Ortho-ruthenation of 1-naphthalenyl in 1-naphthaldehyde 4-R-benzoylhydrazones: Ruthenium(III) CNO pincer complexes

Article abstract of DOI:10.1016/j.jorganchem.2013.08.024

In methanol, reactions of [Ru(PPh₃)₃Cl₂], 1-naphthaldehyde 4-R-benzoylhydrazones (H₂nabhR, where R = H, Me, OMe, Cl and NO₂) and NaOAc in 1:1:2 mol ratio provide ortho-metallated ruthenium(III) complexes of general formula trans-[Ru(nabhR)(PPh₃)₂Cl] (1-5) in 50-58% yields. Elemental analysis, magnetic susceptibility, spectroscopic (IR, UV-Vis and EPR) and cyclic voltammetric measurements were used to characterize the complexes. Single crystal X-ray structures of 1 (R = H), 2 (R = Me) and 5 (R = NO ₂) show pincer like coordination mode of nabhR^2-. The 1-naphthalenyl ortho-C, the azomethine-N and the amidate-O donor nabhR ^2-, two mutually trans PPh₃ and the chloride assemble a distorted octahedral trans-CNOClP₂ coordination sphere around the trivalent metal centre. In the electronic spectra, dichloromethane solutions of 1-5 display multiple strong bands within 506-272 nm due to ligand to metal charge transfer and intraligand transitions. The room temperature (298 K) magnetic moments (μ_eff) of 1-5 are within 1.92-1.99 μ_B and they display rhombic EPR spectra in frozen (130 K) dichloromethane-toluene (1:1). Cyclic voltammetry with dimethylformamide solutions of the complexes reveals ligand substituent sensitive Ru(III) → Ru(II) reduction and Ru(III) → Ru(IV) oxidation in the potential ranges -0.27 to -0.36 V and 0.94-1.13 V (vs. Ag/AgCl), respectively.

Full text of DOI:10.1016/j.jorganchem.2013.08.024

Journal of Organometallic Chemistry 745-746 (2013) 404e408
Contents lists available at ScienceDirect
Journal of Organometallic Chemistry
journal homepage: www.elsevier.com/locate/jorganchem
Ortho-ruthenation of 1-naphthalenyl in 1-naphthaldehyde
4-R-benzoylhydrazones: Ruthenium(III) CNO pincer complexes
*
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:
In methanol, reactions of [Ru(PPh3)3Cl2], 1-naphthaldehyde 4-R-benzoylhydrazones (H2nabhR, where
R ¼ H, Me, OMe, Cl and NO2) and NaOAc in 1:1:2 mol ratio provide ortho-metallated ruthenium(III)
complexes of general formula trans-[Ru(nabhR)(PPh3)2Cl] (1e5) in 50e58% yields. Elemental analysis,
magnetic susceptibility, spectroscopic (IR, UVeVis and EPR) and cyclic voltammetric measurements were
used to characterize the complexes. Single crystal X-ray structures of 1 (R ¼ H), 2 (R ¼ Me) and 5
(R ¼ NO2) show pincer like coordination mode of nabhR2ꢀ. The 1-naphthalenyl ortho-C, the azomethine-
N and the amidate-O donor nabhR2ꢀ, two mutually trans PPh3 and the chloride assemble a distorted
octahedral trans-CNOClP2 coordination sphere around the trivalent metal centre. In the electronic
spectra, dichloromethane solutions of 1e5 display multiple strong bands within 506e272 nm due to
ligand to metal charge transfer and intraligand transitions. The room temperature (298 K) magnetic
moments (meff) of 1e5 are within 1.92e1.99 mB and they display rhombic EPR spectra in frozen (130 K)
dichloromethaneetoluene (1:1). Cyclic voltammetry with dimethylformamide solutions of the com-
plexes reveals ligand substituent sensitive Ru(III) / Ru(II) reduction and Ru(III) / Ru(IV) oxidation in
the potential ranges ꢀ0.27 to ꢀ0.36 V and 0.94e1.13 V (vs. Ag/AgCl), respectively.
Received 29 May 2013
Received in revised form
8 August 2013
Accepted 12 August 2013
Keywords:
Ruthenium(III)
1-Naphthaldehyde
4-R-Benzoylhydrazone
Ortho-ruthenation
Crystal structure
Redox activity
Ó 2013 Elsevier B.V. All rights reserved.
1. Introduction
fused chelate rings at the palladium(II) centre. Recently we have re-
portedaseriesofcycloruthenatedcomplexesofgeneralformulatrans-
Cyclometallates and metallacycles of transition metal ions are of
immense contemporary interest because of their catalytic applica-
tions in a wide range of organic transformation reactions as well as
their potential use as different types of functional materials [1]. We
have been working on cyclometallated complexes with Schiff bases
derived from various mono- and polycyclic aromatic aldehydes and
acid hydrazides for the past several years [2e8]. These deprotonated
acid hydrazones act as CNO pincer like ligands [9e11] in their com-
plexes. The acid hydrazones of benzaldehyde and acetophenone
provide only the ortho-C of the PheC(R)]Ne (R ¼ H or Me) for
metallationandaffordCNO5,5-memberedpincercomplexes[2e5]. In
contrast, depending upon the position of the azomethine function-
ality in acid hydrazones of polycyclic aromatic aldehydes both ortho
and peri positions of the polycyclic aryl moiety may be available as the
potential metallation site [6e8,12]. Earlier we have found that palla-
dation occurs in a regioselective manner at the peri position of the
polycyclic aryl (indole-3 and 1-naphthalenyl) fragment of the acid
hydrazonesofindole-3-aldehydeand4-R-1-naphthaldehydes [6,8]. In
eachof thesecyclopalladates,thedibasicCNO-donorligandforms6,5-
[Ru(pnbhR)(PPh3)2Cl] with 1-pyrenaldehyde 4-R-benzoylhydrazones
(H2pnbhR)[12]. Interestinglyinthesecomplexes,regioselectiveortho-
ruthenation instead of peri-ruthenation of 1-pyrenyl moiety of
(pnbhR)2ꢀ is favoured. As a result, CNO-donor (pnbhR)2ꢀ forms 5,5-
rather than 6,5-fused chelate rings at the ruthenium(III) centre. The
presentworkoriginatesfromourinvestigationtofindoutwhetherthe
ruthenation of the bicyclic aromatic fragment of 1-naphthaldehyde 4-
R-benzoylhydrazone (H2nabhR) occurs at peri position as observed in
its palladium(II) complex [8]orat orthopositionasfoundfor1-pyrenyl
in the ruthenium(III) complexes of (pnbhR)2ꢀ [12]. Herein we report
the synthesis, physical properties and structures of a series of ruth-
enium(III) cyclometallates of the general formula trans-[Ru(n-
abhR)(PPh3)2Cl] where the 1-naphthalenyl fragment of (nabhR)2ꢀ is
ortho-metallated (Scheme 1).
2. Experimental
2.1. Materials
The Schiff bases (H2nabhR) were prepared from ethanol me-
dium in 80e90% yields by condensing 1 mol equivalent of 1-
* Corresponding author. Tel.: þ91 40 2313 4829; fax: þ91 40 2301 2460.
E-mail address: spal@uohyd.ac.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.2013.08.024

K. Nagaraju, S. Pal / Journal of Organometallic Chemistry 745-746 (2013) 404e408
405
grown by slow evaporation of the corresponding dichloromethane-
acetonitrile (1:1) solutions. 1 crystallizes as it is, while the other
two complexes crystallize as 2$0.5CH3CN and 5$1.5CH3CN. An Ox-
ford Diffraction Xcalibur Gemini single crystal X-ray diffractometer
equipped with graphite monochromated Mo
K
a
radiation
ꢀ
(l
¼ 0.71073 A) was used for determination of the unit cell pa-
rameters and intensity data collection at 298 K for all the three
complexes. The CrysAlisPro software [15] was used for data
collection, reduction and absorption correction. In each case, the
structure was solved by direct method and refined on F2 by full-
matrix least-squares procedures. All non-hydrogen atoms with
full occupancy were refined anisotropically. In 2$0.5CH3CN and
5$1.5CH3CN, the non-hydrogen atoms of the partial occupancy
solvent molecules were refined isotropically with geometrical re-
straints. Hydrogen atoms were included in the structure factor
calculations by using a riding model. Structure solution and
refinement were performed with the help of SHELX-97 programs
[16] available in the WinGX package [17]. The Platon [18] and the
Mercury [19] packages were used for molecular graphics. Selected
crystal data and structures refinement summary are listed in
Table 1.
Scheme 1. The Schiff base system 1-naphthaldehyde 4-R-benzoylhydrazone
(H2nabhR) and synthesis of trans-[Ru(nabhR)(PPh3)2Cl] (1 (R ¼ H), 2 (R ¼ Me), 3
(R ¼ OMe), 4 (R ¼ Cl) and 5 (R ¼ NO2)).
naphthaldehyde with 1 mol equivalent of the corresponding 4-R-
benzoylhydrazines (R ¼ H, Me, OMe, Cl and NO2) in presence of a
few drops of acetic acid [8]. [Ru(PPh3)3Cl2] was prepared using a
literature procedure [13]. All other chemicals and solvents were of
analytical grade available commercially and were used without
further purification.
2.2. Physical measurements
3. Results and discussion
A Thermo Finnigan Flash EA1112 series elemental analyzer was
used for the microanalyses (C, H, N). Purity verification of the Schiff
bases was performed with the help of a Shimadzu LCMS 2010 liquid
chromatograph mass spectrometer. Room temperature (298 K)
magnetic susceptibilities were measured using a Sherwood scien-
tific balance. Diamagnetic corrections calculated from Pascal’s
constants [14] were used to obtain the molar paramagnetic sus-
ceptibilities. The infrared spectra of all the compounds were
recorded in KBr pellets on a Jasco-5300 FT-IR spectrophotometer. A
Cary 100 Conc UV/vis spectrophotometer was used to record the
electronic spectra. X-band EPR spectra were recorded on a Jeol JES-
FA200 spectrometer. Cyclic voltammetric measurements were
performed with the help of a CH-Instruments model 620A elec-
trochemical analyzer using dimethylformamide solutions of the
complexes containing tetrabutylammonium perchlorate (TBAP) as
the supporting electrolyte. A platinum disk working electrode, a
platinum wire auxiliary electrode and an Ag/AgCl reference elec-
trode were used in the three electrode measurements at 298 K
under dinitrogen atmosphere. Under identical condition the E1/2
value for the Fcþ/Fc couple was 0.48 V.
3.1. Synthesis and some properties
Complexes trans-[Ru(nabhR)(PPh3)2Cl] (1e5) were synthesized
in moderate yields by reacting [Ru(PPh3)3Cl2] with the corre-
sponding H2nabhR and NaOAc (1:1:2 mol ratio) in methanol
(Scheme 1). They can also be synthesized in comparable yields by
using other bases such as NEt3, NaOH and KOH instead of NaOAc.
The general molecular formula of 1e5 is well supported by the
elemental analyses data (Table 2). The effective magnetic moments
(meff) of 1e5 in powder phase at room temperature (298 K) are in
the range 1.92e1.99 mB. These values are consistent with one elec-
tron paramagnetic character and hence trivalent low-spin state of
ruthenium in 1e5. Presumably oxygen in air acts as the oxidant
Table 1
Selected crystal data and structure refinement summary.
Complex
1
2$0.5CH3CN
5$1.5CH3CN
Chemical formula
C54H42N2
OClP2Ru
933.36
Orthorhombic
Pca21
18.7511(9)
16.9761(12)
14.9408(7)
90
90
90
4756.0(5)
4
1.304
C56H45.5N2.5
OClP2Ru
967.91
Monoclinic
P21/n
15.8404(6)
17.7872(7)
17.2382(6)
90
95.373(4)
90
4835.6(3)
4
1.330
0.487
20,079
C57H45.5N4.5O3
ClP2Ru
1039.94
Orthorhombic
Pbca
18.9835(9)
14.9426(6)
35.7465(18)
90
Formula weight
Crystal system
Space group
2.3. Synthesis of trans-[Ru(nabhH)(PPh3)2Cl] (1)
ꢀ
a (A)
ꢀ
b (A)
To a methanol solution (30 ml) of H2nabhH (57 mg, 0.21 mmol)
and NaOAc (35 mg, 0.43 mmol) solid [Ru(PPh3)3Cl2] (200 mg,
0.21 mmol) was added. The mixture was boiled under reflux for 1 h
and then concentrated to w8 ml on a steam bath. On cooling to room
temperature the complex separated as a red crystalline solid. It was
collected by filtration, washed with little cold methanol followed by
n-hexane and finally dried in air. The yield was 105 mg (54%).
Complexes 2e5 with the same general formula trans-[Ru(n-
abhR)(PPh3)2Cl] (2 (R ¼ Me), 3 (R ¼ OMe), 4 (R ¼ Cl) and 5
(R ¼ NO2)) were synthesized in 50e58% yields using [Ru(PPh3)3Cl2],
corresponding H2nabhR and NaOAc (in 1:1:2 mol ratio) by
following procedures very similar to that described above for 1
(R ¼ H).
ꢀ
c (A)
a
b
g
(ꢁ)
(ꢁ)
(ꢁ)
90
90
3
ꢀ
V (A )
10140.0(8)
8
1.362
0.474
24,459
Z
r
(g cmꢀ3
(mmꢀ1
)
)
m
0.493
Reflections
collected
Reflections
unique
12,635
7518
5803
8499
5221
8915
5767
Reflections
[I ꢂ 2
s(I)]
Parameters
550
573
e
616
e
Flack parameter
0.03(7)
R1, wR2 [I ꢂ 2
s
(I)]
0.0736, 0.1949
0.0996, 0.2155
1.083
0.0684, 0.1678
0.1191, 0.1999
1.033
0.0675, 0.1678
0.1077, 0.1923
1.061
2.4. X-ray crystallography
R1, wR2 [all data]
GOF on F2
Max./min. peaks
1.287/ꢀ0.814
0.926/ꢀ0.351
0.978/ꢀ0.582
X-ray quality single crystals of [Ru(nabhH)(PPh3)2Cl] (1),
[Ru(nabhMe)(PPh3)2Cl] (2) and [Ru(nabhNO2)(PPh3)2Cl] (5) were
ꢀꢀ3
(e A
)

406
K. Nagaraju, S. Pal / Journal of Organometallic Chemistry 745-746 (2013) 404e408
Table 2
Elemental analysis, electronic spectroscopica and effective magnetic momentsb.
Complex
Found (calc) (%)
C
lmax (nm) (10ꢀ4 ꢃ ε (Mꢀ1 cmꢀ1))
meff (mB)
H
N
1
2
3
4
5
69.32 (69.47)
69.56 (69.71)
68.41 (68.55)
67.56 (66.99)
66.75 (66.27)
4.46 (4.54)
4.58 (4.58)
4.67 (4.61)
4.31 (4.27)
4.06 (4.23)
3.07 (3.00)
3.06 (2.96)
2.85 (2.91)
2.79 (2.90)
4.32 (4.30)
506 (0.38), 400c (0.35), 325 (2.13), 277 (4.54)
503 (0.29), 403c (0.45), 327 (1.77), 273 (6.27)
504 (0.32), 402c (0.39), 330 (1.50), 272 (4.35)
506 (0.46), 404c (0.47), 326 (1.86), 273 (3.80)
490c (0.44), 332c (1.51), 273c (3.14)
1.99
1.95
1.97
1.92
1.94
a
In dichloromethane.
In powder phase at 298 K.
Shoulder.
b
c
during the synthesis of 1e5 from the bivalent ruthenium starting
material [Ru(PPh3)3Cl2]. The solubility behaviours of 1e5 are very
similar to that of the analogous complexes of pnbhR2ꢀ [12]. They
are highly soluble in dichloromethane, chloroform, dimethylsulf-
oxide and dimethylformamide and give red solutions. In solution,
all the complexes are electrically non-conducting.
is illustrated in Fig. 1. This type of spectral profile indicates a
rhombically distorted octahedral coordination geometry around
one-electron paramagnetic ruthenium(III) centre in each of 1e5. In
view of the ligand composition in the present series of complexes
rhombic distortion from ideal octahedral geometry is not surpris-
ing. Rhombic distortion and similar EPR features are very common
in analogous ruthenium(III) quaternary complexes with an asym-
metric tridentate ligand and two different unidentate ligands
[2,3,12,20e22]. X-ray molecular structures of 1, 2 and 5 are in
concurrence with the rhombic distortion indicated by the EPR
measurements (vide infra).
3.2. Spectroscopic features
In the infrared spectra of the Schiff bases (H2nabhR), the amide
NeH and the C]O stretches appear in the ranges 3172e3287 and
1632e1671 cmꢀ1, respectively [8,12]. Absence of these stretches in
the spectra of 1e5 indicates deprotonation of the amide function-
ality in the ligand (nabhR)2ꢀ. The C]N stretch of H2nabhR is
observed as a medium to strong band within 1583e1605 cmꢀ1. In
1e5 the C]N stretch appears at a lower frequency range (1560e
1577 cmꢀ1) due its coordination to the metal centre [8,12]. The
three strong bands observed at w740, w695 and w515 cmꢀ1 in the
spectra of the complexes indicate the metal bound PPh3 in all of
them.
Electronic spectra of the Schiff bases and the complexes were
recorded in dichloromethane. The spectra of the Schiff bases are
very similar and display a strong band at w330 nm followed by a
shoulder at w265 nm [8]. The spectra of the complexes are also
comparable but in contrast to the Schiff bases display several strong
to very strong absorptions in the wavelength range 506e272 nm.
The electronic spectral data of 1e5 are listed in Table 2 and a
representative spectrum is illustrated in Fig. S1 (Supplementary
material). By comparing the spectra of the Schiff bases and the
corresponding complexes, the absorptions of 1e5 above 350 nm are
assigned to ligand to metal charge transfer transitions and the
absorptions below 350 nm are attributed to predominantly ligand
centred transitions [8,12].
3.3. X-ray structures
Single crystal X-ray structures of 1 and solvated 2 and 5 have
been determined. The molecular structure of 2 is illustrated in Fig. 2
and that of both 1 and 5 are given in Fig. S2 (Supplementary
material). Bond parameters involving the metal centre for each of
the three complex molecules are listed in Table 4 . The gross mo-
lecular structures of the three complexes are very similar. In each
complex molecule, the ruthenium atom is in distorted octahedral
trans-CNOClP2 coordination sphere. The C(12)eO(1) (1.266(7)e
ꢀ
ꢀ
1.289(14) A) and C(12)eN(2) (1.290(8)e1.310(15) A) bond lengths
in 1, 2 and 5 are consistent with the deprotonated state of the amide
functionality and hence the dibasic nature of their corresponding
tridentate ligands (nabhR)2ꢀ [2e8,12]. The meridionally spanning
(nabhR)2ꢀ acts as 1-naphthalenyl ortho-C, the imine-N and the
amidate-O donor and forms 5,5-fused chelate rings at the
Table 4
ꢁ
ꢀ
Selected bond lengths (A) and bond angles ( ) for 1, 2$0.5CH3CN and 5$1.5CH3CN.
Complex
1
2$0.5CH3CN
5$1.5CH3CN
The EPR spectra of 1e5 in frozen (130 K) dichloromethanee
toluene (1:1) are very similar. Each complex displays three distinct
EPR signals. The g-values are listed in Table 3 and the spectrum of 4
RueC(1)
RueN(1)
RueO(1)
RueCl
RueP(1)
RueP(2)
2.057(9)
2.035(8)
2.153(7)
2.361(3)
2.404(2)
2.397(2)
76.1(3)
150.4(3)
103.6(2)
94.4(3)
89.1(3)
75.1(3)
176.6(3)
92.9(3)
92.5(3)
2.040(6)
2.018(5)
2.138(4)
2.3711(18)
2.4091(17)
2.3935(16)
77.4(2)
2.044(6)
2.016(5)
2.138(4)
2.3574(16)
2.3938(15)
2.3958(15)
77.1(2)
150.43(19)
105.98(16)
91.20(16)
88.27(16)
73.94(17)
175.06(14)
91.97(14)
92.61(14)
103.35(13)
95.50(12)
87.31(12)
84.14(5)
Table 3
EPRa and cyclic voltammetricb data.
C(1)eRueN(1)
C(1)eRueO(1)
C(1)eRueCl
C(l)eRueP(1)
C(1)eRueP(2)
N(1)eRueO(1)
N(1)eRueCl
N(1)eRueP(1)
N(1)eRueP(2)
O(1)eRueCl
O(1)eRueP(1)
O(1)eRueP(2)
CleRueP(1)
CleRueP(2)
P(1)eRueP(2)
150.7(2)
Complex
g1
g2
g3
E1/2(V) (D
Ep (mV))c
113.50(18)
88.01(17)
87.88(17)
73.64(19)
169.04(16)
87.94(14)
90.63(14)
95.57(13)
95.56(12)
87.77(12)
91.33(6)
Reduction
Oxidation
1
2
3
4
5
2.37
2.41
2.41
2.37
2.38
2.09
2.07
2.06
2.09
2.09
1.95
1.95
1.95
1.95
1.94
ꢀ0.31 (100)
ꢀ0.33 (100)
ꢀ0.36 (90)
ꢀ0.30 (90)
ꢀ0.27 (100)
1.06 (120)
1.05d
0.94 (100)
1.10d
1.13d
105.6(2)
93.5(2)
85.6(2)
83.75(10)
90.87(11)
174.11(10)
a
In frozen (130 K) dichloromethaneetoluene (1:1).
In dimethylformamide.
E1/2 ¼ (Epa þ Epc)/2 and
b
c
DEp ¼ Epa ꢀ Epc, where Epa and Epc are anodic and
90.82(6)
175.85(6)
91.36(5)
175.15(5)
cathodic peak potentials, respectively.
d
Epa value.

K. Nagaraju, S. Pal / Journal of Organometallic Chemistry 745-746 (2013) 404e408
407
Fig. 3. Cyclic voltammograms of trans-[Ru(nabhH)(PPh3)2Cl] (1) in dimethylforma-
mide (0.1 M TBAP) at 298 K.
Fig. 1. X-band EPR spectrum of trans-[Ru(nabhCl)(PPh3)2Cl] (4) in frozen (130 K)
dichloromethaneetoluene (1:1).
3.4. Redox properties
ruthenium centre (Fig. 2 and S2). The (nabhR)2ꢀ and the Cl-atom
form a CNOCl square-plane around the metal centre and the P-
atoms of the two PPh3 molecules occupy the two axial positions.
The chelate bite angles, O(1)eRueN(1) and C(1)eRueN(1),
imposed by (nabhR)2ꢀ are in the ranges 73.64(19)e75.1(3)ꢁ and
76.1(3)e77.4(2)ꢁ, respectively. These bite angles are very similar to
those observed in Ru(III) complexes with CNO-pincer ligands
[2,3,12,20,21]. Each of the 5,5-fused chelate rings is satisfactorily
Electron transfer properties of 1e5 have been studied by cyclic
voltammetry. In dimethylformamide, the complexes display
reduction response in the E1/2 range of ꢀ0.27 to ꢀ0.36 V with
a
Ep
D
within 90e100 mV and a quasi-reversible to irreversible oxidation
response in the E1/2/Epa range of 0.94e1.13 V (vs. Ag/AgCl). The po-
tential data are summarized in Table 3 and representative voltam-
mograms are illustrated in Fig. 3. The one-electron nature of these
redox responses is ascertained by comparing the current heights with
the current heights of known one-electron transfer processes under
identicalcondition[2,3,12,20].Takingintoaccounttheredoxinactivity
of the Schiff bases in the above redox potential range and the electron
transfer behaviours of analogous ruthenium(III) complexes with tri-
dentate acid hydrazones [2,3,12], we have ascribed the reduction and
theoxidationresponses of1e5to ruthenium(III) / ruthenium(II) and
ruthenium(III) / ruthenium(IV) processes, respectively. In general,
there is a cathodic shift of both reduction and oxidation potentials
withtheincreasingelectrondonatingabilityofthesubstituentRin the
tridentate ligand (nabhR)2ꢀ. Satisfactory linear relationships are ob-
tained for the reduction (E1/2) as well as the oxidation (Epa) potentials
when the corresponding values are plotted against the Hammett
substituent constants [23] (Fig. S3 in Supplementary material).
ꢀ
planar (mean deviation 0.01e0.03 A). However, the rings are
slightly folded by 3.7(2)e4.9(1)ꢁ along the RueN(1) bond. Other
than the bite angles, the remaining cis bond angles span a much
wider range of 83.75(10)e113.50(18)ꢁ. As expected due to steric
constraint the trans bond angle (C(1)eRueO(1), 150.43(19)e
150.7(2)ꢁ) formed by the two ends of (nabhR)2ꢀ is much smaller
than the remaining two trans bond angles (N(1)eRueCl,
169.04(16)e176.6(3)ꢁ and P(1)eRueP(2), 174.11(10)e175.85(6)ꢁ).
The RueC(aryl), the RueN(imine), the RueO(amidate), the RueCl
and the RueP bond lengths in 1, 2 and 5 (Table 4) are comparable
with the corresponding bond lengths observed for ruthenium(III)
complexes with similar ligands [2,3,12].
4. Conclusion
Synthesis and characterization of a series of cycloruthenates
with 1-naphthaldehyde 4-R-benzoylhydrazones (H2nabhR, R ¼ H,
Me, OMe, Cl and NO2) are described. The magnetic moments and
EPR spectra corroborate the trivalent low-spin state of the metal
centre in each of these complexes of the formula trans-[Ru(n-
abhR)(PPh3)2Cl]. All the complexes are redox active and display a
reduction and an oxidation both being metal centred and substit-
uent sensitive. X-ray structures of three complexes where R ¼ H,
Me, and NO2 show pincer like coordination mode of (nabhR)2ꢀ
through the 1-naphthalenyl ortho-C, the imine-N and the amidate-
O and formation of 5,5-fused chelate rings. Based on the similar
physical properties of all the complexes, it is inferred that
(nabhR)2ꢀ has the same coordination mode in the remaining two
complexes where R ¼ OMe and Cl. The regioselective ortho-ruthe-
nation instead of peri-ruthenation of the 1-naphthalenyl moiety of
(nabhR)2ꢀ is akin to our previous observation for the analogous
cycloruthenates with 1-pyrenaldehyde 4-R-benzoylhydrazones
[12]. In contrast, regioselective peri-palladation of both indole-3
and 1-naphthalenyl fragments of acid hydrazones of indole-3-
Fig. 2. Molecular structure of trans-[Ru(nabhMe)(PPh3)2Cl] (2) with the atom
numbering scheme. Thermal ellipsoids of all non-hydrogen atoms are drawn at the
40% probability level. C-atoms of PPh3 are not labelled for clarity.

408
K. Nagaraju, S. Pal / Journal of Organometallic Chemistry 745-746 (2013) 404e408
aldehyde and 4-R-1-naphthaldehydes leading to the formation of
6,5-fused chelate rings has been observed for bivalent palladium
[6,8]. A possible rationale that may account for this difference in
regioselectivity is as follows. All these cyclopalladates and cyclo-
ruthenates were synthesized from bivalent metal ion containing
starting materials ([PdCl4]2ꢀ and [Ru(PPh3)3Cl2], respectively), tri-
dentate acid hydrazones and the base NaOAc. It is very likely that in
presence of base, coordination of monobasic ligand (e.g. HnabhRꢀ)
to the bivalent metal centre through the imine-N and the amidate-
O with the formation of the 5-membered N,O chelate ring precedes
the CeH activation process [24]. In general, it has been found that
small metal ions prefer 6-membered chelate ring, while large metal
ions prefer 5-membered chelate ring [25,26]. Palladium(II) is ex-
pected to be smaller than ruthenium(II). Perhaps for this size dif-
ference palladium(II) activates the peri-CeH and forms 6-
membered metallacycle, while formation of 5-membered metal-
lacycle by ortho-CeH activation occurs for ruthenium(II). Oxidation
of the metal centre to the trivalent state by oxygen in air is the last
step for the formation of the cycloruthenates. Currently we are
engaged in the synthesis of cyclometallates of various platinum
metal ions with the present and other acid hydrazones of various
polycylic aromatic aldehydes for a better perception of the regio-
selective CeH activation process in this class of ligands.
charge from The Cambridge Crystallographic Data Centre via www.
ccdc.cam.ac.uk/data_request/cif.
Appendix B. Supplementary data
Supplementary Figs. S1eS3 related to this article can be found at
http://dx.doi.org/10.1016/j.jorganchem.2013.08.024.
References
[1] M. Albrecht, Chem. Rev. 110 (2010) 576e623 and references therein.
[2] R. Raveendran, S. Pal, J. Organomet. Chem. 692 (2007) 824e830.
[3] R. Raveendran, S. Pal, J. Organomet. Chem. 694 (2009) 1482e1486.
[4] S. Das, S. Pal, J. Organomet. Chem. 689 (2004) 352e360.
[5] S. Das, S. Pal, J. Organomet. Chem. 691 (2006) 2575e2583.
[6] A.R.B. Rao, S. Pal, J. Organomet. Chem. 696 (2011) 2660e2664.
[7] A.R.B. Rao, S. Pal, J. Organomet. Chem. 701 (2012) 62e67.
[8] A.R.B. Rao, S. Pal, J. Organomet. Chem. 731 (2013) 67e72.
[9] N. Selander, K.J. Szabó, Chem. Rev. 111 (2011) 2048e2076.
[10] D. Gelman, S. Musa, ACS Catal. 2 (2012) 2456e2466.
[11] G. van Koten, D. Milstein (Eds.), Organometallic Pincer Chemistry: Topics in
Organometallic Chemistry, vol. 40, Springer, Heidelberg, 2013, pp. 1e352.
[12] K. Nagaraju, S. Pal, J. Organomet. Chem. 737 (2013) 7e11.
[13] T.A. Stephenson, G. Wilkinson, J. Inorg. Nucl. Chem. 28 (1966) 945e956.
[14] G.A. Bain, J.F. Berry, J. Chem. Educ. 85 (2008) 532e536.
[15] CrysAlisPro Version 1.171.33.55, Oxford Diffraction Ltd., Abingdon, Oxford-
shire UK, 2007.
[16] G.M. Sheldrick, SHELX-97, Structure Determination Software, University of
Gottingen, Gottingen, Germany, 1997.
[17] L.J. Farrugia, J. Appl. Crystallogr. 32 (1999) 837e838.
[18] A.L. Spek, Platon, a Multipurpose Crystallographic Tool, Utrecht University,
Utrecht, The Netherlands, 2002.
[19] C.F. Macrae, I.J. Bruno, J.A. Chisholm, P.R. Edgington, P. McCabe, E. Pidcock,
L. Rodriguez-Monge, R. Taylor, J. van de Streek, P.A. Wood, J. Appl. Crystallogr.
41 (2008) 466e470.
[20] G.K. Lahiri, S. Bhattacharya, M. Mukherjee, A.K. Mukherjee, A. Chakravorty,
Inorg. Chem. 26 (1987) 3359e3365.
Acknowledgements
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.
[21] S. Kannan, R. Ramesh, Y. Liu, J. Organomet. Chem. 692 (2007) 3380e3391.
[22] R. Prabhakaran, R. Huang, R. Karvembu, C. Jayabalakrishnan, K. Natarajan,
Inorg. Chim. Acta 360 (2007) 691e694.
[23] J. March, Advanced Organic Chemistry, fourth ed., Wiley, New York, 1992,
p. 280.
[24] D.N. Neogi, A.N. Biswas, P. Das, R. Bhawmick, P. Bandyopadhyay, J. Organomet.
Chem. 724 (2013) 147e154.
[25] R.D. Hancock, Pure Appl. Chem. 58 (1986) 1445e1452.
[26] R.D. Hancock, Chem. Soc. Rev. 42 (2013) 1500e1524.
Appendix A. Supplementary material
CCDC 941054e941056 contain the supplementary crystallo-
graphic data for this paper. These data can be obtained free of