Tuning of intramolecular charge transfer properties and charge distributions in ferrocene-appended catechol derivatives by chemical substitution

Article abstract of DOI:10.1039/c5dt01998b

In this study, we report intramolecular charge transfer (ICT) properties and charge distributions in a series of FcC derivatives (FcC = 4-ferrocenylcatecholate where Fc = ferrocene and C = catecholate). This series consists of a previously reported complex FcV (4-ferrocenylveratrole) and newly synthesized complexes FcA (4-ferrocenylcatechol bis(acetate) and Pt(^tBu₂bpy)(FcC) (^tBu₂bpy = 4,4′-di-tert-butyl-2,2′-dipyridyl). An electrochemical analysis of Pt(^tBu₂bpy)(FcC) using cyclic voltammetry revealed two well-defined, reversible waves which were assigned to the sequential oxidation of the Pt(^tBu₂bpy)(C) and Fc moieties. The potential splitting between the waves (524 mV) indicated that there was an electronic interaction between both moieties. ICT property and charge distribution of [Pt(^tBu₂bpy)(FcC)]⁺ were rationalized by comparison with the [FcV]⁺ and [FcA]⁺ (4-ferrocenylcatechol bis(acetate)). DFT calculations and UV-vis-NIR spectroscopy revealed that [Pt(^tBu₂bpy)(FcC)]⁺, [FcV]⁺, and [FcA]⁺ were ferrocenium (Fc⁺)-centered rather than semiquinone ligand-centered and that these complexes exhibited ICT transition bands from the catechol-derivatized framework to the Fc⁺ moiety in the near infrared (NIR) region. Both the electronic coupling parameter (H_AB) and delocalization parameter (α) increased in value as the electron-donating strength of the substituent groups in the catechol-derivatized framework increased (OCOCH₃ ([FcA]⁺) < OCH₃ ([FcV]⁺) < O^- ([Pt(^tBu₂bpy)(FcC)]⁺)). The electronic interactions between the organometallic center and the non-innocent framework were tuned by changing the substituents. The potential energy surfaces of the Fc⁺ derivatives, obtained using two-state Marcus-Hush theory, can be modulated by changing the energy level of the molecular orbitals of the appended catechol-derivatized moieties.

Full text of DOI:10.1039/c5dt01998b

Dalton
Transactions
View Article Online
View Journal | View Issue
PAPER
Tuning of intramolecular charge transfer
properties and charge distributions in ferrocene-
appended catechol derivatives by chemical
substitution†
Cite this: Dalton Trans., 2015, 44,
14635
a
a
a
a
a
Keishiro Tahara,* Shogo Akehi, Tetsuhiro Akita, Shohei Katao, Jun-ichi Kikuchi*
b
and Ken Tokunaga
In this study, we report intramolecular charge transfer (ICT) properties and charge distributions in a series
of FcC derivatives (FcC = 4-ferrocenylcatecholate where Fc = ferrocene and C = catecholate). This series
consists of a previously reported complex FcV (4-ferrocenylveratrole) and newly synthesized complexes
t
t
FcA (4-ferrocenylcatechol bis(acetate) and Pt( Bu
2
bpy)(FcC) ( Bu
2
bpy = 4,4’-di-tert-butyl-2,2’-dipyridyl).
t
An electrochemical analysis of Pt( Bu
2
bpy)(FcC) using cyclic voltammetry revealed two well-defined,
t
reversible waves which were assigned to the sequential oxidation of the Pt( Bu
2
bpy)(C) and Fc moieties.
The potential splitting between the waves (524 mV) indicated that there was an electronic interaction
t
•+
between both moieties. ICT property and charge distribution of [Pt( Bu
2
bpy)(FcC)] were rationalized
•
+
•+
by comparison with the [FcV] and [FcA] (4-ferrocenylcatechol bis(acetate)). DFT calculations and UV-
t
•+
•+
•+
+
2
vis-NIR spectroscopy revealed that [Pt( Bu bpy)(FcC)] , [FcV] , and [FcA] were ferrocenium (Fc )-
centered rather than semiquinone ligand-centered and that these complexes exhibited ICT transition
+
bands from the catechol-derivatized framework to the Fc moiety in the near infrared (NIR) region. Both
the electronic coupling parameter (HAB) and delocalization parameter (α) increased in value as the elec-
tron-donating strength of the substituent groups in the catechol-derivatized framework increased
3 3 2
OCOCH ([FcA] ) < OCH bpy)(FcC)] )). The electronic interactions between the
([FcV] ) < O− ([Pt( Bu
•
+
•+
t
•+
(
Received 28th May 2015,
Accepted 16th July 2015
organometallic center and the non-innocent framework were tuned by changing the substituents. The
+
potential energy surfaces of the Fc derivatives, obtained using two-state Marcus–Hush theory, can be
DOI: 10.1039/c5dt01998b
modulated by changing the energy level of the molecular orbitals of the appended catechol-derivatized
moieties.
www.rsc.org/dalton
use in molecular electronics, have been reported, especially for
cobalt catecholate complexes. Switchable molecular devices
Introduction
2
–4
Valence tautomeric (VT) complexes are composed of redox- require a single-bistability, that is, two stable electronic states
1
,2
active ligands and transition metal ions. VT complexes can between which the system can switch in response to physical
4
acquire more than two stable electronic states, which can be stimuli. However, more elaborate devices require multi-bist-
mutually accessed by intramolecular electron transfer (IET) ability, that is, three or more stable electronic states in which
5
induced by absorption of photons and changes in temperature the system can switch among. A promising approach to
and/or pressure. Efforts to connect IET phenomena at a mole- realize these complicated systems is the use of transition
cular level to switching functions at a macroscopic level, for metal ions in which a number of different valence states are
accessible. An example of a three-membered VT interconver-
sion was demonstrated in a manganese catecholate complex
6
a
capable of acquiring the Mn(IV) state. Alternative approaches
include the design of new ligands that can provide a third
stable electronic state and control the energy differences
between stable electronic structures, IET directions, and
charge distributions in VT complexes.
Graduate School of Materials Science, Nara Institute of Science and Technology,
916-5, Takayama, Ikoma 6300192, Japan
8
b
Division of Liberal Arts, Kogakuin University, 2665-1, Nakano, Hachioji, Tokyo
1
†
920015, Japan
Electronic supplementary information (ESI) available: Characterization of new
compounds, UV-vis-NIR spectra of oxidized species, DFT calculation data. CCDC
87989, 987990 and 987994. For ESI and crystallographic data in CIF or other
VT complexes are composed of not only redox-active
ligands and transition metal ions but also larger redox-active
9
electronic format see DOI: 10.1039/c5dt01998b
This journal is © The Royal Society of Chemistry 2015
Dalton Trans., 2015, 44, 14635–14645 | 14635

View Article Online
Paper
Dalton Transactions
1
Chart 1 (a) Structures of Fc derivatives and atom numbering used for H-NMR assignments. (b) Strategy to tune the charge distribution and ICT
+
+
properties between Fc C and FcSQ electronic states and probe the effect of ortho π-conjugation on ICT properties.
+
units. Ferrocene (Fc) has been covalently linked to redox-active jugation, caused by an additional Fc group in complex 2 , on
7
,8
units to probe IET phenomena. The resulting Fc conjugates the ICT properties is also reported.
are attractive redox-active materials as the redox behavior of Fc
is reversible, stable, and the Fe(III)/Fe(II) redox-couple has a low
potential. Additionally, Fc has been reported to donate elec-
trons to quinone/semiquinone/hydroquinone redox systems.
These Fc conjugates are attractive candidates for the study of
Results and discussion
Synthesis and characterization of Fc derivatives
9
IET phenomena in which proton transfer and hydrogen- BBr
bonding accompanies the redox event. To the best of our plexation to Pt( Bu
knowledge, transition metal complexes, in which a catecholate FcC was not stable in air as reported elsewhere, however
ligand is covalently linked to a cyclopentadienyl (Cp) of Fc, direct use of the crude product under a N atmosphere was
have not been reported. We have reported the synthesis of effective to synthesis and isolate 3. In contrast, complex 3 was
-ferrocenylveratrole (1, FcV) and 4,6-diferrocenylveratrole (2, stable in air once the catecholate ligand was coordinated to
3
mediated demethylation of complex 1 followed by com-
t
2
2
bpy)Cl gave 3 in 71% yields (Scheme 1).
9
c
2
4
FcVFc) (Chart 1a) as precursors to 4-ferrocenylcatechol (FcC) the Pt center. A reference compound containing acetyl groups
and 4,5-diferrocenylcatechol (FcCFc), respectively (V = veratrole (5) was synthesized by condensation of the crude catechol with
(
1,2-dimethoxybenzene); C = catechol (or catecholate)), and acetic anhydride. Compounds 3 and 5 were characterized by
1
0
1
1
13
demonstrated their use in borate complexes. In this study,
H- and C-NMR spectroscopy and ESI-MS (Fig. S1–S5†). The
we report intramolecular charge transfer (ICT) properties and
H-NMR spectra of the Fc compounds in CDCl , displaying the
3
charge distributions in a series of FcC derivatives. To tune the relevant regions, are shown in Fig. 1. The proton signals of the
+
+
interconversion between the Fc C and FcSQ electronic states phenyl (1a, 1b, and 1c, Chart 1a) and Cp rings (2b and 3,
SQ = semiquinone), we chemically modified the FcC deriva- Chart 1a) were shifted upfield as the electron-donating
(
1
3
tives at the O atoms by changing the substitution groups, as strength of the substituents on the phenyl rings increased
well as by metal complexation (Chart 1b). To ensure that the (OCOCH
Fc C and FcSQ electronic states were dominant, Pt( Bu bpy)- revealed an enhancement of 7.9% for the 2a proton upon
−
3 3
< OCH < O ). Differential NOE spectroscopy
+
+
t
2
t
(FcC) (3) ( Bu
2
bpy = 4,4′-di-tert-butyl-2,2′-dipyridyl) was syn- irradiation at the 1a proton (Fig. S6†). This was consistent with
t
thesized and characterized. Pt( Bu bpy)(C) was selected as a the H⋯H distances (9H⋯36H and 30H⋯38H) in the DFT-opti-
2
component of the transition metal complex in 3, as closely
related analogues are predominantly oxidized on the C moi-
eties with only a minor contribution from the Pt(II) d orbi-
1
1
tals. In addition, the oxidation potentials of the components
of Fc and related Pt(II) catecholate complexes are very close,
which is advantageous for an electronic interaction between
1
2
the Fc and C moieties. To understand the ICT properties of
+
FcC in 3 , we compare its charge distribution, ICT direction,
and electronic coupling to the ferrocenyl complexes 4 (X =
CH ) and 5 (X = acetyl, Ac) (Chart 1a). The effect of ortho π-con- Scheme 1 Synthesis of 3 and 5.
3
14636 | Dalton Trans., 2015, 44, 14635–14645
This journal is © The Royal Society of Chemistry 2015

View Article Online
Dalton Transactions
Paper
1
Fig. 1 Partial H-NMR spectra of 1, 3, and 5 in CDCl
3
.
a
Table 1 Electrochemical data for Fc derivatives
1
1/2
2
1/2
c
Compound
E
E
ΔE1/2
σ
p
b
e
1
2
3
4
5
1105
90
282
1375
1359
1017
1100
167
524
1350
1273
1047
−0.27
−0.27
−0.81
0
0.31
—
b
e
−77
d
−242
e
e
e
25
5
86
−30
t
Pt( Bu
2
bpy)(C)
2 2
Fig. 2 DFT-optimized structures of Pt(bpy)(FcC) with IEFPCM (CH Cl ).
a
+
Potentials in mV vs. Fc /Fc. In CH
4 6
2
Cl
2
(1.0 mM) containing 0.1 M
n
b
c
Bu NPF . Previous work (ref. 10). Hammett para parameter of the
d
substituents on the phenyl ring (ref. 13). Value for phenolate (ref. 13).
e
2
t
E
ox values were adopted because irreversible waves were observed.
mized structure of Pt(bpy)(FcC) (3′), in which the Bu bpy
2
group of 3 was replaced by bpy (2,2′-dipyridyl); the phenyl and
Cp rings were almost coplanar in 3′ (Fig. 2 and Table S3†).
Compound 1 exhibited similar NOE enhancements (8.7% in
1
plexes 1, 4, and 5 displayed a reversible wave (E1/2) corres-
CDCl
3
) (Fig. S6†) to those of compound 3, indicating a
1
1
ponding to oxidation of the Fc groups. The E
values
/2
common planarity was present in the series of Fc compounds.
decreased as the electron-donating strength of the para-substi-
tuents on the phenyl groups increased as shown in a
Hammett plot (Fig. 3b). The second redox wave for complexes
, 4, and 5 corresponding to oxidation of the C H O X moiety
6 3 2 2
was not reversible. As such, we examined the one-electron-oxi-
dized species formed by chemical oxidation.
1
3
Electrochemical behavior of Fc derivatives
1
The electrochemical behavior of the Fc compounds was inves-
tigated using cyclic voltammetry (CV). All measurements were
n
performed in CH Cl containing Bu NPF as the electrolyte at
2
2
4
6
Complex 3 exhibited two well-defined reversible waves, indi-
2
98 K (Fig. 3a). The redox potentials are listed in Table 1. Com-
t
cating sequential oxidation of the Pt( Bu
2
bpy)(C) and Fc moi-
eties and the formation of the one- and two-electron oxidized
+
2+
species 3 and 3 , respectively (Fig. 3a and Table 1). In con-
trast, the difference in the E1/2 values between the separate Fc
t
and Pt( Bu bpy)(C) complexes was small (30 mV), consistent
2
1
2
1
with previous reports. The low E
explained by substituent effects (Fig. 3b). The E1/2 and E1/2
values for 3 were 212 mV lower and 312 mV higher than for
value for 3 cannot be
/2
1
1
2
1
t
1
the E
value for Pt( Bu bpy)(C), respectively, while the E
2 1/2
1
/2
2
and E1/2 value for 3 was 242 mV lower and 282 mV higher than
the E value for Fc, respectively. These results indicated that
1
1
/2
the large potential splitting (524 mV) observed in 3 was caused
t
2
by an electronic interaction between the Pt( Bu bpy)(C) and Fc
moieties. Indeed, the catecholate and Fc moieties in complex 3
contributed 77% and 12% to the HOMO, respectively
(Fig. S15†). The potential splitting value for 3 was 494 mV
t
Fig. 3 (a) Cyclic voltammograms of 1, 3, 4, 5, and Pt( Bu
2
bpy)(C)
n
−1
(
(
1.0 mM) in CH
2
Cl
2
2
containing Bu
4
NPF
6
(0.1 M). Scan rate: 100 mV s .
1
larger than the difference between the E values (30 mV) of
b) Plot E1/2 and E1/2 potentials for 1, 3, 4, and 5 against the Hammett
1/2
t
para parameter.
the separate Pt( Bu bpy)(C) and Fc compounds, highlighting
2
This journal is © The Royal Society of Chemistry 2015
Dalton Trans., 2015, 44, 14635–14645 | 14637

View Article Online
Paper
Dalton Transactions
+
+
+
Fig. 4 DFT-optimized structures of (a) 3’ , (b) 1 , and (c) 5 with selected H⋯H distances. Increased values of NPA charges of Fc (red), oxolene
(
blue), and X (black) fragments upon one-electron-oxidation from the neutral forms are also shown.
+
the thermodynamic stability of 3 with a comproportionation
8
c
constant (K ) of 7.2 × 10 . Notably, the potential splitting value
for 3 was 3.1 times larger than of 2, which exhibits an inter-Fc
interaction via ortho π-conjugation in the veratrole framework.
DFT calculations
The optimized geometry, electronic structure, and charge dis-
+
tribution of complex 3 were determined using DFT calcu-
lations. The solvent effects of CH Cl were considered with the
2
2
•
+
IEFPCM approach. The optimized structure of [Pt(bpy)(FcC)]
3′ ) showed the phenyl and Cp rings being coplanar (Fig. 4a
+
(
and Table S3†). This was also observed in the optimized struc-
ture of the neutral form. The H⋯H distances (9H⋯36H and
+
3
0H⋯38H) in 3′ were comparable to the neutral form. The
natural population analysis (NPA) charges of the Fc fragment
in 3′ were close to zero (Table 2). The NPA charges of the Fc
+
and C fragments in 3′ increased by 0.761 and 0.177, respect-
ively, when compared with those of 3′ (Fig. 4a). This suggested
that the first oxidation of 3 occurred largely on the Fc fragment
with a partial contribution from the C fragment to the oxi-
+
dation, and that the positive charge of 3 was delocalized
largely on the Fc fragment and partly on the C fragment. Such
delocalization of the positive charges was in good agreement
with the delocalization of the lowest unoccupied molecular
orbital (LUMO) (120β) between the Fc and C fragments (Fig. 5a
and Table 3). On the other hand, the contribution of the
+
Pt(bpy) fragment to the LUMO is almost negligible for 3′ . The Fig. 5 (a) Selected molecular orbital contributions and energy diagrams
+
+
for 3’ calculated using a DFT method (isosurface values 0.02 au). Fron-
NPA spin density of 3′ was localized exclusively on the Fc frag-
+
+
tier orbitals of (b) 1 and (c) 5 .
ments. Notably, the contribution of the Fc fragment to the
a
2 2
Table 2 DFT-calculated NPA charges of fragments with IEFPCM (CH Cl )
Compound
Fc
C H O
6 3 2
bpy
Pt
3
3
′
′
−0.0483
0.713 (0.994)
—
—
−0.021
0.856 (1.025)
0.008
−0.7985
0.2217
0.256 (0.000)
0.188
0.6251
0.653 (0.000)
0.628
0.731 (0.040)
—
—
—
—
+
−0.622 (0.006)
−0.816
Pt(bpy)(C)
•
+
[
Pt(bpy)(C)]
−0.101 (0.948)
−0.637
0.370 (0.012)
b
1
1
5
5
0.658
+
b
b
−0.538 (−0.025)
−0.534
0.682 (0.000 )
b
0.526
+
b
b
0.914 (1.0072)
−0.470 (−0.0071)
0.556 (−0.0001 )
a
b
NPA spin densities are also shown in parentheses. Charge and spin density of X substituent.
14638 | Dalton Trans., 2015, 44, 14635–14645
This journal is © The Royal Society of Chemistry 2015

View Article Online
Dalton Transactions
Paper
1
1d
Table 3 DFT-calculated frontier molecular orbital compositions (%) a coordinated SQ radical.
Similarly, the oxidation of
t
with IEFPCM (CH
2 2
Cl )
Pt( Bu bpy)(C) was centered on the catecholate ligand. Indeed,
2
TD-DFT calculations predicted the presence of electronic tran-
sitions at 479 nm corresponding to the 75β–78β transition,
where 78β (LUMO) based on the SQ ligand serves as the accep-
tor orbital (Fig. S16 and Table S7†).
Compound MO
E/eV
Fc
C
3
77
10.8
75
3
87
88.4
87.5
37.2
42.9
1
6
H
O
3 2
bpy
Pt
3
′
′
121 (LUMO)
20 (HOMO)
120β (LUMO)
−2.51
−4.5
−3.35 87.7
0
12
91
5
1.2
4
91
6
6
6
0.3
8
6
1
+
3
+
The monocation 3 displayed two different bands from
1
19β (HOMO) −5.21 13
t
•+
Pt(bpy)(C)
79 (LUMO)
8 (HOMO)
78β (LUMO)
8α (HOMO)
80 (LUMO)
9 (HOMO)
79β (LUMO)
8β (HOMO)
94 (LUMO)
3 (HOMO)
93β (LUMO)
2β (HOMO)
−2.49
−4.56
−4.23
−6.23
−0.48 62.1
−5.23 55.7
−4.17 99
−6.07 13
−0.83 38.7
−5.27 95
—
—
—
—
those observed for [Pt( Bu bpy)(C)] (Fig. 6a); an intense band
2
7
7
at 594 nm in the visible region and a broad band at 1947 nm
•
+
[
Pt(bpy)(C)]
5.5
3.3
6.1
9.3
—
—
—
—
—
—
—
—
+
+
in the NIR region. Thus, 3 can be described as Fc -centered
7
a
1
1
5
5
0.7
1.5
rather than SQ ligand-centered. This description was in agree-
a
7
+
ment with the DFT calculations for 3 , where the contribution
+
+
a
0
a
of the Fc moiety to the positive charge and spin density was
7
83
58.3
5
4
a
3
a
9
0
a
−4.34 99.31 0.67
−7.01 41.2 56.2
0.02
a
9
2.6
a
Charge and spin density of X substituent.
+
LUMO in 3′ increased by 57.5% compared with that of the
HOMO in Pt(bpy)(FcC); a contribution to HOMO is largest in
the C fragment for 3′ (77%), while a contribution to LUMO is
+
largest in the Fc fragment for 3′ (69.5%). Accordingly, the
+
LUMO properties and charge distributions for 3′ are different
•
+
from those for the reference compound [Pt(bpy)(C)] , in
which the largest contribution to LUMO and NPA charges is
the C fragment (Fig. S16, and Tables 2, 3, and S4†).
+
+
The NPA charges of 1 (Fig. 4b and Table S6†) and 5
Fig. 4c and Table S5†) increased significantly on the Fc frag-
(
ments when compared with those of 1 and 5, while the contri-
butions of other fragments were minor (Fig. 4b and 4c). This
suggested that the first oxidation of 1 and 5 occurred largely
on the Fc fragment. Such localization of the positive charges is
+
in agreement with the localization of the LUMO (79β for 1 ;
+
9
3β for 5 ) on the Fc fragment (Table 3 and Fig. 5b and 5c). The
+
degree of the localization on the Fc fragment was stronger for 5
than for 1 due to the presence of the electron-withdrawing
+
acetyl substituent.
Chemical oxidation of Fc derivatives
+
To probe the electronic structure and charge distribution of 3 ,
complex 3 was chemically oxidized using magic blue in
CH
2
Cl
2
. We also chemically oxidized the reference Pt complex,
t
Pt( Bu bpy)(C), which was monitored using UV-vis-NIR spec-
troscopy (Fig. S7†). The resulting radical cation, [Pt( Bu
2
t
2
bpy)-
•
+
(C)] , displayed two absorption bands at 457 and 596 nm. An
t
analogous Pt complex, Pt(dpphen)( Bu C) (dpphen = 4,7-diphe-
nyl-1,10-phenanthroline; Bu
2
t
2
C = 3,5-di-tert-butylcatechol), was
reported to be oxidized on the center of the catechol ligand.
t
•+
[
Pt(dpphen)( Bu C)] also displayed a band at 457 nm, which
2
was assigned to a d(π)–π* MLCT transition, where the π and π*
Fig. 6 UV-vis-NIR spectra of (a) 3, (b) 1, and (c) 5 in the absence (black
line) and presence of 1 equiv. of magic blue (red line) in CH Cl
2 2
1
1b
t
t
•+
orbitals were based on the SQ ligand.
2 2
[Pt( Bu bpy)( Bu C)]
was also reported to exhibit absorption bands characteristic of (* = solvent peaks).
This journal is © The Royal Society of Chemistry 2015
Dalton Trans., 2015, 44, 14635–14645 | 14639

View Article Online
Paper
Dalton Transactions
largest. Indeed, TD-DFT calculations predicted the presence of Table 4 Parameters of ICT bands and electronic coupling
electronic transitions, where 120β (LUMO) serves as the accep-
+
+
+
3
1
5
tor orbital in the visible region (Table S7†). The predicted tran-
+
−
1
a
b
a
b
a
sitions are close to the first absorption band observed for 3
Δν1/2 (cm
)
3820
5140
3220
3720
9820
1040
4.55
880
3100
2600
12 980
+
−1
c
c
(
Fig. 6a). The second absorption band observed for 3 was
νmax (cm
)
M
—
—
—
—
ε
max (cm−
DA (Å)
1
−1)
5000d
—
c
c
520 e
assigned to an ICT transition from the catecholate moiety to
c
e
c
r
H
α
6.15
—
4.42
+
+
t
•+
−
1
2
the Fc center, as neither Fc or [Pt( Bu bpy)(C)] exhibit
AfB (cm
)
1050
0.20
4230
910
980
810
620
absorption bands in the NIR region. Indeed, TD-DFT calcu-
lations predicted the presence of an electronic transition from
the 119β (HOMO) to 120β (LUMO) at 1396 nm (Table S7†). It
was demonstrated that a strong NIR absorption band was
observed for a binuclear Pt(II) diimine bis-catecholate complex
0.19
0.090
8870
950
0.082
0.048
10 270
2710
ΔG (cm−1)
0
—
c
—
—
c
−1
c
c
λ (cm
)
—
a
b
c
Gaussian-fitted values (see Fig. S10 to S12). Observed values. Same
as the left. The distance between Fe atom and the center of C–C–C–O
of the catecholate moiety. The distances between Fe atom and the
d
e
1
1d
f
in the mixed-valence catecholate/semiquinone state.
Such center of the phenyl ring. Delocalization parameter α = HAB/νmax
.
+
spectroscopic properties are similar to those for 3 , indicating
a common feature of ligand-based charge transfer transitions
in catecholate conjugates.
+
+
+
8
d,e
complexes 3 , 1 , and 5 (Fig. S10–S12†) were determined by
Gaussian deconvolution of the NIR bands (Table 4). Using
these parameters, the donor–acceptor distance (rDA) derived
from the DFT-optimized structure, and eqn (1), a Hush analy-
sis yielded the electronic coupling values (HAB) for each
complex (Table 4). The ground state delocalization parameter
α) for 3 corresponded to those for the weakly coupled class
II MV compounds in the Robin and Day classification. The
AB values increased as the electron-donating strength of the
3 3
substituents on the phenyl rings increased (OCOCH < OCH
< O ). This order correlated to the extent of electronic delocali-
zation as the α value for 3 was a factor of 2.2 larger than for
1 , while the α value for 1 was a factor of 1.9 larger than for
5 . This indicated that the degree of electronic communication
in the FcC-derivatized backbone can be tuned by chemical
substitution of the X group. In particular, metal complexation
with the Pt(II) ion dramatically increased the degree of charge
delocalization between the organometallic center (Fc) and the
catechol-derivatized backbone. Notably, the order of the H
AB
and α values (5 < 1 < 3 ) remained unchanged when Δν
According to a previously reported method,
chemical oxidation of 3 was performed with substoichiometric
amounts of iodine (I ) in CDCl at 294 K, which was monitored
using H-NMR spectroscopy (Fig. S18†). The proton signals of
the Fc and C moieties were paramagnetically broadened,
partial
2
3
1
1
6
6
3 2
H O
1
7
while those of the bpy moiety were less broadened. This indi-
cated that both the Fc and C H O moieties participated in the
1
8
+
(
6
3 2
1
9
first oxidation of 3, although the locus of oxidation was not
discriminated on the NMR timescale.
H
1
3
The chemical oxidation of compounds 1, 4, and 5, was per-
−
+
formed using magic blue in CH
2
Cl
2
. Compound 1 exhibited
+
two absorption bands at 466 nm and 1018 nm (Fig. 6b), which
+
+
+
were analogous to those of 3 . The visible band was blue
+
shifted by 4650 cm−1, and decreased in intensity by a factor of
+
1
.9, when compared with the high-energy band of 3 . The NIR
−
1
band was blue shifted by 4680 cm , and its intensity
decreased by a factor of 4.8, when compared to the NIR band
of 3 . These bands were assigned to an ICT transition between
the V moiety and the Fc center, consistent with the DFT calcu-
lations which predicted 1 was Fc -centered, and reported
+
+
+
+
+
+
+
1/2
was replaced by the observed, rather than the Gaussian-fitted,
absorption data for ferrocenium-polyaromatic dyads contain-
9
c,14
+
value.
ing electron-rich groups.
Indeed, 1 exhibited a shoulder
+
15
peak around 600 nm, typical for Fc species. The absorption
1=2
+
+
+
HAB ¼ 0:0206ðνmax ꢀεmax ꢀΔν1=2Þ =rDA
ð1Þ
ð2Þ
bands of 5 were analogous to those of 1 . Complex 5 exhibi-
ted a shoulder peak around 420 nm and an absorption band
at 770 nm, assigned to the ICT transitions from the V moiety
to the Fc center, as well as an absorption band at 577 nm,
assigned to the Fc center (Fig. 6c). The UV-vis spectrum for 4 given by eqn (2), where ΔG denotes the zero-level energy
0
hνmax ¼ ΔG þ λ
+
+
+
+
The reorganization energy (λ) for complexes 1 , 3 , and 5 is
+
0
+
0
in the presence of magic blue was similar to that for 5
difference between the ground and excited states. The ΔG
(Fig. S8†), implying that the electron-withdrawing strength of values can be determined by the difference between the redox
the acetoxy group was comparable to that of the hydrogen potentials (Table 4). Potential energy diagrams for these com-
+
atom in the Fc -benzene backbone. The change in substitution plexes were constructed based on a two-state Hush model
−
(
X group) in complexes 3 (O ), 1 (CH
3
), and 5 (OCOCH
3
) led to using the parameters listed in Table 4. The diabatic energy sur-
2
2
0
a blue shift for the ICT bands and decreased their intensities. faces, with the parabolic functions λx and λ(1 − x) + ΔG , are
This reflected the strength of the electronic coupling between shown in Fig. 7. The adiabatic energy surfaces are constructed
+
+
+
the Fc moiety and the catechol-derivatized backbone.
according to ref. 16b. The ground state of complexes 1 , 3 ,
+
+
and 5 is the Fc C configuration, while the ICT state is the
FcSQ configuration (Chart 1b). The ΔG value for 1 was com-
Electronic coupling and potential energy curves
+
0
+
+
+
The spectroscopic parameters, energy (νmax), intensity (εmax), parable to that of 5 , while the λ value for 1 was a factor of 2.9
and bandwidth at the full width half maximum (Δν1/2) for smaller than that of 5 . Accordingly, the two parabolas for 5
+
+
14640 | Dalton Trans., 2015, 44, 14635–14645
This journal is © The Royal Society of Chemistry 2015

View Article Online
Dalton Transactions
Paper
+
+
+
+
+
Fig. 7 Diabatic (dashed line) and adiabatic (solid line) potential energy surfaces of the Fc C and FcSQ states for 3 , 1 , and 5 as a function of the
electron transfer reaction coordinate.
Fig. 8 Crystal structures of [FcV](I
the side view of [FcVFc](I
3
), [FcVFc](I
3
), and [FcVFc]
2
(I
3
)
2
. Hydrogen atoms in all the views are omitted for clarity, as well as iodine atoms in
3 2
) .
+
0
+
+
were deeper than those of 1 . The ΔG value for 3 was a factor sition of [FcV](I
3
). The structure of the Fc cation is shown in
+
+
of 2.1 smaller than that of 1 while the λ value for 3 was only Fig. 8 (left). The average distance between Fe1⋯Cp1A and
−
1
+
4
0 cm smaller than that of 1 . Accordingly, the depth of the Fe1⋯Cp1B was 1.708 Å (Table 5), close to the value reported
two parabolas for 3 was comparable to those of 1 , while the for the Fc cation (1.70 Å). This indicated that the positive
gap between the two parabolas for 3 (ΔG ) was smaller than charge of 1 was localized on the Fc moiety. The benzene and
for 1 . The potential energy surfaces of the Fc derivatives can Cp rings were almost coplanar, with a small twist angle of
+
+
+
21
+
0
+
+
+
+
be dramatically modulated by changing the energy level of the 7.39°, consistent with the DFT-optimized structure of 1
molecular orbitals of the appended catechol-derivatized moi- (Table S6† and Fig. 4b). The two Cp rings were tilted at 10.37°
eties. These findings came from the ease of chemical modifi- to each other.
cation at the O atoms not only by changing the substitution
groups but also by metal complexation in the present Fc-conju- both light and deep brown single crystals suitable for XRD
gate system. analysis. The structure of the former crystals had a compo-
sition of [FcVFc](I ) (Fig. 8, middle). The average distance
between Fe1⋯Cp1A and Fe1⋯Cp1B was 1.6515 Å, close to the
2
Compound 2 was oxidized by I in chloroform to afford
3
+
+
2+
Crystal structures of FcV , FcVFc , and FcVFc
2
2
I is widely used as a weak oxidant for preparative oxidation of reported value of Fc (1.65 Å), while the average distance
2
+
20
Fc derivatives (−0.14 V vs. Fc /Fc in CH
Compound 1 was oxidized by I
in chloroform to afford brown reported value of Fc (1.70 Å). These results indicated that
single crystals. Crystals suitable for XRD analysis had a compo- the positive charge in FcVFc was localized on the Fc moiety of
3
CN/n-Bu
4
NPF
6
).
between Fe2⋯Cp2A and Fe2⋯Cp2B was 1.712 Å, close to the
+
21
2
+
This journal is © The Royal Society of Chemistry 2015
Dalton Trans., 2015, 44, 14635–14645 | 14641

View Article Online
Paper
Dalton Transactions
+
Table 5 Selected bond lengths (Å) and angles (°) of [FcV](I
3
), [FcVFc](I
3
),
2
(
exhibited a weak NIR band which extended to 2250 nm
a
3 2
and [FcVFc](I )
Fig. S13 and Table S2†). This band was assigned to an interva-
lence charge transfer (IVCT) transition as it was similar to that
reported for the mixed-valence species o-diferrocenylbenzene.
Compound
[FcV](I
3
)
[FcVFc](I
3
)
[FcVFc](I )
3 2
FcVFc
23
Fe1⋯Fe2
Fe1⋯Cp1A
Fe1⋯Cp1B
Fe2⋯Cp2A
Fe2⋯Cp2B
I1–I2
—
6.691
1.652
1.651
1.710
1.714
2.93420(17)
2.90894(17)
177.676(6)
This work
6.879
1.708
1.715
1.708
1.715
2.8945(4)
2.9391(4)
6.715
1.647
1.646
1.651
1.652
—
The HAB value determined for the IVCT was comparable to that
of the mixed-valence species o-diferrocenylbenzene (HAB = 202
in acetonitrile). This indicated that the inter-ferrocenyl elec-
tronic interaction, which occurred through the ortho connection
in the phenyl ring, was not noticeably affected by the electron-
donating strength of the substituents in the 4- and 5-positions.
1.704
1.712
—
2
3
—
2.9085(4)
2.9421(3)
178.876(10)
This work
I2–I3
I1–I2–I3
—
—
178.835(14)
This work
Ref. 10 This was in contrast to the large effect that varying substituent
had on the HAB and α values for ICT transition in the monofer-
a
CpXA and CpXB (X = 1, 2) denote the centroids of the Cp rings
+
+
+
rocenyl complexes 1 , 3 , and 5 . The HAB value determined for
5 4 5 5
having compositions of C H and C H , respectively.
+
the ICT transition in 2 was a factor of 1.8 smaller than that in
, presumably because the planarity between the Cp and
phenyl rings in 1 was lower than 2 . Potential energy diagrams,
corresponding to the IVCT and ICT transitions observed for 2
+
1
+
+
+
Fe2, and that the 2 salt was in a valence-trapped state in the
crystals. Steric constrains between the Fc and Fc groups
increased the twist angles between the benzene and Cp rings
+
+
(
Fig. S14†), were constructed based on a two-state Hush model
0
and the λ and ΔG parameters. The λ value for the ICT tran-
sition in 2 was a factor of 1.4 smaller than that of 1 , reflecting
+
(52.93° for Fe1 and 38.11° for Fe2). Both the Fc and Fc groups
+
+
were in a near eclipsed conformation. The Cp rings were
almost parallel to each other, with dihedral angles of 3.99°
and 4.00° for Fe 1 and Fe2, respectively.
the difference in size between the cations.
The structure of the latter crystals, having a composition of
+
Conclusions
[
FcVFc](I ) , is shown in Fig. 8 (right). The two Fc groups were
3
2
crystallographically equivalent. The average distance between
t
The novel Pt diimine complex Pt( Bu bpy)(FcC) (3), incorporat-
2
+
Fe⋯Cp was 1.7115 Å, close to the reported value for the Fc
ing the valence tautomeric ligand 4-ferrocenylcatechol, was
synthesized and characterized using H- and C-NMR spec-
troscopy, ESI-MS, and electrochemical measurements. The ICT
2
2
+
cation (1.70 Å). The Fc groups were in a near staggered con-
1
13
formation, while the Cp rings were almost parallel to each other
(5.397°). The twist angle between the benzene and Cp rings was
+
behavior and charge distributions of 3 were explained by com-
greater (80.287°) than those of both the neutral form (32.06° for
Fe1 and 52.65° for Fe2) and the monocation form (52.93° for
Fe1 and 38.11° for Fe2), presumably because of packing-effects
with I3−. To the best of our knowledge, this is the first crystallo-
graphic study of diferrocenyl complexes, which described the
structural differences among the three different oxidation states
parison with related Fc complexes. DFT calculations and UV-
+
vis-NIR spectroscopy revealed that the cationic complexes 1 ,
+
+
+
3
, and 5 , were Fc -centered rather than SQ ligand-centered.
These complexes exhibited ICT transition bands from the cate-
+
chol-derivatized framework to the Fc moiety in the NIR
region. The HAB and α values increased as the electron-donat-
(i.e., the neutral, cationic, and dicationic forms).
ing strength of the substituent groups of the catechol-deriva-
+
+
−
tized framework increased (OCOCH (5 ) < OCH (1 ) < O
(
3
3
+
Characterization of FcVFc
+
3 )). The electronic interactions between the organometallic
The optimized geometry of the diferrocenyl complex in the center and non-innocent framework were tuned by changing
+
one-electron oxidized form (2 ) was calculated using DFT cal- the energy level of the molecular orbitals of the catechol-deri-
culations. The phenyl and Cp rings were twisted because of vatized framework. In contrast, the inter-ferrocenyl electronic
+
steric constrains between the Fc and Fc groups (Fig. S17†), interaction, which occurred through ortho π-conjugation in the
consistent with the crystal structure. The NPA charges of the phenyl ring, was not noticeably affected by the electron-donat-
+
Fc1 and Fc2 fragments in 2 increased by 0.026 and 0.883, ing strength of the substituents in the 5- and 6-positions.
respectively, when compared to those of 2, while those of the V
fragment increased by 0.069 (Table S8†). This indicated that
+
the positive charge of 2 was localized largely on the Fc2 frag-
ment. The NPA spin density of 2 was localized exclusively on
the Fc2 fragment (Table S8†). The localization of the charge
Experimental
Materials and methods
+
and spin density was in agreement with the localization of the All solvents and chemicals used in the syntheses were of
LUMO (121β) on the Fc2 fragment (Fig. S18 and Table S9†). reagent grade and were used without further purification.
1
0
10
24
The localization of the charges resembled to the valence- Ferrocenyl compounds (FcV,
FcVFc,
and FcB ),
were synthesized
t
25
t
11a
trapped state in the crystals (Fig. 8, middle).
PtCl
2
( Bu
2
bpy),
2
and Pt( Bu bpy)(C)
+
The UV-vis spectrum of 2 (Fig. S9†) was analogous to that according to previously reported procedures. Magic blue, (tris-
of the monoferrocenium complex 1 , with the exception that (4-bromophenyl)aminium hexachloridoantimonate, purity:
+
14642 | Dalton Trans., 2015, 44, 14635–14645
This journal is © The Royal Society of Chemistry 2015

View Article Online
Dalton Transactions
Paper
>
97.0%), was purchased from Sigma-Aldrich. Tetra-n-butylam- (s, 18H, CH
̲
), 4.02 (s, 5H, CCp(3)H
̲
̲) ,
n
monium phosphate ( Bu NPF ) (purity: >98.0%) was pur- 4.58 (pt, 4H, C H ), 6.64 (dd, J = 1.8, 7.7 Hz, 1H, CPh(5)H
̲
̲
4
6
5
4
chased from Tokyo Kasei Kogyo (TCI) and recrystallized from (d, J = 7.7 Hz, 1H, CPh(6)H
methanol before use. 7.45 (m, 2H, Cbpy
The H- and C{ H} spectra were recorded using JEOL 2H, Cbpy
JNM-ECP400 and JNM-ECA600 spectrometers installed at the 30.27(C(C
Nara Institute of Science and Technology; tetramethylsilane 69.37 (C
̲
̲
H
̲
̲
̲
1
13
1
13
H
̲
3
̲
3
), 35.83, 35.85, 65.65 (C
), 88.23, 112.57 (C
(5)), 119.09 (Cpy(3)), 119.14 (C
C
p
Cp
(2)), 67.55(C̲ (3)),
̲
5
̲
Ph(3)), 114.06 (C
Ph
̲ (6)), 115.08
1
(
TMS) was used as an internal standard (0 ppm) for H- and (C
̲
̲
p̲ y(3)), 123.88, 123.93, 149.08,
Ph
1
3
1
C{ H}-NMR analysis. The ESI-MS were obtained using a JEOL 149.13, 155.91, 155.94, 161.7, 162.33, 162.58 (Fig. S3†). UV-vis
1
5
JMS-T100CS spectrometer. 1D H-NMR differential NOE (CH
spectra were recorded using JEOL JNM-ECA600 spectrometers. for C H FeN O Pt ([M] ): 755.17739. Found: 755.17718
2
Cl
2
): [λmax/nm], 578 (1.73 × 10 ). HR-ESI-MS (m/z). Calc.
+
3
4
26
2 2
The UV-vis-NIR absorption spectra were measured on a JASCO (Fig. S1†).
V-670 spectrometer at room temperature. Synthesis of FcA (5). The crude product of 4-ferrocenylcate-
All voltammetric experiments were carried out using a BAS chol (0.0500 g), prepared by the same procedures as those for
electrochemical analyzer (Bioanalytical Systems Inc., West synthesis of 3, was treated with pyridine (2 mL) and acetic
Lafayette, IN, USA). All experiments were performed using a anhydride (1 mL) under N
conventional three-electrode system at 298 K. A platinum wire temperature for 12 h, dry dichloromethane (10 mL) was added
1.6 mm diameter) was employed as the counter electrode, a to the reaction mixture. The organic phase was washed with
2
atmosphere. After stirring at room
(
glassy carbon electrode (3.0 mm diameter) as the working elec- water (30 mL × 2) and brine (30 mL) and concentrated to
trode and an Ag–AgCl (3.0 M NaCl) electrode as the reference dryness. The obtained solid was purified by silica-gel column
electrode. Typically, nonaqueous CH
2
Cl
(0.1 M) were deaerated prior to each measure- the eluent. Yield: 20 mg (28%). H-NMR (600 MHz, CDCl
ment, and an argon atmosphere was maintained inside the ppm): δ = 2.30 (s, 3H, CH ), 2.32 (s, 3H, CH ), 4.07 (s, 5H,
2
solutions containing chromatography (Wakogel C-300) using dichloromethane as
n
1
3
and Bu
4
NPF
6
3
,
̲
̲
3
3
cell throughout each measurement. Each experiment was first
performed in the absence of any internal standard and then J = 8.3 Hz, 1H, CPh(6)H
repeated in the presence of decamethylferrocene (Fc*). A separ- (dd, J = 8.3, 2.1 Hz, 1H, CPh(5)H
ate experiment containing only ferrocene and decamethyl- (150 MHz, CDCl , ppm): δ = 20.74 (OC
ferrocene was also performed. The potentials are quoted (C (2)), 69.11 (CCp(3)), 69.67 (C
relative to Fc* /Fc* couple. In this setup, the Fc /Fc couples 123.10 (C (6)), 124.12 (CPh(5)), 138.60, 139.99, 142.91, 168.40
vO) (Fig. S5†). HR-ESI-MS (m/z). Calc. for
C
5
H
̲
5
), 4.31 (pt, 2H, CCp(3)H
̲
̲
), 7.10 (d,
̲
̲) , 7.33
3
1
3
Cp
̲
+
+
̲
̲
Ph
+
+
were observed at 560 mV vs. Fc* /Fc* while the Fc /Fc couples (C̲vO), 168.31 (C̲
n
+
were at 664 mV vs. Ag/AgCl in CH
data quoted relative to the Fc /Fc couple are also shown in
2
Cl
2
/ Bu
4
NPF
6
. The potential
C
20
H
18FeO
4
([M] ): 378.05545. Found: 378.05509 (Fig. S1†).
+
DFT calculation data
Table S1.†
Synthesis of Pt( Bu
t
2
bpy)(FcC) (3). FcV (0.300 g, 1.02 mmol) The DFT calculations were carried out using the Gaussian09
2
6
+
was dissolved in dry degassed dichloromethane (30 mL) and program package. For the Pt complexes (3 and 3 ), the
t
+
cooled to 0 °C. A dichloromethane solution of BBr
mL) was then added to the solution. After stirring for 30 min restricted or unrestricted three-parameterized Becke–Lee–
at 0 °C and then 30 min at room temperature, the starting Yang–Parr (B3LYP or UB3LYP) hybrid exchange–correlation
3
(1.0 M,
2
Bu bpy group was replaced by bpy to afford 3′ and 3′ . The
3
2
7
material was completely converted, as confirmed by TLC. functional was used with the Lanl2DZ (Hay–Wadt ECP) basis
Degassed water (20 mL) was then added to the reaction set for the Fe and Pt atoms and the 6-31G(d) basis set for
2
8
29
mixture using a dropping funnel. After stirring vigorously for the other atoms with taking account of solvent effects. The
30
1
2 2
0 min, the organic phase was obtained using a phase separa- solvent effects of CH Cl were modeled using IEFPCM. The
tor filter and concentrated to dryness. The obtained crude stability of the optimized structures was confirmed by calculat-
product of 4-ferrocenylcatechol (0.220 g) was treated with ing the molecular vibrational frequencies, in which no imagin-
t
NaHCO
3
(0.125 g, 1.48 mmol) and PtCl
2
( Bu
2
bpy) (0.400 g, ary frequencies were observed. Molecular orbital composition
0
.740 mmol) in dry ethanol (20 mL) and dry DMF (4 mL) analysis was conducted using the GaussSum Program. The
under N atmosphere at 95 °C for 24 h. A dark purple solid TD-DFT method was used to calculate transition energies and
2
2
was reprecipitated upon addition of H O to the concentrated oscillator strengths relevant to the absorption spectra.
reaction mixture. The solid was obtained by filtration and
washed with water and ether. The obtained solid was purified
by silica-gel column chromatography (Wakogel C-300) using Oxidized form of FcV: To a CHCl
Single crystal X-ray diffraction (XRD) analysis
2
solution of I FcV was added.
3
chloroform/methanol (99/1) to remove the unreacted To the resulting solution n-hexane was added and kept at
t
PtCl ( Bu bpy) and chloroform/methanol (98/2) to recover the room temperature. After the reprecipitate was washed with
2
2
product as a major purple fraction. The target product was n-hexane, the target compound was obtained as brown rod
obtained by washing with n-hexane. Yield: 400 mg (71%). crystals having a composition of [FcV](I ). Oxidized forms of
3
1
H-NMR (600 MHz, CDCl , ppm): δ = 1.45 (s, 18H, CH
̲
), 1.46 FcVFc: To a CHCl3 solution of I2 FcVFc was added. To the
3
3
This journal is © The Royal Society of Chemistry 2015
Dalton Trans., 2015, 44, 14635–14645 | 14643

View Article Online
Paper
Dalton Transactions
resulting solution n-hexane was added and kept at room tem-
perature. After the reprecipitate was washed with n-hexane, the
target compound was obtained as light brown crystals having a
8 For selected recent examples of Fc conjugates, see:
(a) I. Ratera, C. Sporer, D. Ruiz-Molina, N. Ventosa,
J. Baggerman, A. M. Brouwer, C. Rovira and J. Veciana, J. Am.
Chem. Soc., 2007, 129, 6117–6129; (b) T. Kusamoto,
K. Takada, R. Sakamoto, S. Kume and H. Nishihara, Inorg.
Chem., 2012, 51, 12102–12113; (c) T. Kusamoto, H. Nishihara
and R. Kato, Inorg. Chem., 2013, 52, 13809–13811;
(d) K. Heinze and S. Reinhardt, Organometallics, 2007, 26,
5406–5414; (e) H. Huesmann, C. Förster, D. Siebler, T. Gasi
and K. Heinze, Organometallics, 2011, 31, 413–427.
9 (a) M. Murata, M. Yamada, T. Fujita, K. Kojima,
M. Kurihara, K. Kubo, Y. Kobayashi and H. Nishihara,
J. Am. Chem. Soc., 2001, 123, 12903–12904; (b) S. Fukuzumi,
Y. Yoshida, K. Okamoto, H. Imahori, Y. Araki and O. Ito,
J. Am. Chem. Soc., 2002, 124, 6794–6795; (c) S. B. Colbran,
S. T. Lee, D. G. Lonnon, F. J. D. Maharaj, A. M. McDonagh,
K. A. Walker and R. D. Young, Organometallics, 2006, 25,
2216–2224; (d) A. Neidlinger, V. Ksenofontov and
K. Heinze, Organometallics, 2013, 32, 5955–5965.
composition of [FcVFc](I
3
) and dark brown crystals having a
composition of [FcVFc](I ) .
3
2
Data were collected with
a Rigaku ValiMax RAPID
RA-Micro7HFM using Mo Kα radiation. The diffraction data
were processed with RAPID AUTO on a Rigaku program, and
2
the structures were solved by direct methods and refined on F
by full-matrix least-squares using CrystalStructure and
SHELXL-97. The CCDC numbers in Table S10† contain the
supplementary crystallographic data for this paper.
Acknowledgements
This work was partially supported by a Grant-in-Aid for Young
Scientists B (no. 25790016) and a research grant from the
Murata Science Foundation. The authors would like to thank
Mr Fumio Asanoma and Ms. Yoshiko Nishikawa (NAIST) for 10 K. Tahara, T. Akita, S. Katao and J. Kikuchi, Dalton Trans.,
the NMR and ESI-MS measurements, respectively.
2014, 43, 1368–1379.
1
1 (a) S. S. Kamath, V. Uma and T. S. Srivastava, Inorg. Chim.
Acta, 1989, 166, 91–98; (b) J. A. Weinstein, M. T. Tierney,
E. S. Davies, K. Base, A. A. Robeiro and M. W. Grinstaff,
Inorg. Chem., 2006, 45, 4544–4555; (c) N. M. Shavaleev,
E. S. Davies, H. Adams, J. Best and J. A. Weinstein, Inorg.
Chem., 2008, 47, 1532–1547; (d) J. Best, I. V. Sazanovich,
H. Adams, R. D. Bennett, E. S. Davies, A. J. H. M. Meijer,
M. Towrie, S. A. Tikhomirov, O. V. Bouganov, M. D. Ward
and J. A. Weinstein, Inorg. Chem., 2010, 49, 10041–10056;
(e) H.-C. Chang, K. Komasaka, K. Kishida, T. Shiozaki,
T. Ohmori, T. Matsumoto, A. Kobayashi, M. Kato and
S. Kitagawa, Inorg. Chem., 2011, 50, 4279–4288.
Notes and references
1
For selected reviews, see: (a) E. Evangelio and D. Ruiz-
Molina, Eur. J. Inorg. Chem., 2005, 2957–2971; (b) W. Kaim,
Inorg. Chem., 2011, 50, 9752–9765; (c) D. Michael and
P. Mingos, J. Organomet. Chem., 2014, 751, 153–173.
2
For selected reviews, see: (a) P. Gütlich and A. Dei, Angew.
Chem.,
Int.
Ed.
Engl.,
1997,
36,
2734–2736;
(
b) C. G. J. Pierpont, Coord. Chem. Rev., 2001, 216–217, 99–
1
4
25; (c) C. G. J. Pierpont, Coord. Chem. Rev., 2001, 219–221,
15–433; (d) A. Dei, D. Gatteschi, C. Sangregorio and 12 The reported first and second oxidation potential values
L. Sorace, Acc. Chem. Res., 2004, 37, 827–835; (e) O. Sato,
A. Gui, R. Matsuda, J. Tao and S. Hayami, Acc. Chem. Res.,
for Pt(bpy) (C) is 450 mV and 700 mV vs. Ag–AgCl in aceto-
nitrile. See ref. 11a.
2
007, 40, 361–369.
R. M. Buchanan and C. G. J. Pierpont, J. Am. Chem. Soc.,
980, 102, 4951–4957.
H.-C. Chang and D. Kiriya, Eur. J. Inorg. Chem., 2013, 642–
52.
(a) M. Nihei, Y. Sekine, N. Suganami, K. Nakazawa,
13 C. Hansh, A. Leo and R. W. Taft, Chem. Rev., 1991, 91, 165–
195.
14 L. Cuffe, R. D. A. Hudson, J. F. Gallagher, S. Jennings,
C. J. McAdam, R. B. T. Connelly, A. R. Manning,
B. H. Robinson and J. Simpson, Organometallics, 2005, 24,
2051–2060.
3
4
5
1
6
A. Nakao, H. Nakao, Y. Murakami and H. Oshio, J. Am. 15 Inorganic Electronic Spectroscopy, ed. A. B. P. Lever, Elsevier,
Chem. Soc., 2011, 133, 3592–3600; (b) T. Matsumoto, Amsterdam, 1984, pp. 659–671.
G. N. Newton, T. Shiga, S. Hayami, Y. Matsui, H. Okamoto, 16 (a) K. D. Demadis, C. M. Hartshorn and T. J. Meyer, Chem.
R. Kumai, Y. Murakami and H. Ohio, Nat. Commun., 2014,
, 3865–3865.
D. Kiriya, K. Nakamura, H.-C. Chang and S. Kitagawa,
Chem. Commun., 2009, 4085–4087.
For selected reviews of biferrocene, see: (a) D. O. Cowan,
C. LeVanda, J. Park and F. Kaufman, Acc. Chem. Res., 1973,
Rev., 2001, 101, 2655–2685; (b) B. S. Brunschwig, C. Creutz
and N. Sutin, Chem. Soc. Rev., 2002, 31, 168–184;
(c) D. M. D’Alessandro and F. R. Keene, Chem. Soc. Rev.,
2006, 35, 424–440; (d) D. M. D’Alessandro and F. R. Keene,
Chem. Rev., 2006, 106, 2270–2298; (e) P. Aguirre-Etcheverry
and D. O’Hare, Chem. Rev., 2010, 110, 4839–4864.
5
6
7
6
, 1–7; (b) D. Astruc, Acc. Chem. Res., 1997, 30, 383–391; 17 We defined rDA as the distance between Fe atom and the
+
(
c) H. Nishihara, Bull. Chem. Soc. Jpn., 2001, 74, 19–29. For
center of C–C–C–O of the catecholate moiety in 3 , in con-
sideration of the difficulties in determining the accurate
estimation of rDA because of the wide delocalization of the
π-orbital in the catecholate moiety.
a
selected review of Fc-porphyrin conjugates, see:
(
d) C. Bucher, C. H. Devillers, J.-C. Moutet, G. Royal and
S.-A. Eric, Coord. Chem. Rev., 2009, 253, 21–36.
14644 | Dalton Trans., 2015, 44, 14635–14645
This journal is © The Royal Society of Chemistry 2015

View Article Online
Dalton Transactions
Paper
1
1
8 H. Nishihara, Adv. Inorg. Chem., 2002, 53, 41–86.
9 (a) M. B. Robin and P. Day, Adv. Inorg. Chem. Radiochem.,
G. Zheng, J. L. Sonnenberg, M. Hada, M. Ehara,
K. Toyota, R. Fukuda, J. Hasegawa, M. Ishida,
T. Nakajima, Y. Honda, O. Kitao, H. Nakai, T. Vreven,
J. A. Montgomery Jr., J. E. Peralta, F. Ogliaro,
M. Bearpark, J. J. Heyd, E. Brothers, K. N. Kudin,
V. N. Staroverov, R. Kobayashi, J. Normand,
K. Raghavachari, A. Rendell, J. C. Burant, S. S. Iyengar,
J. Tomasi, M. Cossi, N. Rega, J. M. Millam, M. Klene,
J. E. Knox, J. B. Cross, V. Bakken, C. Adamo, J. Jaramillo,
R. Gomperts, R. E. Stratmann, O. Yazyev, A. J. Austin,
R. Cammi, C. Pomelli, J. W. Ochterski, R. L. Martin,
K. Morokuma, V. G. Zakrzewski, G. A. Voth, P. Salvador,
J. J. Dannenberg, S. Dapprich, A. D. Daniels, Ö. Farkas,
J. B. Foresman, J. V. Ortiz, J. Cioslowski and D. J. Fox,
Gaussian 09, Gaussian, Inc., Wallingford, CT, 2009.
1
1
967, 10, 247–422; (b) C. Creutz, Prog. Inorg. Chem., 1983, 30,
–73; (c) N. S. Hush, Prog. Inorg. Chem., 1967, 8, 391–444.
2
0 (a) I. V. Nelson and R. T. Iwamoto, J. Electroanal. Chem.,
964, 7, 218–221; (b) N. G. Connelly and W. E. Geiger,
1
Chem. Rev., 1996, 96, 877–910.
2
2
2
2
2
1 N. J. Mammano, A. Zalkin, A. Landers and A. L. Rheingold,
Inorg. Chem., 1977, 16, 297–300.
2 P. Seiler and J. D. Dunitz, Acta Crystallogr., Sect. B: Struct.
Crystallogr. Cryst., 1979, 35, 1068–1074.
3 C. Patoux, C. Coudret, J.-P. Launay, C. Joachim and
A. Gourdon, Inorg. Chem., 1997, 36, 5037–5049.
4 C. Imrie, C. Loubser, P. Engelbrecht and C. W. McCleland,
J. Chem. Soc., Perkin Trans. 1, 1999, 2513–2523.
5 J. Yang, D. K. Kersi, L. J. Giles, B. W. Stein, C. Feng, 27 D. Becke, J. Chem. Phys., 1993, 98, 5648–5652.
C. R. Tichnell, D. A. Shultz and M. L. Krik, Inorg. Chem., 28 P. Hay and W. R. Wadt, J. Chem. Phys., 1985, 82, 270–273.
2
014, 53, 4791–4793.
29 P. C. Hariharan and J. A. Pople, Theor. Chim. Acta, 1973, 28,
213–222.
2
6 M. J. Frisch, G. W. Trucks, H. B. Schlegel, G. E. Scuseria,
M. A. Robb, J. R. Cheeseman, G. Scalmani, V. Barone, 30 (a) B. Mennucci, E. Cancès and J. Tomasi, J. Phys. Chem. B,
B. Mennucci, G. A. Petersson, H. Nakatsuji, M. Caricato,
X. Li, H. P. Hratchian, A. F. Izmaylov, J. Bloino,
1997, 101, 10506–10517; (b) J. Tomasi, B. Mennucci and
R. Cammi, Chem. Rev., 2005, 105, 2999–3093.
This journal is © The Royal Society of Chemistry 2015
Dalton Trans., 2015, 44, 14635–14645 | 14645