Synthesis of triruthenium complexes containing a triply bridging pyridyl ligand and its transformations to face-capping pyridine and perpendicularly coordinated pyridyl ligands

DOI: 10.1021/om300379d

Source and publish data:

Organometallics p. 4817 - 4831 (2012)

Update date:2022-07-30

Topics:

Authors:

Takao, Toshiro

Kawashima, Takashi

Kanda, Hideyuki

Okamura, Rei

Suzuki, Hiroharu

Read Full Text PDF DownLoad Join now for total 90,000,000 free articles

Article abstract of DOI:10.1021/om300379d

Unlike the reactions of carbonyl clusters with pyridine leading to the formation of μ-pyridyl complexes, the reaction of the triruthenium pentahydrido complex {Cp*Ru(μ-H)}₃(μ₃-H) ₂ (Cp* = η⁵-C₅Me₅) (1) with pyridines provided μ₃-η²(//)-pyridyl complexes, (Cp*Ru)₃(μ-H)₄(μ₃- η²(//)-RC₅H₃N) (2a, R = H; 2b, R = 4-COOMe; 2c, R = 4-COOEt; 2d, R = 4-Me; 2e, R = 5-Me), in which the molecular plane of the pyridyl group was tilted with respect to the Ru₃ plane. Electron-rich metal centers of the trimetallic core enabled back-donation to the pyridyl group, which caused the additional π-coordination of the C=N bond. The electron-rich metal centers of 2a-2c also promoted further transformation into face-capping pyridine complexes {Cp*Ru(μ-H)} ₃(μ₃-η²:η²: η²-RC₅H₄N) (3a, R = H; 3b, R = 4-COOMe; 3c, R = 4-COOEt) upon heating. In contrast, the thermolysis of 2d did not afford a face-capping picoline complex because of the poor electron-accepting ability of the picolyl moiety. Instead, the coordinatively unsaturated μ₃- picolyl complex (Cp*Ru)₃(μ-H)₂(μ₃- η²-4-Me-C₅H₃N) (4d) was obtained. Owing to its unsaturated nature, 4d can react with γ-picoline to yield 4,4′-dimethyl-2,2′-bipyridine. Although the reaction rate was slow, complex 1 catalyzed the dehydrogenative coupling of 4-substituted pyridines containing an electron-donating group. The protonation of 2a also afforded the coordinatively unsaturated pyridyl complex [(Cp*Ru)₃(μ-H) ₂(μ₃-H)(μ₃-η²: η²(⊥)-C₅H₄N)]⁺ (5a), but the coordination mode of the pyridyl group in 5a was completely different from that in 4d. The pyridyl moiety in 5a was coordinated on one of the Ru-Ru bonds in a perpendicular fashion. The methylation of the face-capping pyridine complex 3a, which led to the formation of the N-methyl pyridinium complex [(Cp*Ru)₃(μ-H)₃ (μ₃- η²:η²:η²-C₅H ₅NMe)]⁺ (7b) was also examined. NMR studies on 7b as well as X-ray diffraction studies suggested enhanced back-donation to the pyridinium moiety because of the localized cationic charge on the nitrogen atom.

Full text of DOI:10.1021/om300379d

Article

pubs.acs.org/Organometallics

Synthesis of Triruthenium Complexes Containing a Triply Bridging

Pyridyl Ligand and Its Transformations to Face-Capping Pyridine and

Perpendicularly Coordinated Pyridyl Ligands

Toshiro Takao, Takashi Kawashima, Hideyuki Kanda, Rei Okamura, and Hiroharu Suzuki*

Department of Applied Chemistry, Graduate School of Science and Engineering, Tokyo Institute of Technology, O-okayama,

Meguro-ku, Tokyo 152-8552, Japan

* Supporting Information

ABSTRACT: Unlike the reactions of carbonyl clusters with

pyridine leading to the formation of μ-pyridyl complexes, the

reaction of the triruthenium pentahydrido complex {Cp*Ru-

(μ-H)}₃(μ₃-H)₂(Cp* = η⁵-C₅Me₅) (1) with pyridines

provided μ₃-η²(//)-pyridyl complexes, (Cp*Ru)₃(μ-H)₄(μ₃-

η²(//)-RC₅H₃N) (2a, R = H; 2b, R = 4-COOMe; 2c, R = 4-

COOEt; 2d, R = 4-Me; 2e, R = 5-Me), in which the molecular

plane of the pyridyl group was tilted with respect to the Ru₃

plane. Electron-rich metal centers of the trimetallic core

enabled back-donation to the pyridyl group, which caused the

additional π-coordination of the CN bond. The electron-rich metal centers of 2a−2c also promoted further transformation

into face-capping pyridine complexes {Cp*Ru(μ-H)}₃(μ₃-η²:η²:η²-RC₅H₄N) (3a, R = H; 3b, R = 4-COOMe; 3c, R = 4-COOEt)

upon heating. In contrast, the thermolysis of 2d did not aﬀord a face-capping picoline complex because of the poor electron-

accepting ability of the picolyl moiety. Instead, the coordinatively unsaturated μ₃-picolyl complex (Cp*Ru)₃(μ-H)₂(μ₃-η²-4-Me-

C₅H₃N) (4d) was obtained. Owing to its unsaturated nature, 4d can react with γ-picoline to yield 4,4′-dimethyl-2,2′-bipyridine.

Although the reaction rate was slow, complex 1 catalyzed the dehydrogenative coupling of 4-substituted pyridines containing an

electron-donating group. The protonation of 2a also aﬀorded the coordinatively unsaturated pyridyl complex [(Cp*Ru)₃(μ-

H)₂(μ₃-H)(μ₃-η²:η²(⊥)-C₅H₄N)]⁺(5a), but the coordination mode of the pyridyl group in 5a was completely diﬀerent from that

in 4d. The pyridyl moiety in 5a was coordinated on one of the Ru−Ru bonds in a perpendicular fashion. The methylation of the

face-capping pyridine complex 3a, which led to the formation of the N-methyl pyridinium complex [(Cp*Ru)₃(μ-H)₃(μ₃-

η²:η²:η²-C₅H₅NMe)]⁺(7b) was also examined. NMR studies on 7b as well as X-ray diﬀraction studies suggested enhanced back-

donation to the pyridinium moiety because of the localized cationic charge on the nitrogen atom.

the chemisorption of pyridine is related to the hydro-

denitrogenation process and the poisoning of catalysis. Thus,

it is important to understand the interaction of pyridine with a

metal surface in detail to reveal the mechanisms of these

processes.

INTRODUCTION

■

The chemistry of organic molecules on a metal surface has

attracted considerable attention in relation to heterogeneous

catalysis. The interaction of an aromatic compound with a

metal surface is one of the most intensively studied subjects in

this area, and various adsorption modes of arenes have thus far

been elucidated by means of high-resolution electron energy

loss spectroscopy (HREELS), low-energy electron diﬀraction

(LEED) study, scanning probe microscopy (SPM), and so on.¹

For example, Somorjai and co-workers used LEED to elucidate

that benzene is adsorbed on a 3-fold site of Rh(111) in a ﬂat

manner with respect to the surface in the presence of CO.^1b

In contrast to benzene, pyridine can interact with a metal

surface by both π electrons and the lone-pair electrons at the

nitrogen atom. This produces the interesting chemistry of

chemisorbed pyridine, in which the pyridine is converted from

a relatively ﬂat-lying π-bonded species to a tilted nitrogen-

bonded species.²Various adsorption modes of pyridine have

thus far been elucidated on several metal surfaces by means of

HREELS,^2a−dnear-edge X-ray absorption ﬁne structure

(NEXAFS) measurements,^2e,fSPM,^2g,hand so on. In addition,

Polynuclear organometallic compounds have been shown to

serve as an appropriate model for the metal surface.³The

spectroscopic data of the well-deﬁned cluster compounds is

often used for the characterization of the chemisorbed species,

and the structural data of these compounds provide detailed

information about the chemisorbed species. More importantly,

information about the reactivity of the chemisorbed species is

also provided by the cluster chemistry. Lewis and co-workers

succeeded in the synthesis of a trimetallic complex having a μ₃-

η²:η²:η²-benzene ligand, which is a counterpart of the adsorbed

benzene at the 3-fold site.⁴They elucidated not only the

structure but also its reactivities. In addition to a face-capping

arene complex, various coordination modes of arenes, such as

Received: May 6, 2012

Published: June 26, 2012

4817

dx.doi.org/10.1021/om300379d | Organometallics 2012, 31, 4817−4831

Organometallics

Article

μ₃-,⁵μ₄-, and μ₅-benzyne complexes,⁶have been prepared, and

their reactivities have also been investigated.

While various adsorption modes of pyridine on a metal

surface have been proposed, pyridine has been shown to attach

to a multimetallic core in a quite limited mode. This is in

contrast to the extensive chemistry of arene clusters. Since Yin

and Deeming synthesized the ﬁrst trimetallic μ-pyridyl complex

Os₃(CO)₁₀(μ-H)(μ-C₅H₄N) by the reaction of Os₃(CO)₁₂

with pyridine,⁷several trimetallic complexes containing a μ-

pyridyl ligand have been prepared.⁸However, whereas many

μ₃-benzyne complexes are known, coordination of a pyridyl

group in a μ₃fashion is less well known.⁹In addition, there

have been no reports on a polynuclear complex containing a

face-capping μ₃-pyridine ligand until we reported the synthesis

of {Cp*Ru(μ-H)}₃(μ₃-η²:η²:η²-C₅H₆N) (Cp* = η⁵-C₅Me₅)

(2a) in a previous communication.¹⁰We report herein novel

coordination modes of pyridine on a trimetallic core, μ₃-η²(//)-

pyridyl, μ₃-η²:η²(⊥)-pyridyl, and face-capping pyridine ligands,

as well as their reactivities.

Figure 1. Time course of the reaction of {Cp*Ru(μ-H)}₃(μ₃-H)₂(1)

with pyridine, yielding μ₃-η²(//)-pyridyl complex 2a and μ₃-η²:η²:η²-

pyridine complex 3a (10 equiv of pyridine, C₆D₆, 80 °C).

and bond distances around the N(1) atom with those of 2c,

which possesses an ethoxycarbonyl group at the 4-position

(Figure 2b). The positions of the four hydrido ligands in 2a

were not determined during the diﬀraction study, but they were

located in 2c, as shown in Figure 2b.

The pyridyl ligand in 2a acts as a 5e donor, and this makes

complex 2a coordinatively saturated according to the EAN rule.

Such a coordination mode is often observed in the trimetallic

imidoyl complexes,¹²but it has never been reported in a

trimetallic pyridyl complex. All of the trimetallic pyridyl

complexes that have ever been reported adopted a μ₂-

coordination, which acts as a 3e donor.⁸While the pyridine

ring is nearly orthogonal to the trimetallic plane in the μ-pyridyl

complexes, that of 2a is tilted from the normal of the Ru₃plane

due to the π-coordination of the CN bond to Ru(1); the

dihedral angle between the pyridine ring and the Ru₃plane is

estimated at ca. 65°.

RESULTS AND DISCUSSION

■

We have shown that the reaction of triruthenium pentahydrido

complex 1 with excess amounts of pyridine aﬀorded the face-

capping pyridine complex 3a.¹⁰During the initial stage of the

reaction carried out at 80 °C, the formation of intermediate 2a,

which has a μ₃-η²(//)-pyridyl group, was observed (eq 1).

While complex 2a is the ﬁrst discrete μ₃-η²(//)-pyridyl

complex, the tilted coordination of an α-pyridyl species has

been elucidated on a Rh(111) surface;^2aSomorjai and co-

workers proposed a tilted structure for a κ(C,N)-pyridyl species

on the basis of the LEED patterns and the HREELS spectrum,

in which the tilted angle was estimated to be between 40° and

60°. This fact indicates that the triruthenium core derived from

1 can faithfully reproduce the nature of a closed-packed metal

surface. Unlike the traditional carbonyl clusters, complex 2 does

not possess an electron-withdrawing group, such as CO.

Furthermore, the trimetallic core of 2 is composed of hydrido

ligands and strong electron-donating Cp* groups. Therefore,

the metal centers of 2 should remain electron-rich, which

enables additional back-donation to the π*(CN) of the pyridyl

group.

The pyridine ring is σ-bonded to Ru(2) and Ru(3) through

the N(1) and the C(1) atoms, respectively (Ru(2)−N(1) =

2.077(2) Å, Ru(3)−C(1) = 2.048(3) Å). The N(1) and the

C(1) atoms are also π-bonded to Ru(1) (Ru(1)−N(1) =

2.181(3) Å, Ru(1)−C(1) = 2.201(3) Å). The N(1)C(1)

distance (1.413(4) Å) lies in the reported range for the NC

bond distances in the μ₃-η²(//)-imidoyl complexes (1.280−

1.431 Å).¹²Because of this π-coordination, the π electrons in

the pyridyl group should be localized; the C(1)−C(2), C(3)−

C(4), and N(1)−C(5) bonds (1.427(4), 1.423(5), and

1.405(4) Å, respectively) are considerably longer than the

C(2)C(3) and C(4)C(5) bonds (1.358(5) and 1.371(5)

Å, respectively). The ¹³C signal of the imino carbon appeared at

δ 168.3. This value is comparable to those of the μ-pyridyl

Once the distribution of the intermediate 2a reached 60%, its

concentration gradually decreased over time. At that point, the

yield of face-capping pyridine complex 3a was 12%, which

increased to 80% with prolonged heating. The time course of

the reaction is shown in Figure 1.

The μ₃-pyridyl group was apparently formed via C−H bond

cleavage at the α-position. The α-C−H bond cleavage of

pyridine is a well-known phenomenon in cluster chemistry⁹as

well as in surface chemistry.^{2a−c,e,g,i,11}The facile C−H bond

scission is thought to be caused by the cooperative interaction

of the neighboring metal centers with pyridine. The nitrile-

substituted triosmium cluster Os₃(CO)₁₀(MeCN)₂has been

shown to react with pyridine even at ambient temperature.^9b

The μ₃-pyridyl complex 2a was isolated from the mixture by

recrystallization, and the molecular structure was determined by

X-ray diﬀraction. Figure 2a clearly shows that the pyridyl ligand

is attached to a trimetallic core in a μ₃-η²(//) fashion. The

relevant bond lengths and angles are listed in Table 1 with the

data of 2c. Although it is diﬃcult to distinguish between

nitrogen and carbon atoms only on the basis of the value of the

cross section during the diﬀraction study, the position of N(1)

was determined by comparing the isotropic temperature factors

4818

dx.doi.org/10.1021/om300379d | Organometallics 2012, 31, 4817−4831

Organometallics

Article

Figure 2. Molecular structures of (a) 2a and (b) 2c with thermal ellipsoids at the 30% level of probability. A solvent molecule (diethyl ether) in the

unit cell of 2a was omitted for clarity.

structure of 2c was determined by X-ray diﬀraction, and the

structure is shown in Figure 2b. The results of the structural

study of the face-capping pyridine complexes 3b and 3c will be

mentioned later.

Table 1. Selected Bond Distances (Å) and Angles (deg) for

2a and 2c

Ru(1)−Ru(2)

Ru(2)−Ru(3)

Ru(1)−Ru(3)

Ru(1)−N(1)

Ru(1)−C(1)

Ru(2)−N(1)

Ru(3)−C(1)

N(1)−C(1)

C(1)−C(2)

C(2)−C(3)

C(3)−C(4)

C(4)−C(5)

N(1)−C(5)

2.8456(3)

2.8654(3)

2.8354(3)

2.181(3)

2.201(3)

2.077(2)

2.048(3)

1.413(4)

1.427(4)

1.358(5)

1.423(5)

1.371(5)

1.405(4)

2.8385(5)

2.8600(5)

2.8496(5)

2.183(3)

2.173(4)

2.067(3)

2.038(4)

1.433(5)

1.420(5)

1.379(6)

1.430(6)

1.354(6)

1.386(5)

1.473(6)

1.217(5)

1.358(5)

60.370(11)

60.007(11)

59.622(12)

109.0(2)

130.1(3)

111.7(2)

130.5(3)

The presence of an ethoxycarbonyl group at the 4-position

enables the straightforward assignment of the N(1) atom, as

shown in Figure 2b. In addition, the positions of the hydrido

ligands were also determined in 2c. The H(1), H(3), and H(4)

atoms are located on each Ru−Ru bond on the face opposite to

the pyridyl group, and the H(2) atom bridges the Ru(2) and

Ru(3) atoms on the same side as the pyridyl group. The

structural parameters of 2c are almost the same as those of 2a.

The μ₃-η²(//)-pyridyl complex 2d was also obtained by the

reaction of 1 with γ-picoline. In this case, however, a face-

capping pyridine complex was not produced upon prolonged

heating. This marked diﬀerence is attributable to the electron-

donating nature of the methyl group on the pyridine ring

because, as the formation of 3c demonstrates, the face-capping

coordination of pyridine to the Ru₃plane is possible even

though it contains a bulkier substituent. The face-capping

coordination would receive a more signiﬁcant back-donation

from the trimetallic core than the μ₃-η²-coordination does. The

presence of an electron-donating group on a pyridine ring raises

the energy level of the π* orbitals considerably, which makes

the face-capping coordination of γ-picoline unfavorable.

The ¹H NMR spectra of 2d were recorded at various

temperatures, as shown in Figure 3. While three sharp Cp*

signals were observed at δ 1.88, 1.82, and 1.56 at −80 °C, the

two that resonated at δ 1.88 and 1.56 became broader and

ﬂatter at −40 °C. At this temperature, the shape of the Cp*

signal at δ 1.82 ppm remained unchanged. Above −20 °C, all

Cp* signals became broader and coalesced into one peak

resonating at δ 1.85.

This spectral change is rationalized by the combination of the

two dynamic processes of the μ₃-pyridyl group accompanied by

the hopping of a hydrido ligand between the two Ru−Ru

bonds, as shown in Scheme 1. We could not determine which

was the lower-energy process, the pivot motion on the carbon

atom or that of the nitrogen atom, but the pivot motion of a μ₃-

η²(//)-imidoyl ligand on carbon has often been proposed for

the dynamic process in the trimetallic imidoyl complexes.¹⁵

Rosenberg and co-workers suggested that the pivot motion on

the carbon atom is the lower-energy process in Os₃(CO)₈(L)-

(μ-H)(μ₃-η²-CNCH₂CH₂CH₂−) (L = CO, CNMe). Cabeza

and co-workers elucidated that the pivot motion on the carbon

atom is the ﬁrst step for the rotation of the μ₃-η²-imidoyl group

C(3)−C(6)

C(6)−O(1)

C(6)−O(2)

Ru(2)−Ru(1)−Ru(3)

Ru(1)−Ru(2)−Ru(3)

Ru(1)−Ru(3)−Ru(2)

Ru(2)−N(1)−C(1)

Ru(2)−N(1)−C(5)

Ru(3)−C(1)−N(1)

Ru(3)−C(1)−C(2)

60.581(8)

59.534(8)

59.884(8)

109.93(18)

129.8(2)

111.30(18)

129.9(2)

complexes, [Ir₂(μ-ArNCH₂NAr)(μ-C₅H₄N)₂(Py)₄]⁺(δ 165.0,

162.4)¹³and Ru₃(CO)₉(μ-H)(dpa) (dpa = di(2-pyridyl)-

amine) (δ 174.4).¹⁴

In the H NMR spectrum of 2a recorded at −80 °C, three

sharp signals assignable to the Cp* groups were observed at δ

1.57, 1.81, and 1.87. This agreed with the molecular structure

shown in Figure 2. These signals, however, became broader as

the temperature increased and coalesced into one signal that

resonated at δ 1.85. As will be mentioned later, this dynamic

behavior arises from the motion of the μ₃-η²(//)-pyridyl group

moving around the Ru₃core. The four hydrido ligands

resonated at δ −17.56, −17.06, −13.60, and −13.42 at −80

°C, which also became broader and ﬂatter as the temperature

increased.

The reaction of 1 with methyl and ethyl isonicotinate also

aﬀorded both face-capping pyridine complexes 3b and 3c as

well as μ₃-η²(//)-pyridyl complexes 2b and 2c. Whereas

complex 2a is decomposed on alumina, complexes 2b and 2c

can be puriﬁed by column chromatography on alumina. The

4819

dx.doi.org/10.1021/om300379d | Organometallics 2012, 31, 4817−4831

Organometallics

Article

Figure 3. VT-NMR spectra of μ₃-η²(//)-pyridyl complex 2d in THF-d₈showing the Cp* (left) and the hydrido (right) regions. The Cp* signal

appearing at δ 1.98 was derived from {Cp*Ru(μ-H)}₃(μ₃-H)₂(1), and the asterisked peak was derived from the residual protons of the solvent.

Scheme 1. Dynamic Behavior of μ₃-η²(//)-Pyridyl Complex

signals were still sharp. Thus, the signals at δ −13.68 and

−13.34 were assigned to H^aand H^c. At higher temperatures,

the environments of H^a, H^b, and H^cbecome equivalent because

of the additional pivot motions of the pyridyl group. At −20

°C, the signal resonating at δ −17.48 started to broaden. At that

point, the shape of the signal at δ −17.08 remained unchanged.

Therefore, the signal at δ −17.48 is assignable to H^band that

observed at δ −17.08 can be assigned to H^d. Above room

temperature, the signal of H^dbecame broader. This most likely

arose from the direct site exchange between H^dand other

hydrides.

The reaction of 1 with β-picoline resulted in the exclusive

formation of the μ₃-η²(//)-picolyl complex 2e (eq 2). Although

by the aid of DFT calculation.¹⁶In the low-temperature region,

the pyridyl group exhibits the ﬁrst pivot motion only between

the two Ru−Ru bonds, most likely a pivot motion on the

carbon atom, which brings a time-averaged C_Sstructure. Hence,

the Cp* signals are seen as a set of two signals with an intensity

ratio of 2:1.

In the high-temperature region, the pyridyl group migrates to

all of the Ru−Ru bonds. This motion requires the additional

pivot motion of the pyridyl group, probably a pivot motion on

the nitrogen atom. These successive pivot motions cause the

environments of the Cp* groups to be equivalent. The

successive pivot motions of the μ₃-η²(//)-imidoyl ligand on

its M−C and M−N bonds on a trimetallic plane have been

clearly elucidated in (Cp*Co)₃(μ-H)(μ₃-η²-HCNCMe₃)¹⁷

and Ru₃(CO)₉(μ-H)(μ₃-η²-MeCNMe),¹⁸but that of a μ-

pyridyl group has not been reported so far.

β-picoline possesses two diﬀerent α-protons, C−H bond

cleavage occurred only at the 6-position. This can be

rationalized by the steric repulsion between the Cp* groups

and the methyl group on the pyridine ring; if the C−H bond at

the 2-position was broken, the μ₃-picolyl group should be

placed on the Ru₃plane with the methyl group directed toward

the Cp*group. The fact that 1 did not react with α-picoline also

shows that the position of the substituents on a pyridine ring is

crucial for the μ₃-η²(//)-coordination.

The H NMR spectrum of 2e resembled that of 2d, but the

characteristic H signal of the α-CH group, which underwent a

In the hydrido region, four sharp signals were observed at δ

−17.48, −17.08, −13.68, and −13.34 at −80 °C. The pivot

motion of the pyridyl group makes two of the four hydrido

ligands, H^aand H^cin Scheme 1, to be equivalent if the pivot

motion on the carbon atom is the lower-energy process. As

seen in the ¹H NMR spectrum at −40 °C, only the two signals

appearing at the lower magnetic ﬁeld coalesced, while the other

considerable downﬁeld shift, appears as a singlet instead of the

doublet found in the H NMR spectrum of 2d. In addition, a

face-capping β-picoline complex was not formed upon further

heating of 2e.

Although further thermolysis of 2d did not aﬀord a face-

capping pyridine complex, thermolysis of 2d at 160 °C resulted

in the exclusive formation of the coordinatively unsaturated μ₃-

4820

dx.doi.org/10.1021/om300379d | Organometallics 2012, 31, 4817−4831

Organometallics

Article

pyridyl complex 4d as a consequence of the elimination of

dihydrogen (eq 3). Because of this coordinatively unsaturated

2.85 Å, the Ru₃core of 4d forms an isosceles triangle, in which

the Ru(1)−Ru(2) bond (2.9142(8) Å) is the longest.

As for isoelectronic μ₃-alkyne complexes, it is commonly

accepted that an alkyne ligand is coordinated on a trimetallic

core in parallel with one of the M−M bonds in a coordinatively

saturated (48-electron) complex, whereas it adopts a diﬀerent

coordination mode in coordinatively unsaturated (46-electron)

complexes, in which an alkyne ligand is coordinated

perpendicular to one of the M−M bonds.¹⁹In a model

complex, {CpRu(μ-H)}₃(HCCH) (Cp = C₅H₅), Morokuma

and co-workers estimated that the perpendicular conformation

is more stable by 4.6 kcal/mol than the parallel one.²⁰As a

consequence of the symmetric properties of the frontier orbitals

of the trimetallic fragment and the alkyne π orbitals, it has been

shown that the perpendicular coordination of an alkyne ligand

is preferred in a cluster having a 46e conﬁguration, while the

parallel mode is stable in a 48e cluster. This classiﬁcation can be

applied to the isoelectronic μ₃-imidoyl complexes, in which all

the coordinatively saturated μ₃-imidoyl complexes adopt a

parallel coordination mode,^15−18,21while we showed the

perpendicular coordination of a μ₃-imidoyl ligand in

(Cp*Ru)₃(μ₃-η²:η²(⊥)-PhCNH)(μ-H)₂, which adopts a 46e

conﬁguration.²²

nature, 4d was highly air-sensitive and thus could not be

isolated in an analytically pure form. However, a red single

crystal of 4d was obtained from a cold diethyl ether solution,

and its molecular structure was determined by X-ray diﬀraction,

as shown in Figure 4. The relevant structural data are listed in

Table 2.

In coordinatively saturated complex 2, the pyridyl group is

attached to the Ru₃core in a parallel fashion, which is in accord

with the trend of the μ₃-alkyne complexes. In contrast, the

structure of 4d violates the above-mentioned “rule”, meaning

that the μ₃-pyridyl group in 4d is not coordinated to the Ru₃

core in a perpendicular fashion, despite its 46e conﬁguration.

Although it is slightly distorted, the coordination mode is

viewed as a parallel mode. Because of this slight distortion,

complex 4d could not be eﬀectively stabilized. Actually,

complex 4d was quite unstable toward air and moisture. This

instability could be crucial for the dehydrogenative coupling of

γ-picoline (vide infra).

In the H NMR spectrum of 4d, a broad signal for the

Figure 4. Molecular structure of 4d with thermal ellipsoids at the 30%

level of probability.

hydrido ligands was observed at −80 °C. At 25 °C, the signal

became sharper and resonated at δ −11.62 as a sharp singlet.

The signals for the Cp* groups were observed at δ 1.62 and

2.09 as a set of broad signals with an intensity ratio of 1:2 at

−80 °C, which coalesced into a sharp signal at δ 1.79 at 25 °C.

These facts indicate that the γ-picolyl group in 4d moves

around the Ru₃plane in the same fashion as the μ₃-η²(//)-

pyridyl group in 2 does, but the motion is not frozen even at

−80 °C. Thus, the dynamic process in 4d seems to be

signiﬁcantly faster than that found in 2. In the ¹³C NMR

spectrum, the imidoyl carbon appeared at δ 154.7, which

underwent a notable upﬁeld shift compared with that of the μ₃-

η²(//)-pyridyl complex 2c (δ 170.4).

Figure 4 clearly represents the μ₃-η²-coordination of the γ-

picolyl group in 4d. The picolyl group bridges the Ru(2) and

the Ru(3) atoms and is π-bonded to Ru(1). Unlike

coordinatively saturated complex 2, the Ru(1)−C(1) bond

(2.220(5) Å) is longer than the Ru(1)−N(1) bond (2.129(4)

Å) by 0.09 Å. In complexes 2a and 2c, the diﬀerences are

minimal: 0.02 Å in 2a and 0.01 Å in 2c. This fact shows the

distorted π-coordination of the γ-picolyl group in 4d. The two

hydrido ligands, H(1) and H(2), are located on the Ru(1)−

Ru(2) and Ru(2)−Ru(3) edges. Unlike the Ru₃core of 2

forming an approximate equilateral triangle with sides of ca.

The perpendicularly coordinated μ₃-pyridyl complex 5a was

obtained upon protonation of 2a. Protonation of a hydrido

Table 2. Selected Bond Distances (Å) and Angles (deg) for 4d

Ru(1)−Ru(2)

Ru(1)−N(1)

Ru(3)−C(1)

C(2)−C(3)

2.9146(9)

2.129(4)

2.049(5)

1.365(8)

1.396(6)

57.69(2)

106.0(3)

131.0(4)

Ru(2)−Ru(3)

Ru(1)−C(1)

N(1)−C(1)

C(3)−C(4)

2.7401(8)

2.220(5)

1.394(6)

1.418(9)

Ru(1)−Ru(3)

Ru(2)−N(1)

C(1)−C(2)

C(4)−C(5)

2.7580(11)

2.081(4)

1.415(7)

1.376(8)

N(1)−C(5)

Ru(2)−Ru(1)−Ru(3)

Ru(2)−N(1)−C(1)

Ru(3)−C(1)−C(2)

Ru(1)−Ru(2)−Ru(3)

Ru(2)−N(1)−C(5)

58.29(2)

123.1(3)

Ru(1)−Ru(3)−Ru(2)

Ru(3)−C(1)−N(1)

64.024(19)

110.9(3)

4821

dx.doi.org/10.1021/om300379d | Organometallics 2012, 31, 4817−4831

Organometallics

Article

complex, followed by liberation of dihydrogen, corresponds to

the removal of two electrons from a metal center. Thus, it can

aﬀord a 46e species. Treatment of 2a with HBF₄in diethyl

ether resulted in the immediate precipitation of the cationic μ₃-

η²:η²(⊥)-pyridyl complex 5a (eq 4). Complex 5a was stable

with its nitrogen atom directed outside the Ru₃core. The

direction of the pyridyl group is the same as that found in the

μ₃-η²:η²(⊥)-imidoyl and the cationic μ₃-η²:η²(⊥)-imidoyl

complexes.²²The direction of the μ₃-pyridyl group was also

conﬁrmed by the marked upﬁeld shift of the inner carbon atom

in the ¹³C NMR spectrum (δ 136.2). The ¹³C signals of the

inner carbon atom underwent an upﬁeld shift by ca. 30 ppm

compared with that of 2a and were comparable to that of the

cationic μ₃-η²:η²(⊥)-imidoyl complex 6 (δ 139.3).^22a

As seen in Figure 5, the μ₃-η²:η²(⊥)-pyridyl group was

attached to the trimetallic core with its molecular plane normal

to the Ru₃plane. α-Pyridyl species normal to the metal surface

have been proposed for Ni(100)^2band Pt(111)^2c,fby means of

HREELS, NEXAFS, and EELS; however, only the angle

between the molecular plane and metal surface was shown. The

coordination mode of the pyridyl group was not taken into

account. The structure of 5a clearly shows the possibility of the

μ₃-η²:η²(⊥)-coordination of the pyridyl group on a metal

surface, in addition to the common μ-coordination.

enough to be isolated in an analytically pure form. The stability

resembled that of the cationic μ₃-η²:η²(⊥)-imidoyl complex

[(Cp*Ru)₃(μ-η²:η²(⊥)-PhCNH)(μ-H)₂(μ₃-H)]⁺(6).^22aThis

is quite a contrast with the instability of 4d that adopts the

same 46e conﬁguration.

While the C(1)−N(1) bond length (1.368(7) Å) is less than

that of the π-coordinated C−N bonds of 2a (1.413(4) Å), it

still lies in the reported range for the π-coordinated CN

bonds (1.280−1.431 Å).¹²The C−N bond length is quite

comparable to that of the cationic μ₃-η²:η²(⊥)-imidoyl complex

6 (1.351(5) Å).²¹The Ru(1)−C(1) length (2.084(6) Å)

implies the hypervalent nature of the inner carbon atom as seen

in 6 and the perpendicularly coordinated alkyne complexes.^20b

Complex 5a is ﬂuxional, similar to other μ₃-η²:η²(⊥)-imidoyl

and μ₃-η²:η²(⊥)-alkyne complexes that shows a switchback

motion.^20cAs a consequence, signals for the Cp* groups were

observed to be equivalent at room temperature and resonated

at δ 1.85 as a sharp singlet.

Thermolysis of 2a at 100 °C in THF-d₈in the absence of

pyridine was then monitored by NMR spectroscopy. At the

initial stage of the reaction, formation of 1, 3a, and a

coordinatively unsaturated μ₃-pyridyl complex, (Cp*Ru)₃(μ₃-

C₅H₄N)(μ-H)₂(4a), was observed along with the consumption

of 2a. After 5.5 h, 57% of 2a was consumed and the yields of 1,

3a, and 4a were 21, 11, and 25%, respectively. At this time, the

liberation of pyridine was also observed. The rate of decrease in

2a then dropped, and the concentrations of 1 and 4a began to

decrease.

Whereas protonation of the face-capping pyridine complex

3a occurred at the nitrogen atom to yield a face-capping

pyridinium complex [{Cp*Ru(μ-H)}₃(μ₃-η²:η²:η²-C₅H₅N-

(H))]⁺(7a),¹⁰protonation of 2a took place at a metal center,

leading to the elimination of dihydrogen. Because the lone-pair

electrons at the nitrogen atom do not participate in bonding

interaction in the face-capping complex 3, protonation can

occur at the nitrogen atom. However, the lone-pair electrons

were already used for the bonding to the metal center in 2.

Therefore, protonation should occur at a metal center. While

the perpendicular coordination of an aromatic ring to a

trimetallic core has been often proposed as an intermediate

state of a dynamic process arising from the μ₃-coordinated

arene ligand,²³complex 5a is the ﬁrst isolated example of such a

species. Complex 5a can be viewed as a model of the

intermediate stage of the pivot motion of the μ₃-η²(//)-pyridyl

on the carbon atom. An X-ray diﬀraction study unambiguously

showed the perpendicular coordination of the μ₃-pyridyl group

in 5a (Figure 5). The structural data of 5a is listed in Table 3.

The Ru₃core forms an isosceles triangle with sides of

2.7389(5), 2.7525(5), and 2.9873(6) Å, in which the pyridyl

group is perpendicularly coordinated to the longest Ru(2)−

Ru(3) bond. The pyridyl group is coordinated to the Ru₃core

Complex 4a was formed by the elimination of dihydrogen

from 2a, as seen in the formation of 4d. The reaction of 2a with

the liberated dihydrogen resulted in the immediate regener-

ation of 1. Actually, pentahydrido complex 1 was exclusively

obtained upon treatment of 3a with 1 atm of H₂at 60 °C with

the liberation of pyridine (eq 5). Although coordinatively

unsaturated 4a was not isolated from the mixture, it was

assumed that 4a would also react smoothly with dihydrogen to

regenerate 2a and 1. Thus, at the initial stage, there would be a

pre-equilibrium between 1, 2a, and 4a via addition and

Figure 5. Molecular structure of 5a with thermal ellipsoids at the 30%

level of probability. An anionic part (BF₄) was omitted for clarity.

−

4822

dx.doi.org/10.1021/om300379d | Organometallics 2012, 31, 4817−4831

Organometallics

Article

Table 3. Selected Bond Distances (Å) and Angles (deg) for 5a

Ru(1)−Ru(2)

Ru(1)−C(1)

Ru(3)−N(1)

C(1)−C(2)

2.7389(5)

2.084(6)

Ru(2)−Ru(3)

Ru(2)−N(1)

Ru(3)−C(1)

C(2)−C(3)

N(1)−C(5)

2.9873(6)

2.119(5)

Ru(1)−Ru(3)

Ru(2)−C(1)

N(1)−C(1)

C(3)−C(4)

2.7525(5)

2.343(6)

1.368(7)

1.399(11)

2.049(5)

2.576(6)

1.429(9)

1.370(11)

1.384(7)

C(4)−C(5)

1.345(10)

65.912(14)

74.63(17)

126.5(5)

Ru(2)−Ru(1)−Ru(3)

Ru(2)−C(1)−Ru(3)

Ru(1)−C(1)−C(2)

Ru(1)−Ru(2)−Ru(3)

Ru(2)−N(1)−Ru(3)

57.262(13)

91.10(19)

Ru(1)−Ru(3)−Ru(2)

Ru(1)−C(1)−N(1)

56.826(13)

117.0(4)

elimination of pyridine and dihydrogen, as shown in Scheme 2.

Complex 2a would then isomerize to the face-capping pyridine

species were converted into 3a, which indicates that the face-

capping pyridine complex 3a is a thermodynamically favored

product.

As mentioned above, the γ-picolyl complex 2d did not aﬀord

a face-capping pyridine complex upon heating. This brought a

diﬀerent reactivity from those seen in 2a−2c. When the

thermolysis was carried out in the presence of an excess amount

of γ-picoline, dehydrogenative coupling of γ-picoline, leading to

the exclusive formation of 4,4′-dimethyl-2,2′-bipyridine, was

observed (Table 4). Although the reaction rate was fairly slow

in comparison with that of the reaction catalyzed by

diruthenium tetrahydrido complex Cp*Ru(μ-H)₄RuCp*,²⁴

the turnover number reached 80 in 120 h when the reaction

was carried out using 0.2 mol % 1 at 180 °C (entry 2). It is

noteworthy that only bipyridine was produced; terpyridine was

not formed during the reaction. This is the crucial diﬀerence

from the coupling reaction catalyzed by heterogeneous

catalysts, such as Raney-Ni and Pd/C.²⁵This selectivity

possibly arose from the shape of the triruthenium core, which

suppresses the formation of a μ₃-η²(//)-pyridyl complex by the

reaction with 2-substituted pyridine because of the steric

repulsion between the substituent and the Cp* groups.

Whereas pyridine and ethyl isonicotinate were only

minimally dimerized (entries 6 and 11), the dehydrogenative

coupling of 4-ethylpyridine (entry 7), 4-dimethylaminopyridine

(entry 8), and 4,4′-bipyridine (entry 9) proceeded in moderate

yields. A solvent having strong coordination ability, in this case,

1,2-dimethoxy ethane, suppressed the reaction (entry 4). It is

Scheme 2. Plausible Mechanism for the Transformation of

μ₃-η²(//)-Pyridyl Complex 2 to Face-Capping Pyridine

Complex 3

complex 3a via reductive C−H bond formation to form the

κ(N)-pyridine intermediate A. Upon further heating, all the

Table 4. Results of the Dehydrogenative Coupling of 4-Substituted Pyridine Catalyzed by Triruthenium Pentahydrido Complex

entry

substrate

R = Me

temp (°C)

time (h)

solvent

decane

substrate/catalyst

yield (%)

160

180

120

500

100

R = Me

decane

R = Me

mesitylene

DME

R = Me

100

mesitylene

R = H

trace

R = Et

R = NMe₂

R = OMe

R = 4-pyridyl

R = COOEt

trace

The reactions were carried out in a 20 mL glass tube equipped with a Teﬂon-seal valve. The catalyst was loaded as a decane or mesitylene solution

(4 mM). A 3 mL amount of solvent was used, and biphenyl was added to the ﬂask as an internal standard. The yield was determined by GLC

analysis. The yield was determined by H NMR analysis.

4823

dx.doi.org/10.1021/om300379d | Organometallics 2012, 31, 4817−4831

Organometallics

Article

Scheme 3. Plausible Mechanism for the Dehydrogenative Coupling of 4-Substituted Pyridines Performed on the Trimetallic

Core Derived from 1

notable that pyridine containing a dimethylamino group can be

dimerized by 1, unlike the coupling reaction catalyzed by

palladium on charcoal.^25dAlthough the yields were not

suﬃcient, these results may open a new route to developing

functionalized bipyridines using a polyhydrido cluster as a

catalyst precursor. Furthermore, this is a rare example of a

direct C−C bond formation at the 2-position of pyridine via

C−H bond activation.²⁶The failure of the coupling reaction of

unsubstituted pyridine and ethyl isonicotinate was most likely

due to the formation of thermally stable face-capping pyridine

complexes 3a and 3c.

Because no intermediate was observed during the reaction,

the mechanistic detail is not clear at present. However, the

dehydrogenative coupling of pyridines is assumed to proceed in

a similar manner to the C−C bond formation between the two

hydrocarbyl ligands placed on each face of the triruthenium

plane,²⁷which we have recently demonstrated. Namely, the

second pyridine molecule seems to approach from the less-

hindered side of the coordinatively unsaturated μ₃-pyridyl

complex 4 to form intermediate I-1 (Scheme 3). The oxidative

addition of the α-C−H bond forms a bis(μ-pyridyl)

intermediate I-2. Reductive C−C bond formation then takes

place upon breaking a Ru−Ru bond, as seen in the formation of

a closo-ruthenacyclopentadiene skeleton.^27aThis leads to the

construction of a bipyridine skeleton in I-3. Coordination of

the third pyridine molecule would eliminate bipyridine from

the trimetallic core and regenerate 4. The slow rate of the

reaction was probably due to the sterically restricted shape of

the trimetallic core, as well as to the contribution of the reverse

reactions, leading to regeneration of 2 and 1 by the uptake of

dihydrogen accommodated during the reaction.

uncoordinated C−C and C−N bond lengths (1.446(5) Å)

implied Kekule distortion as an azacyclohexatriene. This is

consistent with the rigid structure of 3, in which the μ₃-η²:η²:η²-

pyridine ligand does not rotate around the Ru₃core.

Consequently, the Cp* signals were observed to be

inequivalent in the ¹H NMR spectrum. This is quite contrasted

with the μ₃-η²:η²η²-benzene complexes of Ru₃(CO)₈(L)-

(C₆H₆), in which the benzene ligand was shown to rotate on

a trimetallic core within the NMR time scale.⁴

In the cases of 3b and 3c, due to the presence of the

substituent group at the 4-position, the position of the nitrogen

atom can be unambiguously determined by X-ray diﬀraction. X-

ray diﬀraction studies were thus carried out for 3b and 3c using

red single crystals obtained from cold diethyl ether solution.

Because their molecular structures are almost the same, only

the molecular structure of 3b is shown in Figure 6, and

structural data are listed in Table 5 (the results of the X-ray

diﬀraction study of 3c are shown in the Supporting

Information).

Figure 6 clearly shows the face-capping coordination of

methyl isonicotinate to the Ru₃core. The substituent group

placed on the 4-position enables the straight assignment of the

nitrogen atom. The sum of the interior angles in the pyridine

ring in 3b is 719.9°, which shows that the six atoms are nearly

coplanar. The length of the coordinated N(1)C(1) bond is

1.395(11) Å, which is slightly shorter than the noncoordinated

N(1)−C(5) bond by 0.026 Å. Diﬀerences are not apparent in

the CC and C−C bond distances; the lengths of the

coordinated CC bonds are 1.454(12) and 1.416(13) Å,

whereas those of the noncoordinated C−C bonds are

1.428(12) and 1.462(13) Å.

Face-Capping Pyridine Complexes. In our previous

communication, we reported the results of a diﬀraction study of

the face-capping pyridine complex 3a;¹⁰although the position

of the nitrogen atom was not determined because of the

disordered structures around the six-membered ring, the

diﬀerences between the average values of the coordinated

CC and CN bond lengths (1.395(6) Å) and the

Back-donation to the pyridine ring causes the methox-

ycarbonyl group to bend away from the molecular plane. The

bent-back angles are shown to be ca. 25°, which is comparable

to the bent-back angle of the face-capping benzene complex,

(CpCo)₃{μ₃-η²:η²:η²-C₆H₅CH(Me)Ph}(μ₃-H), in which the

phenethyl group is bent away from the C₆plane by 20°.²⁸

4824

dx.doi.org/10.1021/om300379d | Organometallics 2012, 31, 4817−4831

Organometallics

Article

1.86. The hydrides resonated at δ −20.89, −20.67, and −19.24.

These facts clearly showed the rigid structure of the pyridinium

ring on the Ru₃core, as seen in the face-capping pyridine

complex 3. The ﬁve ¹³C signals of the pyridinium ring were

observed at δ 25.4, 26.8, 32.7, 48.7, and 54.6, which appeared at

the notably upﬁeld region compared with those of 3a (δ 34.5−

60.3)¹⁰and 3c (δ 34.9−58.7). A similar upﬁeld shift was

observed in the μ₃-pyridinium complex [{Cp*Ru(μ-H)}₃(μ₃-

η²:η²:η²-C₅H₅NH)]⁺(7a).¹⁰Since methylation and protonation

occurred at the nitrogen atom, the cationic charge would be

localized mainly at the nitrogen atom. This causes strong back-

donation from a metal center to the pyridinium moiety,

therefore, inducing a signiﬁcant shielding eﬀect.

An X-ray diﬀraction study was carried out using a single

crystal of a tetraphenylborate salt of 7b. The molecular

structure is shown in Figure 7, and structural data are listed

Figure 6. Molecular structure of 3b with thermal ellipsoids at the 30%

level of probability.

Similar to the protonation leading to the formation of the

cationic μ₃-pyridinium complex 7a,¹⁰methylation took place at

the nitrogen atom. Treatment of 3a with methyl triﬂate in

diethyl ether resulted in the immediate formation of the μ₃-

η²:η²:η²-N-methylpyridinium complex 7b, as a purple precip-

itate (eq 6).

In the ¹H NMR spectrum of 7b, three sharp signals

assignable to the Cp* groups were observed at δ 1.78, 1.79, and

Figure 7. Molecular structure of 7b with thermal ellipsoids at the 30%

level of probability. An anionic part (BPh₄) was omitted for clarity.

−

Table 5. Selected Bond Distances (Å) and Angles (deg) for 3b and 7b

Ru(1)−Ru(2)

Ru(2)−Ru(3)

Ru(1)−Ru(3)

Ru(1)−N(1)

Ru(1)−C(1)

Ru(2)−C(2)

Ru(2)−C(3)

Ru(3)−C(4)

Ru(3)−C(5)

N(1)−C(1)

C(1)−C(2)

C(2)−C(3)

C(3)−C(4)

C(4)−C(5)

N(1)−C(5)

3.0473(9)

3.0167(10)

3.0078(9)

2.134(7)

2.166(8)

2.183(8)

2.222(8)

2.158(9)

2.186(7)

1.395(11)

1.428(12)

1.454(12)

1.462(13)

1.416(13)

1.421(11)

1.465(14)

1.209(13)

1.374(12)

59.76(2)

59.47(2)

60.77(2)

3.0709(5)

3.0186(5)

3.0168(6)

2.1219(15)

2.1314(16)

2.1602(16)

2.1604(16)

2.1635(15)

2.1150(16)

1.412(2)

1.451(2)

1.421(2)

1.449(2)

1.415(2)

1.446(2)

C(3)−C(6)

C(6)−O(1)

C(6)−O(2)

N(1)−C(6)

1.478(2)

Ru(2)−Ru(1)−Ru(3)

Ru(1)−Ru(2)−Ru(3)

Ru(1)−Ru(3)−Ru(2)

59.444(11)

59.387(12)

61.169(10)

4825

dx.doi.org/10.1021/om300379d | Organometallics 2012, 31, 4817−4831

Organometallics

Article

in Table 5. The structure clearly represents the presence of a

methyl group at the nitrogen atom. The N(1)−C(6) bond is

bent away from the six-membered ring by 38°, which is notably

larger than the bent-back angles of the methoxy group observed

in 3b (25°). The average of the Ru−E bond lengths in 7b (E =

C or N) is 0.03 Å less than those of 3b. These facts also suggest

the enhanced back-donation to the pyridinium moiety and are

quite consistent with the density functional theory (DFT)

calculations for the adsorbed pyridine molecule on a MoS₂

surface, which demonstrates that the pyridinium ion is

adsorbed more tightly than the pyridine molecule.²⁹

The sum of the interior angles of the six-membered ring is

719.5°, which shows that the six atoms are still coplanar. The π-

bonded N(1)C(1) bond (1.412(2) Å) is shorter than the

uncoordinated N(1)−C(5) bond (1.446(2) Å). The average

length of the π-bonded CC bond (1.42 Å) is slightly shorter

than that of the uncoordinated C−C bond (1.45 Å). The

N(1)−C(6) length of 1.476(2) Å is almost the same as the N−

C bond length of the noncoordinated N-methylpyridinium

cation (1.463−1.473 Å).³⁰

drido complex 1 with pyridine exclusively aﬀorded a μ₃-η²(//)-

pyridyl complex 2, in which the pyridyl group is tilted with

respect to the Ru₃plane. Such a tilted coordination mode of the

pyridyl group was proposed to be formed on a metal surface,

and complex 2 is the ﬁrst discrete example of a tilted μ₃-pyridyl

species. Additional π-coordination of the pyridyl group was

probably due to the electron-rich metal centers composed of

the [Cp*Ru] fragments.

Strong back-donation to the pyridyl group causes further

isomerization into the face-capping pyridine complex. A

pyridine molecule is shown to adsorb on a metal surface with

its molecular plane parallel to a metal surface only in the low-

temperature region and is subsequently converted to μ-pyridyl

species upon warming. In contrast to this, the face-capping

pyridine complex 3 is a thermodynamically favored product.

Therefore, the nature of the face-capping pyridine ligand seems

to be diﬀerent from that of the physisorbed pyridine on a metal

surface. Somorjai showed that thermolysis of the surface pyridyl

species resulted in decomposition, leading to evolution of

dihydrogen and formation of C_xH fragments.^2aThey also noted

that the reaction resembles the decomposition of the adsorbed

benzene, which adopted face-capping coordination. Thus, the

formation of 3 implies that face-capping coordination would be

also adopted in the high-temperature region on a metal surface.

Protonation and methylation of the face-capping pyridine

complex aﬀorded cationic pyridinium complex 7. The

diﬀraction and NMR data suggest that the cationic charge is

localized at the nitrogen atom. As a result, interaction between

the trimetallic core and the pyridinium moiety seems to be

considerably strengthened. This result relates to the poisoning

of the hydrodesulfurization process by pyridine.

Although complex 3a is stable upon thermolysis and stable

toward air and moisture, it transformed into the μ-η²(//)-

pyridyl complex 2a upon irradiation. Irradiation of the THF-d₈

solution of 3a in an NMR tube using a high-pressure Hg lamp

for 10 h resulted in the exclusive formation of 2a in 68% yield

(eq 7), which was estimated by comparing the signal intensity

When the pyridine has an electron-donating group, the

pyridine moiety did not adopt a face-capping coordination

mode. Instead, coordinatively unsaturated μ₃-pyridyl complex

4d was obtained upon thermolysis of 2d, accompanied by the

liberation of dihydrogen, which seems to be an active species

for the dehydrogenative coupling of 4-substituted pyridines.

Protonation of the μ₃-pyridyl complex also resulted in

liberation of dihydrogen, but yielded the cationic μ₃-pyridyl

complex 5, whose pyridyl group is coordinated to the Ru₃plane

in a perpendicular fashion.

These results obtained here provide novel methods for the

transformation of pyridine using a polyhydrido cluster as well as

important information about the nature of an adsorbed pyridyl

species in relation to hydrodenitrogenation processes and

catalyst poisoning. We are currently investigating the reactivity

of 4d and 5 toward other small molecules in order to reveal the

reaction mechanism of the catalytic reaction.

of 2a to that of the internal standard (cyclooctane). The

transformation also proceeded when the I line (365 nm) was

irradiated by using a cutoﬀ-ﬁlter, although the rate decreased.

This transformation is quite similar to the isomerization of the

triosmium complex having a face-capping benzene ligand to

yield a μ₃-η²(//)-benzyne complex upon irradiation, as

reported by Lewis and co-workers.³¹We have already reported

the synthesis of the face-capping benzene complex {Cp*Ru(μ-

H)}₃(μ₃-η²:η²:η²-C₆H₆) (8),³²which is a benzene analogue of

3a. Unlike the photoreactivity of 3a, a detectable change was

not observed upon irradiation of 8.

The UV−vis spectrum of 3a closely resembles that of 8;

whereas complex 3a showed two adsorptions centered at 373

and 529 nm, 8 showed two peaks at 381 and 528 nm. Because

of the similarity between them, it was assumed that the

transitions were mainly derived from the triruthenium skeleton

having Cp* groups. Thus, the diﬀerence in reactivity was

probably due to the presence of a nitrogen atom in 3a, which

enabled facile C−H bond activation on a trimetallic plane.

EXPERIMENTAL SECTION

■

General Procedures. All experiments were carried out under an

argon atmosphere. All compounds were treated with Schlenk

techniques. Dehydrated toluene, pentane, methanol, THF, and

diethylether used in this study were purchased from Kanto Chemicals

and stored under an argon atmosphere. Mesitylene, benzene-d₆, p-

xylene-d₁₀, and tetrahydrofuran-d₈were dried over sodium-benzophe-

none ketyl and stored under an argon atmosphere. Other materials

used in this research were used as purchased. {Cp*Ru(μ-H)}₃(μ₃-H)₂

(1) was prepared according to a previously published method.³³UV−

vis spectra were recorded on a Shimadzu UV-2550 spectrophotometer.

¹H and ¹³C NMR spectra were recorded on a Varian INOVA-400

spectrometer. ¹H NMR spectra were referenced to tetramethylsilane as

an internal standard. ¹³C NMR spectra were referenced to the natural-

abundance carbon signal of the solvent employed. The numbering

CONCLUSION

■

The synthesis of triruthenium complexes having an unprece-

dented μ₃-η²(//)-pyridyl ligand and its transformations into a

face-capping pyridine ligand and a perpendicularly coordinated

μ₃-η²:η²(⊥)-pyridyl group were discussed. Unlike the well-

known reaction of carbonyl clusters with pyridine yielding μ-

pyridyl complexes, the reaction of the triruthenium pentahy-

4826

dx.doi.org/10.1021/om300379d | Organometallics 2012, 31, 4817−4831

Organometallics

Article

schemes of the pyridyl and the pyridine moieties are shown in Chart 1.

Elemental analysis was performed on a PerkinElmer 2400II series

mmol) was added to the solution, the reaction mixture was heated at

100 °C for 7 days. The color of the solution turned from reddish-

brown to purple. Toluene and the remaining pyridine were removed

under reduced pressure. The residual solid was puriﬁed by the use of

column chromatography on alumina (Merck, Art. No. 1097) with

tetrahydrofuran. The second purple band including 3a was collected,

and 3a was obtained as a purple solid by the removal of solvent under

reduced pressure (123.0 mg, 0.155 mmol, 54%). ¹H NMR (400 MHz,

benzene-d₆, 25 °C): δ −21.50 (dd, J_H−H= 3.8, 3.4 Hz, 1H, RuH),

−19.68 (dd, J_H−H= 4.6, 3.8 Hz, 1H, RuH), −19.65 (dd, J_H−H= 4.6, 3.4

Hz, 1H, RuH), 1.66 (s, 15H, Cp*), 1.67 (s, 15H, Cp*), 1.78 (s, 15H,

Cp*), 2.36 (dd, J_H−H= 6.0, 4.4 Hz, 1H, C^βH), 2.42 (dd, J_H−H= 6.0, 4.4

Chart 1. Numbering Schemes of the Pyridyl and the Pyridine

Moieties

Hz, 1H, C^βH), 2.52 (dd, J_H−H= 6.0, 6.0 Hz, 1H, C^γH), 3.47 (d, J_H−H

4.4 Hz, 1H, C^αH), 3.60 ppm (d, J_H−H= 4.4 Hz, 1H; C^αH). ¹³C NMR

(100 MHz, benzene-d₆, 25 °C): δ 10.8₉(q, J_C−H= 128 Hz, C₅Me₅),

10.9₃(q, J_C−H= 127 Hz, C₅Me₅), 11.2 (q, J_C−H= 127 Hz, C₅Me₅), 34.5

(d, J_C−H= 168 Hz, C^βor C^γ), 35.2 (d, J_C−H= 165 Hz, C^βor C^γ), 35.7

(d, J_C−H= 163 Hz, C^βor C^γ), 58.5 (d, J_C−H= 173 Hz, C^α), 60.3 (d,

J_C−H= 168 Hz; C^α), 89.5 (s, C₅Me₅), 89.6 (s, C₅Me₅), 90.5 (s, C₅Me₅)

ppm. Anal. Calcd for C₃₅H₅₃N₁Ru₃: C, 53.14; H, 6.75; N, 1.77. Found:

C, 53.19; H, 6.50; N, 1.73.

CHN analyzer. GLC analyses were performed on a Shimadzu GC-17A

using a capillary column (J&W DB-1; 30 m × 0.53 mm × 1.50 μm)

with helium gas as a carrier. UV irradiation experiments were

performed using an Asahi Spectra REX-250 high power mercury light

source.

Reaction of 1 with Methyl Isonicotinate. A 20 mL glass tube

equipped with a Teﬂon valve was charged with {Cp*Ru(μ-H)}₃(μ₃-

H)₂(1) (64.0 mg, 0.090 mmol) and toluene (10 mL). After methyl

isonicotinate (53 μL, 0.448 mmol) was added to the solution, the

reaction mixture was stirred at 100 °C for 5 days. The color of the

solution turned from reddish-brown to purple. The solvent and

remaining methyl isonicotinate were then removed in vacuo. The

residual solid was then dissolved in 5 mL of THF and puriﬁed by the

use of column chromatography on alumina (Merck, Art. No. 1097)

with pentane/THF = 10/1. The ﬁrst black band including 2b and the

second purple band including 3b were, respectively, collected.

Removal of the solvents under reduced pressure aﬀorded 2b as a

dark-red solid (30.9 mg, 0.036 mmol, 41% yield) and 3b as a purple

solid (20.4 mg, 0.024 mmol, 27% yield). A single crystal of 3b used for

the diﬀraction study was prepared by the recrystallization from the

cold diethyl ether solution stored at −30 °C.

X-ray Diﬀraction Studies. Single crystals of 2a, 2c, 3b, 4d, 5a,

and 7b for the X-ray analyses were obtained directly from the

preparations described below and mounted on glass ﬁbers. Diﬀraction

experiments were performed on a Rigaku R-AXIS RAPID imaging

plate diﬀractometer with graphite-monochromated Mo Kα radiation

(λ = 0.71069 Å). Cell reﬁnement and data reduction were performed

using the PROCESS-AUTO program.³⁴Intensity data were corrected

for Lorentz-polarization eﬀects and numerical (2a) and empirical

absorption (2c, 3b, 4d, 5a, and 7b). The structures were solved by the

Patterson method using the SHELX-97 program package.³⁵All non-

hydrogen atoms were found by the diﬀerence Fourier synthesis and

were reﬁned anisotropically, except for the disordered carbon atoms in

the Cp* groups attached to the Ru(3) atom in 3b. The reﬁnement was

carried out by least-squares methods based on F²with all measured

reﬂections. The metal-bound hydrogen atoms of 2c, 4d, 5a, and 7b

were located in the diﬀerence Fourier map and reﬁned isotropically.

The positions of the hydrogen atoms attached to the metal centers

were not determined for 2a and 3b. In addition, the positions of the

following hydrogen atoms attached to the carbon atoms, hydrogen

atoms on the solvent molecule in 2a, hydrogen atoms on the face-

capping pyridine ligand in 3b, and the hydrogen atom on C(5) in 4d,

could not be reﬁned. Crystal data and results of the analyses are listed

in Table 6.

(Cp*Ru)₃(μ-H)₄(μ₃-η²(//)-4-COOMe-C₅H₃N) (2b): ¹H NMR (400

MHz, −80 °C, THF-d₈): δ −17.71 (m, 1H, RuH), −16.61 (m, 1H,

RuH), −13.84 (m, 1H, RuH), −13.41 (d, J_H−H= 6.4 Hz, 1H, RuH),

1.58 (s, 15H, C₅Me₅), 1.84 (s, 15H, C₅Me₅), 1.90 (s, 15H, C₅Me₅),

3.71 (s, 3H, COOMe), 6.32 (d, J_H−H= 6.4 Hz, 1H, C⁵H), 6.60 (d,

J_H−H= 6.4 Hz, 1H, C⁶H), 7.66 ppm (s, 1H, C³H). Anal. Calcd for

C₃₇H₅₅NO₂Ru₃: C, 52.34; H, 6.53; N, 1.65. Found: C, 52.40; H, 6.57;

N, 1.80.

{Cp*Ru(μ-H)}₃(μ₃-η²:η²:η²-4-COOMe-C₅H₄N) (3b): H NMR (400

Preparation of (Cp*Ru)₃(μ-H)₄(μ₃-η²(//)-C₅H₄N) (2a). A 50 mL

Schlenk tube was charged with {Cp*Ru(μ-H)}₃(μ₃-H)₂(1) (156.1

mg, 0.219 mmol) and toluene (4 mL). After pyridine (90 μL, 1.16

mmol) was added to the solution, the reaction mixture was stirred at

90 °C for 4 days. The color of the solution turned from reddish-brown

to reddish-purple. After the solvent and remaining pyridine was

removed in vacuo, the residue was extracted three times with 5 mL of

pentane. After the combined solution was dried under reduced

pressure, the residual solid was washed two times with 3 mL of MeOH

and dried under vacuum. Recrystallization from the cold THF/MeOH

solution stored at −20 °C aﬀorded 2a as a purple crystal (58.8 mg,

MHz, benzene-d₆, 25 °C): δ −21.78 (m, 1H, RuH), −20.04 (m, 1H,

RuH), −19.25 (m, 1H, RuH), 1.67 (s, 15H, Cp*), 1.69 (s, 15H, Cp*),

1.71 (s, 15H, Cp*), 2.96 (d, J_H−H= 4.4 Hz, 1H, C₅NH₃), 3.37 (d, J_H−H

= 4.8 Hz, 1H, C₅NH₃), 3.49 ppm (s, 3H, COOMe). * Two ¹H signals

arising from the face-capping methyl isonicotinate moiety were

obscured by the COOMe signal appearing at δ 3.49 ppm. Anal.

Calcd for C₃₇H₅₅NO₂Ru₃: C, 52.34; H, 6.53; N, 1.65. Found: C, 52.56;

H, 6.47; N, 1.73.

Preparation of (Cp*Ru)₃(μ-H)₄(μ₃-η²(//)-4-COOEt-C₅H₃N) (2c).

A 20 mL glass tube equipped with a Teﬂon valve was charged with

{Cp*Ru(μ-H)}₃(μ₃-H)₂(1) (156.3 mg, 0.219 mmol) and toluene (10

mL). After ethyl isonicotinate (66 μL, 0.441 mmol) was added to the

solution, the reaction mixture was stirred at 100 °C for 18 h. The color

of the solution turned from reddish-brown to purple. After the solvent

and remaining ethyl isonicotinate were removed in vacuo, the residue

was dissolved in 5 mL of THF. The residual solid was then puriﬁed by

the use of column chromatography on alumina (Merck, Art. No. 1097)

with pentane/THF = 10/1. The ﬁrst black band including 2c was

collected. Removal of the solvent under reduced pressure aﬀorded 2c

as a black crystalline solid (153.6 mg, 0.178 mmol, 81% yield). A single

crystal used for the diﬀraction studies was prepared by the

recrystallization from the cold diethylether solution of 2c stored at

0.0704 mmol, 34% yield). H NMR (400 MHz, −80 °C, THF-d₈): δ

−17.56 (m, 1H, RuH), −17.06 (m, 1H, RuH), −13.60 (m, 1H, RuH),

−13.42 (d, J_H−H= 7.2 Hz, 1H, RuH), 1.57 (s, 15H, C₅Me₅), 1.81 (s,

15H, C₅Me₅), 1.87 (s, 15H, C₅Me₅), 5.95 (dd, J_H−H= 6.4, 6.4 Hz, 1H,

C⁵H), 6.07 (dd, J_H−H= 9.2, 6.4 Hz, 1H, C⁴H), 6.58 (d, J_H−H= 6.4 Hz,

1H, C⁶H), 6.85 ppm (d, J_H−H= 9.2 Hz, 1H, C³H). ¹³C NMR (100

MHz, −80 °C, THF-d₈): δ 11.1 (q, J_C−H= 125 Hz, C₅Me₅), 12.1 (q,

J_C−H= 124 Hz, C₅Me₅), 12.2 (q, J_C−H= 124 Hz, C₅Me₅), 85.5 (s,

C₅Me₅), 86.7 (s, C₅Me₅), 93.3 (s, C₅Me₅), 109.9 (d, J_C−H= 160 Hz,

C⁵H), 114.8 (d, J_C−H= 159 Hz, C⁴H), HCCH), 143.3 (d, J_C−H= 159

Hz, C³H), 149.5 (d, J_C−H= 174 Hz, C⁶H), 168.9 ppm (s, C²).

Preparation of {Cp*Ru(μ-H)}₃(μ₃-η²:η²:η²-C₅H₅N) (3a). A 20 mL

glass tube equipped with a Teﬂon valve was charged with 1 (206.1 mg,

0.289 mmol) and toluene (10 mL). After pyridine (0.12 mL, 1.44

−30 °C. H NMR (400 MHz, −80 °C, THF-d₈): δ −17.71 (m, 1H,

RuH), −16.63 (m, 1H, RuH), −13.85 (m, 1H, RuH), −13.42 (d, J_H−H

4827

dx.doi.org/10.1021/om300379d | Organometallics 2012, 31, 4817−4831

Organometallics

Article

Table 6. Crystallographic Data for 2a, 2c, 3b, 4d, 5a, and 7b

(a) crystal data

empirical formula C₃₅H₅₃Ru₃·C₄H₁₀O

C₃₈H₅₇N O₂Ru₃

863.06

C₃₇H₅₅N O₂Ru₃

849.03

C₃₆H₅₃N Ru₃

803.00

C₃₅H₅₂B F₄N Ru₃C₆₀H₇₆B N Ru₃

formula weight

cryst description

cryst color

865.11

878.81

1125.24

prism

platelet

needle

platelet

prism

red

yellow

red

cryst size (mm)

0.30 × 0.30 × 0.12

diethyl ether (−30 °C) diethyl ether (25 °C) diethyl ether

0.13 × 0.07 × 0.02

0.07 × 0.04 × 0.01

0.20 × 0.13 × 0.02

diethyl ether

(−30 °C)

0.11 × 0.07 × 0.04

THF/Et₂O (25 °C)

0.45 × 0.41 × 0.29

THF/Et₂O (25 °C)

crystallizing

solution

(−30 °C)

cryst system

space group

a (Å)

monoclinic

P2₁/n (No. 14)

11.7790(2)

18.5780(3)

16.5703(3)

triclinic

monoclinic

triclinic

P1 (No. 2)

C2/c (No. 15)

22.7341(11)

18.8043(8)

20.4728(8)

P1 (No. 2)

8.8245(7)

11.0624(8)

20.5986(16)

78.9596(19)

77.611(2)

72.0478(19)

1851.3(2)

8.7652(5)

10.8209(7)

19.2871(10)

77.3390(15)

77.7690(14)

74.7230(14)

1698.54(16)

10.860(4)

10.789(3)

16.040(5)

92.581(12)

97.913(14)

113.972(12)

1690.4(9)

11.5539(17)

13.726(3)

17.284(4)

70.873(10)

86.569(10)

81.514(10)

2561.1(9)

b (Å)

c (Å)

α (deg)

β (deg)

γ (deg)

102.2453(7)

124.2934(13)

V (Å³)

3543.58(11)

7230.7(6)

Z value

D_calc(g/cm³)

1.622

−150

1.548

1.660

1.578

1.611

−100

1.459

measurement

temp (°C)

−80

−150

−80

μ(Mo Kα)

1.294

1.240

1.350

1.347

1.282

0.912

(mm⁻¹

)

(b) intensity

measurements

diﬀractometer

radiation

RAXIS-RAPID

Mo Kα

graphite

60°

RAXIS-RAPID

Mo Kα

graphite

55°

RAXIS-RAPID

Mo Kα

graphite

55°

RAXIS-RAPID

Mo Kα

graphite

55°

RAXIS-RAPID

Mo Kα

graphite

55°

RAXIS-RAPID

Mo Kα

graphite

60°

monochromator

2θ max

reﬂns collected

42 782

16 533

16 982

15 886

32 067

29 674

independent

reﬂns

10 586 (R_int= 0.0213) 8180 (R_int= 0.0328) 7724 (R_int= 0.0862) 7618 (R_int= 0.0318) 8515 (R_int= 0.0355) 14 691

(R_int= 0.0238)

reﬂns observed

(>2σ)

9621

6376

4482

6075

7096

13 409

abs. correction

type

numerical

empirical

abs. transmission 0.7272 (min.)

0.8534 (max.)

0.6499 (min.)

1.0000 (max.)

0.2433 (min.)

1.0000 (max.)

0.6844 (min.)

1.0000 (max.)

0.7411 (min.)

1.0000 (max.)

0.8337 (min.)

1.0000 (max.)

(Shelxl-97-2)

R₁(I > 2σ(I))

wR₂(I > 2σ(I))

R₁(all data)

0.0397

0.0374

0.0573

0.0403

0.0530

0.0244

0.0697

0.0778

0.1262

0.0914

0.1355

0.0597

0.1004

0.0555

0.1255

0.0570

0.0616

0.0273

wR₂(all data)

0.1021

0.086

0.1877

0.1082

0.1415

0.0612

data/restraints/

params

10260/0/411

8150/0/430

7724/0/391

7592/0/430

8260/0/431

14673/0/175

GOF

1.044

1.022

1.118

1.055

1.039

1.043

largest diﬀ. peak

7.758 and −1.126

0.0695 and −1.132

1.782 and −2.250

2.184 and −1.269

5.080 and −1.190

0.946 and −0.784

and hole

(e·Å⁻³

)

= 6.4 Hz, 1H, RuH), 1.26 (t, J_H−H= 7.2 Hz, 3H, −CH₂CH₃), 1.58 (s,

15H, C₅Me₅), 1.83 (s, 15H, C₅Me₅), 1.90 (s, 15H, C₅Me₅), 4.17 (m,

2H, −CH₂CH₃), 6.32 (d, J_H−H= 6.8 Hz, 1H, C⁵H), 6.59 (d, J_H−H= 6.8

Hz, 1H, C⁶H), 7.68 ppm (s, 1H, C³H). Anal. Calcd for

C₃₈H₅₇NO₂Ru₃: C, 52.88; H, 6.66; N, 1.62. Found C, 53.18; H,

6.55; N, 1.91.

purple band including 3c was collected, and 3c was obtained as a

purple solid by the removal of solvent under reduced pressure (25.1

mg, 0.029 mmol, 37%). A single crystal used for the diﬀraction studies

was prepared from the diethylether solution stored at −30 °C. H

NMR (400 MHz, benzene-d₆, 25 °C): δ −21.79 (dd, J_H−H= 3.8, 3.4

Hz, 1H, RuH), −20.02 (dd, J_H−H= 4.6, 3.8 Hz, 1H, RuH), −19.27

(dd, J_H−H= 4.6, 3.4 Hz, 1H, RuH), 1.02 (dd, J_H−H= 7.2, 7.2 Hz, 3H,

CH₂CH₃), 1.66 (s, 15H, Cp*), 1.67 (s, 15H, Cp*), 1.78 (s, 15H, Cp*),

2.98 (dd, J_H−H= 4.4, 1.6 Hz, 1H, C^βH), 3.39 (d, J_H−H= 4.4 Hz, 1H,

C^αH), 3.49 (d, J_H−H= 4.4 Hz, 1H, C^αH), 3.54 (dd, J_H−H= 4.4, 1.6 Hz,

1H, C^βH), 4.02 (dd, J_H−H= 11.2, 7.2 Hz, 1H, CH₂CH₃), 4.12 ppm

(dd, J_H−H= 11.2, 7.2 Hz, 1H, CH₂CH₃). ¹³C NMR (100 MHz,

Preparation of {Cp*Ru(μ-H)}₃(μ₃-η²:η²:η²-4-COOEt-C₅H₄N)

(3c). A 20 mL glass tube equipped with a Teﬂon valve was charged

with 1 (56.1 mg, 0.079 mmol) and toluene (5 mL). Ethyl isonicotinate

(18 μL, 0.120 mmol) was added, and the reaction mixture was heated

at 120 °C for 9 days. The color of the solution turned from reddish-

brown to purple. Toluene was removed under reduced pressure. The

residual solid was puriﬁed by the use of column chromatography on

alumina (Merck, Art. No. 1097) with tetrahydrofuran. The second

benzene-d₆, 25 °C): δ 10.8 (q, J_C−H= 127 Hz, C₅Me₅), 10.9 (q, J_C−H

126 Hz, C₅Me₅), 11.9 (q, J_C−H= 126 Hz, C₅Me₅), 14.6 (q, J_C−H= 126

4828

dx.doi.org/10.1021/om300379d | Organometallics 2012, 31, 4817−4831

Organometallics

Article

Hz, CH₂CH₃), 34.9 (d, J_C−H= 162 Hz, C^β), 37.7 (s, C^γ), 39.2 (d, J_C−H

= 161 Hz, C^β), 55.7 (d, J_C−H= 175 Hz, C^α), 58.7 (d, J_C−H= 173 Hz,

C^α), 59.7 (dd, J_C−H= 145, 145 Hz, CH₂CH₃), 90.1 (s, C₅Me₅), 91.2 (s,

C₅Me₅), 91.4 (s, C₅Me₅), 175.8 ppm (s, COOEt). Anal. Calcd for

C₃₈H₅₇NO₂Ru₃: C, 52.88; H, 6.66; N, 1.62. Found: C, 53.00; H, 6.40;

N, 1.94.

Thermolysis of (Cp*Ru)₃(μ-H)₄(μ₃-η²(//)-C₅H₄N) (2a) in Vacuo.

A 20 mL glass tube equipped with a Teﬂon valve was charged with 2a

(21.6 mg, 0.027 mmol), toluene (3 mL), and ferrocene as an internal

standard. The ﬂask was degassed and heated at 140 °C for 4 h under

vacuum. The color of the solution turned from reddish-brown to dark

brown. After the solvent was removed under reduced pressure, the

residual solid was dissolved in 0.5 mL of C₆D₆. The ¹H NMR

spectrum of the residual solid showed that 34% of 2a remained and

complexes 4a, 3a, and 1 were formed in 59, 6, and 1% yields,

Preparation of (Cp*Ru)₃(μ-H)₄(μ₃-η²(//)-4-Me-C₅H₃N) (2d). A

20 mL glass tube equipped with a Teﬂon valve was charged with

{Cp*Ru(μ-H)}₃(μ₃-H)₂(1) (131.0 mg, 0.183 mmol) and toluene (5

mL). After 4-picoline (180 μL, 1.84 mmol) was added to the solution,

the reaction mixture was stirred at 120 °C for 4 days. The color of the

solution turned from reddish-brown to purple. After the solvent and

remaining 4-picoline were removed in vacuo, the residue was washed

three times with 5 mL of MeOH. Dryness under reduced pressure

aﬀorded 2c as a brown crystalline solid (112.5 mg, 0.140 mmol, 77%

respectively. Complex 4a was characterized on the basis of H NMR

spectra of the mixture. H NMR (400 MHz, benzene-d₆, 25 °C): δ

−11.02 (s, 2H, RuH), 1.77 (s, 45H, Cp*), 6.13 (dd, J_H−H= 9.2, 6.0 Hz,

1H, C³H), 6.45 (dd, J_H−H= 6.4, 6.0 Hz, 1H, C⁴H), 6.68 (d, J_H−H= 9.2

Hz, 1H, C²H), 9.58 ppm (d, J_H−H= 6.4 Hz, 1H, C⁵H).

Preparation of (Cp*Ru)₃(μ-H)₂(μ₃-η²-4-Me-C₅H₃N) (4d). A 100

mL Schlenk tube was charged with {Cp*Ru(μ-H)}₃(μ₃-H)₂(1)

(111.8 mg, 0.157 mmol) and toluene (10 mL). After 4-picoline (154

μL, 1.57 mmol) was added to the solution, the reaction mixture was

stirred at 160 °C for 90 h. The color of the solution turned from

reddish-brown to reddish-purple. The solvent and remaining 4-

picoline were removed under reduced pressure. The ¹H NMR

spectrum of the residual solid showed exclusive formation of 4d.

Recrystallization from a cold diethylether solution stored at −30 °C

aﬀorded 4d as a purple crystal (8 mg, 0.010 mmol, 1% yield). ¹H NMR

(400 MHz, 25 °C, benzene-d₆): δ −11.62 (s, 2H, RuH), 1.60 (s, 3H,

C⁴CH₃), 1.79 (s, 45H, Cp*), 6.38 (d, J_H−H= 6.4 Hz, 1H, C⁵H), 6.53

(s, 1H, C³H), 9.55 ppm (d, J_H−H= 6.4 Hz, 1H, C⁶H). ¹³C NMR (100

MHz, benzene-d₆, 25 °C): δ 12.3 (q, J_C−H= 126 Hz, C₅Me₅), 20.9 (q,

J_C−H= 125 Hz, C⁴CH₃), 82.3 (br s, C₅Me₅), 114.3 (d, J_C−H= 161 Hz,

yield). H NMR (400 MHz, −80 °C, THF-d₈): δ −17.48 (m, 1H,

RuH), −17.08 (m, 1H, RuH), −13.68 (m, 1H, RuH), −13.34 (d, J_H−H

= 7.2 Hz, 1H, RuH), 1.56 (s, 15H, C₅Me₅), 1.82 (s, 15H, C₅Me₅), 1.88

(s, 15H, C₅Me₅), 2.00 (d, J_H−H= 0.8 Hz, 3H, −CH₃), 5.87 (dd, J_H−H

6.8, 1.6 Hz, 1H, C⁵H), 6.57 (d, J_H−H= 6.8 Hz, 1H, C⁶H), 6.72 ppm

(m, 1H, C³H). ¹³C NMR (100 MHz, 25 °C, THF-d₈): δ 11.8 (q, J_C−H

= 128 Hz, C₅Me₅), 20.7 (q, J_C−H= 127 Hz, C⁴Me), 88.9 (br s, C₅Me₅),

113.0 (d, J_C−H= 168 Hz, C⁵H), 124.6 (s, C⁴H), 141.5 (d, J_C−H= 163

Hz, C³H), 149.2 (d, J_C−H= 173 Hz, C⁶H), 170.4 ppm (s, C²).

Preparation of (Cp*Ru)₃(μ-H)₄(μ₃-η²(//)-5-Me-C₅H₃N) (2e). A

20 mL glass tube equipped with a Teﬂon valve was charged with 1

(31.2 mg, 0.044 mmol) and toluene (5 mL). After β-picoline (21 μL,

0.219 mmol) was added to the solution, the reaction mixture was

heated at 120 °C for 4 days. The color of the solution turned from

reddish-brown to purple. Toluene and the remaining β-picoline were

removed under reduced pressure. The ¹H NMR spectrum of the

residual solid showed exclusive formation of 2e. The residual solid was

then washed two times with 2 mL of methanol. Drying under vacuum

C⁵), 140.6 (d, J_C−H= 160 Hz, C³), 154.7 (s, C²), 155.6 ppm (d, J_C−H

177 Hz, C⁶). A singlet signal derived from C⁴of the μ₃-picolyl group

was not observed in the spectrum probably due to the obstruction by

the solvent signals

Preparation of [(Cp*Ru)₃(μ-H)₂(μ₃-H)(μ₃-η²:η²(⊥)-C₅H₄N)]⁺

(5a). A 50 mL Schlenk tube was charged with 2a (32.5 mg, 0.041

mmol) and diethylether (5 mL). After the tetraﬂuoroboric acid−

dimethylether complex (5.6 μL, 0.041 mmol) was added to the

solution at 25 °C with vigorous stirring, the reaction mixture was

stirred for 15 min. An immediate formation of a dark red precipitate

was observed. The precipitate was then separated by removing the

supernatant and washed four times with 5 mL of diethylether. Dryness

under reduced pressure aﬀorded a tetraﬂuoroborate salt of 5a as a dark

red crystalline solid (33.3 mg, 0.038 mmol, 93% yield). A single crystal

used for the diﬀraction studies was prepared by the slow evaporation

of the THF/diethylether solution of 5a stored at ambient temperature.

¹H NMR (400 MHz, acetone-d₆, 25 °C): δ −11.10 (s, 3H, RuH), 1.85

aﬀorded 2e as a brown solid (13.9 mg, 0.017 mmol, 40% yield). H

NMR (400 MHz, −80 °C, THF-d₈): δ −17.70 (m, 1H, RuH), −17.03

(m, 1H, RuH), −13.59 (m, 1H, RuH), −13.47 (d, J_H−H= 7.2 Hz, 1H,

RuH), 1.59 (s, 15H, C₅Me₅), 1.81 (s, 3H, NMe), 1.82 (s, 15H, C₅Me₅),

1.87 (s, 15H, C₅Me₅), 6.03 (d, J_H−H= 8.8 Hz, 1H, C⁴H), 6.47 (s, 1H,

C⁶H), 6.85 ppm (d, J_H−H= 8.8 Hz, 1H, C³H). ¹³C{¹H} NMR (100

MHz, −80 °C, THF-d₈): δ 11.3 (C₅Me₅), 12.2 (C₅Me₅), 12.3 (C₅Me₅),

18.2 (C⁵Me), 85.4 (C₅Me₅), 87.0 (C₅Me₅), 93.2 (C₅Me₅), 118.0 (C⁴or

C⁵), 118.5 (C⁴or C⁵), 143.2 (C³or C⁶), 147.3 (C³or C⁶), 165.5 ppm

(C²).

Reaction of 1 with α-Picoline. An NMR tube equipped with a J-

Young valve was charged with 1 (3.0 mg, 4.2 μmol), α-picoline (2 μL,

20.3 μmol), p-xylene-d₁₀(0.5 mL), and ferrocene as an internal

standard. The NMR tube was heated at 120 °C, and the reaction was

(s, 30H, Cp*), 2.05 (s, 15H, Cp*), 6.54 (ddd, J_H−H= 8.8, 1.2, 1.2 Hz,

1H, C³H), 6.65 (ddd, J_H−H= 8.8, 6.4, 1.2 Hz, 1H, C⁴H), 7.24 (ddd,

J_H−H= 6.4, 6.4, 1.2 Hz, 1H, C⁵H), 10.12 (ddd, J_H−H= 6.4, 1.2, 1.2 Hz,

1H, C⁶H) ppm. ¹³C NMR (100 MHz, acetone-d₆, 25 °C): δ 11.5 (q,

J_C−H= 128 Hz, C₅Me₅), 12.2 (q, J_C−H= 128 Hz, C⁴CH₃), 90.8 (s,

C₅Me₅), 98.6 (s, C₅Me₅), 117.3 (d, J_C−H= 168 Hz, C₅H₄N), 126.7 (d,

J_C−H= 158 Hz, C₅H₄N), 136.2 (s, C²), 141.1 (d, J_C−H= 168 Hz,

C₅H₄N), 157.1 (d, J_C−H= 191 Hz, C⁶) ppm. Anal. Calcd for

C₃₅H₅₂BF₄NRu₃: C, 47.94; H, 5.98; N, 1.60. Found: C, 47.56; H, 6.05;

N, 1.65.

monitored by the H NMR spectroscopy. After 10 days, any reaction

occurred with α-picoline and 1 still remained unchanged.

Reaction of (Cp*Ru)₃(μ-H)₄(μ₃-η²(//)-4-Me-C₅H₃N) (2d) with

H₂. An NMR tube equipped with a J-Young valve was charged with 2d

(6.0 mg, 7 μmol), tetrahydrofuran-d₈(0.45 mL), and cycloheptane as

an internal standard. After the solution was degassed by one freeze−

pump−thaw cycle, 1 atm of dihydrogen was introduced into the NMR

tube at ambient temperature. The reaction mixture was heated at 60

Preparation of [(Cp*Ru)₃(μ-H)₃(μ₃-η²:η²:η²-C₅H₅NMe)]⁺(7b). A

50 mL Schlenk tube was charged with 3a (49.3 mg, 0.062 mmol) and

diethylether (20 mL). After methyl triﬂate (7.0 μL, 0.062 mmol) was

added to the solution at 25 °C with vigorous stirring, the reaction

mixture was stirred for 30 min. An immediate formation of purple

precipitate was observed. The precipitate was then separated by

removing the supernatant and washed four times with 5 mL of

diethylether. Dryness under reduced pressure aﬀorded a triﬂate salt of

7 as a purple solid (58.3 mg, 0.061 mmol, 98% yield). The X-ray

diﬀraction study was carried out using a tetraphenylborate salt of 7,

which was obtained by the addition of a large excess amount of

NaBPh₄to a methanol solution of 7. A single crystal used for the

diﬀraction studies was prepared by the slow evaporation of the THF/

diethylether solution of a tetraphenylborate salt of 7 stored at ambient

°C. The reaction was monitored by H NMR spectroscopy. Exclusive

formation of 1, accompanied by liberation of γ-picoline, was observed.

After 216 h, all of 2d was converted into 1 quantitatively. The reaction

of 2a with 1 atm of H₂also resulted in a quantitative formation of 1.

Thermolysis of (Cp*Ru)₃(μ-H)₄(μ₃-η²(//)-C₅H₄N) (2a) in THF-

d₈. An NMR tube was charged with 2a (10.1 mg, 0.026 mmol),

tetrahydrofuran-d₈, and cycloheptane as an internal standard. The tube

was sealed and heated at 100 °C. The reaction was periodically

monitored by H NMR spectroscopy, and the distributions of the

product were estimated from the intensities of the hydrido signals

comparing to that of the internal standard. After 5.5 h, conversion of

2a reached 57% and complexes 1, 3a, and 4a were formed in 21, 11,

and 25% yields, respectively. After 325 h, the distributions of 2a, 1, 3a,

and 4a turned to 6, 5, 86, and 3%, respectively.

4829

dx.doi.org/10.1021/om300379d | Organometallics 2012, 31, 4817−4831

Organometallics

Article

temperature. H NMR (400 MHz, acetone-d₆, 25 °C): δ −20.89 (dd,

389−396. (f) Ohtani, H.; Wilson, R. J.; Chiang, S.; Mate, C. M. Phys.

Rev. Lett. 1988, 60, 2398−2401. (g) Weiss, P. S.; Eigler, D. M. Phys.

Rev. Lett. 1993, 71, 3139−3142. (h) Kamna, M. M.; Stranick, S. J.;

Weiss, P. S. Science 1996, 274, 118−119. (i) Yau, S.-L.; Kim, Y.-G.;

Itaya, K. J. Am. Chem. Soc. 1996, 118, 7795−7803.

J_H−H= 5.6, 4.0 Hz, 1H, RuH), −20.67 (dd, J_H−H= 5.6, 3.6 Hz, 1H,

RuH), −19.24 (dd, J_H−H= 4.0, 3.6 Hz, 1H, RuH), 1.78 (s, 15H, Cp*),

1.79 (s, 15H, Cp*), 1.86 (s, 15H, Cp*), 2.74 (dd, J_H−H= 6.0, 6.0 Hz,

1H, C^γH), 2.78 (dd, J_H−H= 6.0, 4.8 Hz, 1H, C^βH), 2.88 (s, 3H, NMe),

3.09 (d, J_H−H= 5.2 Hz, 1H, C^αH), 3.65 ppm (d, J_H−H= 4.8 Hz, 1H,

(2) (a) Mate, C. M.; Somorjai, G. A.; Tom, H. W. K.; Zhu, X. D.;

Shen, Y. R. J. Chem. Phys. 1988, 88, 441−450. (b) DiNardo, N. J.;

Avouris, Ph.; Demuth, J. E. J. Chem. Phys. 1984, 81, 2169−2180.

5907. (d) Demuth, J. E.; Sanda, P. N. Phys. Rev. Lett. 1981, 47, 57−60.

(e) Bader, M.; Haase, J.; Frank, K.-H.; Puschmann, A.; Otto, A. Phys.

Rev. Lett. 1986, 56, 1921−1924. (f) Johnson, A. L.; Muetterties, E. L.;

C^αH). The other H signal derived from C^βH was obscured by the

Cp* signal appearing at δ 1.79. A cross-peak with the C^αH (δ 5.02)

and the C^γH (δ 2.74) protons was found at δ 1.8 in the H−H COSY

spectrum. ¹³C NMR (100 MHz, acetone-d₆, 25 °C): δ 10.7 (q, J_C−H

127 Hz, C₅Me₅), 10.8 (q, J_C−H= 127 Hz, C₅Me₅), 11.6 (q, J_C−H= 127

Hz, C₅Me₅), 25.4 (d, J_C−H= 142 Hz, C^β), 26.8 (d, J_C−H= 140 Hz, C^β),

32.7 (d, J_C−H= 166 Hz, C^γ), 48.7 (d, J_C−H= 177 Hz, C^α), 52.7 (q, J_C−H

= 141 Hz, NMe), 54.6 (d, J_C−H= 181 Hz, C^α), 93.0 (s, C₅Me₅), 93.8 (s,

C₅Me₅), 98.0 ppm (s, C₅Me₅). Anal. Calcd for C₃₇H₅₆F₃NO₃Ru₃S: C,

46.53; H, 5.91; N, 1.47. Found: C, 46.86; H, 5.81; N, 1.36.

Irradiation of the Face-Capping Pyridine Complex 2a. An

NMR tube equipped with a J-Young valve was charged with 3a (2.0

mg, 2.5 μmol), benzene-d₆(0.5 mL), and cyclooctane as an internal

standard. The solution was exposed to UV light at 365 nm for 24 h by

Stohr, J.; Sette, F. J. Phys. Chem. 1985, 89, 4071−4075. (g) Cai, W.-B.;

Wan, L.-J.; Noda, H.; Hibino, Y.; Ataka, K.; Osawa, M. Langmuir 1998,

14, 6992−6998. (h) Andreasen, G.; Vela, M. E.; Salvarezza, R. C.;

Arvia, A. J. Langmuir 1997, 13, 6814−6819. (i) Haq, S.; King, D. A. J.

Phys. Chem. 1996, 100, 16957−16965.

(3) (a) Johnson, B. F. G.; Lewis, J.; Gallup, M.; Martinelli, M.

Faraday Discuss. 1991, 92, 241−254. (b) Muetterties, E. L.; Rhodin, T.

N.; Band, E.; Brucjer, C. F.; Pretzer, W. R. Chem. Rev. 1979, 79, 91−

137. (c) Muetterties, E. L. Pure Appl. Chem. 1982, 54, 83−96.

(d) Zaera, F. Chem. Rev. 1995, 95, 2651−2693. (e) Barlow, S. M.;

Raval, R. Surf. Sci. Rep. 2003, 50, 201−341.

using a high-pressure Hg lamp equipped with a ﬁlter. The H NMR

spectrum of the solution was then measured, and the exclusive

formation of 2a in a 40% yield was observed. When the irradiation was

performed without a ﬁlter, the yield of 2a increased to 68% after 10 h.

Dehydrogenative Coupling of Pyridines by 1. The reactions of

1 with excess 4-substituted pyridines were performed in a glass tube

equipped with a Teﬂon valve in appropriate reaction conditions. After

the appropriate reaction time, the solution was analyzed by GLC (for

pyridine, 4-picoline, and 4-ethylpyridine) and ¹H NMR (for 4-

dimethylaminopyridine, 4-methoxypyridine, 4,4′-bipyridine, and ethyl

isonicotionate) analyses. The results are listed in Table 4. A typical

reaction was carried out as follows (entry 5): 3 mL of a mesitylene

solution of 1 (4.0 mM, 0.012 mmol) and biphenyl (48.0 mg, 0.311

mmol) was charged in the reaction ﬂask equipped with a Teﬂon valve.

After a 100 equiv amount of γ-picoline (0.118 mL, 1.20 mmol) was

added, the solution was heated at 180 °C for 100 h. Formation of 4,4′-

dimethyl-2,2′-bipyridine was analyzed by means of GLC. After the

solvent was removed under reduced pressure with unreacted γ-

picoline, the residual solid was analyzed by means of ¹H NMR

spectroscopy.

(4) Lewis; Braga, D.; Dyson, P. J.; Grepioni, F.; Johnson, B. F. G.

Chem. Rev. 1994, 94, 1585−1620.

(5) (a) Deeming, A. J.; Underhill, M. J. Organomet. Chem. 1972, 42,

C60−C62. (b) Bruce, M. I.; Shaw, G.; Stone, F. G. A. J. Chem. Soc.,

Dalton Trans. 1972, 2094−2099. (c) Bradford, C. W.; Nyholm, R. S. J.

Chem. Soc., Dalton Trans. 1973, 529−533. (d) Azam, K. A.; Yin, C. C.;

Deeming, A. J. J. Chem. Soc., Dalton Trans. 1978, 1201−1206.

(e) Adams, R. D.; Katahira, D. A.; Yang, L.-W. Organometallics 1982, 1,

235−239. (f) Goudsmit, R. J.; Johnson, B. F. G.; Lewis, J.; Raithby, P.

R.; Rosales, M. J. J. Chem. Soc., Dalton Trans. 1983, 2257−2261.

(g) Deeming, A. J.; Kabir, S. E.; Powell, N. I.; Bates, P. A.; Hursthouse,

M. B. J. Chem. Soc., Dalton Trans. 1987, 1529−1534. (h) Deeming, A.

J.; Marshall, J. E.; Nuel, D.; O’Brien, G.; Powell, N. I. J. Organomet.

Chem. 1990, 384, 347−360. (i) Tay, C. T.; Leong, W. K. J. Organomet.

Chem. 2001, 625, 231−235. (j) Chan, K. H.; Leong, W. K.; Mak, K. H.

G. Organometallics 2006, 25, 250−259. (k) Moriya, M.; Tahara, A.;

Takao, T.; Suzuki, H. Eur. J. Inorg. Chem. 2009, 2009, 3393−3397.

ASSOCIATED CONTENT

(6) (a) Knox, S. A. R.; Lloyd, B. R.; Orpen, A. G.; Vinas, J. M.;

■

Weber, M. J. Chem. Soc., Chem. Commun. 1987, 1498−1500.

(b) Cullen, W. R.; Rettig, S. J.; Zhang, H. Organometallics 1991, 10,

2965−2969. (c) Bruce, M. I.; Humphrey, P. A.; Okucu, S.; Schmutzler,

R.; Skelton, B. W.; White, A. H. Inorg. Chim. Acta 2004, 357, 1805−

1812.

* Supporting Information

Results of the X-ray diﬀraction study of 3c; H and ¹³C NMR

spectra of 2a, 2d, 2e, and 4d; H NMR spectrum of 4a; and

crystallographic ﬁles, including CIF ﬁles of 2a, 2c, 3b, 3c, 4d,

5a, and 7b. This material is available free of charge via the

Internet at http://pubs.acs.org.

(7) Yin, C. C.; Deeming, A. J. J. Chem. Soc., Dalton Trans. 1975,

2091−2096.

(8) (a) Deeming, A. J.; Peters, R.; Hursthouse, M. B.; Backer-Dirks, J.

D. J. J. Chem. Soc., Dalton Trans. 1982, 787−791. (b) Burgess, K.;

Johnson, B. F. G.; Lewis, J. J. Organomet. Chem. 1982, 233, C55−C58.

Organometallics 1985, 4, 2033−2039. (d) Foulds, G. A.; Johnson, B. F.

G.; Lewis, J. J. Organomet. Chem. 1985, 294, 123−129. (e) Bruce, M.

I.; Humphrey, M. G.; Snow, M. R.; Tiekink, E. R. T.; Wallis, R. C. J.

Organomet. Chem. 1986, 314, 311−322. (f) Deeming, A. J.; Smith, M.

B. J. Chem. Soc., Dalton Trans. 1993, 2041−2046. (g) Beringhelli, T.;

D’Alfonso, G.; Ciani, G.; Proserpio, D. M.; Sironi, A. Organometallics

1993, 12, 4863−4870. (h) Cifuentes, M. P.; Humphrey, M. G.;

Skelton, B. W.; White, A. H. J. Organomet. Chem. 1994, 466, 211−220.

(i) Ellis, D.; Farrugia, L. J. J. Cluster Sci. 1996, 7, 71−83. (j) Cifuentes,

M. P.; Humphrey, M. G.; Skelton, B. W.; White, A. H. J. Organomet.

Chem. 1996, 513, 201−211. (k) Azam, K. A.; Das, A. R.; Hursthouse,

M. B.; Kabir, S. E.; Malik, K. M. A. J. Chem. Crystallogr. 1998, 28, 283−

288. (l) Darling, S. L.; Goh, P. K. Y.; Bampos, N.; Feeder, N.;

Montalti, M.; Prodi, L.; Johnson, B. F. G.; Sanders, J. K. M. Chem.

Commun. 1998, 2031−2032. (m) Hong, F.-E.; Chen, S.-C.; Tsai, Y.-T.;

Chang, Y.-C. J. Organomet. Chem. 2002, 655, 172−181. (n) Begum,

AUTHOR INFORMATION

Corresponding Author

*E-mail: hiroharu@o.cc.titech.ac.jp.

Notes

■

The authors declare no competing ﬁnancial interest.

ACKNOWLEDGMENTS

■

This work was supported by a Grant-in-Aid for Scientiﬁc

Research in Innovative Areas “Molecular Activation Directed

toward Straightforward Synthesis” from NEXT, Japan.

REFERENCES

■

(1) See, for example: (a) Koel, B. E.; Crowell, J. E.; Mate, C. M.;

Somorjai, G. A. J. Phys. Chem. 1984, 88, 1988−1996. (b) Van Hove,

M. A.; Lin, R. F.; Somorjai, G. A. J. Am. Chem. Soc. 1986, 108, 2532−

2537. (c) Somorjai, G. A. J. Phys. Chem. 1990, 94, 1013−1023.

(d) Van Hove, M. A.; Somorjai, G. A. J. Mol. Catal. A 1998, 131, 243−

257. (e) Grassian, V. H.; Muetterties, E. L. J. Phys. Chem. 1987, 91,

4830

dx.doi.org/10.1021/om300379d | Organometallics 2012, 31, 4817−4831

Organometallics

Article

N.; Kabir, S. E.; Hossain, G. M. G.; Rahman, A. F. M. M.; Rosenberg,

E. Organometallics 2005, 24, 266−271.

(24) Kawashima, T.; Takao, T.; Suzuki, H. J. Am. Chem. Soc. 2007,

129, 11006−11007.

(25) (a) Badger, G. M.; Sasse, W. H. F. J. Chem. Soc. 1956, 616−620.

(b) Sasse, W. H. F.; Whittle, C. P. J. Chem. Soc. 1961, 1347−1350.

485. (d) Hagelin, H.; Hedman, B.; Orabona, I.; Åkermark, T.;

Åkermark, B.; Klug, C. A. J. Mol. Catal. A 2000, 164, 137−146.

(26) (a) Jordan, R. F.; Taylor, D. F. J. Am. Chem. Soc. 1989, 111,

778−779. (b) Moore, E. J.; Pretzer, W. R.; O’Connell, T. J.; Harris, J.;

LaBounty, L.; Chou, L.; Grimmer, S. S. J. Am. Chem. Soc. 1992, 114,

5888−5890. (c) Murakami, M.; Hori, S. J. Am. Chem. Soc. 2003, 125,

4720−4721. (d) Lewis, J. C.; Bergman, R. G.; Ellman, J. A. J. Am.

Chem. Soc. 2007, 129, 5332−5333. (e) Nakao, Y.; Kanyiva, K. S.;

Hiyama, T. J. Am. Chem. Soc. 2008, 130, 2448−2449. (f) Berman, A.

M.; Lewis, J. C.; Bergman, R. G.; Ellman, J. A. J. Am. Chem. Soc. 2008,

130, 14926−14927. (g) Tobisu, M.; Hyodo, I.; Chatani, N. J. Am.

Chem. Soc. 2009, 131, 12070−12071. (h) Do, H.-Q.; Daugulis, O. J.

Am. Chem. Soc. 2009, 131, 17052−17053. (i) Truong, T.; Alvarado, J.;

Tran, L. D.; Daugulis, O. Org. Lett. 2010, 12, 1200−1203.

(9) To the best of our knowledge, two examples for a polymetallic

complex that contains a μ₃-pyridyl group have been known, but the μ₃-

η²-coordination of a pyridyl group has never been reported.

(a) Adams, C. J.; Bruce, M. I.; Skelton, B. W.; White, A. H. J.

Organomet. Chem. 1993, 445, 211−217. (b) Cauzzi, D.; Graiﬀ, C.;

Massera, C.; Predieri, G.; Tripicchio, A. Eur. J. Inorg. Chem. 2001,

721−723.

(10) Kawashima, T.; Takao, T.; Suzuki, H. Angew. Chem., Int. Ed.

2006, 45, 7615−7618.

(11) (a) Wexler, R. M.; Tsai, M.-C.; Friend, C. M.; Muetterties, E. L.

J. Am. Chem. Soc. 1982, 104, 2034−2036. (b) Haq, S.; King, D. A. J.

Phys. Chem. 1996, 100, 16957−16965. (c) Lauhon, L. J. J. Phys. Chem.

A 2000, 104, 2463−2467. (d) Andrade, G. F. S.; Temperini, M. L. A. J.

Raman Spectrosc. 2009, 40, 1989−1995.

(12) Structural data for 27 trimetallic complexes having a μ₃-η²(//)-

iminoacyl ligand were obtained from Cambridge Structural Database

System, version 5.32 (November 2010 + four updates). Allen, F. H.

Acta Crystallogr. 2002, B52, 380−388.

(27) (a) Moriya, M.; Tahara, A.; Takao, T.; Suzuki, H. Eur. J. Inorg.

Chem. 2009, 2009, 3393−3397. (b) Tahara, A.; Kajigaya, M.; Moriya,

M.; Takao, T.; Suzuki, H. Angew. Chem., Int. Ed. 2010, 49, 5898−5901.

(13) Cotton, F. A.; Poli, R. Organometallics 1987, 6, 1743−1751.

(14) Cabeza, J. A.; del Río, I.; García-Granda, S.; Riera, V.; Suarez, M.

(28) Wadepohl, H.; Buchner, K.; Herrmann, M.; Pritzkow, H. J.

Organometallics 2002, 21, 2540−2543.

Organomet. Chem. 1999, 573, 22−29.

(15) (a) Howell, J. A. S.; Mathur, P. J. Chem. Soc., Chem. Commun.

1981, 263−265. (b) Howell, J. A. S.; Mathur, P. J. Chem. Soc., Dalton

Trans. 1982, 43−49. (c) Aime, S.; Gobetto, R.; Padovan, F.; Botta, M.;

Rosenberg, E.; Gellert, R. E. Organometallics 1987, 6, 2074−2078.

(d) Rosenberg, E.; Kabir, S. E.; Hardcastle, K. I.; Day, M.; Wolf, E.

Organometallics 1990, 9, 2214−2217. (e) Day, M.; Espitia, D.;

Hardcastle, K. I.; Kabir, S. E.; McPhillips, T.; Rosenberg, E.; Gobetto,

R.; Milone, L.; Osella, D. Organometallics 1993, 12, 2309−2324.

(29) (a) Logadottir, A.; Moses, P. G.; Hinnemann, B.; Topsøe, N.-Y.;

Knudsen, K. G.; Topsøe, H.; Nørskov, J. K. Catal. Today 2006, 111,

44−51. (b) Temel, B.; Tuxen, A. K.; Kibsgaard, J.; Topsøe, N.-Y.;

Hinnemann, B.; Knudsen, K. G.; Topsøe, H.; Lauritsen, J. V.;

Besebbacher, F. J. Mol. Catal. 2010, 271, 280−289.

(30) (a) Kiviniemi, S.; Nissinen, M.; Alviuhkola, T.; Rissanen, K.;

Pursiainen, J. J. Chem. Soc., Perkin Trans. 2 2001, 2364−2369.

(b) Tafeenko, V. A.; Nikolaev, A. N.; Peschar, R.; Kaukova, O. V.;

Schenk, H.; Aslanov, L. A. Acta Crystallogr., Sect. C 2004, 60, o297−

o299. (c) Lalancette, R. A.; Furey, W.; Costanzo, J. N.; Hemmes, P. R.;

Jordan, F. Acta Crystallogr. 1978, B34, 2950−2953.

(31) Gallop, M. A.; Johnson, B. F. G.; Lewis, J.; McCamley, A.;

Perutz, R. N. J. Chem. Soc., Chem. Commun. 1988, 1071−1073.

(32) Inagaki, A.; Takaya, Y.; Takemori, T.; Suzuki, H.; Tanaka, M. J.

Am. Chem. Soc. 1997, 119, 625−626.

(33) Suzuki, H.; Kakigano, T.; Tada, K.; Igarashi, M.; Matsubara, K.;

Inagaki, A.; Oshima, M.; Takao, T. Bull. Chem. Soc. Jpn. 2005, 78, 67−

87.

(16) Cabeza, J. A.; del Río, I.; Goite, M. C.; Perez-Carreno, E.;

Pruneda, V. Chem.Eur. J. 2009, 15, 7339−7349.

(17) Casey, C. P.; Windenhoefer, R. A.; Hallenbeck, S. L.; Hayashi,

R. K.; Gavney, J. A., Jr. Organometallics 1994, 13, 4720−4731.

(18) Rosenberg, E.; Milone, L.; Gobetto, R.; Osella, D.; Hardcastle,

K.; Hajela, S.; Moizeau, K.; Day, M.; Wolf, E.; Espitia, D.

Organometallics 1997, 16, 2665−2673.

(19) (a) Sappa, E.; Tiripicchio, A.; Braunstein, P. Chem. Rev. 1983,

83, 203−239. (b) Sappa, E.; Tiripicchio, A.; Braunstein, P. Coord.

Chem. Rev. 1985, 65, 219−284. (c) Deabate, S.; Giordano, R.; Sappa,

E. J. Cluster Sci. 1997, 8, 407−460.

(20) (a) Riehl, J.-F.; Koga, N.; Morokuma, K. Organometallics 1994,

13, 4765−4780. (b) Takao, T.; Takaya, Y.; Murotani, E.;

Tenjimbayashi, R.; Suzuki, H. Organometallics 2004, 23, 6094−6096.

E.; Suzuki, H. Organometallics 2004, 23, 6090−6093.

(34) PROCESS-AUTO: Automatic Data Acquisition and Processing

Package for Imaging Plate Diﬀractometer; Rigaku Corporation: Tokyo,

Japan, 1998.

(35) Sheldrick, G. M. SHELX-97: Program for Crystal Structure

Determination; University of Gottingen: Gottingen, Germany, 1997.

(21) See, for example: (a) Cifuentes, M. P.; Humphrey, M. G.;

Skelton, B. W.; White, A. H. J. Organomet. Chem. 1993, 458, 211−218.

(b) Andrews, M. A.; Buskirk, G.; Knobler, C. B.; Kaesz, H. D. J. Am.

Chem. Soc. 1979, 101, 7245−7254. (c) Dawoodi, Z.; Mays, M. J.;

Raithby, P. R. J. Organomet. Chem. 1981, 219, 103−113. (d) Basu, A.;

Bhaduri, S.; Sharma, K.; Jones, P. G. J. Chem. Soc., Chem. Commun.

1987, 1126−1127. (e) Aime, S.; Gobetto, R.; Padovan, F.; Botta, M.;

Rosenberg, E.; Gellert, R. W. Organometallics 1987, 6, 2074−2078.

(f) Imhof, W. J. Chem. Soc., Dalton Trans. 1996, 1429−1436.

(22) (a) Takao, T.; Kawashima, T.; Matsubara, K.; Suzuki, H.

Organometallics 2005, 24, 3371−3374. (b) Kawashima, T.; Takao, T.;

Suzuki, H. Angew. Chem., Int. Ed. 2006, 45, 485−488. (c) Kanda, H.;

Kawashima, T.; Takao, T.; Suzuki, H. Organometallics 2012, 31, 1917−

1926.

(23) (a) Deeming, A. J.; Kimber, R. E.; Underhill, M. J. Chem. Soc.,

Dalton Trans. 1973, 2589−2595. (b) Deeming, A. J.; Rothwell, I. P.;

Hursthouse, M. B.; Backer-Dirks, J. D. J. J. Chem. Soc., Dalton Trans.

1981, 1879−1885. (c) Cullen, W. R.; Chacon, S. T.; Bruce, M. I.;

Einstein, F. W. B.; Jones, R. H. Organometallics 1988, 7, 2273−2278.

(d) Deeming, A. J.; Marshall, J. E.; Nuel, D.; O’Brien, G.; Powell, N. I.

J. Organomet. Chem. 1990, 384, 347−360.

4831

dx.doi.org/10.1021/om300379d | Organometallics 2012, 31, 4817−4831

Products guided by the article

Product name:[((η5-C5Me5)Ru)3(μ-H)3(μ3-η2:η2:η2-C5H5NMe)]BPh4

Cas No:1384193-94-5

R&D Labs maybe for 1384193-94-5

Taizhou Shengxing Chempharm Co.,Ltd

Contact:+86-576-88516600

Address:Yantou Chemical Zone Jiaojiang Taizhou Zhejiang China
Nanjing Chemlin Chemical Co., Ltd.

website:http://www.echemlin.cn

Contact:+86-25-83697070

Address:Rm.902 Longyin Plaza, No. 217 Zhongshan Rd.(N) Nanjing 210009,China
JiangXi Hong Run Chemical Co., Ltd

Contact:+86-0791-88521351

Address:XingHuo industrial zone in YongXiu county
Zhejiang Sucon Silicone Co.,Ltd

Contact:+86-575-88046692

Address:Qisheng Rd., Paojiang Industrial Zone, Shaoxing, Zhejiang, China.
Hubei ShiNan Pharmaceutical Chemical co., Ltd.(expird)

Contact:+86-13554447107

Address:Wuhan HongShanOu wu no road 378 future residence building 1 unit 14 layer no. 1401 A

Relevant to this article

Copper-catalyzed oxidation of azolines to azoles

Doi:10.1039/c2dt00025c
(2012)
Urotropine-bromine promoted synthesis of functionalized oxaspirotricyclic furopyrimidines via a domino Knoevenagel condensation/Michael addition/α-bromination/Williamson cycloetherification sequence in water

Doi:10.1016/j.tet.2013.06.030
(2013)
Automated solid-phase synthesis of hyaluronan oligosaccharides

Doi:10.1021/ol301666n
(2012)
Application of efficient glycosylation of 2,6-anhydro-2-thio sugar to the total synthesis of erythromycin A

Doi:10.1016/0040-4039(91)80777-4
(1991)
Synthesis of 1S,2R,3S,4R,5R-methyl[2,3,4-trihydroxy-5-(hydroxymethyl)cyclopentyl]amine: A potent α-mannosidase inhibitor

Doi:10.1016/S0040-4039(00)97253-8
(1990)
Highly stereoselective total synthesis of octopyranose derivatives

Doi:10.1016/S0040-4020(01)81954-2
(1991)

Article Doi

Synthesis of triruthenium complexes containing a triply bridging pyridyl ligand and its transformations to face-capping pyridine and perpendicularly coordinated pyridyl ligands

DOI: 10.1021/om300379d

Source and publish data:

Authors:

Article abstract of DOI:10.1021/om300379d

Full text of DOI:10.1021/om300379d

Products guided by the article

R&D Labs maybe for 1384193-94-5

Relevant to this article

Hot Product