Variable coordination modes of benzaldehyde thiosemicarbazones - Synthesis, structure, and electrochemical properties of some ruthenium complexes

Article abstract of DOI:10.1002/ejic.200800547

Reaction of benzaldehyde thiosemicarbazones [H₂LR, where H ₂ stands for the two protons, the hydrazinic proton, and the phenyl proton at the ortho position, with respect to the imine function and R (R = OCH₃, CH₃, H, Cl, and NO₂) for the para substituent] with [Ru(PPh₃)₂(CO)₂Cl ₂], carried out in refluxing ethanol, afforded monomeric complexes of type [Ru(PPh₃)₂(CO)(HLR)(H)]. The crystal structure of the [Ru(PPh₃)₂(CO)(HLNO₂)(H)] complex was determined. The thiosemicarbazone ligand is coordinated to the ruthenium center as a bidentate N,S-donor ligand forming a four-membered chelate ring. When the reaction of the thiosemicarbazones with [Ru(PPh₃)₂(CO) ₂Cl₂] was carried out in refluxing toluene, a family of dimeric complexes of type [Ru₂(PPh₃) ₂(CO) ₂(LR)₂] were obtained. The crystal structure of [Ru ₂(PPh₃)₂(CO)₂(LCl)₂] was determined. Each thiosemicarbazone ligand is coordinated to one ruthenium atom, by dissociation of the two protons, as a dianionic tridentate C,N,S-donor ligand, and at the same time the sulfur atom is also bonded to the second ruthenium center. ¹H NMR spectra of the complexes of both types are in excellent agreement with their compositions. All the dimeric and monomeric complexes are diamagnetic (low-spin d⁶, S = 0) and show intense absorptions in the visible and ultraviolet regions. Cyclic voltammetry of the [Ru(PPh₃)₂(CO)(HLR)(H)] and [Ru₂(PPh ₃)₂-(CO)₂(LR)₂] complexes show the ruthenium(II)-ruthenium(III) oxidation within 0.48-0.73 V vs. SCE followed by a ruthenium(III)-ruthenium(IV) oxidation within 1.09-1.47 V vs. SCE. Potentials of both the oxidations are found to correlate linearly with the electron-withdrawing character of the substituent R. Wiley-VCH Verlag GmbH & Co. KGaA, 2008.

Full text of DOI:10.1002/ejic.200800547

FULL PAPER
DOI: 10.1002/ejic.200800547
Variable Coordination Modes of Benzaldehyde Thiosemicarbazones –
Synthesis, Structure, and Electrochemical Properties of Some Ruthenium
Complexes
Swati Dutta,[a] Falguni Basuli,[a] Alfonso Castineiras,[b] Shie-Ming Peng,[c]
Gene-Hsiang Lee,[c] and Samaresh Bhattacharya*[a]
Keywords: Thiosemicarbazones / S ligands / N ligands / Ruthenium / Coordination modes
Reaction of benzaldehyde thiosemicarbazones [H2LR, where
H2 stands for the two protons, the hydrazinic proton, and the
phenyl proton at the ortho position, with respect to the imine
function and R (R = OCH3, CH3, H, Cl, and NO2) for the para
ciation of the two protons, as a dianionic tridentate C,N,S-
donor ligand, and at the same time the sulfur atom is also
bonded to the second ruthenium center. 1H NMR spectra of
the complexes of both types are in excellent agreement with
substituent] with [Ru(PPh3)2(CO)2Cl2], carried out in re- their compositions. All the dimeric and monomeric com-
fluxing ethanol, afforded monomeric complexes of type
[Ru(PPh3)2(CO)(HLR)(H)]. The crystal structure of the
[Ru(PPh3)2(CO)(HLNO2)(H)] complex was determined. The
thiosemicarbazone ligand is coordinated to the ruthenium
center as a bidentate N,S-donor ligand forming a four-mem-
bered chelate ring. When the reaction of the thiosemicarb-
azones with [Ru(PPh3)2(CO)2Cl2] was carried out in refluxing
toluene, a family of dimeric complexes of type [Ru2(PPh3)
2(CO)2(LR)2] were obtained. The crystal structure of
[Ru2(PPh3)2(CO)2(LCl)2] was determined. Each thiosemicarb-
azone ligand is coordinated to one ruthenium atom, by disso-
plexes are diamagnetic (low-spin d6, S = 0) and show intense
absorptions in the visible and ultraviolet regions. Cyclic vol-
tammetry of the [Ru(PPh3)2(CO)(HLR)(H)] and [Ru2(PPh3)2-
(CO)2(LR)2] complexes show the ruthenium(II)–rutheni-
um(III) oxidation within 0.48–0.73 V vs. SCE followed by a
ruthenium(III)–ruthenium(IV) oxidation within 1.09–1.47 V
vs. SCE. Potentials of both the oxidations are found to corre-
late linearly with the electron-withdrawing character of the
substituent R.
(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim,
Germany, 2008)
in 1), which is indeed the case for several ligands of this
family.[4] However, we have observed that in their reactions
with ruthenium and osmium, benzaldehyde thiosemicarb-
azones 2 display a rather unusual coordination mode (3)
where they form four-membered chelate rings.[3a–3c]
Introduction
The chemistry of transition-metal complexes of thiosemi-
carbazone ligands has been receiving considerable attention
primarily because of their bioinorganic relevance[1] in gene-
ral and for their biological (viz. antibacterial, antimalarial,
antiviral, and antitumor) activities[2] in particular. We have
been exploring the chemistry of thiosemicarbazone com-
plexes of the platinum metals[3] mainly with the objective of
manipulating the different possible coordination modes of
the thiosemicarbazone ligands in their complexes, and the
present work has originated from this exploration. Thio-
semicarbazones are usually expected to bind to a metal ion,
by loss of the hydrazinic proton, as monoanionic bidentate
N,S-donor ligands forming five-membered chelate rings (as
Such a mode of coordination is also known for some
other thiosemicarbazones.[5] Our search for the reason be-
hind such an unusual mode of binding (as in 3) has revealed
that five-membered chelate ring formation (as shown in 1)
is not possible for benzaldehyde thiosemicarbazones, be-
cause they have a rigid geometry across the C=N bond (as
shown in 2), and in case they are forced to form a five-
membered chelate ring, the phenyl ring comes close to the
metal center (as shown in 4) and thus creates an unavoid-
[a] Department of Chemistry, Inorganic Chemistry Section, Ja-
davpur University,
Kolkata 700032, India
E-mail: samaresh_b@hotmail.com
[b] Departmento de Quimica Inorganica, Universidad de Santiago
de Compostela,
15782 Santiago de Compostela, Spain
[c] Department of Chemistry, National Taiwan University,
Taipei, Taiwan, ROC
Supporting information for this article is available on the
WWW under http://www.eurjic.org or from the author.
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Variable Coordination Modes of Benzaldehyde Thiosemicarbazones
able steric problem.[3c] It is relevant to mention here that we tion mode of the benzaldehyde thiosemicarbazones in these
have not been able to find a single example of a structurally [Ru(PPh3)2(CO)(HLR)(H)] complexes, the structure of a
characterized benzaldehyde thiosemicarbazone complex in representative complex, viz. [Ru(PPh3)2(CO)(HLNO2)(H)],
the literature, in which the ligand is coordinated as in 4. was determined by X-ray crystallography. The structure is
However, closeness of the phenyl ring to the metal center shown in Figure 1 and selected bond parameters are pre-
in this sterically unfavorable coordination mode (as in 4) sented in Table 1. The thiosemicarbazone ligand is coordi-
points to the possibility of ortho-metalation of the phenyl
ring (as in 5) by C–H bond activation under suitable reac-
tion conditions. The present study was initiated to explore
such a possibility by using ruthenium as the metal and a
group of five benzaldehyde thiosemicarbazones 2, differing
in the para substituent R (R = OCH3, CH3, H, Cl, and
NO2) of the phenyl ring, as the ligands.
Figure 1. View of the [Ru(PPh3)2(CO)(HLNO2)(H)] complex.
These ligands are abbreviated in general as H2LR, where
H2 stands for the two protons [the phenyl proton at the
ortho position with respect to the azomethine group and the
hydrazininc N-H proton, which were expected to undergo
dissociation during complexation in the C,N,S-mode (5)]
and R for the para substituent. These para substituents with
a gradual variation in their inductive effect are chosen in
order to study their influence, if any, on the metal-centered
redox potentials. As the ruthenium starting material, the
[Ru(PPh3)2(CO)2Cl2] complex was selected, particularly be-
Table 1. Selected bond lengths and angles for [Ru(PPh3)2(CO)-
(HLNO2)(H)]·CH3CN and [Ru2(PPh3)2(CO)2(LCl)2]·2CH2Cl2.
[Ru(PPh3)2(CO)(HLNO2)(H)]·CH3CN
Bond lengths [Å]
Bond angles [°]
Ru(1)–C(1)
Ru(1)–N(13)
Ru(1)–P(1)
Ru(1)–P(2)
1.864(8)
2.157(6)
2.344(2)
2.351(2)
2.545(2)
1.58(6)
1.384(7)
1.285(8)
1.309(8)
1.703(7)
1.348(8)
P(1)–Ru(1)–P(2)
C(1)–Ru(1)–N(13) 172.9(3)
O(1)–C(1)–Ru(1)
S(1)–Ru(1)–H(1)
C(18)–N(13)–Ru(1) 103.8(5)
C(18)–S(1)–Ru(1) 78.9(3)
N(13)–Ru(1)–S(1) 64.23(17)
172.55(8)
179.3(7)
163.0(19)
cause in its reaction with benzaldehyde semicarbazones it Ru(1)–S(1)
Ru(1)–H(1)
was found to be very useful in affording complexes where
N(12)–N(13)
the coordination mode of the semicarbazones could be ma-
N(12)–C(17)
N(13)–C(18)–S(1)
113.0(6)
nipulated by simple variation of the experimental condi-
N(13)–C(18)
C(18)–S(1)
N(14)–C(18)
tions.[6] Reaction of [Ru(PPh3)2(CO)2Cl2] with benzalde-
hyde thiosemicarbazones 2 indeed has afforded complexes
of two different types, and herein we report the chemistry
of these two groups of complexes, with special reference to
their formation, structure, and electrochemical properties.
[Ru2(PPh3)2(CO)2(LCl)2]·2CH2Cl2
Bond angles [°]
Bond lengths [Å]
Ru(1)–C(1)
Ru(1)–C(10)
Ru(1)–N(1)
Ru(1)–P(1)
Ru(1)–S(1)
Ru(1)–S(2)
C(1)–O(1)
C(3)–S(1)
C(4)–N(1)
N(1)–N(2)
Ru(2)–C(2)
Ru(2)–C(18)
Ru(2)–N(4)
Ru(2)–P(2)
Ru(2)–S(2)
Ru(2)–S(1)
C(2)–O(2)
C(11)–S(2)
C(12)–N(4)
N(4)–N(5)
1.857(3)
2.050(3)
2.092(2)
2.3071(7)
2.4786(7)
2.4804(7)
1.153(4)
1.781(3)
1.294(4)
1.389(3)
1.857(3)
2.056(3)
2.098(2)
2.3082(8)
2.4709(7)
2.4795(7)
1.148(4)
1.783(3)
1.284(4)
1.398(3)
C(1)–Ru(1)–N(1)
P(1)–Ru(1)–S(2)
C(10)–Ru(1)–S(1)
Ru(1)–S(1)–Ru(2)
C(3)–S(1)–Ru(1)
C(3)–S(1)–Ru(2)
C(2)–Ru(2)–N(4)
P(2)–Ru(2)–S(1)
C(18)–Ru(2)–S(2)
Ru(2)–S(2)–Ru(1)
C(11)–S(2)–Ru(2)
C(11)–S(2)–Ru(1)
173.29(11)
172.34(3)
157.19(8)
93.24(2)
95.84(10)
108.59(9)
171.48(11)
168.84(3)
156.84(8)
93.40(2)
Results and Discussion
Reaction of the benzaldehyde thiosemicarbazones
(H2LR, 2) with [Ru(PPh3)2(CO)2Cl2], carried out in re-
fluxing ethanol, afforded a group of complexes of the type
[Ru(PPh3)2(CO)(HLR)(H)] in good yields. Elemental (C, H,
N) analytical data of the complexes agree well with their
compositions. It is interesting to note here that a hydride
ion is coordinated to ruthenium in all these complexes and
the solvent (ethanol) appears to have served as the source
of this hydride. Conversion of a Ru–Cl bond into a Ru–H
bond in alcoholic medium has precedent in the literature.[7]
Indirect support of this speculation comes from the fact
that similar reactions carried out in toluene do not afford
any hydride complex (vide infra). To elucidate the coordina-
95.97(10)
111.16(10)
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FULL PAPER
nated to ruthenium as a monoanionic bidentate N,S-donor importance in molecular recognition processes as well as in
ligand forming a four-membered chelate ring (e.g., 3) with a crystal engineering.[10] As all the [Ru(PPh3)2(CO)-
bite angle of 113.0(9)°. Formation of such a four-membered (HLR)(H)] complexes were synthesized similarly, and as
chelate ring by the benzaldehyde thiosemicarbazone and they display similar properties (vide infra), the other four
similar ligands is quite normal.[3,5] Ruthenium has a [Ru(PPh3)2(CO)(HLR)(H)] (R ϶ NO2) complexes are as-
HCNP2S coordination sphere in this complex, which is dis- sumed to have a structure similar to that of [Ru(PPh3)2-
torted octahedral in nature as indicated by the bond param- (CO)(HLNO2)(H)].
eters around the ruthenium center. The thiosemicarbazone
ligand, ruthenium, carbonyl, and hydride constitute one
equatorial plane of the octahedron with the metal at the
center, and the two triphenylphosphane ligands take up the
remaining two axial positions; hence, they are mutually
trans. The carbonyl is trans to the coordinated nitrogen
atom of the thiosemicarbazone and the hydride is trans to
the sulfur atom. In complexes of ruthenium(II) containing
the Ru(PPh3)2 fragment, the PPh3 ligands usually occupy
mutually cis positions for optimum π interaction.[8] How-
ever, in the present group of complexes they are mutually
trans, probably due to steric reasons as well as the presence
of the stronger π acid CO. The Ru–H, Ru–C(CO), and Ru–
P distances are normal, as reported in structurally charac-
terized complexes of ruthenium(II) containing these
bonds.[9] Within the Ru(HLNO2) fragment the Ru–N length
is comparable to that found in similar four-membered che-
lates,[3a–3c] whereas the Ru–S distance is a little longer than
usually observed. The elongation of the Ru–S bond, which
is trans to the Ru–H bond, may be attributed to the trans
effect of the hydride ligand. Comparison of the bond
lengths in the coordinated thiosemicarbazone ligand with
those in the uncoordinated ligand[3c] shows that upon coor-
dination the C–S bond has undergone elongation, whereas
the adjacent C–N bond has undergone contraction. These
changes in bond lengths are consistent with the iminothio-
late form of the thiosemicarbazone ligand that appears to
be stabilized upon coordination to the metal through loss
of the hydrazinic proton.
Figure 2. The hydrogen bonding interactions in the crystal lattice
of [Ru(PPh3)2(CO)(HLNO2)(H)]: (a) C–H···O and (b) C–H···N and
C–H···S interactions.
In the crystal lattice of the [Ru(PPh3)2(CO)(HLNO2)(H)]
complex there is one molecule of acetonitrile per complex
Facile formation of the hydride complexes in ethanol
molecule. In order to discover any noncovalent interactions prompted us to try other solvents that cannot serve as hy-
in the lattice in general, and the link between the solvent dride sources. The fact that the benzaldehyde semicarba-
molecule and the complex molecules in particular, the pack- zone ligands displayed different coordination modes in their
ing pattern in the lattice was scrutinized, and it shows that reaction with [Ru(PPh3)2(CO)2Cl2] under different reaction
hydrogen-bonding interactions of three types, viz. C–H···O, conditions has further boosted this idea.[6] Encouraged by
C–H···S, and N–H···N, are active in the lattice (Figure 2, these ideas, reaction of benzaldehyde thiosemicarbazone li-
Table S1). One oxygen atom of the nitro group of each gands 2 with [Ru(PPh3)2(CO)2Cl2] has also been carried out
molecule is hydrogen bonded to a phenyl hydrogen of a in refluxing toluene, wherefrom a new series of orange com-
PPh3 belonging to a neighboring complex molecule leading plexes were obtained in decent yields. Elemental (C, H, N)
to a strong intermolecular interaction (Figure 2a). One analytical data of the complexes could not help us to know
methyl hydrogen of the acetonitrile is hydrogen bonded to the composition of the complexes. To know the composi-
the sulfur atom of a coordinated thiosemicarbazone of a tion structural characterization was done of a representative
complex molecule, whereas the nitrogen atom of the same member of this family by X-ray crystallography. The struc-
acetonitrile is hydrogen bonded to a hydrogen atom of the ture is shown in Figure 3 and selected bond parameters are
NH2 group of a second complex molecule (Figure 2b). given in Table 1. The structure reveals that the complex is
Thus, the acetonitrile bridges two complex molecules dimeric, where each monomeric unit consists of a square-
through strong intermolecular interactions. These extended pyramidal Ru(PPh3)(CO)(LCl) moiety. The Ru(CO)(LCl)
hydrogen-bonding interactions seem to be responsible for fragment constitutes the square base with the metal at the
holding the crystal together. It may be relevant to note here center and the PPh3 ligand takes up the apical position. The
that such hydrogen-bonding interactions are of significant thiosemicarbazone ligand is coordinated to ruthenium as a
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Variable Coordination Modes of Benzaldehyde Thiosemicarbazones
dianionic tridentate C,N,S-donor ligand by dissociation of cules through C–H···S, C–H···Cl, and C–Cl···π interactions.
two protons forming two five-membered chelate rings. Two The same dichloromethane molecule is also linked to the
such monomeric units are bridged by the sulfur atoms of second dichloromethane molecule through a C–H···Cl in-
the thiosemicarbazone ligands (as in 6). Hence, the benzal- teraction (Figure 4a). Additionally, there also exists inter-
dehyde thiosemicarbazone ligands are actually serving as molecular C–H···O and C–H···π interactions (Figure 4b). In
tetradentate ligands in these complexes.
view of the similarity in synthetic procedures and properties
(vide infra), the other four [Ru2(PPh3)2(CO)2(LR)2] (R ϶
Cl) complexes are assumed to have a structure similar to
that of [Ru2(PPh3)2(CO)2(LCl)2].
Figure 3. View of the [Ru2(PPh3)2(CO)2(LCl)2] complex.
Figure 4. Hydrogen-bonding interactions in the crystal lattice of
[Ru2(PPh3)2(CO)2(LCl)2]: (a) C–H···S, C–H···Cl and C–Cl···π, and
(b) C–H···O and C–H···π interactions.
There are only a few examples known where such a coor-
dination mode is displayed by the benzaldehyde thiosemi-
The mechanisms for the formation of the two types of
carbazone ligands.[11] Each ruthenium is sitting at the center complexes are not completely clear to us, but the sequences
of a C2NPS2 coordination sphere, which is distorted from shown in Schemes 1 and 2 seem probable. In solution the
ideal octahedral geometry, as reflected in the bond param- benzaldehyde thiosemicarbazones are known to exist in two
eters around each ruthenium atom. Although the Ru– tautomeric thione and thiol forms. In ethanol, the thiol tau-
C(CO) distance is similar to that observed in the previous tomer is likely to be the dominant species, which reacts with
structure, the Ru–P length is a bit shorter,[12] which is attrib- [Ru(PPh3)2(CO)2Cl2] to afford complex 7 by elimination of
utable to a stronger π interaction in the Ru(PPh3) fragments CO and HCl. In 7, the thiosemicarbazone ligand is coordi-
of this complex. This interaction was weaker in the previous nated as an N,S-donor ligand forming a four-membered
complex for the trans disposition of the two PPh3 ligands. chelate ring. Subsequently, the Ru–Cl bond is converted
The observed Ru–C, Ru–N, and Ru–S distances are quite into a Ru–H bond under prevailing reaction conditions to
normal.[1,3a,6] Comparison of bond lengths with those of give the final product.[7] However, in toluene the thione tau-
the uncoordinated thiosemicarbazone ligand[3c] shows that tomer appears to be more dominant and it reacts with
significant changes have taken place in the S–C–N–N–C– [Ru(PPh3)2(CO)2Cl2] to form reactive intermediate 8, in
Ru fragment of the ligand upon its coordination to the which the ligand is bound to ruthenium as an N,S-donor
metal by dissociation of the two protons. In the crystal lat- ligand forming a five-membered ring. Intermediates 7 and
tice there are two molecules of dichloromethane per mole- 8 are basically linkage isomers of the same species, and their
cule of the dimeric complex. The packing pattern in the formation probably proceeds through different kinetic
lattice (Figure 4, Table S1) shows that one of the two routes. In intermediate 8, the pendent phenyl ring comes
dichloromethane molecules is bridging two dimeric mole- very close to the metal center, resulting in cyclometalation
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S. Dutta, F. Basuli, A. Castineiras, S.-M. Peng, G.-H. Lee, S. Bhattacharya
FULL PAPER
by elimination of another HCl. Simultaneously loss of PPh3
All the complexes are diamagnetic, which is consistent
from the cyclometalated complex occurs, probably triggered with the bivalent state of ruthenium (low-spin d6, S = 0) in
by the relatively larger quantity of accumulated HCl, re- these complexes. In the 1H NMR spectra of the [Ru(PPh3)2-
sulting in the formation of a five-coordinate species, which (CO)(HLR)(H)] complexes the hydride signal is clearly ob-
undergoes rapid dimerization through a sulfur bridge to served as a triplet due to coupling with the two magnetically
yield the diruthenium complexes. Formation of the two equivalent phosphorus nuclei near –4.5 ppm. Though the
types of complexes from the two different solvents thus ap- aromatic region of the spectra is a bit complicated due to
pears to be due to domination of either the thione or thiol broad signals displayed by the PPh3 ligands (7.1–7.7 ppm),
tautomer in the respective solvents. Difference in the rela- most of the expected signals from the coordinated thiosemi-
1
tive concentrations of the two tautomers in the two solvents carbazone ligand were identified. The H NMR spectra of
is evidenced from the difference in the electronic spectral the [Ru2(PPh3)2(CO)2(LR)2] complexes show that the two
properties (Figure S1) of the thiosemicarbazone ligands in Ru(PPh3)(CO)(LR) fragments in these dimeric complexes
the two solvents. It may be mentioned in this context that are magnetically equivalent, as has also been indicated in
the display of different binding modes by thiosemicarb- the structural characterization of [Ru2(PPh3)2(CO)2(LCl)2].
azones in different solvents has precedent in the litera- Besides the absence of the hydride signal, the spectrum of
ture.[13]
each [Ru2(PPh3)2(CO)2(LR)2] complex is qualitatively sim-
ilar to that of the corresponding [Ru(PPh3)2(CO)(HLR)(H)]
complex. The 1H NMR spectroscopic data of the [Ru(PPh3)2-
(CO)(HLR)(H)] and [Ru2(PPh3)2(CO)2(LR)2] complexes
are therefore consistent with their composition and stereo-
chemistry.
The infrared spectra of the [Ru(PPh3)2(CO)(HLR)(H)]
complexes show many vibrations of different intensities in
the 2000–400 cm–1 region. A strong band near 1925 cm–1
indicates the presence of coordinated CO. The Ru–H
stretch could not be observed as an isolated signal, as it
falls in the same region of the ν(CO) stretch, but it appears
as a shoulder (near 1860 cm–1) on the intense ν(CO) band.
Strong vibrations are also observed near 746, 694, and
520 cm–1, which are attributed to the PPh3 ligands. Com-
parison with the spectrum of [Ru(PPh3)2(CO)2Cl2] shows
the presence of some new bands (e.g., bands near 1589,
1562, 1523, 1302, and 1091 cm–1) in the spectra of the
[Ru(PPh3)2(CO)(HLR)(H)] complexes, which must be aris-
ing due to the coordinated thiosemicarbazone ligand. Infra-
red spectra of the [Ru2(PPh3)2(CO)2(LR)2] complexes are
mostly similar to those of the [Ru(PPh3)2(HLR)(CO)(H)]
complexes.
Scheme 1.
The [Ru(PPh3)2(CO)(HLR)(H)] and [Ru2(PPh3)2(CO)2-
(LR)2] complexes are soluble in dichloromethane, chloro-
form, acetonitrile, acetone, etc., producing intense yellow
and orange-yellow solutions, respectively. The electronic
spectra of the complexes were recorded in dichloromethane
solution. The spectroscopic data are presented in Table 2.
Each [Ru(PPh3)2(CO)(HLR)(H)] complex shows one in-
tense absorption in the visible region and two intense ab-
sorptions[14] in the ultraviolet region. The absorptions in the
ultraviolet region are assignable to transitions within the
ligand orbitals, whereas that in the visible region is probably
due to an allowed metal-to-ligand charge-transfer transi-
tion. In order to gain insight into the nature of the observed
transition in the visible region, qualitative extended
Hueckel molecular orbital (EHMO) calculations were per-
formed[15] on computer-generated models of all the
[Ru(PPh3)2(CO)(HLR)(H)] complexes, where the phenyl
rings of PPh3 are replaced by hydrogen atoms. The partial
MO diagram for a representative complex is shown in Fig-
ure 5 and the composition of selected molecular orbitals is
Scheme 2.
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Variable Coordination Modes of Benzaldehyde Thiosemicarbazones
Table 2. Electronic spectral and cyclic voltammetric data.
Compound
Electronic spectroscopic data[a]
Cyclic voltammetric data[b]
E [V] vs. SCE
λmax [nm] (ε, –1 cm–1)
[Ru(PPh3)2(CO)(HLOCH3)(H)] 456 (1850), 342[c] (9600), 310 (14000)
0.51[d] (80)[e]
0.54[d] (70)[e]
0.57[d] (60)[e]
0.66[f]
1.12[f]
1.14[f]
1.19[f]
1.27[f]
1.43[f]
1.09[f]
1.18[f]
1.20[f]
1.23[f]
1.47[f]
[Ru(PPh3)2(CO)(HLCH3)(H)]
[Ru(PPh3)2(CO)(HLH)(H)]
[Ru(PPh3)2(CO)(HLCl)(H)]
[Ru(PPh3)2(CO)(HLNO2)(H)]
[Ru2(PPh3)2(CO)2(LOCH3)2]
[Ru2(PPh3)2(CO)2(LCH3)2]
[Ru2(PPh3)2(CO)2(LH)2]
466 (1700), 338[c] (7160), 302 (13200)
462 (1400), 346[c] (5400), 298 (11000)
474 (2500), 346[c] (9900), 310 (18830)
436 (1610), 302 (11260)
0.73[f]
456 (4600), 350[c] (1600), 308 (36400), 276[c] (46800)
468 (3200), 348[c] (10900), 310[c] (23000), 274[c] (35000)
472 (2900), 350[c] (14000), 304[c] (30000), 274[c] (44000)
468 (2700), 350[c] (25100), 292[c] (42000), 274[c] (49400)
562 (2800), 396[c] (8800), 352[c] (10090), 270[c] (29000)
0.48[d] (70)[e]
0.53[d] (80)[e]
0.56[d] (70)[e]
0.55[d] (80)[e]
0.72[d] (80)[e]
[Ru2(PPh3)2(CO)2(LCl)2]
[Ru2(PPh3)2(CO)2(LNO)2]
[a] Dichloromethane solution. [b] Dichloromethane/acetonitrile (1:19), TBAP supporting electrolyte. [c] Shoulder. [d] E1/2 = 0.5 (Epa
Epc), where Epa and Epc are anodic and cathodic peak potentials, respectively. [e] ∆Ep = Epa – Epc in mV. [f] Epa value.
+
presented in Table S2. Results of these calculations were shown in Figures S3 and S4. Each complex shows two oxi-
found to be similar for all the complexes. The highest occu- dative responses on the positive side of SCE. For the three
pied molecular orbital (HOMO) has a major (64–80%) [Ru(PPh3)2(CO)(HLR)(H)] complexes, where R = OCH3,
contribution from the ruthenium t2 orbitals and the lowest CH3, and H, this oxidation is observed to be reversible,
unoccupied molecular orbital (LUMO) is localized almost characterized by a peak-to-peak separation (∆Ep) of 60–
entirely (95–97%) on the thiosemicarbazone ligand, where 80 mV, which remains unchanged upon variation in scan
a considerable contribution (≈55%) comes from the unco- rates, whereas for others this oxidation is irreversible. The
ordinated imine fragment.[16] Therefore, the absorption in first oxidation is reversible in the case of the [Ru2(PPh3)2-
the visible region may be assigned to the charge-transfer (CO)2(LR)2] complexes, with ∆Ep = 70–80 mV. For the re-
transition occurring from the filled ruthenium t2 orbital versible oxidations, the values of ∆Ep remain unchanged
(HOMO) to the vacant π*(imine)-orbital of the thiosemi- upon variation in the scan rate and ipa = ipc. For the remain-
carbazone ligand (LUMO). The electronic spectral proper- ing two [Ru(PPh3)2(CO)(HLR)(H)] (R = Cl and NO2) com-
ties of the [Ru2(PPh3)2(CO)2(LR)2] complexes were found plexes, this oxidation is found to be irreversible. In view of
to be similar to those of the [Ru(PPh3)2(CO)(HLR)(H)] the composition of the HOMO, the first oxidative response
complexes. EHMO calculations of the [Ru2(PPh3)2(CO)2- is assigned to RuII–RuIII oxidation. The second oxidative
(LR)2] complexes also support the similarity. The HOMO response is irreversible for all the complexes and this is ten-
is again concentrated largely on the metal center and the tatively assigned to RuIII–RuIV oxidation. The one-electron
LUMO is delocalized mostly on the thiosemicarbazone li- nature of both oxidations was established by comparing
gands (Figure S2, Table S2). Hence, the absorption in the their current heights (ipa) with those of standard ferrocene–
visible region is assigned to a metal-to-thiosemicarbazone ferrocenium couple under identical experimental condi-
charge-transfer transition, and those in the ultraviolet re- tions. The potential of both the RuII–RuIII and RuIII–RuIV
gion are believed to be due to intraligand transitions.
oxidations is found to be sensitive to the nature of the R
substituent in the thiosemicarbazone ligands. The potential
increases with increasing electron-withdrawing character of
R. The plots of the oxidation potentials (Epa) for both the
RuII–RuIII and RuIII–RuIV couples versus the Hammett
substituent constant (σ) of R[17] [σ values of the substituents
are OCH3 = –0.27, CH3 = –0.17, H = 0.00, Cl = 0.23, NO2
= 0.78] are linear (Figure S3). The slope of these lines,
which is known as the reaction constant (ρ)[18] and is a mea-
sure of the sensitivity of the oxidation potentials with R, is
0.17 for the RuII–RuIII oxidation and 0.30 for the RuIII
–
RuIV oxidation for the [Ru(PPh3)2(CO)(HLR)(H)] complex.
The values for the [Ru2(PPh3)2(CO)2(LR)2] complexes are
0.21 and 0.33, respectively. The potential of both the oxi-
dations is found to correlate linearly with the Hammett sub-
stituent constant (σ) of the substituent R in the thiosemi-
Figure 5. Partial molecular orbital diagram of [Ru(PPh3)2(CO)-
(HLH)(H)].
carbazone ligands (Figure S4) This indicates that the RuIII
–
RuIV oxidation potential is more sensitive to the nature of
R. It is interesting to note that a single substituent, which
is four bonds away from the electroactive metal center, can
still influence the metal-centered redox potentials in a pre-
dictable manner.
Electrochemical properties of the [Ru(PPh3)2(CO)-
(HLR)(H)] and [Ru2(PPh3)2(CO)2(LR)2] complexes were
studied by cyclic voltammetry. The voltammetric data are
presented in Table 2 and selected voltammograms are
Eur. J. Inorg. Chem. 2008, 4538–4546
© 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
4543

S. Dutta, F. Basuli, A. Castineiras, S.-M. Peng, G.-H. Lee, S. Bhattacharya
FULL PAPER
carbonyl stretch), 746 (νPPh ), 694 (νPPh ), 520 (νPPh ), 1589, 1562,
Conclusions
3
3
3
1523, 1302, 1091 cm–1. H NMR[21] (300 MHz, CDCl3): δ = –4.47
1
The present study shows that the coordination mode of
benzaldehyde thiosemicarbazones (H2LR) can be manipu-
lated by simply varying the experimental conditions used
for the synthesis of their complexes. This has been mani-
fested in the reaction of benzaldehyde thiosemicarbazones
(t, J = 19.2 Hz, 1 H, hydride), 5.19 (s, 2 H, NH2), 7.10 (3 H)*,
7.25–7.70 (2 PPh3), 7.99 (d,
J = 8.6 Hz, 2 H) ppm.
C45H38N4O3P2RuS (877.5): calcd. C 61.57, H 4.33, N 6.38; found
C 61.54, H 4.34, N 6.37.
[Ru(PPh3)2(CO)(HLCl)(H)]: This complex was prepared by follow-
with [Ru(PPh3)2(CO)2Cl2] under different experimental ing the above procedure by using H2LCl instead of H2LNO2. Puri-
fication of the complex was achieved by thin-layer chromatography
on a silica plate by using benzene/acetonitrile (10:1) as the eluant.
A yellow band separated, which was extracted with acetonitrile.
Evaporation of the acetonitrile extract afforded [Ru(PPh3)2-
(CO)(HLCl)(H)] as a yellow crystalline solid. Yield: 90 mg (78%).
conditions affording monomeric [Ru(PPh3)2(CO)(HLR)-
(H)] and dimeric [Ru2(PPh3)2(CO)2(LR)2] complexes. The
monomeric hydride complexes appear suitable for exploring
reactivities of the Ru–H bond and such studies are currently
in progress.
IR (KBr): ν = 1924 (νCO), 1861 (νH, overlapped with carbonyl
˜
stretch), 746 (νPPh ), 694 (νPPh ), 520 (νPPh ), 1587, 1561, 1520, 1300,
1094 cm–1. 1H NMR (300 MHz, CDCl3):3δ = –4.61 (t, J = 19.0 Hz,
1 H, hydride), 5.18 (s, 2 H, NH2), 7.09 (3 H)*, 7.25–7.70 (2 PPh3),
7.97 (d, J = 8.6 Hz, 2 H) ppm. C45H37ClN3OP2RuS (866): calcd.
C 62.35, H 4.27, N 4.85; found C 62.37, H 4.37, N 4.88.
3
3
Experimental Section
General Procedure: Commercial ruthenium trichloride, purchased
from Arora Matthey, Kolkata, India, was converted into
RuCl3·3H2O by repeated evaporation with concentrated hydrochlo-
ric acid. Triphenylphosphane was purchased from Loba Chemie,
Mumbai, India. [Ru(PPh3)2(CO)2Cl2] was synthesized following a
reported procedure.[19] Benzaldehyde, para-substituted benzalde-
hydes and thiosemicarbazide were obtained from S.D. Fine-Chem,
Mumbai, India. The thiosemicarbazone ligands were prepared by
treating equimolar amounts of thiosemicarbazide and the respec-
tive para-substituted benzaldehyde in an ethanol/water (1:1) mix-
ture. All other chemicals and solvents were reagent grade commer-
cial materials and were used as received. Purification of dichloro-
methane and acetonitrile, and preparation of tetrabutylammonium
perchlorate (TBAP) for electrochemical work were performed as
reported in the literature.[20] Microanalyses (C, H, N) were per-
formed by using a Heraeus Carlo Erba 1108 elemental analyzer.
IR spectra were obtained with a Perkin–Elmer 783 spectrometer
with samples prepared as KBr pellets. Electronic spectra were re-
corded with a JASCO V-570 spectrophotometer. Magnetic suscep-
tibilities were measured by using a PAR 155 vibrating sample mag-
netometer fitted with a Walker scientific L75FBAL magnet. 1H
NMR spectra were recorded in CDCl3 solution with a Bruker drx
500 NMR spectrometer by using TMS as the internal standard.
Electrochemical measurements were done in dichloromethane/ace-
[Ru(PPh3)2(CO)(HLH)(H)]: This complex was prepared by follow-
ing the procedure for the preparation of [Ru(PPh3)2(CO)-
(HLCl)(H)] by using the H2LH ligand instead of H2LCl. Yield:
83 mg (75%). IR (KBr): ν = 1925 (νCO), 1860 (νH, overlapped with
˜
carbonyl stretch), 746 (νPPh ), 694 (νPPh ), 520 (νPPh ), 1586, 1563,
3
3
3
1519, 1301, 1095 cm–1. H NMR (300 MHz, CDCl3): δ = –4.57 (t,
J = 19.1 Hz, 1 H, hydride), 5.18 (s, 2 H, NH2), 6.30 (d, J = 9.0 Hz,
1 H), 6.60 (s, 1 H, azomethine proton), 6.73 (2 H)*, 7.25–7.70 (2
PPh3) ppm. C45H39N3OP2RuS (831.5): calcd. C 64.90, H 4.68, N
5.05; found C 64.91, H 4.66, N 5.00.
1
[Ru(PPh3)2(CO)(HLCH3)(H)]: This complex was prepared by fol-
lowing the procedure for the preparation of [Ru(PPh3)2(CO)-
(HLCl)(H)] by using the H2LCH3 ligand instead of H2LCl. Yield:
87 mg (77%). IR (KBr): ν = 1925 (νCO), 1860 (νH, overlapped with
˜
carbonyl stretch), 746 (νPPh ), 694 (νPPh ), 520 (νPPh ), 1586, 1564,
3
3
3
1519, 1301, 1095 cm–1. H NMR (300 MHz, CDCl3): δ = –4.61 (t,
J = 18.9 Hz, 1 H, hydride), 1.98 (s, 3 H, methyl), 5.19 (s, 2 H,
NH2), 6.27 (d, J = 8.9 Hz, 1 H), 6.59 (s, 1 H, azomethine proton),
1
6.67 (d,
J = 7.8 Hz, 1 H), 7.11–7.36 (2 PPh3) ppm.
C46H41N3OP2RuS (845.5): calcd. C 65.25, H 4.85, N 4.97; found C
65.24, H 4.85, N 4.97.
tonitrile (1:9) solution (0.1  TBAP) by using a CH Instruments [Ru(PPh3)2(CO)(HLOCH3)(H)]: This complex was prepared by
model 600A electrochemical analyzer. As the complexes have poor
solubility in acetonitrile, a little dichloromethane was initially em-
ployed to take them into solution. The presence of acetonitrile in
large excess was necessary for recording the redox responses in
proper shape, as the responses become distorted in pure dichloro-
methane solution. A platinum disc working electrode, a platinum
wire auxiliary electrode, and an aqueous saturated calomel refer-
ence electrode (SCE) were used in a three-electrode configuration.
Electrochemical measurements were made under a nitrogen atmo-
sphere. All electrochemical data were collected at 298 K and are
uncorrected for junction potentials.
following the procedure for the preparation of [Ru(PPh3)2-
(CO)(HLCl)(H)] by using the H2LOCH3 ligand instead of H2LCl.
Yield: 94 mg (82%). IR (KBr): ν = 1924 (νCO), 1860 (νH, over-
˜
lapped with carbonyl stretch), 746 (νPPh ), 694 (νPPh ), 520 (νPPh ),
3
3
1586, 1564, 1519, 1301, 1096 cm–1. 1H NMR (300 MHz, CDCl33):
δ = –4.60 (t, J = 8.0 Hz, 1 H, hydride), 3.10 (s, 3 H, methoxy), 5.19
(s, 2 H, NH2), 6.17 (d, J = 8.8 Hz, 1 H), 6.49 (s, 1 H, azomethine
proton), 6.60 (d, J = 8.4 Hz, 1 H), 7.01–7.26 (2 PPh3) ppm.
C46H42N3O2P2RuS (861.5): calcd. C 64.03, H 4.76, N 4.88; found
C 64.04, H 4.77, N 4.87.
General Procedure for the Preparation of [Ru2(PPh3)2(CO)2(LR)2]:
[Ru(PPh3)2(CO)(HLNO2)(H)]: To a solution of H2LNO2 (32 mg, [Ru(PPh3)2(CO)2Cl2] (100 mg, 0.14 mmol) and H2LR (0.14 mmol)
0.14 mmol) in ethanol (30 mL) was added [Ru(PPh3)2(CO)2Cl2]
(100 mg, 0.14 mmol), and the mixture was heated at reflux for 24 h
to afford a red solution. The solvent was then evaporated under
reduced pressure, and the solid mass thus obtained was purified by
thin-layer chromatography on a silica plate by using benzene as
the eluant. An orange band separated, which was extracted with
acetonitrile. Evaporation of the acetonitrile extract gave [Ru(PPh3)2-
(CO)(HLNO2)(H)] as an orange microcrystalline solid. Yield:
were taken up in toluene (30 mL). The mixture was heated at reflux
for 25 h to afford a yellow solution (brown in the case of R = NO2).
The solvent was then evaporated under reduced pressure, and the
solid mass obtained was purified by thin-layer chromatography on
a silica plate by using acetonitrile/benzene (1:10) as the eluant. A
yellow (purplish-brown in the case of R = NO2) band separated,
which was extracted with acetonitrile; evaporation of the acetoni-
trile extract afforded an orange (purplish-brown in the case of R =
NO2) crystalline solid.
93 mg (80%). IR (KBr): ν = 1925 (νCO), 1860 (νH, overlapped with
˜
4544
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© 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Inorg. Chem. 2008, 4538–4546

Variable Coordination Modes of Benzaldehyde Thiosemicarbazones
Table 3. Crystallographic data for [Ru (PPh3)2(CO)(HLNO2)(H)]·CH3CN and [Ru2(PPh3)2(CO)2(LCl)2]·2CH2Cl2.
[Ru (PPh3)2(CO)(HLNO2)(H)]·CH3CN
[Ru2(PPh3)2(CO)2(LCl)2]·2CH2Cl2
Empirical formula
Formula mass
Crystal system
Space group
A [Å]
b [Å]
c [Å]
C47H41N5O3P2SRu
918.92
C56H46Cl6N6O2P2S2Ru2
1375.89
monoclinic
P21/c
12.7896(4)
24.2852(7)
18.7290(5)
90
99.635(1)
90
5735.1(3)
4
triclinic
¯
P1
9.4870(15)
13.707(3)
17.923(4)
103.83(2)
99.911(15)
98.617(11)
2184.3(7)
2
α [°]
β [°]
γ [°]
V [Å3]
Z
λ [Å]
0.71073
0.40ϫ0.12ϫ0.08
293(2)
0.527
0.0639
0.1020
0.940
0.71073
0.40ϫ0.30ϫ0.30
150(1)
0.983
0.0351
0.0971
1.079
Crystal size [mm]
T [K]
µ [mm–1]
[a]
R1
[b]
wR2
GOF[c]
2
2 2
2
2 2
[a] R1 = Σ ||Fo| – |Fc||/Σ|Fo|. [b] wR2 = {Σ[w(Fo – Fc ) ]/Σ [w(Fo2)2]}1/2. [c] GOF = [Σ[w(Fo – Fc ) ]/(M – N)]1/2, where M is the number of
reflections and N is the number of parameters refined.
[Ru (PPh ) (CO) (LNO ) ]: Yield: 125 mg (77%). IR (KBr): ν =
lected crystal data and data collection parameters are given in
˜
2
3 2
2
2 2
1914 (νCO), 743 (νPPh ), 694 (νPPh ), 519 (νPPh ), 1480, 1432, 1307, Table 3. Data were collected with a SMART CCD diffractometer
3
3
3
1092 cm–1. H NMR (300 MHz, CDCl3): δ = 4.27 (s, 2 H, NH2), by using Mo-Kα (λ = 0.71073 Å) radiation. The data were corrected
1
6.83 (d, J = 6.0 Hz, 1 H), 7.23–7.46 (PPh3), 7.75 (s, 1 H, azomethine
proton) ppm. C54H42N8O6P2Ru2S2 (1227): calcd. C 52.85, H 3.43,
N 9.13; found C 52.86, H 3.42, N 9.13.
for absorption by using SADABS. X-ray data reduction, structure
solution, and refinement were done with the use of the SHELXS-
97 and SHELXL-97 packages.[22] Hydrogen atoms were placed geo-
metrically and positional parameters were refined by using a riding
model. The hydride was located from difference syntheses and re-
fined isotropically. The structure was solved by the direct methods.
[Ru (PPh ) (CO) (LCl ) ]: Yield: 123 mg (79%). IR (KBr): ν =
˜
2
3 2
2
2 2
1914 (νCO), 743 (νPPh ), 694 (νPPh ), 519 (νPPh ), 1480, 1433, 1307,
3
3
3
1092 cm–1. H NMR (300 MHz, CDCl3): δ = 3.80 (s, 2 H, NH2),
1
[Ru2(PPh3)2(CO)2(LCl)2]·2CH2Cl2: Single crystals were grown by
slow diffusion of hexane into a dichloromethane solution of the
complex. Selected crystal data and data collection parameters are
given in Table 3. Data were collected as above and semiempirical
absorption correction was performed by multiscan. X-ray data re-
duction, structure solution, and refinement were done as above.
6.56 (d, J = 6.1 Hz, 1 H), 6.84 (d, J = 6.0 Hz, 1 H), 7.16–7.29
(PPh3),
7.78
(s,
1
H,
azomethine
proton)
ppm.
C54H42Cl2N6O2P2Ru2S2 (1170.5): calcd. C 53.78, H 3.49, N 6.97;
found C 53.77, H 3.48, N 6.99.
[Ru (PPh ) (CO) (LH ) ]: Yield: 122 mg (80%). IR (KBr): ν =
˜
2
3 2
2
2 2
1914 (νCO), 743 (νPPh ), 694 (νPPh ), 519 (νPPh ), 1479, 1433, 1308,
3
3
3
1092 cm–1. H NMR (300 MHz, CDCl3): δ = 3.80 (s, 2 H, NH2),
6.44 (d, J = 6.2 Hz, 1 H), 6.85 (d, J = 5.9 Hz, 1 H), 7.12–7.28
(PPh3), 7.77 (s, 1 H, azomethine proton) ppm. C54H44N6O2P2Ru2S2
(1136): calcd. C 57.04, H 3.87, N 7.39; found C 57.00, H 3.88, N
7.40.
1
CCDC-683479 and -683480 contain the supplementary crystallo-
graphic 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.
Supporting Information (see footnote on the first page of this arti-
cle): Hydrogen-bonding parameters; composition of selected mo-
lecular orbitals for all complexes; electronic spectra of H2LCl in
ethanol and toluene; partial molecular orbital diagram of
[Ru2(PPh3)2(CO)2(LH)2]; cyclic voltammograms of [Ru(PPh3)2-
(CO)(HLH)(H)] and [Ru2(PPh3)2(CO)2(LCH3)2] and least-squares
plots of Epa values of ruthenium(II)–ruthenium(III) and rutheni-
um(III)–ruthenium(IV) couples vs. σ.
[Ru (PPh ) (CO) (LCH ) ]: Yield: 115 mg (75%). IR (KBr): ν =
˜
2
3 2
2
3 2
1914 (νCO), 743 (νPPh ), 694 (νPPh ), 519 (νPPh ), 1480, 1432, 1308,
3
3
3
1092 cm–1. 1H NMR (300 MHz, CDCl3): δ = 1.94 (s, 3 H, methyl),
4.04 (s, 2 H, NH2), 6.33 (d, J = 6.6 Hz, 1 H), 6.64 (s, 1 H), 6.73
(d, J = 6.2 Hz, 1 H), 7.20–7.43 (PPh3), 7.78 (s, 1 H, azomethine
proton) ppm. C56H48N6O2P2Ru2S2 (1150): calcd. C 57.73, H 4.12,
N 7.22; found C 57.74, H 4.11, N 7.24.
[Ru (PPh ) (CO) (LOCH ) ]: Yield: 121 mg (78%). IR (KBr): ν =
˜
2
3 2
2
3 2
Acknowledgments
1914 (νCO), 743 (νPPh ), 694 (νPPh ), 519 (νPPh ), 1481, 1433, 1307.6,
3
3
1091 cm–1. 1H NMR3(300 MHz, CDCl3): δ = 3.20 (3 H, methoxy),
4.04 (s, 2 H, NH2), 6.27 (d, J = 6.5 Hz, 1 H), 6.61 (s, 1 H), 6.70
(d, J = 6.0 Hz, 1 H), 7.20–7.43 (PPh3), 7.78 (s, 1 H, azomethine
proton) ppm. C56H48N6O4P2Ru2S2 (1166): calcd. C 56.19, H 4.01,
N 7.02; found C 56.20, H 4.00, N 7.01.
Financial assistance received from the Council of Scientific and
Industrial Research, New Delhi, India [Grant No. 01(1952)/04/
EMR-II] is gratefully acknowledged. The authors thank the refer-
ees for their critical comments and constructive suggestions, which
have been of great help in preparing the revised manuscript. Sincere
thanks are due to Professor S. Lahiri of the Department of Organic
X-ray Crystallography
[Ru(PPh3)2(CO)(HLNO2)(H)]·CH3CN: Single crystals were grown Chemistry, Indian Association for the Cultivation of Science, Kolk-
by slow evaporation of an acetonitrile solution of the complex. Se- ata, for her help. The authors also thank the Bose Institute, Kolk-
Eur. J. Inorg. Chem. 2008, 4538–4546
© 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
4545

S. Dutta, F. Basuli, A. Castineiras, S.-M. Peng, G.-H. Lee, S. Bhattacharya
FULL PAPER
[8] a) S. Bhattacharya, C. G. Pierpont, Inorg. Chem. 1991, 30,
1511; b) M. Menon, A. Pramanik, N. Bag, A. Chakravorty, J.
Chem. Soc., Dalton Trans. 1995, 1417; c) A. Pramanik, N. Bag,
G. K. Lahiri, A. Chakravorty, J. Chem. Soc., Dalton Trans.
1990, 3823.
[9] a) A. C. Skapski, P. G. H. Troughton, Chem. Commun. (Lon-
don) 1968, 1230; b) M. I. Bruce, J. Howard, I. W. Nowell, G.
Shaw, P. Woodward, J. Chem. Soc., Chem. Commun. 1972,
1041; c) L. D. Brown, S. D. Robinson, A. Sahajpal, J. A. Ibers,
Inorg. Chem. 1977, 16, 2728.
[10] a) S. K. Burley, G. A. Petsko, Science 1985, 229, 23; b) H. C.
Weiss, D. Blaser, R. Boese, B. M. Doughan, M. M. Haley,
Chem. Commun. 1997, 1703; c) N. N. L. Madhavi, A. K. Katz,
H. L. Carrell, A. Nangia, G. R. Desiraju, Chem. Commun.
1997, 1953; d) S. K. Burley, G. A. Petsko, Adv. Protein Chem.
1988, 39, 125; e) M. Nishio, M. Hirota, Y. Umezawa, The CH-π
Interactions (Evidence, Nature and Consequences), Wiley-VCH,
New York, 1998; f) Y. Umezawa, S. Tsuboyama, K. Honda, J.
Uzawa, M. Nishio, Bull. Chem. Soc. Jpn. 1998, 71, 1207; g)
G. R. Desiraju, T. Steiner, The Weak hydrogen Bond (IUCr
Monograph on Crystallography 9), Oxford Science Pub., 1999;
h) M. J. Hannon, C. L. Painting, N. W. Alcock, Chem. Com-
mun. 1999, 2023; i) B. J. Mcnelis, L. C. Nathan, C. J. Clark, J.
Chem. Soc., Dalton Trans. 1999, 1831; j) K. Biradha, C. Sew-
ard, M. J. Zaworotko, Angew. Chem. Int. Ed. 1999, 38, 492; k)
M. J. Calhorda, Chem. Commun. 2000, 801; l) C. Janiak, S.
Temizdemir, S. Dechert, Inorg. Chem. Commun. 2000, 3, 271;
m) C. Janiak, S. Temizdemir, S. Dechert, W. Deck, F. Girgsdies,
J. Heinze, M. J. Kolm, T. G. Scarmann, O. M. Zipffel, Eur. J.
Inorg. Chem. 2000, 1229; n) T. Steiner, Angew. Chem. Int. Ed.
2002, 41, 48; o) I. Dance, New J. Chem. 2003, 27, 22.
ata 700054, for NMR spectral measurements and the Central Drug
Research Institute, Lucknow for elemental analysis. S.D. thanks
CSIR for her fellowship [Grant No. 9/96(410)/2003-EMR-I].
[1] a) M. J. M. Campbell, Coord. Chem. Rev. 1975, 15, 279; b) S. B.
Padhye, G. B. Kaffman, Coord. Chem. Rev. 1985, 63, 127; c) I.
Haiduc, C. Silvestru, Coord. Chem. Rev. 1990, 99, 253; d) D. X.
West, S. B. Padhye, P. B. Sonawane, Struct. Bonding (Berlin)
1992, 76, 1; e) D. X. West, A. E. Liberta, S. B. Padhye, R. C.
Chikate, P. B. Sonawane, A. S. Kumbhar, R. G. Yerande, Co-
ord. Chem. Rev. 1993, 123, 49.
[2] a) F. A. French, E. Blanz Jr, J. Med. Chem. 1970, 13, 1117; b)
A. C. Sartorellic, K. C. Agrawal, A. S. Tsiftsoglou, A. C.
Moore, Adv. Enz. Reg. 1977, 15, 117; c) K. C. Agrawal, A. C.
Sartorelli, Prog. Med. Chem. 1978, 15, 321; d) J. P. Scovill,
D. L. Klayman, C. F. Franchino, J. Med. Chem. 1982, 25, 1261;
e) A. Kraker, S. Krezoski, J. Schneier, D. Mingel, H. Petering,
J. Biol. Chem. 1985, 260, 13710; f) A. E. Liberta, D. X. West,
Biometals 1992, 5, 121; g) D. Kovala-Demertzi, A. Domopau-
lou, M. A. Demertzis, C. P. Raptopoulou, A. Terzis, Polyhedron
1994, 13, 1917; h) A. Papageorgiou, Z. Iakovidou, D. Mourel-
atos, E. Mioglou, L. Boutis, A. Kotsis, D. Kovala-Demertzi,
D. X. Domopoulou, M. A. Demertzis, Anticancer Res. 1997,
17, 247; i) M. C. Miller III, C. N. Stineman, J. R. Vance, D. X.
West, I. H. Hall, Anticancer Res. 1998, 18, 4131; j) D. Kovala-
Demertzi, J. R. Miller, N. Kourkoumelis, S. K. Hajikakou,
M. A. Demertzis, Polyhedron 1999, 18, 1005; k) Z. Iakovidou,
A. Papageorgiou, M. A. Demertzis, E. Mioglou, D. Mourel-
atos, A. Kotsis, P. N. Yadav, D. Kovala-Demertzi, Anticancer
Drugs 2001, 12, 65.
[3] a) F. Basuli, S. M. Peng, S. Bhattacharya, Inorg. Chem. 1997, [11] A. Amoedo, M. Graña, J. Martínez, T. Pereira, M. López-
36, 5645; b) F. Basuli, M. Ruf, C. G. Pierpont, S. Bhattacharya,
Inorg. Chem. 1998, 37, 613; c) F. Basuli, S. M. Peng, S. Bhatta-
charya, Inorg. Chem. 2000, 39, 1120; d) I. Pal, F. Basuli,
T. C. W. Mak, S. Bhattacharya, Angew. Chem. Int. Ed. 2001,
40, 2923; e) S. Dutta, F. Basuli, S. M. Peng, G. H. Lee, S. Bhat-
tacharya, New J. Chem. 2002, 26, 4623.
Torres, A. Fernández, J. J. Fernández, J. M. Vila, Eur. J. Inorg.
Chem. 2002, 613.
[12] a) H. Yamazaki, K. Aoki, J. Organomet. Chem. 1976, C54, 122;
b) G. R. Clark, J. Organomet. Chem. 1977, 134, 51.
[13] T. S. Lobana, G. Bawa, A. Castineiras, R. J. Butcher, M. Zeller,
Organometallics 2008, 27, 175.
[14] Only one absorption in the ultraviolet region has been observed
in the [Ru(PPh3)2(CO)(HLNO2)(H)] complex.
[15] a) C. Mealli and D. M. Proserpio, CACAO Version 4.0, July,
1994, Firenze, Italy; b) C. Mealli, D. M. Proserpio, J. Chem.
Educ. 1990, 67, 399.
[16] J. G. Tojal, T. Rojo, Polyhedron 1999, 18, 1123.
[17] L. P. Hammett, Physical Organic Chemistry, 2nd ed., Mcgraw
Hill, New York, 1970.
[4] Y. P. Tion, C. Y. Duan, Z. L. Lu, X. Z. You, H. K. Fun, S.
Kandasamy, Polyhedron 1996, 15, 2263.
[5] a) A. Castineiras, E. Bermejo, D. X. West, A. K. EI-Sawaf,
J. K. Swearingen, Polyhedron 1998, 17, 275; b) A. Castineiras,
M. Gil, E. Bermejo, D. X. West, Z. Naturforsch., Teil B 2000,
55, 863; c) E. Bermejo, A. Castineiras, L. J. Ackerman, M. D.
Owens, D. X. West, Z. Allg. Anorg. Chem. 2001, 627, 1966; d)
C. A. Brown, W. Kaminsky, K. A. Claborn, K. I. Goldberg,
D. X. West, J. Brazilian Chem. Soc. 2002, 13, 10; e) D. Mishra,
S. Naskar, M. G. B. Drew, S. K. Chattopadhyay, Polyhedron
[18] R. N. Mukherjee, O. A. Rajan, A. Chakravorty, Inorg. Chem.
1982, 21, 785.
2005, 24, 1861; f) D. Mishra, S. Naskar, M. G. B. Drew, S. K. [19] A. Ahmed, S. D. Robinson, M. F. Uttley, J. Chem. Soc., Dalton
Chattopadhyay, Inorg. Chim. Acta 2006, 359, 585; g) T. S. Lob- Trans. 1972, 843.
ana, G. Bawa, A. Castineiras, R. J. Butcher, B. J. Liaw, C. W. [20] a) D. T. Sawyer, J. L. Roberts Jr, Experimental Electrochemistry
Liu, Polyhedron 2006, 25, 2897.
for Chemists, Wiley, New York, 1974, pp. 167–215; b) M. Wal-
ter, L. Ramaley, Anal. Chem. 1973, 45, 165.
[21] Chemical shifts are given in ppm and multiplicity of the signals
along with the associated coupling constants (J in Hz) are
given in parentheses. Overlapping signals are marked with an
asterisk.
[22] G. M. Sheldrick, SHELXS-97 and SHELXL-97, Fortran Pro-
grams for Crystal Structure Solution and Refinement, University
of Gottingen, 1997.
[6] F. Basuli, S. M. Peng, S. Bhattacharya, Inorg. Chem. 2001, 40,
1126.
[7] a) J. J. Levison, S. D. Robinson, J. Chem. Soc. A 1970, 2947; b)
R. Young, G. Wilkinson, Inorg. Synth. 1977, 17, 79; c) R. F.
Winter, F. M. Hornung, Inorg. Chem. 1997, 36, 6197; d) C. S.
Yi, S. Y. Yun, I. A. Guzei, Organometallics 2004, 23, 5392; e) T.
Li, R. Churlaud, A. J. Lough, K. Abdur-Rashid, R. H. Morris,
Organometallics 2004, 23, 6239; f) R. CelenligilCetin, L. A.
Watson, C. Guo, B. M. Foxman, O. V. Ozerov, Organometallics
2005, 24, 186.
Received: May 30, 2008
Published Online: August 29, 2008
4546
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Eur. J. Inorg. Chem. 2008, 4538–4546