Click synthesis and redox chemistry of mono- and heterobimetallic triazolyl and triazolium-ferrocene and cobalticinium complexes

Article abstract of DOI:10.1002/ejic.201200755

Mono- and heterobimetallic triazolylferrocene and cobalticinium complexes and triazolium derivatives were synthesized by click reactions between the ethynylmetallocenes and benzyl azide or (azidomethyl)ferrocene followed by methylation reactions, respecti

Full text of DOI:10.1002/ejic.201200755

Job/Unit: I20755
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FULL PAPER
DOI: 10.1002/ejic.201200755
Click Synthesis and Redox Chemistry of Mono- and Heterobimetallic Triazolyl
and Triazolium-Ferrocene and Cobalticinium Complexes
Amalia Rapakousiou,[a] Claire Mouche,[a] Mathieu Duttine,[b] Jaime Ruiz,[a] and
Didier Astruc*[a]
Keywords: Metallocenes / Sandwich complexes / Iron / Cobalt / Redox chemistry / Click chemistry / Reduction / Nitrogen
heterocycles
Mono- and heterobimetallic triazolylferrocene and co-
balticinium complexes and triazolium derivatives were syn-
thesized by click reactions between the ethynylmetallocenes
and benzyl azide or (azidomethyl)ferrocene followed by
methylation reactions, respectively. Cyclic voltammetry data
shed light on the electron-withdrawing character of the
cenes, and cathodic reduction of the triazolium group was
found to be irreversible even at –50 °C. Chemical reduction
of orange triazolylcobalticinium hexafluorophosphate using
NaBH4 yielded a mixture of red isomeric triazolyl η4-cyclo-
pentadiene–cobalt–η5-cyclopentadienyl complexes, whereas
reduction by the single-electron reductant [FeICp(η6-
1,2,3-triazolyl and triazolium substituents of the metallo- C6Me6)] yielded the brown 19-electron triazolylcobaltocene.
results are a key step towards potential analytical and syn-
Introduction
thetic redox chemistry of large nanosystems involving click
assemblies.[47]
The concept of “click” reactions by Sharpless el al. pro-
poses to easily assemble molecular fragments.[1] The CuI-
The alkylation of triazole (trz) to yield the triazolium
(trz*) group has been reported as well as the properties of
trz and trz* derivatives as molecular sensors.[27–29] The re-
dox chemistry of ferrocene and cobalticinium have been
known since Wilkinson’s seminal reports on these metallo-
cenes,[48,49] and these properties have been extensively
studied by cyclic voltammetry and used in organometallic
synthesis, sensing, and catalysis.[32–36,42,50] However, we are
not aware of redox or electrochemical studies of trz and
trz* derivatives.
catalyzed
regioselective
azide–alkyne
cycloaddition
(CuAAC),[2,3] which is presently the most frequent exam-
ple,[4–22] was reported in 2002 by the research groups of
Sharpless et al.[2] and Meldal et al.[3] This synthetic advan-
tage is not the only one, since the resulting 1,2,3-triazolyl
derivatives that are selectively produced are also good li-
gands in a variety of transition-metal complexes that have
new luminescent,[23–26] sensor,[27–29] or catalytic proper-
ties.[30,31] In this context, one of the key functions of transi-
tion-metal complexes is their redox behavior,[32–38] and in
particular late transition-metal sandwich complexes are
known to withstand stability under two or three oxidation
states.[36,39–41] The latter property indeed allows their use as
redox reagents,[36] redox catalysts,[42] and redox sen-
sors.[43–47] Therefore, we wish to investigate the redox be-
havior of simple ferrocene and cobalticinium complexes
bound to 1,2,3-triazolyl using click (CuAAC) reactions of
the ethynylmetallocene precursors and the related triazol-
ium derivatives subsequently obtained by the methylation
of the latter. The investigation of these syntheses and that
of the redox properties of the metallocene triazolyl and tri-
azolium derivatives are the subject of this article, and the
Results and Discussion
1. CuAAC Reactions and Syntheses of the Mono- and
Heterobimetallic Triazole Compounds
The CuAAC reactions were conducted between benzyl
azide and the known ethynylmetallocenes[51,52] to produce
the triazolyl derivatives 1 and 3 [Equation (1)], and with
ethynylbenzene to produce the reference organic compound
5.
This CuAAC click reaction is, as is well known, com-
pletely selective in the formation of 1,4-disubstituted trz,
contrary to the non-catalyzed Huisgen azide–alkyne dipolar
cycloaddition that produces both 1,4 and 1,5 isomers.[53] As
a CuI catalyst, we used a mixture of CuSO4·5H2O and the
reductant sodium ascorbate that is the initial Sharpless cat-
alyst.[2] (Azidomethyl)ferrocene[54] was also used in the
CuAAC reaction with ethynylcobalticinium to produce the
heterobimetallic triazolyl complex 7; see Equation (2).
[a] ISM, UMR CNRS N° 5255, Univ. Bordeaux,
33405 Talence Cedex, France
E-mail: d.astruc@ism.u-bordeaux1.fr
Homepage: http://astruc.didier.free.fr/welcome.htm
[b] ICMCB, UPR CNRS N° 9048, Univ. Bordeaux,
33608 Pessac Cedex, France
Supporting information for this article is available on the
WWW under http://dx.doi.org/10.1002/ejic.201200755.
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resulted in the formation of the trz* compounds 2, 4, and
6, respectively, in yields of about 90% and dimethyl ether
that was removed under vacuum; see Equation (3).
1
The H and 13C NMR spectra of the trz* compounds 2,
4, and 6 show the proton and carbon signals, respectively,
of the N–CH3 methyl group. All the signals in the NMR
spectra of these new trz* products were shifted downfield
compared to their trz precursors, because of the cationic
nature of the trz* species. However, the quaternary carbon
of the cobalticinium cation linked to the trz* group was
shifted upfield in the 13C NMR spectrum. The infrared
spectra of the trz* compounds 2, 4, and 6 show the appear-
–
ance of the characteristic band of BF4 at 1070 cm–1, and
for trz* cobalticinium hexafluorophosphate (2) the charac-
teristic band of the PF6 anion is observed at 872 cm–1. The
structure of the new trz* derivatives was confirmed by the
molecular peak in the mass spectra and by elemental analy-
ses (see the Supporting Information).
All the triazole derivatives were obtained after precipi-
tation in an overall yield of around 80%. The infrared spec-
tra were a very useful tool in following all these click reac-
tions (compounds 1, 3, 5, and 7), because the characteristic
peak of the azido groups at about 2094 cm–1 disappears at
the end of each reaction confirming that these azido groups
were replaced by the trz. For triazolyl cobalticinium hexa-
fluorophosphate (1), which was soluble only in polar sol-
vents such as acetone and acetonitrile, but also in THF, the
characteristic band of the PF6 anion is observed at
837 cm–1. The formation of trz is clearly shown by 1H
NMR spectroscopy by the appearance of the trz CH peak.
This is also confirmed in particular by the characteristic
peaks of Cq and CH of trz in the 13C NMR spectra. Fi-
nally, the structures of all of the new trz compounds were
also confirmed by the observation of the molecular peak
in the mass spectrum and by elemental analysis (see the
Supporting Information).
3. Cyclic Voltammetry Studies
The cyclic voltammograms (CVs) of all the trz and trz*
compounds have been recorded in order to investigate the
redox properties of the trz and trz* groups and their influ-
ence on the redox properties of the neutral and cationic
metallocenic groups to which they are directly attached.
The results are reported in Table 1.
The new compound 1 shows two chemically and electro-
chemically reversible reduction waves in THF at the Pt elec-
trode, assigned to the two successive single-electron re-
ductions of cobalticinium[55] (Figure 1). The first (less cath-
odic) wave corresponds to the reduction of the 18-electron,
d6 CoIII complex to the 19-electron, d7 CoII complex. This
wave at –0.85 V vs. [FeCp2*]+/0 (Cp* = η5-C5Me5) in THF
is located at a potential that is 40 mV less negative than
that of the parent cobalticinium complex, which can be at-
tributed to the electron-withdrawing properties of the 1,2,3-
triazolyl group. The second single-electron cathodic wave
that is located at –1.90 V vs. [FeCp2*]+/0 corresponds to the
2. Methylation of the Triazole Compounds to Produce
Triazolium Derivatives
Further methylation of the trz rings of the compounds reduction of the 19-electron, d7 CoII complex to the 20-
1, 3, and 5, using Me3OBF4 as the methylating agent,[29] electron, d8 CoI species. It is remarkable that this second
2
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Table 1. Redox potentials and chemical (ia/ic) and electrochemical (Epa – Epc = ΔE) reversibility data for compounds 1–7. Supporting
electrolyte: [nBu4N][PF6] (0.1 m); working and counter electrodes: Pt; reference electrode: Ag; internal reference: FeCp*2 (Cp* = η5-
C5Me5); scan rate: 0.200 Vs–1.
Solvent
–
FeII/III [V]
CoIII/II [V]
CoII/I [V]
trz*(0/+1)
ΔE
E1/2
ΔE
ia/ic
E1/2
ΔE
ia/ic
E
ΔE
ia/ic
Ep
1
1
2
3
3
4
6
6
7
7
MeCN
THF
MeCN
MeCN
THF
MeCN
MeCN
THF
MeCN
THF
–
–
–
0.55
0.43
0.84
–
–
0.62
0.48
–
–
–
0.50
0.60
0.50
–
–
0.50
0.65
–
–
–
1
1
1
–
–
1
1
–0.75
–0.85
–0.46
–
–
–
0.60
0.65
0.50
–
–
–
–
–
0.50
0.65
1
1
1
–
–
–
–
–
0.5
1
Ep = –1.76
E1/2 = –1.90
Ep = –1.32
0
0.90
0
–
–
–
–
–
0
0
0.9
0
–
–
–
–
–
0
–
–
–
–
0
–
–
0
0
0
–
–
–2.20
–
–
–1.64
–1.60
–1.72
–
–
–
–
–
–
–
–
–0.76
–0.88
Ep = –1.81
E1/2 = –1.92
0.80
0.3
–
group is found at a more positive potential than ferrocene
itself in MeCN (Table 1), whereas for 7 (Figure 2) the ad-
ditional influence of the cobalticinium group shifts the oxi-
dation of the ferrocenyl group anodically (Table 1).
Figure 1. CV of 1 in THF. The wave at 0.0 V corresponds to the
internal reference FeCp*2. Solvent: THF; reference electrode: Ag;
working and counter electrodes: Pt; scan rate: 0.2 Vs–1; supporting
electrolyte: [nBu4N][PF6].
cathodic wave is also chemically and electrochemically re-
versible, which means that both the 19-electron and 20-elec-
tron species are stable on the electrochemical time scale,
and the trz substituent does not destabilize these oxidation
states that are already rendered fragile by the presence of
electrons in the antibonding e1* orbitals. The influence of
the electron-withdrawing properties of the trz substituent
on the redox potentials appears to be the same for both the
first and second reduction wave. In MeCN, the reduction
waves are chemically irreversible, which can be attributed to
fast ligand substitution by the MeCN ligand in high con-
centration. Indeed, MeCN is a much stronger ligand than
THF, and we know that ligand substitution of π-hydro-
carbon ligands in 19-electron late transition-metal com-
plexes by good ligands such as MeCN is of the order of
109 faster than the analogous exchange in the 18-electron
complexes.[56,57] Thus the 19-electron CoII complexes are ki-
netically very unstable in MeCN even on the electrochemi-
cal time scale, and the 20-electron CoI species even more
so. This irreversibility in MeCN (partial for the first wave,
total for the second one) is observed for all the compounds
containing the cobalticinium group (1, 2, and 7). For the
Figure 2. CV of 7 in THF. The wave at 0.0 V corresponds to the
internal reference of FeCp*2. Solvent: THF; reference electrode,
Ag; working and counter electrodes: Pt; scan rate: 0.2 Vs–1; sup-
porting electrolyte: [nBu4N][PF6].
Cathodic reduction of the trz ring in the triazolyl deriva-
tives 1, 3, 5, and 7 was not observed until –2.5 V vs.
[FeCp2*]+/0. On the other hand, cathodic reduction of the
Figure 3. CV of 6 in CH3CN. The wave at 0.0 V corresponds to
the internal reference of FeCp*2. Solvent: CH3CN; reference elec-
trode: Ag; working and counter electrodes: Pt; scan rate: 0.2 Vs–1;
triazolylferrocene complex 3, oxidation of the ferrocenyl supporting electrolyte: [nBu4N][PF6].
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trz* derivatives 2, 4, and 6 was observed, but it was totally 0.3 V and 0.65 V vs. [FeCp2*]+/0. It is suggested that these
chemically irreversible even at –50 °C. The trz* group in the two waves correspond to the oxidation of the triazolylcyclo-
organic compound 6 (Figure 3) was reduced at a slightly pentadiene–cobalt–Cp and triazolylcyclopentadienyl–co-
less negative potential (Ep) than the trz* group in the ferro- balt–cyclopentadiene, respectively. The first wave at 0.3 V is
cene derivative 4 because of the electron-releasing property more intense than the other, which would be in agreement
of the ferrocenyl group (compared to the phenyl group), with the preferential hydride reduction of the substituted
although the comparison between the Ep values does not ring that is more electron poor than the free ring.
reflect the exact difference of the E0 values that are not
Reduction of 1 by Na/Hg in THF led to decomposition,
easily accessible. The trz* group in the cobaltocenyltriazole probably because of the thermal instability of the 20-elec-
complex 2 was reduced at a much more negative potential tron triazolylcobaltocene anion, which is easily formed with
because the 20-electron cobaltocene anionic species that is reduction by Na/Hg. Therefore we synthesized the known
generated at a less negative potential is strongly electron- crystalline forest-green 19-electron complex [FeICp(η5-
releasing. Finally, the trz* group behaves as an even more C6Me6)].[59] This complex has a potential E0 of –1.53 V in
electron-withdrawing substituent than trz because of the THF vs. [FeCp2*]+/0 [60–61] that is much more cathodic than
cationic charge of the former. For instance, reversible sin- the first potential of the reduction of 1 but less negative
gle-electron anodic oxidation of the ferrocenyl group in than its second reduction potential. Reduction of 1 by a
MeCN occurs at a potential 220 mV more positive for 4 stoichiometric amount of [FeICp(η5-C6Me6)] in THF in-
than for the ferrocenyl group in 7.
stantaneously provoked a color change from orange to
brown and formation of a yellow precipitate of [FeIICp(η5-
C6Me6)][PF6]; see Equation (5).[58] The reduced brown, air-
sensitive compound 9 (the color of cobaltocene) was soluble
in diethyl ether and was characterized by UV/Vis and EPR
(Figure 4) spectroscopy as well as mass spectrometry. It was
also characterized by its re-oxidation in air to the 18-elec-
tron complex as shown by 1H NMR spectroscopy (the
shape of the signal of the trz proton therein is broad and
different from that of the peak observed in 1, which may
tentatively be assigned to a change of anion for OH– that
forms a hydrogen bond with the trz proton).
4. Reduction of Triazolylcobalticinium 2 with NaBH4 and
Single-Electron Reductants
Reduction of the orange cationic triazolylcobalticinium
complex 1 by NaBH4 at 0 °C in THF, in which it was solu-
ble, produced the red, air-sensitive compound 8 that was
soluble in diethyl ether enabling its extraction under N2
[Equation (4)]. Its thermal stability under N2 is modest un-
der ambient conditions, allowing standard spectroscopic
analysis.
The disappearance of the PF6– band in the infrared spec-
trum of 8 is consistent with the formation of a neutral com-
pound in 95% yield, the structure being confirmed by ob-
servation of the molecular peak in the mass spectrum.
Compound 8 has a rather complex 1H NMR spectrum
showing the formation of a mixture of isomeric triazolyl η4-
cyclopentadiene–cobalt–η5-cyclopentadienyl complexes.[58]
Indeed the hydride reduction of the cationic cobalt sand-
wich can occur either on the ipso 1,2 or 1,3 position of the
cyclopentadienyl ligand to which the trz group is attached
or to the free cyclopentadienyl ligand. No attempt was
made to separate the isomers. The cyclic voltammogram in
CH2Cl2 shows two totally irreversible oxidation waves at
4
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Click Synthesis and Redox Chemistry
Figure 4. EPR analysis of 9 and approximate simulations of signals B and C[62]. Signal A gives gʈ = 2.037 and gЌ = 2.003. Signal B gives
g = 2.015 and the hyperfine coupling constant A (Co – I = 7/2) = 150 G. The g values of signal C are g1 = 1.17, g2 = 1.9, and g3 = 5.09.
In conclusion, this study has afforded useful information
Conclusions
concerning the electronic properties of trz and trz* groups
Three triazolylmetallocenes, including a heterobimetallic
and their effect on the redox potentials of late transition-
complex, have been synthesized by CuAAC click reactions,
metal metallocenes. The stability of reduction products syn-
and their redox chemistry has been investigated including
thesized using specific reductants is of the utmost impor-
the determination of the oxidation/reduction potentials of
tance if similar procedures are envisaged for large nanosys-
the redox-active groups and the nature of the products of
tems such as metallodendrimers and nanoparticles.[47] The
reduction by NaBH4 and the electron-reservoir complex
satisfying results show that such further steps can be under-
taken in the future.
[FeICp(η5-C6Me6)]. The relatively strong electron-with-
drawing nature of trz shifts the redox potentials of the
metallocenes anodically. The reduction potential of the trz
group itself in the trz-containing compounds was not local-
Experimental Section
ized until –2.5 V in THF.
Additionally, trz* tetrafluoroborate derivatives, including
those attached to the metallocenes, have been synthesized.
The cationic charge of the trz* renders it even more elec-
General: Reagent-grade diethyl ether and tetrahydrofuran (THF)
were predried with Na foil and distilled from sodium/benzo-
phenone under argon immediately prior to use. Dichloromethane
tron-withdrawing than the trz group, which is reflected in was distilled from calcium hydride just before use. All other sol-
vents and chemicals were used as received. Ethynylferrocene, sty-
rene, benzyl azide, and Me3OBF4 were purchased from Aldrich. 1H
NMR spectra were recorded at 25 °C with a Bruker AC 300 MHz
spectrometer. The 13C NMR spectra were obtained in the pulsed
FT mode at 75.0 MHz with a Bruker AC 300 spectrometer. The
NMR spectra were recorded in d6 acetone unless noted otherwise.
All chemical shifts are reported in parts per million (δ, ppm) with
reference to Me4Si (TMS). The mass spectra were recorded at the
CESAMO (Univ. Bordeaux) with a QStar Elite mass spectrometer
(Applied Biosystems). The instrument is equipped with an ESI
source, and spectra were recorded in the positive mode. The electro-
the cyclic voltammetry data. The reduction potential of the
trz* group is reported here, but the trz* cathodic reduction
is totally chemically irreversible, even at –50 °C. In 1-
benzyl-3-methyl-4-cobalticinium hexafluorophosphate-1H-
triazolium (2) the addition of the third electron (reduction
of trz* group) is hifted cathodically, i.e. reduction is ren-
dered much more difficult (Ep = –2.20 V), because of the
negative charge of cobaltocene than in compounds 4 and 6
for which the reduction of the trz* group attached to a neu-
tral ferrocenyl or phenyl takes place around Ep = –1.60 V.
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spray needle was maintained at 5000 V and operated at room temp.
Samples were introduced by injection through a 20 μL sample loop
into a 4500 μLmin–1 flow of methanol from the LC pump. Mass
spectra of 8 were performed by the CESAMO with an AccuTOF-
GcV (JEOL), which is a GC-TOF. The instrument is equipped with
a sample introduction system named FD (Field Desorption). The
EPR spectrum was recorded with a Bruker EMX X-band spec-
trometer (microwave frequency 9.46 GHz). Parameters: microwave
power: 50 mW; modulation frequency (magnetic field): 100 kHz;
modulation amplitude: 8 Gauss; magnetic field sweep width
(Gauss): [0; 7000]; T = 4 K. All electrochemical measurements were
recorded under nitrogen in dry CH3CN, THF, or CH2CH2 at 20 °C.
Supporting electrolyte: [nBu4N][PF6] (0.1 m); working and counter
electrodes: Pt; reference electrode: Ag; internal reference: FeCp*2;
scan rate: 0.200 Vs–1.
of Cp), 86.51, 84.96 (CH of Cp sub.), 85.63 (Cq of Cp sub.), 57.36
(Ar-CH2), 39.64 (N-CH3) ppm. MS (m/z): calcd. for C20H19N3Co
360.0905; found 360. C20H19BCoF10N3P·Et2O (426.01): calcd. C
43.19, H 4.71; found C 43.39, H 4.11.
Synthesis of 4: The compound 4 was synthesized from 1 equiv. of
3 (120 mg, 0.35 mmol) and 1 equiv. of Me3OBF4 (51.72 mg,
0.35 mmol) according to the same procedure as for 2. It was puri-
1
fied by precipitation in ether; yield 93%. H NMR (1D 1 H): δ =
8.65 (1 H, CH of trz*), 7.52, 7.40 (5 H, CH of Ar), 5.67 (2 H, CH
of Ar-CH2), 4.72 (2 H, CH of Cp sub.), 4.47 (2 H, CH of Cp sub.),
4.22 (5 H, CH of Cp), 4.20 (3 H, CH of N-CH3) ppm. 13C NMR
(1D 1 H): δ = 145.04 (Cq of trz*), 133.64 (Cq of Ar), 130.29,
130.12, 130.01 (CH of Ar), 128.38 (CH of trz*), 72.08 (CH of Cp
sub.), 71.16 (CH of Cp), 69.96 (CH of Cp sub.), 66.98 (Cq of Cp
sub.), 57.63 (Ar-CH2), 39.73 (N-CH3) ppm. MS (m/z): calcd. for
C20H20N3Fe 358.1001; found 358.1000. C20H20BF4FeN3 (445.05):
calcd. C 53.98, H 4.53; found C 53.63, H 4.44.
Click Synthesis of 1: A mixture of 1 equiv. of benzyl azide (70 mg,
0.53 mmol) and 1 equiv. of ethynyl cobalticinium hexafluorophos-
phate[52] (189.79 mg, 0.53 mmol) were dissolved in 3:2 distilled
THF/H2O. At 0 °C, CuSO4 was added (1 equiv.; 1 m aqueous solu-
tion), followed by dropwise addition of a freshly prepared solution
of sodium ascorbate (2 equiv.; 1 m aqueous solution). The solution
was allowed to stir for 12 h at room temp. under N2. An aqueous
solution of ammonia was added, and the mixture was allowed to
stir for 10 min. The organic phase was washed twice with water,
dried with sodium sulfate, filtered through paper, and the solvent
was removed under vacuum. Complex 1 was purified by precipi-
tation with diethyl ether, and obtained as an orange-red powder;
Synthesis of 6: The compound 6 was synthesized from 1 equiv. of
5 (120 mg, 0.51 mmol) and 1 equiv. of Me3OBF4 (75.49 mg,
0.51 mmol) according to the same procedure as for 2. It was puri-
fied by precipitation in ether; yield 91%. 1H NMR (1D, 1 H)
CDCl3: δppm = 9.01 (1 H, CH of trz*), 7.79 (2 H, CH of Ph), 7.66
(5 H, 2 CH of Ar and 3 CH of Ph), 7.46 (2 H, CH of Ar), 5.98 (2
H, CH of Ar-CH2), 4.41 (3 H, CH of N-CH3) ppm. 13C NMR (1D,
1 H): δ = 144.42 (Cq of trz*), 133.54 (Cq of Ar), 132.51, 130.10
(CH of Ph), 130.47, 130.36, 130.29 (CH of Ar), 129.59 (CH of
trz*), 123.75 (Cq of Ph), 57.91 (Ar-CH2), 39.47 (N-CH3) ppm. MS
(m/z): calcd. for C16H16N3 250.1338; found 250.1337. C16H16BFN3
(280.13): calcd. C 57.00, H 4.78; found C 56.75, H 4.56.
1
yield 80%. H NMR (1D, 1 H): δ = 8.55 (1 H, CH of trz), 7.39 (5
H, CH of Ar), 6.38 (2 H, CH of Cp sub.), 5.97 (2 H, CH of Cp
sub.), 5.70 (7 H, CH of Cp and Ar-CH2) ppm. 13C NMR (1D 1
H): δ = 138.28 (Cq of trz), 135.5 (Cq of Ar), 128.98, 128.52, 128.21
(CH of Ar), 124.52 (CH of trz), 96.04 (Cq of Cp sub.), 85.96 (CH
of Cp), 84.53, 80.92 (CH of Cp sub.), 53.82 (Ar-CH2) ppm. MS
(m/z): calcd. for C19H17N3Co 346.0748; found 346.0746.
Synthesis of 8: A mixture of 1 equiv. of 1 (150 mg, 0.31 mmol) with
1.1 equiv. of NaBH4 (12.71 mg, 0.34 mmol) in distilled THF
(20 mL) was stirred for 20 min at 0 °C under N2. Then, the solvent
was evaporated under vacuum, and distilled diethyl ether was
added to solubilize the neutral product. After filtration under N2
and evaporation of the solvent, the product was obtained as a deep
red powder; yield 95%. The complex 8 is not air stable and stored
under N2. It is thermally stable under N2 for a few hours, then
degradation appears as indicated by the 1H NMR spectrum and
Click Synthesis of 7: The compound 7 was synthesized according
to the same procedure as for 1 above by the click synthesis between
(azidomethyl)ferrocene[53] (80 mg, 0.33 mmol) and ethynylco-
balticinium hexafluorophosphate[52] (118.84 mg, 0.33 mmol) and
obtained as orange-red needles after precipitation in ether; yield
84%. 1H NMR (1D 1 H): δ = 8.48 (1 H, CH of trz), 6.39 (2 H,
1
precipitation. H NMR (1D, 1 H) CDCl3: δ = 7.41–7.31 (5 H, CH
of Ph), 7.13 and 6.66 (1H of trz), 5.51–5.34 (2H of Ph-CH2 and
2H of diene), 4.88–4.52 (5H of free Cp and 4H of substituted Cp
when H– is added to free Cp), 2.93–2.88 (2H of diene), 2.09–2.04
(2H free) ppm. 13C NMR (1D, 1 H) C6D6: δ = 149.59 (Cq of tri-
azole), 133.62 (Cq of Ar), 129.37, 129.19 (CH of Ar), 121.51 (CH
of triazole), 80.755–80.60 (CH of Cp), 78.84–75.16 (CH of cyclo-
pentadiene), 55.14 (Ar-CH2), 43.17–39.72 (CH2 of cyclopentadi-
ene) ppm. MS (m/z): calcd. for C19H18CoN3 347.08327; found
347.08422.
–
CH of Cp sub. of CoCp2+PF6 ), 5.98 (2 H, CH of Cp sub. of
CoCp2+PF6 ), 5.71 (5 H, CH of Cp of CoCp2+PF6 ), 5.46 (2H of
trz-CH2), 4.42 (2 H, CH of Cp sub. of FeCp2), 4.23 (2 H, CH of
Cp sub. of FeCp2), 4.22 (5 H, CH of Cp of FeCp2) ppm. 13C NMR
(1D 1 H): δ = 138.75 (Cq of trz), 124.81 (CH of trz), 97.30 (Cq of
–
–
Cp sub. of CoCp2+PF6 ), 86.85 (CH of Cp of CoCp2+PF6 ), 85.39,
–
–
–
81.85 (CH of Cp sub. of CoCp2+PF6 ), 82.65 (Cq of Cp sub. of
FeCp2), 69.98 (CH of Cp sub. of FeCp2), 69.80 (CH of Cp of
FeCp2), 50.89 (trz-CH2) ppm. MS (m/z): calcd. for C23H21FeCoN3
454.0429; found 454.0413. C23H21CoF6FeN3P (599.18): calcd. C
46.10, H 3.53; found C 45.92, H 3.46.
Synthesis of 9: A solution of 1 (1 equiv., 120 mg, 0.24 mmol) in
distilled THF (20 mL) was prepared in a Schlenk flask. Then ad-
dition under N2 of a solution of a stoichiometric amount of the
forest-green complex [FeICp(η5-C6Me6)][59] (1 equiv., 0.24 mmol,
67.97 mg) in distilled THF was performed by canula. A color
Synthesis of 2: A mixture of 1 equiv. of 1 (120 mg, 0.24 mmol) with
1 equiv. of Me3OBF4 (36.14 mg, 0.24 mmol) in distilled dichloro-
methane (30 mL) was stirred for 3 d at room temp. under N2. Then,
the organic phase was washed twice with water, dried with sodium
sulfate, and the solvent was evaporated under vacuum. Compound
change from orange to brown and
a yellow precipitate of
[FeIICp(η5-C6Me6)][PF6] appeared immediately. After evaporation
of the solvent under vacuum, the neutral brown product 9 was
solubilized in distilled diethyl ether and filtered to obtain 9 as a
brown powder; yield 97%. The paramagnetic complex 9 is not air
stable and was stored under N2. Oxidation of the product in air
1
2 was purified upon washing with THF; yield 90%. H NMR (1D,
1 H): δ = 9.47 (1 H, CH of trz*), 7.62, 7.46 (5 H, CH of Ar), 6.61
(2 H, CH of Cp sub.), 6.21 (2 H, CH of Cp sub.), 6.03 (5 H, CH
of Cp), 5.96 (2 H, CH of Ar-CH2), 4.53 (3 H, CH of N-CH3) ppm.
13C NMR (1D, 1 H): δ = 136.15 (Cq of trz*), 132.25 (Cq of Ar),
131.32 (CH of trz*), 129.58, 129.46, 129.22 (CH of Ar), 87.37 (CH
1
yielded 1 after addition of NaPF6. H NMR (1D 1 H), ([D6]acet-
one, 300 MHz), after oxidation of 9 in air: δ = 8.57 (1 H, CH of
triazole), 7.41 (5 H, CH of Ar), 6.41 (2 H, CH of substituted Cp),
6
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Eur. J. Inorg. Chem. 0000, 0–0

Job/Unit: I20755
/KAP1
Date: 10-09-12 16:11:19
Pages: 8
Click Synthesis and Redox Chemistry
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Received: July 6, 2012
Published Online: ᭿
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7

Job/Unit: I20755
/KAP1
Date: 10-09-12 16:11:19
Pages: 8
A. Rapakousiou, C. Mouche, M. Duttine, J. Ruiz, D. Astruc
FULL PAPER
Click Reactions
The click syntheses (CuAAC) of triazole
and access to triazolium derivatives con-
taining ferrocene and/or cobalticinium al-
lowed us to evaluate their redox chemistry
by cyclic voltammetry and with the use of
redox reagents.
A. Rapakousiou, C. Mouche, M. Duttine,
J. Ruiz, D. Astruc* ........................... 1–8
Click Synthesis and Redox Chemistry of
Mono- and Heterobimetallic Triazolyl and
Triazolium-Ferrocene and Cobalticinium
Complexes
Keywords: Metallocenes / Sandwich com-
plexes / Iron / Cobalt / Redox chemistry /
Click chemistry / Reduction / Nitrogen het-
erocycles
8
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