Ruthenium(III) cyclometallates: Regioselective metallation of 1-pyrenyl in 1-pyrenaldehyde 4-R-benzoylhydrazones

Article abstract of DOI:10.1016/j.jorganchem.2013.03.040

Reactions of [Ru(PPh₃)₃Cl₂] with 1-pyrenaldehyde 4-R-benzoylhydrazones (H₂pnbhR, where R = H, Me, OMe, Cl and NO₂) in presence of NaOAc afford ortho-metallated ruthenium(III) complexes of formula trans-[Ru(pnbhR)(PPh₃) ₂Cl] (1-5). The complexes have been characterized by elemental analysis, magnetic susceptibility, spectroscopic (IR, UV-vis and EPR) and cyclic voltammetric measurements. Molecular structure of 2 (R = Me) determined by single crystal X-ray crystallography shows a distorted octahedral CNOClP ₂ coordination sphere around the trivalent metal centre assembled by the 1-pyrenyl ortho-C, azomethine-N and amidate-O donor pnbhMe^2-, two mutually trans PPh₃ and the chloride. Electronic spectra of 1-5 in dichloromethane display several strong bands within 555-276 nm due to ligand to metal charge transfer and ligand centred transitions. The complexes are one-electron paramagnetic (μ_eff = 1.90-1.99 μ_B) and display rhombic EPR spectra in frozen (130 K) dichloromethane-toluene (1:1). Cyclic voltammograms of the complexes in dimethylformamide display a ligand substituent sensitive metal centred one electron reduction couple in the E _1/2 range -0.24 to -0.31 V (vs. Ag/AgCl).

Full text of DOI:10.1016/j.jorganchem.2013.03.040

Journal of Organometallic Chemistry 737 (2013) 7e11
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Journal of Organometallic Chemistry
journal homepage: www.elsevier.com/locate/jorganchem
Ruthenium(III) cyclometallates: Regioselective metallation of 1-pyrenyl in
1-pyrenaldehyde 4-R-benzoylhydrazones
*
Koppanathi Nagaraju, Samudranil Pal
School of Chemistry, University of Hyderabad, Hyderabad 500 046, India
a r t i c l e i n f o
a b s t r a c t
Article history:
Reactions of [Ru(PPh3)3Cl2] with 1-pyrenaldehyde 4-R-benzoylhydrazones (H2pnbhR, where R ¼ H, Me,
OMe, Cl and NO2) in presence of NaOAc afford ortho-metallated ruthenium(III) complexes of formula trans-
[Ru(pnbhR)(PPh3)2Cl] (1e5). The complexes have been characterized by elemental analysis, magnetic sus-
ceptibility, spectroscopic (IR, UVevis and EPR) and cyclic voltammetric measurements. Molecular structure
of 2 (R ¼ Me) determined by single crystal X-ray crystallography shows a distorted octahedral CNOClP2
coordination sphere around the trivalent metal centre assembled by the 1-pyrenyl ortho-C, azomethine-N
and amidate-O donor pnbhMe2ꢀ, two mutually trans PPh3 and the chloride. Electronic spectra of 1e5 in
dichloromethane display several strong bands within 555e276 nm due to ligand to metal charge transfer
and ligand centred transitions. The complexes are one-electron paramagnetic (meff ¼ 1.90e1.99 mB) and
display rhombic EPR spectra in frozen (130 K) dichloromethaneetoluene (1:1). Cyclic voltammograms of the
complexes in dimethylformamide display a ligand substituent sensitive metal centred one electron reduc-
tion couple in the E1/2 range ꢀ0.24 to ꢀ0.31 V (vs. Ag/AgCl).
Received 1 March 2013
Received in revised form
20 March 2013
Accepted 21 March 2013
Keywords:
Ruthenium(III)
1-Pyrenaldehyde
Aroylhydrazone
Ortho-metallation
Crystal structure
Redox activity
Ó 2013 Elsevier B.V. All rights reserved.
1. Introduction
on the ruthenium coordination chemistry with 1-pyrenaldehyde 4-
R-benzoylhydrazones (H2pnbhR). The objectives were to explore the
Compared to the vast literature on ruthenium(II) complexes
having MeC bond [1e7], ruthenium(III) complexes of that kind are a
handful [8e27]. For the past few years we have been working on
cyclometallated palladium and ruthenium complexes with aroyl-
hydrazones of various monocyclic and polycyclic aromatic aldehydes
[26e32]. It has been found that this pincer like [32e35] aryl-C,
azomethine-N and amidate-O donor ligand system is very efficient
to stabilize ruthenium not only in the trivalent state but also makes
its tetravalent state accessible [26,27]. The aroylhydrazones of
benzaldehyde and acetophenone can afford only ortho-metallated
complexes [26e29]. On the other hand, aroylhydrazones of poly-
cyclic aromatic aldehydes provide both ortho and peri positions of
the polycyclic aryl moiety as the potential metallation site depending
upon the position of the azomethine functionality on it [30e32].
Recently we have reported some cyclopalladated complexes with
aroylhydrazones of indole-3-aldehyde and 4-R-1-naphthaldehydes
[30,32]. In each type of complexes, the tridentate ligand forms 6,5-
membered fused chelate rings due to regioselective peri pallada-
tion of its polycyclic aryl (indole-3 and 1-naphthalenyl) fragment. In
the present work, we have reported the results in our investigation
possibility of CeH activation and formation of cyclometallated spe-
cies, stabilization of ruthenium(III) and regioselective metallation of
the 1-pyrenyl moiety if any. In this effort, we have isolated a series
of ortho-metallated ruthenium(III) complexes of formula trans-
[Ru(pnbhR)(PPh3)2Cl] (Chart 1). In the following account, we have
described synthesis, characterization and physical properties of
these complexes. X-ray crystal structure of one representative
complex has been also reported.
2. Experimental
2.1. Materials
[Ru(PPh3)3Cl2] was prepared by following a reported procedure
[36]. All other chemicals were of analytical grade available
commercially and were used as supplied without further purifica-
tion. The solvents used were purified by following standard
methods [37].
2.2. Physical measurements
Microanalyses (C, H, N) were performed by using a Thermo
Finnigan Flash EA1112 series elemental analyzer. Magnetic sus-
ceptibilities were measured with the help of a Sherwood scientific
* Corresponding author. Tel.: þ91 40 2313 4829; fax: þ91 40 2301 2460.
E-mail addresses: spsc@uohyd.ernet.in, spscuh2000@yahoo.co.in (S. Pal).
0022-328X/$ e see front matter Ó 2013 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.jorganchem.2013.03.040

8
K. Nagaraju, S. Pal / Journal of Organometallic Chemistry 737 (2013) 7e11
band eluted with dichloromethane/n-hexane (2:3) was discarded.
The following red band containing the complex (1) was eluted
using the same dichloromethane/n-hexane mixture but in the ratio
3:2. The red solution thus obtained was evaporated to dryness and
the complex was collected as a dark red solid. The yield was 140 mg
(62%).
The other four complexes 2e5 having the general formula
[Ru(pnbhR)(PPh3)2Cl] (2 (R ¼ Me), 3 (R ¼ OMe), 4 (R ¼ Cl) and 5
(R ¼ NO2)) were synthesized in 56e64% yield using [Ru(PPh3)3Cl2],
NaOAc and the corresponding Schiff bases (in 1:2:1 mole ratio) by
following procedures very similar to that described above for 1
(R ¼ H).
2.5. X-ray crystallography
Single crystals of [Ru(pnbhMe)(PPh3)2Cl] (2) were grown by
slow evaporation of its dichloromethaneeacetonitrile (1:1) solu-
tion. Unit cell parameters and intensity data at 298 K were obtained
on an Oxford Diffraction Xcalibur Gemini single crystal X-ray
Chart 1. The chemical structure diagrams of the Schiff base system 1-pyrenaldehyde
4-R-benzoylhydrazone (H2pnbhR, where R ¼ H, Me, OMe, Cl and NO2) and the com-
plex with it (trans-[Ru(pnbhR)(PPh3)2Cl]).
diffractometer fitted with graphite monochromated Mo K
a
radia-
ꢀ
tion (
l
¼ 0.71073 A). The CrysAlisPro software [39] was used for
data collection, reduction and absorption correction. The structure
was solved by direct method and refined on F2 by full-matrix least-
squares procedures. All non-hydrogen atoms were refined with
anisotropic thermal parameters. A riding model was used to
include the hydrogen atoms in the structure factor calculations. The
SHELX-97 programs [40] provided in the WinGX package [41] were
used for structure solution and refinement. The Platon [42] and the
Mercury [43] packages were used for molecular graphics. Selected
crystallographic data are summarized in Table 1.
balance. Diamagnetic corrections calculated from Pascal’s constants
[38] were used to obtain the molar susceptibilities. A Digisun DI-
909 conductivity meter was used to measure the solution elec-
trical conductivities. The infrared spectra were obtained by using
KBr pellets on a Jasco-5300 FT-IR spectrophotometer. A Shimadzu
LCMS 2010 liquid chromatograph mass spectrometer was used for
the purity verification of the Schiff bases. The electronic spectra
were recorded on a Cary 100 Conc UV/vis spectrophotometer. A Jeol
JES-FA200 spectrometer was used to record the X-band EPR
spectra. The NMR spectra were obtained with the help of a Bruker
400 MHz NMR spectrometer. A CH-Instruments model 620A elec-
trochemical analyzer was used for cyclic voltammetric experiments
with dimethylformamide solutions of the complexes containing
tetrabutylammonium perchlorate (TBAP) as the supporting elec-
trolyte. The three electrode measurements were carried out at
298 K under dinitrogen atmosphere with a platinum disk working
electrode, a platinum wire auxiliary electrode and a Ag/AgCl
reference electrode. Under identical condition the E1/2 value of the
Fcþ/Fc couple was observed at 0.42 V.
3. Results and discussion
3.1. Synthesis and characterization
The Schiff bases H2pnbhR (R ¼ H, Me, OMe, Cl and NO2) were
obtained in very good yields (w90%) in the condensation reactions
of 1-pyrenaldehyde and the corresponding 4-R-benzoylhydrazines
in 1:1 mole ratio in ethanol. The identity and structures of the Schiff
bases were established by elemental analysis and spectroscopic
(infrared, electronic, mass and 1H NMR) measurements. These
characterization data are given in Tables S1 and S2 (Supplementary
material). Reactions of [Ru(PPh3)3Cl2], the corresponding H2pnbhR
and NaOAc in 1:1:2 mole ratio in methanol under aerobic
2.3. Synthesis of H2pnbhH
Benzoylhydrazine (177 mg, 1.3 mmol) was added to an ethanol
solution (20 ml) of 1-pyrenaldehyde (300 mg, 1.3 mmol). The
mixture was boiled under reflux for 3 h and then cooled to room
temperature. The pale yellow solid separated was collected by
filtration, washed with ethanol and finally dried in air. The yield
was 420 mg (92%).
The same procedure described above was used for the synthesis
of each of the four remaining Schiff bases (H2pnbhMe, H2pnbhOMe,
H2pnbhCl and H2pnbhNO2) in w90% yield from 1 mol equiv each
of 1-pyrenaldehyde and the corresponding 4-substituted
benzoylhydrazine.
Table 1
Selected crystallographic data for trans-[Ru(pnbhMe)(PPh3)2Cl] (2).
Empirical formula
Formula weight
Crystal system
Space group
RuC61H46N2OP2Cl
1021.46
Monoclinic
P21/c
15.0653(4)
14.8940(4)
22.3055(5)
94.404(2)
4990.2(2)
4
ꢀ
a (A)
ꢀ
b (A)
ꢀ
c (A)
b
(ꢁ)
3
ꢀ
V (A )
Z
r
2.4. Synthesis of [Ru(pnbhH)(PPh3)2Cl] (1)
(g cmꢀ3
(mmꢀ1
)
)
1.360
0.476
m
Reflections collected
Reflections unique
18,056
8773
6451
614
0.0434, 0.0926
0.0688, 0.1046
1.032
0.594 and ꢀ0.356
Solid [Ru(PPh3)3Cl2] (200 mg, 0.21 mmol) was added to a
methanol solution (30 ml) of H2pnbhH (73 mg, 0.21 mmol) and
NaOAc (35 mg, 0.43 mmol). The mixture was refluxed for 30 min
and then cooled to room temperature. The red solid deposited was
collected by filtration and dried in air. This material was dissolved
in minimum amount of dichloromethane and transferred to a silica
gel column packed with dichloromethane. The first moving yellow
Reflections (I ꢂ 2
s(I))
Parameters
R1, wR2 (I ꢂ 2
s
(I))
R1, wR2 (all data)
GOF (F2)
ꢀꢀ3
Largest diff. peak and hole (e A
)

K. Nagaraju, S. Pal / Journal of Organometallic Chemistry 737 (2013) 7e11
9
Table 2
Elemental analysis, electronic spectroscopica and effective magnetic moments.b
Complex
Found (calc) (%)
C
lmax (nm) (10ꢀ4
ꢃ
3
(Mꢀ1 cmꢀ1))
meff (mB)
H
N
1
2
3
4
5
71.38 (71.51)
71.56 (71.71)
70.81 (70.61)
68.95 (69.15)
68.57 (68.45)
4.51 (4.40)
4.61 (4.54)
4.41 (4.47)
4.23 (4.16)
4.18 (4.12)
2.71 (2.78)
2.65 (2.74)
2.65 (2.70)
2.61 (2.69)
3.86 (3.99)
535c (0.51), 501 (0.57), 447 (1.47), 421 (1.22), 369 (1.77), 276 (2.78)
1.99
1.98
1.90
1.93
1.97
536c (0.50), 500 (0.56), 446 (1.44), 420 (1.19), 369 (1.73), 313c (1.65), 279 (2.32)
537c (0.47), 497 (0.57), 445 (1.37), 419 (1.15), 370 (1.65), 312c (1.65), 279 (2.37)
537c (0.50), 500 (0.58), 449 (1.44), 423 (1.21), 370 (1.68), 312c (1.66), 279 (2.18)
555c (0.51), 518 (0.55), 452 (1.05), 409c (1.15), 371 (1.41), 280 (2.30)
a
In dichloromethane.
In powder phase at 298 K.
Shoulder.
b
c
conditions produce red coloured complexes of formula trans-
[Ru(pnbhR)(PPh3)2Cl] (1e5) in 56e64% yield. The elemental anal-
ysis data (Table 2) of the complexes are in good agreement with the
above general molecular formula. All of 1e5 are one-electron
paramagnetic. The room temperature (298 K) magnetic moments
are within 1.90e1.99 mB. These values suggest the low-spin trivalent
oxidation state of ruthenium in each of 1e5. In all probability the
oxygen in air oxidizes the metal centre during the synthesis of the
complexes from [Ru(PPh3)3Cl2]. All the complexes are highly solu-
ble in dichloromethane, chloroform, dimethylsulfoxide and dime-
thylformamide and provide red solutions. In solution, they behave
as non-electrolyte.
Electronic spectral profiles of 1e5 obtained using the corre-
sponding dichloromethane solutions are very similar. The spectral
data are listed in Table 2. A representative spectrum is shown in
Fig. 1. The complexes display several strong to very strong absorp-
tions in thewavelength range555e276 nm. The electronic spectra of
all the Schiff bases (H2pnbhR) in dichloromethane were also recor-
ded for comparison. The spectra of H2pnbhR are also very similar
and display two groups of intense absorptions centred at w370 and
w285 nm (Table S1). The spectrum of H2pnbhH is shown in Fig. 1.
Below 400 nm the spectral profiles of the complexes are somewhat
similar to those of the Schiff bases. Thus the absorptions observed
above 400 nm for 1e5 are assigned to ligand-to-metal charge
transfer transitions and the absorptions observed below 400 nm are
primarily due to ligand centred transitions [20e22,25e27].
3.2. Spectroscopic properties
The one-electron paramagnetic complexes are EPR active. All the
complexes in dichloromethaneetoluene (1:1) solution display an
isotropic spectrum with g z 2.12 at room temperature (298 K).
However, the spectra of 1e5 in frozen (130 K) solution show three
distinct EPR signals. The spectrum of 3 is illustrated in Fig. 2 and the
g-values for all five complexes are listed in Table 3. Such EPR spectra
are typical of rhombically distorted octahedral low-spin ruth-
enium(III) species [11,14,18,20e23,26,27]. Considering the type of
ligands in each of these quaternary complexes (1e5) and hence the
stereochemistry of the molecule, rhombic distortion of the coordi-
nation sphere around the metal centre from ideal octahedral ge-
ometry is quite anticipated. The molecular structure of trans-
[Ru(pnbhMe)(PPh3)2Cl] (2) determined by X-ray crystallography
(vide infra) corroborates the observed EPR characteristics.
Infrared spectra of the Schiff bases and the complexes (1e5)
were recorded using KBr pellets. The Schiff bases display the NeH
and C]O stretches of the amide functionality in the ranges 3222e
3162 and 1663e1633 cmꢀ1, respectively. A medium to strong band
observed within 1605e1592 cmꢀ1 is assigned to the C]N
stretching vibration of the Schiff bases. Complexes 1e5 do not
display any band associated with the amide NeH and C]O groups.
Thus the amide functionality of the tridentate ligand (pnbhR2ꢀ) is
deprotonated in the complexes. A medium intensity band observed
in the range 1582e1574 cmꢀ1 for 1e5 is attributed to the metal
coordinated C]N stretching vibration of pnbhR2ꢀ. Each of 1e5
shows three strong bands at w743, w693 and w17 cmꢀ1 typical of
metal bound PPh3 [20e22,25e27].
Fig. 1. Electronic spectra of H2pnbhH (---) and trans-[Ru(pnbhH)(PPh3)2Cl] (1) (e) in
dichloromethane.
Fig. 2. X-band EPR spectrum of trans-[Ru(pnbhOMe)(PPh3)2Cl] (3) in frozen (130 K)
dichloromethaneetoluene (1:1) solution.

10
K. Nagaraju, S. Pal / Journal of Organometallic Chemistry 737 (2013) 7e11
Table 3
Table 4
EPRa and cyclic voltammetricb data.
Selected bond lengths (A) and angles ( ) for trans-[Ru(pnbhMe)(PPh3)2Cl] (2).
ꢁ
ꢀ
Complex
g1
g2
g3
E1/2 (V) (
D
Ep (mV))c
RueC(1)
RueO
RueP(1)
2.048(3)
2.132(2)
2.4030(9)
77.38(11)
106.58(9)
92.39(9)
173.84(8)
87.49(7)
84.10(6)
93.47(3)
178.01(3)
RueN(1)
RueCl
RueP(2)
C(1)eRueO
C(1)eRueP(1)
N(1)eRueO
N(1)eRueP(1)
OeRueCl
2.025(3)
2.3651(8)
2.3941(9)
150.65(11)
88.89(9)
74.34(9)
91.30(7)
102.27(6)
94.04(6)
87.63(3)
1
2
3
4
5
2.36
2.36
2.35
2.36
2.36
2.09
2.09
2.09
2.10
2.09
1.95
1.96
1.96
1.95
1.95
ꢀ0.28 (90)
ꢀ0.29 (100)
ꢀ0.31 (90)
ꢀ0.27 (90)
ꢀ0.24 (130)
C(1)eRueN(1)
C(1)eRueCl
C(1)eRueP(2)
N(1)eRueCl
N(1)eRueP(2)
OeRueP(1)
CleRueP(1)
P(1)eRueP(2)
a
In frozen (130 K) dichloromethaneetoluene (1:1).
In dimethylformamide.
E1/2 ¼ (Epa þ Epc)/2 and
b
c
OeRueP(2)
CleRueP(2)
D
Ep ¼ Epa ꢀ Epc, where Epa and Epc are anodic and
cathodic peak potentials, respectively.
3.4. Electron transfer properties
3.3. X-ray structure of trans-[Ru(pnbhMe)(PPh3)2Cl] (2)
Electron transfer behaviour of 1e5 was studied using cyclic vol-
tammetry. All the complexes in dimethylformamide display a
reduction response on the cathodic side of Ag/AgCl reference elec-
The X-ray molecular structure of trans-[Ru(pnbhMe)(PPh3)2Cl]
(2) is depicted in Fig. 3. All the bond lengths and angles involving
the metal centre and the coordinating atoms are listed in Table 4.
These bond parameters indicate a distorted octahedral CNOP2Cl
coordination sphere around the ruthenium atom. The meridionally
spanning pnbhMe2ꢀ coordinates the metal centre through the 1-
pyrenyl ortho-C, the azomethine-N and the amidate-O atoms and
forms 5,5-fused chelate rings. The chlorine atom completes a
CNOCl square-plane around the metal centre and the two PPh3
molecules occupy the two axial positions. Both bite angles
(77.38(11)ꢁ and 74.34(9)ꢁ) in the 5,5-fused chelate rings of 2 are
comparable with those reported for trivalent ruthenium complexes
containing similar fused chelate rings formed by C,N,O-donor
pincer like ligands [11,22,26,27]. The remaining cis angles are in
the range 84.10(6)ꢁe106.58(9)ꢁ. The P(1)eRueP(2) angle
(178.01(3)ꢁ) formed by the two mutually trans PPh3 molecules is
very close to the ideal value, while trans N(1)eRueCl angle
(173.84(8)ꢁ) is somewhat shorter than that. In contrast, due
to steric requirement the trans C(1)eRueO angle (150.65(11)ꢁ)
formed by the two ends of the C,N,O-donor pnbhMe2ꢀ is signifi-
cantly shorter than 180ꢁ. The two very similar trans oriented RueP
bond lengths are somewhat longer than the RueCl bond length but
significantly longer than the bond lengths between the metal
centre and the coordinating atoms from pnbhMe2ꢀ (Table 4). On the
whole, the Ru to the aryl-C, the azomethine-N, the amidate-O and
the Cl-atom bond lengths and the two RueP bond lengths are
within the ranges observed for ruthenium(III) complexes having
similar coordinating atoms [11,22,23,26,27].
trode. The E1/2 values are within ꢀ0.24 to ꢀ0.31 V and the
DEp values
span the range 90e130 mV (Table 3). The cyclic voltammogram of 4 is
illustrated in Fig. 4. The one electron nature of this reduction
response has been inferred by comparing the current heights with
known one electron transfer processes under identical condition
[26,27]. The trend in the E1/2 values of this reduction reflects the ef-
fect of the electronic nature of the substituent (R) on the aroyl frag-
ment of pnbhR2ꢀ. There is a satisfactory linear relationship between
the E1/2 values and the Hammett constants [44] of the substituents
(Fig. 4). The free Schiff bases do not display any such response in this
potential range under identical condition. Thus the electron transfer
process observed for 1e5 is assigned to the ruthenium(III)eruth-
enium(II) reduction couple. Our previously reported cyclometallated
complexes of trans-{Ru(PPh3)2Cl}2þ with aroylhydrazones of benz-
aldehyde display only a metal centred oxidation couple within 0.35e
0.58 V [26], while analogous complexes with aroylhydrazones of
acetophenone display both reduction (ꢀ0.66 to ꢀ0.70 V) and
oxidation (0.75e0.80 V) of the metal centre [27]. In these complexes,
C11
P2
C12
C14
C15
C4 C5
C9
C17
C24
C23
N2
C10
N1
C16
C13
C3
C22
C18
O
C8
C25
C19
Ru
C1
C20
C6
C7
C21
Cl
C2
P1
Fig. 3. X-ray molecular structure of trans-[Ru(pnbhMe)(PPh3)2Cl] (2) with the atom
labelling schemes. Carbon atoms of the PPh3 molecules are not labelled for clarity. All
non-hydrogen atoms are represented by their 40% probability thermal ellipsoids.
Fig. 4. Cyclic voltammogram of trans-[Ru(pnbhCl)(PPh3)2Cl] (4) in dimethylformamide
(0.1 M TBAP) 298 K. Inset: linear correlation between the E1/2 and the Hammett sub-
stituent constant (s).

K. Nagaraju, S. Pal / Journal of Organometallic Chemistry 737 (2013) 7e11
11
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amidate-O donor, while pnbhR2ꢀ uses the ortho-C of 1-pyrenyl
together with the azomethine-N and the amidate-O to bind the
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4. Conclusion
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A
series of cycloruthenated complexes, trans-[Ru(pnbhR)
(PPh3)2Cl] (H2pnbhR ¼ 1-pyrenaldehyde 4-R-benzoylhydrazone
(R ¼ H, Me, OMe, Cl and NO2)) is reported. The magnetic moments
and the EPR spectra are consistent for trivalent state of the metal ion
in these complexes. X-ray structure of trans-[Ru(pnbhMe)(PPh3)2Cl]
reveals an unsymmetrical pincer like coordination mode of
pnbhMe2ꢀ through the 1-pyrenyl ortho-C, the azomethine-N and
the amidate-O. Very similar spectroscopic and electron transfer
properties suggest the same coordination mode of pnbhR2ꢀ in all the
complexes. Thus regioselective ortho-metallation over peri-metal-
lation of the 1-pyrenyl fragment of pnbhR2ꢀ and hence formation of
5,5- instead of 6,5-fused chelate rings at the trivalent ruthenium is
preferred in the present series of cycloruthenates.
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Financial support for this work has been received from the
Department of Science and Technology (DST) (IYC Grant No. IR/S1/
CF-01E/2011). K. Nagaraju thanks the Council of Scientific and In-
dustrial Research (CSIR) for a research fellowship. We are thankful to
the DST and the University Grants Commission (UGC) for the facil-
ities provided under the FIST and the CAS programs, respectively.
Appendix A. Supplementary material
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Utrecht, The Netherlands, 2002.
CCDC 924431 (for trans-[Ru(pnbhMe)(PPh3)2Cl] (2)) contains
the supplementary crystallographic data for this paper. These data
can be obtained free of charge from The Cambridge Crystallo-
graphic Data Centre via www.ccdc.cam.ac.uk/data_request/cif.
Supplementary data (Tables S1 and S2) associated with this
article can be found in the online version, at http://dx.doi.org/10.
1016/j.jorganchem.2013.03.040.
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