Comparative study on ortho-C-H vs ortho-C-X (X = C, Cl, S) bond activation in ortho-Caromatic-N bond fusion in substituted anilines using ruthenium(II) mediators: Isolation and characterization of unusual Ru 2 complexes

Article abstract of DOI:10.1021/om300241y

The chemical reactions of a selection of ortho-mono- and disubstituted anilines with two ruthenium polyene mediator complexes, CpRu ^IICl(PPh₃)₂ (Cp^- = cyclopentadienyl anion) and (Bnz)₂Ru^II₂Cl₄ (Bnz = benzene), have been undertaken with a primary aim to make a comparison between ortho-C-H and ortho-C-X (X = Cl, C, S) bond activation processes in ortho-C-N bond fusion reactions. The reaction of ortho-monosubstituted anilines, viz., 2-chloroaniline (HL^1a), 2-methylaniline (HL^1c), and 2-methylthioaniline (HL^1b), with CpRu^IICl(PPh ₃)₂ yielded mononuclear complexes [CpRu^IIL ^2a-cCl] (1, 3, and 5), containing in situ generated ligands N-(aryl)-ortho-quinonediimine, L^2a-c, along with anilido-bridged Ru^III₂ complexes (2, [CpClRu^III{μ- η²-(L^1a)^-}]₂; 4, [CpClRu ^III{μ-η²-(L^1c)^-}] ₂; and [6]Cl₂, [CpRu^III{μ-η²: η¹-(L^1b)^-}]₂), respectively. The new ligands, L^2a-c are formed via ortho-C-H bond activation reactions, whereas ortho-C-X bonds remained unaffected. However, the ortho-C-Cl bond activation reaction is also noted in the reaction between CpRu ^IICl(PPh₃)₂ and ortho-disubstituted aniline 2,6-dichloroaniline (HL^3a) in more forceful conditions. The ruthenium(III) binuclear complex [CpRu^III{μ-η²: η¹-(L^3a)^-}(μ-η²: η¹-L^2d)(μ-η²-acetate)Ru ^IIICl]Cl, [7]Cl, of an in situ generated N-(2,6-dichlorophenyl)-6- chloro-ortho-quinonediimine ligand, L^2d, has been isolated from the above reaction. The ligand L^2d coordinates in a η²- binding mode through an imine (=NH) nitrogen atom. The coordination mode of 2,6-dichloroanilide, (L^3a)^-, in [7]Cl is unusual in that an aromatic-C-Cl group is coordinated to a Ru(III) center, and it represents the first authentic crystallographic evidence of such a coordination mode in a transition metal complex. Similar reactions on a redox-inert mediator complex, (Bnz)₂Ru^II₂Cl₄ (Bnz = benzene), with the aforesaid aromatic amines failed to result in ortho-C-N bond fusion reactions and afforded the mononuclear anilino complexes and an anilido-bridged Ru^II₂ compound, [9]Cl₂. The complexes have been characterized by using a host of physical methods as well as single-crystal X-ray structure determination. Their redox and spectroscopic properties have been thoroughly characterized by cyclic voltammetry and UV-vis and electron paramagnetic resonance spectroscopy. Density-functional theory calculations were employed to confirm their structural features and to support the spectral and redox properties.

Full text of DOI:10.1021/om300241y

Article
pubs.acs.org/Organometallics
Comparative Study on ortho-C−H vs ortho-C−X (X = C, Cl, S) Bond
Activation in ortho-Caromatic−N Bond Fusion in Substituted Anilines
Using Ruthenium(II) Mediators: Isolation and Characterization of
Unusual Ru2 Complexes
Sutanuva Mandal,† Subhas Samanta,† Tapan K. Mondal,‡ and Sreebrata Goswami*,†
†Department of Inorganic Chemistry, Indian Association for the Cultivation of Science, Kolkata 700 032, India
‡Department of Chemistry, Jadavpur University, Kolkata, 700032, India
S
* Supporting Information
ABSTRACT: The chemical reactions of a selection of ortho-
mono- and disubstituted anilines with two ruthenium polyene
mediator complexes, CpRuIICl(PPh3)2 (Cp− = cyclopenta-
dienyl anion) and (Bnz)2RuII Cl4 (Bnz = benzene), have been
2
undertaken with a primary aim to make a comparison between
ortho-C−H and ortho-C−X (X = Cl, C, S) bond activation
processes in ortho-C−N bond fusion reactions. The reaction of
ortho-monosubstituted anilines, viz., 2-chloroaniline (HL1a), 2-
methylaniline (HL1c), and 2-methylthioaniline (HL1b), with
CpRuIICl(PPh3)2 yielded mononuclear complexes
[CpRuIIL2a−cCl] (1, 3, and 5), containing in situ generated
ligands N-(aryl)-ortho-quinonediimine, L2a−c, along with
anilido-bridged RuIII complexes (2, [CpClRuIII{μ-η2-(L1a)−}]2; 4, [CpClRuIII{μ-η2-(L1c)−}]2; and [6]Cl2, [CpRuIII{μ-η2:η1-
2
(L1b)−}]2), respectively. The new ligands, L2a−c are formed via ortho-C−H bond activation reactions, whereas ortho-C−X bonds
remained unaffected. However, the ortho-C−Cl bond activation reaction is also noted in the reaction between CpRuIICl(PPh3)2
and ortho-disubstituted aniline 2,6-dichloroaniline (HL3a) in more forceful conditions. The ruthenium(III) binuclear complex
[CpRuIII{μ-η2:η1-(L3a)−}(μ-η2:η1-L2d)(μ-η2-acetate)RuIIICl]Cl, [7]Cl, of an in situ generated N-(2,6-dichlorophenyl)-6-chloro-
ortho-quinonediimine ligand, L2d, has been isolated from the above reaction. The ligand L2d coordinates in a η2-binding mode
through an imine (NH) nitrogen atom. The coordination mode of 2,6-dichloroanilide, (L3a)−, in [7]Cl is unusual in that an
aromatic-C−Cl group is coordinated to a Ru(III) center, and it represents the first authentic crystallographic evidence of such a
coordination mode in a transition metal complex. Similar reactions on a redox-inert mediator complex, (Bnz)2RuII Cl4 (Bnz =
2
benzene), with the aforesaid aromatic amines failed to result in ortho-C−N bond fusion reactions and afforded the mononuclear
anilino complexes and an anilido-bridged RuII compound, [9]Cl2. The complexes have been characterized by using a host of
2
physical methods as well as single-crystal X-ray structure determination. Their redox and spectroscopic properties have been
thoroughly characterized by cyclic voltammetry and UV−vis and electron paramagnetic resonance spectroscopy. Density-
functional theory calculations were employed to confirm their structural features and to support the spectral and redox
properties.
in the context of the above chemical transformations. For this
purpose a selection of ortho-mono- and disubstituted aromatic
amines (Chart 1) have been chosen as the substrates. The
primary objective of this work is to make a comparison of
different Carom−X bond activation processes that are operative
in the above ortho-Carom−N bond forming reactions. Accord-
ingly the amines, as shown in Chart 1, were reacted separately
with the two mediator complexes, CpRuIICl(PPh3)2 and
INTRODUCTION
■
During the past decade we have been engaged in transition
metal promoted regioselective ortho-Carom−N bond fusion
reactions in anilines.1 Our research in this area began with the
studies on dimerization of anilines using ruthenium(III) and
osmium(III) chelates as mediators.1a Subsequently, using the
more potent oxidant OsO4 as the mediator we were successful
in regioselective ortho-kniting of up to six anilido substrates.2
To gain insight into the above aniline fusion reactions, we have
established the role of the central metal ion in Carom−N bond
fusion reactions using two polyene ruthenium(II) mediator
complexes, CpRuIICl(PPh3)2 (Cp− = cyclopentadienyl anion)
(Bnz)2RuII Cl4. While the redox-active RuII−Cp complex
2
mediates the C−N bond fusion reactions successfully, the
and (Bnz)2RuII Cl4 (Bnz = benzene).3 In this work we have
Received: March 22, 2012
Published: July 31, 2012
2
investigated the effect of ortho-substitution in aromatic amines
© 2012 American Chemical Society
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1.a. Reaction of CpRuIICl(PPh3)2 and ortho-Monosubsti-
tuted Anilines: 2-Chloroaniline (HL1a), 2-Methylthioaniline
(HL1b), and 2-Methylaniline (HL1c). The chemical reaction of
CpRuIICl(PPh3)2 in neat 2-chloroaniline (HL1a) for two hours
at 80 °C afforded a brownish-red mass (Scheme 1). Rapid
Chart 1
Scheme 1
redox-innocent RuII−Bnz complex failed to bring about the
above reactions.3
In the reactions between the above ortho-monosubstituted
aromatic amines and the RuII−Cp mediator complex, it was
anticipated that C−H bond activation would compete with the
C−X (X = C, Cl, S) bond activation processes. In this respect
the coordination ability of 2-methylthioaniline4 also plays an
important role in the formation of the isolated compounds. The
reactions of two ortho-disubstituted anilines, viz., 2,6-dichlor-
oaniline and 2,6-dimethylaniline, were also studied. While we
could successfully follow the reaction of 2,6-dichloroaniline via
isolation of products, the substrate 2,6-dimethylaniline, on the
other hand, failed to produce any isolable compound. The
product from the reaction of 2,6-dichloroaniline is a cationic
binuclear Ru(III) complex of a newly formed N-(2,6-
dichlorophenyl)-6-chloro-ortho-quinonediimine ligand. The
new ligand was formed in situ as a result of aromatic C−Cl
bond activation and ortho−C−N bond fusion reactions.
Interestingly the coordination modes of 2,6-dichloroanilide
and the new reference ligand in the above complex are unusual
in that they include aromatic C−Cl group coordination to a
Ru(III) center and a rare type of η2-binding of an imine (
NH) nitrogen atom, respectively. It is relevant to note here that
due to the expected relatively low electron donor capability of
the aromatic-chlorine atom, its coordination to a Ru(III) center
is a rare phenomenon. There are only a few reports on the
complexes of p-block elements having such structural motifs.5
The aromatic-chlorine atom coordination mode was first
argued to exist in solution in the cases of nickel and cobalt
complexes of a bidentate ligand, triazene-3-(2-halophenyl)-1-
oxide.6 However, subsequent X-ray structure analysis of the
cobalt complex indicated the presence of only secondary
interactions having a long M−Cl bond.6b
crystallization of the crude reaction mixture from a dichloro-
methane−hexane solvent mixture furnished a major product, 1
(intense red), along with a minor product, 2 (yellowish-
brown). While compound 1 is highly soluble in common
nonpolar solvents, compound 2 is sparingly soluble in the
above solvents. Thus fractional crystallization of the mixture
using dichloromethane−hexane was useful for their separation.
Compound 1 is a mononuclear ruthenium(II) compound that
contains an N-(2-chlorophenyl)-6-chloro-ortho-quinonediimine
ligand, L2a, formed in situ via ortho-C−H bond activation and
dimerization of HL1a. Compound 2 is a symmetrical binuclear
RuIII complex containing a Ru−Ru bond and bridged by two
2
2-chloroanilide, (L1a)−, ligands. Similar products (complexes 3
and 4) were isolated from the reaction of 2-methylaniline, HL1c,
and the above mediator complex (Scheme 1). Characterization
of the isolated compounds is discussed in the following sections
(vide infra).
A similar reaction with 2-methylthioaniline, HL1b, with the
reference mediator complex under identical reaction conditions
afforded the mononuclear red compound 5 as a minor product,
which is an analogue of complexes 1 and 3, and a new type of
binuclear green complex, [6]Cl2, as the major product. The
chemical reaction is depicted in Scheme 2. Though the
compound [6]Cl2 has a similar composition to that of
compounds 2 and 4 (Scheme 1), its coordination mode and
geometry are distinctly different. This is primarily because of
the presence of an additional thioether binding site, which has
led to a μ-η2:η1 mode of coordination of the anilido nitrogen
and thiomethyl sulfur atom. This coordination mode of a
closely related system, viz., 2-aminothiophenol, has been
known7 in a few selected examples. However such coordination
of a 2-monothioether function is new.
RESULTS AND DISCUSSION
■
A. Chemical Reactions. As it was noted before,1 the
polyene mediator complexes CpRuIICl(PPh3)2 and
(Bnz)2RuII Cl4 allow the incoming substrates (aromatic amines
2
in these reactions) to occupy only the cis-positions, which in
fact is a prerequisite for the ortho-Carom−N bond formation in
aromatic amines. While the complex (Bnz)2RuII Cl4 is redox
2
inert, the CpRuIICl(PPh3)2 is oxidizable at 0.5 V vs SCE, and
consequently their reactivity patterns are totally different.5 In
the following sections each of the above reactions has been
dealt with separately by isolation and complete characterization
of the products. The above reactions have yielded some unusual
complexes that are not otherwise accessible.
Microanalytical, positive-ion ESI-MS spectra, together with
the 1H NMR spectral data of the compounds 1−[6]Cl2
convincingly support their formulations as shown in Schemes
1 and 2. For example, the ESI-MS spectra of these compounds
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bond parameters of 2, 5, and [6]Cl2 are collected in Table 1,
and for 1 these are submitted in Table S1.
Scheme 2
Figure 1. ORTEP drawing and atom-numbering scheme of 1 with
30% probability thermal ellipsoids. All hydrogen atoms except at N11
are omitted for clarity.
showed high-intensity peaks at m/z 417, 292, 377, 639, 441,
and 304 amu, respectively, corresponding to the molecular ion
peak of [M − Cl]+ for 1, 3, and 5, [M/2 − Cl]+ for 2, [M +
Na]+ for 4, and [M/2]+ for [6]Cl2 where M represents the
molecular mass of the respective compounds. The binuclear
complexes 2 and [6]Cl2 also showed a low-intensity peak at m/
z 583 and 608 amu, respectively, which correspond to the
molecular ion peak of [M − (H+ + 2Cl−)]+ and [M]+,
respectively. The experimental spectral features of the above
compounds correspond very well to their simulated isotopic
patterns. Experimental and simulated ESI-MS spectra of all the
compounds 1−[6]Cl2 are submitted as Supporting Information
(Figures S1−6).
The molecular compounds 1−5 showed reasonably resolved
1H NMR spectra in chloroform-d solvent. The spectrum of the
cationic compound [6]Cl2, however, was recorded in methanol-
d4 solvent. Characteristic resonances due to the imine proton
(NH) of the coordinated ligands, viz., L2a−c, appeared at δ
12−13 ppm for complexes 1, 3, and 5. The cyclopentadienyl
ring proton resonances in these complexes appeared as a single
peak near 5 ppm. In addition, aromatic proton resonances of
the phenyl ring in L2a−c ligands appeared in the range δ 6.5 to
7.8 ppm. For compounds 3 and 5 methyl (−CH3) and
thiomethyl (−SCH3) proton resonances appeared between δ
2.1 and 2.5 ppm. The resonance due to the anilido (−NH−)
proton in the binuclear complex [6]Cl2 appeared at 5.0 ppm,
whereas in the case of the complexes 2 and 4 it shifted to the
low-field region at 9.0 and 14.9 ppm, respectively. These
disappeared on D2O shake as expected. This shift of the anilido
proton resonance may be attributed to the presence of adjacent
electronegative chlorine atoms in the latter complexes. 1H
NMR spectra of compounds 1−[6]Cl2 are submitted as
Supporting Information (Figures S7−12).
Figure 2. ORTEP drawing and atom-numbering scheme of 5 with
30% probability thermal ellipsoids. All hydrogen atoms except at N1
are omitted for clarity.
X-ray crystal structure analysis of mononuclear compounds
(1 and 5) reveal that the central ruthenium atom is coordinated
to three different ligands, viz., a monoanionic chloro, a η5-
bonded cyclopentadienyl anion, and a bidentate N-(aryl)-ortho-
1.b. X-ray Crystal Structure. Three-dimensional X-ray
structures of the compounds 1, 2, 5, and [6]Cl2 further
confirm their formulations as well as geometries. The methyl-
substituted compounds 3 and 4 are analogous to the complexes
1 and 2, respectively, and hence no attempt to solve their X-ray
structures was made. Suitable single crystals for X-ray
diffraction studies of complexes 1, 2, and 5 were obtained by
slow evaporation of a dichloromethane−hexane solution of the
corresponding compounds; single crystals of the compound
[6]Cl2 were, however, grown by slow evaporation of its
solution in methanol. ORTEP drawings and atom-numbering
schemes of these complexes are shown in Figures 1−4. Selected
Figure 3. ORTEP drawing and atom-numbering scheme of 2 with
30% probability thermal ellipsoids. All the hydrogen atoms except at
N1 and N2 are omitted for clarity.
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ortho-quinonediimine state. The elongation of Carom−Nimine
lengths may be attributed to strong d(Ru)−π*(ligand) back-
bonding in the ground state of the complexes. A similar
situation was noted8b in the bivalent ruthenium complexes of
very closely similar diimine ligands. This issue on oxidation
state assessment has been considered again by the analyses of
EPR spectra of the electrogenerated complexes and examina-
tion of the results of DFT calculations (vide infra).
Single-crystal X-ray structure determination of the molecular
complex 2 has revealed that it is a metal−metal-bonded Ru2
system with a Ru−Ru distance of 2.683(8) Å, which is very
similar to a typical9 Ru−Ru single bond length (Figure 3, Table
1). Here the two ruthenium centers are bridged by the anilido-
nitrogen (−NH−) atoms of two deprotonated 2-chloroanilide
ligands, and as a result, a four-membered Ru2N2 metallocyclic
ring is formed. The average Ru−Nanilido distance is 2.062(6) Å,
which indicates a monoanionic amido state of the coordinated
2-chloroanilide ligand.10 In addition each ruthenium center is
coordinated to a monoanionic η5-cyclopentadienyl ring and a
terminal monoanionic chloride, and thus the oxidation state of
each Ru center is +3. Each of the two Ru(III) centers has 17
valence electrons with an unpaired spin, and thus the EAN of
these two Ru(III) centers is achieved via the formation of a
Ru−Ru single bond. A nearly similar situation exists in the
dicationic complex [6]2+. However, the difference here arose
due to the presence of an ortho-SCH3 group in the two bridging
amido ligands. Two terminal chloride ligands present in 2 are
substituted by SCH3 coordination, leading to the formation of
two five-membered chelates (Figure 4). Since the thiomethyl
function binds as a neutral donor, the resultant compound as a
whole is dicationic. The μ-η2:η1 coordination of the 2-
methylthioanilide ligand supported by the coordination of the
thiomethyl sulfur atom makes it more rigid11 in comparison to
complex 2. Furthermore, in complex [6]2+ the two cyclo-
pentadienyl rings are oriented on the same side of the Ru2N2
Figure 4. ORTEP drawing and atom-numbering scheme of [6]Cl2
with 30% probability thermal ellipsoids. All hydrogen atoms except at
N1 and N2 are omitted for clarity.
quinonediimine ligand (L2a for 1, Figure 1, and L2b for 5, Figure
2). The most notable feature in their structure is the elongation
of C−N bonds of the imine chromophore compared to the
normal imine C−N bond length:8 1.292−1.315 Å. In
comparison the two C−N bond lengths in representative
compound 5 are C(1)−N(1)H = 1.327(3) and C(6)−N(2)Ph
= 1.343(3) Å. This bond length is an indicator of the oxidation
state of the coordinated imine group, and the above C−N
lengths lie intermediate between an anionic ortho-semi-
quinonediimine and a neutral ortho-quinonediimine formula-
tion.8 Moreover, these two bond lengths are shorter than the
N(2)−C(8)Ph single bond (1.432(3) Å) present in the same
molecule. Furthermore, the two meta-C−C lengths, viz.,
dC(2/4)−(3/5) at 1.367(4) and 1.363(4) Å, indicate a quinone-
diimine oxidation state. The oxidation state of the N,N-donor
ligand in this case may best be argued in favor of an oxidized
Table 1. Selected Bond Distances (Å) and Bond Angles (deg) of Complexes 2, 5, [6]Cl2, [7]Cl, and [9]Cl2
a
parameter
2
5
[6]Cl2
[7]Cl
[9]Cl2
Ru1−Ru2
Ru1−N1
Ru1−N2
Ru2−N1
Ru2−N2
Ru1−S1
Ru2−S2
Ru1−Cl4
Ru1−Cl6
N1−C1
2.683(8)
2.067(4)
2.063(5)
2.068(4)
2.050(4)
×
×
×
×
×
2.646(7)
2.042(4)
2.096(4)
2.101(4)
2.047(4)
2.363(13)
2.358(13)
×
2.596(9)
1.961(5)
2.087(5)
×
×
×
3.299(5)
2.125(4)
2.146(4)
2.146(4)
2.125(4)
2.382(13)
2.382(13)
×
1.996(2)
2.006(2)
×
×
×
×
×
×
×
2.441(19)
2.358(2)
1.296(8)
1.321(8)
×
×
×
1.430(9)
×
×
1.327(3)
1.428(6)
×
1.432(7)
×
1.423(6)
×
×
N2−C6
N2−C8
N2−C7
1.343(3)
×
×
1.419(8)
×
×
C1−C6
C2−C3
C4−C5
N1−Ru1−N2
N1−Ru2−N2
Ru2−Ru1−N1
Ru2−Ru1−N2
Ru1−Ru2−N1
Ru1−Ru2−N2
1.442(3)
1.405(7)
1.392(7)
1.389(10)
93.93(15)
93.64(15)
51.31(10)
49.48(10)
49.31(10)
51.14(12)
1.465(9)
1.328(11)
1.346(13)
77.0(2)
×
48.43(15)
×
48.55(16)
×
1.409(7)
1.389(8)
1.386(9)
78.82(16)
78.82(16)
×
×
×
×
1.367(4)
1.363(4)
81.99(19)
82.25(18)
49.57(12)
49.10(11)
49.52(13)
49.49(11)
76.93(9)
×
×
×
×
×
a
For [9]Cl2 N2  N1_a, Ru2  Ru1_a, and S2  S1_a because its two halves are related by an inversion center.
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heterocyclic ring, and this ring is puckered. This geometry is
favored because of the better overlap between the lone-pair
orbitals on the anilido-nitrogen and acceptor orbitals on the
ruthenium(III) atoms.10a−d
in detail in a Section, 2.b. The carboxylate anion, in the isolated
complex, originated from contaminated ethanol in the reference
mediator complex, which got oxidized to carboxylic acid during
the course of the reaction. To establish the issue further, a
similar reaction was performed in the presence of sodium
acetate, and the isolated yield of the complex increased
substantially (cf. Experimental Section).
Electrospray ionization mass spectral data (ESI-MS) of
compound [7]Cl has provided strong support in favor of the
formulation of the complex as shown in Scheme 3a. It showed
an intense peak at m/z 806 amu, which corresponds to the
molecular ion peak of [M − Cl]+, where M represents the
molecular mass of the compound. The observed spectrum
exactly corroborates with its simulated spectrum and is
submitted as Supporting Information (Figure S13). Compound
[7]Cl is diamagnetic and showed a resolved 1H NMR spectrum
in methanol-d4 solvent. The characteristic resonances due to
cyclopentadienyl and methyl protons of the acetate moiety
appeared at δ 5.8 and 1.5 ppm, respectively. Signals of aromatic
proton resonances of the reference quinonediimine and 2,6-
dichloroanilide ligands appeared in the range δ 6.8−7.6 ppm
(Supporting Figure S14).
Isolation of the products from the reactions, discussed above,
has led to new insights into the ortho-Carom−N bond forming
reactions in ortho-monosubstituted aromatic amines. Clearly
the Carom−N bond fusion reactions in these examples
proceeded via involvement of an ortho-C−H bond activation
process, revealing that the aromatic-C−H bond activation
process is more facile over the aromatic-C−X (X = Cl, S, C)
bond activation process. With this background we now turn our
focus to the reactions of ortho-disubstituted anilines with the
aforesaid mediator complex with the hope of isolating some
intermediate(s) complex of higher oxidation state with terminal
amido or imido ligands, which have been argued3 to be the
intermediate in the reference dimerization of aromatic amines.
Accordingly, we chose 2,6-dichloroaniline, HL3a, and 2,6-
dimethylaniline, HL3b, as the substrates. While the reaction with
HL3b did not produce any isolable product, the reaction with
HL3a was smooth and is described below.
2.a. Reaction of CpRuIICl(PPh3)2 and 2,6-Dichloroaniline
(HL3a). The reaction of CpRuIICl(PPh3)2 with 2,6-dichloroani-
line (HL3a) under similar reaction conditions proceeded slowly
to form an unsymmetrical binuclear dark red complex, [7]Cl, of
a new ligand, N-(2,6-dichlorophenyl)-6-chloro-ortho-quinone-
diimine, L2d, as shown in Scheme 3. This new ligand is formed
2.b. X-ray Crystal Structure. The formulation and geometry
of compound [7]Cl are further authenticated by its X-ray
crystal structure determination. The ORTEP drawing and
atom-numbering scheme of the compound is displayed in
Figure 5, and selected bond lengths and angles are collected in
Scheme 3
Figure 5. ORTEP drawing and atom-numbering scheme of [7]Cl with
30% probability thermal ellipsoids. All hydrogen atoms except at N3
are omitted for clarity.
as a result of ortho-dimerization of 2,6-dichloroaniline via a less
facile ortho-Carom−Cl bond activation (vide supra) and an ortho-
Carom−N bond fusion reaction (Scheme 3a). However, in 2,6-
dichloroaniline there indeed exists a possibility of a para-C−H
bond activation reaction.12 Thus formation of the ortho-
quinonediimine ligand via an ortho-C−Cl bond activation
reaction here clearly points to the occurrence of coordination of
aromatic amine residues to the metal center prior to the
reference ortho-C−N bond formation reaction. The mono-
cationic complex [7]+ is a RuIII2 compound containing a single
Ru−Ru bond and supported by three bridging ligands: one
ortho-quinonediimine ligand coordinated by an imine nitrogen
(CphenylNH) atom in a η2-fashion, one deprotonated 2,6-
dichloroanilide ligand coordinated by an anilido nitrogen atom
in a η2-fashion, and an in situ generated acetate ligand
coordinated via O,O-coordination. We wish to note here that
the coordination modes of the reference ortho-quinonediimine
ligand and 2,6-dichloroanilide ligand are unique and discussed
Table 1. X-ray crystal structure analysis has revealed that
complex [7]Cl is a binuclear cationic compound consisting of
two ruthenium centers that are connected by a single bond
(dRu1−Ru2: 2.596(9) Å). Here the two ruthenium centers, Ru1
and Ru2, are bridged by three ligands, viz., a new N-(2,6-
dichlorophenyl)-6-chloro-ortho-quinonediimine ligand, a 2,6-
dichloroanilide ligand, and an acetate ligand, as noted in the
previous section and in Scheme 3a.
The new ortho-quinonediimine ligand here acts as a bridge
connecting the two Ru1 and Ru2 centers through the imine
(N(1)H) nitrogen atom in a η2-fashion, and the second
imine nitrogen atom (N(2)Ph) coordinates the Ru1 center
in a normal η1-fashion. While the bidentate N,N-donor
chelation mode (A) of the ortho-quinonediimine ligand is
common in the literature,1−3,8 the η2-coordination mode along
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with simultaneous bidentate N,N-donor chelation (B) of the
reference ligand is unknown in the literature (Scheme 4).
cyclopentadienyl anion. As a whole, the structural analysis thus
has revealed the trivalent oxidation state of both Ru1 and Ru2
centers in the complex [7]Cl.
3.a. Reaction of (Bnz)2RuII Cl4 and ortho-Mono- and
Scheme 4. Coordination Mode of ortho-Quinonediimine
2
Disubstituted Anilines. To explore the role of metal ion in
ortho-C−N bond fusion in amines, the aforesaid aromatic
amines were reacted separately with another polyene mediator
Ligand
complex, (Bnz)2RuII Cl4. In a recent communication we have
2
shown that the precursor RuII−Bnz complex strongly resists
oxidation of the metal center, and hence no dimerization of
aromatic amines is possible. Similar expected complexes3 were
isolated from the reaction of 2-chloroaniline, 2-methylaniline,
2,6-dichloroaniline, and 2,6-dimethylaniline with the above
mediator complex. The results are summarized in Scheme 5a,
Scheme 5
Selected bond parameters of compound [7]Cl are as follows:
C(1)N(1)H, 1.296(8) Å; C(6)N(2)Ph, 1.321(8) Å; and
C(2/4)C(3/5)(meta), 1.328(11) and 1.346(13) Å, which
indicate8 a neutral ortho-quinonediimine oxidation state of the
reference ortho-quinonediimine ligand.
In this complex, the 2,6-dichloroanilide ligand also acts as a
bridge between Ru1 and Ru2 centers via the anilido
(−N(3)H−) nitrogen atom in a η2-fashion, which is similar
to that observed in the previous two binuclear complexes, 2 and
[6]Cl2 (Schemes 1 and 2). The two Ru(1/2)−anilido nitrogen
(−N(3)H−) distances are 2.024(5) and 2.096(6) Å, indicating
a monoanionic amido state9 of the coordinated 2,6-dichlor-
oanilide ligand. The most significant observation in this
structure is the presence of a distinct Ru(1)−Cl(4) (aromatic
Cl) bond. A chloro group (attached to an aryl or alkyl group) is
normally considered to be a very poor donor, and only a few
compounds of p-block elements are known to form such
bonds.5 However, in the cases of transition metal complexes
such a coordination mode of an aromatic-Cl atom is virtually
unknown. As far as we are aware there exists only one report6 in
which the existence of such an unusual bond between Co/Ni
and Cl(aromatic) atoms has been argued in the respective
transition metal complexes of the ligand, triazene-2-(2-
halophenyl)-1-oxide. The bonding was primarily characterized
by the analyses of their spectral data in solution. The Ru(1)−
Cl(4) distance in compound [7]Cl is 2.441(19) Å, which is
substantially shorter than the sum of their van der Waals radii,
3.75 Å. For comparison, the reported Co−Cl bond length (av
2.98 Å) in the above-noted cobalt-triazene complex is too long
to be regarded as a real coordination bond and may be
considered only as a weak Co−Cl interaction.6b Hence we wish
to claim that the compound [7]Cl is the first example of an
authentic transition metal complex (M = RuIII in this case) with
genuine crystallographic evidence of a M−Cl(aromatic)
coordination. The above bonding phenomenon is further
supported by the calculated atomic charge density of the
chlorine atoms by the natural population analysis method,
which shows more positive atomic charge density on the
coordinated Cl(4) atom (0.241) in comparison to the similar
uncoordinated Cl(5) atom (0.072). Moreover the C(18)−
Cl(4) length (1.760(7) Å) is appreciably longer than the
otherwise identical bond C(14)−Cl(5) (1.703(8) Å). Coordi-
nation of the anionic acetate ligand in this complex is usual and
binds Ru1 and Ru2 centers via two oxygen atoms in a typical
η1-fashion.
and an ORTEP diagram, as revealed by X-ray structure
determination of a representative compound, 8, is submitted as
Supporting Information (Figure S15). These results are not
discussed any further. However, the reaction of (Bnz)2RuII Cl4
2
with 2-methylthioaniline under identical reaction conditions
produced an interesting anilido-bridged binuclear RuII
2
compound, [9]Cl2, in 42% yield (Scheme 5b). Here, the two
deprotonated 2-methylthioanilide ligands coordinate in a μ-
η2:η1-fashion, bridging the two Ru centers as shown in Scheme
5b. The compound was cleaned by removing the unreacted
amines via washing with diethyl ether and subsequent
crystallization from its solution in methanol.
The complex [9]Cl2 gave satisfactory elemental analyses (cf.
Experimental Section). The ESI-MS spectrum of the
compound showed an intense peak at m/z 317 amu,
corresponding to the molecular ion peak of [M/2]+ where M
represents the molecular mass of the compound. The
experimental spectral feature of the complex corroborates its
simulated isotopic pattern, and these are submitted as
Supporting Information (Figure S16). The complex is
Besides the coordination of three bridging ligands, the Ru1
center is terminally coordinated to a monoanionic chloride
ligand, and the Ru2 center is coordinated to a monoanionic η5-
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1
a
diamagnetic and showed a well-resolved H NMR spectrum in
methanol-d4 solvent. The resonance due to a characteristic
aromatic η6-benzene proton appeared at δ 6.0 ppm, and for the
anilido (−NH−) proton it appeared at 7.8 ppm. The signals
due to aromatic proton resonances of the coordinated ligand
Table 2. Cyclic Voltammetric Data
oxidation
reduction
b
b
compound
E1/2
,
V (ΔEp, mV)
E1/2, V (ΔEp, mV)
c
c
1
0.82 (100)
1.02 (100)
0.54 (100)
−0.93, 1.27
c
2
−0.70
−1.04
(L1b)− appeared in the range δ 6.5−8.0 ppm. The H NMR
spectrum of the compound [9]Cl2 is submitted as Supporting
Information (Figure S17).
3.b. X-ray Crystal Structure. The identity of complex [9]Cl2
was finally confirmed by solution of its single-crystal X-ray
structure. Suitable single crystals were developed by slow
evaporation of its methanolic solution. The ORTEP diagram
and atom-numbering scheme of complex [9]Cl2 is shown in
Figure 6, and selected bond lengths and angles are summarized
1
c
3
c
4
1.20
−0.69 (100)
−0.70, −1.11
c
c
c
5
0.67
c
[6]Cl2
0.76
−0.42 (40), −0.71 (30)
a
In acetonitrile solution, supporting electrolyte TEAP, reference
electrode Ag/AgCl. E1/2 = 0.5(Epa + Epc) where Epa and Epc are anodic
and cathodic peak potentials, respectively, ΔEp = Epa − Epc, scan rate
b
c
50 mV s−1. Quasireversible/irreversible.
Figure 7. Cyclic voltammogram of complex 1 in CH3CN−0.1 M
NEt4ClO4 and (inset) EPR spectrum of electrochemically generated
[1]+ in CH2Cl2−0.1 M Bu4NClO4 at 77 K.
Figure 6. ORTEP drawing and atom-numbering scheme of [9]Cl2
with 30% probability thermal ellipsoids. All hydrogen atoms except at
N1 and N1_a are omitted for clarity.
confirmed by comparison of the current height with the redox
response of the ferrocene/ferrocenium couple under identical
experimental conditions, and the reversible wave showed one
electron stoichiometry in constant potential electrolysis experi-
ments. To gain further insight into the electron transfer
phenomena associated with the reversible redox process in
complex 1, the EPR spectrum of the electrogenerated one-
electron-oxidized species was studied at 77 K. The one-
electron-oxidized compound, [1]+, showed a ruthenium(III)-
centered rhombic spectrum with ⟨g⟩av = 2.0675 (g1 = g2 =
2.1160 and g3 = 1.9670), confirming that the oxidation process
primarily occurs at the RuII center (Figure 7). Irreversibility of
the first cathodic wave is presumably due to the reduction of
the quinonediimine ligand and was supported by the DFT
studies (cf. below) of the reduced complex, [1]−. A similar type
of electrochemical response with small potential shift was
exhibited by the other two mononuclear complexes, viz., 3 and
5, and the data are collected in Table 2 for comparison. The
binuclear complex 2, on the other hand, displayed one
irreversible cathodic response at −0.70 V and one reversible
anodic response at 1.02 V (Figure 8). The one-electron-
oxidized species [2]+, generated by exhaustive electrolysis of
compound 2 at 1.25 V, showed an axial EPR spectrum with
⟨g⟩av = 2.0313 (g1 = 2.5292, g2 = 2.4417, and g3 = 1.8786,
Figure 8), confirming the presence of a Ru(III) center. Thus
the oxidative response may be assigned to the oxidation of one
of the two Ru(III) centers, producing a mixed-valent Ru(III)−
Ru(IV) or Ru(3.5)−Ru(3.5) compound. This ambiguity was
further clarified by DFT calculations (cf. below). Another
binuclear compound, 4, exhibited similar redox properties with
in Table 1. The asymmetric unit of the complex consists of the
cationic complex [9]2+, two Cl− as counteranions, and two
water molecules as solvate. It is a homobinuclear RuII2 complex
in which the two halves are related by an inversion center. Two
units of 2-methylthioanilide bridge the two ruthenium centers
by a μ-η2:η1 coordination mode through anilido nitrogen and
thiomethyl sulfur atoms with the formation of a stable Ru2N2
metallocyclic ring. The situation here is somewhat similar to
that in the previously described compound [6]Cl2. In addition,
each ruthenium atom is coordinated by a η6-Bnz ligand. In
complex [9]Cl2 two phenyl rings of the bridging ligands are
disposed trans, which is opposite (cis) to that in the complex
[6]Cl2. The Ru2N2 metallocyclic ring is completely planar,
whereas in the complex [6]Cl2 it is puckered. The two Ru(II)
́
centers in [9]Cl2 are widely separated (dRu1−Ru2: 3.299(5) Å),
signifying the absence of any metal−metal bond.
B. Cyclic Voltammetry and EPR. Redox properties of all
the complexes were examined by cyclic voltammetry in
acetonitrile solution containing 0.1 M TEAP as the supporting
electrolyte in the potential range +1.5 to −1.5 V using platinum
as the working electrode. The potentials are referenced to the
saturated Ag/AgCl electrode, and the results are summarized in
Table 2. The E1/2 of the ferrocenium−ferrocene couple under
our experimental conditions was 0.39 V.
Cyclic voltammetry of complex 1 exhibits two irreversible
responses at potentials −0.93 and −1.27 V and one reversible
oxidative response at potential 0.82 V (Figure 7). For
irreversible waves the one-electron redox response has been
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delocalized over the ligand (62%) orbitals; the metal orbitals
contribute 28% to this orbital. The next lowest unoccupied
orbital (LUMO+1) consists of metal (43%) and ligand orbitals
(N-(2-chlorophenyl)-6-chloro-ortho-quinonediimine: 22% and
cyclopentadienyl: 26%). However for the binuclear complex 2
both HOMO and LUMO orbitals are primarily localized over
the metal orbitals with very little contributions of Cl− and 2-
chloroanilide ligand, (L1a)− (HOMO: Ru: 45%; Cl: 26%;
(L1a)−: 11%; Cp: 08%; and LUMO: Ru: 54%; Cp: 11%; (L1a)−:
27%; Cl: 08%).
The most probable electronic structure in the native state of
compound 1 is [RuII(Cp)(Q)Cl], and accordingly, the one-
electron-reduced and oxidized species are [RuII(Cp)(Q•−)Cl]−,
[1]−, and [RuIII(Cp)(Q)Cl]+, [1]+, respectively. In line with
these descriptions, the Mulliken spin density population in the
reduced complex [1]− is more populated (0.5845) over the
ligand center (Figure 9a), whereas in the oxidized complex [1]+
Figure 8. Cyclic voltammogram of complex 2 in CH3CN−0.1 M
NEt4ClO4 and (inset) EPR spectrum of electrochemically generated
[2]+ in CH2Cl2−0.1 M Bu4NClO4 at 77 K.
insignificant shift of redox potentials. The redox behavior of the
binuclear complex [6]Cl2 showed two reductive responses at
−0.42 and −0.70 V (Figure S18). However, our efforts to trap
the reduced species [6]+ and [6] were unsuccessful. These
electrogenerated species revert to the parent compound
quickly. The complex [9]Cl2, on the other hand, is redox
inert within the above potential window.
C. Electronic Structures of the Complexes 1 and 2.
The above-noted N,N-donor ligands can exist in multiple
oxidation states, and hence the electronic structures of the two
representative complexes 1 and 2 were analyzed by density
functional theory (DFT). Complex 1 was optimized in three
conditions: singlet closed shell, singlet broken symmetry (BS)
open shell, and triplet open shell (Table S1). The attempts to
locate the open-shell singlet [RuIII(Cp)(Q•−)Cl] configuration
for the native state of compound 1 using the BS-DFT approach
converged back to the closed-shell configuration, [RuII(Cp)-
(Q)Cl], where Q stands for the quinonediimine formulation of
the ligand N-(2-chlorophenyl)-6-chloro-ortho-quinonediimine,
L2a. The energies of singlet, triplet, and BS-singlet states of
compound 1 are −8.28903 × 105, −8.28888 × 105, and 8.28902
× 105 kcal/mol, respectively. Compound 2 was also optimized
in both closed-shell singlet (18.76252 × 105 kcal/mol) and in
open-shell triplet (18.76237 × 105 kcal/mol) configurations
(Table S1). The triplet state was found to reside much higher
in energy (15.16 kcal/mol) relative to the singlet state. In
addition compound 2 showed a resolved 1H NMR spectrum in
the normal range for diamagnetic compounds, indicating a
further closed-shell singlet configuration. There is a good
agreement between the calculated bond lengths and angles with
the crystallographically established metrical parameters of the
complexes 1 and 2 (Tables S2 and S3). The energies and
compositions of the DFT calculated frontier orbitals of the
complexes 1 and 2 are summarized in the Supporting
Information (Tables S4 and S5). Analyses of the frontier
molecular orbitals of complex 1 reveal that the highest occupied
MO (HOMO) is a combination of metal (major) and
coordinated N-(2-chlorophenyl)-6-chloro-ortho-quinonedii-
mine ligand (minor) orbitals (1: Ru: 53%; Cl: 17%; L2a:
16%; Cp: 14%). Closely lying occupied HOMO−1 is formed
by nearly equal contributions of metal (38%) and N-(2-
chlorophenyl)-6-chloro-ortho-quinonediimine ligand orbitals
(41%). The lowest unoccupied MO (LUMO) is primarily
Figure 9. Spin density plots of (a) [1]+ and (b) [1]−.
(Figure 9b) it is more populated over the metal center
(0.7379). We believe that a similar electronic structure
description is valid for the analogous complexes 3 and 5. In
the case of binuclear complex 2, however, the two ruthenium
centers are present in a trivalent oxidation state and are
connected by two bridging deprotonated ligands, (L1a)−.
Accordingly, the electronic structure of complex 2 in its native
state is [CpClRuIII{μ-η2-(L1a)−}2RuIIIClCp]. Thus the possible
descriptions for the one-electron-oxidized and reduced species
are as follows: unsymmetrical mixed-valent formulation with
different valences [CpClRuIII{μ-η2-(L1a)−}2RuIVClCp], [2]+,
and [CpClRuIII{μ-η2-(L1a)−}2RuIIClCp]−, [2]−, respectively,
or symmetrical alternative mixed-valent formulation with
average net metal valences [CpClRu3 . 5 {μ-η2 -
(L1a)−}2Ru3.5ClCp], [2]+, and [CpClRu2.5{μ-η2-(L1a)−}2Ru2.5Cl
Cp]−, [2]−, respectively. Since the unpaired spin densities in
species [2]+ and [2]− are populated nearly equally on the two
metal centers ([2]+: Ru1: 0.383739, Ru2: 0.380776 and [2]‑:
Ru1: 0.3420; Ru2: 0.3426, and the rest are populated on the
coordinated ligands) (Figure 10), the best descriptions for both
[2]+ and [2]− are completely delocalized symmetrical mixed-
valent formulations.
D. Electronic Spectra. Electronic spectra of all the
complexes reported herein were recorded in acetonitrile
solvent, and data are collected in Table 3. To assign the
transitions of the complexes, time-dependent DFT (TD-DFT)
calculations were performed on the two representative
complexes 1 and 2, and the data are collected in Tables S6
and S7. Their electronic spectra are displayed in Figure 11.
The mononuclear complex 1 exhibited an intense broad
transition at 488 nm. TD-DFT calculations revealed that this
low-energy transition compared well with the calculated values
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(HOMO−1 and HOMO−2) and acceptor (LUMO+1) orbitals
here are delocalized primarily over the metal orbitals, one can
assign this low-energy transition as a d(Ru)−d(Ru) transition
(Table S7). Similarly the analogous complex 4 displayed this
transition at 475 nm (cf. Table 3). In comparison the dicationic
complex [6]Cl2 showed an intense transition at 860 nm (Figure
11). DFT analyses on this (Tables S8 and S9) revealed that the
HOMO is nearly equally populated over metal (48%) and
ligand orbitals (40%) and the LUMO is composed of metal
(55%) and ligand orbitals (35%). Further TD-DFT analysis
(Table S10) has indicated that the above near-IR range
transition compares well with the calculated value of the
HOMO → LUMO transition. This type of low-energy
transition in anilido-bridged RuIII complexes has been rarely
2
Figure 10. Spin density plots of (a) [2]+ and (b) [2]−.
observed.5a
Table 3. UV−Vis−NIR Absorption Spectral Data of
Complexes 1−[7]Cl in Acetonitrile
CONCLUSION
■
In summary, using ortho-mono- and disubstituted anilines we
have discussed competitive C−H vs C−X bond (X = Cl, C, S)
activation reactions in ruthenium-mediated ortho-Carom−N
bond fusion reactions. It has been found that the C−H bond
activation process is undoubtedly preferable over the above C−
X bond activation processes. However, the C−Cl bond
activation reaction did occur in the case of ortho-disubstituted
2,6-dichloroaniline in more forceful conditions. The reactions
of monosubstituted anilines have afforded the anilido-bridged
binuclear ruthenium(III) complexes (2, 4, and [6]Cl2) in
addition to the mononuclear ruthenium(II) complexes (1, 3,
and 5) containing N-aryl-ortho-quinonediimine ligands (L2a−c).
The reaction of CpRuIICl(PPh3)2 with 2,6-dichloroaniline has
resulted in an unusual binuclear ruthenium(III) complex, [7]Cl,
in which the new N-(2,6-dichlorophenyl)-6-chloro-ortho-
quinonediimine ligand (L2d) is formed via ortho-C−Cl bond
activation and ortho-C−N bond fusion reactions. As far as we
are aware, this compound is the first example of an authentic
transition metal complex (M = RuIII in this case) with genuine
crystallographic evidence of a M−Cl(aromatic) coordination.
In the courses of these reactions several metal−metal-bonded
RuIII2 complexes (2, [6]Cl2, and [7]Cl) have been isolated and
characterized. These complexes are rich in both spectral and
redox properties and have been thoroughly studied by cyclic
voltammetry, UV−vis spectra, and EPR, and the conclusions
are supported by DFT studies. Finally, the chemical reactions
reported herein not only have generated new scopes in the area
of metal-mediated ortho-Carom−N bond fusion reaction but also
have produced new classes of novel organometallic compounds
that otherwise are not achievable following the available
synthetic protocols.
complex
λmax/nm (ε/M−1 cm−1
)
1
489(18311), 278(30492)
2
448(31487), 365(43667), 260(109548)
495(15901), 268(37288)
3
4
475(96688), 288(24064)
5
495(3941), 256(sh)(7199)
[6]Cl2
[7]Cl
872(34802), 461(7051), 269(sh)(20329)
477(2424), 398(1664), 357(1867)
Figure 11. UV−vis−NIR absorption spectra of the compounds 1
(red), 2 (orange), and [6]Cl2 (green) in 10−5 M acetonitrile solution.
Inset: [7]Cl in 10−4 M acetonitrile solution.
for HOMO−1 → LUMO+1 and HOMO−2 → LUMO
transitions. Although these four participating orbitals are
delocalized over both metal and ligand orbitals, the metal
orbitals have major contributions in the donor orbital
(HOMO−2: 72%) and the ligand orbitals have major
contributions in the acceptor orbital (LUMO: 62%). Thus
the above transition may best be described as a metal to ligand
charge transfer (MLCT) transition (Table S6). This transition
was computationally predicted to appear at 466 nm. The
analogous complexes 3 and 5 also showed similar MLCT
transition near 500 nm (cf. Table 3). However, the neutral
binuclear complex 2 exhibited a broad transition in the visible
region at 447 nm. This transition is computationally predicted
to appear at 468 nm and is attributed to HOMO−1 → LUMO
+1 and HOMO−2 → LUMO+1 transitions. Since, both donor
EXPERIMENTAL SECTION
■
Materials. The ruthenium salt RuCl3 was obtained from Arora-
Matthey, Kolkata, and aromatic amines, viz., 2-chloroaniline, 2-
methylthioaniline, and 2,6-dichloroaniline, were obtained from
13
Sigma-Aldrich. The mediator complexes CpRuIICl(PPh3)2 and
(Bnz)2RuII Cl414 and the supporting electrolytes tetraethylammonium-
2
perchlorate (TEAP) and tetrabuthylammoniumperchlorate (TBAP)
for the electrochemical measurements were prepared and crystallized
following the published procedures.15 Solvents and other chemicals
used for syntheses were of analytical grade and used as received.
Instrumentation. UV−vis−NIR absorption spectra were recorded
either on a Perkin-Elmer Lambda 950 UV/vis spectrophotometer or
on a J&M TIDAS instrument. The IR spectra were recorded with a
Perkin-Elmer 783 spectrophotometer. Cyclic voltammetry was carried
out in 0.1 M TEAP solutions using a three-electrode configuration
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Table 4. Crystallographic Data of Complexes 1, 2, 5, [6]Cl2, [7]Cl, and [9]Cl2
parameter
1
2
5
[6]Cl2
[7]Cl
[9]Cl2
empirical formula
fw
C17H13Cl3N2Ru
452.71
C22H20Cl4N2Ru2
656.34
C19H19ClN2RuS2
476.02
C48H52N4Ru4S4Cl3O7
1435.85
monoclinic
C2/c
C25H18Cl7N3O4Ru2
874.71
C26H28N2Ru2S2Cl4O4
840.58
cryst syst
orthorhombic
Pca21
monoclinic
P21/n
triclinic
triclinic
triclinic
space group
P1
̅
P1
̅
P1
̅
́
́
a (Å)
20.932(4)
7.503(17)
20.915(4)
90
18.964(3)
15.138(2)
19.467(3)
90
9.422(11)
10.710(12)
11.157(14)
64.183(2)
85.266(2)
72.337(2)
964.1(2)
2
36.395(6)
8.770(13)
18.326(3)
90
10.178(17)
12.442(2)
13.129(2)
83.865(4)
77.925(4)
69.202(4)
1518.9(4)
2
9.089(8)
9.413(8)
10.684(9)
64.083(10)
76.070(2)
74.921(2)
785.37(12)
1
b (Å)
́
c (Å)
α (deg)
β (deg)
γ (deg)
90
100.946(4)
90
108.519(3)
90
90
3
́
V (Å )
3284.8(12)
8
5486.9(14)
8
5546.5(15)
4
Z
Dcalcd (g/cm3)
1.831
1.589
1.640
1.719
1.913
1.777
cryst dimens (mm3)
0.06 × 0.08 ×
0.11
0.07 × 0.17 × 0.20 0.05 × 0.09 × 0.12 0.06 × 0.10 × 0.19
0.11 × 0.13 × 0.16
0.10 × 0.10 × 0.10
θ range for data collection 2.0−26.0
1.4−20.2
2.0−26.3
1.2−25.0
1.6−27.4
2.1−25.0
(deg)
GOF on F2
1.08
0.99
0.78
1.10
1.07
1.12
reflns collected
unique reflns
35 623
3327
31 902
10 002
25 431
20 488
9111
5232
3874
4887
6743
2765
final R indices [I > 2σ(I)] R1 = 0.0419
R1 = 0.0306
wR2 = 0.0684
293
R1 = 0.0262
wR2 = 0.0760
293
R1 = 0.0353
wR2 = 0.1055
293
R1 = 0.0540
wR2 = 0.1692
293
R1 = 0.0376
wR2 = 0.1157
293
wR2 = 0.1198
temperature (K)
120
(platinum working electrode, platinum counter electrode, Ag/AgCl
reference electrode) and a PC-controlled PAR model 273A electro-
chemistry system. The E1/2 for the ferrocenium−ferrocene couple
under our experimental conditions was 0.39 V. EPR spectra in the X-
band were recorded with a JEOL JES-FA200 spectrometer. A Perkin-
Elmer 240C elemental analyzer was used to collect microanalytical
data (C, H, N). 1H NMR spectra were taken on a Bruker Avance DPX
300 spectrometer, and SiMe4 was used as the internal standard. C−H
protons are assigned according to their labeling scheme in the
respective figures as shown in the Supporting Information. Due to the
presence of overlapping protons, assignments have not been made for
the compound [7]Cl. ESI mass spectra were recorded on a micro mass
Q-TOF mass spectrometer (serial no. YA 263).
2. 2-Methylaniline (HL1c). The reaction of CpRuIICl(PPh3)2 with 2-
methylaniline under identical reaction conditions to those described in
the previous section produced the mononuclear red compound 3 and
the binuclear yellow compound 4. Their yield and characterization
data are as follows:
3. Yield: 61 mg (53%). ESI-MS, m/z: 377 [M − Cl]+ (M =
C19H20ClN2Ru). Anal. Calcd for C19H20ClN2Ru: C, 55.27; H, 4.85; N,
6.78. Found: C, 55.22; H, 4.90; N, 6.75. 1H NMR (500 MHz, CDCl3):
12.23(s, 1H, N−H), 7.75(d, 1H, J = 7.5 Hz, H4), 7.25 (d, IH, J = 7.5,
H5), 7.15(t, 1H, J = 7.5 Hz, H7), 7.11(d, 1H, J = 7.5 Hz, H6), 6.71(d,
2H, J = 5.5 Hz, H2, H3), 6.61(t, 1H, J1 = 5.5 Hz, J2 = 5.0 Hz, H1),
4.73(s, 5H, Cp), 2.54(s, 3H), 2.22(s, 3H, CH3).
4. Yield: 24 mg (14%). ESI-MS, m/z: 639 [M + Na]+ (M =
C24H26Cl2N2Ru2). Anal. Calcd for C24H26Cl2N2Ru2: C, 46.75; H, 4.22;
A. Chemical Reactions of CpRuIICl(PPh3)2 with ortho-Monosub-
stituted Anilines. 1. 2-Chloroaniline (HL1a). A 200 mg (0.28 mmol)
amount of CpRuIICl(PPh3)2 in 3 mL of 2-chloroaniline was heated at
80 °C in air for six hours. During this period the color of the solution
changed from orange to reddish-brown. The reaction mixture was then
washed with a dichloromethane−hexane solvent mixture (1:10)
several times to remove unreacted ligand. Rapid crystallization of the
crude reaction mixture from 30 mL of a dichloromethane−hexane
(1:10) solvent mixture furnished a major product, 1 (intense red),
along with a minor product, 2 (yellowish-brown). Compound 2 was
precipitated from this solvent mixture, and compound 1 was collected
by the evaporation of solvent. These two compounds were
recrystallized by slow evaporation of their solutions in a dichloro-
methane−hexane solvent mixture. Yield and characterization data of
the compounds are as follows:
1
N, 4.24. Found: C, 46.72; H, 4.26; N, 4.22. H NMR (500 MHz,
CDCl3): 14.99(s, 1H, N−H), 6.72(d, 1H, J = 7.5 Hz, H2), 6.71(t, 1H,
J1 = 7.5, J2 = 8.0 Hz, H4), 6.42(d, 1H, J = 6.5 Hz, H3), 6.14(d, 2H, J =
9.0 Hz, H1), 4.98(s, 5H, Cp), 2.96(s, 3H, CH3).
3. 2-Methylthioaniline (HL1b). A similar reaction with 2-
methylthioaniline produced the red complex 5 and the binuclear
green complex [6]Cl2. Yield and characterization data of these
compounds are as follows:
5. Yield: 37 mg (28%). ESI-MS, m/z: 441 [M − Cl]+ (M =
C19H19ClN2RuS2). Anal. Calcd for C19H19ClN2RuS2: C, 47.90; H,
3.99; N, 5.88. Found: C, 47.94; H, 3.95; N, 5.91. 1H NMR (500 MHz,
CDCl3): 12.93(s, 1H, N−H), 7.71(d, 1H, J = 8.0 Hz, H7), 7.26(t, 1H,
J = 7.5 Hz, H5), 7.15(t, 1H, J1 = 8.0 Hz, J2 = 7.5 Hz, H6), 7.10(d, 1H, J
= 7.5 Hz, H4), 6.97(d, 1H, J1 = 7.0 Hz, H1), 6.82(t, 1H, J1 = 8.0 Hz, J2
= 7.0 Hz, H2), 6.69(d, 1H, J = 8.5, H3), 4.86(s, 5H, Cp), 2.46(s, 3H,
CH3), 2.24(s, 3H, CH3).
1. Yield: 62 mg (49%). ESI-MS, m/z: 417 [M − Cl]+ (M =
C17H13Cl3N2Ru). Anal. Calcd for C17H13Cl3N2Ru: C, 45.13; H, 2.88;
1
[6]Cl2. Yield: 48 mg (25%). ESI-MS, m/z: 304 [M/2]+ (M =
C24H26N2Ru2S2). Anal. Calcd for C24H26N2Ru21S2: C, 47.37; H, 4.28;
N, 4.60. Found: C, 47.34; H, 4.25; N, 4.63. H NMR (500 MHz,
CD3OD): 4.94(s, 1H, N−H), 7.64(d, 1H, J = 13.5 Hz, H1), 7.41(t,
1H, J1 = 11.8 Hz, J2 = 13.5 Hz, H3), 7.27(t, 1H, J1 = 13.4 Hz, J2 = 11.8
Hz, H2), 7.14(d, 1H, J = 11.8 Hz, H4), 5.92(s, 5H, Cp), 2.54(s, 3H,
CH3).
N, 6.19. Found: C, 45.07; H, 2.91; N, 6.15. H NMR (500 MHz,
CDCl3): 12.79(s, 1H, N−H), 7.95(d, 1H, J = 7.5 Hz, H4), 7.42(d, 1H,
J = 9.0 Hz, H7), 7.36(t, 1H, J1 = 7.5 Hz, J2 = 9.0 Hz, H5), 7.30(t, 1H,
J1 = 8.0 Hz, J2 = 7.5 Hz, H6), 7.14(d, 1H, J = 6.5 Hz, H1), 6.89(t, 1H,
J1 = 9.0 Hz, J2 = 7.0 Hz, H2), 6.84(d, 1H. J = 9.0 Hz, H3), 4.96(s, 5H,
Cp).
2. Yield: 32 mg (17%). ESI-MS, m/z: 292 [M/2 − Cl]+ (M =
C22H20Cl4N2Ru2). Anal. Calcd for C22H20Cl4N2Ru2: C, 40.24; H, 3.05;
B. Reaction of CpRuIICl(PPh3)2 and 2,6-Dichloroaniline (HL3a). A
mixture of 200 mg (0.28 mmol) of CpRuIICl(PPh3)2 and 3 mL of 2,6-
dichloroaniline (HL3) was stirred for 24 hours at 80 °C in air. During
this period, the color of the mixture became reddish-brown. The
1
N, 4.27. Found: C, 40.28; H, 3.10; N, 4.22. H NMR (500 MHz,
CDCl3): 9.0(s, 1H, N−H), 7.23(d, 1H, J = 9.0 Hz, H3), 7.01(m, 2H,
H2, H4), 6.43(d, 1H, J = 9.0 Hz, H1), 5.26(s, 5H, Cp).
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Organometallics
Article
reaction mixture was then cooled and washed with a dichloro-
methane−hexane solvent mixture (1:10) several times to remove
excess 2,6-dichloroaniline. The crude mass thus obtained was dissolved
in a minimum volume of dichloromethane and purified by rapid
crystallization using hexane as the precipitant. The compound [7]Cl
was recrystallized by slow evaporation of a methanolic solution of the
compound. Its yield and characterization data are as follows:
[7]Cl. Yield: 68 mg (29%). ESI-MS, m/z: 806 [M]+ (M =
C25H18Cl6N3O2Ru2). Anal. Calcd for C25H18Cl6N3O2Ru2: C, 49.42; H,
2.96; N, 6.92. Found: C, 49.37; H, 3.99; N, 6.88. 1H NMR (500 MHz,
CD3OD): 7.66(m, 3H), 7.52(m, 1H), 7.35(m, 4H), 6.88(m, 1H),
5.73(s, 5H, Cp), 4.85(s, 1H, N−H), 1.53(s, 3H, CH3).
ASSOCIATED CONTENT
■
S
* Supporting Information
X-ray crystallographic files in CIF format for the complexes 1,
2, 5, [6]Cl2, [7]Cl, and [9]Cl2; figures of ESI-MS and 1H NMR
of 1−[7]Cl and [9]Cl2; DFT and TD-DFT results of
complexes 1, 2, and [6]Cl2 are provided. This material is
available free of charge via the Internet at http://pubs.acs.org.
AUTHOR INFORMATION
■
Corresponding Author
*E-mail: icsg@iacs.res.in.
The reaction in the presence of sodium acetate under identical
reaction conditions produced the complex [7]Cl2 with a higher yield
of 45%.
Notes
C. Reactions of (Bnz)2RuII Cl4 with 2-Methylthioaniline (HL1b). A
The authors declare no competing financial interest.
2
200 mg (0.45 mmol) portion of (Bnz)2RuII Cl4 was added to 3 mL of
2
2-methylthioaniline, and the mixture was stirred for 80 °C in air for six
hours. During this reaction period the color of the solution became
yellowish-brown. The reaction mixture was then cooled and washed
with diethyl ether several times to remove excess ligand. The crude
mass thus obtained was dissolved in a minimum volume of
dichloromethane and purified by rapid crystallization using diethyl
ether as the precipitant. Purification of the crude mass furnished a
yellow-colored compound, [9]Cl2. It was recrystallized by slow
evaporation of the methanolic solution of the compound. Its yield
and characterization data are as follows:
ACKNOWLEDGMENTS
■
Financial support received from the Department of Science and
Technology (Project SR/S1/IC/0031/2010), New Delhi, is
gratefully acknowledged. S.G. sincerely thanks DST for a J. C.
Bose fellowship. Crystallography was performed at the DST-
funded National Single Crystal Diffractometer Facility at the
Department of Inorganic Chemistry, IACS. S.M. and S.S. thank
the Council of Scientific and Industrial Research for their
fellowship.
[9]Cl2. Yield: 132 mg (42%). ESI-MS, m/z: 317 [M/2]+ (M =
C26H28N2Ru2S2). Anal. Calcd for C26H28N2Ru21S2: C, 49.21; H, 4.41;
N, 4.41. Found: C, 49.18; H, 4.45; N, 4.44. H NMR (500 MHz,
CD3OD): 7.87(s, N−H), 7.37(d, 1H, J = 13.5 Hz, H1), 7.11(m, 2H,
H2, H4), 6.97(m, 1H, H3), 6.08(s, 6H, Bnz), 3.31(s, 3H, CH3).
Computational Details. Full geometry optimizations were carried
out using the density functional theory method at the B3LYP level.16
All elements except ruthenium were assigned the 6-31G(d) basis set.
The SDD basis set with effective core potential was employed for the
ruthenium atom.17 The vibrational frequency calculations were
performed to ensure that the optimized geometries represent the
local minima and there are only positive Eigen values. All calculations
were performed with the Gaussian03 program package.18 Natural
bond orbital analyses were performed using the NBO 3.1 module of
Gaussian03.19 Vertical electronic excitations based on B3LYP-
optimized geometries were computed using the TD-DFT formalism20
in acetonitrile using the conductor-like polarizable continuum
model.21 GaussSum22 was used to calculate the fractional contribu-
tions of various groups to each molecular orbital.
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