Long-distance electronic coupling in diferrocenyl compounds with cross-conjugated germinal-diethynylethene bridges

Article abstract of DOI:10.1016/j.jorganchem.2018.01.052

A series of germinal-diethynylethene (gem-DEE) bridged diferrocenyl compounds, including 1,1-[bis(ferrocenylethynyl)methylene]cyclohexane (1), 1,1-[bis(ferrocenylethynyl)methylene]tetrahydro-2H-pyran (2), and 1,1-[bis(ferrocenylethynyl)methylene]tetrahydr

Full text of DOI:10.1016/j.jorganchem.2018.01.052

Accepted Manuscript
Long-distance electronic coupling in diferrocenyl compounds with cross-conjugated
germinal-diethynylethene bridges
Yang Fan, Hua-Min Li, Guo-Dong Zou, Xu Zhang, Meng Li, Jia-Hui Wu, Xin Zhang,
Hai-Ting Lu
PII:
S0022-328X(18)30070-6
10.1016/j.jorganchem.2018.01.052
JOM 20290
DOI:
Reference:
To appear in: Journal of Organometallic Chemistry
Received Date: 28 October 2017
Revised Date: 17 January 2018
Accepted Date: 29 January 2018
Please cite this article as: Y. Fan, H.-M. Li, G.-D. Zou, X. Zhang, M. Li, J.-H. Wu, X. Zhang,
H.-T. Lu, Long-distance electronic coupling in diferrocenyl compounds with cross-conjugated
germinal-diethynylethene bridges, Journal of Organometallic Chemistry (2018), doi: 10.1016/
j.jorganchem.2018.01.052.
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Long-distance electronic coupling in diferrocenyl compounds with
cross-conjugated germinal-diethynylethene bridges
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Yang Fana, *, Hua-Min Lia, Guo-Dong Zoua, Xu Zhangb, Meng Lia, Jia-Hui Wua, Xin Zhang,
Hai-Ting Lua
aCollege of Chemistry and Chemical Engineering, Xinyang Normal University, Xinyang 464000, China
bFujian Institute of Research on the Structure of Matter, Chinese Academy of Sciences, Fuzhou 350002,
China
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Abstract: A series of germinal-diethynylethene (gem-DEE) bridged diferrocenyl compounds,
including
1,1-[bis(ferrocenylethynyl)methylene]cyclohexane
(2),
(1),
1,1-[bis(ferrocenylethynyl)methylene]tetrahydro-2H-pyran
and
1,1-[bis(ferrocenylethynyl)methylene]tetrahydro-2H-thiopyran (3) were synthesized and
characterized. The Fe…Fe distance between the two ferrocenyl termini reaches up to ~9 Å for
compounds 2 and 3. The electrochemical measurements demonstrate moderate electronic
coupling between the gem-DEE-bridged ferrocenyl (Fc) termini in this cross-conjugated
system. UV-vis-NIR spectroscopy studies suggest that the monocation species of these
compounds belong to class II mixed-valence systems in Robin–Day classification. DFT
calculations further reveal electronic structures of these cross-conjugated diferrocenyl
compounds.
Keywords: Diferrocenyl; Diethynylethene; Cross-conjugated; Electronic coupling;
Mixed-valence.
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1. Introduction
The binuclear and poly-nuclear mixed-valence metal complexes with π conjugated
bridging ligand have attracted continuous interests for decades, which offer a good deal of
molecular models for the fundamental study of electron transfer processes [1–26]. In
particular, the long-distance electronic coupling involving metal–metal distance up to
nanometer-scale is of great importance from both fundamental and practical point of view
[27–30]. These nanometer-scale molecular systems with controllable electron transfer
properties have potential applications in molecular electronics and optoelectronic materials.
For instance, Ren and co-workers reported a series of Ru2(Xap)4 (ap = 2-anilinopyridinate)
capped polyyn-diyl (µ-C2m, m = 4–10) diruthenium compounds with the distance between two
Ru2 termini up to ~28 Å [28]. It is revealed that the electronic coupling between the Ru2
termini depends on the length of polyyn-diyl with an attenuation constant between 0.12 and
0.15 Å-1. These results provide in-depth understanding on the long-distance electron transfer
mediated by polyyn-diyl bridge.
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Compared to the extensively investigated linearly conjugated bridging ligands, the
redox-active binuclear complexes bridged by cross-conjugated ligands have only been started
to be explored in recent years [31–40]. The weak electronic coupling between two Fc centers
bridged by the cross-conjugated 3-(dibromomethylidene)penta-1,4-diyne ligand was firstly
reported by Xu et al [35]. The Fe…Fe distance in the crystal structure of this diferrocenyl
compound reaches to ~10.5 Å. The diruthenium compounds bearing cross-conjugated
σ-geminal-diethynylethene (gem-DEE) ligand exhibit attenuated electronic coupling between
the two Ru2 termini compared to that of the counterpart with buta-1,3-diyne bridge [36]. In
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the recent report by Low and co-workers, using the weakly coordinating electrolyte
n-Bu4N[B{C6H3(CF3)2-3,5}4], the electronic coupling was more clearly resolved in
cross-conjugated bis- and tris-ferrocenyl complexes Ph2C=C(C≡CFc)2 and FcCH=C(C≡CFc)2
with Fe…Fe distance up to ~10.3 Å [33]. The weakly coordinating electrolyte
Na[B{C6H3(3,5-CF3)2}4] was also used in our recent investigation on the electron transfer
properties of a series of gem-DEE bridged diferrocenyl compounds [40].
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Herein we reported the syntheses, voltammetric and spectroscopic studies of a series of
diferrocenyl compounds bridged by cross-conjugated gem-DEE ligands with different pendent
substituents including cyclohexane, tetrahydro-2H-pyran, and tetrahydro-2H-thiopyran. The
single-crystal X-ray diffraction analyses reveal that the Fe…Fe distances between the Fc
termini in the crystal structures of these compounds reaches up to ~9 Å for compounds 2 and
3. The experimental and computational studies suggest that these cross-conjugated
diferrocenyl compounds belong to the weakly coupled Robin–Day class II systems.
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15 2. Experimental
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2.1. Reagents
Tetrabromomethane (98%), cyclohexanone (99%), tetrahydro-4H-pyran-4-one (98%),
tetrahydro-4H-thiopyran-4-one (98%), triphenylphosphine (99%), heptane (98%),
triethylamine (99%) and NOBF4 (98%) was purchased from commercial suppliers. These
reagents were used as received without further purification. Ethynylferrocene [41],
(1,1-dibromomethylene)cyclohexane [42], and Na[B{C6H3(3,5-CF3)2}4] [43] were
synthesized by literature methods.
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2.2. Instruments
1H and 13C NMR spectra were recorded on a Bruker BioSpin GmbH 600 MHz
spectrometer using CDCl3 as solvent. Chemical shifts were reported in ppm relative to
internal TMS (0 ppm). Elemental analyses were performed using a Vario MICRO elemental
analyzer. UV–vis–NIR spectra of the samples in CH2Cl2 solutions were obtained on
PerkinElmer Lamda-950 spectrophotometer.
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2.3. Single-crystal X-ray diffraction analysis
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The X-ray diffraction data for compounds 1–3 were collected on a Xcalibur Eos Gemini
CCD diffractometer with graphite–monochromated Mo Kα radiation (λ = 0.71073 Å) at room
temperature. The structures were solved by direct methods and refined by full-matrix
least-squares on F2 by using the program SHELX-2016 [44]. Anisotropic thermal factors were
assigned to all the non-hydrogen atoms. The positions of the hydrogen atoms were generated
geometrically, assigned isotropic thermal parameters, and allowed to ride on their respective
parent atoms before the final cycle of least-squares refinement. Detailed crystal data and
structure refinements parameters for compounds 1–3 are listed in Table S1. Further
crystallographic details for the compounds are summarized in CCDCs 1582342 (1), 1582343
(2) and 1582344 (3).
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2.4. Electrochemistry
The electrochemical experiments were carried out with a CHI 660E electrochemical
workstation (CH Instruments). Cyclic voltammetry (CV) and differential pulse voltammetry
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(DPV) measurements were performed using a three-electrode system with a glassy carbon
working electrode, a Pt wire counter electrode, and a Ag/AgCl (3 M KCl) reference electrode
in CH2Cl2 solution containing 0.01 M Na[B{C6H3(3,5-CF3)2}4] (N2-degassed) as electrolyte.
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2.5. DFT calculations
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DFT calculations were carried out using Gaussian 09 software with the B3LYP
exchange-correlation functional and 6-31G** basis set. Geometry optimizations of the
structures were done using parameters from the corresponding crystal structure data as
starting points. No symmetry constraints were used in the optimization. The optimized
geometries were fully characterized as true minima via analytical frequency calculations (no
imaginary eigenvalues). The solvent (CH2Cl2) effects were considered using the polarized
continuum model (PCM).
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2.6. Syntheses of compounds 1–3
2.6.1. Synthesis of 1,1-[bis(ferrocenylethynyl)methylene]cyclohexane (1)
A mixture of (1,1-dibromomethylene)cyclohexane (100 mg, 0.4 mmol), ethynylferrocene
(189 mg, 0.9 mmol), Pd(PPh3)2Cl2 (30 mg, 0.04 mmol) and CuI (20 mg, 0.1 mmol) in
triethylamine (5 mL) was sealed in a 120 mL Teflon screwed tube under N2 atmosphere. The
reaction mixture was heated at 95 oC with stirring for 24 h. After cooling to room temperature,
the reaction mixture was diluted with CH2Cl2 (100 mL), washed with saturated aq. NH4Cl
solution (2 × 50 mL) and distilled water (2 × 50 mL). The organic layer was dried over
anhydrous Na2SO4, and concentrated under reduced pressure. The crude product was purified
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by column chromatography on silica gel (CH2Cl2 : petroleum ether = 1 : 5) to yield the title
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compound 1 as red solid (105 mg, 51% yield). H NMR (600 MHz, CDCl3): δ 4.47 (s, 4H,
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C5H4), 4.23 (s, 10H, C5H5), 4.19 (s, 4H, C5H4), 2.57 (s, 4H, CH2), 1.66 (s, 4H, CH2), 1.62 (s,
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2H, CH2). C NMR (150 MHz, CDCl3): δ 158.82, 98.75, 89.51, 82.65, 71.38, 69.93, 68.68,
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65.67, 32.86, 27.56, 26.28. Anal. Calcd for C31H28Fe2: C, 72.69; H, 5.51. Found: C, 72.90; H,
5.54.
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2.6.2. Synthesis of 4-(dibromomethylene)tetrahydro-2H-pyran (2a)
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In an oven-dried three-necked flask, a mixture of tetrahydro-4H-pyran-4-one (1.0 g, 10
mmol), CBr4 (6.63 g, 20 mmol), PPh3 (10.5 g, 40 mmol) in heptane (100 mL) was refluxed
under N2 atmosphere for 48 h. After cooling to room temperature, the reaction mixture was
filtered through Celite, and the solid residue was washed with petroleum ether. The solvent
was removed under reduced pressure to give crude products. Chromatography on silica gel
using petroleum ether as the eluent afforded the product as white solid (1.3 g, 51% yield). 1H
NMR (600 MHz, CDCl3): δ 3.68 (t, J = 4.9 Hz, 4H, CH2), 2.51 (t, J = 4.9 Hz, 4H, CH2).
13CNMR (150 MHz, CDCl3): δ 139.96, 84.49, 67.37, 35.15. Anal. Calcd for C6H8OBr2: C,
28.16; H, 3.15. Found: C, 28.31; H, 3.16.
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2.6.3. Synthesis of 1,1-[bis(ferrocenylethynyl)methylene]tetrahydro-2H-pyran (2)
This compound was prepared from 2a by the same procedure for that of 1.
Chromatography on silica gel (CH2Cl2 : petroleum ether = 1 : 1) gave the desired product as
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red solid (120 mg, 59% yield). H NMR (600 MHz, CDCl3): δ 4.47 (s, 4H, C5H4), 4.23 (s,
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10H, C5H5), 4.21 (s, 4H, C5H4), 3.78 (t, J = 4.4 Hz, 4H, CH2), 2.69 (t, J = 4.3 Hz, 4H, CH2).
13C NMR (150 MHz, CDCl3): δ 151.75, 100.65, 90.70, 81.90, 71.41, 69.97, 68.86, 68.18,
65.17, 33.28. Anal. Calcd for C30H26OFe2: C, 70.07; H, 5.10. Found: C, 70.15; H, 5.11.
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2.6.4. Synthesis of 4-(dibromomethylene)tetrahydro-2H-thiopyran (3a)
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This compound was prepared from tetrahydro-4H-thiopyran-4-one by the same procedure
for that of 2a. Chromatography on silica gel using petroleum ether as eluent gave the desired
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product as light yellow solid (1.5 g, 56% yield). H NMR (600 MHz, CDCl3): δ 2.76 (d, J =
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5.3 Hz, 4H, CH2), 2.70 (d, J = 5.4 Hz, 4H, CH2). C NMR (150 MHz, CDCl3): δ 141.99,
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85.43, 36.62, 29.27. Anal. Calcd for C6H8SBr2: C, 26.49; H, 2.96. Found: C, 26.61; H, 2.98.
2.6.5. Synthesis of 1,1-[bis(ferrocenylethynyl)methylene]tetrahydro-2H-thiopyran (3)
This compound was prepared from 3a by the same procedure for that of 1.
Chromatography on silica gel (CH2Cl2 : petroleum ether = 1 : 1) gave the desired product as
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red solid (115 mg, 54% yield). H NMR (600 MHz, CDCl3): δ 4.47 (s, 4H, C5H4), 4.24 (s,
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10H, C5H5), 4.22 (s, 4H, C5H4), 2.92 (s, 4H, CH2), 2.78 (d, J = 4.2 Hz, 4H, CH2). C NMR
(150 MHz, CDCl3): δ 153.77, 101.56, 91.18, 81.92, 71.42, 69.96, 68.89, 65.08, 34.38, 30.16.
Anal. Calcd for C30H26SFe2: C, 67.95; H, 4.94. Found: C, 68.09; H, 4.95.
20 3. Results and discussion
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The gem-DEE bridged diferrocenyl compounds (Fig. 1) were readily synthesized from
the
ketones,
including
cyclohexanone,
tetrahydro-4H-pyran-4-one
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tetrahydro-4H-thiopyran-4-one, by the Corey-Fuchs olefination and subsequent Sonogashira
coupling
1,1-[bis(ferrocenylethynyl)methylene]cyclohexane
1,1-[bis(ferrocenylethynyl)methylene]tetrahydro-2H-pyran
1,1-[bis(ferrocenylethynyl)methylene]tetrahydro-2H-thiopyran
with
ethynylferrocene
(Scheme
1).
The
resulting
compounds
(1),
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(2),
(3),
and
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and
the
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1,1-dibromoalkene intermediates 4-(dibromomethylene)tetrahydro-2H-pyran (2a) and
4-(dibromomethylene)tetrahydro-2H-thiopyran (3a) were characterized by NMR spectroscopy
and elemental analysis. The diferrocenyl compounds are all stable under ambient conditions
in solution or in the solid state.
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The molecular structures of compounds 1–3 were determined by single-crystal X-ray
diffraction analysis (Fig. 2). The compounds crystalize in the triclinic space group P-1 (1) and
the monoclinic space group P21/c (2 and 3) with one crystallographically independent
molecule in the asymmetric unit (Table S1). As shown in Fig. 2, the central gem-DEE
backbone exhibits a typical planar Y-shape geometry. The C≡C and C=C bond lengths in the
gem-DEE backbone as well as the alkylidene bond angles are comparable to other
cross-conjugated enediynes (Table 1). A typical chair conformation was observed for the
cyclohexane and tetrahydro-2H-thiopyran pendent substituents in compounds 1 and 3,
respectively, while the tetrahydro-2H-pyran substituent in 2 exhibits an approximately planar
conformation. The Fe…Fe distance between the two ferrocenyl units is 6.761 (10), 9.043 (7),
and 9.172 (6) Å for the compounds 1, 2 and 3, respectively. In our previous report, the four
gem-DEE bridged diferrocenyl compounds show very similar Fe…Fe distance of 6.74–7.18 Å
[40]. For the present diferrocenyl compounds, the obviously increased Fe…Fe distances of 2
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and 3 could be attributed to the different orientation of the two ferrocenyl groups in crystal
structures. This is probably due to the intermolecular interactions including the C–H…π
hydrogen bonds and π…π stacking interactions. As can be seen from Fig. S6 and Table S2–4,
the compounds 2 and 3 exhibit stronger C–H…π interactions compared to that for compound 1.
Moreover, the π…π interactions were observed for compounds 2 and 3, while it is absent in
compound 1.
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The electrochemistry of these gem-DEE bridged diferrocenyl compounds were
investigated by cyclic voltammetry (CV) and differential pulse voltammetry (DPV)
measurements. The weakly coordinating supporting electrolyte Na[B{C6H3(3,5-CF3)2}4] was
used in electrochemical experiments. Due to the substantially suppressed ion-pairing effect,
this kind of electrolyte has been proved to be very efficient to improve the resolution between
the coupled oxidation processes in mixed-valence poly-ferrocene compounds [41–46]. The
cyclic voltammograms and differential pulse voltammograms of these compounds are
characterized by a pair of overlapping but partially resolved redox couples, indicating the
stepwise one-electron oxidation of two Fc units (Fig. 3). As estimated from the DPV curves,
the potential difference (∆E) for the pairwise redox couples is 168, 156, and 152 mV for
compounds 1, 2, and 3, respectively (Table 2). This result suggests the moderate electronic
coupling between two Fc centers over the cross-conjugated gem-DEE bridge [33, 36, 40]. It is
noteworthy that, although the Fe…Fe distances reach up to ~9.1 Å for compounds 2 and 3,
they still exhibit comparable degree of electronic coupling in comparison to compound 1 with
Fe…Fe distance of ~6.7 Å. This implies that the electronic coupling between the two Fc
termini more likely occurs via the through-bond mechanism. Moreover, in the recent report by
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Low and co-workers, the tris(ferrocenyl) compound FcCH=C(C≡CFc)2 exhibit more strong
electronic coupling (∆E = 216 mV) over the gem-DEE bridge with the Fe…Fe distance up to
~10.3 Å [33]. These results are suggestive of the capability of cross-conjugated gem-DEE
bridging ligand in mediating electronic coupling between Fc termini. The similar ∆E values
also indicate that the heterocyclic pendent substituents in compounds 2 and 3 have little
effects on Fc–Fc electronic coupling in the cross-conjugated system.
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Fig. 4a shows UV-vis-NIR spectra recorded during the stepwise chemical oxidation of
compound 1 by NOBF4 [51–53]. The weak and broad low-energy absorption band around 750
nm was gradually generated in the spectrum, which is indicative of the intervalence charge
transfer (IVCT) transition of the mixed-valence monocation 1+. The generation of IVCT
transition was also observed with the broad absorption band at ~800 nm for 2+ and 3+,
respectively (Fig. S7a and S8a). The deconvolution analysis shows that the NIR band of the
mixed-valence species is composed of Gaussian-shaped sub-bands corresponding to the IVCT
transition and the possible ligand-to-FeIII charge transfer (LMCT) transition (Fig. 4b, Fig. S7b,
and Fig. S8b). The spectroscopic parameters for IVCT band are listed in Table 3. According to
the Hush model, the electronic coupling metric element (Hab) can be estimated from the IVCT
band parameters by using the equation: Hab = 2.05 × 10-2[(νmax εmax ∆ν1/2)1/2/rab] [48]. The
value of Hab is calculated to be 560, 470, and 382 cm-1 for compounds 1, 2, and 3,
respectively (Table 3). These results suggest that the monocation for these gem-DEE-bridged
diferrocenyl compounds can be described as the weakly coupled Robin–Day class II
mixed-valence species [55].
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The electronic structure of these diferrocenyl compounds was studied by DFT
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calculations at the B3LYP level of theory with 6-31G** basis set. As shown in Fig. 5, the
HOMO on the gem-DEE backbone is the out-of-phase combination of three π orbitals on two
acetylene and one ethene units, and it is the in-phase combination of the three π* orbitals for
LUMO. This result is indicative of π electron delocalization across the gem-DEE bridge, as
that revealed by the theoretical investigations on free gem-DEE ligand by Ren and co-workers
[39]. The HOMO of these diferrocenyl compounds has dominant contribution from the Fc
termini mainly on the Fe 3d orbitals, while the electron density on Fc units is significantly
reduced in the LUMO. The pendent substituents in these compounds have little contribution
to the frontier orbitals due to their saturated structure. DFT calculations on the monocation 1+
show the predominant spin localization on one Fc unit along with some contribution from half
of the gem-DEE skeleton (Fig. 6). This result suggests the localized oxidation on Fc unit in
the monocation 1+ that is characteristic for the electronic structure of class II mixed-valence
species [56–58].
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15 4. Conclusions
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In this study, a series of diferrocenyl compounds bridged by cross-conjugated gem-DEE
ligands with different pendent substituents including cyclohexane, tetrahydro-2H-pyran, and
tetrahydro-2H-thiopyran were synthesized and characterized. The X-ray crystallographic
study reveals the varying Fe…Fe distances between the Fc termini in the crystal structures of
these compounds, which reaches up to ~9 Å for compounds 2 and 3. The gem-DEE-bridged
Fc termini exhibit moderate electronic coupling in this cross-conjugated system. The
electronic coupling only show slight attenuation with increasing Fe…Fe distances from 1 to 3.
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Hush analysis on IVCT bands of the monocation species is suggestive of the Robin–Day class
II mixed-valence system.
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Acknowledgements
We acknowledge support by the National Natural Science Foundation of China (No.
21002082) and the Nanhu Scholars Program for Young Scholars of XYNU.
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Appendix A. Supplementary material
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Crystal data and structure refinements summary for compounds 1–3; Analysis of C–H...π
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(Cp-ring) interactions for compound 1–3; H and 13C NMR spectra of 1, 2a, 2, 3a, 3;
UV-Vis-NIR spectra recorded during stepwise chemical oxidation of compound 2 and 3 by
NOBF4 in CH2Cl2; The Gaussian deconvolution of NIR absorptions for the monocation 2+
and 3+.
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References
2
3
[1] P.J. Low, Coord. Chem. Rev. 257 (2013) 1507.
[2] J.-F. Halet, C. Lapinte, Coord. Chem. Rev. 257 (2013) 1584.
[3] W.-Y. Wong, C.-L. Ho, Coord. Chem. Rev. 250 (2006) 2627.
[4] W.-Y. Wong, Comments Inorg. Chem. 26 (2005) 39.
4
5
6
[5] P. Aguirre-Etcheverry, D. O’Hare, Chem. Rev. 110 (2010) 4839.
[6] D.M. D’Alessandro, F.R. Keene, Chem. Rev. 106 (2006) 2270.
[7] K.D. Demadis, C.M. Hartshorn, T.J. Meyer, Chem. Rev. 101 (2001) 2655.
[8] R.F. Winter, Organometallics 33 (2014) 4517.
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
[9] A. Hildebrandt, H. Lang, Organometallics 32 (2013) 5640.
[10] R. Breuer, M. Schmittel, Organometallics 32 (2013) 5980.
[11] R. Breuer, M. Schmittel, Organometallics 31 (2012) 6642.
[12] R. Breuer, M. Schmittel, Organometallics 31 (2012) 1870.
[13] W.-Y. Wong, G.-L. Lu, K.-F. Ng, K.-H. Choi, Z. Lin, J. Chem. Soc. Dalton Trans. 22
(2001) 3250.
[14] W.-Y. Wong, G.-L. Lu, K.-F. Ng, C.-K. Wong, K.-H. Choi, J. Organomet. Chem. 637–
639 (2001) 159.
[15] W.-Y. Wong, K.-Y. Ho, S.-L. Ho, Z. Lin, J. Organomet. Chem. 683 (2003) 341.
[16] W.-Y. Wong, G.-L. Lu, K.-H. Choi, Y.-H. Guo, J. Organomet. Chem. 690 (2005) 177.
[17] S. Mishra, S. Dewangan, S. Giri, S. M. Mobin, S. Chatterjee, Eur. J. Inorg. Chem. 35
(2016) 5485.
[18] S. Roué, H. Sahnoune, L. Toupet, J.-F. Halet, C. Lapinte, Organometallics 35 (2016)
2057.
[19] A.K. Diallo, J.-C. Daran, F. Varret, J. Ruiz, D. Astruc, Angew. Chem. Int. Ed. 48 (2009)
3141.
[20] W.Y. Chan, A.J. Lough, I. Manners, Angew. Chem. Int. Ed. 46 (2007) 9069.
[21] R.C. Quardokus, Y. Lu, N.A. Wasio, C.S. Lent, F. Justaud, C. Lapinte, S.A. Kandel, J.
Am. Chem. Soc. 134 (2012) 1710.
[22] S.W. Lehrich, A. Hildebrandt, M. Korb, H. Lang, J. Organomet. Chem. 847 (2017) 105.
13

ACCEPTED MANUSCRIPT
1
2
[23] G.-T. Xu, B. Li, J.-Y. Wang, D.-B. Zhang, Z.-N. Chen, Chem. Eur. J. 21 (2015) 3318.
[24] Y.-P. Ou, J. Zhang, M.-X. Zhang, F. Zhang, D. Kuang, F. Hartl, S. H. Liu, Inorg. Chem.
56 (2017) 11074.
3
4
[25] S. Muratsugu, M. Kishida, R. Sakamoto, H. Nishihara, Chem. Eur. J. 19 (2013) 17314.
[26] A. Sundararaman, K. Venkatasubbaiah, M. Victor, L. N. Zakharov, A. L. Rheingold, F.
Jäkle, J. Am. Chem. Soc. 128 (2006) 16554.
5
6
7
[27] J.-P. Launay, Chem. Soc. Rev. 30 (2001) 386.
8
[28] Z. Cao, B. Xi, D.S. Jodoin, L. Zhang, S.P. Cummings, Y. Gao, S.F. Tyler, P.E. Fanwick,
R.J. Crutchley, T. Ren, J. Am. Chem. Soc. 136 (2014) 12174.
[29] G.-L. Xu, R.J. Crutchley, M.C. DeRosa, Q.-J. Pan, H.-X. Zhang, X. Wang, T. Ren, J.
Am. Chem. Soc. 127 (2005) 13354.
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
[30] G.-L. Xu, G. Zou, Y.-H. Ni, M.C. DeRosa, R.J. Crutchley, T. Ren, J. Am. Chem. Soc.
125 (2003) 10057.
[31] K.B. Vincent, Q. Zeng, M. Parthey, D.S. Yufit, J.A.K. Howard, F. Hartl, M. Kaupp, P.J.
Low, Organometallics 32 (2013) 6022.
[32] M.I. Bruce, A. Burgun, M.A. Fox, M. Jevric, P.J. Low, B.K. Nicholson, C.R. Parker,
B.W. Skelton, A.H. White, N.N. Zaitseva, Organometallics 32 (2013) 3286.
[33] K.B. Vincent, J.B.G. Gluyas, Q. Zeng, D.S. Yufit, J.A.K. Howard, F. Hartl, P.J. Low,
Dalton Trans. 46 (2017) 5522.
[34] K.B. Vincent, J.B.G. Gluyas, S. Gückel, Q. Zeng, F. Hartl, M. Kaupp, P.J. Low, J.
Organomet. Chem. 821 (2016) 40.
[35] G.-L. Xu, B. Xi, J.B. Updegraff, J.D. Protasiewicz, T. Ren, Organometallics 25 (2006)
5213.
[36] W.P. Forrest, M.M.R. Choudhuri, S.M. Kilyanek, S.N. Natoli, B.M. Prentice, P.E.
Fanwick, R.J. Crutchley, T. Ren, Inorg. Chem. 54 (2015) 7645.
[37] W.P. Forrest, Z. Cao, K.M. Hassell, B.M. Prentice, P.E. Fanwick, T. Ren, Inorg. Chem.
51 (2012) 3261.
[38] S.N. Natoli, T.J. Azbell, P.E. Fanwick, M. Zeller, T. Ren, Organometallics 35 (2016)
3594.
[39] Z. Cao, T. Ren, Organometallics 30 (2011) 245.
14

ACCEPTED MANUSCRIPT
1
2
[40] Y. Fan, H.-M. Li, G.-D. Zou, X. Zhang, Y.-L. Pan, K.-K. Cao, M.-L. Zhang, P.-L. Ma,
H.-T. Lu, Organometallics 36 (2017) 4278.
3
[41] M. Rosenblum, N. Brawn, J. Papenmeier, M. Applebaum, J. Organometallic Chem. 6
(1966) 173.
4
5
[42] P.J. Kropp, S.A. McNeely, R.D. Davis, J. Am. Chem. Soc. 105 (1983) 6907.
[43] D.L. Reger, T.D. Wright, C.A. Little, J.J.S. Lamba, M.D. Smith, Inorg. Chem. 40 (2001)
3810.
6
7
8
[44] G.M. Sheldrick, Acta Cryst. C71 (2015) 3.
9
[45] W.E. Geiger, F. Barrière, Acc. Chem. Res. 43 (2010) 1030.
[46] M.S. Inkpen, S. Scheerer, M. Linseis, A.J.P. White, R.F. Winter, T. Albrecht, N.J. Long,
Nat. Chem. 8 (2016) 825.
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
[47] A.K. Diallo, C. Absalon, J. Ruiz, D. Astruc, J. Am. Chem. Soc. 133 (2011) 629.
[48] Y. Li, M. Josowicz, L.M. Tolbert, J. Am. Chem. Soc. 132 (2010) 10374.
[49] S.W. Lehrich, A. Hildebrandt, M. Korb, H. Lang, J. Organomet. Chem. 792 (2015) 37.
[50] E.A. Poppitz, A. Hildebrandt, M. Korb, H. Lang, J. Organomet. Chem. 752 (2014) 133.
[51] A. Vecchi, N.R. Erickson, J.R. Sabin, B. Floris, V. Conte, M. Venanzi, P. Galloni, V.N.
Nemykin, Chem. Eur. J. 21 (2015) 269.
[52] V.N. Nemykin, A.A. Purchel, A.D. Spaeth, M.V. Barybin, Inorg. Chem. 52 (2013)
11004.
[53] L.E. Wilson, C. Hassenrück, R.F. Winter, A.J.P. White, T. Albrecht, N.J. Long, Angew.
Chem. Int. Ed. 56 (2017) 6838.
[54] N.S. Hush, Coord. Chem. Rev. 64 (1985) 135.
[55] M.B. Robin, P. Day, Adv. Inorg. Chem. Radiochem. 9 (1967) 247.
[56] M. Parthey, M. Kaupp, Chem. Soc. Rev. 43 (2014) 5067.
[57] N.J. Brown, H.N. Lancashire, M.A. Fox, D. Collison, R. Edge, D.S. Yufit, J.A.K.
Howard, M.W. Whiteley, P.J. Low, Organometallics 30 (2011) 884.
[58] O. Gidron, Y. Diskin-Posner, M. Bendikov, Chem. Eur. J. 19 (2013) 13140.
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Scheme 1. Synthetic route for compounds 1–3.
2
3
Conditions: (i) CBr4 (2.0 equiv), PPh3 (4.0 equiv), heptane, reflux 48 h; (ii) FcC≡CH (3.0
4
5
equiv), Pd(PPh3)2 (0.13 equiv), CuI (0.33 equiv), Et3N, 95 oC, 24 h.
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Table 1. Selected bond lengths (Å) and angles (deg) for compounds 1–3.
1
2
3
C21–C22
C24–C25
C23–C26
Fe1…Fe2
1.179(4)
1.198(4)
1.347(4)
1.180(4) 1.193(4)
1.195(4) 1.190(4)
1.348(5) 1.340(4)
6.761(10) 9.043(7) 9.172(6)
115.6(3) 115.3(3)
C22–C23–C24 113.5(3)
3
4
5
6
Table 2. Electrochemical fata from DPV measurements (vs Ag/AgCl).
Compd Ox1, mV Ox2, mV ∆E, mV
Kc
1
2
3
40
68
56
208
224
208
168
156
152
692
434
371
7
8
9
Table 3. Parameters for the IVCT band of 1+–3+.
νmax
ε
∆ν1/2
rab
∆ν1/2(theor)
Hab
(cm-1)
Compd
(cm-1) (L mol-1 cm-1) (cm-1)
(Å)
(cm-1)
1+
2+
3+
14278
12950
12300
426
901
712
5557
3650
3300
6.761
9.043
9.172
5743
5469
5330
560
470
382
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Fig. 1. The gem-DEE bridged diferrocenyl compounds 1–3.
2
3
4
5
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Fig. 2. X-ray crystal structures of compounds 1–3. The ellipsoids are drawn at the 30%
probability level. H atoms are omitted for clarity.
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Fig. 3. CV (top) and DPV (bottom) of compounds 1 (a), 2 (b), and 3 (c) recorded in CH2Cl2
solution containing 0.01 M Na[B{C6H3(3,5-CF3)2}4] at room temperature. Scan rate: 50 mV
s-1.
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Fig. 4. (a) UV-Vis-NIR spectra recorded during stepwise chemical oxidation of compound 1
by NOBF4 in CH2Cl2. (b) The Gaussian deconvolution of NIR absorptions for the monocation
1+.
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Fig. 5. HOMO and LUMO for compounds 1–3.
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3
4
Fig. 6. Spin-density isosurface plot (left) and SOMO (right) of the monocation 1+.
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Highlights
• A series of gem-DEE bridged diferrocenyl compounds were synthesized.
• The Fe…Fe distance between the two ferrocenyl termini reaches up to ~9 Å.
• The cross-conjugated systems exhibit moderate electronic coupling between two
ferrocenyl termini.