Diethynyldiazafluoren-9-ylidene as a πcross-Conjugated Platform for Redox Active Transition Metal Fragments

Article abstract of DOI:10.1021/acs.organomet.9b00232

Synthetic routes were developed to attach three redox-active metal fragments to cross-conjugated 3-methylidenepentadiyne covalently expanded by diazafluorenylidene: The two alkyne termini of this new ligand were end-capped via a phenylene spacer with ethy

Full text of DOI:10.1021/acs.organomet.9b00232

Article
pubs.acs.org/Organometallics
Cite This: Organometallics XXXX, XXX, XXX−XXX
Diethynyldiazafluoren-9-ylidene as a π Cross-Conjugated Platform
for Redox Active Transition Metal Fragments
†
,†
Djawed Nauroozi,†,‡ Clemens Bruhn, and Rudiger Faust*
̈
†Institute for Chemistry and CINSaT − Centre for Interdisciplinary Nanostructure Science and Technology, University of Kassel,
Heinrich-Plett-Str. 40, 34132 Kassel, Germany
‡Ulm University, Institute for Inorganic Chemistry I, Albert-Einstein-Allee 11, 89081 Ulm, Germany
S
* Supporting Information
ABSTRACT: Synthetic routes were developed to attach three redox-active metal fragments
to cross-conjugated 3-methylidenepentadiyne covalently expanded by diazafluorenylidene:
The two alkyne termini of this new ligand were end-capped via a phenylene spacer with
ethynyl ferrocene, and a [Ru(bpy)2]2+ fragment was coordinated in the diimine binding site.
The photophysical and electrochemical properties of both the diferrocenyl-terminated ligand
and its corresponding Ru-complex were investigated by UV−vis absorption spectroscopy and
cyclic voltammetry. The absorption data reveal significant interactions of the metal centers
with the cross-conjugated ligand system. In the electrochemical experiments the ferrocenyl
and the ruthenium centers could be addressed individually as they are separated by almost
1 V. While the presence of the Ru-fragment manifests itself in the reduction potential of the
diazafluorenylidene-ligand, communication between the ferrocenyl end-caps on one hand and
between the ferrocenes and the Ru-fragment on the other appears to be reduced through the
freely rotating phenylene spacers.
olecular ensembles featuring transition metal fragments
along oligoalkyne chains (such as A, B in Figure 1) have
evidence for electronic interactions between the cross-
conjugated ligand system and a coordinated [PdCl2]-frag-
ment.10
M
long served for the exploration of fundamental electronic and
structural properties.1−7 In this context, π cross-conjugated
carbon-rich topologies as in C (Figure 1) have been of
particular interest as they provide competing, at times
cooperative pathways for the electronic communication across
the molecular backbone.8,9 We have recently revisited the
cross-conjugated 3-methylidenepentadiyne motif and have
devised a synthetic route to attach to this π-system the
diazafluoren-9-ylidene moiety as a pendant diimine metal
fragment binding site (D, Figure 1).10 This modification
allowed us to assemble spectroscopic and crystallographic
We have now extended this work and have implemented
redox-active transition metal fragments across the organic π-
perimeter of D. Such a design could allow the delocalization of
charges and electrons along the cross-conjugated framework
and could generate, upon the initiation of redox processes,
mixed valence species, a topic of continuing interest.11,12 We
chose ferrocenyl units at the alkyne termini (R in structure D)
as established redox probes in conjugated13−24 and cross-
conjugated π-systems25 together with a [Ru(bpy)2]2+ moiety at
the diimine binding site of D. Herein, we report synthesis and
characterization of this system together with a detailed
photophysical and electrochemical analysis.
Initial attempts to attach a ferrocenyl unit directly at the
alkyne termini of the 3-methylidenepentadiyne substructure
were significantly hampered by the low solubility of the
resulting products. We therefore decided to extend the linear
conjugation path by an ethynylphenylene. Starting from
ethynylferrocene 126 the desired ferrocenyl-capped diethynyl-
benzene 4 was obtained in excellent yield using a sequence of
Pd-mediated Sonogashira coupling reactions (Scheme 1, for
details see the Supporting Information). Hence, chemo-
selective coupling of 1-bromo-4-iodobenzene with 1 furnished
2,27 which in turn was coupled to TMS-acetylene to deliver 3.
Protodesilylation of 3 to provide 4 was accomplished smoothly
Figure 1. Selected conjugated (A, B) and cross-conjugated (C, D)
metal-(oligo)alkyne complexes.
Received: April 10, 2019
© XXXX American Chemical Society
A
DOI: 10.1021/acs.organomet.9b00232
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interactions along the possible (cross-)conjugated paths. As
noted previously in the solid state structures of alkyne-
substituted diazafluorenylidene molecules10 the olefinic CC-
bond (d[C21−C22]: 1.41(2) Å) iswith all due precau-
tionsrelatively long, a fact that may be interpreted as a
manifestation of fulvene-type substructures. The two ferro-
cenyl units of 6 are oriented perpendicular to each other. The
two Cp-rings in each ferrocenyl unit deviate only slightly
(rotational angle of ca. 3°) from an almost perfectly eclipsed
conformation.
Scheme 1. Synthesis of Ferrocene-Capped Diethynyl
Benzene 4
The complexation of 6 to the [Ru(bpy)2]2+ fragment was
achieved by refluxing a mixture of [Ru(bpy)2Cl2] and 6 in
dichloromethane/ethanol (Scheme 3). After refluxing the
mixture for 12 h and cooling to room temperature, 7 could
be obtained as its hexafluorophosphate salt upon precipitation
with aqueous NH4PF6 solution and filtration of the resulting
red solid. The formation of 7 was confirmed by elemental
analysis and high resolution mass spectrometry. UV−vis
absorption spectra of 6 and 7 in CH2Cl2 along with those of
reference compounds 3 and [Ru(bpy)2Cl2] are shown in
Figure 3. Pertinent data are summarized in Table 1.
with fluoride ions in protic THF. Since 4 was prone to thermal
and/or oxidative decomposition, it was used in subsequent
reactions immediately after the protodesilylation from 3 to 4
and the necessary purification/isolation steps.
The spectral features of 6 in a range between 270 and 570
nm include distinct absorption maxima at 320 nm, 395 nm,
and a broad transition around 492 nm, respectively. The
shortest and the longest wavelength absorption maxima
presumably arise from ferrocene-centered transitions, as
suggested by a comparison with the spectral profile of 3.
However, in 6 these absorptions are significantly red-shifted as
a result of the extended π-conjugated system of 6. In
comparison to the data of 6, the absorption of the trinuclear
complex 7 are of much higher intensity and span a significantly
broader range up to ca. 700 nm. Notable for solutions of 7 are
two broad absorption maxima, namely a ligand centered (LC)
transition at 284 nm with a shoulder at 316 nm, and a
pronounced featureless metal-to-ligand charge-transfer
(MLCT) band peaking at 424 nm.29−31 The comparison
with data from [Ru(bpy)2Cl2] and 6 reveals that in 7 the
features relating to the cross-conjugated ligand system are
maintained, but red-shifted through the interaction of the
ligand with the [Ru(bpy)2]2+ fragment. Absorptions associated
with the bpy-ligands on the ruthenium are not prominent in
the spectrum of 7, suggesting that the dominant electronic
interactions in the complex are those between metal-centered
and diazafluorene-located orbitals. These results are in line
with our previous findings in similar cross-conjugated
systems.10
At the core of our efforts to devise the targeted cross-
conjugated ligand system lies dibromoolefin 5, which we
recently made accessible via a microwave-assisted dibromo
olefination from the corresponding ketone.28 Hence, with 4
and 5 in hand, formation of 6 was accomplished again under
the conditions of a Sonogashira coupling reaction as outlined
in Scheme 2. The constitution of 6 was ascertained by
Scheme 2. Synthesis of the Redox Active Ligand 6
The redox behavior of diferrocenyl compound 6 and of the
trinuclear complex 7 have been studied electrochemically by
means of cyclic voltammetry (CV) and differential pulse
voltammetry (DPV, see Figure 4, Table 2). The measurements
were performed in CH2Cl2 solutions of the compounds
containing nBu4NPF6 as electrolyte. For comparison 3 and the
ethynylferrocene-terminated butadiyne 8 have been inves-
tigated as well. The data are referenced against Fc+/Fc. All
compounds show a dominant reversible redox wave at around
0.1 V against Fc+/Fc which can be attributed to the redox
processes of the terminal ferrocenes. Obviously, there is no
rapid electronic interaction between the two terminal
ferrocenes as they are oxidized simultaneously at the scan
rates used. Attempts to distinguish between the redox
processes at any of the diferrocenyl compounds 6, 7, and 8
using CV and DPV measurements even at low temperatures
were met with no success (see Figure S1). It is somewhat
spectroscopic methods, by high resolution mass spectrometry,
and, in addition, by crystallographic analysis (Figure 2).
Unfortunately, the crystals obtained by recrystallizing 6 from
acetone were of modest quality in that they showed solvent
accessible voids that may contain additional nonrefineable
solvent molecules. Overall, only 27% of the expected unique
reflections could be observed. A meaningful discussion of the
structure of 6 in the solid state is therefore limited to its global
features. The ligand 6 crystallizes in the triclinic space group
̅
P1 with four molecules in the unit cell. The cross-conjugated
3-methylidenepentadiyne-substructure and one of the phenyl
rings of 6 are coplanar with the diazafluorenylidene moiety.
The other phenyl ring is tilted with respect to this plane by an
angle of ca. 14°. It is evident from this arrangement, that the
core π-system of 6 is set to maximize the electronic
B
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Figure 2. Structure of 6 in the crystal as determined by X-ray diffraction analysis. Details of the structure determination are documented in the
Supporting Information (Table S1).
Scheme 3. Synthesis of Trinuclear Complex 7
Table 1. UV−Vis Data of Compounds 3, 6, 7, and
[Ru(bpy)2Cl2]
compound
λ [nm]
ε × 103 [M−1 cm−1
]
3
6
7
274, 288, 306, 360, 447
320, 395, 492
284, 316(sh), 424, 445(sh)
276, 366, 561
38, 36, 37, 8, 4
42, 39, 11
87, 55, 50, 47
82, 17, 17
[Ru(bpy)2Cl2]
conjugation between the two ferrocenyl end-caps. This
argument, if correct, would then also hold for the cross-
conjugated structures 6 and 7. Molecule 8 shows an additional
irreversible reduction at −2.40 V, typical for tolane-type
(sub-)structures.32,33 A reversible one-electron reduction of the
diazafluorene unit at −1.55 V can be observed for diferrocenyl
compound 6, which is in line with our previous findings.10 Not
surprising in light of the argument made above, the current
intensities for the redox processes at the ferrocenyl sites of 6
underline a 2-fold one-electron transfer. A pronounced
potential shift of about 440 mV for the diazafluorenylidene
reduction can be observed for complex 7. Evidently, the
electron withdrawing (cationic) nature of the Ru-moiety
facilitates the reduction of the attached diazafluorene unit.
However, the redox properties of the distal ferrocenyl sites is
apparently not influenced by the presence of the [Ru(bpy)2]2+
fragment. Clearly, more sophisticated investigations are needed
to identify interactions between the three metal sites across the
cross-conjugated ligand. The reduction potentials associated
with the bipyridyl ligands in 7 have not been assessed as the
diazafluorenylidene unit suffers degradation beyond a reduc-
tion potential of −1.80 V (see Supporting Information). In the
cathodic part of the CV of 7, the quasi-reversible oxidation of
RuII/RuIII is centered at 1.00 V, which is in the typical range
for Ru-complexes and thus appears to be unaffected by the
presence of the cross-conjugated ligand.
Figure 3. UV−vis absorption spectra of 3, 6, 7, and [Ru(bpy)2Cl2],
measured in CH2Cl2 at r.t.
In summary, this article introduces the π cross-conjugated
diazafluorenylidene ligand 6 equipped with redox active
ferrocenyl probes at the termini. Coordination of a
[Ru(bpy)2]2+ fragment in the diimine binding site of 6 leads
to trinuclear complex 7. A comparative UV−vis spectroscopic
surprising that even in the case of the rigid and linear 8 no
communication could be observed between the ferrocenyl
termini. One explanation might lie in the freely rotating
phenylene groups in solution that undermine a more efficient
C
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will extend the main conjugation paths by appropriate
synthetic transformations.
ASSOCIATED CONTENT
* Supporting Information
■
S
The Supporting Information is available free of charge on the
ACS Publications website at DOI: 10.1021/acs.organo-
met.9b00232.
Synthetic procedures and figures giving CV/DPV
1
profiles, ESI-HRMS, H and 13C NMR, as well as X-
ray structure of 6 (PDF)
Accession Codes
CCDC 1917587 contains the supplementary crystallographic
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 Cam-
bridge Crystallographic Data Centre, 12 Union Road,
Cambridge CB2 1EZ, UK; fax: +44 1223 336033.
AUTHOR INFORMATION
Corresponding Author
*E-mail: r.faust@uni-kassel.de.
■
ORCID
Rudiger Faust: 0000-0002-9231-591X
̈
Notes
The authors declare no competing financial interest.
REFERENCES
■
(1) Brady, M.; Weng, W.; Gladysz, J. A. New families of coordinated
carbon: oxidative coupling and cross-coupling of a transition metal
butadiynyl complex to bimetallic M−CCCCCCCC−M
and M−CCCCCC−M adducts. J. Chem. Soc., Chem. Commun.
1994, 2655.
Figure 4. Cyclic voltammograms of 3 and 6−8, performed in separate
n
CH2Cl2 solutions at room temperature containing 0.1 M Bu4NPF6
with Ag/AgCl as reference electrode, Pt wire as counter electrode and
Pt disk as working electrode; scan rate: 100 mV s−1; all data
referenced against external Fc+/Fc.
(2) Dembinski, R.; Bartik, T.; Bartik, B.; Jaeger, M.; Gladysz, J. A.
Toward Metal-Capped One-Dimensional Carbon Allotropes: Wire-
like C6−C20 Polyynediyl Chains That Span Two Redox-Active (η5-
C5Me5)Re(NO)(PPh3) Endgroups. J. Am. Chem. Soc. 2000, 122, 810.
(3) Xu, G.-L.; Xi, B.; Updegraff, J. B.; Protasiewicz, J. D.; Ren, T. 1,6-
Bis(ferrocenyl)-1,3,5-hexatriyne: Novel Preparation and Structural
Study. Organometallics 2006, 25, 5213.
(4) Faust, R.; Diederich, F.; Gramlich, V.; Seiler, P. Linear and
Cyclic Platinum σ-Acetylide Complexes of Tetraethynylethene. Chem.
- Eur. J. 1995, 1, 111−117.
(5) Diederich, F.; Faust, R.; Gramlich, V.; Seiler, P. Mono- and di-
nuclear platinum σ-acetylide complexes of tetraethynylethene. J.
Chem. Soc., Chem. Commun. 1994, 0, 2045.
a
Table 2. Cyclic Voltammetry Data of 3, 6, 7, and 8
b
b
c
compound
E1/2red [V]
E1/2ox [V]
ΔE [mV]
3
6
7
8
0.14
0.12
0.14/1.00
0.10
70
−1.55
−1.11
−2.40
80/80
60/60/100
80
a
b
For conditions, see Figure 4. E1/2red/E1/2ox = half-wave potentials of
the redox processes. ΔE = difference of peak potentials (Epc − Epa).
c
(6) (a) Forrest, W. P.; Choudhuri, M. M. R.; Kilyanek, S. M.; Natoli,
S. M.; Prentice, B. M.; Fanwick, P. E.; Crutchley, R. J.; Ren, T.
Synthesis and Electronic Structure of Ru2(Xap)4(Y-gem-DEE) Type
Compounds: Effect of Cross-Conjugation. Inorg. Chem. 2015, 54,
7645. (b) Campbell, K.; McDonald, R.; Ferguson, M. J.; Tykwinski,
R. R. Functionalized Macrocyclic Ligands: Big Building Blocks for
Metal Coordination. Organometallics 2003, 22, 1353.
(7) Bruce, M. I.; Burgun, A.; Fox, M. A.; Jevric, M.; Low, P. J.;
Nicholson, B. K.; Parker, C. R.; Skelton, B. W.; White, A. H.; Zaitseva,
N. N. Some Ruthenium Derivatives of Penta-1,4-diyn-3-one. Organo-
metallics 2013, 32, 3286.
(8) Gholami, M.; Tykwinski, R. R. Oligomeric and Polymeric
Systems with a Cross-conjugated π-Framework. Chem. Rev. 2006, 106,
4997.
(9) Natoli, S. N.; Azbell, T. J.; Fanwick, P. E.; Zeller, M.; Ren, T. A
Synthetic Approach to Cross-Conjugated Organometallic Complexes
Based on geminal-Diethynylethene and CoIII(cyclam). Organometallics
2016, 35, 3594.
study of these complexes reveals significant contributions of
each substructure to the conjugation pathway across the
molecular backbone. Results emanating from cyclic voltam-
metry experiments point at a reduced conjugation path in
diethynylphenylene substructures as a result of phenylene
rotation. A distinct shift of the diazafluorene reduction is
observed upon coordination of 6 with [Ru(bpy)2]2+ pointing
at the influence of positive charge on the electronic properties
of the cross-conjugated ligand system.
In light of the research presented here and in light of recent
theoretical considerations34 that attest rigid fulvene-type cross-
conjugated systems an enhanced π delocalization, we aim to
develop the diethynyldiazafluoren-9-ylidene system into
optically switchable molecular wires.35 To this end we will
further explore the coordination of photoresponsive metal
fragments to modified diethynyldiazafluoren-9-ylidenes and
D
DOI: 10.1021/acs.organomet.9b00232
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Article
(10) Nauroozi, D.; Bruhn, C.; Faust, R. Cross-Conjugated π-
Scaffolding with Pendant N-Heterocyclic Metal Binding-Sites. Eur. J.
Org. Chem. 2017, 21, 3101.
(11) Diallo, A. K.; Daran, J. C.; Varret, F.; Ruiz, J.; Astruc, D. How
Do Redox Groups Behave around a Rigid Molecular Platform?
Hexa(ferrocenylethynyl)benzenes and Their “Electrostatic” Redox
Chemistry. Angew. Chem., Int. Ed. 2009, 48, 3141.
(12) Astruc, D. Electron-transfer processes in dendrimers and their
implication in biology, catalysis, sensing and nanotechnology. Nat.
Chem. 2012, 4, 255.
(13) Vincent, K. B.; Zeng, Q.; Parthey, M.; Yufit, D. S.; Howard, J.
A. K.; Hartl, F.; Kaupp, M.; Low, P. J. Syntheses, Spectroelec-
trochemical Studies, and Molecular and Electronic Structures of
Ferrocenyl Ene-diynes. Organometallics 2013, 32, 6022.
(14) Ren, T. Diruthenium σ-Alkynyl Compounds: A New Class of
Conjugated Organometallics. Organometallics 2005, 24, 4854.
(15) Paul, F.; Lapinte, C. Organometallic molecular wires and other
nanoscale-sized devices: An approach using the organoiron (dppe)-
Cp*Fe building block. Coord. Chem. Rev. 1998, 178, 431.
(16) Barnsley, J. E.; Scottwell, S. Ø.; Elliott, A. B. S.; Gordon, K. C.;
Crowley, J. D. Structural, Electronic, and Computational Studies of
Heteroleptic Cu(I) Complexes of 6,6′-Dimesityl-2,2′-bipyridine with
Ferrocene-Appended Ethynyl-2,2′-bipyridine Ligands. Inorg. Chem.
2016, 55, 8184.
(30) Ackermann, M. N.; Interrante, L. V. Ruthenium(II) complexes
of modified 1,10-phenanthrolines. 1. Synthesis and properties of
complexes containing dipyridophenazines and a dicyanomethylene-
substituted 1,10-phenanthroline. Inorg. Chem. 1984, 23, 3904.
(31) Juris, A.; Balzani, V.; Barigelletti, F.; Campagna, S.; Belser, P.;
von Zelewsky, A. Ru(II) polypyridine complexes: Photophysics,
Photochemistry, Electrochemistry, and Chemiluminescence. Coord.
Chem. Rev. 1988, 84, 85.
(32) Sioda, R. E.; Cowan, D. O.; Koski, W. S. Study of the Radical
Anion Formation of Some Diphenylacetylenes in Dimethylforma-
mide. J. Am. Chem. Soc. 1967, 89, 230.
(33) Horner, L.; Dickerhof, K. Studien zum Vorgang der
̈
Wasserstoffubertragung, 68. Die reduktive Uberfuhrung aromatischer
̈ ̈
̈
Saurechloride in Diarylacetylene mit Lithiumamalgam in einer
Eintopfreaktion. Chem. Ber. 1983, 116, 1615.
(34) Gu, J.; Wu, W.; Stuyver, T.; Danovich, D.; Hoffmann, R.; Tsuji,
Y.; Shaik, S. Cross Conjugation in Polyenes and Related Hydro-
carbons: What Can Be Learned from Valence Bond Theory about
Single-Molecule Conductance? J. Am. Chem. Soc. 2019, 141, 6030.
(35) Russew, M.-M.; Hecht, S. Photoswitches: From Molecules to
Materials. Adv. Mater. 2010, 22, 3348.
́
(17) Roue, S.; Sahnoune, H.; Toupet, L.; Halet, J.-F.; Lapinte, C.
Double Insertion of Thiophene Rings in Polyynediyl Chains to
Stabilize Nanoscaled Molecular Wires with [Cp*(dppe)Fe] Termini.
Organometallics 2016, 35, 2057−2070.
(18) Misra, R.; Maragani, R.; Jadhav, T.; Mobin, S. M. Ferrocenyl
end capped molecular rods: synthesis, structure, and properties. New
J. Chem. 2014, 38, 1446.
(19) Morikita, T.; Maruyama, T.; Yamamoto, T.; Kubota, K.;
Katada, M. New type of polymer containing 1,1′-ferrocenediyl unit in
π-conjugated main chain. Preparation and redox behavior. Inorg.
Chim. Acta 1998, 269, 310.
(20) Engtrakul, C.; Sita, L. R. Ferrocene-Based Nanoelectronics:
Regioselective Syntheses and Electrochemical Characterization of α-
Monothiol and α,ω-Dithiol, Phenylethynyl-Conjugated, 2,5-Dieth-
ynylpyridyl- and Pyridinium-Linked Diferrocene Frameworks Having
an End-to-End Distance of ∼ 4 nm. Organometallics 2008, 27, 927.
(21) Hsung, R. P.; Chidsey, C. E. D.; Sita, L. R. Synthesis and
Characterization of Unsymmetric Ferrocene-Terminated Phenyl-
ethynyl Oligomers Cp2Fe-[CC-C6H4]n-X, (X = SH, SMe, SOMe,
and SO2Me). Organometallics 1995, 14, 4808.
(22) Carr, J. D.; Coles, S. J.; Hursthouse, M. B.; Light, M. E.; Munro,
E. L.; Tucker, J. H. R.; Westwood, J. Facile Control of the Redox
Properties of Ferrocene-Containing Dipyridyl Derivatives That Bind
Platinum(II). Organometallics 2000, 19, 3312.
(23) Sprigings, T. G.; Hall, C. D. Synthesis and Properties of the
First Ferrocene-Functionalized Ligand in Which All the Donor Atoms
Are Cyclopentadienyl-Conjugated. Organometallics 2001, 20, 2560.
(24) Vincent, K. B.; Zeng, Q.; Parthey, M.; Yufit, D. S.; Howard, J.
A. K.; Hartl, F.; Kaupp, M.; Low, P. J. Syntheses, Spectroelec-
trochemical Studies, and Molecular and Electronic Structures of
Ferrocenyl Ene-diynes. Organometallics 2013, 32, 6022.
(25) Zhao, Y.; Zhou, N.; Slepkov, A. D.; Ciulei, S. C.; McDonald, R.;
Hegmann, F. A.; Tykwinski, R. R. Donor/Acceptor Effects on the
Linear and Nonlinear Optical Properties of Geminal Diethynyle-
thenes (g-DEEs). Helv. Chim. Acta 2007, 90, 909.
(26) Rosenblum, M.; Brawn, N.; Papenmeier, J.; Applebaum, M.
Synthesis of ferrocenylacetylenes. J. Organomet. Chem. 1966, 6, 173.
(27) Misra, R.; Maragani, R.; Jadhav, T.; Mobin, S. M. Ferrocenyl
end capped molecular rods: synthesis, structure, and properties. New
J. Chem. 2014, 38, 1446.
(28) Nauroozi, D.; Bruhn, C.; Furmeier, S.; Holzhauer, J.-U.; Faust,
̈
R. Microwave-Assisted Dibromoolefination of Aromatic and Hetero-
aromatic Aldehydes and Ketones. J. Heterocyclic Chem. 2016, 53, 615.
(29) Sullivan, B. P.; Salmon, D. J.; Meyer, T. J. Mixed phosphine
2,2′-bipyridine complexes of ruthenium. Inorg. Chem. 1978, 17, 3334.
E
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