Two novel reactions of a ruthenium-coordinated phenazine - Oxidative aromatic ring hydroxylation and dimerization via a new C-N bond formation

Article abstract of DOI:10.1002/ejic.200600864

The reaction of [Ru(CH₃OH)₂(N∧N) ₂]²⁺ [N∧N = 2,2′-bipyridine (bpy) and 1,10-ortho-phenanthroline(phen)] with the phenazine ligand, [HL¹ = 6-p-anisyl-2-(p-anisylamino)-3(4H)-p-anisylimine-9-methoxyphenazine] in the presence of a base (NEt₃) afforded two mononuclear ruthenium complexes, [Ru(L¹)(N∧N)₂]X (2), and [Ru(LO)(N∧N)₂]X₂ (3), [LO = 7-methoxy-5-(4- methoxyphenyl)-2,3-bis(4-methoxyphenylimino)-3,5-dihydro-2H-phenazin-1-one] together with a diruthenium complex [(N∧N)₂RuL ²Ru(N∧N)₂]X₃ (4), [L² = 7,8′-dimethoxy-5,10′-bis(4-methoxyphenyl)-2,3′-bis(4- methoxyphenylamino)-3,2′-bis(4′-methoxyphenylimino)-3,5,2′, 10′-tetrahydro-[1,5′]biphenazinyl-5′-ylium], (X = ClO ₄^- or CF₃SO₃^-). The complexes 3 and 4 were also obtained from the pure complex 2 under two different experimental condi-tions. Oxidative aromatic ring hydroxylation of the complex 2 produced 3 while the diruthenium complex, 4, was formed by dimerization of 2 via a new C-N bond formation. The products were thoroughly characterized with the help of ¹H NMR and ESI-MS spectral measurements. Final authentication of the two coioeplexes of the transformed phenazine ligands viz. 3 and 4 were made by single-crystal X-ray structure determination of the two representative complexes. These compounds are intensely colored and show transitions in the visible region, which are ascribed as metal-to-ligand charge transfer (MLCT). Notably, intensities of the two MLCT of the compound 4 are significantly higher than those of 2 and 3. Redox properties of the complexes are reported. Electrochemical oxidation of compound 2, even in the presence of trace moisture, produced compound 3. Cyclic voltammetry of compound 3 shows a reductive response near -0.35 V. Its one-electron reduced product is blue and shows an intense EPR signal at g = 2.001. The voltammogram of the diruthenium complex 4 consists of two responses near 0.70 and 0.85 V. Wiley-VCH Verlag GmbH & Co. KGaA, 2007.

Full text of DOI:10.1002/ejic.200600864

FULL PAPER
DOI: 10.1002/ejic.200600864
Two Novel Reactions of a Ruthenium-Coordinated Phenazine – Oxidative
Aromatic Ring Hydroxylation and Dimerization via a New C–N Bond
Formation
Priyabrata Banerjee,[a] Golam Mostafa,[b] Alfonso Castiñeiras,[c] and Sreebrata Goswami*[a]
Keywords: Metal-mediated reaction / Phenazine / Ruthenium / Redox chemistry
The reaction of [Ru(CH3OH)2(N∧N)2]2+ [N∧N = 2,2Ј-bipyri-
dine (bpy) and 1,10-ortho-phenanthroline(phen)] with the
NMR and ESI-MS spectral measurements. Final authentica-
tion of the two complexes of the transformed phenazine li-
gands viz. 3 and 4 were made by single-crystal X-ray struc-
ture determination of the two representative complexes.
These compounds are intensely colored and show transitions
in the visible region, which are ascribed as metal-to-ligand
charge transfer (MLCT). Notably, intensities of the two
MLCT of the compound 4 are significantly higher than those
of 2 and 3. Redox properties of the complexes are reported.
Electrochemical oxidation of compound 2, even in the pres-
ence of trace moisture, produced compound 3. Cyclic voltam-
metry of compound 3 shows a reductive response near
–0.35 V. Its one-electron reduced product is blue and shows
an intense EPR signal at g = 2.001. The voltammogram of the
diruthenium complex 4 consists of two responses near 0.70
and 0.85 V.
phenazine ligand, [HL1
= 6-p-anisyl-2-(p-anisylamino)-
3(4H)-p-anisylimine-9-methoxyphenazine] in the presence
of a base (NEt3) afforded two mononuclear ruthenium com-
plexes, [Ru(L1)(N∧N)2]X (2), and [Ru(LO)(N∧N)2]X2 (3), [LO
=
7-methoxy-5-(4-methoxyphenyl)-2,3-bis(4-methoxyphen-
ylimino)-3,5-dihydro-2H-phenazin-1-one] together with a di-
ruthenium complex [(N∧N)2RuL2Ru(N∧N)2]X3 (4), [L2 = 7,8Ј-
dimethoxy-5,10Ј-bis(4-methoxyphenyl)-2,3Ј-bis(4-methoxy-
phenylamino)-3,2Ј-bis(4Ј-methoxyphenylimino)-3,5,2Ј,10Ј-
–
tetrahydro-[1,5Ј]biphenazinyl-5Ј-ylium], (X
=
ClO4 or
CF3SO3–). The complexes 3 and 4 were also obtained from
the pure complex 2 under two different experimental condi-
tions. Oxidative aromatic ring hydroxylation of the complex
2 produced 3 while the diruthenium complex, 4, was formed
by dimerization of 2 via a new C–N bond formation. The
products were thoroughly characterized with the help of 1H
(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim,
Germany, 2007)
chloride-mediated oxidative polymerization of p-anisidine,
which produces N-substituted 2-amino-3-iminophenazines
via a multiple C–N bond fusion reaction (Scheme 1).
Introduction
Transition-metal mediated functionalization of C–H
bonds is one of the most vigorously pursued[1–4] areas of
current synthetic research. In many instances these reac-
tions lead to the synthesis of unusual molecules, which
otherwise are difficult or even impossible to synthesize
using conventional procedures. In recent years we have been
working[5–6] on transition-metal promoted aromatic amine
fusion reactions, via C–H functionalization, for the synthe-
sis of new organic ligands whose coordination chemistry is
rich with novel features. One such example[7] is the ferric
[a] Department of Inorganic Chemistry, Indian Association for the
Cultivation of Science,
Kolkata 700032, India
Fax: +91-33-2473-2805
E-mail: icsg@iacs.res.in
[b] Department of Physics, Jadavpur University,
Jadavpur, Kolkata 700032, India
Scheme 1.
[c] Departamento de Química Inorgánica, Universidade de Santi-
ago de Compostela, Campus, Universitario Sur,
15782 Santiago de Compostela, Spain
Our interest[6] in the coordination chemistry of 1,2-di-
imine ligands and their redox partners prompted us to ex-
plore the ligand chemistry of [HL1]. We have shown[7] that
Supporting information for this article is available on the
WWW under http://www.eurjic.org or from the author.
412
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Reactions of a Ruthenium-Coordinated Phenazine
FULL PAPER
the deprotonated phenazine ligand coordinates to the [Ru- mina TLC plate. The first blue complex 2 was unstable and
(pap)2]2+ moiety [pap = 2-(phenylazo)pyridine] spontane- with time slowly converted into the violet product 3 in air
ously. The redox behavior of the resultant complex [Ru(L1)- even at room temperature. The 2 Ǟ 3 conversion was much
(pap)2]+ (1) was of particular interest, since it seemed to faster in boiling aqueous methanol.
follow[7] the EC-type pathway to produce a new ruthenium
Prolonged boiling of compound 2 in a dry and inert at-
complex, following the oxidation of complex 1. In practice, mosphere, on the other hand, produced a stable blue com-
however, chemical oxidation of complex 1 resulted in a mix- pound 4 as the major product (vide infra). Schematic pres-
ture of several products from which no pure compound entation of the reaction along with compound identification
could be isolated. The ESI-MS spectrum of the above crude numbers are summarized in Scheme 2.
mixture showed the presence of a moderately intense peak
The sum total of the yields of the above three products
at m/z = 1041 amu. For comparison we note here that the exceeded 85%. There were a few minor fractions, which
parent complex, 1, showed a strong ESI-MS signal at m/z could not be purified and their identities remain uncertain.
= 1026 amu due to the [Ru(L1)(pap)2]+ ion. The difference
The complexes gave satisfactory elemental analyses (see
in mass between the two compounds indicates the addition Exp. Sect.). These showed characteristic infrared stretches
of an oxygen atom to the parent complex 1. Subsequently, of the phenazine and coordinated ancillary ligands viz. bpy
we have found that the similar ruthenium complexes of and phen. The most notable feature in the infrared spectra
[L1]–, [Ru(L1)(N∧N)2]+ [N∧N = 2,2Ј-bipyridine (bpy) or of 3a and 3b is the appearance of a sharp band at ca.
1,10-ortho-phenanthroline (phen)] also undergo similar 1680 cm–1, which confirms the presence of a carbonyl func-
chemical transformations upon oxidation. In these cases the tion[12] (vide infra). These complexes are diamagnetic and
1
transformed compounds are stable and suitable for follow- displayed H NMR resonances in the normal range. The
ing the above-mentioned metal-mediated redox reactions.
spectral patterns in the aromatic region (δ = 5–9) are com-
In this paper we report the results of the reaction of plex in nature (see Figure S1, supporting information) ow-
the 2-amino-3-iminophenazine, HL1 and [Ru(CH3OH)2- ing to the presence of a large number of unique protons.
(N∧N)2]2+. The chemical reaction resulted in the formation The methyl resonances were, however, diagnostic and useful
of the three products 2–4, of which the complexes 3 and 4 for assessing their preliminary identities (Figure 1). For ex-
are formed due to an unprecedented type of chemical trans- ample, while the compounds 2 and 3 showed four –OMe
formation of the coordinated ligand [L1]– in the complex signals each in the range δ, 3.38–3.75, compound 4 dis-
2. While oxidative hydroxylation of the ligand produced a played eight –OMe resonances in the range δ = 3.25–3.80.
ruthenium complex 3 of the oxidized phenazine ligand For comparison, the uncoordinated ligand, [L1]–, displayed
(LO), dimerization of it, on the other hand, produced a four[7] such resonances at δ = 3.55–3.85. Thus, the 1H NMR
diruthenium complex 4 of a diphenazine bridge [L2]–. The spectrum of complex 4 indicated the presence of two phena-
latter reaction is associated with a new C–N bond fusion zine moieties. Electrospray mass spectra of the complexes
process. In the present context it is relevant to add that the were found to be informative for the identification of the
coordination chemistry of the phenazine ligands, in general, complexes. The charge state distributions of these ranging
has been developed in recent years; however, this work is from (+1) to (+3) are clearly observed, which exactly cor-
confined[8] mostly to the complexes of pyridyl-containing roborated with the ionization of the respective complexes
phenazines. Some of these bind DNA and RNA and are in the acetonitrile solution. For example an abundant peak,
– +
an important class of molecular probes.[9] In contrast, the called a base peak, was observed for [2a-ClO4 ] at m/z =
coordination chemistry of the related 2-amino-3-imino- 971 amu. The complex 3a showed a weak signal at m/z =
phenazine or its redox partners is not available in the litera- 1085 amu, and was accompanied by a strong signal at m/z
– +
ture. Thus, the reference reactions are noteworthy in the = 493 amu. These were ascribed to the [3a – ClO4 ] and
– 2+
context of understanding the metal-mediated redox pro- [3a – 2ClO4 ] ions, respectively. The compound 4a exhib-
cesses that are operative in amino-imino-phenazine[10] and ited peaks at 1020 and 647 amu, respectively. The peak
related systems.
at 647 amu was most intense and ascribed to the [4a –
3ClO4 ] ion. Similarly, the substituted complexes viz. 2b,
– 3+
3b and 4b displayed peaks at expected m/z values (Exp.
Sect.). From the ESI-MS spectral nature it is inferred that
complex 4 is a dimetallic compound with a relatively high
molecular weight. Notably, the experimental ESI-MS spec-
Results and Discussion
The synthetic reaction involved refluxing a methanolic tral features of the above compounds exactly corresponded
solution of [Ru(N∧N)2(CH3OH)2]2+, generated in situ,[11] to simulated patterns for the given formulations. Three rep-
with an equimolar quantity of HL1 in the presence of a resentative ESI-MS spectra of 2–4, are submitted as supple-
base (NEt3) for 6 h. The initial red brown color of the solu- mentary materials (Figure S2). Electrolytic natures of dilute
tion mixture gradually turned bluish-violet and finally it be- acetonitrile (1 m) solutions of the complexes were of dif-
came blue. The complexes were precipitated as their per- ferent type: 2, 1:1, 3, 1:2 and 4, 1:3.
chlorate or triflate salts. The crude mass, so formed, was a
Preliminary characterization of the above compounds
mixture of three major products: blue 2, violet 3 and blue was made from their physicochemical data. However, X-
4, which were successfully separated on a preparative alu- ray crystal analyses of the two complexes (3 and 4) of the
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413

P. Banerjee, G. Mostafa, A. Castiñeiras, S. Goswami
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Scheme 2.
1
Figure 1. Segmented H NMR spectra of (a) HL1, (b) 2a, (c) 3a, and (d) 4a CD3CN at 298 K.
transformed ligands were indeed necessary for authentica- [Ru(N∧N)2(L1)](X) (2) could not be grown. However, a
tion of their formulations and structures.
complete characterization was obtained (vide supra) from
The solutions of the complexes 2a and 2b were found to the physicochemical data. The two representative complexes
undergo chemical transformations to 3a and 3b, respec- of the transformed ligands viz. 3b and 4a formed single
tively, hence X-ray quality crystals of the parent complex, crystals suitable for X-ray structure determination.
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Reactions of a Ruthenium-Coordinated Phenazine
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[Ru(phen)2(LO)](CF3SO3)2·2H2O (3b)
[(bpy)2RuL2Ru(bpy)2](ClO4)3 (4a)
A view of the cationic part of the molecule [Ru(phen)2-
(LO)](CF3SO3)2·2H2O is shown in Figure 2 and selected
bond lengths and angles are collected in Table 1. In this
complex, two bidentate 1,10-ortho-phenanthroline (phen) li-
gands and a neutral phenazine ligand [LO], formed via suc-
cessive hydroxylation and oxidation of the coordinated li-
gand [L1]–, surround a ruthenium(II) center. The complex
as a whole is dicationic and the crystallographic asymmetric
unit also contains two triflate anions and two water mole-
cules. Hydroxylation of the phenazine ligand occurred at
the α-carbon (C13) to a N-aryl imine function [C(12)–
N(11)]. The C(13)–O(130) bond length, 1.209(4) Å, indi-
cates a localized double bond. The two C–N (imine) bond
lengths, 1.300(4) Å [C(12)–N(11)] and 1.290(6) Å [C(25)–
N(26)], respectively confirm[6a,13] their double bond charac-
ter. The six Ru–N lengths are similar, and lie in the range
1.997–2.083 Å. The average of chelate bite angles of the
phen ligand is 79.1(2)°, while the corresponding N(11)–
Ru(1)–N(26) angle of the phenazine ligand has a value of
76.71(12)°.
Figure 3 shows the ORTEP and atom numbering scheme
for the cationic complex [4a]3+ and its bond parameters are
collected in Table 1. Herein, two [RuII(bpy)2] moieties are
bridged across a dimeric phenazine ligand [L2]–, formed via
an unusual type of C–N fusion between the two [Ru(bpy)2-
L1]+ units. In this reaction a new C–N bond is formed be-
tween the free pyrazine nitrogen N(9) of one unit and the
α-carbon C(36) of the second unit. The bridging ligand,
[L2]–, is a zwitterion with two anionic chelating sites and a
cationic pyrazine nitrogen. The bridging ligand is thus
mono-negative and coordinates to two ruthenium(II) cen-
ters in a bis chelating tetradentate fashion. The resulting
diruthenium complex as a whole is tri-cationic and the
asymmetric unit contains three perchlorate counterions.
The C–N lengths viz. C(35)–N(5) 1.387(4) Å, C(40)–N(6)
1.314(4) Å, C(71)–N(11) 1.343(4) Å and C(72)–N(12)
1.348(4) Å are all longer than the corresponding distances
in coordinated LO in the compound 3b (Table 1). Notably,
the C(35)–N(5) length is appreciably longer than C(40)–
N(6) suggesting that the anionic charge in this part of the
bridging ligand is localized on N(5). In contrast the two C–
N lengths of the other part viz. C(71)–N(11) and C(72)–
N(12) are nearly identical indicating effective charge delo-
calization over the N(11)–C(71)–C(72)–N(12) skeleton. The
average of the above C–N lengths of L2 lies in between a
single and a double C–N bond length. The five-membered
chelate rings of the bridging ligand have the expected bite
angles, N(5)–Ru(1)–N(6) 76.12(9)° and N(11)–Ru(2)–N(12)
76.94(11)°.
The two reference chemical transformations, viz. 2 Ǟ 3
and 2 Ǟ 4, occur due to induced C–H activation[6,14] at the
ortho carbon of the coordinated phenazine. The plausible
initial step for the formation of 3 is the oxidation reaction,
2 Ǟ 2+. The oxidized product 2+ is then converted to 3 in
the presence of water and aerial oxygen. Water adds to the
polarized phenazine ring and the hydroxo-intermediate, so
formed, is oxidized to 3 in air. Exposure of an aqueous
methanolic solution of 2 to air thus produces the com-
Figure 2. ORTEP and atom numbering scheme for 3b. Hydrogen
atoms are omitted for clarity.
Table 1. Selected bond lengths [Å] and angles [°] for the complexes 3b and 4a.
[Ru(phen)2(LO)](CF3SO3)2·2H2O (3b)
[(bpy)2RuL2Ru(bpy)2](ClO4)3 (4a)
Bond lengths
Bond lengths
Ru(1)–N(11)
Ru(1)–N(26)
Ru(1)–N(61)
Ru(1)–N(72)
Ru(1)–N(81)
Ru(1)–N(92)
1.997(4)
2.053(3)
2.082(5)
2.038(4)
2.042(3)
2.066(4)
N(11)–C(12)
C(12)–C(13)
C(12)–C(25)
N(26)–C(25)
C(25)–C(24)
C(13)–O(130)
1.300(4)
1.523(5)
1.457(5)
1.290(6)
1.369(6)
1.209(4)
Ru(1)–N(5)
Ru(1)–N(6)
Ru(2)–N(11)
Ru(2)–N(12)
N(6)–C(40)
N(9)–C(36)
N(11)–C(71)
N(12)–C(72)
2.072(3)
2.056(2)
2.034(3)
2.050(3)
1.314(4)
1.470(4)
1.343(4)
1.348(4)
C(35)-C(36)
C(39)–C(40)
C(35)–C(40)
C(70)–C(71)
C(71)–C(72)
C(72)–C(73)
C(35)–N(5)
1.393(4)
1.389(4)
1.393(4)
1.396(5)
1.388(5)
1.395(5)
1.387(4)
Bond angles
Bond angles
N(11)–Ru(1)–N(26) 76.71(12)
N(92)–Ru(1)–N(81) 79.64(15)
N(72)–Ru(1)–N(61) 78.6(2)
N(1)–Ru(1)–N(2)
N(5)–Ru(1)–N(6)
N(13)–Ru(2)–N(14) 77.80(13)
78.27(10)
76.12(9)
N(3)–Ru(1)–N(4)
N(11)–Ru(2)–N(12) 76.94(11)
N(15)–Ru(2)–N(16) 79.52(13)
78.14(9)
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Figure 3. ORTEP and atom numbering scheme for 4a. Hydrogen atoms are omitted for clarity.
pound 3 in almost quantitative yield. The plausible steps respectively. Notably, the two-phenazine moieties in the
of this transformation[15] are shown in Scheme 3. Since the bridging ligand [L2]– are not identical and hence the two
oxidation potential of complex 2 is low (vide infra), the ae- major transitions in the visible region are believed to be due
rial oxidation, 2 Ǟ 2+ is reasonable and is believed to be to the presence of two acceptor chromophores in the bridg-
the key step for the formation of 3 from 2. Furthermore, ing ligand. Interestingly, the intensities of MLCT transi-
the fact that electrochemical oxidation of the complex 2 tions in 4 are significantly higher than those of the mononu-
(vide infra) produces the compound 3, also supports our clear compounds 2 and 3. This spectral behavior of the
proposition. The conversion of 2 to 4 occurs only in dry polynuclear complexes with repeating acceptor chromo-
and boiling methanol. Nucleophilic attack of the phenazine phores has been reported[6b] in the literature. The complexes
nitrogen of one molecule of 2 at the activated ortho C–H of also showed multiple UV-range transitions, which are as-
another molecule followed by (-H+ – 2e–) transfer produces signed to inter- or intra-ligand transitions.
the compound 4.
The redox behavior of the complexes 2–4 was studied in
Hence, we conclude that 2 Ǟ 3 conversion is facilitated dichloromethane {maintaining 10–3  concentration of the
by the initial oxidation of the ruthenium(II) center of 2. complex and 10–1  concentration of the supporting elec-
However, if the initial oxidation of 2 is arrested, dimeriza- trolyte, [nBu4N](ClO4)} in the potential range 2.0 to –1.5 V
tion of the phenazine occurs preferably so as to initiate the by using platinum or glassy carbon working electrodes. The
formation of the dimetallic complex 4. The results are sum- reported potentials (Table 2, Figure 5) are referenced to the
marized in Scheme 4.
saturated calomel electrode (SCE). The value for the ferro-
The electronic spectroscopic data of all the complexes cene/ferrocenium couple under our experimental conditions
are collected in Table 2 and their representative spectra are was 0.39 V.
displayed in Figure 4. The visible range spectra of these
The mononuclear complex [Ru(bpy)2L1]ClO4 (2a)
complexes consisted of strong absorptions. For example, the showed an electrochemically reversible RuIII/RuII response
mononuclear complexes 2a and 3a each showed an allowed at 0.15 V. Associated with it is an irreversible response,
transition at 585 nm (ε = 16385 –1 cm–1) and 565 nm (ε = which appeared at a potential of 1.05 V. The redox behavior
23490 –1 cm–1), respectively. These are ascribed to charge of the closely related system, [Ru(phen)2L1]ClO4 2b, is sim-
transfer, RuII(dπ)Ǟπ*(phenazine) (MLCT). The bimetallic ilar to that of 2a. Constant potential coulometry at 0.40 V
compound 4a displayed two intense transitions at 690 nm of both 2a and 2b resulted in rapid transformations to 3a
(ε = 36450 –1 cm–1) and 645 nm (ε = 32300 –1 cm–1), and 3b, respectively. The voltammetric behavior of the com-
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Reactions of a Ruthenium-Coordinated Phenazine
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Scheme 3.
the parent bivalent complex, 3a under our experimental
conditions. However, we managed to record an EPR spec-
trum of the reduced complex, by performing the controlled
potential bulk electrolysis of 3a at 260 K and quickly freez-
ing the electrolyzed solution at 77 K. The EPR spectrum
showed (Figure S3) an intense signal at g = 2.001 without
any g-anisotropy, indicating large free radical[16] (ligand)
contributions to the SOMO. We thus conclude that upon
reduction of 3a, an electron is added to the ketonic function
of the phenazine ligand to result in a free radical-containing
phenazine ligand [LO·]– that resembles[10] pyocyanine. The
main feature of the cyclic voltammogram of the dimetallic
Scheme 4.
plexes, 3a and 3b was similar. These showed a reversible complexes 4a and 4b consisted of two closely spaced re-
reductive response near –0.35 V. Exhaustive electrolysis of sponses at 0.70, 0.85 V and 0.75, 0.90 V, respectively. These
3a at –0.60 V produced a blue solution, which reverted to are assigned to two successive electron transfers at the two
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Table 2. Electronic spectra and cyclic voltammetric data.
Compound Abs. [λmax /nm (ε/–1 cm–1)][a]
Cyclic voltammetry[c,d]
Oxidation E1/2 [V]
(∆Ep [mV])
Reduction E1/2 [V]
(∆Ep [mV])
2a
3a
4a
2b
3b
4b
585 (16385), 420 (8770), 285 (41555)
0.15 (70), 1.05[e]
0.85 (100)
0.70 (80), 0.85 (90)
0.15 (75), 1.10[e]
0.90 (100)
–1.33 (90)
565 (23490), 400[b] (12085), 320[b] (18790), 290 (43830)
690 (36450), 645 (32300), 340 (20480), 295 (36310)
585 (17390), 415 (8900), 285(44250)
–0.35 (100), –0.91[f]
–0.88 (90)
–1.35 (100)
565(29610), 390[b] (12340), 320[b] (14640), 265 (45770), 225 (61135)
690 (42155), 645 (36190), 325 (23060), 265 (116680), 225 (129170)
–0.30 (80), –1.00[f]
–0.85 (80)
0.75 (70), 0.90 (80)
[a] Solvent: acetonitrile. [b] Shoulder. [c] Solvent: dichloromethane, supporting electrolyte: [nBu4N](ClO4) 10–1 ; scan rate: 50 mV–1 s–1.
[d] Sample concentration ca. 10–3 . [e] Irreversible, the value corresponds to Epa. [f] Irreversible, the value corresponds to Epc.
Figure 4. UV/Vis spectra of (L1)–, (Ϫ); (2a), (····); (3a), (-·-·-·-·);
(4a), (-----) in acetonitrile.
ruthenium centers. The magnitude of ∆E signifies moderate
electronic interactions between the ruthenium centers.
Our present work has demonstrated that the phenazine
ligand [6-p-anisyl-2-(p-anisylamino)-3(4H)-p-anisylimine-9-
methoxyphenazine], HL1, upon coordination to ruthenium
is susceptible to fascinating metal-mediated chemical trans- Figure 5. Cyclic voltammograms for the compounds (a) 2a, (b) 3a,
and (c) 4a in dichloromethane at a scan rate 50 mVs–1.
formations leading to isolation of the three new ruthenium
complexes 2–4 of three different ligands (viz. [L1]–, LO and
[L2]–) from the reaction of [Ru(CH3OH)2(N∧N)2]2+ and
Experimental Section
HL1. The latter two ligands are formed in situ due to oxi-
Materials: The precursor compounds cis-[Ru(bpy)2Cl2]·2H2O and
dative hydroxylation and dimerization reactions of the co-
cis-[Ru(phen)2Cl2]·2H2O were prepared according to the reported
ordinated ligand, [L1]–. To authenticate these transforma-
procedures.[17] The ligand HL1 was synthesized as before.[7] Silica
tions, X-ray structure analyses of a mononuclear ruthenium
gel and aluminum oxide for TLC were obtained from Merck, India
and Sisco Research Laboratories Pvt. Ltd., Bombay. RuCl3·nH2O
was purchased from Arora Mathey Ltd., and 2,2Ј-bipyridine and
complex of LO as well as a diruthenium complex of the
bridging ligand [L2]– were analyzed. Presently, we are pur-
suing our work to understand the effects of ancillary li-
gands and the metal ions on the chemical transformations
of the reference phenazine ligands.
1,10-phenanthroline monohydrate were obtained from Qualigens
and Merck, India, respectively. Tetrabutylammonium perchlorate
(TBAP) was used as the supporting electrolyte, for spectroscopic
418
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Eur. J. Inorg. Chem. 2007, 412–421

Reactions of a Ruthenium-Coordinated Phenazine
FULL PAPER
and electrochemical studies HPLC-grade solvents were used. Other
chemicals and reagents were of reagent-grade and used as received.
1464 m, 1446 m, 1423 m, 1285 w, 1245 s, 1115 vs, 1100 vs, 838 m,
– +
770 s, 625 s cm–1. ESI-MS: m/z (%): 971 [M – ClO4 ] , where M
= molecular mass of the compound. ΛM in acetonitrile at 25 °C:
Physical Measurements
130 Ω–1 cm2 M–1.
Microanalytical data (C, H and N) were collected with a Perkin–
Elmer 240C elemental analyzer. A Perkin–Elmer 783 spectropho-
tometer was used for the measurement of IR spectral data. 1H
NMR spectroscopic data was recorded with a Bruker Avance 300
spectrometer using SiMe4 as an internal standard. Electrochemical
measurements were performed at 298 K under a dry nitrogen atmo-
sphere on a PC-controlled PAR Model 273A electrochemistry sys-
tem with a gas tight single-compartment cell. Voltammetric experi-
ments were carried out in dichloromethane maintaining the sample
concentration at ca. 10–3 . The solution was degassed with the
flow of dry nitrogen and the working electrode surface was polished
before each measurement. A platinum disk working electrode, plati-
num wire auxiliary electrode and an aqueous saturated calomel ref-
erence electrode (SCE) were used in a three-electrode configuration.
All redox potentials in this work are reported against the saturated
calomel electrode. The value for the ferrocenium/ferrocene couple
under our experimental conditions was 0.39 V. EPR spectral mea-
surements were carried out with a Varian Model 109C E-line X-
band spectrometer as described before,[18] fitted with a quartz De-
war for measurements at 77 K, and the spectroscopic data were
calibrated against the spectrum of DPPH. Electrospray mass spec-
tra were recorded with a micro mass Q-TOF mass spectrometer
(Serial no. YA. 263). Electronic spectroscopic data were recorded
with a Perkin–Elmer Lambda 950 UV/Vis spectrophotometer.
[Ru(bpy)2(LO)](ClO4)2 (3a): This was crystallized from an acetoni-
trile/toluene (1:4) solvent mixture. Yield: 0.069 g (45%).
C54H44Cl2N8O13Ru (1184.10): calcd. C 54.72, H 3.71, N 9.46;
found C 54.73, H 3.74, N 9.41. IR (KBr): ν = 1670 s, 1605 s, 1550
˜
s, 1504 s, 1463 m, 1444 m, 1278 w, 1248 s, 1248 s, 1115 s, 1090 s,
–
2+
836 m, 767 s, 620 s cm–1. ESI-MS: m/z (%): 493 [M – 2ClO4 ]
.
ΛM in acetonitrile at 25 °C: 250 Ω–1 cm2 M–1.
[(bpy)2RuL2Ru(bpy)2](ClO4)3 (4a): Evaporation of the third fraction
from the TLC plate yielded the dimeric blue 4a. Yield: 0.054 g
(35%). This fraction was recrystallized from acetonitrile/toluene.
C108H89Cl3N16O20Ru2 (2239.38): calcd. C 57.87, H 3.97, N 10.00;
found C 57.95, H 4.00, N 10.01. IR (KBr): ν = 1605 s, 1565 w,
˜
1504 s, 1481 m, 1464 w, 1445 m, 1382 vs, 1250 s, 1115 vs, 1030 s,
– 3+
837 w, 768 s, 625 s cm–1. ESI-MS: m/z (%): 647 [M – 3ClO4 ]
.
ΛM in acetonitrile at 25 °C: 370 Ω–1 cm2 M–1.
Reactions of [Ru(phen)2(MeOH)2]2+ with HL1: This reaction was
performed as described above, except that cis-Ru(phen)2Cl2 was
used in place of cis-Ru(bpy)2Cl2. The yields and characterization
data of the complexes are collected below.
[Ru(phen)2(L1)](ClO4) (2b): This was recrystallized using a dichlo-
romethane/THF/hexane solvent mixture (1:1:1). Yield: 0.013 g
(8%). C58H45ClN8O8Ru (1117.50): calcd. C 62.28, H 4.02, N 10.02;
found C 62.25, H 4.10, N 9.98. IR (KBr): ν = 1610 s, 1548 m, 1504
˜
CAUTION! Although no problems were encountered in this work,
transition metal perchlorate complexes with organic ligands are po-
tentially explosive. Heating of dried samples must be avoided; hand-
ling of small quantities must proceed with great caution using proper
protection.
s, 1427 s, 1384 s, 1245 s, 1175 m, 1100 m, 1027 w, 721 m, 620 s cm–1.
– +
ESI-MS: m/z (%): 1018 [M – ClO4 ] . ΛM in acetonitrile at 25 °C:
140 Ω–1 cm2 M–1.
[Ru(phen)2(LO)](CF3SO3)2·2H2O (3b): Crystalline compound of 3b
was obtained by slow evaporation of the solution of the compound
in a dichloromethane/acetonitrile (1:2) solvent mixture. Yield:
0.075 g (47%). C60H48F6N8O13RuS2 (1368.21): calcd. C 52.62, H
Syntheses
The complexes 2–4 were synthesized following a general procedure.
Specific details for representative complexes are given below.
3.50, N 8.18; found C 52.55, H 3.60, N 8.10. IR (KBr): ν = 1670
˜
s, 1610 s, 1552 s, 1505 m, 1463 w, 1430 w, 1412 w, 1276 vs, 1250 s,
Reactions of [Ru(bpy)2(MeOH)2]2+with HL1: A mixture of cis-
[Ru(bpy)2Cl2]·2H2O (0.065 g, 0.125 mmol) and AgNO3 (0.042 g,
0.25 mmol) in dry methanol (25 mL) was heated at reflux for 2 h.
The initial violet solution changed to orange red. The cooled solu-
tion was filtered through Whatman 42 filter paper to remove the
precipitated AgCl. The ligand HL1 (0.070 g, 0.125 mmol) along
with two drops of NEt3 was then added to the above filtrate. The
resulting mixture was heated at reflux for 6 h. The solution finally
became blue and its volume was reduced to ca. 10 mL. The concen-
trated solution was then poured into diethyl ether (50 mL) to pre-
cipitate a dark product. The crude product was then subjected to
chromatography on a preparative alumina TLC plate for purifica-
tion. It was first eluted with CHCl3; a small band of unreacted
phenazine ligand was first separated, which was followed by a blue
(2) band. The unmoved dark band was collected and was again
loaded on a fresh TLC plate and chloroform/acetonitrile (3:2) was
then used as the eluent. This resulted in the separation of two dis-
tinct bands, viz. violet (3) and blue (4). The compounds 2–4 were
collected by complete evaporation of the eluates. Recrystallization
of these from different solvent mixtures yielded the products in
their crystalline states. The yields and characterization data of the
complexes are as follows.
1163 m, 1116 s, 1030 s, 840 m, 721 w, 638 s cm–1. ESI-MS: m/z (%):
– 2+
517 [M
–
2CF3SO3 ]
.
ΛM in acetonitrile at 25 °C:
270 Ω–1 cm2 M–1.
[(phen)2RuL2Ru(phen)2](ClO4)3 (4b): The thin rod-shaped crystal-
line compound was obtained from an acetonitrile/toluene (1:1) sol-
vent mixture. Yield: 0.040 g (25%). C116H89Cl3N16O20Ru2
(2333.64): calcd. C 59.65, H 3.81, N 9.60; found C 59.63, H 3.87,
N 9.55. IR (KBr): ν = 1605 s, 1564 w, 1502 s, 1481 s, 1427 w, 1408
˜
m, 1383 vs, 1130 s, 1029 m, 842 m, 610 s cm–1. ESI-MS: m/z (%):
678 [M – 3ClO4–]3+. ΛM in acetonitrile at 25 °C: 400 Ω–1 cm2 M–1.
Syntheses of Compounds 3 and 4 from 2. 2aǞ3a Conversion: A solu-
tion of the compound [Ru(bpy)2(L1)](ClO4) (2a) [50 mg in 250-mL
aqueous methanol (1:9)] was heated at reflux in air for 0.5 h. The
blue solution became violet. The mixture was evaporated to dryness
and the crude product was purified on an alumina TLC plate using
a chloroform/acetonitrile (3:2) solvent mixture as the eluent. A vi-
olet band of the compound 3a was collected. It was finally crys-
tallized from an acetonitrile/toluene solvent mixture, yield 90%.
The compound 3b was similarly obtained from 2b, the yield was
86%.
[Ru(bpy)2(L1)](ClO4) (2a): This was crystallized from a dichloro-
methane/hexane (1:1) solvent mixture. Yield: 0.015 g (10%).
C54H45ClN8O8Ru (1069.50): calcd. C 60.58, H 4.20, N 10.47; found
2aǞ4a Conversion: A solution of the compound 2a in dry meth-
anol was heated at reflux under a dry nitrogen atmosphere for 6 h.
The resultant blue solution was evaporated to dryness and was
loaded on an Al2O3-TLC plate for purification. A minor violet
C 60.56, H 4.25, N 10.45. IR (KBr): ν = 1615 s, 1560 s, 1502 s,
˜
Eur. J. Inorg. Chem. 2007, 412–421
© 2007 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
419

P. Banerjee, G. Mostafa, A. Castiñeiras, S. Goswami
FULL PAPER
band (3a, yield 5%) and a major blue band (4a, yield 75%) were
eluted using a chloroform/acetonitrile (3:2) solvent mixture.
tion correction was made with the help of the SAINT[19] program.
A total of 21643 reflections were measured, of which 15050 reflec-
tions were unique (Rint = 0.060). The data [I Ͼ 2σ(I)] were used
for solution and refinement by full-matrix least-squares on F2 using
the SHELXL-97 package.[22] The non-hydrogen atoms having full
occupancies were refined using anisotropic thermal parameters.
Hydrogen atoms were included in the structure factor calculation
at idealized positions, but not refined. The refinement was con-
verged at R = 0.0695 and wR2 = 0.1021 with residual electron den-
sity 1.36 eÅ3 and –0.64 eÅ3. The maximum electron densities have
no chemical significance as they were located at ca. 0.7 Å from a
heavy atom. The calculations were performed using the Bruker
Smart 5.63 software for data reduction, all other calculations and
graphics were done using the PLATON[23] software package and
ORTEP.[25]
The compound 4b was similarly obtained from 2b. The yield of 4b
was 80 %.
X-ray Crystallography: Single crystals of [Ru(phen)2(LO)](CF3-
SO3)2·2H2O (3b) were grown by slow evaporation of an acetonitrile/
dichloromethane (2:1) solvent mixture and the single crystals of
[{(bpy)2Ru}2(L2)–](ClO4)3 (4a) were grown by slow diffusion of an
acetonitrile solution of 4a into toluene. Crystallographic data are
collected in Table 3 and further details are noted below.
Table 3. Crystallographic data and refinement results for 3b and
4a.
Compound
3b
4a
Empirical formula
Molecular mass
T [K]
Wavelengths [Å]
Crystal system
Space group
a [Å]
b [Å]
c [Å]
α [°]
β [°]
C60H48F6N8O13RuS2 C108H89Cl3N16O20Ru2
Crystal data and refinement details are listed in Table 3. CCDC-
290869 (for 3b) and -290868 (for 4a) contain the supplementary
crystallographic data for this paper. These data can be obtained
free of charge from The Cambridge Crystallographic Data Centre
via www.ccdc.cam.ac.uk/data_request/cif.
1368.25
2239.44
293(2)
273(2)
0.71073
0.71073
monoclinic
P21/c (no. 14)
11.3828(13)
22.640(2)
24.2105(19)
90
109.044(4)
90
5897.7(10)
4
triclinic
P-1 (no. 2)
11.6057(18)
15.236(2)
33.086(5)
79.286(3)
89.143(3)
75.031(3)
5550.0(15)
2
Supporting Information (see also the footnote on the first page of
this article): NMR spectra of a class of representative complexes
(Figure S1). Observed ESI-MS spectra for representative complexes
(a) (2a)+, (b) (3a)2+, (c) (4a)3+ (Figure S2) and EPR spectrum of a
frozen acetonitrile/toluene glass (1:1) of (3a)– at 77 K (Figure S3).
γ [°]
V [Å3]
Z
Acknowledgments
Dcalcd. [mgm–3
]
1.541
1.340
Crystal dimensions [mm]
θ range for data collection [°] 1.27–28.08
0.23ϫ0.18ϫ0.16
0.03ϫ0.16ϫ0.21
1.3–26.1
21643
Financial support received from the Department of Science and
Technology, and the Council of Scientific and Industrial Research,
New Delhi is gratefully acknowledged. P. B. is thankful to the
Council of Scientific and Industrial Research, New Delhi, for his
fellowship. We are also thankful to the School of Chemistry, Uni-
versity of Hyderabad, for X-ray data collection for one of the sam-
ples.
Reflections collected
Unique reflections
Largest diff. between
28248
13468
15050
peak and hole [eÅ–3
Final R indices
[IϾ2σ(I)]
]
–1.085, 2.731
R1 = 0.0451
wR2 = 0.1597
–0.64, 1.36
R1 = 0.0695
wR2 = 0.1021
[Ru(phen)2(LO)](CF3SO3)2·2H2O (3b): X-ray quality crystals of 3b
were obtained by slow evaporation of an acetonitrile/dichloro-
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Reactions of a Ruthenium-Coordinated Phenazine
FULL PAPER
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Eur. J. Inorg. Chem. 2007, 412–421
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