Role of Substituents at 3-position of Thienylethynyl Spacer on Electronic Properties in Diruthenium(II) Organometallic Wire-like Complexes

Article abstract of DOI:10.1002/asia.202000755

A series of organometallic complexes [Cl(dppe)₂Ru?C≡C-(3-R?C₄H₂S)-C≡C?Ru(dppe)₂Cl] (3-R-C₄H₂S=3-substituted thienyl moiety; R=?H, ?C₂H₅, ?C₃H₇, ?C₄H₉, ?C₆H₁₃, ?OMe, ?CN in 5 a–5 g respectively) have been synthesized by systematic variation of 3-substituents at the thienylethynyl bridging unit. The diruthenum(II) wire-like complexes (5 a–5 g) have been achieved by the reaction of thienylethynyl bridging units, HC≡C-(3-R-C₄H₂S)-C≡CH (4 a–4 g) with cis-[Ru(dppe)₂Cl₂]. The wire-like diruthenium(II) complexes undergo two consecutive electrochemical oxidation processes in the potential range of 0.0 - 0.8 V. Interestingly, the wave separation between the two redox waves is greatly influenced by the substituents at the 3-position of the thienylethynyl. Thus, the substitution on 3-position of the thienylethynyl bridging unit plays a pivotal role for tuning the electronic properties. To understand the electronic behavior, density functional theory (DFT) calculations of the selected diruthenium wire-like complexes (5 a–5 e) with different alkyl appendages are performed. The theoretical data demonstrate that incorporation of alkyl groups to the thienylethynyl entity leaves unsymmetrical spin densities, thus affecting the electronic properties. The voltammetric features of the other two Ru(II) alkynyl complexes 5 f and 5 g (with ?OMe and ?CN group respectively) show an apparent dependence on the electronic properties. The electronic properties in the redox conjugate, (5 a⁺) with K_c of 3.9×10⁶ are further examined by UV-Vis-NIR and FTIR studies, showing optical responses in NIR region along with changes in “?Ru?C≡C?“ vibrational stretching frequency. The origin of the observed electronic transition has been assigned based on time-dependent DFT (TDDFT) calculations.

Full text of DOI:10.1002/asia.202000755

CHEMISTRY
AN ASIAN JOURNAL
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Accepted Article
Title: Role of Substituents at 3-position of Thienylethynyl Spacer on
Electronic Properties in Diruthenium(II) Organometallic Wire-like
Complexes.
Authors: Sourav Saha Roy, Sabyasachi Roy Chowdhury, Sabyashachi
Mishra, and Sanjib Kumar Patra
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Role of Substituents at 3-position of Thienylethynyl Spacer on
Electronic Properties in Diruthenium(II) Organometallic Wire-like
Complexes
Sourav Saha Roy, Sabyasachi Roy Chowdhury, Sabyashachi Mishra and Sanjib K. Patra*[a]
[
a]
[a]
*[a]
Abstract: A series of organometallic complexes [Cl(dppe)
2
Ru-C≡C-
resulting in an interesting class of organometallic wire-like
conjugates.[2b-c,3] Such metal alkynyls possess promising
properties which include luminescence,[4] tuning the band
gap,[5] liquid crystallinity,[6] nonlinear optics[7] and the ability
to convey information through metal-metal communication.
4 2 2 4 2
(3-R-C H S)-C≡C-Ru(dppe) Cl] (3-R-C H S
= 3-substituted thienyl
moiety; R = -H, -C
2
H
5
, -C
3
H
7
, -C ,-C
4
H
9
6
H13, -OMe, -CN in 5a-5g
respectively) have been synthesized by systematic variation of 3-
substituents at the thienylethynyl bridging unit. The diruthenum(II)
wire-like complexes (5a-5g) have been achieved by the reaction of
[
8]
Thus, organometallic wire-like complexes have been
thienylethynyl bridging units, HC≡C-(3-R-C
4
H
2
S)-C≡CH (4a-4g) with
recognized as the next generation smart materials for
applications such as in solar cells, [9] organic light emitting
diodes,[10] optical signal processing and molecular
switches.[11]
cis-[Ru(dppe) Cl ]. The wire-like diruthenium(II) complexes undergo
2
2
two consecutive electrochemical oxidation processes in the potential
range of 0.0 - 0.8 V. Interestingly, the wave separation between the
two redox waves is greatly influenced by the substituents at the 3-
position of the thienylethynyl. Thus, the substitution on 3-position of
the thienylethynyl bridging unit plays a pivotal role for tuning the
electronic properties. To understand the electronic behavior, density
functional theory (DFT) calculations of the selected diruthenium wire-
like complexes (5a-5e) with different alkyl appendages are
performed. The theoretical data demonstrate that incorporation of
alkyl groups to the thienylethynyl entity leaves unsymmetrical spin
densities, thus affecting the electronic properties. The voltammetric
features of the other two Ru(II) alkynyl complexes 5f and 5g (with - -
OMe and -CN group respectively ) show an apparent dependence
on the electronic properties. The electronic properties in the redox
Organometallic wire-like complexes, of the type [L
n
M-
C≡C-Ar-C≡C-ML ] (L = ancillary ligands, Ar = aromatic π-
n
conjugated spacers, M = redox active transition metal
cation) in which two (or more) redox active metal centres
are connected by a π-conjugated organic bridge are ideal
candidates for the study of facile electron transport (ET)
processes.[8] The degree of ET process is highly dependent
on the stability of the mixed-valence state which can be
quantified with the help of the comproportionation constant
c
K as evaluated from electrochemical studies. In recent
studies, we have convincingly demonstrated the long-range
electron transfer properties of soluble thienylethynyl bridged
molecular wires with redox active ‘-Ru(dppe)
2
’ termini.[12]
+
6
conjugate, (5a ) with K
c
of 3.9×10 are further examined by UV-Vis-
NIR and FTIR studies, showing optical responses in NIR region
along with changes in “-Ru-C≡C-“ vibrational stretching frequency.
The origin of the observed electronic transition has been assigned
based on time-dependent DFT (TDDFT) calculations.
The efficient tuning of the electron transfer properties can
be modulated with appropriate extension of the conjugation
in the thienylethynyl bridging spacers. However, the degree
of the electron transfer processes can be perturbed to
different extents, depending on several key factors such as
the degree of conjugation,[13] nature of electron-
rich/deficient groups on the bridging moiety[14] and different
metal precursors.[15] Therefore, the electronic properties of
the organometallic wire-like complexes can be tuned by
controlling these parameters and by judicious designing.
Thienyl systems have been emerged as promising
materials for their fascinating applications as organic
semiconductors mainly due to its chemical stability and
ease of functionalization at 3-position. The ethynyl moiety
provides rigidity to the entire molecule, helping in
intramolecular electronic delocalization throughout the
molecular backbone. Thienyl moieties with terminal ethynyl
groups can also act as potential π-conjugated ligands to
access metal-alkynyl σ-bonds with suitable metal
precursors, enabling facile electron transfer properties.[13a,16]
In 2009, Liu and co-workers have reported a series of
binuclear ruthenium(II)-vinyl complexes bearing 1,4-
diethenylphenylene bridge, and finely tuned the
Introduction
There is a rapidly growing field of interest for last two
decades to design and develop different types of π-
conjugated organometallic complexes for their potential
applications in the emerging field of molecular-scale
electronics.[1] Organometallic wire-like complexes with
suitable π-conjugated bridge serve as important building
blocks to synthesize active multifunctional materials.[2]
Incorporation of metal ions in organic rigid π-conjugated
oligomers and polymers offers tuning their chemical,
optical, redox, magnetic as well as the physical properties
[
a]
S. Saha Roy, S. Roy Chowdhury, Dr. S. Mishra, Dr. S. K. Patra
Department of Chemistry
Indian Institute of Technology Kharagpur
Kharagpur 721302, WB, India.
E-mail: skpatra@chem.iitkgp.ac.in, mishra@chem.iitkgp.ac.in
Supporting information for this article is given via a link at the end of
the document.
II
III
electrochemical coupling between the Ru /Ru couples by
varying the substituents on the bridging spacers.[14] Low
and co-workers have also synthesized a series of binuclear
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Chemistry - An Asian Journal
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FULL PAPER
ruthenium complexes bridged with phenylene[17] and
divinylchalcogenophene[13a] units and investigated the
charge transfer properties by varying the substituents on
bridging unit. Subsequently, Fu and co-workers[18] have
precursors were brominated at 2- and 5- positions by a
brominating agent like N-bromosuccinimide (NBS).[25]
Incorporation of alkynyl groups at 2- and 5- positions by
Sonogashira
coupling
in
DCM
yielded
2,5-
developed
1,4-diethenylphenylene
bridged
Ru(II)
bis[ethynyl(trimethylsilyl)] derivatives (3a-3g). The TMS-
termini of thienylethynyl derivatives 3a-3g were desilylated
complexes with oligo(ethylene glycol)methyl ether side
chains and studied their electron transfer characteristics.
Recently, Winter and co-workers reported a series of
divinylheterocycle bridged diruthenium(II) complexes and
tuned the electronic coupling by modification of bridging
spacers.[19] The degree of electronic coupling can be well
tuned not only by the bridging spacers but also by varying
the metal termini. For example, Ou and co-workers have
2 3
using K CO in DCM/MeOH affording the corresponding
desired thienylethynyl spacers (4a-4g) with-C≡C-H termini
as shown in Scheme 1. All these 3-substituted
thienylethynyl
compounds
were
purified
by
chromatographic separation and characterized by standard
NMR techniques. The single resonance signal corresponds
to thienyl proton in the region of 7.28-7.01 ppm and two
singlets in the region of 3.44-3.32 ppm for two terminal
ethynyl protons clearly confirm the formation of
successfully
demonstrated
the
modulation
of
electrochemical communication by varying Ru(II) and Fe(II)
termini in benzo[1,2-b;4,5-bʹ]dithiophene bridged bimetallic
complexes.[20]
thienylethynyl spacers, 4a-4g
.
Keeping this information in mind, herein in this report,
we have designed and synthesized
a
series of
diruthenium(II) wire-like complexes with a 2,5-thienylethynyl
spacer by varying the alkyl groups as well as introducing
electron donating (-OMe) and withdrawing group (-CN) at
the 3-position of thienylethynyl bridging core. We aim to
investigate the effect of systematic variation of the
substituents at the 3-position of thienyl bridge on the
intramolecular electronic delocalization in diruthenium(II)
organometallic wire-like complexes by electrochemical,
spectroscopic and DFT studies.
Results and Discussion
Scheme 1. Synthetic route for 3-substituted π-conjugated thienylethynyl
congeners 4a-4g. Reagents and conditions: a) Mg turnings, RBr (R = -
Synthesis and characterization of 3-substituted π-
conjugated thienylethynyl congeners: Rigid-rod like π-
conjugated organic compounds with terminal -C≡CH
linkages are efficient candidates to access metal-alkynyl σ-
2 5 3 7 4 9 6 2
C H , -C H , -C H , -C H13), 0.5 mol% Ni(dppp)Cl , THF, reflux, 24h. b) 2
eqv. NaOMe, 0.1 eqv. CuI, MeOH/NMP, reflux 48h; c) 4 eqv. CuCN,
DMF, reflux, 16h; d) 2.2 eqv. NBS, THF, 25 °C, 12h. e) 3.6 eqv.
ethynyltrimethylsilane, 3.5 mol% Pd(PPh
3 2 2 3
) Cl , 3 mol% CuI, Et N, DCM,
2
5 °C, 24h; f) K CO , MeOH/DCM, 25 °C, 2h. (Yield in parenthesis).
2
3
bonded wire-like organometallic complexes for facile
electronic transfer.[2d,12,13,21] To understand the influence of
Synthesis of diruthenium(II) wire-like complexes:
Binuclear Ru(II) organometallic wire-like complexes with the
substituents on the organic backbone a series of 3-
substituted thienylethynyl π-conjugated spacers were
synthesized following a sequence of Pd(II)/Cu(I) catalyzed
Sonogashira coupling and deprotection reactions. The key
redox-active terminals
through
reaction
of
cis-
[
Ru(dppe) Cl ] [dppe= 1,2 bis(diphenylphosphino) ethane]
2
2
with the ‘C≡C-H’ termini of the synthesized π-conjugated
thienylethynyl spacers were intended. The general synthetic
route for the preparation of diruthenium(II) wire-like
complexes is presented in Scheme 2. The rigid rod-like
thienylethynyl precursors with alkynyl termini were treated
starting
precursors
of
3-substituted
thienylethynyl
analogues (1b-1g) were synthesized from the commercially
available 3-bromothiophene by following the literature
procedures.[22-24] 3-substituted thienylethynyl congeners
with 2.1 equivalent of cis-[Ru(dppe)
leading to the slow formation of the vinylidene intermediate.
The vinylidene intermediate was subsequently
deprotonated by Et N base in DCM affording Ru(II)-Cl
2 2 6 ,
Cl ] and NaPF in DCM
(1b-1e) were synthesized from 3-bromothiophene through
Ni(II) catalyzed Grignard coupling reaction with respective
bromides.[22] 3-methoxythiophene (1f) was prepared from 3-
3
bromothiophene through
a reaction involving sodium
methoxide (NaOMe) as nucleophile.[23] Furthermore, 3-
capped rigid rod-like organometallic σ-complexes (5a-5g),
where the substituents at 3-position of thienylethynyl core
were varied judiciously to investigate the redox properties.
The synthesized diruthenium(II) wire-like complexes were
cyanothiophene (1f) was achieved in good yield from 3-
bromothiophene with CuCN in DMF medium.[24] To afford
the dibromo thienylethynyl derivatives (2a-2g), the following
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Chemistry - An Asian Journal
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obtained in an analytically pure form after chromatographic
thienylethynyl moiety.13b The organometallic wire-like
purification under inert atmosphere. These complexes (5a-
complexes 5a-5g exhibit transitions with λmax of 392-400 nm
4
-1
-1
5
g
) were characterized by spectroscopic methods such as
and ε values in the range of 4.69-4.79×10 M cm (Figure
1 and Table 1). However, the broad absorption feature are
attributed to the overlapping of thienylethynyl ligand based
π-π* transitions and MLCT transition.[28]
multinuclear NMR, FTIR and elemental analyses.
Scheme 2. Synthesis of diruthenium(II) wire-like complexes 5a-5g
.
2 2 6
Reagents and conditions: a) i) 2.1 eqv. cis-Ru(dppe) Cl , 2.2 eqv. NaPF ,
DCM, 25 °C, 24h; ii) Et N, DCM, 25 °C, 12h. (Yield in parenthesis).
3
1H NMR specta of the organometallic diruthenium(II)
wire-like complexes (5a-5g) exhibit resonance signals in the
region of 8.00-7.01 ppm as multiplets corresponding to the
aromatic protons of the dppe and thienyl rings. A broad
multiplet in the region of 2.78-2.63 ppm may be attributed to
Figure 1. UV-Vis absorption spectra of diruthenium(II) wire-like complexes
-
5
(
3
5a-5g) recorded in CHCl (1×10 M) at 25 °C.
the alkyl CH
integral ratio of aromatic protons are in accordance with the
integral ratio of alkyl CH protons, unambiguously indicating
the successful insertion of [-Ru(II)(dppe)] unit to the
2 2
(dppe and hexyl-CH adjacent to thienyl). The
2
Table 1. UV-Vis spectral data of the diruthenium(II)
-
1
-1
complexes in CHCl
3
(ε in M cm )
1
3
1
thienylethynyl spacers
(
4a-4g).
C{ H} NMR of the
Compound
Absorbance
max , nm (log ε)
complexes (5a, 5c and 5d) shows a characteristic signal of
Ru-C≡C bond at 126.9 ppm, whereas for 5b and 5f, the
signals are observed at at 127.2 and 127.1 ppm
λ
5
a
392 (4.79)
393 (4.65)
392 (4.57)
394 (4.45)
392 (4.69)
400 (br)
5b
respectively. However, low solubility in common organic
solvents restricted the resolution of 13C{1H} NMR spectrum
5c
5d
of complex 5g 31
.
P{ H} NMR spectra shows a sharp singlet
1
resonance in the region of 49.4-49.1 ppm for the eight
phosphorus nuclei of dppe moiety, indicating the trans
geometry around the Ru(II) centres.[12,26] FTIR spectra also
display the characteristic stretching frequency for Ru-C≡C
5e
5
f
5g
398 (br)
-
1 [12,13a]
bond in the region of 2030-2053 cm .
For complex 5g
the presence of the ‘-C≡N’ group is further confirmed by the
appearance of diagnostic vibration stretches near 2233 cm-
Electrochemical properties: The extent of the electronic
properties in wire-like complexes bridged by thienylethynyl
spacers were examined by electrochemical techniques. The
redox behavior of the wire-like complexes (5a-5g) was
investigated by using cyclic voltammetry (CV) and differential
pulse voltammetry (DPV) at scan rate of 100 mVs-1 using
1.
MALDI-TOF of 5a exhibits the molecular ion [M] peak at
+
1996.319. The characteristic isotopic distribution pattern is
perfectly matched with the simulated distribution. Attempts
to acquire mass spectrometry using MALDI-TOF
spectrometry in case of 5b-5g revealed fragmentation and
+
[27]
exhibited the base peak of [-Ru(dppe)
2
] .
4 6
Bu NPF (0.1 M) as supporting electrolyte, Pt disk working
electrode and a Ag/AgCl reference electrode in DCM solution
strictly under argon atmosphere. Cyclic and differential pulse
voltammograms for wire-like complexes are depicted in Figure
2., whereas the electrochemical data are compiled in Table 2.
The diruthenium(II) wire-like complexes display two consecutive
one-electron oxidation processes in a potential window from 0.0
to 0.8 V. Complexes 5a-5c exhibit two successive reversible
redox waves. In contrast, 5d-5f undergo first oxidation process
as electrochemically quasi-reversible or irreversible while the
UV-Vis absorption studies: The electronic absorption of
the π-conjugated congeners 4a-4g and their
diruthenium(II) wire-like complexes 5a-5g were
investigated in CHCl The π-conjugated thienylethnyl
π
(
)
(
)
3
.
congeners 4a-4g exhibit an absorption band λmax, in the
region of 297-300 nm (Figure S19, Supporting Information)
with extinction coefficient (ε) values in the range of 9.26-
-1
-1
4
.30×104 M cm , ascribing to π-π* transitions of the
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6
3.9×10 . A large K
c
in 5a is indicative of a strong electronic
second oxidation process is reversible. The free π-conjugated
organic bridging ligands do not undergo any redox prpcess in
the potential window of 0.2 to 0.8 V following a similar
delocalization transmitted through the thienylethynyl bridge.
Incorporation of alkyl groups to the 3-position further decreases
the peak-to-peak separation of redox conjugates as observed
from their K values. In comparison with complex 5a, the 3-ethyl
c
substituted thienylethynyl analogue 5b shows relatively lower
electrochemical set up. The peak-to-peak separation ΔE1/2
=
E
1/2(2)-
E
1/2(1) and the comproportionation constant
K
c
=
exp(ΔE1/2/25.69 at 298 K)[29] are the two critical parameters to
evaluate the electron transfer kinetics along the molecular
backbones in redox conjugates.[13,16a-b,21b] Complex 5a exhibits
two successive oxidation processes at E1/2 of 0.053 V and 0.443
V. The potential difference (Epa − Epc) of 79 and 87 mV
respectively, for the individual reversible redox wave,
supports one-electron redox process. A careful investigation
reveals that the first oxidation process is perfectly reversible with
2
wave separation (ΔE1/2) of 170 mV with K
c
of 7.5×10 . The wave
separation for the oxidation in the other homologues complexes
follows decreasing order from 5c to 5d (ΔE1/2; 135 and 126 mV
respectively), attributable to the gradual decrease in
thermodynamic stability of the electrochemically generated
redox conjugates. However, oxidation on only metal termini may
not be predominant, as the major contribution of oxidation in
these oranometallic redox conjugate arises from the bridging
ligand orbitals as evaluated from DFT studies (vide infra).
i
pa/ipc = 1.01, whereas for the second oxidation process the ipa/ipc
is 1.82. The current values for the two redox process are
different although both are one-electron oxidation process.
Winter and coworkers also noticed that the peak heights were
different to an extent of 1.17-1.19 in [{(PiPr
3
)
3
Cl(CO)Ru(-CH꞊CH-
Liu and
C
4
H
2
NMe-CH꞊CH-)RuCl(CO)(PiPr
3 3
)
}].[19] Later,
coworkers also observed a similar trend of different peak height,
for a series of divinylchalcogenophene bridged biruthenium
complex of type [{(PMe
3 3 4 2
) Cl(CO)Ru(-CH꞊CH-C H E-CH꞊CH-
)
RuCl(CO)(PMe
3 3
)
}; E= O, S, Se, Te].[13b] In those diruthenium(II)
systems, the ipa/ipc ratio of the two oxidation waves was in
the range of 1.07-1.04 (for the first redox wave) and 1.73-
1.42 (for the second
Table 2. Electrochemical data of diruthenium(II) wire-like complexes.
a
a
E
(
1/2 (1), V
)
E
1/2 (2), V
Compound
d
d
ΔE1/2b, mV
c
K
c
ΔE
p
p
(ΔE )
5
5
5
5
5
5
5
a
b
c
d
e
f
0.053 (79)
0.353 (72)
0.425 (75)
0.426 (72)
-
0.443 (87)
0.523 (74)
0.559 (72)
0.552 (73)
390
170
135
126
-
3.9×106
7.5×102
1.8×102
1.3×102
e
0.530 (78)
-
-
-
0.372 (75)
-
0.557 (80)
0.583 (76)
185f
g
-
a
in DCM at scan rate of 100 mV s-1.
CV was recorded in 0.1 M Bu NPF
4 6
b
ΔE1/2 = E1/2(2) - E1/2(1), potential difference between two reversible redox
waves. cThe comproportionation constants (K
) was calculated from the
= exp(ΔE1/2/25.69) at 298 K. difference between Epa and Epc in
c
d
formula K
c
Figure 2. Cyclic voltammograms (CV) and differential pulse voltammograms
e
f
mV. CV shows one reversible redox wave. Wave separation (ΔE) has been
(
DPV) of diruthenium(II) wire-like complexes (5a-5g) at a scan rate of 100 mV
-1
calculated considering the second quasi-reversible redox wave obtained at
s . Potentials are given relative to the Ag/AgCl reference electrode.
[
14a,18]
0.37 in DPV for 5f.
Interestingly, for complex 5e, a single well-resolved redox wave
was
observed
suggesting
negligible
electrochemical
redox wave). Moreover, recording CV with varying scan rate (50-
communication. For complex 5f, in which a methoxy (-OMe)
group is attached to the 3-position of thienylethynyl unit, two
redox waves were also observed in DPV study with wave
separation of 185 mV. Presumably, the electron-donating
property of the -OMe group results in an increase in the electron
density of thienylethynyl ring, facilitating better electronic
-1
300 mVs ) and with different working electrodes, similar redox
waves were witnessed in our diruthenium(II) conjugates (Figure
S21, Table S1, Supporting Information). Multiple cycles (up to 20
segments) under potential window of -0.1 to +0.8 V did not lead
to any change in electrochemical behavior or decomposition
(
Figure S22, Supporting Information). For complex 5a, without
any substituent at 3-position of thienylethynyl core, the wave
separation (ΔE1/2) is 390 mV, with the corresponding K of
delocalization in heteroaromatic system. Unlike 5f
unresolved CV and DPV suggests insignificant electronic
,
c
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Chemistry - An Asian Journal
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FULL PAPER
delocalization in 5g with electron-withdrawing –CN group
attached to 3-position of bridging thienylethynyl. Thus, it is
very clear indication that 3-substitution on thienylethynyl
unit plays a pivotal role for modulating the electrochemical
coupling on diruthenium(II) wire-like complexes with π-
conjugated spacer.
conjugates. The FTIR spectra of chemically oxidized species
+
2+
(
5a and 5a ) were obtained by reaction of neutral complex 5a
Fe]+ at room temperature (298
with organometallic oxidant [Cp
K) in DCM (Figure 4). Complex 5a shows very strong and single
2
-1
ῡ
as(C≡C) band in the IR region at 2041 cm . Upon oxidation to
mono-oxidized 5a+ species by adding 1.0 equivalents of the
UV-Vis-NIR studies: High electrochemical coupling (in the
oxidant, the single ῡas(C≡C) band associated to neutral species
6
order of 10 ) in complex 5a, encouraged us to gain more
knowledge on the insight of electronic delocalization in
redox conjugates
changes upon incremental addition of ferrocenium
tetrafluoroborate [Cp Fe][BF ] oxidant to 5a in CHCl at 298
K were monitored (Figure 3). The band with λmax of 392 nm
π-π* transition of thienylethynyl moiety) decreases
gradually in magnitude upon sequential oxidation by
Cp
Fe]+ (0-2 eqv. with 0.5 incremental eqv.). The
[
5a]+
.
The UV-Vis-NIR absorption
2
4
3
(
[
2
associated absorption band at 620 nm in the visible region
can be attributed to vibrationally structured aromatic
radical.[16a] More interestingly, a new low-energy absorption
band emerged at λmax of 1308 nm with ε value of 6.46 × 103
Figure 4. Changes in the FTIR spectra of complex 5a in the presence of
+
0
, 1.0 and 2.0 equiv. of oxidant [Cp
2
Fe] .
is decreased gradually accompanied by new lower
-1
frequency band centered at 1934 cm . This convincingly
-
1
-1
M cm in the NIR region. As expected, the intensity of NIR
absorption reaches a maximum ε value upon consumption
of one equivalent of oxidant. Adding more than one
equivalent of oxidant, the NIR band amplitude gradually
decreases and finally disappears, illustrating that no
electronic transitions occur in
indicates the formation of mesomeric structures between
the thienyl unit and two C≡C bonds favoring electronic
delocalization along the π-conjugated bridge.[15a,16a] Upon
further oxidation to the dicationic species by the addition of
+
2
.0 equivalents of [Cp
2
Fe] , the IR band shifts to a lower
-1
[16a]
frequency of 1925 cm , however to a smaller extent.
This change in shift of C≡C bonds along the two step
oxidation clearly indicates that ethynyl moieties are strongly
participate in oxidation processes, manifesting the
noninnocent redox character of bridging ligands.
DFT Calculations: To gain further insight into the influence of
alkyl groups (at 3-position of thienylethynyl entity) on the
electronic structures of the diruthenium(II) wire-like complexes
(
5a-5e), DFT calculations were performed. The geometries of
the respective binuclear ruthenium(II) complexes, 5a-5e were
optimized in the truncated model systems [5a-H] to [5e-H],
3
where the “-Ph” groups of the PPh moiety were replaced by “-H”
to reduce the computational cost. Spin density distributions were
computed for the monocations of the five complexes in order to
examine the roles of the metal centres and bridging moieties in
the oxidation. To investigate the matching electrochemical trend
in more detail, the orbital composition analyses of the frontier
molecular orbitals in terms of metal d-character were performed.
In complexes [5a-H] to [5e-H], it is found that the electron
density in the HOMO resides largely on the entire metal-organic
π-system with 83% to 86% contribution arising from the
3
Figure 3. Changes in the UV-Vis-NIR spectra of 5a in CHCl with gradual
addition of [Cp Fe] . Asterisk (*) indicates artifacts.
2
+
π-conjugated metal−organic conjugates. For the other
diruthenium(II) wire-like complexes (5b-5e), no notable NIR
absorptions could be observed during the stepwise
oxidation process. This may be presumably due to lower
stability of the redox conjugates generated in reaction
medium.
FTIR spectroscopy: FTIR spectroscopy is a powerful tool to
investigate the changes in the stretching frequencies of redox
conjugates that contain ‘C≡C’ functional group in different redox
states.[13a,16a] The changes in C≡C stretching frequency are often
helpful to understand the degree of delocalization in redox
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Table 3: Orbital contribution to HOMO for the diruthenium(II) wire-like
complexes obtained from DFT calculations.
Complex
Ru(II) d-orbital contribution to
HOMO (%)
Bridging ligand orbital
contribution to HOMO (%)
[5a-H]
[5b-H]
[5c-H]
[5d-H]
[5e-H]
15.0
14.6
17.1
15.9
14.5
85.0
85.4
82.9
84.1
85.5
The origin of this asymmetric spin-density distribution in
complexes [5b-H]+ to [5e-H]+ can be traced back to the
presence of the alkyl groups introduced at the 3-position of
thienylethynyl moiety. A significant change in the spin-
density has been observed between complex [5a-H]+ and
[
5b-H]+
,
however this change is minimal between
complexes [5c-H]+ to [5e-H]+. The effect of longer alkyl
groups exerts an asymmetric electronic distribution at the
molecular backbone. The lack of uniform distribution
(
compared to [5a-H]+) of the spin-density in complexes [5b-
H]+ to [5e-H]+ indicates that mixed valence characteristics
which generate from variation of electronic delocalization is
consistent with the electrochemical data. Notably, Liu and
co-workers have also described unsymmetrical spin
distribution and its effect on electronic properties by DFT
studies in homo-dinuclear ruthenium(II) complexes of type
Figure 5. HOMOs of the model complexes [5a-H] to [5e-H]. Contour values:
3
1/2
±
0.02 (e/bohr ) . HOMO-1 and LUMOs are shown in Supporting Information.
bridging moiety. The remaining (17% to 14%) contribution
arises from the two ruthenium(II) centres (Figure 5, Table
[
M(dppe)Cp*-C≡C-X-C≡C-M(dppe)Cp*] (X = triphenylamine
3). Due to the large contribution of the bridging ligand to the
and N,N,N′,N′-tetraphenylphenylene-1,4-diamine].[28b]
HOMOs with very less involvement of metallic termini,
subsequent oxidation of these complexes indicates that the
dominant contributions may come from the bridging ligand
orbitals. The relative contribution from the d-orbitals of the
two metal centres are found to be identical in complex [5a-
H], while alkyl substitution at 3-position of thienylethynyl
moiety leads to an unequal contribution from the two metal
centres as observed in [5b-H] to [5e-H]. The calculated
spin density in the monocationic species [5a-H]+ to [5e-H]+
is distributed entirely on the π-conjugated thienylethynyl
systems (Figure 6), reflecting the same trend as observed
in HOMO. For complex [5a-H]+, 97% of the spin-density
was found to be distributed symmetrically over the bridging
thienylethynyl moiety, whereas upon alkylation the overall
spin density distribution on the bridging moiety reduces to
8
9-91% with an accompanying increase in the spin-density
over the two metal centres in complexes [5b-H]+ to [5e-H]+
.
The symmetric distribution of the spin-density over the two
halves of complex [5a-H]+ is clearly replaced by an
asymmetric spin-density distribution in complexes [5b-H]+
to [5e-H]+
.
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H
]+ are displayed in Figure 7. The lowest energy transition
in the NIR region at 1125 nm with an oscillator strength of
.5525 corresponds to β-HOSO→β-LUSO transition having
0
a dominant π-π*(thienylethynyl) character mixed with some
ML(bridge)CT.[13a,16a,d] The vibrationally structured aromatic
radical band centred at 536 nm with oscillator strength of
0.0242, arises predominantly from β-HOSO-9→β-LUSO
transition, exhibiting similar absorption characteristics
bearing π-π*(bridge) mixed with MLCT.[16a,d] Finally, in the
UV region, the most intense band is calculated at λmax of
386 nm (oscillator strength 0.6015), being mainly assigned
to electronic transition from α-HOSO→α-LUSO which can
be attributed to intraligand π-π* transition with some
admixture of MLCT character.
Conclusions
In summary, we have successfully synthesized and
characterized
a
series of [-Ru(II)-Cl] end capped
organometallic wire-like complexes by varying the
substituents (alkyl and electron donating/withdrawing group)
at 3-position of thienylethynyl bridging unit. A combination of
cyclic voltammetry, differential pulse voltammetry, UV-Vis-
NIR, and DFT calculations have been employed to
investigate and to witness the effect of substituents of the
thienyl on the electrochemical, spectroscopic, and electronic
properties in these diruthenium(II) diacetylide complexes.
Electrochemical studies have revealed that all of these
diruthenium(II) wire-like complexes display one electron
oxidation processes. As demonstrated by electrochemistry,
the introduction of alkyl substituents at 3-position of
thienylethynyl ring has a significant effect on the redox
processes of the Ru(II)-thienyl conjugates. Effect of alkyl
groups with increasing carbon atoms on the electronic
properties has been realized by the asymmetric spin density
distribution which resides mainly on the organic bridging unit,
as evident from DFT calculations. The specific evolution of
the UV-Vis-NIR absorption upon stepwise oxidation on 5a by
Figure 6. Spin-density distributions in [5a-H]+ to [5e-H]+ with the
corresponding compositions (C≡C/thienylethynyl/C≡C). Contour values:
3
±
0.0004 e/bohr .
The DFT method, chosen for the truncated model
complexes [5a-H]n+ (n = 0, 1), also helped to compare the
relative ν(C≡C) shifts caused by oxidation of the neutral
complex to the mono-oxidized species with the
corresponding experimental wave numbers of the
asymmetric C≡C stretching vibration of thienylethynyl unit.
Considering the harmonic normal-mode vibrational
frequency of C≡C asymmetric stretching mode in [5a-H]
(
2251 cm ) and [5a-H]+ (2171 cm ), the calculated value of
−
1
-1
[Cp Fe] clearly demonstrates the electronic delocalization
+
2
−
1
relative shift (Δῡ) is 80 cm , which is in a good agreement
with the corresponding experimental data for 5a and [5a]+
within the redox conjugates. An absorption band in the NIR
region at 1308 nm in the mono-oxidized species originates
mainly due to the π-π* admixed with MLCT transition instead
of purely Ru(II)-Ru(III) mixed valence transition. The studies
of electrochemical and electronic properties of the rod-like
−
1
(
Δῡ = 107 cm ). This observation suggests that ethynyl
linker has a strong involvement in the oxidation process.
The assignment of the electronic transitions was
Ru(II) conjugates in this report have led to
understanding and provided helpful information in designing
a good
explored by TDDFT calculations on the optimized truncated
+
model mono-oxidized system,
[
5a-H] . The TDDFT
π-conjugated bridging ligands for new redox-responsive
calculations gave three predominant transitions for [5a-H]+
which are listed in Table 4. The corresponding molecular
orbitals involved in the major electronic excitations in [5a-
bimetallic
conjugates.
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Figure 7. Molecular orbitals that are involved in the electronic transitions in the mono-oxidized complex, [5a-H] . Contour values: ±0.02 (e/bohr )1/2. Orbital
+
3
energies and the corresponding compositions (Ru/C≡C/thienylethynyl/C≡C/Ru) are provided
.
Table 4: Major electronic excitations of [5a-H]+ determined by using TDDFT method
Complex
5a-H]+
λ (nm)
Oscillator Strength (f)
Major Contributions
Assignment
[
1125
0.5525
0.0242
0.6015
β-HOSO→β-LUSO
β-HOSO-9→β-LUSO
α-HOSO→α-LUSO
π-π*(thienylethynyl) ML(bridge)CT
π-π*(thienylethynyl) ML(bridge)CT
π-π*(thienylethynyl) ML(bridge)CT
5
3
36
86
3 3 4
) or an external capillary of 85% H PO
for 31P{ H}
1
CDCl
NMR. All coupling constants (J) are reported in hertz (Hz).
MALDI-TOF study was measured with Bruker
UltrafleXtreme instrument using 2,5-dihydroxybenzoic acid
DHB) as matrix. FTIR spectroscopy was recorded in
Experimental Section
General Materials
All moisture sensitive reactions and manipulations
were performed under an atmosphere of pre-purified argon
or nitrogen using dual manifold standard Schlenk
techniques. The glasswares were oven-dried (at 180 °C)
and cooled under vacuum. Drying of Tetrahydrofuran was
carried out over Na/benzophenone. Dry DCM and methanol
(
Spectrum-BX (Perkin Elmer) with KBr pellets. Elemental
analyses were carried out on a PerkinElmer Series II CHN
2
400 analyzer. Cyclic voltammetric studies were conducted
on a BASi Epsilon electrochemical workstation in DCM with
.1 tetra-n-butylammonium hexafluorophosphate
TBAPF as the supporting electrolyte at room
0
M
2 3
were obtained by distillation over CaH . Et N was purified
(
6
)
by distillation from KOH pellets. Unless otherwise
mentioned all the chemicals were of analytical grade,
obtained from Aldrich, and used without further purification.
temperature. The working electrode was a BASi Pt disk
electrode, the reference electrode was Ag/AgCl and the
auxiliary
electrode
was
a
Pt
wire.
The
2 3 2
Metal precursors (PdCl , RuCl .H O) were acquired from
ferrocene/ferrocenium couple occurs at E1/2 = +0.51 (70) V
versus Ag/AgCl under the same experimental conditions.
The UV-Vis-NIR spectra were measured on a Varian
Arora Matthey. Silica gel (60–120 mesh) used for column
chromatography were purchased from Merck. Eluting
systems for column chromatography purifications were
determined by thin layer chromatography (TLC) analysis.
TLC plates were visualized under UV light (254 nm) or in
(
Model- Cary 5000) UV-Vis-NIR spectrometer. For the
absorption measurements, the compound was dissolved in
CHCl solution (~1
10-5 M). To this solution, an
organometallic oxidant [Cp Fe][BF ] in CHCl was added
3
×
iodine chamber. The starting materials such as compound
30]
4e,[12] 5e,[12] cis-Ru(dppe) ,[31] Pd(PPh ,[32]
2
4
3
2
a-2g [
,
Cl ) Cl
2 2 3 2 2
incrementally (0-2 equivalent) and the resulting solution
was quickly mixed and immediately subjected to UV-Vis-
NIR measurements.
were synthesized by the procedures described in literature
methods.
Physical Measurements
Computational details
1H (600 MHz and 400 MHz), 13C{ H} (150 MHz, and
1
The geometry optimizations were carried out using CAM-
B3LYP[33] functional together with def2-TZVP[34] basis set
for all the atoms. Dispersion correction was employed using
the empirical dispersion method implemented in Gaussian
3
1
1
1
00 MHz), and P{ H} (162 MHz) NMR spectra were
recorded from Bruker Lambda spectrometer using CDCl
3
unless otherwise mentioned. Spectra were internally
referenced with respect to residual solvent peaks (δ = 7.26
ppm for proton and δ = 77.2 for carbon (middle peak) in
0
9 software[35]. Thermodynamic stabilities of the optimized
complexes were confirmed by analysis of normal mode of
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vibrations, obtained from the Hessian calculations. Single
point energy calculations were carried out for the
complexes in their one-electron and two-electron oxidized
forms, i.e., the two Ru centres were treated in (II,III) and
CDCl
3
,) δ (ppm): 148.9, 133.9 (CH thienyl), 122.2, 119.1,
84.2 (-C≡CH), 81.9 (-C≡CH), 76.9 (-C≡CH), 76.2 (-C≡CH),
32.3, 22.4, 14.0.
2,5-Diethynyl-3-butylthiophene (4d): Compound 4d was
prepared by an analogues method to that for 4a. From 3d
(210 mg 0.63 mmol) and potassium carbonate (211 mg,
(III,III) oxidations states, at the geometries obtained from
the optimization of the respective complexes in their (II,II)
states to obtain the one-electron and two-electron oxidation
potentials, respectively. The wave separation (ΔE1/2) is
calculated from the difference in the one-electron and two-
electron oxidation potentials. TDDFT calculations were
performed for the monooxidized species using CAM-B3LYP
functional and def2-TZVP basis set. The orbital composition
analysis[36] of the resultant wave functions were performed
using Multiwfn program.[37]
1.52 mmol), 4d was obtained as yellowish oil (110 mg,
1
93%). H NMR (400 MHz, CDCl
3
,) δ (ppm): 7.01 (s, 1H, CH
thienyl), 3.44 (s, 1H, -C≡CH), 3.32 (s, 1H, -C≡CH), 2.65 (t, J
= 4 Hz, 2H, Th-CH -C ), 1.59 (m, 2H, Th-CH - CH
), 1.34 (m, 2H, Th-C -CH -CH ), 0.92 (m, 3H, Th-
). 13C{ H} NMR (100 MHz, CDCl
,) δ (ppm):
2
3
H
7
2
2
-
C
C
2
2
H
H
5
4
2
H
4
2
3
1
-CH
2
-CH
3
3
148.9, 133.9 (CH thienyl), 122.2, 119.1, 84.2 (-C≡CH), 81.9
(-C≡CH), 76.8 (-C≡CH), 76.2 (-C≡CH), 32.4, 29.2, 22.4,
1
4.1.
Synthesis and characterization
2,5-Diethynyl-3-methoxythiophene (4f): Compound 4f
The synthesis and characterization of the π-conjugated
was prepared by an analogues method to that for 4a. From
(0.249 mg 0.81 mmol) and potassium carbonate (288
spacers with –C≡C–TMS termini (3a–3g) are included in
3
f
the Supporting Information.
mg, 2.12 mmol), 4f was obtained as yellowish oil (115 mg,
1
Syntheses of Diethynyl Heterocyclic Derivatives 4a-4g.
,5-Diethynylthiophene (4a): The dark yellow oily 2,5-
88%). H NMR (400 MHz, CDCl
thienyl), 3.48 (s, 1H, -C≡CH), 3.35 (s, 1H, -C≡CH). 13C{ H}
3
,) δ (ppm): 6.90 (s, 1H, CH
1
2
bis[ethynyl(trimethylsilyl)]thiophene (1 g, 2.97 mmol) and
potassium carbonate (820 mg, 5.94 mmol) were dissolved
in a solution of DCM (15 mL) and methanol (10 mL). The
solution was allowed to stir at room temperature (25 °C) for
3
NMR (100 MHz, CDCl ,) δ (ppm): 160.4, 121.5 (CH thienyl),
121.1, 101.9, 84.6 (-C≡CH), 82.5 (-C≡CH), 74.7 (-C≡CH),
59.2 (-OMe).
2,5-Diethynyl-3-cyanothiophene (4g): Compound 4g was
prepared by an analogues method to that for 4a. From 3g
(198 mg 0.66 mmol) and potassium carbonate (230 mg,
1.65 mmol), 4g was obtained as yellowish oil (84 mg, 81%).
2h. The reaction mixture was poured into water and
extracted with DCM. The organic extract was washed with
brine solution. The combined organic layers were dried over
anhydrous MgSO
4
. The solvent was removed by rotary
1H NMR (500 MHz, CDCl
thienyl), 3.80 (s, 1H, -C≡CH), 3.45 (s, 1H, -C≡CH). 13C{ H}
3
,) δ (ppm): 7.28 (s, 1H, CH
1
evaporator. Finally, it was purified using silica gel column
chromatography (hexane as eluent) to afford 2,5-
diethynylthiophene as yellowish oil with 600 mg (94% yield).
1H NMR (500 MHz, CDCl
thienyl), 3.35 (s, 2H, -C≡CH). 13C{ H} NMR (100 MHz,
3
NMR (100 MHz, CDCl ,) δ (ppm): 133.3 (CH thienyl), 132.3,
124.8, 115.6 (Th-CN), 113.3, 89.6 (-C≡CH), 84.7 (-C≡CH),
74.4 (-C≡CH), 73.1 (-C≡CH).
3
,) δ (ppm): 7.12 (s, 2H, CH
1
Syntheses of diruthenium(II) wire-like complexes 5a-5g.
Complex 5a: A solution of cis-Ru(dppe)
mmol), 4a (30 mg, 0.22 mmol) and NaPF
mmol) in dry DCM (25 mL), were stirred at room
temperature under argon atmosphere for 24h. The reaction
mixture was filtered through Schlenk frit containing
activated Celite 545 to remove NaCl by-product and
CDCl
3
,) δ (ppm): 133.9 (CH thienyl), 122.2, 81.8 (-C≡CH),
6.8 (-C≡CH).
,5-Diethynyl-3-ethylthiophene (4b): Compound 4b was
2
Cl
2
(451 mg, 0.46
7
6
(84 mg, 0.50
2
prepared by an analogous method to that for 4a. From 3b
180 mg 0.59 mmol) and potassium carbonate (201 mg,
.47 mmol), 4b was obtained as yellowish oil (82 mg, 89%).
1H NMR (500 MHz, CDCl
,) δ (ppm): 7.04 (s, 1H, CH
thienyl), 3.45 (s, 1H, -C≡CH), 3.32 (s, 1H, -C≡CH), 2.66 (m,
(
1
3
6 3
unreacted NaPF , if any. Then, Et N was added to that
reaction mixture, and stirred for another 15h. The whole
solution was evaporated to dryness. It was purified by
column chromatography through a silica gel column (60-120
mesh) with 25% ethyl acetate-hexane mixture as eluent in
). 13C{ H} NMR
1
2
H, Th-CH
2
-CH
3
), 1.21 (m, 3H, Th-CH
,) δ (ppm): 148.9, 133.9 (CH thienyl),
22.2, 119.1, 84.2 (-C≡CH), 81.8 (-C≡CH), 76.9 (-C≡CH),
-CH
2 3
(100 MHz, CDCl
3
1
7
2
inert atmosphere to afford 5a as yellow solid (320 mg, 72
6.2 (-C≡CH), 22.4, 14.1.
1
%
). H NMR (600 MHz, CDCl
3
,) δ (ppm): 7.40-7.27 (m, 30H,
,5-Diethynyl-3-propylthiophene (4c): Compound 4c was
Ph of dppe), 7.21-7.11 (m, 11H, Ph of dppe), 7.08-7.0 (m,
0H+2H, Ph of dppe+CH of thienyl), 2.65-2.56 (m, 16H,
prepared by an analogous method to that for 4a. From 3c
191 mg 0.60 mmol) and potassium carbonate (210 mg,
.55 mmol), 4c was obtained as yellowish oil (91 mg, 91%).
1H NMR (400 MHz, CDCl
,) δ (ppm): 7.01 (s, 1H, CH
thienyl), 3.44 (s, 1H, -C≡CH), 3.32 (s, 1H, -C≡CH), 2.63 (t, J
4
(
2 3
CH ,) δ (ppm):
of dppe). 13C{ H} NMR (150 MHz, CDCl
1
1
1
1
1
=
35.1, 134.7, 134.5, 134.1, 134.0, 130.3, 129.6, 129.3,
3
29.1, 129.0, 128.9, 128.5, 127.6, 127.3, 127.2, 127.1,
, 1JP,C+3JP,C
2 2
27.0, 126.9 (Ru-C≡C-), 30.9 (quint. PCH PCH
=
4 Hz, 2H, Th-CH
2
-C
2
H
5
), 1.65 (m, 2H, Th-CH
2
- CH
2
-CH
3
),
24Hz). 31P{1H} NMR (162 MHz, CDCl
3
,) δ (ppm): 49.2 (s,
). 13C{ H} NMR (100 MHz,
1
-1
0.94 (m, 3H, CH
2
- CH
2
-CH
3
PPh ). FTIR (KBr, cm ): ῡ(Ru-C≡C) = 2041. Anal. Calcd for
2
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C
112
H
98Cl
2
P
8
Ru
2
S: C, 67.37; H, 4.95. Found: C, 67.31; H,
127.6, 127.5, 127.4, 127.2, 127.1 (Ru-C≡C-), 59.2 (-OMe),
, 1JP,C+3JP,C = 23 Hz). 31P{ H} NMR
1
5.56.
30.8 (quint. PCH
(162 MHz, CDCl
2
PCH
2
-
Complex 5b: Complex 5b was prepared by an analogous
method to that for 5a. From cis-Ru(dppe)
mmol), 4b (20 mg, 0.12 mmol) and NaPF
mmol), 5b was obtained as yellow solid (187 mg, 77 %). H
3
,) δ (ppm): 49.1 (s, PPh
): ῡ(Ru-C≡C) = 2031. Anal. Calcd for C113
C, 66.96; H, 4.97. Found: C, 66.86; H, 5.58.
Complex 5g: Complex 5g was prepared by an analogous
2
). FTIR (KBr, cm
1
2
Cl
2
(257 mg, 0.26
H
100Cl
2
OP Ru
8
2
S:
6
(46 mg, 0.27
1
NMR (600 MHz, CDCl
dppe), 7.20-7.16 (m, 16H, Ph of dppe), 7.03-6.99 (m,
1H+H, Ph of dppe+CH of thienyl), 2.73-2.63 (m, 18H, CH
3
,) δ (ppm): 7.54-7.32 (m, 33H, Ph of
method to that for 5a. From cis-Ru(dppe)
mmol), 4g (13 mg, 0.08 mmol) and NaPF
mmol), 5g was obtained as yellow solid (116 mg, 72 %). H
2
Cl
2
(164 mg, 0.17
6
(30 mg, 0.18
1
3
2
), 0.89-0.84 (m, 3H). 13C{ H} NMR
1
NMR (600 MHz, CDCl
of dppe+Th-CH
2
-CH
3
3
,) δ (ppm): 7.55-7.49 (m, 13H, Ph of
(
150 MHz, CDCl ,) δ (ppm): 135.1, 134.7, 134.56, 134.1,
3
dppe), 7.47-7.43 (m, 14H, Ph of dppe), 7.02-6.99 (m,
1
34.0, 131.8, 131.7, 131.1, 131, 129.2, 129.1, 129.0, 128.7,
53H+H, Ph of dppe+CH of thienyl), 2.73-2.72 (m, 16H, CH
2
of dppe). 31P{ H} NMR (162 MHz, CDCl
1
,) δ (ppm): 49.2 (s,
). FTIR (KBr, cm ): ῡ(Ru-C≡C), ῡ(-C≡N) = 2053, 2233.
128.6, 127.6, 127.4, 127.2 (Ru-C≡C-), 30.9 (quint.
3
, 1JP,C+3JP,C = 23 Hz), 22.9, 14.4. P{ H} NMR
31
1
PPh
-1
PCH
2
PCH
2
2
(
162 MHz, CDCl
)
3
,) δ (ppm): 49.3 (s, PPh
2
). FTIR (KBr, cm-
Ru S: C,
2 8 2
Anal. Calcd for C113H97Cl NP Ru S: C, 67.13; H, 4.84.
1
13
1
: ῡ(Ru-C≡C) = 2041. Anal. Calcd for C114
H
102Cl
2
P
8
2
Found: C, 67.29; H, 4.94. Note: C{ H} NMR spectrum of
67.62; H, 5.08. Found: C, 67.72; H, 5.28.
compound 5g could not be recorded due to very poor
Complex 5c: Complex 5c was prepared by an analogous
3
solubility in common deuterated solvents including CDCl .
method to that for 5a. From cis-Ru(dppe)
mmol), 4c (15 mg, 0.08 mmol) and NaPF
mmol), 5c was obtained as yellow solid (122 mg, 74 %). H
2
Cl
2
(172 mg, 0.17
Conflicts of interest
6
(30 mg, 0.18
1
The authors declare no competing financial interests.
NMR (600 MHz, CDCl
dppe), 7.22-7.20 (m, 16H, Ph of dppe), 7.04-6.99 (m,
1H+H, Ph of dppe+CH of thienyl), 2.74-2.62 (m, 18H, CH
of dppe+Th-CH -C ), 1.27 (bs, 10H), 0.88-0.86 (m, 3H).
C{ H} NMR (150 MHz, CDCl ,) δ (ppm): 134.7, 134.5,
3
,) δ (ppm): 7.39-7.30 (m, 33H, Ph of
Acknowledgements
SKP is grateful to IIT Kharagpur for funding through
3
2
Competitive
Research
Infrastructure
SKP
Seed
and
Grant
SM
2
2 5
H
(IIT/SRIC/CHY/PBR/2014-15/44).
1
3
1
3
acknowledge the support from DST, Govt. of India
SR/FST/CSII-026/2013). SM acknowledges the support
134.3, 134.2, 134.1, 134.0, 129.5, 129.3, 129.2, 129.1,
(
1
29.0, 128.9, 128.8, 127.8, 127.5, 127.2, 126.9 (Ru-C≡C-),
from SERB, Govt. India (EMR/2015/001890 and CSIR,
India (01(2897)/19/EMRII). Central Research Facility, IIT
Kharagpur is gratefully acknowledged for providing
analytical facilities. SSR and SRC thank IIT Kharagpur for
doctoral fellowship.
3
1
2.1, 30.9 (quint. PCH
2
PCH
2
, 1 P,C+3JP,C = 23 Hz), 22.9,
J
4.5. 3 P{ H} NMR (162 MHz, CDCl
1
1
3
,) δ (ppm): 49.1 (s,
). FTIR (KBr, cm ): ῡ(Ru-C≡C) = 2041. Anal. Calcd for
Ru S: C, 67.74; H, 5.14. Found: C, 67.31; H,
-
1
PPh
C
2
115
H
104Cl
2
P
8
2
5.36.
Complex 5d: Complex 5d was prepared following the
Keywords: Thienylethynyl • Ruthenium • Organometallic wire-
like complex • Electronic properties • Redox conjugates.
similar method as followed for 5a. From cis-Ru(dppe)
2
Cl
2
6
(
(
263 mg, 0.27 mmol), 5d (25 mg, 0.13 mmol) and NaPF
50 mg, 0.29 mmol), 5d was obtained as yellow solid (205
1
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mg, 77 %). H NMR (600 MHz, CDCl
3
,) δ (ppm): 7.50-7.303
(
m, 30H, Ph of dppe), 7.20-7.19 (m, 20H, Ph of dppe), 7.04-
6
.99 (m, 30H+H, Ph of dppe+CH of thiophene), 2.73-2.63
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.87 (m, 5H). 1 C{ H} NMR (150 MHz, CDCl
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1
0
1
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27.2, 126.9 (Ru-C≡C-), 32.1, 30.9 (quint. PCH
P,C+ JP,C = 23 Hz), 29.5, 22.9, 14.5. P{ H} NMR (162
2
PCH
2
,
1
3
31
1
-
1
MHz, CDCl
ῡ(Ru-C≡C) = 2040. Anal. Calcd for C116
7.86; H, 5.20. Found: C, 67.51; H, 5.60.
Complex 5f: Similarly, Complex 5f was prepared from cis-
Ru(dppe) Cl (183 mg, 0.19 mmol), 4f (15 mg, 0.09 mmol)
and NaPF (35 mg, 0.21 mmol). Complex 5f was obtained
as yellow solid (134 mg, 74 %). H NMR (600 MHz, CDCl
δ (ppm): 7.44-7.38 (m, 21H, Ph of dppe), 7.22-7.18 (m,
7H, Ph of dppe), 7.04-6.98 (m, 42H+H, Ph of dppe+CH of
thienyl), 3.90 (m, 3H, OMe), 2.74-2.65 (m, 16H, CH of
,) δ (ppm): 134.8,
34.7, 134.6, 134.5, 134.2, 134.1, 134, 133.9, 131.7, 127.7,
3
,) δ (ppm): 49.3 (s, PPh
2
). FTIR (KBr, cm ):
555-563.
H
106Cl
2
P
8
Ru S: C,
2
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Chemistry - An Asian Journal
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FULL PAPER
Entry for the Table of Contents
FULL PAPER
Electronic properties are governed by
the substituent at 3-position of thienyl
Key Topic*
Sourav Saha Roy,[a] Sabyasachi Roy
Chowdhury,[a] Sabyashachi Mishra*[a]
unit
in
diruthenium(II)
wire-like
organometallic complexes with π-
conjugated thienylethynyl bridge.
and Sanjib K. Patra*[a]
Page No. – Page No.
Title: Role of Substituents at 3-
position of Thienylethynyl Spacer on
Electronic
Properties
in
Diruthenium(II) Organometallic Wire-
like Complexes
.
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