piano-stool
geometry around each of two Ru atoms, which are linked by
the singly bridging ligand (η5-C5H4)2(CMe2); each Ru atom is
also bonded to two carbonyls and one methyl group. The most
remarkable feature of the molecular structure is that the two
Ru(CO)2Me fragments are coordinated in an exo disposition
with respect to the Cp rings of the bridging ligand and are
located in a mutually cis orientation. This structural feature is
quite different from that of the dichloro complex [(η5-
C5H3)2(SiMe2)]Ru2(CO)4Cl2 reported by Gimeno’s group,12
in which two metal fragments adopt a trans arrangement.
Complex 5b, as reported by Gimeno, was synthesized by a
Complexes 7a,b were also isolated as air-stable colorless
crystals, which show spectroscopic patterns similar to those for
6a,b, except that the phenyl group on ruthenium atom in 7a,b
replaces the methyl group in 6a,b. The molecular structure of
7b (Figure 8) is also very similar to that of ruthenium methyl
complex 6a. The Ru(1)−C(12) bond distance (2.080(7) Å) in
7b compares very well with data (2.079(4) Å) for 6a. The five-
membered ring Ru(1)−C(1)−Si(1)−C(8)−C(12) adopts a
stable envelope form, in which C(1) lies 0.21 Å out of the plane
defined by the other four atoms away from Ru(2).
Figure 6. Thermal ellipsoid drawing of [(η5-C5H4)2(CMe2)]Ru2(CO)4Me2 (5a) showing the labeling scheme and 30% probability ellipsoids.
Hydrogens are omitted for clarity. Selected bond lengths (Å) and angles (deg): Ru(1)−C(9) 1.863(3), Ru(1)−C(10) 1.878(4), Ru(1)−C(11)
2.138(4), Ru(1)−Cp(centroid) 1.918, Ru(2)−C(17) 1.858(4), Ru(2)−C(18) 1.872(4), Ru(2)−C(19) 2.141(4), Ru(2)−Cp(centroid) 1.922;
∠C(4)−C(1)−C(12) 105.7(2), ∠C(2)−C(1)−C(3) 108.4(3), ∠Cp-Cp fold angle 95.1.
E
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Scheme 6
Cp*Ru(CO)2Me has been described to activate the C−H bond
of benzene by photolysis to give the similar Ru−phenyl
complex Cp*Ru(CO)2Ph.6 The photolysis of 6a in benzene
was carried out and indeed yielded the expected product 7a (eq
2).
C6H6, hν
(2)
6a ⎯⎯⎯⎯⎯⎯⎯⎯→ 7a
CONCLUSION
■
UV irradiation of bridged dicyclopentadienyl dimethyl
dinuclear complexes in benzene affords different types of
products which depend on whether there are one or two
bridges. Photolysis of the doubly bridged dicyclopentadienyl
dimethyl dinuclear complexes [(η5-C5H2R)2(SiMe2)2]-
M2(CO)4Me2 (2a−c) in benzene yields the corresponding
bridging methylene complexes [(η5-C5H2R)2(SiMe2)2]-
M2(CO)2(μ-CO)(μ-CH2) (3a−c) and the M−M-bonded
complexes [(η5-C5H2R)2(SiMe2)2]M2(CO)4 (1a-c). However,
photolysis of the singly bridged dicyclopentadienyl dimethyl
diruthenium complexes [(η5-C5H4)2(EMe2)]Ru2(CO)4Me2 (E
= C (5a); E = Si (5b)) in benzene yields the “twisted”
ruthenium methyl complexes (η5,η5:η1-C5H4(EMe2)C5H3)[Ru-
(CO)2][Ru(CO)2Me] (6a,b) and the phenyl complexes
(η5,η5:η1-C5H4(EMe2)C5H3)[Ru(CO)2][Ru(CO)2Ph] (7a,b).
A labeling experiment confirms that the μ-CH2 moiety in 3a
comes from the methyl group attached to the Ru atom. Excess
carbon monoxide in solution inhibits the loss of CO to afford
3a. Plausible mechanisms for the formation of different types of
products are proposed to involve intramolecular activation of
C−H bonds on different groups, which depend on the rigid
structure of the doubly bridged complexes and the flexible
structure of the singly bridged complexes. Photolysis of the
diethyl analogue 4 only gives 1a via preferential β-hydride
elimination. In summary, the bridged dimethyl dinuclear
complexes show photochemical reactivity different from that
of the mononuclear methylruthenium complex Cp*Ru-
(CO)2Me in aromatic solvents. Studies of catalytic applications
of the bridged dicyclopentadienyl dimethyl dinuclear complexes
in organic reactions are in progress.
Figure 7. Thermal ellipsoid drawing of (η5,η5:η1-C5H4CMe2C5H3)-
[Ru(CO)2][Ru(CO)2Me] (6a) showing the labeling scheme and 30%
probability ellipsoids. Hydrogens are omitted for clarity. Selected bond
lengths (Å) and angles (deg): Ru(1)−C(1) 2.249(4), Ru(1)−C(10)
2.079(4), Ru(1)−C(14) 1.885(4), Ru(1)−C(15) 1.871(5), Ru(1)−
Cp(centroid) 1.900, Ru(2)−C(16) 1.863(8), Ru(2)−C(17) 1.862(5),
Ru(2)−C(18) 2.154(6), Ru(2)−Cp(centroid) 1.923; ∠C(7)−C(6)−
C(8) 108.8(4), ∠C(1)−C(6)−C(9) 106.4(3), ∠C(6)−C(9)−C(10)
122.3(3), ∠C(9)−C(10)−Ru(1) 116.4(3), ∠C(10)−Ru(1)−C(1)
78.3(2), ∠Ru(1)−C(1)−C(6) 115.9(3), ∠Cp-Cp fold angle 91.7.
A plausible pathway for the formation of 6a,b is proposed in
Scheme 7. First, a CO dissociates from 6 under UV radiation to
give a 16e unsaturated ruthenium species (D). This is followed
by oxidative addition of an ortho C−H bond on the other
cyclopentadienyl ring to form E; this is the key step which
distinguishes the singly bridged dicyclopentadienyl dimethyl
dinuclear complexes from the doubly bridged analogues. In the
doubly bridged system, the unsaturated ruthenium center in
intermediate A could not approach a C−H bond on the other
cyclopentadienyl ring because of the rigid structure of the
doubly bridged ligand; therefore, it activates an adjacent C−H
bond on the methyl group attached to the other ruthenium
atom. However, in the singly bridged system, due to free
rotation around the E−C σ bond, the structure of intermediate
D is more flexible, and the unsaturated ruthenium center can
reach an ortho C−H bond on the other cyclopentadienyl ring,
to form the stable five-membered-ring structure E. In the final
step, elimination of CH4 and recoordination of CO in E results
in the final product 6a,b.
EXPERIMENTAL SECTION
General Considerations. Schlenk and vacuum line techniques
■
were employed for all manipulations. All solvents were distilled from
appropriate drying agents under nitrogen prior to use. H and 13C
1
NMR spectra were recorded on a Bruker AV400 instrument at room
temperature with TMS as internal standard. IR spectra were recorded
as KBr disks on a Nicolet 560 ESP FTIR spectrometer. Elemental
analyses were performed on a Perkin-Elmer 240C analyzer. Photolyses
were conducted with a 250 W high-pressure Hg lamp with the reaction
vessel in an ice−water bath. The complexes [(η5-C5H2R)2(SiMe2)2]-
M2(CO)4 (1a−c),19−21 [(η5-C5H4)2(CMe2)]Ru2(CO)4,16 and [(η5-
We considered that complexes 7a,b are obtained from the
C−H bond activation of benzene by 6a,b, since the complex
17
C5H4)2(SiMe2)]Ru2(CO)4 were prepared by literature methods.
F
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Figure 8. Thermal ellipsoid drawing of (η5,η5:η1-C5H4SiMe2C5H3)[Ru(CO)2][Ru(CO)2Ph] (7b) showing the labeling scheme and 30% probability
ellipsoids. Hydrogens are omitted for clarity. Selected bond lengths (Å) and angles (deg): Ru(1)−C(1) 2.236(7), Ru(1)−C(12) 2.080(7), Ru(1)−
C(19) 1.894(9), Ru(1)−C(20) 1.87(1), Ru(1)−Cp(centroid) 1.892, Ru(2)−C(13) 2.095(8), Ru(2)−C(21) 1.853(9), Ru(2)−C(22) 1.871(9),
Ru(2)−Cp(centroid) 1.923; ∠C(6)−Si(1)−C(7) 110.6(5), ∠C(1)−Si(1)−C(8) 98.6(4), ∠Si(1)−C(8)−C(12) 119.7(6), ∠C(8)−C(12)−Ru(1)
121.0(5), ∠C(12)−Ru(1)−C(1) 84.2(3), ∠Ru(1)−C(1)−Si(1) 115.5(3), ∠Cp-Cp fold angle 83.4.
KBr): 2020 (s), 1957 (s), 1941 (s) cm−1. Anal. Calcd for
Scheme 7
C20H24O4Ru2Si2: C, 40.94; H, 4.12. Found: C, 40.73; H, 4.06.
t
Synthesis of [(η5-C5H2 Bu)2(SiMe2)2]Ru2(CO)4Me2 (2b). When
1b (100 mg, 0.15 mmol) was reacted with Na/Hg and then
iodomethane (45 mg, 0.32 mmol) in THF, 2b (40 mg, 38%, colorless
crystals) was obtained, using the same method as in the preparation of
2a. 1H NMR (400 MHz, CDCl3): δ 5.38 (s, 4H, C5H2), 1.23 (s, 18H,
C(CH3)), 0.52 (s, 6H, Si(CH3)), 0.40 (s, 6H, Si(CH3)), 0.39 (s, 6H,
Ru(CH3)). IR (νCO): 2013 (s), 1959 (s), 1936 (s) cm−1. Anal. Calcd
for C28H40O4Ru2Si2: C, 48.12; H, 5.77. Found: C, 48.25; H, 5.61.
Synthesis of [(η5-C5H3)2(SiMe2)2]Fe2(CO)4Me2 (2c). When 1c
(100 mg, 0.21 mmol) was reacted with Na/Hg and then iodomethane
(64 mg, 0.45 mmol) in THF, 2c (55 mg, 52%, yellow crystals) was
obtained, using the same method as in the preparation of 2a. 1H NMR
(400 MHz, CDCl3): δ 4.95 (t, 2H, C5H3), 4.90 (d, 4H, C5H3), 0.66 (s,
6H, Si(CH3)), 0.25 (s, 6H, Fe(CH3)), 0.21 (s, 6H, Si(CH3)). IR
(νCO): 2009 (s), 1952 (s), 1937 (s)) cm−1. Anal. Calcd for
C20H24Fe2O4Si2: C, 48.40; H, 4.87. Found: C, 48.57; H, 4.66.
Photolysis of 2a in Benzene. A solution of 2a (20 mg, 0.03
mmol) in benzene (5 mL) was irradiated with UV light for 4 h.
Solvent was pumped off from the resulting yellow solution, and the
residue was chromatographed on an alumina column using petroleum
ether/CH2Cl2 (6/1) as eluent; a yellow band was eluted and collected.
Then, another yellow band was eluted with petroleum ether−CH2Cl2
Synthesis of [(η5-C5H3)2(SiMe2)2]Ru2(CO)4Me2 (2a). A solution
(4/1). After vacuum removal of the solvents from the above two
eluates, the residues were recrystallized from n-hexane/CH2Cl2 (1/1)
at −10 °C. From the first fraction, 6 mg (32%) of yellow crystalline 1a
was obtained. From the second fraction, 8 mg (43%) of yellow
crystalline 3a was obtained. 1H NMR (400 MHz, CDCl3): δ 8.77 (d, J
= 2.0 Hz, 1H, μ-CH2), 6.64 (d, J = 2.0 Hz, 1H, μ-CH2), 6.02 (t, 2H,
C5H3), 5.65 (dd, 2H, C5H3), 5.61 (dd, 2H, C5H3), 0.76 (s, 3H,
Si(CH3)), 0.61 (s, 3H, Si(CH3)), 0.49 (s, 3H, Si(CH3)), 0.48 (s, 3H,
Si(CH3)). 13C NMR (100 MHz, CDCl3): δ −3.01, −2.14, 3.07, 3.80
(Si(CH3)), 91.47, 92.79, 94.25, 107.24, 112.05 (Cp), 106.02 (μ-CH2),
202.28, 205.00 (CO). IR (νCO): 1976 (s), 1942 (s), 1781 (s) cm−1.
Anal. Calcd for C18H20O3Ru2Si2: C, 39.84; H, 3.71. Found: C, 40.03;
H, 7.62.
of 1a (100.0 mg, 0.18 mmol) in THF (40 mL) was added to Na/Hg
(50 mg/2 mL) and THF (20 mL). After the mixture was stirred for 20
h at ambient temperature, the resulting solution was cannulated from
the amalgam layer and added to a solution of iodomethane (57 mg,
0.40 mmol) in THF (20 mL). The resulting solution was stirred for 4
h; volatiles were removed under reduced pressure, and the residue was
chromatographed on an alumina column. Elution with petroleum
ether developed a colorless band. After vacuum removal of the solvents
from the above eluate, the residue was recrystallized from n-hexane/
CH2Cl2 (1/1) at −10 °C to afford 2a (48 mg, 46%) as colorless
1
crystals. H NMR (400 MHz, CDCl3): δ 5.42 (t, J = 2.4 Hz, 2H,
C5H3), 5.33 (d, J = 2.4 Hz, 4H, C5H3), 0.54 (s, 6H, Si(CH3)), 0.36 (s,
6H, Ru(CH3)), 0.32 (s, 6H, Si(CH3)). 1H NMR (400 MHz, C6D6): δ
4.81 (t, J = 2.4 Hz, 2H, C5H3), 4.73 (d, J = 2.4 Hz, 4H, C5H3), 0.58 (s,
Photolysis of 2b in Benzene. A solution of 2b (20 mg, 0.03
mmol) in benzene (5 mL) was irradiated with UV light for 4 h. Using
the same method as in the photolysis of 2a, 1b (4 mg, 21%, yellow
6H, Si(CH3)), 0.50 (s, 6H, Si(CH3)), 0.09 (s, 6H, Ru(CH3)). IR (νCO
,
G
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crystals) and 3b (5 mg, 27%, yellow crystals) were obtained. 1H NMR
(400 MHz, CDCl3): δ 8.67 (d, J = 2.0 Hz, 1H, μ-CH2), 6.56 (d, J = 2.0
Hz, 1H, μ-CH2), 5.49 (d, J = 1.2 Hz, 2H, C5H2), 5.46 (d, J = 1.2 Hz,
2H, C5H2), 1.33 (s, 18H, C(CH3)), 0.72 (s, 3H, Si(CH3)), 0.56 (s,
3H, Si(CH3)), 0.46 (s, 3H, Si(CH3)), 0.45 (s, 3H, Si(CH3)). IR (νCO):
1980 (s), 1962 (s), 1937 (s), 1796 (s) cm−1. Anal. Calcd for
C26H36O3Ru2Si2: C, 47.69; H, 5.54. Found: C, 47.55; H, 5.62.
Photolysis of 2c in Benzene. A solution of 2c (20 mg, 0.04
mmol) in benzene (5 mL) was irradiated with UV light for 8 h. Using
the same method as in the photolysis of 2a, 1c (7 mg, 37%, dark green
Using the same method as in the photolysis of 2a, 6b (21 mg, 43%,
colorless crystals) and 7b (5 mg, 9%, colorless crystals) were obtained.
Data for 6b are as follows. H NMR (400 MHz, CDCl3): δ 5.72 (m,
1
1H, Cp-H), 5.55 (m, 1H, Cp-H), 5.45 (m, 1H, Cp-H), 5.42 (m, 1H,
Cp-H), 5.20 (m, 1H, Cp-H), 5.15 (m, 1H, Cp-H), 4.96 (m, 1H, Cp-
H), 0.50 (s, 3H, Si(CH3)), 0.42 (s, 3H, Si(CH3)), 0.25 (s, 3H,
Ru(CH3)). IR (νCO): 2037 (s), 1993 (s), 1973 (s), 1929 (s) cm−1.
Anal. Calcd for C17H16O4Ru2Si: C,39.68; H, 3.13. Found: C, 39.73; H,
3.09. Data for 7b are as follows. 1H NMR (400 MHz, CDCl3): δ 7.45
(m, 2H, Ph-H), 6.93 (m, 3H, Ph-H), 5.80 (m, 1H, Cp-H), 5.60 (m,
1H, Cp-H), 5.41 (m, 3H, Cp-H), 5.16 (m, 1H, Cp-H), 4.99 (m, 1H,
Cp-H), 0.52 (s, 3H, Si(CH3)), 0.42 (s, 3H, Si(CH3)). IR (νCO): 2026
(s), 2001 (s), 1970 (s), 1945 (s) cm−1. Anal. Calcd for
C22H18O4Ru2Si: C, 45.83; H, 3.15. Found: C, 45.65; H, 3.23.
Photolysis of 6a in Benzene. A solution of 6a (20 mg, 0.04
mmol) in benzene (5 mL) was photolyzed with UV light for 4 h.
Using the same method as in the photolysis of 2a, 7a (7 mg, 31%,
colorless solid) was obtained.
Crystallographic Studies. Single crystals of complexes 2a,c, 3a,c,
4, 5a, 6a, and 7b suitable for X-ray diffraction were obtained by
crystallization from n-hexane/CH2Cl2 (1/1). Data collection was
performed on a Bruker SMART 1000 diffractometer, using graphite-
monochromated Mo Kα 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 in the Supporting
Information.
1
crystals) and 3c (2 mg, 11%, red crystals) were obtained. H NMR
(400 MHz, CDCl3): δ 10.05 (m, 1H, μ-CH2), 6.68 (m, 1H, μ-CH2),
5.68 (m, 2H, C5H3), 5.63 (m, 2H, C5H3), 5.32 (m, 2H, C5H3), 0.40 (s,
12H, Si(CH3)). IR (νCO): 1968 (s), 1936 (s), 1769 (s) cm−1. Anal.
Calcd for C18H20Fe2O3Si2: C, 47.81; H, 4.46. Found: C, 47.95; H,
4.62.
Photolysis of 2a and CO in Benzene. A solution of 2a (20 mg,
0.03 mmol) in benzene (5 mL) was bubbled with CO for 5 min and
then photolyzed with UV light for 2 h. Using the same method as in
the photolysis of 2a, only 1a (10 mg, 53%, yellow crystals) was
obtained.
Synthesis of [(η5-C5H3)2(SiMe2)2]Ru2(CO)4Et2 (4). When 1a (100
mg, 0.15 mmol) was reacted with Na/Hg and then iodoethane (50
mg, 0.32 mmol) in THF, 2b (72 mg, 65%, colorless crystals) was
obtained, using the same method as in the preparation of 2a. 1H NMR
(400 MHz, CDCl3): δ 5.38 (t, J = 2.4 Hz, 2H, C5H3), 5.32 (d, J = 2.4
Hz, 4H, C5H3), 1.76 (q, J = 7.6 Hz, 4H, CH2CH3), 1.35 (t, J = 7.6 Hz,
6H, CH2CH3), 0.54 (s, 6H, Si(CH3)), 0.31 (s, 6H, Si(CH3)). IR
(νCO): 2020 (s), 1999 (s), 1960 (s) cm−1. Anal. Calcd for
C22H28O4Ru2Si2: C, 42.98; H, 4.59. Found: C, 42.71; H, 4.37.
Photolysis of 4 in Benzene. A solution of 4 (20 mg, 0.03 mmol)
in benzene (5 mL) was photolyzed with UV light for 4 h. Using the
same method as in the photolysis of 2a, only 1a (12 mg, 66%, yellow
crystals) was obtained.
ASSOCIATED CONTENT
* Supporting Information
■
S
Crystallographic data tables and CIF files giving crystallo-
graphic details for complexes 2a,c, 3a,c, 4, 5a, 6a, and 7b. This
material is available free of charge via the Internet at http://
pubs.acs.org.
Synthesis of [(η5-C5H4)2(CMe2)]Ru2(CO)4Me2 (5a). When the
complex [(η5-C5H4)2(CMe2)]Ru2(CO)4 (200 mg, 0.41 mmol) was
reacted with Na/Hg and then iodomethane (120 mg, 0.85 mmol) in
THF, 5a (110 mg, 52%, white wax solid) was obtained, using the same
1
method as in the preparation of 2a. H NMR (400 MHz, CDCl3): δ
AUTHOR INFORMATION
Corresponding Author
*B.Z.: fax, 86-22-23766532; e-mail, hxxyzbl@gmail.com.
■
5.24 (t, J = 2.4 Hz, 4H, Cp-H), 5.04 (t, J = 2.4 Hz, 4H, Cp-H), 1.49 (s,
6H, C(CH3)), 0.31 (s, 6H, Ru(CH3)). IR (νCO): 2014 (s), 1952 (s)
cm−1. Anal. Calcd for C19H20O4Ru2: C, 44.35; H, 3.92. Found: C,
44.54; H, 4.15.
Notes
Synthesis of [(η5-C5H4)2(SiMe2)]Ru2(CO)4Me2 (5b). When the
complex [(η5-C5H4)2(SiMe2)]Ru2(CO)4 (200 mg, 0.40 mmol) was
reacted with Na/Hg and then iodomethane (120 mg, 0.85 mmol) in
THF, 5b (125 mg, 59%, white solid) was obtained, using the same
method as in the preparation of 2a.
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
We sincerely thank Prof. Robert J. Angelici for improving the
English for this article. We also gratefully acknowledge financial
support from the National Natural Science Foundation of
China (No. 21002069) and the Scientific Research Foundation
for Returned Overseas Chinese Scholars, the State Education
Ministry.
Photolysis of 5a in Benzene. A solution of 5a (50 mg, 0.10
mmol) in benzene (10 mL) was photolyzed with UV light for 3 h.
Using the same method as in the photolysis of 2a, 6a (27 mg, 56%,
colorless crystals) and 7a (6 mg, 11%, colorless solid) were obtained.
1
Data for 6a are as follows. H NMR (400 MHz, CDCl3): δ 5.67 (m,
1H, Cp-H), 5.57 (m, 1H, Cp-H), 5.38 (m, 1H, Cp-H), 5.26 (m, 1H,
Cp-H), 5.04 (m, 1H, Cp-H), 4.78 (m, 1H, Cp-H), 4.68 (m, 1H, Cp-
H), 1.50 (s, 3H, C(CH3)), 1.47 (s, 3H, C(CH3)), 0.26 (s, 3H,
Ru(CH3)). 1H NMR (400 MHz, C6D6): δ 5.00 (dd, 1H, Cp-H), 4.73
(m, 1H, Cp-H), 4.70 (m, 1H, Cp-H), 4.49 (dd, 1H, Cp-H), 4.43 (m,
1H, Cp-H), 4.39 (t, 1H, Cp-H), 4.32 (dd, 1H, Cp-H), 1.18 (s, 3H,
C(CH3)), 0.93 (s, 3H, C(CH3)), 0.67 (s, 3H, Ru(CH3)). IR (νCO):
2038 (s), 1990 (s), 1974 (s), 1924 (s) cm−1. Anal. Calcd for
C18H16O4Ru2: C, 43.37; H, 3.24. Found: C, 43.43; H, 3.07. Data for 7a
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H
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dx.doi.org/10.1021/om400986a | Organometallics XXXX, XXX, XXX−XXX