Synthesis, Structure, Electrochemical, and Spectroscopic Properties of Hetero-Bimetallic Ru(II)/Fe(II)-Alkynyl Organometallic Complexes

Article abstract of DOI:10.1021/acs.inorgchem.8b02440

A series of heterobimetallic wire-like organometallic complexes [(tpy-C₆H₄-R)(PPh₃)₂Ru-C-C-Fc]⁺ (tpy-C₆H₄-R = 4′-(aryl)-2,2′:6′,2′′-terpyridyl, Fc = [(η⁵-Cp)₂Fe], R = -H, -Me, -F, -NMe₂ in complexes 5-8, respectively) featuring ferrocenyl and 4′-(aryl)-2,2′:6′,2′′-terpyridyl ruthenium(II) complexes as redox active metal termini, have been synthesized. Various spectroscopic tools, such as multinuclear NMR, IR spectra, HRMS, CHN analyses, and single crystal X-ray crystallography have been utilized to characterize the heterobimetallic complexes. The electrochemical and UV-vis-NIR spectroscopic studies have been investigated to evaluate the electronic delocalization across the molecular backbones of the Ru(II)-Fe(II) heterobinuclear organometallic dyads. Electrochemical studies reveal two well-separated reversible redox waves as a result of successive oxidation of the ferrocenyl and Ru(II) redox centers. The spin density distribution analyses reveal that the initial oxidation process is associated with the Fe(II)/Fe(III) couple followed by one electron oxidation of the ruthenium(II) center. The high K_c value (0.11-1.73 × 10¹²) and intense NIR absorption, with molar absorption coefficient (in the order of 10³ M^-1 cm^-1) for the Ru^IIFe^III mixed-valence species, signify strong electronic communication between the two metal termini. The electronic coupling constant (H_ab) has been estimated to be 492 and 444 cm^-1 for the structurally characterized complexes 6 and 7, respectively. The redox and NIR absorption features indicate that the mixed-valence system of the heterobinuclear dyads belongs to a Robin and Day "class II" system.

Full text of DOI:10.1021/acs.inorgchem.8b02440

Article
Cite This: Inorg. Chem. XXXX, XXX, XXX−XXX
pubs.acs.org/IC
Synthesis, Structure, Electrochemical, and Spectroscopic Properties
of Hetero-Bimetallic Ru(II)/Fe(II)-Alkynyl Organometallic Complexes
Amit Sil, Utsav Ghosh, Vipin Kumar Mishra, Sabyashachi Mishra,* and Sanjib K. Patra*
Department of Chemistry, Indian Institute of Technology Kharagpur, Kharagpur-721302, West Bengal, India
*
S Supporting Information
+
ABSTRACT: A series of heterobimetallic wire-like organometallic complexes [(tpy-C H -R)(PPh ) Ru−CC−Fc] (tpy-
6
4
3 2
5
C H -R = 4′-(aryl)-2,2′:6′,2′′-terpyridyl, Fc = [(η -Cp) Fe], R = -H, -Me, -F, -NMe in complexes 5−8, respectively) featuring
6
4
2
2
ferrocenyl and 4′-(aryl)-2,2′:6′,2′′-terpyridyl ruthenium(II) complexes as redox active metal termini, have been synthesized.
Various spectroscopic tools, such as multinuclear NMR, IR spectra, HRMS, CHN analyses, and single crystal X-ray
crystallography have been utilized to characterize the heterobimetallic complexes. The electrochemical and UV−vis−NIR
spectroscopic studies have been investigated to evaluate the electronic delocalization across the molecular backbones of the
Ru(II)−Fe(II) heterobinuclear organometallic dyads. Electrochemical studies reveal two well-separated reversible redox waves
as a result of successive oxidation of the ferrocenyl and Ru(II) redox centers. The spin density distribution analyses reveal that
the initial oxidation process is associated with the Fe(II)/Fe(III) couple followed by one electron oxidation of the
1
2
ruthenium(II) center. The high K value (0.11−1.73 × 10 ) and intense NIR absorption, with molar absorption coefficient (in
c
3
−1
−1
II III
the order of 10 M cm ) for the Ru Fe mixed-valence species, signify strong electronic communication between the two
metal termini. The electronic coupling constant (H ) has been estimated to be 492 and 444 cm for the structurally
−
1
ab
characterized complexes 6 and 7, respectively. The redox and NIR absorption features indicate that the mixed-valence system of
the heterobinuclear dyads belongs to a Robin and Day “class II” system.
INTRODUCTION
end-capped heterobimetallic complexes, supported by different
■
metal centers, have been developed by various research
Bimetallic or polymetallic inorganic and organometallic
complexes bridged by π-conjugated spacers have received
remarkable interest not only for their fascinating mixed valence
9
j,11a−n
5
groups.
Sato and co-workers reported [(η -Cp)-
5
(
PP) Ru(II)-CC-Fc], while Bruce developed [η -Cp*(PP)-
2
1
M(II)-CC-Fc] (M = Ru, Os; PP = (PPh ) , dppe or dppf;
3
2
chemistry but also for their emerging potential applications in
2
3
Cp = C H , Cp* = C Me ) based heterobimetallic complexes
5 5 5 5
molecular electronics, electrochromism,6 information stor-
4
5
to investigate electrochemical communication between Fe(II)
and Ru(II)/Os(II) termini.
age, ion sensing, molecular magnetism, and dye sensitized
11a,g
7
8
Long and co-workers have
solar cells. The pioneering discovery of Creutz−Taube ion,
(NH ) Ru-pyrazine-Ru(NH ) ] , led the scientists to design
5
+
developed a series of heterobimetallic bis(acetylide) ferrocenyl
complexes capped with Ru(II)(dppm)2 [dppm = 1,2-bis-
[
3 5 3 5
and develop binuclear complexes to examine the extent of
charge delocalization in their mixed-valence states and its
fascinating spectroscopic properties. Homobimetallic com-
plexes capable of imparting remote metal−metal communica-
tion across the bridging ligand often generate stable mixed-
valence systems and can be coined as molecular wires.
More interestingly, special attention has been devoted on the
heterobimetallic molecular wires having intrinsically redox
asymmetry of the metal centers.
(
diphenylphosphino)methane] by varying the electronic
9
nature of the aromatic acetynyl ligands, and the electro-
11d
chemical properties have been studied. Jia and co-workers
reported heterobimetallic ferrocene-ruthenium(II) complexes,
[Fc(CHCH) RuCl(CO)(PhPy)(PPh ) ] showing two
1
a,10
3
3 2
partially reversible redox waves for one electron oxidation of
the ferrocenyl moiety and the ruthenium(II) metal center,
11f
9
j,11
respectively.
The Zhong group investigated the electro-
Among the heterobime-
chemical and consequent NIR absorbing properties of a series
tallic complexes, introduction of ferrocenyl (Fc) acetylide gives
a wide diversity of the heterobimetallic complexes which are
advantageous for long-range electron transfer.
9j,11a−n
The
Received: August 29, 2018
synthesis and application of such linear ferrocenyl acetylide
©
XXXX American Chemical Society
A
DOI: 10.1021/acs.inorgchem.8b02440
Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
Scheme 1. Synthesis of the Hetero-bimetallic Complexes (5−8)
+
5
of bis-tridentate complexes [Ru(Fcdpb)(tpyR)] (Fcdpb = 2-
(R = -H, -Me, -F, -NMe ; Fc = [(η -Cp) Fe]), have been
2 2
deprotonated form of 1,3-di(2-pyridyl)-5-ferrocenylbenzene;
tpyR = 2,2′:6′,2′′-terpyridyl derivative), consisting of ferrocene
and cyclometalated ruthenium centers by varying the auxiliary
synthesized by varying the electronic nature of the ligands. The
heterobimetallic complexes have been characterized by differ-
ent spectroscopic tools including multinuclear NMR, HRMS,
and single crystal X-ray diffraction studies. The electrochemical
and UV−vis−NIR spectroscopic studies have been performed
to evaluate the electronic delocalization across the molecular
backbones of the heterobimetallic complexes. Moreover, spin
density distribution analysis and TD-DFT studies have also
been carried out to understand the electronic communication
between the two redox termini in this series of Ru(II)/Fe(II)
organometallic dyads.
1
1s
ligands. Later, Zhong and co-workers studied cyclometalated
and noncyclometalated ruthenium-ferrocenyl complexes and
demonstrated relatively weaker intermetallic interaction in the
1
1m
case of noncyclometalated heterobimetallic complexes.
Later, Chen and co-workers developed a ruthenium(II)
complex of 1,3-bis(2-pyridylimino)isoindolate capped with an
acetynyl ferrocenyl unit, showing a remarkable K (compro-
c
10
9j
portionation constant) value of 4.18 × 10 . Recently, the
Chen group examined ruthenium(II) complexes of 2,3,5,6-
tetrakis(2-pyridyl)pyrazine capped with ferrocenyl acetylide
RESULTS AND DISCUSSION
■
2
exhibiting remarkable NIR absorption at 1230 nm with high K
c
Synthesis and Characterization. A series of 4′-(aryl)-
8
value of 2.82 × 10 revealing efficient electronic communica-
,2′-6′,2′′-terpyridyl ligands (aryl = phenyl, tolyl, 4-fluoro-
11n
tion between ruthenium(II) and the ferrocenyl moiety.
phenyl, 4-(dimethylamino)phenyl for L1−L4, respectively)
have been synthesized by varying the electron donating or
withdrawing nature of the 4′-aryl group to investigate the role
of terminal group on electronic communication in the targeted
heterobimetallic complexes. Condensation of aryl aldehyde
with 2 equiv of acetylpyridine in the presence of ammonia as a
These complexes exhibited promising metal−metal communi-
cation depending on the electronic and redox nature of
organometallic congeners. In ferrocenyl acetylide capped
heterobimetallic complexes, the metal-to-metal charge transfer
(
MMCT) from one metal site to the other metal center
depends on the electrochemical nature of the redox active
metal termini [M] as well as the nature of the π-conjugated
bridging spacers and ligands. When the one-electron reduction
potential of the ferrocenyl unit (Fc) is lower than that of the
14
base led to the formation of the desired terpyridyl ligands.
1
13
Formation of the ligands was ascertained by H, C NMR and
mass spectrometry (SI). The corresponding Ru(II) complexes
(
1−4), [(tpy-C H -R)(PPh ) RuCl][PF ] (R = -H, -Me, -F,
6
4
3 2
6
[M] moiety, the electrochemical communication is operative
-
6
NMe ) were synthesized by the reaction of 4′-(aryl)-2,2′-
2
from [M] to Fc and vice versa. 2,2′:6′,2′′-Terpyridine (tpy) and
their structural analogs exhibit versatile coordination chemistry
with most of the transition metal cations. It is well documented
in the literature that the ligands with different electronic nature
influence the redox potential of the metal centers and splitting
′,2′′-terpyridine (L1−L4) and [Ru(PPh ) Cl ] in degassed
3
3
2
refluxing methanol. After filtration of the reddish brown
reaction mixture through a pad of Celite, the filtrate was dried
under reduced pressure. The solid residue was subsequently
dissolved in a minimum amount of distilled MeOH, and the
1
1c,q
of redox wave arising from electronic interaction.
The
solution was finally treated with 2 equiv of NaPF . The
6
metal−metal communication in mixed-valence systems de-
pends on various factors such as the electronic nature of the
ligand, the length of the bridging spacer between the two redox
active metal termini, and the intrinsic properties of the
terminal metal centers. Typically, the mixed-valence systems
are categorized into three classes (class I to class III)
depending upon the degree of metal−metal electronic
analytically pure products (1−4) were obtained with a high
yield of 80−86% after subsequently being washed with a
copious amount of Et O, followed by recrystallization by
2
layering diethyl ether on an acetonitrile solution of the
1
complexes. In H NMR studies of Ru(II) complexes (1−4),
the protons attached to the carbon next to the nitrogen atom
of the pyridyl ring resonate at 9.03−9.05 ppm, which is
substantially downfield shifted by 0.35 ppm with respect to the
free 4′-(aryl)-2,2′-6′,2′′-terpyridines, revealing coordination of
12
communication according to Robin and Day classification
13
and Hush theoretical analysis. Electrochemistry and spectro-
scopic measurement in the near-infrared region (NIR) have
been utilized to estimate the magnitude of electronic
communication between the two redox active metal centers.
As a result, the judicious selection of ligands with proper
electronic nature is important for tuning the electronic
communication along molecular backbones.
1
the terpyridyl moiety to the metal center. In H NMR, the
characteristic singlet peak for the methyl protons of complexes
2 and 4 resonates at 2.49 ppm (CH ) and 3.10 ppm (NMe ),
3
2
respectively. The signals for the other aromatic protons are
observed in the region of 7.08−8.45 ppm whereas the aromatic
carbons resonated in the region of 120.1−158.3 ppm. A sharp
3
1
1
In this work, a series of acetylide bridged heterobimetallic
singlet at 20.1−20.4 ppm in P{ H} NMR of 1−4 confirms
+
Ru(II)/Fe(II) dyads, [(tpy-C H -R)(PPh ) Ru−CC-Fc]
the presence of two coordinated PPh ligands having similar
6
4
3
2
3
B
DOI: 10.1021/acs.inorgchem.8b02440
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Inorganic Chemistry
Article
Table 1. Important Bond Distances and Angles for Complexes 3, 6, and 7
Complex 3
Bond Distances (Å)
Complex 6
Complex 7
Ru1−Cl1
Ru1−P1
Ru1−P2
Ru1−N3
Ru1−N1
Ru1−N2
2.4469(7)
2.4131(7)
2.4245(7)
2.117(2)
2.098(2)
1.964(2)
Ru1−P1
Ru1−P2
Ru1−N3
Ru1−N2
Ru1−N1
Ru1−C23
C23−C24
2.380(2)
2.385(2)
2.104(7)
2.021(6)
2.120(6)
2.057(9)
1.149(11)
Ru1−P1
Ru1−P2
Ru1−N3
Ru1−N2
Ru1−N1
Ru1−C22
C22−C23
2.3848(12)
2.3786(12)
2.092(4)
2.009(3)
2.097(4)
2.052(5)
1.187(7)
Bond Angles (deg)
P1−Ru1−Cl1
P1−Ru1−P2
P2−Ru1−Cl1
N3−Ru1−Cl1
N3−Ru1−P1
N3−Ru1−P2
N1−Ru1−Cl1
N1−Ru1−P1
N1−Ru1−P2
N2−Ru1−Cl1
N2−Ru1−P1
N2−Ru1−P2
88.93(2)
174.50(2)
85.57(2)
104.25(6)
89.69(6)
91.84(6)
98.00(6)
90.48(6)
90.10(6)
176.78(6)
91.75(6)
93.73(6)
P1−Ru1−P2
N3−Ru1−P1
N3−Ru1−P2
N2−Ru1−P1
N2−Ru1−P2
N2−Ru1−N3
N2−Ru1−N1
N2−Ru1−C23
N1−Ru1−P1
N1−Ru1−P2
N3−Ru1−N1
174.63(9)
90.14(19)
90.07(19)
93.82(19)
91.48(18)
78.0(3)
P2−Ru1−P1
N3−Ru1−P1
N3−Ru1−P2
N2−Ru1−P1
N2−Ru1−P2
N2−Ru1−N3
N2−Ru1−N1
N2−Ru1−C22
N1−Ru1−P1
N1−Ru1−P2
N1−Ru1−N3
C22−C23−C24
Ru1−C22−C23
173.51(5)
92.99(10)
88.39(10)
94.34(10)
92.16(10)
77.85(13)
78.30(14)
177.84(16)
90.37(10)
90.92(10)
156.10(15)
177.1(6)
77.5(3)
177.9(3)
89.94(18)
92.09(18)
155.5(3)
175.4(10)
178.5(8)
C23−C24−C25
Ru1−C23−C24
177.5(4)
Torsional Angles (deg)
C9−C8−C16−C21
C7−C8−C16−C17
34.69
36.02
C7−C8−C16−C17
C9−C8−C16−C21
−34.78
−33.17
C7−C8−C16−C17
C9−C8−C16−C21
−36.06
−35.80
coordination environment. In FTIR spectra, the stretching
frequency at 840−845 cm validates the presence of PF6 as a
counteranion. Finally, HRMS spectrometry of the Ru(II)
characteristic singlet for the methyl protons of complexes 6
and 8 resonates at 2.16 (CH ) and 3.11 ppm (NMe ),
respectively. In C{ H} NMR spectra of the heterobimetallic
complexes (5−8), the aromatic carbons exhibit signals in the
region of 120.1−157.8 ppm whereas the ferrocenyl carbons
appear in the region of 64.6−70.1 ppm, revealing the
incorporation of ferrocenyl moiety. The methyl carbon for
−
1
−
3
2
1
3
1
complexes (1−4) confirms their formation by revealing the
+
molecular ion peaks ([M-PF ] ) at m/z of 970.1848, 984.1983,
6
9
88.1804, and 1013.2243, respectively (SI). The isotopic
distribution patterns for the molecular ion peaks obtained from
the experimental data are in perfect agreement with the
simulated data for all the Ru(II) complexes. After successful
synthesis of the Ru(II) complexes (1−4), incorporation of
ferrocenyl alkynyl moiety was accomplished to furnish the
desired heterobimetallic complexes (5−8). The heterobime-
complexes 6 and 8 resonate at 21.6 (CH ) and 40.5 ppm
3
3
1
1
(NMe ), respectively. In P{ H} NMR spectra, the singlet
2
resonances at 27.9−28.5 ppm are attributed to the coordinated
PPh , having a downfield shift of 7 ppm compared to the
3
coordinated PPh in the mononuclear Ru(II) complexes (1−
3
+
tallic wires [(tpy-C H -R)(PPh ) Ru−CC-Fc] (R = H, Me,
4). Moreover, the presence of counteranion is confirmed by
6
4
3 2
5
31
1
F, NMe ; Fc = [(η -Cp) Fe]) (5−8) were synthesized by
P{ H} NMR showing multiplet at about −143.6 ppm as well
2
2
−
1
treating the chloride coordinated Ru(II) complexes (1−4)
with the ethynyl ferrocene in refluxing MeOH/THF solution
in the presence of KF (Scheme 1). The reaction was
accomplished with a distinct color change of the reaction
mixture from brownish to intense wine red. The solvent was
evaporated after completion of the reaction, and the product
was washed with diethyl ether and hexanes to remove the
unreacted ethynyl ferrocene. The synthesized complexes were
purified by neutral alumina column chromatography using
methanol as an eluent. The second band was collected as
analytically pure heterobimetallic complexes (5−8) with a
moderate yield (60−66%). The complexes were characterized
unambiguously by multinuclear NMR, FTIR, and HRMS
as by IR spectra exhibiting ν(PF ) at 840−844 cm .
̅
6
Furthermore, the characteristic ν(Ru−CC) stretching
̅
frequency for all the heterobimetallic dyads (5−8) appears at
−
1
2063−2070 cm . This further confirms the formation of
Ru(II)-acetylide σ-bond by replacement of the coordinated
chloride ligand. Finally, HRMS analyses of the heterobimetallic
wire-like complexes (5−8) reveal the molecular ion peaks ([M-
+
PF ] ) at 1144.2102, 1158.2356, 1162.2069, and 1187.2685,
6
respectively, with perfect agreement in the isotropic distribu-
tion pattern to the simulated pattern.
Solid State Structure. The molecular structures of the
synthesized complexes have been determined by X-ray
crystallography to gain an insight into the structure property
relationship. The reddish brown colored single crystals for the
complexes 3 and 6 suitable for single crystal X-ray diffraction
were grown by layering hexanes on DCM solution, whereas
complex 7 was crystallized upon layering hexanes on CHCl3
solution in a sealed glass tube. In mononuclear Ru(II) complex
3, the P1−Ru1−N1, P1−Ru1−N2, and P1−Ru1−N3 bond
angles are in the range of 89.69(6)°−91.75(6)° whereas the
1
spectrometry as well as by elemental analyses. In H NMR
spectra of the heterobimetallic complexes (5−8), the protons
adjacent to the pyridyl-N resonate at 8.80−8.87 ppm with an
upfield shift of about 0.22 ppm relative to that of the
complexes 1−4. The remaining aromatic protons resonate in
the region of 6.88−7.94 ppm whereas the ferrocenyl protons
resonate in the region at 4.13−4.46 ppm as multiplets. The
C
DOI: 10.1021/acs.inorgchem.8b02440
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Inorganic Chemistry
Article
25
Figure 1. ORTEP diagrams of complexes 3, 6, and 7. Hydrogen atoms are omitted for the sake of clarity. The thermal ellipsoids are drawn at 40%
probability.
Figure 2. Cyclic voltammograms (CV) and differential pulse voltammograms (DPV) of the Ru(II) complexes (1−4) and heterobinuclear
−
1
ruthenium(II)-ferrocenyl organometallic dyads (5−8) in DCM at a scan rate of 100 mV s . Potentials are given relative to the Ag/AgCl reference
electrode.
bond angles for P2−Ru1−N1, P2−Ru1−N2, and P2−Ru1−
N3 are found as 90.10(6)°−93.73(6)°, respectively, attributing
Thus, the molecular structure of complex 3 reveals a
hexacoordinated Ru(II) center forming a slightly distorted
octahedron formed by three “N” donors of the terpyridyl unit,
that the two PPh ligands adopt nearly orthogonal arrangement
3
above the planar NNN terpyridyl ring. The P1−Ru1−Cl1 and
P2−Ru1−Cl1 bond angles are 88.93(2)° and 85.57(2)°,
respectively, ascribing that Cl1 is positioned orthogonally to
one chloride, and two trans-positioned “P” donors of PPh . In
3
complex 6, the C23−C24−C25 and Ru1−C23−C24 angles
are 175.4(10)° and 178.5(8)°, respectively, revealing the
almost linear linkage of − Fc−CC− and −Ru−CC−.
Similarly, the linear linkages of −Fc−CC− and −Ru−C
C− are manifested for complex 7 showing the C22−C23−C24
both the P atoms (P1 and P2) of the two PPh ligands. The
3
P1−Ru1−P2 bond angle is 174.50(2)° for complex 3,
suggesting the trans orientation of the two PPh ligands.
3
D
DOI: 10.1021/acs.inorgchem.8b02440
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Inorganic Chemistry
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Table 2. Electrochemical Data for Ru(II) Complexes (1−4) and Hetero-binuclear Ruthenium(II)-ferrocenyl Organometallic
Wires (5−8)
a
a
a
b
c
Complex
E1/2(1),
V
E1/2(2),
V
E1/2(3),
V
ΔE1/2
,
mV
Kc
1
2
3
4
5
6
7
8
0.930(96)
0.948(94)
0.962(95)
0.900(91)
0.995(114)
1.02(165)
1.01(180)
1.14(115)
1.11(115)
0.283(104)
0.296(140)
0.299(137)
0.326(94)
712
724
711
654
1.08 × 1012
1.73 × 101
1.04 × 10
1.12 × 1011
2
12
0.980(78)
a
b
c
Corresponding Epa − Epc values (in mV) in parentheses. ΔE = E1/2(2) − E1/2(1). K = exp(ΔE1/2/25.69) at 298 K.
1/2
c
and Ru1−C22−C23 angles are of 177.1(6)° and 177.5(4)°,
respectively. The P1−Ru1−N1, P1−Ru1−N2, and P1−Ru1−
N3 bond angles for complex 6 are in the range of 89.94(18)°−
the two successive reversible redox waves occurred at 0.283 V
(Fc/Fc ) and 0.995 V (Ru /Ru ), respectively, with a
+
II
III
potential difference [ΔE = E1/2(2) − E1/2(1)] of 712 mV
1
/2
9
3.82(19)° whereas the bond angles for P2−Ru1−N1, P2−
between the two consecutive redox waves in complex 5. The
formation of Ru−CC−Fc σ- bond by the replacement of
chloride ligand in Ru(II) complexes (1−4) increases the
reduction potential of the Ru(II) center (in complexes 5−8)
because of appreciable Ru···Fe metal−metal electronic
Ru1−N2, and P2−Ru1−N3 are found in the range of
9
0.07(19)°−92.09(18)°, respectively, ascribing the nearly
orthogonal position of two PPh ligands above the planar
3
NNN terpyridyl moiety. Similar bond angles (Table 1) are also
observed for complex 7 manifesting the identical coordination
1
1n
interaction.
However, the reduction potential for the
+
environment of the PPh ligands. Thus, in the heterobimetallic
3
ferrocene/ferrocenium (Fc/Fc ) couple occurred in less
positive potential in comparison to ethynyl ferrocene due to
combined inductive and electron delocalization effect induced
by the Ru(II) center. The assignment of the redox potentials
was supported by the electrochemical studies as described in
complexes (6 and 7) the Ru(II) center is also hexacoordinated
showing slightly distorted octahedral geometry in which two
axially bonded “P” donors of PPh are trans oriented. The
3
equatorial plane of the Ru(II) centers is surrounded by the
three “N” atoms of the terpyridyl unit and one “C” atom of
acetylide. The Ru···Fe distances for complexes 6 and 7 are
found to be 6.192 and 6.221 Å, respectively. The two
cyclopentadienyl rings in the ferrocenyl group are approx-
imately eclipsed as manifested by the rotational angles which
are in the range of 9.31−12.14 Å and 2.26−6.66 Å for the
complexes 6 and 7, respectively. The ORTEP diagrams of the
complexes 3, 6, and 7 are depicted in Figure 1, while the
selected bond angles and bond lengths are listed in Table 1.
Electrochemical Studies. The electrochemical properties
of the mononuclear Ru(II) (1−4) and heterobimetallic
Ru(II)/Fe(II) (5−8) complexes were investigated using cyclic
the literature with analogous heterobimetallic wires combined
11a−n
with ruthenium(II) and ferrocenyl redox centers.
The
separation between the two successive oxidation waves
(
(
ΔE ) and the comproportionation constant [K = exp-
1
/2
c
ΔE /25.69) at 298 K] are the critical parameters to assess
1
/2
II
thermodynamic stability of the mono-oxidized states (Ru /
Fe ) and the electronic delocalization between the two redox
III
termini through the molecular backbones. The corresponding
12
K of complex 5 has been estimated to be 1.08 × 10 ascribing
c
II
III
the good stability of the Ru /Fe mixed-valence intermediate
as a result of the inherent redox asymmetric nature of the metal
centers. Similarly, the heterobimetallic complexes 6 and 7 also
exhibited two successive reversible redox waves showing E1/2 at
voltammetry (CV) and differential pulse voltammetry (DPV)
at a scan rate of 100 mVs−1 using nBu NPF (0.1 M) as
4
6
0
.296 and 0.299 V, respectively, originating from oxidation of
supporting electrolyte, Ag/AgCl reference electrode, and Pt
disc working electrode in dry dichloromethane. The Ru(II)
complexes (1−4) exhibit a reversible redox wave at 0.93 V,
+
the Fe(II)/Fe(III) (Fc/Fc ) couple, while the consecutive E
1
/2
owing to the oxidation of the Ru(II)/Ru(III) couple occurred
at 1.02 and 1.01 V, respectively. The comproportionation
constants for the complexes 6 and 7 were estimated to be 1.73
0
.948 V, 0.962 V, and 0.90 V, respectively, due to the oxidation
II
III
(
Ru /Ru ) process. The potential difference (E − E ) of
pa
pc
1
2
12
II III
× 10 and 1.04 × 10 respectively. In contrast, complex 8
the individual Ru /Ru redox couple for all the complexes
were around 91−96 mV ascribing good correlation with one
electron Nernstian process. Unlike others, complex 4 showed a
quasi-reversible oxidation wave at higher positive potential (Epa
showed two successive redox processes occurred at 0.326 and
1
1
0
.98 V, respectively, with K of 1.12 × 10 , along with a third
c
redox process at relatively higher positive potential (E1/2 = 1.11
0
•+
V) attributed to the oxidation of the −NMe group (N /N ).
=
+1.14 V), which is likely to be associated with the oxidation
2
However, the degree of metal−metal interaction cannot be
evaluated directly from the wave separation of the sequential
oxidation of ferrocenyl and ruthenium center (ΔE1/2) due to
the structural asymmetry and inherent differences in redox
of the -NMe group resulting in situ generation of radical
cation, Me N . Interestingly, for all the heterobinuclear
2
•
+
2
ruthenium(II)-ferrocenyl organometallic dyads (5−8), two
distinctly separated reversible redox waves were observed due
to the presence of the redox active ferrocenyl (Fc) and
ruthenium(II) centers (Figure 2, Table 2). For all the
heterobimetallic complexes, the reduction potential of the
9
d,11n
potentials of these systems.
the K is determined not only by the resonance contribution
(ΔG ) but also by the several nonresonance contribution
It should also be noted that
c
r
+
II
III
15
Fc/Fc couple and Ru /Ru couple showed substantial
cathodic and anodic shift, respectively, with respect to
reduction potential of ethynylferrocene (E1/2 = 0.76 V) and
the Ru(II) complexes (1−4) (Figure 2 and SI). For example,
(ΔGnr) by a significant extent. The careful examination of the
electrochemical data (Table 2) suggests that the redox
potentials are dependent on the electronic nature of the
functional terpyridyl moieties, but to a lesser degree.
E
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Inorganic Chemistry
Article
5
Figure 3. a) UV−vis-NIR spectra of binuclear Ru(II) complexes (5-8) in DCM after the gradual addition of organometallic oxidant [(η -
Cp) Fe][BF ]. b) Illustration of MM′CT transition inducing NIR absorption in the heterobinuclear Ru(II)/Fe(II) complexes.
2
4
1
2
UV−vis−NIR Studies. For all the Ru(II) complexes (1−
mV) and K (0.11−1.73 × 10 ) values of the heterobimetallic
c
4
), the intense absorption bands in the UV region appeared in
complexes (5−8) are the characteristic of a “class III” mixed-
valence system. However, for the heterobimetallic complexes,
the large ΔE and K values are presumably caused by both
the redox dissymmetry and inherent differences in redox
12
the range of 270−325 nm which is presumably due to the
π−π* transition associated with the terpyridyl moiety (Figure
S26, SI). The Ru(II) complexes (1−4) exhibited broad
1
/2
c
11d,n
absorption bands in the visible region of λ
at 492−507
max
potentials.
To gain more insight into the extent of
4
−1
−1
nm (ε = 0.67−1.23 × 10 M cm ) due to metal-to-ligand
electronic communication, the electronic coupling constants
have been calculated following Hush’s theory. For the
heterobimetallic wires (5-8), the observed half-width, Δν
16
charge transfer (MLCT) transitions. On the other hand, the
heterobimetallic complexes (5−8) exhibited strong absorption
1
/2
4
−1
bands in the region of 312−316 nm (ε = 3.68−4.44 × 10 M
−1
(
1930−2823 cm ) was found to be comparable to the
−
1
cm ) due to the ligand centered π−π* transition. The
absorption band in the visible region centered at 492−499 nm
−1
calculated half-width values (1745−2029 cm ) as established
0
1/2
0
by the equation Δν = [2310(ν − ΔG )] (where ΔG is
1
/2
max
4
−1
−1
(
ε = 0.51−1.37 × 10 M cm ) in the complexes 5−8 was
estimated from ΔE as upper bound value) according to
1
/2
ascribed to metal-to-ligand charge transfer transitions (MLCT
Hush theory assuming two-state model for electron transfer in
for both the Ru(II) and Fe(II) centers). High K values due to
9p,13
c
unsymmetrical bimetallic complexes.
heterobimetallic dyads (5−8) belong to the “class II” mixed-
valence complexes. In view of these redox and absorption
features, it can be concluded that the mixed-valence
intermediates of the heterobimetallic dyads likely belong to
the “class II” mixed-valence system.
coupling matrix element (Hab), which determines the extent of
charge delocalization in mixed-valence compounds, has been
evaluated from the NIR absorption band induced by the
MM′CT transition. We are able to calculate the electronic
coupling constant for complexes 6 and 7 which have been
structurally characterized by single crystal X-ray crystallog-
raphy giving intermetallic distances (R) of 6.19 and 6.22 Å,
respectively. The electronic coupling constants of the mixed-
This suggests that the
the inherent redox asymmetry prompted us to explore the
UV−vis−NIR absorbing property of the heterobimetallic wires.
To investigate the electron transfer process of complexes 5−8,
the changes in their UV−vis−NIR spectra were investigated
12
5
upon incremental charging of [(η -Cp) Fe][BF ] in DCM at
2
4
11d,n,12
The electronic
2
(
5 °C. Interestingly, upon treating with incremental equivalent
5
0−1.0) of organometallic oxidant [(η -Cp) Fe][BF ], the
2
4
MLCT band (λ = 492−498 nm) gradually increased for all
the heterobimetallic complexes. More importantly, a new
broad band started to appear in the NIR region centered at
max
1
1
401−1417 nm with remarkable ε value in the range of 1.11−
3 −1 −1
.65 × 10 M cm as a result of MM′CT (metal-to-metal
II
III
charge transfer) from Ru to Fe metal center. On addition of
equiv of oxidant, the ferrocenyl groups were completely
1
II
III
valence complexes 6 and 7 were calculated by the equation H
oxidized (Fe to Fe ) inducing the MM′CT transition with
the maximum ε value. Adding more than 1 equiv of oxidant,
the intensity of the MLCT band (λmax = 492−498 nm) started
to diminish with concomitant disappearance of the MM′CT
band in the NIR region, illustrating decrease in electronic
communication between the heterobimetallic redox centers
ab
−2
1/2
=
[{(2.05 × 10 )(νmaxε Δν1/2) }/R] considering “class II”
max
mixed-valence complexes where εmax, ν , and Δν are molar
max
1/2
extinction coefficient, absorption maximum, and observed
bandwidth at half-maximum height (in wave numbers) of NIR
absorption band, respectively. The electronic coupling
constant (H ) of 6 is estimated to be 492 cm . Similarly,
complex 7 exhibits observed half-width as 2119 cm ,
II III
−1
because of gradual conversion of Ru Fe mixed-valence
ab
III III
−1
species to Ru Fe (Figure 3). The large ΔE1/2 (654−724
F
DOI: 10.1021/acs.inorgchem.8b02440
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Inorganic Chemistry
Article
−
1
+
+
calculated half-width as 1784 cm , and electronic coupling
and 6 (i.e., 5 and 6 ) have been performed to predict the
origin of the first one-electron reversible oxidation process.
Interestingly, the electron spin density distribution in the
mono-oxidized species is predominately delocalized over the
ferrocenyl moiety (>90%), whereas very slight spin density
distribution is resident on the Ru(II) center (Figure 5). The
constant, Hab = 444 cm− (Table 3).
1
Table 3. Electrochemical Data of Hetero-binuclear
Ruthenium(II)-Ferrocenyl Organometallic Wires (5−8)
−
1
obsd
calcd
λmax
εmax (M
ν
max
(cm
Δν
1/2
Δν
1/2
H
ab
−
1
−1
(cm−1)a
(cm−1)b (cm
1795
1745
1784
2029
−1
c
Complex (nm)
cm
)
)
)
5
6
7
8
1403
1401
1411
1417
1114
1223
1315
1650
7137
7158
7112
7057
1930
2823
2119
492
444
2336
a
b
Observed half-width of MM′CT band. Calculated half-width
0
1/2
0
following the equation Δν [2310(Δν − ΔG )] where ΔG
1
/2
max
13 c
is estimated from ΔE as the upper bound value.
Electronic
1
/2
coupling constant for class II mixed-valence compounds.
+
Figure 5. Spin density distributions in mono-oxidized complexes, 5
and 6 . Contour values: ±0.0004 e/bohr .
+
3
Theoretical Studies. To gain insight into the electronic
structures and spectroelectrochemical properties further,
density functional theoretical studies have been performed
for all the heterobinuclear wires. The optimized geometries of
the complexes are found to be in good agreement with the
corresponding molecular structures obtained from SCXRD
studies, such as for compounds 6 and 7 (Table S4). The
frontier molecular orbitals of the complexes in their neutral
and cationic forms were analyzed by doing a molecular orbital
decomposition analysis over different “fragments” of the
complexes. The contributions of the two metal centers, the
acetylide group, and the Cp groups to the frontier MOs are
summarized in Tables S6 and S7. The HOMO of neutral
complex 5 is primarily contributed by “Fc−CC” (64%) and
a relatively smaller contribution from the ruthenium(II) center
higher spin density on the ferrocenyl moiety than that on the
Ru(II) center clearly indicates that the first one-electron
oxidation processes (0.28−0.32 V) in the studied bimetallic
+
complexes are associated with the Fc/Fc couple, while the
oxidation states of the Ru(II) centers remain unperturbed.
Moreover, upon one-electron oxidation, the geometries of
these complexes are found to undergo minimal changes. The
most important changes in the geometry of the oxidized
species occur in the form of (a) shortening of Ru(II)−Cacetylide;
(b) elongation of the “CC” bond (acetylide); and (c)
increasing in the Fe−Cp distances (Table S5). The changes in
the bond lengths indicate that the one-electron oxidation in the
complexes is accompanied by a net charge transfer from the
Ru(II) metal center to the Fe(III) center via the alkyne bridge.
This is further confirmed by the decrease in the CC
stretching frequency estimated in the oxidized species (from
(
(
23.8%). In contrast, the lowest occupied molecular orbital
LUMO) of the complex (5) has predominant contribution
from the 4′-(aryl)-2,2′:6′,2′′- terpyridyl moiety (87.6%) with a
minor contribution from the Ru(II) metal center (3.85%). The
contributions of the different fragments in the HOMO/
LUMOs for the other complexes (6−8) are similar to that of 5
as depicted in Figure 4. Moreover, the spin density calculation
of the corresponding singly oxidized species of complexes 5
−1
−1
+
2245 cm in 5 to 2173 cm in 5 ). To obtain more detailed
insight into the electronic transition and spectroscopic
properties in the series of synthesized heterobimetallic dyads,
the time-dependent density functional theory (TDDFT) was
performed for complex 5 and its corresponding singly oxidized
Figure 4. Selected frontier molecular orbitals of the heterobinuclear complexes. Contour values: ±0.02 (e/bohr3)1/2
.
G
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Inorganic Chemistry
Article
+
species (5 ) as a case study. The UV−vis−NIR spectra
by varying the electronic nature of the terpyridyl unit to
modulate the intermetallic electronic communication and
consequent NIR absorption. Further investigation on the
modulation of electronic communication is underway in our
laboratory by varying the ancillary ligand, bridging spacer, and
redox-active metal termini to access novel heterobimetallic
wires for the application in molecular electronics.
obtained from TDDFT calculations of complex 5 and its
oxidized form are shown in Figure S31. The computed UV−vis
absorption spectrum appears in the region of 450 to 550 nm
and is in good agreement with experimental absorption.
Additionally, the computed absorption spectrum of the singly
+
oxidized species, 5 shows an absorption band in the NIR
region (centered at 1127 nm), albeit with very low oscillator
strength. This band was absent in the neutral complexes. The
NIR band at λmax of 1127 nm mainly arises from the electronic
transition from the highest occupied spin−orbital (HOSO)-26
to the lowest unoccupied spin orbital LUSO (53%), with
additional minor contribution from HOSO-25 and HOSO-24
to LUSO transitions (18% and 9%, respectively) (Figure S32).
The HOSO-26 spin orbital is found to be dominated by the
electronic population on the ruthenium(II) center along with
the 4′-phenyl-2,2′:6′,2′′-terpyridyl moiety, and a minor
contribution is observed from the ferrocenyl moiety (Figure
S32). On the other hand, the LUSO exhibits a majority of the
probability density on the ferrocenyl moiety of the complex
EXPERIMENTAL SECTION
■
General Considerations. All moisture sensitive reactions and
manipulations were performed under an inert atmosphere of
prepurified Ar or N by using standard dual-manifold Schlenk lines.
2
The glassware was oven-dried (at 180 °C) and cooled under vacuum.
Dry DCM, methanol and CCl were obtained by distillation over
4
CaH , whereas Na/benzophenone was used for drying tetrahydrofur-
2
an and toluene. Unless otherwise mentioned all the chemicals were of
analytical grade, obtained from Aldrich, and used without further
purification. Metal precursor (RuCl ·xH O) was acquired from Arora
3 2
Matthey Ltd. For column chromatography, neutral Alumina was
purchased from SRL chemicals. Thin layer chromatography (TLC)
analysis was used to determine the eluting systems for column
chromatography purifications. Solvents were evaporated under
(
67% contribution from Fe 3d orbitals), with minor
contribution from the ruthenium(II) center and the bridging
acetylide group. Therefore, the NIR electronic transition at
17
reduced pressure using a rotary evaporator. Acetynyl ferrocene,
5
18
19
[
(η -Cp) Fe][BF ] and Ru(PPh ) Cl were synthesized following
2
4
3
3
2
1
127 nm, arising from the HOSO-26 to LUSO, can be
the literature reported procedure.
1
13
1
described by a charge transfer from Ru(II) to Fe(III) in the
singly oxidized species, 5 (Figure S32, Table S9).
H (600, 500, and 400 MHz), C{ H} (150, 125, and 100 MHz)
+
31
1
and P{ H} (162 MHz) NMR spectra were recorded with a Bruker
Lambda spectrometer using CDCl3 unless otherwise mentioned.
Spectra were internally referenced to residual solvent peaks (δ = 7.26
CONCLUSIONS
■
ppm for proton and δ = 77.23 for carbon (middle peak) in CDCl or
3
In conclusion, we have designed, synthesized, and charac-
terized a series of Ru(II)−Fe(II) heterobimetallic organo-
metallic wires by varying the substituents on the terminal
terpyridyl ligands to tune the electronic communication
between the metal termini. Electrochemical studies revealed
two well-separated redox waves due to both inherent redox
asymmetry and metal−metal interactions for the Ru(II)−
Fe(II) heterobinuclear dyads. The reversible redox waves in the
31
1
an external capillary of 85% H PO for P{ H} NMR. All coupling
3
4
constants (J) are given in Hz. The HRMS mass spectra were recorded
+
in ESI mode (70 eV) in Waters (Model: Xevo-G2QTOF) and
Bruker MicrOTOF-Q-II mass spectrometers. Elemental analysis was
carried out in a PerkinElmer Series II CHNS/O 2400 analyzer. The
absorption spectra were collected using a Shimadzu (Model UV-
2
450) spectrophotometer. Vis−NIR absorption spectra were recorded
in a CARY-5000 UV−vis−NIR spectrophotometer. FTIR studies
were performed using Spectrum-BX (PerkinElmer). Cyclic voltam-
metric studies were performed on a BASi Epsilon electrochemical
workstation in DCM with 0.1 M tetra-n-butylammoniumhexafluoro-
range of 0.28−0.33 V (E1 ) originated from the oxidation of
/2
+
the Fe(II)/Fe(III) (Fc/Fc ) couple, while the consecutive
reversible redox waves observed at E1/2 of 0.98−1.02 V were
phosphate (TBAPF ) as the supporting electrolyte. The working
6
due to the Ru(II)/Ru(III) couple. The high K value (0.11−
c
electrode was a BASi Pt disc electrode, the reference electrode wa+s
1
2
II III
1
.73 × 10 ) in the Ru Fe mixed-valence intermediates
Ag/AgCl, whereas the auxiliary electrode was a Pt wire. The Fc/Fc
ascribes strong electronic communication present between the
two metal termini. However, the substituents on tpy ligands do
not play a significant role in electrochemical communication
between the two redox termini. Most interestingly, the
heterobimetallic complexes showed NIR absorption (λMM′CT
couple shows the oxidation wave at E1/2 = +0.51(70) V versus Ag/
AgCl reference electrode under the same experimental set up.
X-ray Data Collections and Refinement. Single-crystal X-ray
diffraction study was carried out on a Bruker-APEX-II CCD X-ray
diffractometer equipped with an Oxford Instruments low-temperature
attachment. Data were collected at 100(2) K using graphite-
=
1401−1417 nm) induced by MM′CT after treating with 1
5 +
monochromated Mo Kα radiation (λ = 0.71073 Å). The frames
α
equiv of oxidant, [(η -Cp) Fe] , showing remarkable molar
extinction coefficient (ε) in the order of 10 M cm .
2
were indexed, integrated, and scaled using the SMART and SAINT
3
−1
−1
20
software package. The SADABS program was used for absorption
Moreover, the electronic coupling constant (H ) was
21
ab
correction. The single crystals were harvested on an 8 mm O.D.
calculated for the structurally characterized heterobimetallic
sealed glass tube. For complexes 3 and 7, one independent molecule
was located in the asymmetric unit. For complex 6, two independent
molecules were present in the asymmetric unit with negligible
differences in their metrical parameters. These data can be obtained
free of charge from The Cambridge Crystallographic Data Centre via
www.ccdc.cam.ac.uk/data_request/cif. The structures were solved by
dyads (6 and 7), and it was found to be in the range of 444−
−
1
4
92 cm . From electrochemical and UV−vis-NIR spectral
studies, it can be concluded that the mixed-valence species of
the heterobimetallic wires belong to the Robin and Day “Class
II” categories of mixed-valence complexes. Moreover, the DFT
calculations (spin density distribution analysis) reveal that the
22
23
24
SHELXT and refined with SHELXL using the Olex2 program.
The molecular structure was generated by using ORTEP-3 for
“
(
Ru−CC−Fc” moiety heavily participates in redox processes
25
Windows Version 2.02.37. Because of the failure to identify the
electrochemical communication) in the mono-oxidized
disordered solvent molecules in complexes 6 and 7, the SQUEEZE
option in the PLATON program was used to remove the unidentified
mixed-valence species and the metal to metal electron transfer
occurs from the ruthenium(II) center to the ferrocenyl moiety.
This work clearly reveals a promising platform for further
development of ferrocenyl capped terpyridyl Ru(II) complexes
26
intensities from the overall intensity data. The hydrogen atoms were
included in geometrically calculated positions in the final stages of the
refinement and were refined according to the typical riding model. All
H
DOI: 10.1021/acs.inorgchem.8b02440
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Inorganic Chemistry
Article
non-hydrogen atoms were refined with anisotropic thermal parame-
ters.
Complex 4. 4 was prepared using a similar procedure for the
synthesis of complex 1. RuCl (PPh ) (0.096 g, 0.1 mmol) and 4′-(4-
2
3 3
Computational Details. The geometries of complexes 5−8 were
dimethylaminophenyl)-2,2′:6′,2′′-terpyridine (0.035 g, 0.1 mmol)
optimized using density functional theory with the hybrid CAM-
were reacted in degassed MeOH (12 mL) under refluxing condition.
27
B3LYP functional that takes care of long-range interactions. The Fe
Anion exchange by charging NaPF
cationic ruthenium(II) complex 4. Yield: 0.097 g, (84%). H NMR
(CDCl , 600 MHz): δ 9.02−9.01 (m, 2H, Py), 7.88−7.86 (m, 2H,
Py), 7.71−7.64 (m, 4H, Py), 7.58 (s, 2H, Py), 7.20−7.17 (m, 18H),
7.07−7.03 (m, 14H), 6.90−6.88 (m, 2H), 3.10 (s, 6H, NMe );
), −143.5 (septet,
) δ 158.6, 156.9, 155.5, 151.8,
146.4, 136.7, 133.2, 132.3, 130.5, 130.4, 129.9, 128.4, 128.2, 126.1,
6
(0.265g, 1.6 mmol) produced
28
1
and Ru metal centers were described by the LANL2DZ basis set,
29
while the 6-31G** basis set was employed for all other atoms.
Starting from the optimized geometries of the complexes in their
nonoxidized states (where both the metal centers are in +2 oxidation
state), the geometry was also optimized for the one-electron oxidized
species of the complexes 5−8. The basis set and functional used for
the nonoxidized complexes were also used for the one-electron
oxidized species. All the optimized geometries were subjected to
further confirmation by carrying out Hessian calculations. The
electronic transitions from the ground electronic state to the excited
states of all the complexes as well as their one-electron oxidized
3
2
3
1
1
P{ H} NMR (CDCl
, 162 MHz) δ 20.0 (s PPh
3
3
1
3
1
PF
); C{ H} NMR (125 MHz, CDCl
6
3
−
1
123.1, 122.6, 119.2, 112.9, 40.5 (NMe
).; FTIR (KBr, υ
, cm ): 842
(PF ); HRMS ESI (m/z): 1013.2205 ([M-PF ] , calcd: 1013.2243).
6 6
2
̅
+
+
Synthesis of Ru(II)−Fe(II) Heterobimetallic Wires. Complex 5.
In a 100 mL Schlenk flask, a solution of complex 1 (100 mg, 0.089
mmol), ethynylferrocene (38 mg, 0.18 mmol), and KF (15 mg, 0.22
3
3
0
1
counterparts were evaluated by carrying out TDDFT calculations.
All calculations were carried out using the Gaussian 09 program.
mmol) in dry THF (5 mL) and CH OH (20 mL) was heated to
3
reflux under Ar atmosphere for 24 h to form deep brown red solution.
After cooling, the solvent was evaporated to a minimum volume (ca. 2
mL) and the crude product was precipitated after addition of dry
diethyl ether (10 mL) through a syringe. The crude product was
filtered through a Schlenk frit, and washed with hexanes. The product
was purified by neutral alumina column chromatography (1.8 cm dia,
The orbital composition analysis of the resultant wave functions was
performed using the Multiwfn program.
32
Synthesis and Characterization. Ligands L1−L4 have been
14
synthesized following the literature procedure (SI).
Synthesis of 4′-(Aryl)-2,2′:6′,2′’-terpyridyl Ru(II) complexes.
Complex 1. In an oven-dried Schlenk flask, a mixture of 4′-(phenyl)-
6
cm alumina packed bed) using distilled methanol as an eluent to
2
,2′:6′,2′′-terpyridine (0.031 g, 0.1 mmol) and RuCl (PPh ) (0.096
2
3 3
collect the second band to afford an analytically pure brown solid of 5.
Yield: 0.063 g (62%). H NMR (CDCl , 600 MHz): δ (ppm) 8.82−
g, 0.1 mmol) and degassed MeOH (12 mL) were added and heated
to reflux for 24 h under argon atmosphere. After cooling to room
temperature, the reaction mixture was filtered through a bed of Celite,
which was washed several times by dry MeOH (3 × 5 mL). Then
1
3
8
7
7
.79 (m, 2H, Py), 7.94−7.87 (m, 2H, Py), 7.75−7.72 (m, 4H, Py),
.63−7.61 (m, 4H), 7.52−7.36 (m, 10 H), 7.22−7.18 (m, 6H), 7.10−
1
3
1
.07 (m, 15H), 6.89−6.87 (m, 2H), 4.48−4.15 (m, 9H, Fc). C{ H}
NaPF (0.265 g, 1.6 mmol) was charged to the concentrated solution,
6
(CDCl , 125 MHz): δ 157.9, 156.6, 155.3, 146.8, 136.9, 136.3, 133.2,
and it was left in the freezer for overnight to precipitate a brown fine
crystalline solid product. After filtration, the solid was washed with
3
1
1
31.9, 131.1, 130.9, 130.7, 130.2, 129.9, 129.8, 128.5, 128.4, 128.3,
3
1
1
27.5, 126.1, 122.8, 120.3, 70.1, 69.9, 69.7, 69.3.; P{ H} (CDCl ,
3
diethyl ether (3 × 10 mL) and dried under vacuum to achieve
1
162 MHz): 28.5 ppm (s, PPh ), −143.9 (septet, PF ); FTIR (KBr, υ,
3
6
̅
analytically pure complex 1. Yield: 0.089 g, (80%). H NMR (CDCl ,
3
−1
+
cm ): 840 (PF ), 2070 (CC); HRMS ESI (m/z): 1144.2102
6
6
00 MHz): δ 7.08−7.19 (m, 14H), 7.20−7.23 (m, 17H), 7.53−7.56
+
(
[M-PF ] , calcd: 1144.2185); Anal. Calcd for C H N P F RuFe:
6
69 54
3 3 6
(
m, 2H), 7.58−7.66 (m, 4H), 7.72−7.75 (m, 4H, Py), 7.94 (d, J = 6
3
1
1
C, 64.29; H, 4.22; N, 3.26. Found: C, 63.48; H, 4.05; N, 3.45.
Complex 6. 6 was prepared using a similar procedure as that for
complex 5. A mixture of complex 2 (100 mg, 0.082 mmol),
ethynylferrocene (37 mg, 0.176 mmol), and KF (15 mg, 0.22 mmol)
Hz, 2H, Py), 9.05 (d, J = 6 Hz, 2H, Py); P{ H}NMR (CDCl , 162
3
1
3
1
MHz) δ 20.0 (s, PPh ), −143.6 (septet, PF ); C{ H} NMR
3
6
(
CDCl , 150 MHz): δ 114.1, 120.5, 122.6, 126.2, 127.1, 128.2, 128.5,
3
1
1
29.7, 129.9, 131.9, 132.1, 132.9, 133.0, 136.2, 136.6, 139.6, 145.8,
in dry THF (5 mL) and CH OH (20 mL) was heated to reflux under
−1
+
3
55.3, 157.2, 158.0.; FTIR (KBr, υ, cm ): 844 (PF ); HRMS ESI
̅
6
Ar atmosphere for 24 h. The product was purified by neutral alumina
column chromatography using distilled methanol as eluent to collect
the second band to afford an analytically pure brown solid of 6. Yield:
+
(m/z): 970.1848 ([M-PF ] , calcd: 970.1821).
6
Complex 2. Treating 4′-(4-methylphenyl)-2,2′:6′,2′′-terpyridine
(
0.032 g, 0.1 mmol) with RuCl (PPh ) (0.096 g, 0.1 mmol) in
1
2
3 3
0
(
7
7
3
1
1
.056 g (60%). H NMR (CDCl , 600 MHz): δ (ppm) 8.87−8.85
3
degassed MeOH (12 mL) under reflux condition, followed by
m, 2H, Py), 7.94−7.87 (m, 2H, Py), 7.78−7.72 (m, 4H, Py), 7.65−
addition of NaPF (0.265 g, 1.6 mmol) yielded complex 2. Yield:
6
.61 (m, 2H, Py), 7.40−7.37 (m, 11 H), 7.21−7.18 (m, 6H), 7.10−
1
0
7
2
.096 g, (86%). H NMR (CDCl , 400 MHz): δ 2.49 (s, methyl 3H),
3
.08 (m, 15H), 6.91−6.87 (m, 2H), 4.25−4.17 (m, 9H, Fc), 2.16 (s,
.07−7.10 (m, PPh 14H), 7.20−7.28 (m, 18H), 7.45 (d, J = 8 Hz,
13
1
3
H, -Me). C{ H} (CDCl , 150 MHz): δ 158.5, 156.5, 155.3, 147.2,
3
H), 7.65−7.67 (m, J = 8 Hz, 4H, Py), 7.73 (t, J = 8 Hz, 2H, Py), 7.94
40.7, 136.3, 134.0, 133.2, 132.3, 131.2, 131.0, 130.9, 130.7, 129.8,
28.8, 128.2, 127.3, 126.1, 122.8, 120.1, 69.7, 69.6, 69.5, 69.4, 21.6
3
1
1
(
d, J = 8 Hz, 2H, Py), 9.05 (d, J = 4 Hz, 2H, Py); P{ H} NMR
1
3
1
(
CDCl , 162 MHz): δ 20.2 (s, PPh ), −143.6 (septet, PF ); C{ H}
31
1
3
3
6
(methyl).; P{ H} (CDCl , 162 MHz): 28.1 ppm (s, PPh ), −143.6
3
3
NMR (CDCl , 100 MHz): δ 21.4, 120.2, 122.6, 126.1, 126.9, 128.2,
−1
3
(septet, PF ); FTIR (KBr, υ, cm ): 842 (PF ); 2063 (CC);
6
̅
6
1
1
8
9
28.5, 128.6, 129.7, 129.8, 129.9, 130.1, 130.5, 132.0, 132.1, 132.9,
+
+
HRMS ESI (m/z): 1158.2356 ([M-PF ] , calcd: 1158.2343); Anal.
6
−1
33.3, 136.6, 140.5, 145.9, 155.3, 157.1, 158.1.; FTIR (KBr, υ, cm ):
̅
Calcd for C H N P F RuFe: C, 64.52; H, 4.33; N, 3.22. Found: C,
7
0
56
3 3 6
+
+
45 (PF ); HRMS ESI (m/z): 984.1983 ([M-PF ] , calcd:
6
6
64.03; H, 4.39; N, 3.37.
Complex 7. A solution of 3 (100 mg, 0.086 mmol),
ethynylferrocene (37 mg, 0.172 mmol), and KF (13 mg, 0.21
84.1977).
Complex 3. 3 was prepared using a similar procedure as described
for complex 1, by treating RuCl (PPh ) (0.096 g, 0.1 mmol) and 4′-
2
3
3
mmol) in dry THF (5 mL) and CH OH (20 mL) was heated to
3
(
4-fluorophenyl)-2,2′:6′,2′′-terpyridine (0.033 g, 0.1 mmol) in
reflux under Ar atmosphere for 24 h to form a deep brown red
solution. Following the similar procedure as described for 6, the
product was purified by neutral alumina column chromatography
degassed MeOH (12 mL) under refluxing condition followed by
anion exchange using NaPF (0.265g, 1.6 mmol). Yield: 0.096 g,
6
1
(
7
87%). H NMR (CDCl , 600 MHz): δ 7.05−7.08 (m, 14H), 7.17−
using distilled methanol as an eluent to afford complex 7. Yield: 0.066
3
1
.21 (m, 20H), 7.62 (m, 2H), 7.70−7.76 (m, 4H, Py), 7.94 (d, J = 6
g (66%). H NMR (CDCl , 600 MHz): δ (ppm) 8.85−8.84 (m, 2H,
3
3
1
1
Hz, 2H, Py), 9.03 (d, J = 6 Hz, 2H, Py); P{ H} NMR (CDCl , 162
Py), 7.93 (d, J = 6 Hz, 2H, Py), 7.80−7.78 (m, 2H, Py), 7.72 (s, 2H,
Py), 7.64−7.61 (m, 2H, Py), 7.39−7.38 (m, 10H), 7.29−7.27 (m,
2H), 7.21−7.18 (m, 6H), 7.10−7.08 (m, 14H), 6.90−6.88 (m, 2H),
3
1
3
1
MHz): δ 19.9 (s, PPh ), −143.6 (septet, PF ); C{ H} NMR
CDCl , 150 MHz): δ 116.8, 116.9, 120.2, 122.7, 126.2, 128.2, 128.3,
3
6
(
3
1
3
1
1
1
9
29.1, 129.2, 129.7, 129.8, 129.9, 130.0, 132.9, 133.0, 136.6, 155.3,
4.28−4.18 (m, 9H, Fc); C{ H} (CDCl , 100 MHz): δ 157.9, 156.7,
3
−
1
+
57.3, 157.9.; FTIR (KBr, υ, cm ): 840 (PF ); HRMS ESI (m/z):
155.3, 145.7, 136.4, 133.2, 133.1, 131.1, 130.9, 130.7, 129.7, 129.5,
129.4, 128.2, 126.1, 122.9, 120.1, 117.1, 116.9, 70.1, 69.6, 69.4, 67.4.;
̅
6
+
88.1804 ([M-PF ] , calcd: 988.1727).
6
I
DOI: 10.1021/acs.inorgchem.8b02440
Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
3
1
1
P{ H} (CDCl , 162 MHz): 27.9 ppm (s, PPh ), −143.5 (septet,
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3
3
■
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̅
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(
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(
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-
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1
1
33.2, 131.4, 131.2, 131.0, 129.7, 128.5, 128.2, 125.8, 123.7, 123.2,
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1
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(
(
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CDCl , 162 MHz): 28.1 ppm (s, PPh ), −143.6 (septet, PF ); FTIR
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6
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̅
6
+
187.2685 ([M-PF ] , calcd: 1187.2607); Anal. Calcd for
6
C H N P F RuFe: C, 64.02; H, 4.46; N, 4.21. Found: C, 63.76;
71
59
4 3 6
H, 4.47; N, 4.19.
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ASSOCIATED CONTENT
■
* Supporting Information
S
The Supporting Information is available free of charge on the
ACS Publications website at DOI: 10.1021/acs.inorg-
chem.8b02440.
(
e) Tanaka, Y.; Kato, Y.; Tada, T.; Fujii, S.; Kiguchi, M.; Akita, M.
Doping of polyyne with an organometallic fragment leads to highly
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40, 10080−10084. (f) Haque, A.; Al-Balushi, R. A.; Al-Busaidi, I. J.;
Experimental details; characterization data; photophys-
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crystallographic data (PDF)
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Accession Codes
(3) (a) Simao, C.; Mas-Torrent, M.; Crivillers, N.; Lloveras, V.;
Artes, J. M.; Gorostiza, P.; Veciana, J.; Rovira, C. A robust molecular
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Memory effects in molecular films of free-standing rod-shaped
ruthenium complexes on an electrode. Angew. Chem., Int. Ed. 2011,
CCDC 1864202−1864204 contain the supplementary crys-
tallographic data for this paper. These data can be obtained
free of charge via www.ccdc.cam.ac.uk/data_request/cif, or by
emailing data_request@ccdc.cam.ac.uk, or by contacting The
Cambridge Crystallographic Data Centre, 12 Union Road,
Cambridge CB2 1EZ, UK; fax: +44 1223 336033.
5
0, 6287−6291. (c) Gong, Z. L.; Yao, C. J.; Shao, J. Y.; Nie, H. J.;
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AUTHOR INFORMATION
■
*
(
*
(
Corresponding Authors
E-mail: skpatra@chem.iitkgp.ac.in. Tel: +913222283338
S.K.P.).
E-mail: mishra@chem.iitkgp.ac.in. Tel: +913222282328
S.M.).
ORCID
Sabyashachi Mishra: 0000-0002-2551-1021
Sanjib K. Patra: 0000-0002-1591-6762
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
IIT Kharagpur is acknowledged for funding the purchase of an
electrochemical workstation through a Competitive Research
Infrastructure Seed Grant (IIT/SRIC/CHY/PBR/2014-15/
4
4). The authors acknowledge DST (India) for funding a 500
MHz NMR spectrometer (SR/FST/CSII-026/2013). Central
Research Facility, IIT Kharagpur, is gratefully acknowledged
for the analytical facility. AS acknowledges IIT Kharagpur, and
UG thanks CSIR, while VKM thanks UGC for doctoral
fellowship.
J
DOI: 10.1021/acs.inorgchem.8b02440
Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
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