A perfluorocyclopentene based diarylethene bearing two terpyridine moieties - Synthesis, photochemical properties and influence of transition metal ions

Article abstract of DOI:10.3762/bjoc.6.53

The synthesis of a perfluorocyclopentene based diarylethene bearing two terpyridine units is reported. Furthermore studies of the free ligand's photochromism and investigations regarding the influence of various transition metal ions on the photochromic reaction are presented. The photochromism of the central diarylethene unit is strongly dependent on the transition metal present, vice versa the photochromic reaction seems to influence the MLCT transition of a binuclear Ru(II) complex.

Full text of DOI:10.3762/bjoc.6.53

A perfluorocyclopentene based diarylethene bearing
two terpyridine moieties – synthesis, photochemical
properties and influence of transition metal ions
Falk Wehmeier2 and Jochen Mattay*1
Full Research Paper
Open Access
Address:
Beilstein J. Org. Chem. 2010, 6, No. 53. doi:10.3762/bjoc.6.53
1Department of Chemistry, Organic Chemistry 1, Bielefeld University,
P.O. Box 10 01 31, D-33501 Bielefeld, Germany and 2Institut für
Chemie, Humboldt-Universität zu Berlin, Brook-Taylor-Str. 2, D-12489
Berlin, Germany
Received: 10 March 2010
Accepted: 07 May 2010
Published: 26 May 2010
Email:
Associate Editor: P. Skabara
Jochen Mattay* - oc1jm@uni-bielefeld.de
© 2010 Wehmeier and Mattay; licensee Beilstein-Institut.
License and terms: see end of document.
* Corresponding author
Keywords:
coordination chemistry; diarylethene; photochromism; terpyridine
Abstract
The synthesis of a perfluorocyclopentene based diarylethene bearing two terpyridine units is reported. Furthermore studies of the
free ligand’s photochromism and investigations regarding the influence of various transition metal ions on the photochromic reac-
tion are presented. The photochromism of the central diarylethene unit is strongly dependent on the transition metal present, vice
versa the photochromic reaction seems to influence the MLCT transition of a binuclear Ru(II) complex.
Introduction
2,2′:6′,2″-Terpyridines have been of great interest over the last bisterpyridines linked by a diazogroup has been reported [7,8],
years, mostly because of their ability to chelate transition as well as the connection of terpyridines to spiropyran moieties
metals. The special (photochemical) properties of their metal [9]. There have also been recent reports about terpyridines
complexes have led to the development of various luminescent linked to dithienylethenes [10,11]. Herein we report the syn-
metal compounds [1] and sensitizers for photovoltaic devices thesis of terpyridine functionalized diarylethenes based on
[2,3]. Ditopic terpyridyl units have been recently used to perfluorocyclopentene, their photochemistry and investigations
develop electrochemical sensors [4,5]. A microreview regarding the influence of transition metals.
concerning the synthesis of functionalized terpyridines has also
Results and Discussion
been published since the electronic properties of the ligand are
influenced by the substituents present [6].
Synthetic key steps
The basic photochromic diarylethene unit (3) can be obtained
Because of this impact of terpyridine derivatives in photochem- by lithiation of 3-bromo-2-methylbenzo[b]thiophene (1)
istry, we focused our attention on the synthesis and studies of followed by quenching with perfluorocyclopentene (2),
photoswitchable terpyridine ligands. The synthesis of according to the method described by Irie [12]. Electrophilic
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Beilstein J. Org. Chem. 2010, 6, No. 53.
Scheme 1: Synthesis of twofold iodinated bis(benzo[b]thiophenyl)perfluorocyclopentene 4.
iodination leads to the diiodo photoswitch 4 (Scheme 1)
[13,14].
We decided to use the diiodo switch 4 for catalytic cross coup-
ling reactions, since approaches to a direct terpyridine synthesis,
starting from suitable diarylethene aldehydes (Kröhnke conden-
sation), were unsuccessful. Moreover, the diiodo switch 4 has
been previously used for Suzuki-type cross coupling reactions
[14]. Synthetic routes to terpyridine substituted diarylethenes
via the above mentioned catalytic cross coupling reactions
require suitably functionalized terpyridine precursors, e.g.
boronic acid derivatives for Suzuki type cross coupling reac-
tions. 4′-(4-Bromophenyl)-2,2′:6′,2″-terpyridine (7a) and its
meta-substituted analogue 7b can be synthesized by Kröhnke-
condensation of 2-acetylpyridine (5) with p-bromobenzalde-
hyde (6a) or m-bromobenzaldehyde (6b), respectively [15].
Miyaura type cross coupling reactions of 7a and 7b with
Scheme 3: Synthesis of the bis(terpyridinyl)diarylethenes 10a and
10b.
5,5,5′,5′-tetramethyl-2,2′-di(1,3,2-dioxaborinan) (8) led to the
formation of boronic acid derivatives 9a [16] and 9b
(Scheme 2).
Whilst 10a can be purified by column chromatography, all
The terpyridine moieties can be attached to the diarylethene unit efforts to obtain highly pure meta-substituted 10b have, so far,
by Suzuki type cross coupling of the diiodo switch 4 with the been unsuccessful – MALDI-TOF-measurements nevertheless
boronic esters 9a and 9b under conditions similar to those indicate the formation of 10b, and the proton-NMR spectrum
described for other aryl boronic acids and their derivatives to displays the expected signals (see Experimental Section and
yield the target molecules 10a and 10b (Scheme 3) [14].
Supporting Information File 1).
Scheme 2: Synthesis of terpyridinyl boronic acids 9a and 9b.
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Beilstein J. Org. Chem. 2010, 6, No. 53.
Scheme 4: Photochromic reaction of the free ligand 10a.
Photochromism of the free ligand
The obtained terpyridine substituted diarylethene 10a shows the
anticipated photochromic behavior, undergoing photocycliza-
tion under irradiation with UV-light (Scheme 4).
Figure 1 shows the absorption spectra of 10a (solid line), 10aC
(dashed line, formed by irradiation with λ = 350 nm) and after
re-opening with vis light (dotted line).
Influence of transition metals
A binuclear Ru(II)-complex
For investigations of the photochemical behavior of 10a in the
coordination sphere of ruthenium(II), we synthesized the binuc-
lear complex 12, from ruthenium(III) chloride hydrate via the
monoterpyridine complex 11 (Scheme 5).
The UV–vis-spectra of the binuclear complex 12 in acetonitrile
solution are shown in Figure 2 – before (solid), after UV-irradi-
ation (dashed) and after irradiation with vis light (dotted).
Figure 1: UV–vis-spectra of 10a before (solid), after UV-irradiation
(dashed) and after irradiation with vis light (dotted).
Scheme 5: Synthesis of the binuclear Ru(II)-complex 12.
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Beilstein J. Org. Chem. 2010, 6, No. 53.
reduced by the bridging photoreaction of the diarylethene [9].
On one hand this seems quite unexpected, since the extended
π-system of the closed isomer 10aC should facilitate charge
transfer processes between the ruthenium nuclei. On the other
hand the closed isomer 10aC might act as an acceptor; a similar
effect has been observed with a spiropyran moiety bridging two
terpyridine units, whose (closed) merocyanine form inhibits the
energy transfer between metal centres and thus acts as a T-junc-
tion relay [9].
Influence of other transition metal ions in solution
In the following photochemical investigations we added various
transition metal ions to methanolic suspensions of the
bisterpyridine 10a to generate terpyridine-complexes in situ
[17]. Table 1 shows the results obtained with Fe(II), Co(II),
Ni(II) and Zn(II).
Figure 2: UV–vis-spectra of 12 before (solid), after UV-irradiation
(dashed) and after irradiation with vis light (dotted).
Table 1: Influence of different 3d-transition metals on the photo-
chromic reaction of 10a in solution.
The absorption of the strong MLCT band at λ = 490 nm
decreases upon UV-irradiation, while absorption in the visible
region of the spectrum increases. This may be regarded as
indication that the photochromic reaction of the ligand not only
takes place in presence of ruthenium, but also influences the
MLCT transition. This supposition is supported by the differ-
ence spectra (Figure 3, the absorption of the free ligand 10aC is
shown in grey for comparison).
Transition metal ion
Photochromic reaction
(precursor)
Fe2+ (FeCl2 × 4 H2O)
Co2+ (CoCl2)
No reactiona
Slow reactionb
Slow reactionb
Fast reactionc
Ni2+ ([Ni(acac)2])
Zn2+ (Zn(OTf)2)
aFigure 4.
bSee Supporting Information File 1.
cFigure 5.
The UV–vis-spectra of the iron(II) complex [Fe2+@10a],
obtained by reaction of 10a with ferric chloride tetrahydrate, are
shown in Figure 4.
Figure 3: UV–vis-spectra of 12 before (dashed), after UV-irradiation
(dotted), the difference (solid) and free 10aC for comparison (grey).
According to studies with similar ruthenium(II) complexes of
terpyridine functionalized dithienylethenes [10], the intensity of
the MLCT band can be attributed to communication between
the ruthenium nuclei. In this case communication is obviously
Figure 4: UV–vis-spectra of [Fe2+@10a] before (solid), after UV-irradi-
ation (dashed) and after irradiation with vis light (dotted).
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Beilstein J. Org. Chem. 2010, 6, No. 53.
Apart from the expected bathochromic shift of the UV-bands of photochromism of the central diarylethene unit. A rather special
the ligand [18], an MLCT band at λ = 570 nm was observed. case is the binuclear ruthenium(II) complex 12: The diaryl-
While the UV absorption decreases upon UV-irradiation, no ethene seems to undergo the expected photochromic reaction,
significant change of the absorption in the visible region but at the same time the absorption intensity of the MLCT band
occurred. This indicates inhibition of the photochromic reac- of the complex decreased, indicating a diminution in communi-
tion of the diarylethene by the MLCT transition, as previously cation between the metal centres. The synthesis and investi-
reported for other iron(II) complexes of bisterpyridine gation of asymmetrical complexes such as [LnOs(tpy-diae-
thienylethenes [10].
tpy)RuLn] should provide further insight into the role the diaryl-
ethene unit plays in the ditopic ligand.
In contrast to the iron(II) complex, the ditopic ligand seems to
retain its photochromic properties in the cobalt(II) and nickel(II) Experimental
complexes – synthesized from CoCl2 and [Ni(acac)2], respect- General: p-Bromobenzaldehyde (6a), m-bromobenzaldehyde
ively – although the photocyclisation takes much longer than (6b) and 5,5,5′,5′-tetramethyl-2,2′-di(1,3,2-dioxaborinan) (8)
with free 10a (about 5 minutes compared to ca. 30 seconds). are commercially available and were used as supplied.
This observation may be due to side processes involving charge Perfluorocyclopentene (2) was a generous gift from Masahiro
transfer transitions at the transition metal centres.
Irie (see Acknowledgements). 2-Acetylpyridine (5) was
distilled before use. 3,3′-(Perfluorocyclopent-1-ene-1,2-
The corresponding zinc(II) complex [Zn2+@10a] was synthe- diyl)bis(2-methylbenzo[b]thiophene) (3) [12], 3,3′-(perfluoro-
sized from zinc(II) trifluoromethansulfonate and 10a in meth- cyclopent-1-ene-1,2-diyl)bis(6-iodo-2-methylbenzo[b]thio-
anol. The UV–vis-spectra are shown in Figure 5.
phene) (4) [13,14], 4′-(4-bromophenyl)-2,2′:6′,2″-terpyridine
(7a) [15] and 4′-[4-(5,5-dimethyl-1,3,2-dioxaborinan-2-
yl)phenyl]-2,2′:6′,2″-terpyridine (9a) [16] were synthesized
according to previously reported procedures. Solvents and
chemicals were dried by standard methods.
Irradiation experiments were carried out in a quartz cuvette (d =
1 cm) and the solutions were not degassed before irradiation.
UV-spectra were recorded with a Lambda 40 (Perkin-Elmer) at
room temperature.
NMR-spectra were recorded with a Bruker DRX 500. EI-mass
spectra were recorded with an Autospec X (Vacuum Gener-
ators), ESI-mass spectra were recorded with a Bruker Esquire
3000; high resolution-mass spectra were recorded with a Bruker
Apex III-FT-ICR. Measured and calculated masses are true ion
masses, taking into account the mass of lost (or added) elec-
trons.
Figure 5: UV–vis-spectra of [Zn2+@10a] before (solid), after UV-irradi-
ation (dashed) and after irradiation with vis light (dotted).
Synthesis of 4′-(3-bromophenyl)-2,2′:6′,2″-
terpyridine (7b)
In this case neither inhibition nor any significant slowing of the
photoreaction of the ligand was observed.
1.5 g (8 mmol) m-Bromobenzaldehyde (6b) was dissolved in
Conclusion
220 mL methanol followed by the addition of 2.0 g (16 mmol)
We have developed the synthesis of two highly fatigue resistant freshly distilled 2-acetylpyridine (5) and 0.65 g (16 mmol)
bis(terpyridinyl) diarylethenes by Suzuki cross coupling sodium hydroxide. Subsequently, 55 mL (0.8 mol) of 25%
methods. The photochemical behavior of the free ligand 10a aqueous ammonia was added and the reaction mixture heated to
met our expectations regarding reversibility. It was shown that reflux for 48 h. After cooling to rt the solid was filtered off and
the presence of various transition metal ions significantly influ- dissolved in 20 mL methylene chloride. 20 mL Methanol was
ences the photochromism of the bridging unit: While iron(II)- added and the methylene chloride removed under reduced pres-
ions completely inhibit the photochromic reaction, cobalt(II) sure. The precipitate was filtered off and dried in vacuo to yield
and nickel(II) appear to slow down the photoreaction consider- 1.82 g (4.7 mmol, 58%) of 4′-(3-bromophenyl)-2,2′:6′,2″-
ably. Zinc(II)-ions, on the other hand, had no influence on the terpyridine (7b) as a colorless solid. 1H NMR (500 MHz,
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Beilstein J. Org. Chem. 2010, 6, No. 53.
CDCl3, δ in ppm): 7.40–7.43 (m, 3 H, Artpy-H5,5″/ArPh-H5), solution added. 515 mg (1.22 mmol) 4′-[4-(5,5-dimethyl-1,3,2-
7.61 (d, 3J = 8.8 Hz, 1 H, ArPh-H6), 7.87 (d, 3J = 7.5 Hz, 1 H, dioxaborinan-2-yl)phenyl]-2,2′:6′,2″-terpyridine (9a) was added
ArPh-H4), 7.93 (m, 2 H, Artpy-H4,4″), 8.08 (s, 1 H, ArPh-H2), and the reaction mixture thoroughly degassed by the freeze-
8.71 (d, 3J = 8.2 Hz, 2 H, Artpy-H6,6″), 8.74 (s, 2 H, Artpy- pump-thaw technique. 140 mg (60 μmol) [Pd(PPh3)4] was
H3′,5′), 8.77 (d, 3J = 4.4 Hz, 2 H, Artpy-H3,3″). 13C NMR (125 added and the mixture stirred for 20 h at 80 °C. After cooling to
MHz, CD2Cl2, δ in ppm): 118.6 (tpy3′,5′), 121.1 (tpy3,3″), 123.0 rt the mixture was extracted with methylene chloride (3 × 50
(C-Br), 124.0 (tpy5,5″), 126.0 (Ph6), 130.2 (Ph4), 130.6 (Ph5), mL), the combined organic layers washed several times with 1
131.9 (Ph2), 136.9 (tpy4,4″), 140.7 (Ph1), 148.6 (tpy4′), 149.2 M hydrochloric acid, dried over MgSO4 and filtered. After
(tpy6,6″), 155.8 (tpy2,2″), 156.1 (tpy2′,6′). EI-MS (70 eV, m/z, removal of the solvent under reduced pressure the crude yellow
%): 154 (12, [M−C6H5Br−C5H4N]+), 204 (8), 229 (15, product was purified by column chromatography (basic
[M−C6H6Br]+), 308 (100, [M−Br]+), 309/311 (25, alumina, eluting with THF) to yield 421 mg (389 μmol, 70%) of
[M−C5H4N]+), 387/389 (86, [M]+).
3,3′-(perfluorocyclopent-1-ene-1,2-diyl)bis(2-methyl-6-(4-
(2,2′:6′,2″-terpyridin-4′-yl)phenyl)benzo[b]thiophene) (10a) as
a pale yellow solid. 1H NMR (500 MHz, CDCl3, δ in ppm):
Synthesis of 4′-[3-(5,5-dimethyl-1,3,2-dioxa-
borinan-2-yl)phenyl]-2,2′:6′,2″-terpyridine (9b) 2.33/2.59 (ap/p, s, 6 H, CH3), 7.42–7.47 (m, 5 H, Ar-H),
584 mg (1.5 mmol) 4′-(3-Bromophenyl)-2,2′:6′2″-terpyridine 7.72–7.84 (m, 7 H, Ar-H), 7.94–8.12 (m, 10 H, Ar-H),
(7b), 550 mg (5.6 mmol) dry potassium acetate and 444 mg (2.0 8.78–8.92 (m, 12 H, Ar-H). 13C NMR (125 MHz, THF-d8, δ in
mmol) 5,5,5′,5′-tetramethyl-2,2′-di(1,3,2-dioxaborinan) (8) ppm): 14.5 (CH3), 118.1 (t), 118.8 (q), 120.3 (q), 120.5 (t),
were dissolved in 12 mL dry DMSO. The reaction mixture was 120.7 (t), 123.7 (q), 123.8 (t), 124.1 (t), 127.4 (t), 127.5 (t),
thoroughly degassed by the freeze-pump-thaw technique and 127.6 (t), 136.5 (t), 137.0 (q), 137.6 (m, CF2), 139.3 (q), 141.08
subsequently 46 mg (63 μmol) [(dppf)PdCl2] was added and the (q), 141.15 (q), 143.9 (q), 149.1 (t), 149.2 (q), 156.0(q), 156.06
mixture stirred for 6 h at 80 °C. The mixture was diluted with (q), 156.12 (q). 19F NMR (470 MHz, THF-d8, δ in ppm):
100 mL toluene and the resulting organic layer washed with −109.4 to −112.0 (m, 4 F, 3-/5-CF2), −132.7 to −134.2 (m, 2 F,
water (4 × 100 mL), dried over MgSO4 and filtered. The solvent 4-CF2). ESI-MS (positive mode, CHCl3/MeCN, m/z): 1083
was removed in vacuo and the residue dissolved in 20 mL [M]+. HRMS: calc. for [C65H40F6N6S2+H]+: 1083.27328;
methylene chloride. 20 mL Methanol was added and the found: 1083.27181.
methylene chloride removed under reduced pressure. The
precipitate was filtered off and dried in vacuo to yield 497 mg
Synthesis of 3,3′-(perfluorocyclopent-1-ene-
(1.18 mmol, 78%) of 4′-[3-(5,5-dimethyl-1,3,2-dioxaborinan-2-
1,2-diyl)bis(2-methyl-6-(3-(2,2′:6′,2″-
yl)phenyl]-2,2′:6′,2″-terpyridine (9b) as a colorless solid. 1H
terpyridin-4′-yl)phenyl)benzo[b]thiophene)
NMR (500 MHz, CD2Cl2, δ in ppm): 1.09 (s, 6 H, CH3), 3.87
(s, 4 H, CH2), 7.41 (m, 2 H, Artpy-H5,5″), 7.57 (v tr, 1 H, ArPh- (10b)
H5), 7.93 (m, 3 H, Artpy-H4,4″/ArPh-H), 8.00 (d, 1 H, ArPh-H), 120 mg (167 μmol) 3,3′-(Perfluorocyclopent-1-ene-1,2-
8.33 (s, 1 H, ArPh-H2), 8.71 (m, 2 H, Artpy-H6,6″), 8.77 (m, 4 H, diyl)bis(6-iodo-methylbenzo[b]thiophene) (4) was dissolved in
Artpy-H3,3″), 8.81 (s, 2 H, Artpy-H3′,5′). 13C NMR (125 MHz, 20 mL THF and 10 mL of 2 M aqueous sodium carbonate solu-
CD2Cl2, δ in ppm): 21.6 (CH3), 31.8 (C(CH3)2), 72.3 (CH2), tion added. 154 mg (367 μmol) 4′-[3-(5,5-dimethyl-1,3,2-dioxa-
118.7 (tpy3′,5′), 121.1 (tpy3,3″), 123.9 (tpy5,5″), 128.3 (Ph6), borinan-2-yl)phenyl]-2,2′:6′,2″-terpyridine (9b) was added and
129.4 (Ph5), 132.5 (Ph), 134.5 (Ph), 136.8 (tpy4,4″), 137.6 (Ph1), the reaction mixture thoroughly degassed by the freeze-pump-
149.1 (tpy6,6″), 150.3 (tpy4′), 155.9 (tpy2,2″), 156.1 (tpy2′,6′). thaw technique. 42 mg (18 μmol) [Pd(PPh3)4] was added and
EI-MS (70 eV, m/z, %): 257 (10, [tpy-C=CH]••+), 309 (34, the mixture stirred for 20 h at 80 °C. After cooling to rt the mix-
[M−BO2C5H9]+), 335 (20, [M−C5H10O]••+), 406 (25, ture was extracted with methylene chloride (3 × 20 mL), the
[M−CH2]+), 421 (100, [M]+).
combined organic layers washed several times with 1 M hydro-
chloric acid, dried over MgSO4 and filtered. After removal of
the solvent under reduced pressure, the crude yellow product
was purified by column chromatography (basic alumina, eluting
with THF) to yield 105 mg (97 μmol, 58%) of 3,3′-(perfluoro-
cyclopent-1-ene-1,2-diyl)bis(2-methyl-6-(3-(2,2′:6′,2″-
terpyridin-4′-yl)phenyl)benzo[b]thiophene) (10b) as a yellow
Synthesis of 3,3′-(perfluorocyclopent-1-ene-
1,2-diyl)bis(2-methyl-6-(4-(2,2′:6′,2″-
terpyridin-4′-yl)phenyl)benzo[b]thiophene)
(10a)
400 mg (555 μmol) 3,3′-(Perfluorocyclopent-1-ene-1,2- solid which still contained impurities. 1H NMR (500 MHz,
diyl)bis(6-iodo-2-methylbenzo[b]thiophene) (4) was dissolved CDCl3, δ in ppm): 2.32/2.58 (ap/p, s, 6 H, CH3), 7.38–7.44 (m,
in 50 mL THF and 50 mL of 2 M aqueous sodium carbonate 5 H, Ar-H), 7.73–7.83 (m, 7 H, Ar-H), 7.92–8.10 (m, 10 H,
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Beilstein J. Org. Chem. 2010, 6, No. 53.
Ar-H), 8.71–8.88 (m, 12 H, Ar-H). MALDI-TOF (m/z): 1083
Supporting Information
[M]+, 1106 [M+Na]+.
Supporting information contains UV–vis-spectra of
[Co2+@10a], [Ni2+@10a], 1H NMR-spectra of 7b, 9b,
10a, 10b and 12, 13C NMR-spectra of 7b, 9b and 10a, the
19F NMR-spectrum of 10a and the simulated
ESI-MS-spectra of 12.
Synthesis of (4′-(4-bromophenyl)-2,2′:6′,2″-
terpyridine)ruthenium(III)chloride (11)
500 mg (1.29 mmol) 4′-(4-Bromophenyl)-2,2′:6′,2″-terpyridine
(7a) was suspended in 10 mL methanol and 337 mg (1.29
mmol) ruthenium(III) chloride trihydrate added. The dark
brown suspension was heated to reflux for 2 h and then cooled
to rt. Filtration gave 423 mg (0.17 mmol, 55%) of the
monoterpyridine complex 11 as a dark brown solid which was
immediately used for the following reaction.
Supporting Information File 1
NMR-, UV- and MS-spectra.
[http://www.beilstein-journals.org/bjoc/content/
supplementary/1860-5397-6-53-S1.pdf]
Synthesis of [(7a)Ru(tpy-diae-
tpy)Ru(7a)](PF6)4 (12)
Acknowledgements
150 mg (251 μmol) (4′-(4-Bromophenyl)-2,2′:6′,2″- We would like to thank the Studienstiftung des deutschen
terpyridine)ruthenium(III) chloride (11) was suspended in 10 Volkes for financial support and Masahiro Irie and Zeon
mL ethanol and treated with 0.5 mL (3.9 mmol) N-ethylmor- Corporation (Japan) for a generous gift of a large quantity of
pholine. Subsequently, 136 mg (126 μmol) 3,3′-(perfluorocyclo- perfluorocyclopentene.
pent-1-ene-1,2-diyl)bis(2-methyl-6-(4-(2,2′:6′,2″-terpyridin-4′-
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General procedures for transition metal
complexes of 3,3′-(perfluorocyclopent-1-ene-
1,2-diyl)bis(2-methyl-6-(4-(2,2′:6′,2″-
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12.Hanazawa, M.; Sumiya, R.; Horikawa, Y.; Irie, M.
J. Chem. Soc., Chem. Commun. 1992, 206–207.
doi:10.1039/C39920000206
terpyridin-4′-yl)phenyl)benzo[b]thiophene)
(10a)
3,3′-(Perfluorocyclopent-1-ene-1,2-diyl)bis(2-methyl-6-(4-
(2,2′:6′,2″-terpyridin-4′-yl)phenyl)benzo[b]thiophene) (10a)
was suspended in methanol. FeCl2 × 4 H2O, CoCl2, [Ni(acac)2]
or Zn(F3CSO3)2 was added and the resulting suspension stirred
vigorously until all solid had dissolved. The formation of the
iron(II) and cobalt(II) complexes can be traced by the color
change from colorless to blue (iron(II)) and red (cobalt(II)),
respectively.
13.Mattern, D. L. J. Org. Chem. 1984, 49, 3051–3053.
doi:10.1021/jo00191a003
14.Matsuda, K.; Irie, M. Chem.–Eur. J. 2001, 7, 3466–3473.
doi:10.1002/1521-3765(20010817)7:16<3466::AID-CHEM3466>3.0.C
O;2-X
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doi:10.1002/hlca.19840670214
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Beilstein J. Org. Chem. 2010, 6, No. 53.
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doi:10.1039/b103062k
17.Aryl substituted 2,2′:6′,2″-terpyridines are virtually insoluble in
methanol, so by choosing this solvent for our investigations we could
make sure no free ligand contributed to the recorded spectra.
18.Schubert, U. S.; Hofmeier, H.; Newkome, G. R. Modern Terpyridine
Chemistry; Wiley-VCH: New York, 2006; p 40.
doi:10.1002/3527608486
19.It was impossible to get HRMS-spectra of the binuclear complex 12,
because the monoisotopic cation [(7a)Ru(10a)Ru(7a)]4+ is too low in
intensity. We therefore calculated the isotopic distribution of the cation
{[(7a)Ru(10a)Ru(7a)](PF6)3}+ and the anion
{[(7a)Ru(10a)Ru(7a)](PF6)5}− in order to compare the calculated with
the recorded ESI-MS-spectra. See Supporting Information for details.
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