Inorganica Chimica Acta 374 (2011) 366–372

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Inorganica Chimica Acta

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ortho-Carom–N bond fusion in aniline associated with electrophilic chlorinationreactions at ruthenium(III) coordinated acetylacetonates

Sudipta Chatterjee a, Sutanuva Mandal a, Sucheta Joy a, Chen-Hsiung Hung b, Sreebrata Goswami a,⇑a Department of Inorganic Chemistry, Indian Association for the Cultivation of Science, Kolkata 700 032, Indiab Department of Chemistry, National Changhua University of Education, Changhua-50058, Taiwan, ROC

a r t i c l e i n f o

Article history:Available online 3 March 2011

Dedicated to Prof. Dr. Wolfgang Kaim

Keywords:Ruthenium complexesortho-SemidineChemical transformationsortho-Carom–N bond fusionChlorination of ruthenated acetylacetonateX-ray crystal structure

0020-1693/$ - see front matter � 2011 Elsevier B.V. Adoi:10.1016/j.ica.2011.02.071

⇑ Corresponding author.E-mail address: icsg@iacs.res.in (S. Goswami).

a b s t r a c t

In an unusual reaction of [RuIII(acac)2(CH3CN)2](ClO4) ([1], acac = acetylacetonate) and aniline (Ph-NH2),resulted in the formation of ortho-semidine due to dimerisation of aniline via oxidative ortho-Carom–Nbond formation reaction. This oxidation reaction is associated with stepwise chlorination of coordinatedacac ligands at the c-carbon atom resulting in the formation of [RuIII(acac)2L��] [2a], [RuIII(Cl-acac)(acac)L��] [2b], [RuIII(acac)(Cl-acac)L��] [2c] and [RuIII(Cl-acac)2L��] [2d] (L�� = N-phenyl-ortho-sem-iquinonediimine) complexes, respectively. These have been characterized by 1H NMR, UV–Vis–NIR,ESI-MS and cyclic voltammetry studies. Single crystal X-ray structures of 2c and 2d are reported. Crystal-lographic structural bond parameters of 2c and 2d revealed bond length equalization of C–C, C–O and M–O bonds. It has been shown that perchlorate (ClO4

�) counter anion, present in the starting rutheniumcomplex, acts as the oxidizing agent in bringing about oxidation of Ph-NH2 to ortho-semidine. The chlo-ronium ions, produced in situ, chlorinate the coordinated acac ligands at the c-carbon atom. Such electro-philic substitution of coordinated acac ligands indicates that the Ru-acac metallacycles in the referencecompounds are aromatic. The complexes showed an intense and featureless band centered near520 nm, and a structured band near 275 nm. These displayed one reversible cathodic response in therange, �1.1 to �0.8 V and one reversible anodic response between 0.4 and 0.6 V versus the Saturated Cal-omel reference Electrode, SCE. The response at the anodic potential is due to oxidation of the coordinatedligand L, while the reversible response at cathodic potential is due to reduction of the metal center.

� 2011 Elsevier B.V. All rights reserved.

1. Introduction

During the recent past we have been interested on metalmediated oxidations of aniline like aromatic amines, which haveproduced several novel systems of redox non-innocentN-aryl-ortho-semidine ligands via regioselective ortho C–N bondfusion [1–6]. The first example of such transformation was notedby us [3] sometimes ago in the reaction between RuIII(acac)3 andaniline (Scheme 1). The reaction occurs only in neat amine andthe oxidation is brought about by air.

We proposed that cis-coordination of aromatic amines to themetal ion and subsequent oxidative dimerisations are the twokey steps of this reaction. In solution, the amines could not substi-tute the coordinated acetylacetonate from Ru(acac)3 and hence thereaction did not occur. We then chose a labile mediator complex,viz. [Ru(acac)2(CH3CN)2](ClO4) [1] (acac = acetylacetonate) to per-form a similar reaction in solution. It was anticipated that the com-plex [1] would serve our purpose because of the presence of two

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labile acetonitrile ligands allowing amine coordination to the me-tal center. The anticipated oxidation reaction of Ph-NH2 occurredspontaneously in the afore-said reaction. However, the oxidativedimerisation reaction is associated with an unprecedented electro-philic substitution at the coordinated acac ligands. Isolation of theproducts from the crude reaction mixture revealed that the aboveoxidation reaction is associated with stepwise chlorination of coor-dinated acac ligand at the c-carbon atom. The primary purpose ofthis paper is to report the experimental observations of the abovechemical transformations that occur in a concerted fashion. Wealso look for rational of these chemical transformations. Our exper-imental evidences suggest that aromaticity of the ruthenated-acac rings in the starting complex is responsible for theelectrophilic substitution reactions in the coordinated acac ligands.

In the present context it is worth noting that the physical prop-erties of metal acetylacetonates have been studied extensively overmany years but very little attention was given to the chemicalreactivity of this heterocyclic ring system [7–14]. It was shownthat metal acetylacetonates can undergo a wide variety of electro-philic substitution reactions such as Friedel–Crafts alkylation andacylation, nitration and halogenations that are characteristics ofaromatic systems [15].

Scheme 1. Synthesis of the complexes.

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2. Results and discussion

2.1. The reaction

When a reaction mixture of [1] and aniline in 1:2 M propor-tion was refluxed in 2-methoxyethanol in the presence of NEt3

a dark red mixture of products was obtained. Upon chromato-graphic separation on a preparative TLC plate using chloroformas the eluent four compounds were isolated with a total yieldca. 85%. Notably, all the compounds, 2a–2d contain one ortho-semidine ligand (L), which was formed due to oxidative dimerisa-tion of Ph-NH2 via ortho-Carom–N bond fusion reaction. Anothernotable result of the reaction is the stepwise chlorination ofcoordinated acac in the formation of 2b–2d. The overall reactionis shown in Scheme 2.

While X-ray structures of the three compounds 2a, 2c and 2dcharacterize their identities, the ESI-MS (Supporting informationFig. S1) and other spectral data of the compound 2b unequivocallyconfirm its composition. Notably, the ClO4

� counter anion in the

Scheme 2. Schematic representation of

starting material is the only source of chlorine in the present chem-ical transformation. A similar reaction even in an inert atmosphereproduced identical products, which indirectly provided evidencesin favor of oxidation of Ph-NH2 by ClO4

�. For comparison, such oxi-dative dimerisation of aniline was known to bring about only byaerial oxygen [1,3]. Our proposition was further strengthened bythe fact that the corresponding salt, [Ru(acac)2(CH3CN)2]2(SO4)did not produce any such chlorinated product in an inert atmo-sphere. It is thus reasonably assumed that the chloronium ion, gen-erated in situ [16–20] due to reduction of ClO4

�, is the activespecies for bringing about the substitution reaction of the ruthe-nated acetylacetonates. The chlorinated products 2b–2d are the re-sults of sequential electrophilic substitution of 2a – a reactiontypical of metalla-acac aromatic rings. To have further insight intothis reaction, the non-chlorinated compound, 2a was reacted witha potential source of chloronium ion, viz. N-chlorosuccinimide. Thereaction formed 2b–2d spontaneously. To exclude the possibility ofa radical pathway of chlorination, the above reaction was tried butfailed in the presence of a radical scavenger TEMPO (TEM-PO = 2,2,6,6-tetramethylpiperidine-Noxyl).

We also performed a similar reaction of 1,2-diaminobenzeneand [Ru(acac)2(CH3CN)2](ClO4) [1] under identical reaction condi-tions. The three compounds, as shown in Scheme 3, were isolatedfrom a preparative TLC plate with a total yield of 80%. Spectro-scopic and mass spectral analysis (Supporting informationFig. S2) revealed that the complex 3a is identical in all respect tothat of the previously reported compound [4]. The other two com-pounds, 3b and 3c are chlorinated at the c carbon atom of the ace-tylacetonate ring. Since the 1,2-diaminobenzene ligand, is asymmetrical bidentate ligand, only one monochlorinated productwas obtained. However, a similar reaction of 1,2-diaminobenzenewith the corresponding bivalent complex, [Ru(acac)2(CH3CN)2],produced only 3a in 40% yield. All these observations taken to-gether establish that the counter anion, ClO4

� acts as an oxidantas well as the source of chloronium ion for bringing about thechemical reactions shown in Schemes 1 and 2. The reference reac-tion occurs only at reflux. Similar dimerisation of aniline was re-ported to occur only at high temperature [3].

reaction between [1] and aniline.

Scheme 3. Schematic representation of reaction between [1] and 1,2-diaminobenzene.

368 S. Chatterjee et al. / Inorganica Chimica Acta 374 (2011) 366–372

2.2. Mass and NMR spectral analysis

The electrospray ionization mass spectral data (ESI-MS) of thecompounds 2a–2d and 3a–3c have provided strong support in fa-vor of their formulations. The complexes 2a–2d showed intensepeaks at m/z, 484, 518, 518 and 552 amu due to the molecularion [2a + H]+, [2b + H]+, [2c + H]+ and [2d + H]+, respectively. Simi-larly, the complexes 3a–3c showed intense peaks due to themolecular ion [3a + H]+, [3b + H]+ and [3c + H]+ at m/z, 408, 442and 476 amu, respectively. Notably, the experimental spectral fea-tures of the complexes correspond very well to the simulated iso-topic pattern for the given formulation. Representative spectra ofall the complexes along with the simulated spectra are submittedas Supporting information, Figs. S1 and S2.

The compounds 2a–2d are diamagnetic and showed resolved1H NMR and 13C NMR spectra in CDCl3 at room temperature. The1H NMR spectrum of 2a displayed two resonances at d, 5.4 and5.1 ppm due to two c-CH protons (H3 and H8) of the coordinatedacetylacetonate rings. The complexes 2b and 2c, on the other hand,showed single resonance for c-CH (acetylacetonate) at d, 5.1 (for2b) and 5.4 (for 2c). Interestingly this resonance is absent in 2d.The methyl protons of the acac ligands and NH proton of the ligandL resonate in the range, d 1.7–2.8 ppm and d 10.5–11.0 ppm,respectively. The 13C NMR spectrum of 2a follows the same trendas seen in the 1H NMR spectrum. The 13C{1H} NMR spectrumshowed signals of C(2), C(4), C(7) and C(9) at 190.1, 190.5, 187.6and 189.5 ppm, respectively for the two acac rings whereas thec-carbon for the two rings resonate at 100.1 and 100.3 ppm. The13C NMR signals for c-carbon in 2c (C8) and 2b (C3) are shifteddownfield and appear at 108.8 and 107.8 ppm, respectively. Forthe compound 2d these two signals shifted to 109.1 and108.2 ppm, respectively. The NMR data and spectra of the com-plexes 2a–2d are submitted as Supporting information Table S1and Figs. S3–S6. Notably the spectral data for the complex 2a, iso-lated from the above reaction (Scheme 1), is identical to that re-ported before [5]. Similarly the complexes 3a–3c show resolved1H NMR and 13C NMR spectra in CDCl3. The methyl and NH reso-nances of 3a–3c appear in the range d, 1.7–2.7 and at around d,10.5, respectively. The NMR data and spectra of the complexes

3a–3c are submitted as Supporting information Table S2 andFigs. S7–S9.

2.3. Crystal structures

Suitable X-ray quality crystals were obtained by slow diffusionof dichloromethane solutions of the compounds 2c and 2d intohexane. Oak Ridge Thermal Ellipsoid Plot (ORTEP) and atom number-ing schemes of the above two complexes are shown in Figs. 1 and2; their crystallographic parameters are collected in Table 1.

X-ray structure solution of the compounds 2c and 2d reconfirmtheir formulations and geometry as well. The central ruthe-nium(III) in these two complexes is coordinated to two monoan-ionic mono- or di-chlorinated acetylacetonate ring(s) and onemonoanionic form of N-phenyl-ortho-semidine ligands (Figs. 1and 2). The coordination environment around Ru is pseudo-octahedral. Four oxygen atoms of the two cis coordinated acetyl-acetonate ligands and the two nitrogen atoms of the ortho-semidine ligand satisfy the coordination number. The asymmetricunit of 2c consists of one crystallographic distinct molecule. In thiscomplex the c-carbon atom of one of the two acetylacetonate li-gands is chlorinated. The asymmetric unit of the compound 2d,on the other hand, consists of two crystallographic distinct mole-cules. In this case both the c-hydrogen of the two acetylacetonateligands is substituted by Cl-atoms. The average Ru–O(acac) andRu–N(L) bond lengths of these two complexes are 2.047 and1.966 Å, respectively. The bond lengths in 2c: C@NPh, 1.344 (5);C@NH, 1.326 (4) and average C@C (meta), 1.366 (5) Å are in goodagreement with the monoanionic o-semiquinonediimine formula-tion of ligand, L [21–23] and thus by implication the oxidationstate of Ru in 2c is +3. Similar bond length trend was also notedfor the complex 2d. Thus the two compounds, 2c and 2d are formu-lated as [RuIII(acac)(Cl-acac)L��] and [RuIII(Cl-acac)2L��], respec-tively. Diamagnetism in these complexes is due to strongantiferromagnetic interactions between the unpaired spin ofRu(III) and the anionic radical ligand. Similar description of the oxi-dation states for the compound 2a was recently reported by us [5].

Another interesting observation regarding the structural fea-tures of the complexes is that the Ru-acetylacetonate rings are

Fig. 1. ORTEP representation and atom numbering scheme for 2c. All the hydrogenatoms except at C3 are omitted for clarity.

Fig. 2. ORTEP representation and atom numbering scheme for 2d. All the hydrogenatoms are omitted for clarity.

Table 1Selected bond lengths (Å) for 2a, 2c and 2d.

Parameter 2aa 2c 2d

Ru1–O1 2.018(5) 2.061(2) 1.9992(15)Ru1–O2 2.067(5) 2.018(3) 2.0462(14)O1–C2 1.270(10) 1.272(4) 1.289(3)O2–C4 1.277(9) 1.284(4) 1.268(3)C2–C3 1.399(10) 1.403(5) 1.392(3)C3–C4 1.375(10) 1.392(5) 1.420(3)Ru1–O3 2.031(5) 2.036(3) 2.0718(14)Ru1–O4 2.051(5) 2.078(2) 2.0383(15)O3–C7 1.281(9) 1.288(4) 1.264(3)O4–C9 1.241(9) 1.259(4) 1.293(3)C7–C8 1.378(11) 1.388(5) 1.419(3)C8–C9 1.383(13) 1.417(5) 1.391(3)Ru1–N1 1.947(6) 1.943(3) 1.9397(17)Ru1–N2 1.999(6) 1.988(2) 1.9956(17)N1–C11 1.333(8) 1.326(4) 1.329(3)N2–C16 1.352(8) 1.344(5) 1.341(3)C12–C13 1.346(10) 1.362(6) 1.357(3)C14–C15 1.354(10) 1.360(6) 1.364(3)

a Ref. [5].

Table 2HOMA values of complexes 2a, 2c, 2d and 3a.

Compound HOMA value

Ring 1 Ring 2

2a 0.926 0.8992c 0.938 0.9192d 0.956 0.9183a 0.921 0.921

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nearly planar and have C–C, C–O and M–O bond lengths lying be-tween single and double bonds (Table S3). For example, the aver-age of Ru–O bond lengths in 2c is 2.048 Å which lies between asingle (2.241 Å) and a double (1.815 Å) bond lengths as reportedin other systems [24]. This trend was also observed in the cases

of 2a and 2d. Based on the observations of planar structure to-gether with bond-length equalization, one can anticipate thatthese systems are aromatic. In all these three complexes the biteangles of the two six-membered acac-containing chelate ringshave the values near to 90� whereas the five-memberedo-semiquinonediimine containing chelate ring has the bite angleabout 79�.

To have further insight into the problem of aromaticity we alsohave calculated a geometry based aromaticity index, harmonicoscillator model of aromaticity (HOMA) [25–33] using the follow-ing bond parameters,

HOMA ¼ 1

�aCC

PRopt

CC � Ri� �2 þ aCO

PRopt

CO � Ri� �2 þ aRuO

PRopt

RuO � Ri� �2

n

Here Ropt is an empirically estimated optimum bond length, a is anempirical constant dependent upon the kind of bond and are spec-ified by the type of bonds indicated in parentheses, Ri is the bondlength being considered and n is the number of bonds taken intoconsideration. Table S1 (Supporting information) lists the Ropt anda values used in this work. The high HOMA values in all these com-plexes point to the aromatic character of Ru-acetylacetonate ring.The HOMA values are collected in Table 2.

2.4. UV–Vis spectral analysis

The UV–Vis spectra of the four compounds 2a–2d were re-corded in acetonitrile solvent. Each of these showed an intenseand featureless band centered at 515, 520, 520 and 525 nm, anda structured band at around 270, 275, 275 and 280 nm, respec-tively. Table 3 summarizes the optical data for the above four com-plexes. Interestingly, the lowest energy transition in thesecomplexes appears nearly at same wavelength. It may be inter-preted by considering that participating orbitals (HOMO and

Table 3Redox potentials and optical data for 2a, 2b, 2c and 2d in acetonitrile.

2a 2b 2c 2d

Cyclic voltammetrya E½/V (DEp/mV) 0.42b, �1.02c 0.49b, �0.94c 0.49b, �0.94c 0.57b, �0.84c

Electronic spectra [kmax/nm (e/M�1 cm�1)]

514 (19 000), 350d, 271(24 550)

518 (20 100), 359d, 274(25 050)

518 (20 450), 355d, 275(25 100)

523 (19 100), 361d, 282(26 200)

a Supporting electrolyte: TEAP.b Reversible anodic response.c Reversible cathodic response.d Shoulder.

Fig. 3. Cyclic voltammograms of compounds 2a (brown), 2c (black) and 2d (blue)(v = 50 mV s�1) in CH3CN containing 0.1 M NEt4ClO4. (For interpretation of thereferences to color in this figure legend, the reader is referred to the web version ofthis article.)

370 S. Chatterjee et al. / Inorganica Chimica Acta 374 (2011) 366–372

LUMO) are mainly of p type and are sensitive to the nature of sub-stitution. With an increase in electron-withdrawing ability of thesubstituent like Cl, the coulombic attraction forces for electronsin the frontier molecular orbitals are strengthened. So upon chlori-nation LUMO is stabilized almost to the same extent as that forHOMO. Consequently, the HOMO–LUMO gap remains unalteredand so the absorption maxima in all the above complexes remaininvariant.

2.5. Electrochemical properties

The redox behavior of all the reference complexes were studiedby cyclic voltammetry in the potential range 2.0 to �2.5 V in ace-tonitrile solvent using a platinum working electrode. The poten-tials are referenced to the saturated calomel electrode (SCE) andthe data are collected in Table 3. Recently [21] there have beenthorough studies on 2a in respect of assignment of redox state ofthe non-innocent ortho-semidine ligand and its electron transferproperties. Similar assignment of redox processes are believed tobe operative in all the chlorinated complexes. All the complexesshowed four one electron redox responses. Among these two areoxidative in nature, occur at positive potentials and the othertwo are reductive responses and appear at negative potential. Ofthese two redox responses, viz. I and II, are electrochemicallyreversible.

[Ru(acac)2L]2+ [Ru(acac)2L][Ru(acac)2L]+

[Ru(acac)2L]–[Ru(acac)2L]2–

I II

III

IV

The reversible anodic response within 0.40–0.6 V correspondsto the oxidation of semiquinone ligand, L whereas the reversiblereduction (�0.8 to �1.1 V) is due to the reduction of Ru(III) centerin the complexes. Interestingly the electrochemical responses inchlorinated compounds moved anodic, however the DE (EII � EIII)remained invariant. The voltammograms of 2a, 2c and 2d areshown in Fig. 3 for comparison.

3. Conclusions

In this paper we have reported an unprecedented oxidation ofcoordinated aromatic amine by perchlorate anion. The productsare thoroughly characterized using several spectroscopic and X-ray diffraction techniques. Such amine oxidation reactions by per-chlorate anion are unavailable in the literature. As a result, theabove chemical reactions led to stepwise chlorination at the c-carbon atom of the coordinated acac ligands by chloronium ion(Cl+), which is produced due to the reduction of ClO4

� counter-an-ion. Such electrophilic substitution reactions occur commonly inaromatic rings and hence these metal complexes may be consid-

ered as metalla-aromatics. Analyses of X-ray structural bond param-eters in these complexes also point to similar conclusion. However,thorough theoretical analyses of these systems are required formaking any definitive conclusions on the issue of aromaticity inthe present systems, which will be reported in due course.

4. Experimental

4.1. Materials

Bis(acetonitrile)bis(acetylacetonato)ruthenium(III) perchlorate[34] was prepared by the reported methods. Solvents and chemi-cals used for syntheses were of analytical grade. The supportingelectrolyte (tetraethylammonium perchlorate) and solvents forelectrochemical work were obtained as before. CAUTION: Perchlo-rates have to be handled with care and appropriate safetyprecautions.

4.2. Physical measurements

A Perkin–Elmer Lambda 950 spectrophotometer was used to re-cord UV–Vis–NIR spectra in solutions. NMR data were collected ona Bruker Avance 300 spectrophotometer and SiMe4 as the internalstandard. The chemical shifts were reported in ppm. CDCl3 was ref-erenced to the residual proton peak (7.26 ppm). A Perkin–Elmer240C elemental analyzer was used to collect microanalytical data(C, H, N). Electrochemical measurements were performed at298 K under a dry nitrogen atmosphere on a PC-controlled PARModel 273A electrochemistry system. Cyclic voltammetry was car-ried out in CH3CN/0.1 M Et4NClO4 solutions using a three-electrodeconfiguration (platinum disk working electrode working platinumwire auxiliary electrode and saturated calomel referenceelectrode). The value of E1/2 for the ferrocenium–ferrocene coupleunder our experimental conditions was 0.42 V. The mass spectra

Table 4Crystallographic data of 2c and 2d.

2c 2d

Empirical formula C22H23ClN2O4Ru 2(C22H22Cl2N2O4Ru),0.5(C6H14)

Crystal system triclinic triclinicSpace group P�1 P�1Z 2 2T (K) 150 150Formula weight 515.94 1143.86Unit cell dimensionsa (Å) 8.9573(18) 12.3967(3)b (Å) 11.079(2) 12.8738(3)c (Å) 11.493(2) 17.5984(4)a (�) 95.74(3) 74.9680(10)b (�) 91.00(3) 88.9420(10)c (�) 105.80(3) 66.6120(10)V (Å3) 1090.8(4) 2478.27(10)Dcald (g cm�3) 1.571 1.533Crystal dimension

(mm3)0.12 � 0.14 � 0.29 0.08 � 0.23 � 0.25

h range (�) 1.8–26.0 1.2–30.1Reflections collected 14 773 44 183Independent reflections 4215 14 430GOF 1.08 0.963Final R indices

[I > 2r(I)]R1 = 0.0348wR2 = 0.0968

R1 = 0.0286wR2 = 0.0607

S. Chatterjee et al. / Inorganica Chimica Acta 374 (2011) 366–372 371

were recorded on a Micromass LCT electrospray mass spectrome-ter equipped electrospray (ESI) system.

4.3. Syntheses of complexes

4.3.1. Reaction of [Ru(acac)2(CH3CN)2](ClO4) with anilineTo a solution of [Ru(acac)2(CH3CN)2](ClO4) [1] (0.24 g,

0.50 mmol) in 2-methoxyethanol 0.1 ml (1.0 mmol) aniline wasadded followed by the addition of two drops of NEt3 and the mix-ture was refluxed for 4 h. The initial blue color of the reaction mix-ture gradually became intense pink during this reaction period. Thecrude compound obtained after evaporation of the solvent waspurified on a preparative silica gel TLC plate. Toluene–chloroformsolvent mixture (3:2) was used as the eluent. Three pink bandsof 2b, 2c and 2d were separated gradually after allowing sufficienttime. The compound 2a was isolated as a distinct band using chlo-roform as the eluent. On evaporation of the solvent and subsequentslow diffusion of the dichloromethane solutions of 2a, 2c and 2dinto hexane yielded plate like single crystals. Suitable X-ray diffrac-tion quality single crystal could not be obtained for the compound2b. However its identity was fully established by spectral measure-ments.The yields and analytical data of 2a, 2c, 2b and 2d are asfollows.

2a. Yield, 35% FT-IR (KBr, cm�1): 1571 [m(C@O)], 1516[m(C@C) + d(C–H)], 1197 [d(C–H)]. ESI-MS, m/z: 483.9 [MH]+. (Anal.Calc. for C22H24N2O4Ru: C, 54.87; H, 4.99; N, 5.82. Found: C, 54.75;H, 5.01; N, 5.85%).

2b. Yield, 25% FT-IR (KBr, cm�1): 1581 [m(C@O)], 1512[m(C@C) + d(C–H)], 1193 [d(C–H)]. ESI-MS, m/z: 517.9 [MH]+. (Anal.Calc. for C22H23ClN2O4Ru: C, 51.20; H, 4.46; N, 5.43. Found: C,51.13; H, 4.39; N, 5.46%).

2c. Yield, 15% FT-IR (KBr, cm�1): 1566 [m(C@O)], 1512[m(C@C) + d(C–H)], 1188 [d(C–H)]. ESI-MS, m/z: 517.9 [MH]+. (Anal.Calc. for C22H23ClN2O4Ru: C, 51.20; H, 4.46; N, 5.43. Found: C,51.17; H, 4.49; N, 5.41%).

2d. Yield, 10% FT-IR (KBr, cm�1): 1552 [m(C@O)], 1527[m(C@C) + d(C–H)]. ESI-MS, m/z: 551.8 [MH]+. (Anal. Calc. forC22H22Cl2N2O4Ru: C, 47.99; H, 3.99; N, 5.09. Found: C, 47.94; H,3.91; N, 5.13%).

4.3.2. Reaction of [2a] with N-chlorosuccinimideA solution of N-chlorosuccinimide (0.4 g, 3.0 mmol) in 10 ml

glacial acetic acid was slowly added to a solution of 2a (0.5 g,1.0 mmol) in 10 ml of acetic acid at room temperature in stirringconditions. After 5 min the solution was diluted with chloroformand the acid was neutralized with sodium carbonate. The solutionwas then evaporated to dryness and the crude mass was purifiedon a preparative TLC plate using toluene–chloroform mixture(3:2) as the eluent. Two pink bands of 2b and 2d were separatedafter allowing sufficient time.

4.3.3. Reaction of [Ru(acac)2(CH3CN)2](ClO4) with 1,2-diaminobenzene

The reaction of [Ru(acac)2(CH3CN)2](ClO4) (0.24 g, 0.50 mmol)with 1,2-diaminobenzene (0.1 g, 1.0 mmol) in 2-methoxyethanolwas carried out under identical reaction conditions. The crudemass thus obtained after evaporation of the solvent was loadedon a preparative silica gel TLC plate for purification. Toluene–chloroform solvent mixture (1:2) was used as the eluent and thethree products, viz. 3a, 3b and 3c were isolated. The yields andanalytical data of 3a, 3b and 3c are as follows.

3a. Yield 40% FT-IR (KBr, cm�1): 1577 [m(C@O)], 1512[m(C@C) + d(C–H)], 1197 [d(C–H)]. ESI-MS, m/z: 407.6 [MH]+. (Anal.Calc. for C16H20N2O4Ru: C, 47.39; H, 4.94; N, 6.91. Found: C, 47.44;H, 4.85; N, 6.98%).

3b. Yield 30% FT-IR (KBr, cm�1): 1558 [m(C@O)], 1512[m(C@C) + d(C–H)], 1190 [d(C–H)]. ESI-MS, m/z: 441.8 [MH]+. (Anal.Calc. for C16H19N2O4ClRu: C, 43.68; H, 4.32; N, 6.37. Found: C,43.65; H, 4.28; N, 6.32%).

3c. Yield 10% FT-IR (KBr, cm�1): 1558 [m(C@O)], 1529[m(C@C) + d(C–H)]. ESI-MS, m/z: 475.7 [MH]+. (Anal. Calc. forC16H18N2O4Cl2Ru: C, 40.49; H, 3.79; N, 5.91. Found: C, 40.41; H,3.72; N, 5.83%).

4.4. X-ray structure determination

Crystallographic data for the compounds 2c and 2d are col-lected in Table 4. Suitable X-ray quality crystals of the compounds2c and 2d were obtained by slow diffusion of dichloromethanesolutions into hexane.

2c. The data were collected on a Brucker SMART diffractometer,equipped with graphite monochromated Mo Ka radiation(k = 0.71073 Å), and were corrected for Lorentz-polarization ef-fects. A total of 14 773 reflections were collected out of which4215 were unique (Rint = 0.013), satisfying the (I > 2r(I)) criterion,and were used in subsequent analysis.

2d. The data were collected on a Brucker SMART diffractometer,equipped with graphite monochromated Mo Ka radiation(k = 0.71073 Å), and were corrected for Lorentz-polarization ef-fects. A total of 44 183 reflections were collected out of which14 430 were unique (Rint = 0.053), satisfying the (I > 2r(I)) crite-rion, and were used in subsequent analysis.

All the structures were solved by employing the SHELXS-97 [35]program package and refined by full-matrix least-squares basedon F2 (SHELXL-97) [36]. All the hydrogen atoms were added in calcu-lated positions

Acknowledgements

The research was supported by Council of Scientific and Indus-trial Research, New Delhi (Project 01/2358/09/EMRII). Crystallog-raphy of the compound 2c was performed at the DST-fundedNational Single Crystal Diffractometer Facility at the Departmentof Inorganic Chemistry, IACS.

372 S. Chatterjee et al. / Inorganica Chimica Acta 374 (2011) 366–372

Appendix A. Supplementary material

CCDC 672038 and 672040 contain the supplementary crystallo-graphic data for this paper. These data can be obtained free ofcharge from The Cambridge Crystallographic Data Centre viahttp://www.ccdc.cam.ac.uk/data_request/cif. Supplementary dataassociated with this article can be found, in the online version, atdoi:10.1016/j.ica.2011.02.071.

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