Synthesis, characterization and catalytic property of ruthenium-terpyridyl complexes

Article abstract of DOI:10.1016/j.poly.2011.09.014

The known compound 4′-(carboxyphenyl)-2,2′:6,2″- terpyridine (LH) was prepared and complexed with RuCl₃.3H ₂O. The resulting complex [Ru(LH)Cl₃] was then allowed to react separately with 2,2′-bipyridine (bpy), 1,10-phenant

Full text of DOI:10.1016/j.poly.2011.09.014

Polyhedron 31 (2012) 227–234
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Polyhedron
journal homepage: www.elsevier.com/locate/poly
Synthesis, characterization and catalytic property of ruthenium–terpyridyl
complexes
⇑
Priti Sinha, Dushyant Singh Raghuvanshi, Krishna Nand Singh, Lallan Mishra
Department of Chemistry, Faculty of Science, Banaras Hindu University, Varanasi 221 005, India
a r t i c l e i n f o
a b s t r a c t
The known compound 40-(carboxyphenyl)-2,20:6,200-terpyridine (LH) was prepared and complexed with
RuCl3.3H2O. The resulting complex [Ru(LH)Cl3] was then allowed to react separately with 2,20-bipyridine
(bpy), 1,10-phenanthroline (phen), triphenylphosphine (PPh3) and 1,2-bis-(diphenylphosphino)ethane
(dppe). The compositions of corresponding complexes [Ru(LH)bpyCl](BF4) 1, [Ru(LH)phenCl](BF4) 2,
[Ru(LH)(PPh3)(CH3CN)2] (BF4)2 3 and [Ru(LH)(dppe)Cl](BF4) 4 were assigned on the basis of their FAB-
mass spectra, elemental analysis, spectroscopic (IR, NMR) data and X-ray diffraction measurements.
The diamagnetic, cationic complexes displayed strong MLCT transitions in the visible region with signif-
icant shift in MLCT band energy corresponding to the strength of substituted ligands. The redox behav-
iour of the complexes was investigated using cyclic voltammetry measurements. Among all the
complexes, 3 efficiently catalyzed the synthesis of propargylamine via three components coupling
reaction.
Article history:
Received 2 June 2011
Accepted 12 September 2011
Available online 21 September 2011
Keywords:
40-(Carboxyphenyl)-2,20:6,200-terpyridine
Ruthenium(II) complexes
Catalyst
Propargylamines
Multicomponent reaction
Ó 2011 Elsevier Ltd. All rights reserved.
1. Introduction
alkyne and amines. Propargylamines are used as important syn-
thetic intermediates for the preparation of polyfunctional amino
It is well reported that 40 substituted terpyridine (terpy) deriv-
atives provides ideal building block with which to assemble the
multicomponent molecular systems around photoactive transition
metal centers [1]. The main advantages of the terpy module over a
bpy analogue owe to its facile functionalization [2], ability to con-
struct linear arrays [3] and facilitate the formation of achiral metal
complexes. Thus, the problem inherent in the use of [Ru(bpy)3]2+ as
structural motif providing diastereomeric complexes as a mixture
of fac and mer isomer could be minimized by the use of a tridentate
ligand. The polypyridyl complexes have shown several interesting
properties such as photochemistry, electron transfer reaction,
catalysis and photosensitizers [4,5]. In this regard, a number of
luminescent and redox active compounds using bridging polypyr-
idyl ligands have been prepared and their properties extensively
studied [6–11]. Based on this and in view of our earlier interest
in ruthenium polypyridyl complexes [12], it was initially planned
to synthesize a ruthenium terpyridyl complex appended with
three substitutable chloro groups. Recently, Crabtree et al. have re-
ported Beckmann rearrangement for one pot synthesis of amides
using terpyridines–ruthenium complexes as catalyst [13]. In view
of this novel report, it was considered worthwhile to explore the
catalytic potential of the prepared complexes for the synthesis of
propargylamines via three – components coupling of aldehydes,
derivatives and possess diverse biologically activities [14,15]. Clas-
sical methods for the preparation of propargylamines have
exploited the relatively high acidity of a terminal acetylenic C–H
bond to form alkynyl–metal reagents by the reaction with strong
bases such as butyllithium, organomagnesium compounds or lith-
ium diisopropylamide in multiple steps [16,17]. These reagents are
highly moisture sensitive and require their stoichiometric quanti-
ties under strictly controlled reaction conditions.
In recent years, enormous work has been done which extended
the scope of the direct addition of alkynes to carbon–nitrogen dou-
ble bonds either preformed (imines) or in one-pot (from aldehyde
and amine) by employing various complexes and salts of transition
metals such as iron, zinc, copper, ruthenium–copper, indium, sil-
ver, gold, mercury and nickel [18–26]. The synthesis of propargyl-
amines using new transition metal complexes as catalyst has
enthused organic chemists to employ multi-component strategies.
However, longer reaction time that is frequently required for full
conversions has limited such exploitation. Therefore, rapid and
reliable controlled microwave assisted approach is adopted for
high-speed production of new chemicals [27] as such irradiation
accelerates the process with considerable increase in yield of the
product. Thus, in view of the above reports the newly prepared
complexes were investigated as a catalyst for the synthesis of
propargylamines using multi-component approach. However,
among all the complexes, only 3 efficiently catalyzed the synthesis
of several propargylamines employing different aldehydes, amines
and alkyne under controlled microwave irradiation.
⇑
Corresponding author. Tel.: +91 542 6702449; fax: +91 542 2368174.
E-mail address: lmishrabhu@yahoo.co.in (L. Mishra).
0277-5387/$ - see front matter Ó 2011 Elsevier Ltd. All rights reserved.
doi:10.1016/j.poly.2011.09.014

228
P. Sinha et al. / Polyhedron 31 (2012) 227–234
0
0
J = 5.1 Hz), 9.22 (s, 2H, Hm,Hm ), 8.93 (m, 3H, Hd, Hl,Hl ), 8.63 (d,
2. Experimental
2.1. Materials
0
0
1H, He, J = 8.1 Hz), 8.37 (m, 3H, Hh,Hi,Hi ), 8.17 (m, 2H, Hj,Hj ),
8.05 (dd, 3H, Hb, Hk,Hk ), 7.77 (t, 1H, Hc, J = 8.1 Hz), 7.63 (d, 2H,
Ho,Ho , J = 4.8 Hz), 7.38 (m, 3H, Hg, Hn,Hn ), 7.07 (t, 1H, Hf,
J = 6.3 Hz).
0
0
0
The chemicals 2-acetylpyridine, 4-carboxybenzaldehyde,
RuCl3ꢀ3H2O, 1,2-bis-(diphenylphosphino)-ethane, 2,20-bipyridine,
triphenylphosphine, 1,10-phenanthroline, phenylacetylene and so-
dium tetrafluoroborate were purchased from Sigma–Aldrich, USA.
The aldehydes, morpholine, piperidine, KOH, aqueous ammonia
solution and solvents were of AR grade. The ligand 40-(carboxy-
phenyl)-2,20:6,200-terpyridine (LH) and Ru(LH)Cl3 (precursor) were
prepared using published procedures [28,29], respectively.
2.3.3. Synthesis of [Ru(LH)(phen)Cl]BF4
2
This complex was prepared using procedure given for the com-
plex 1, except that 1,10-phenanthroline (0.180 g, 1.0 mmol) was
ꢁ
used in place of 2,20-bipyridine. The complex containing BF4 as
counter anion was isolated and purified similarly using column
chromatography. The brown coloured solid was obtained after
reducing the volume of the corresponding eluate and by the addi-
tion of an aqueous solution of NaBF4. It was then filtered and
washed with water followed by ethanol and diethyl ether. The
complex was found soluble in DMSO, DMF, C2H5OH, CH3OH and
CH3CN. The solution of complex in CH3CN: H2O (1: 1, v/v) gave
block shaped dark brown crystals after its slow evaporation. Yield:
0.367 g (45%). Anal. Calc. for C34H23N5O2BF4ClRu: C, 54.01; H, 3.04;
N, 9.26. Found: C, 54.03; H, 3.01; N, 9.28%. FAB MS: m/z: 755[M]+,
2.2. Physical measurements
Elemental analysis was performed using a Exeter Analytical
CHN analyzer (model CE-440). However, UV–Vis spectra of the
complexes were recorded at 25 °C using JASCO V630 spectropho-
tometer. The infrared spectra of complexes were recorded on Var-
ian 3100 FTIR spectrometer and 1H and 31P NMR spectra (d ppm)
were recorded on JEOL AL-300 MHz spectrometer using TMS as
internal reference. FAB mass spectra were recorded on JEOL/SX
102/Da-600. Cyclic voltammetric measurements of complexes
(10ꢁ4 M, DMF) were performed using a CHI 620c electrochemical
analyzer. A glassy carbon working electrode, platinum wire auxil-
iary electrode and Ag/AgCl reference electrode were used in a
standard three-electrode configuration and tetrabutylammonium
perchlorate (TBAP) was used as a supporting electrolyte.
669[M–BF4]+, 634[M–BF4–Cl]+. IR (KBr pellet, cmꢁ1) 1716 (
mCOOH),
ꢁ
1605 (
m
CH@N), 1083 (mBF ). 1H NMR (300 MHz, DMSO-d6, d ppm):
4
0
10.33 (d, 1H, Ha, J = 5.1 Hz), 9.28 (s, 2H, Hm,Hm ), 8.94–9.00 (m,
3H, Hc,Hl,Hl ), 8.38–8.46 (m, 5H, Hb,Hj,Hj ,Hk,Hk ), 8.23 (m, 3H, Hi,-
Hi ,Hf), 7.96–8.01 (m, 2H, Hd, He), 7.82 (d, 1H, Hh, J = 5.1 Hz), 7.50
(d, 2H, Ho,Ho , J = 5.4 Hz), 7.40–7.45 (m, 1H, Hg), 7.23–7.28 (m,
2H, Hn,Hn ). Its solution in DMF emitted at room temperature
(kem = 600 nm) after excitation at kex 520 nm.
0
0
0
0
0
0
MW study was made using CEM – Discover single mode micro-
wave reactor (Benchmate model, USA) with infrared temperature
probe and adjustable 0–300 W output power.
2.3.4. Synthesis of [Ru(LH)(PPh3)(MeCN)2] (BF4)2
3
The complex 3 was prepared by the addition of a solution of
PPh3 (0.262 g, 1 mmol) in dichloromethane (5 mL) to a solution
of [Ru(LH)Cl3] in ethanol (15 mL) and the mixture was heated at re-
flux with stirring for ꢂ6 h. An aqueous saturated solution of NaBF4
was then added to it which gave orange coloured solid. The solid
product thus obtained was washed with water and ethanol and
dried in vacuo. It was then purified using column chromatography
similar to that used for complex 1. The solid thus obtained was
then dissolved in CH3CN:H2O (1:1, v/v) mixture and its solution
was slowly evaporated then red coloured parallelopiped shaped
crystals were obtained. The crystals were soluble in DMSO, DMF,
C2H5OH, CH3OH and CH3CN. Yield: 0.709 g (45%). Anal. Calc. for
2.3. Synthesis and purification
2.3.1. Synthesis of precursor [Ru(LH)Cl3]
A solution of ligand (LH) (0.353 g, 1.0 mmol) and RuCl3ꢀ3H2O
(0.261 g, 1.0 mmol) in ethanol (20 mL) was refluxed for 8 h. The
solution was then cooled to room temperature and solid mass thus
obtained was filtered and dried in vacuo. It was assigned a compo-
sition [Ru(LH)Cl3] on the basis of its analytical and spectroscopic
data. Yield: 0.336 g (60%). Soluble in DMSO, DMF and hot ethanol.
Anal. Calc. for C22H15N3O2Cl3Ru: C, 47.10; H, 2.67; N, 7.49. Found:
C, 47.07 3; H, 2.65; N, 7.51%. IR (KBr pellet, cmꢁ1) 1716 (
1601( CH@N).
m
COOH),
C
44H36N5O2PB2F8Ru: C, 54.43; H, 3.71; N, 7.21. Found: C, 54.39;
H, 3.69; N, 7.19%. FAB MS: m/z: 970[M]+, 883[M–BF4]+, 797[M–
m
2BF4]+ IR (KBr pellet, cmꢁ1) 2398 (
mCN), 1709 (
m
COOH), 1606 (
m
CH@N),
1080(mBF ). 1H NMR (300 MHz, DMSO-d6, d ppm): 9.13 (d, 2H,
ꢁ
4
2.3.2. Synthesis of [Ru(LH)(bpy)Cl]BF4
1
0
0
0
Hl,Hl , J = 5.1 Hz), 8.76 (s, 2H, Hm,Hm ), 8.63 (d, 2H, Hi,Hi ,
The precursor complex Ru(LH)Cl3 (0.560 g, 1 mmol) and 2,20-
bipyridine (0.156 g, 1.0 mmol) were taken together in ethanol
(10 mL) and the mixture was heated at reflux with stirring for
10 h. The resulting solution was then reduced to ꢂ5 mL. A metha-
nolic solution of NaBF4 was then added to it. The resulting solid
was separated from the solution by filtration and finally washed
with water and ethanol and then dried in vacuo. The crude product
was then purified by column chromatography using SiO2 as sup-
porting material with MeCN, aqueous saturated solution of KNO3
and water (v/v ratio of 14:2:1) as eluent. To the eluate thus ob-
tained, a methanolic solution of NaBF4 was added which gave red
coloured solid product. It was then filtered and repeatedly washed
with water and finally with a little ethanol followed by diethyl
ether. The complex was found soluble in DMSO, DMF, C2H5OH,
CH3OH and CH3CN. Yield: 0.197 g (27%). Anal. Calc. for
0
0
0
J = 8.1 Hz), 8.14–8.21 (m, 4H, Hj,Hj ,Hk,Hk ), 7.70 (m, 2H, Ho,Ho ),
0
7.41 (m, 2H, Hn,Hn ), 7.24 (m, 9H, Hq), 6.95 (m, 6H, Hp), 2.07 (s,
6H, Hr). 31P NMR (300 MHz, DMSO-d6, d ppm): 32.56.
2.3.5. Synthesis of [Ru(LH)(dppe)Cl]BF4
4
The complex 4 was also prepared by the addition of a solution of
dppe (0.398 g, 1 mmol) in dichloromethane (5 mL) to an ethanolic
solution (15 mL) of [Ru(LH)Cl3] (0.560 g, 1 mmol). The mixture was
then heatedꢁat reflux with stirring for 8 h. Finally, it was precipi-
tated as BF4 salt upon addition of aqueous saturated solution of
NaBF4 to it. This complex was washed with water, dried in vacuo
and purified by column chromatography. Yield: 0.584 g (61%). Anal.
Calc. for C48H39N3O2P2ClBF4Ru: C, 59.18; H, 4.00; N, 4.31. Found: C,
59.15; H, 3.97; N, 4.34%. FAB MS: m/z: 973[M]+, 886[M–BF4]+,
C
32H23N5O2BF4ClRu: C, 52.49; H, 3.14; N, 9.56. Found: C, 52.45;
850[M–BF4–Cl]+. IR (KBr pellet, cmꢁ1) 1708 (
m
COOH), 1609 (
mCH@N),
H, 3.12; N, 9.59%. FAB MS: m/z: 731 [M]+, 645 [M–BF4]+, 609 [M–
1081 (mBF ). 1H NMR (300 MHz, DMSO-d6, d ppm): 9.09 (d, 2H,
ꢁ
4
BF4–Cl]+. IR (KBr pellet, cmꢁ1) 1721 (
m
COOH), 1606 (
m
CH@N), 1084
Hl,Hl , J = 6 Hz), 8. 54 (s, 2H, Hm,Hm ), 8.24 (d, 2H, Hi,Hi ), 7.79–
0
0
0
mBF ). 1H NMR (300 MHz, DMSO-d6, d ppm): 10.11 (d, 1H, Ha,
8.00 (m, 4H, Hk,Hk ,Hj,Hj ), 7.65 (d, 2H, Ho,Ho , J = 5.3 Hz), 7.57 (m,
ꢁ
0
0
0
(
4

P. Sinha et al. / Polyhedron 31 (2012) 227–234
229
2H, Hn,Hn ), 7.39–6.91 (m, 20H, Ha), 1.35–1.23 (m, 4H, Hb), 31P NMR
Table 1
0
Summary of crystallographic data for complexes 2 and 3.
(300 MHz, DMSO-d6, d ppm): 28.06.
Complex 2
Complex 3
2.3.6. General procedure for the Synthesis of propargylamines 8
Aldehyde 5 (1 mmol), amine 6 (1.1 mmol), alkyne 7 (1.2 mmol),
complex 3 (10 mol%) and chlorobenzene (2 mL) were placed in a
sealed pressure regulation 10 mL vial with ‘‘snap-on’’ cap and the
mixture was irradiated in single-mode microwave synthesis sys-
tem using 250 W power at 130 °C for 10 min. After completion of
the reaction (as monitored by TLC), the solvent was evaporated
in vacuo and water (20 mL) was added to the reaction mixture.
The product was extracted with ethylacetate (3 ꢃ 10 mL). The
combined organic phase was dried over anhydrous MgSO4, filtered
and the solvent was evaporated in vacuo. The residue was then
purified by column chromatography on silica gel (ethyl acetate:
hexane = 1:9 v/v) to afford the pure propargylamine.
Empirical formula
Formula weight
T (K)
C
36H26N6ClO3BF4Ru
C44H36N5O2B2F8Ru
974.15
293(2)
813.96
150(2)
0.71073
triclinic
P1
9.5999(4)
12.0751(6)
14.3605(7)
90.177(4)
95.159(4)
98.717(4)
1638.53(13)
2
k (Å)
0. 71073
Crystal system
Space group
a (Å)
b (Å)
c (Å)
triclinic
ꢀ
ꢀ
P1
12.4520(13)
13.6700(12)
14.9784(15)
90.311(8)
114.501(10)
102.047(8)
2256.8(4)
2
a
(°)
b (°)
c
(°)
V (Å3)
Z
Absorption coefficient
0.703
0.465
(mmꢁ1
)
4-(1,3-Diphenyl-prop-2-ynyl)-morpholine 8a: Yield: 55%. Anal.
Calc. for C19H19NO: C, 82.28; H, 6.90; N, 5.05. Found: C, 82.30; H,
6.85; N, 5.09%. 1H NMR (300 MHz, CDCl3, d ppm) 2.62–2.64 (m,
4H, 2 ꢃ CH2), 3.72–3.75 (m, 4H, 2 ꢃ CH2), 4.78 (s, 1H, CH), 7.25–
7.39 (m, 6H, H–Ar), 7.49–7.52 (m, 2H, H–Ar), 7.61 (d, 2H,
J = 7.2 Hz, H–Ar). 13C NMR (300 MHz, CDCl3, d ppm) 49.8, 62.0,
67.1, 84.9, 88.4, 122.9, 127.7, 128.0, 128.2, 128.3, 128.5, 131.7,
137.7. The spectrum is depicted as S10.
F(000)
832
948
Crystal size (mm)
Theta range for data
collection
0.28 ꢃ 0.23 ꢃ 0.18
0.34 ꢃ 0.31 ꢃ 0.3
3.30–25.00°
2.03–28.77°
Reflections collected/unique
11732/5765
[Rint = 0.0586]
99.8
full-matrix least-
squares on F2
0.943
R1 = 0.0557,
wR2 = 0.1291
R1 = 0.0802,
wR2 = 0.1363
1.656 and ꢁ1.135
15479/9586
[Rint = 0.0684]
96.6
full-matrix least-
squares on F2
1.035
R1 = 0.0880,
wR2 = 0.2295
R1 = 0.1116,
wR2 = 0.2458
2.148 and ꢁ1.36
Completeness to theta (%)
Refinement method
Goodness-of-fit (GOF) on F2
Final R indices [I > 2
The physical and spectral data of all the products are in full
agreement with their assigned structures and the characterization
data of products 8b–8h are given as S11.
r
(I)]
R indices (all data)
Largest difference in peak
and hole (e Aꢁ3
2.4. X-ray structural studies
)
Single crystal X-ray diffraction data for the complexes were col-
lected in the temperature range of 100(2) to 293(2) K on a Oxford
diffraction XCALIBUR-EOS diffractometer using graphite monochro-
matized MoKa radiation (k = 0.71073 ÅA). Intensities of these reflec-
0
0
protons. The protons marked as Hk and Hk also appeared at
d = 8.05 ppm. However, peak observed at d = 8.63 ppm (J = 8.1 Hz)
is assigned to Hd proton which appeared as doublet owing to its
tions were measured periodically to monitor crystal decay. The
crystal structures were solved by direct methods and refined by full
matrix least squares (SHELX-97) [30]. Drawings were carried out using
MERCURY [31]. The crystal refinement data is shown in Table 1. The
X-ray quality crystals of only two complexes [Ru(LH)-
phenCl]BF4ꢀH2OꢀCH3CN 2 and [Ru(LH)(CH3CN)2PPh3](BF4)2 3 could
be obtained.
0
coupling with Hc proton. The protons marked as He, Hl and Hl ap-
peared together as multiplet at d = 8.93 ppm. The peak observed at
d = 7.07 ppm as triplet is assigned to Hf proton. However, Ho and
Ho protons are observed at d = 7.63 ppm (J = 4.8 Hz) as doublet
and showed its coupling with Hn and Hn protons. The latter both
0
0
protons together with Hg proton appeared at d = 7.38 ppm. The
0
Protons marked as Hh, Hi and Hi appeared at d = 8.37 ppm. The ter-
0
py (LH) protons Hj and Hj appeared as multiplet at d = 8.17 ppm
3. Result and discussion
0
where as Hm and Hm protons appeared together at d = 9.22 ppm.
3.1. Synthesis
In a similar way, protons of complex 2 were also assigned and its
spectrum is depicted in S3 along with the assignment of the differ-
ent protons supported by its 1H–1H COSY NMR spectrum (S4). The
assignments were made in view of reported data [34] and also in
view of the position and integration intensity of the peaks. The
peaks observed at d =7.24–6.95 ppm were assigned to PPh3 protons
of the complex 3 (S5) in view of earlier report [35]. The assignment
is also supported by its 1H–1H COSY NMR spectrum (S6). In the
spectrum of this complex, methyl protons of acetonitrile appeared
at d = 2.07 ppm as singlet. The protons of dppe in complex 4 ap-
peared as multiplet from d 7.39–6.91 ppm (S7) were found in con-
sistence with the earlier report [36]. Its 1H–1H COSY NMR spectrum
(S8) supported the assigned structure of this complex. The pres-
ence of phosphorus nuclei in complexes 3 and 4 was also sup-
ported by their 31P NMR spectra which showed peaks at d (ppm)
32.56 for PPh3 and 28.06 for dppe, respectively(S9a,S9b). Thus,
The synthetic route for the preparation of complexes is summa-
rized in scheme 1. The ligand was prepared using published proce-
dure [28]. The complexes were prepared by direct reaction of
precursor complex [Ru(LH)Cl3] in ethanol with different ligands
in equimolar ratio. The yields were good to moderate. The desired
ruthenium(II) complexes were isolated as tetrafluoroborate salts
and purified using column chromatography. These complexes were
found soluble in solvents such as DMSO, DMF, ethanol, methanol,
acetonitrile, and acetone. The composition of the complexes were
initially identified by their elemental and spectroscopic data. The
structure of the complexes were further supported by their 1H
NMR and 1H–1H COSY NMR spectra. The numbering of protons
are same as shown in scheme 1. The 1H NMR spectrum of 1 (S1)
showed all protons which were assigned in view of earlier reports
for terpy complexes [32,33]. The proton of bpy marked as Ha
appeared at d = 10.11 ppm (J = 5.1 Hz) as doublet. Its 1H–1H COSY
NMR spectrum (S2) showed that Ha proton coupled with its
neighbouring Hb proton. The Hb proton appeared at d = 8.05 ppm
as multiplet owing to its coupling with Ha and Hc (d = 7.77 ppm)
1
1H NMR spectra of the complexes together with their H–1H COSY
NMR spectra tentatively assigned the presence of different types of
protons in their structures. However, some of the peaks overlapped
together and calls for separate NMR study using high field NMR
spectrometer.

230
P. Sinha et al. / Polyhedron 31 (2012) 227–234
3.2. Molecular structures of complexes 2 and 3
The molecular structure of the complex 2, a triclinic system
ꢀ
with space group P1 is shown in Fig. 1. The Selected bond lengths
and bond angles are given in Table 2. The bond length of LH (N3, N4
and N5) to Ru(II) centre varies from 1.956 to 2.068 Å. The central
nitrogen atom (N4) of LH ligand lies at shortest distance of
1.956 Å from ruthenium centre. It could be considered in view that
to optimize the chelation of this ligand with metal centre, this
bond shortens but the terminal Ru–N bonds lengthen to relieve
strain hence it retains a typical terpyridine bite angle (N–Ru–N)
of ꢂ79°[37]. The bond length of phenanthroline nitrogen to ruthe-
nium centre varies from 2.046 to 2.072 Å. The bond distance of
0
Ru(1)–Cl(1) was found to be 2.398 ÅA.
The complex 3 crystallized in triclinic crystal system with space
ꢀ
group P1. A red colour rod shaped crystal was chosen for the dif-
fraction study and resulting molecular structure of the complex 3
is shown in Fig. 2. The selected bond angles and bond distances
are given in Table 2. The coordination sphere of this complex
showed asymmetrical bond distances with different donors. The
bond distance between ruthenium and nitrogen (N1, N2, N3) are
in the range 1.966–2.097 Å. The ruthenium ion in each structure
occupied a distorted octahedral environment with a terpy bite an-
gle found in consistence with the value reported for other terpy–
Fig. 1. Molecular structure of complex 2 (30% probability ellipsoid), hydrogen
atoms are omitted for clarity.
ruthenium complexes [38–41]. Both coordinated acetonitrile
groups were bonded to Ru(II) centre at different distance varying
from 2.059 to 2.115 Å.
Scheme 1.

P. Sinha et al. / Polyhedron 31 (2012) 227–234
231
Table 2
Selected bond lengths (Å) and bond angles (°) for complexes 2 and 3.
Complex 2
Ru(1)–N(4)
1.956(4)
Ru(1)–N(3)
2.069(4)
Ru(1)–N(2)
2.046(4)
Ru(1)–N(1)
2.072(4)
Ru(1)–N(5)
2.068(4)
Ru(1)–Cl(1)
2.398(14)
79.56(17)
79.06(17)
158.35(16)
79.99(16)
103.00(17)
171.40(12)
92.42(12)
N(4)–Ru(1)–N(2)
N(2)–Ru(1)–N(5)
N(2)–Ru(1)–N(3)
N(4)–Ru(1)–N(1)
N(5)–Ru(1)–N(1)
N(4)–Ru(1)–Cl(1)
N(3)–Ru(1)–Cl(1)
98.32(17)
93.09(16)
86.64(16)
177.19(18)
98.25(17)
89.17(12)
90.67(12)
N(4)–Ru(1)–N(5)
N(4)–Ru(1)–N(3)
N(5)–Ru(1)–N(3)
N(2)–Ru(1)–N(1)
N(3)–Ru(1)–N(1)
N(2)–Ru(1)–Cl(1)
N(5)–Ru(1)–Cl(1)
Complex 3
Ru(1)–N(2)
Ru(1)–N(3)
Ru(1)–N(1)
Ru(1)–N(5)
1.966(5)
2.075(4)
2.097(4)
2.115(5)
2.059(5)
175.51(17)
79.45(17)
97.57(18)
79.46(18)
87.39(17)
92.16(13)
91.41(14)
93.93(13)
91.87(14)
179.08
Ru(1)–P(1)
P(1)–C(35)
P(1)–C(23)
P(1)–C(29)
2.340(16)
1.829(6)
1.837(6)
1.840(6)
103.16(18)
158.31(19)
88.25(17)
88.23(18)
86.96(17)
101.9(3)
105.9(3)
104.7(3)
114.6(2)
117.2(2)
111.3(2)
Ru(1)–N(4)
N(4)–Ru(1)–N(1)
N(3)–Ru(1)–N(1)
N(2)–Ru(1)–N(5)
N(4)–Ru(1)–N(5)
N(3)–Ru(1)–N(5)
C(35)–P(1)–C(23)
C(35)–P(1)–C(29)
C(23)–P(1)–C(29)
C(35)–P(1)–Ru(1)
C(23)–P(1)–Ru(1)
C(29)–P(1)–Ru(1)
N(2)–Ru(1)–N(4)
N(2)–Ru(1)–N(3)
N(4)–Ru(1)–N(3)
N(2)–Ru(1)–N(1)
N(1)–Ru(1)–N(5)
N(2)–Ru(1)–P(1)
N(4)–Ru(1)–P(1)
N(3)–Ru(1)–P(1)
N(1)–Ru(1)–P(1)
N(5)–Ru(1)–P(1)
Fig. 3. Overlaid UV–Vis absorption spectra of complexes 1, 2, 3 and 4 in DMF
(10ꢁ4 M).
Table 3
Electronic spectral data for complexes 1, 2, 3 and 4.
Complexes
kmax (nm) (10ꢁ4 , Mꢁ1, cmꢁ1
e )
Precursor
294 (2.86), 332 (1.39), 407 (0.42)
1
2
3
4
286 (2.34), 317 (1.37), 364 (0.36), 517 (0.46)
288 (2.76), 324 (1.6), 336 (1.30) 434(0.56), 520 (0.50)
298 (2.10), 339 (1.08), 469 (0.35)
298 (2.12), 314 (2.10), 495 (0.22)
Fig. 2. Molecular structure of complex 3 (30% probability ellipsoid), hydrogen
atoms are omitted for clarity.
3.3. Absorption and emission spectra
The absorption spectra of the complexes recorded in DMF
(10ꢁ4 M) are depicted in Fig. 3 and spectral data are shown in Table
3. The absorptions in UV region were assigned to intraligand p–
p⁄
transitions within terpy, bpy, phen and phenyl rings of PPh3 and
dppe in view of earlier reports [42,43]. However, broad absorption
Fig. 4. Fluorescence spectrum of complex 2 in DMF (10ꢁ4 M).
bands observed at lower energy were assigned to Ru (dp)–terpy/
bpy/phen/PPh3/dppe (p⁄) metal to ligand charge transfer (MLCT)
transitions observed at kmax 517, 520, 469 and 495 nm for 1, 2, 3
and 4, respectively. These bands were red shifted as compared to
the band observed from the precursorcomplex at kmax 407 nm. Thus,
spectral features of the complexes were found sensitive to the
from complexes 1, 3 and 4. This observation is not unusual, having
been observed in several earlier reported ruthenium complexes
[44].
3.4. Electrochemistry
nature of substituted ligands, from weaker
acceptor ligands (bpy, phen) to stronger
r
r
donor and stronger
donor and weaker
p
Electrochemical properties of the complexes was studied in
DMF (10ꢁ4 M) using cyclic voltammetry. The cyclic voltammo-
grams of 1 and 2 are shown in Fig. 5 and redox data are presented
in Table 4. These complexes are found redox active and their metal
p
acceptor ligands (PPh3, dppe). The emission spectrum obtained
from complex 2 in DMF (10ꢁ4 M) is depicted in Fig. 4. However no
detectable luminescence could be obtained under similar condition

232
P. Sinha et al. / Polyhedron 31 (2012) 227–234
Fig. 5. Cyclic voltammograms of representative complexes (a) 1, and (b) 2 in DMF (10ꢁ4 M).
Table 4
Electrochemical data for complexes 1, 2, 3 and 4 at 298 K.
E°298/V( Ep/V)
D
mMLCT (cmꢁ1
)
Complex
Rulll–Rull
Ligand reduction
D
E° = E°298(RuIIIRuII)–
D
E°298(L)
Observed
Calculated
1
2
3
4
0.5
ꢁ1.42
ꢁ1.38
ꢁ1.45
ꢁ1.36
1.92
2.12
2.24
2.04
19342
19230
21321
20202
18484
20097
21065
19452
0.74
0.79
0.68
X
X
Complex 3(10% mol)
R1CHO +
R2C
CH
+
MW,250W,130 oC
N
N
H
6
5
7
C
R1
R2
8a-h
R1 =C6H5(a),MeOC6H4(b),MeC6H4(c) BrC6H4(d)
R2 = C6H5,
= O (6),
X
R =C H (e), MeOC H (f), MeC H (g), BrC H (h)
, R2 = C6H5,
X = CH2 (6)
1
6
5
6
4
6
4
6
4
Scheme 2.
Table 5
Screening of reaction parameters for the synthesis of 8a.
Entry
Catalyst (mol%)
Solvent
Conventional
Microwave
Temp (°C)
Time (h)
Yielda
Power (Watt)
Temp (°C)
Time (min)
Yieldb
1.
2.
3.
4.
5.
6.
RuCl3
precursor
2
3
3
3
chlorobenzene
chlorobenzene
chlorobenzene
chlorobenzene
chlorobenzene
chlorobenzene
130
130
130
130
125
120
8
10
8
8
10
8
nrc
20
trace
35
15
300
300
300
250
300
200
130
130
130
130
130
130
20
20
20
10
15
20
nrc
35
trace
55
55
35
trace
a
b
c
Used benzaldehyde:morpholine:phenylacetylene (1:1.1:1.2).
Isolated yield based on benzaldehyde.
nr = no reaction.

P. Sinha et al. / Polyhedron 31 (2012) 227–234
233
Table 6
conditions by varying the MW power (200, 250 and 300 W) and
time. The 250 W power output and reflux temperature of the sol-
vent were important to obtain the maximum conversion of the
product in 10 min. Further increase in MW power and time could
not enhance the product yield. Under the optimized set of MW
reaction conditions (250 W, 10 min), a number of aldehydes and
amines (Scheme 2) were subsequently made to react with phenyl-
acetylene to provide various propargylamines in appreciable yields
(Table 6). It was interesting to observe that aldehydes such as
benzaldehyde, p-methoxybenzaldehyde, p-methylbenzaldehyde
and p-bromobenzaldehyde reacted smoothly with morpholine/
piperidine and phenylacetylene to produce the corresponding
propargylic amines in 48–56% yields (Table 6, entries 1–8). The
physical and spectral data of all the products are in full agreement
with their assigned structures (S11).
One – pot synthesis of propagylaminesa using complex 3 as catalyst.
Entry R1
Amine
R2
Product Time (min) Yield (%)b
1.
2.
3.
4.
5.
6.
7.
8.
C6H5
Morpholine C6H5 8a
10
10
10
10
10
10
10
10
55
50
48
52
56
52
50
52
p-MeOC6H4 Morpholine C6H5 8b
p-MeC6H4
p-BrC6H4
C6H5
p-MeOC6H4 Piperidine
p-MeC6H4
p-BrC6H4
Morpholine C6H5 8c
Morpholine C6H5 8d
Piperidine
C6H5 8e
C6H5 8f
C6H5 8g
C6H5 8h
Piperidine
Piperidine
a
Reaction condition: aldehyde (1 mmol), amine (1.1 mmol), phenylacetylene
(1.2 mmol), complex
3 (10 mol%), chlorobenzene (2 mL), microwave (250 W,
130 °C).
b
Isolated yield based on aldehyde.
based oxidation was observed between 0.49 and 0.79 V. The low
value observed for metal based oxidation potential could be attrib-
uted to the presence of phenylcarboxy group at 40-position of terpy
ring and other ligands which substituted Cl atoms of the parent
complex. The decrease of metal oxidation potential shows the
4. Conclusion
The Present article embodies the synthesis of four new com-
plexes [Ru(LH)bpyCl]+ 1, [Ru(LH)phenCl]+ 2, [Ru(LH)PPh3(CH3
CN)2]2+ 3 and [Ru(LH)dppeCl]+ 4 obtained after the substitution
destabilization of metal centered (dp) HOMO of the complexes
of chloro groups of precursor complex [Ru(LH)Cl3] by stronger
donor and poor acceptors (PPh3, dppe) and poor donor and
stronger acceptors (bpy, phen). The complexes have been charac-
r
[45].
p
r
p
3.5. Spectroelectrochemical correlation
terized using their spectral and analytical data along with X-ray
diffraction data of complexes [Ru(LH)phenCl]+ 2 and [Ru(LH)PPh3
(CH3CN)2]2+ 3. The latter complex 3 catalyzes the formation of
propargylamines using one-pot multicomponent approach.
The lowest energy MLCT transition involves excitation of the
filled t2 electron of ruthenium(II) to the lowest p⁄ orbital of the ter-
py (LH) ligand. The energy of the MLCT transition is calculated
using observed electrochemical data by using Eqs. (1) and (2) [46].
Acknowledgement
m
MLCT ¼ 8065ð
D
EꢄÞ þ 3000
ð1Þ
ð2Þ
The authors are thankful to DRDE (Grant No. TC/05414/Proj/
Task-81/2008 to L.M.) Gwalior India for the financial assistance.
D
Eꢄ ¼ Eꢄ298ðRuIII—RuIIÞ ꢁ Eꢄ298ðLHÞ;
mMLCT is the frequency of the lowest energy MLCT transition (in
cmꢁ1). The factor 8065 in Eq. (1) is used to convert potential differ-
ence
E from volt to cmꢁ1 and the term 3000 cmꢁ1 is of empirical
Appendix A. Supplementary data
D
origin where as E°298(RuIII–RuII) and E°298(LH) are the formal
potentials (in V) of the ruthenium(III)–ruthenium(II) couple as well
as the first ligand reduction potential, respectively. The calculated
and experimentally observed mMLCT transition frequencies for the
complexes are listed in Table 4. The calculated values lie within
900 cmꢁ1 of the experimentally observed energies, which are in
very good agreement with the previously observed correlation in
other ruthenium complexes [47].
CCDC 793026 and 760553 contains the supplementary crystal-
lographic data for compounds 2 and 3. These data can be obtained
free of charge via http://www.ccdc.cam.ac.uk/conts/retriev-
ing.html, or from the Cambridge Crystallographic Data Centre, 12
Union Road, Cambridge CB2 1EZ, UK; fax: (+44) 1223 336 033; or
e-mail: deposit@ccdc.cam.ac.uk. Supplementary data associated
with this article can be found, in the online version, at
doi:10.1016/j.poly.2011.09.014.
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