Electrochemical nickel-induced fluoroalkylation: Synthetic, structural and mechanistic study

Article abstract of DOI:10.1039/c1dt11299f

Electrocatalytic generation of nickel catalysts in low oxidation states by reduction of nickel complexes with various ligands (2,2′-bipyridine, 2,2′:6′,2′′-terpyridine, (S,S)-2,6-bis(4-phenyl-2- oxazolin-2-yl)-pyridine) in the presence of olefinic substra

Full text of DOI:10.1039/c1dt11299f

View Article Online / Journal Homepage / Table of Contents for this issue
Dynamic Article Links
Dalton
Transactions
Cite this: Dalton Trans., 2012, 41, 165
www.rsc.org/dalton
PAPER
Electrochemical nickel-induced fluoroalkylation: synthetic, structural and
mechanistic study†
Dmitry Mikhaylov,a Tatyana Gryaznova,a Yulia Dudkina,a Mikhail Khrizanphorov,a Shamil Latypov,a
Olga Kataeva,a,b David A. Vicic,c Oleg G. Sinyashina and Yulia Budnikova*a
Received 7th July 2011, Accepted 4th October 2011
DOI: 10.1039/c1dt11299f
Electrocatalytic generation of nickel catalysts in low oxidation states by reduction of nickel complexes
with various ligands (2,2¢-bipyridine, 2,2¢:6¢,2¢¢-terpyridine, (S,S)-2,6-bis(4-phenyl-2-oxazolin-2-
yl)-pyridine) in the presence of olefinic substrates and fluoroalkyl halides leads to new organic products
derived from addition-dimerization processes. Due to the presence of two stereocenters in the
dimerization products two diastereomers were characterized by a variety of analytical techniques
including multi-dimensional NMR methods and X-ray single crystal diffraction. The formation of
dimers was prevented by the inclusion of the hydrogen atom donor tributyltin hydride. The cyclic
voltammetry study of selected nickel complexes along with fluoroalkyl halides demonstrated that
Ni(I)L is the active form of the catalyst.
Another disadvantage of preparing highly fluorinated com-
1
Introduction
pounds is the lack of reactive or reliable fluoroalkyl nucleophiles.
Fluoroalkyl Grignard reagents are known, however, these reagents
suffer from severe thermal instability. Smith and co-workers
had found that perfluoroaliphatic Grignard reagents decompose
Today, the significant expansion in the use of fluorinated molecules
is rooted in the outstanding progress made in the field of synthetic
organic chemistry.1–4 Indeed, the synthesis of fluorinated molecules
is a very challenging area of organic chemistry because the
rules that govern the synthesis of non-fluorinated analogs cannot
necessarily be transposed to fluorinated compounds. Nevertheless,
due to a better comprehension of the factors that modulate
the reactivity of organofluorines, remarkable progress in the
field have been achieved. Fluorine is one of the most reactive
elements in the periodic table yet some of its compounds are
the most stable and least reactive. Many modern pharmaceutical
compounds (anti-cancer, antibiotics, anti-malarial etc.) include
fluorine, or fluorinated groups. Consequently, synthetic method-
ology to incorporate fluorine synthons must be improved in
order to prepare sophisticated organofluorine molecules on a
practical scale. Existing methods which employ the addition of
fluoroalkyl synthons to different substrates have a number of
disadvantages, such as high reaction temperature, low yields, and
low selectivities.5–11
◦
rapidly at -70 C.5 Moreover, RF-X (X = Br, I) substrates
do not react cleanly with Mg metal, so the most convenient
method to prepare perfluoroalkyl Grignard reagents is through
metal-halogen exchange reactions.6–7 Such procedures have many
disadvantages as the resulting solutions are also contaminated
with organic halides. Perfluoroalkyl silanes such as the Ruppert-
Prakash reagent can also be unreliable in the sense that one has
to control the amount of “perfluoroalkyl anion” which is released
and also have to be wary of “Me3Si+” that can react with multiple
bonds.12 An attractive strategy is to avoid the use of perfluoroalkyl
nucleophiles all together and simply use perfluoroalkyl halides
as the source of the perfluoroalkyl group. Methods that lend
themselves for performing this and doing so asymmetrically13–17
would be of high synthetic value.
We have previously reported our preliminary findings that
electrogenerated nickel can catalyze the addition of perfluoroalkyl
halides to olefins18 to yield new dimeric species. Here we report
on the scope of the reaction as well as demonstrate a new method
to prevent dimerization and yield monomeric products. This new
method opens up the possibility for doing these electrosyntheses
asymmetrically. Detailed information about reaction mechanisms
of the electrocatalytic processes is also discussed.
aA. E. Arbuzov Institute of Organic and Physical Chemistry, Kazan
Scientific Center of Russian Academy of Sciences, 8, Arbuzov str., 420088,
Kazan, Russian Federation. E-mail: yulia@iopc.ru; Fax: +7(843)273-22-
53; Tel: +7(843)279-53-35
bLeibniz Institute for Solid State and Materials Research IFW Dresden,
D-01171, Dresden, Germany
cDepartment of Chemistry, University of Hawaii, 2545 McCarthy Mall,
Honolulu, Hawaii, 96822, USA
2
Results and Discussion
† Electronic supplementary information (ESI) available. CCDC reference
numbers 832892–832894. For ESI and crystallographic data in CIF or
other electronic format see DOI: 10.1039/c1dt11299f
The aims of the current contribution are to distinguish effects
of substrate and catalyst nature on the yields and selectivity of
This journal is
The Royal Society of Chemistry 2012
Dalton Trans., 2012, 41, 165–172 | 165
©

View Article Online
Table 1 Conditions employed for electrocatalytic fluoroalkylations
Entry
RFX
R1
R2
Producta
Catalyst (10 mol %)
Solvent
Yield
1
2
3
4
5
6
7
8
C6F13I
Me
Me
Me
Me
Me
Me
H
H
H
Me
Ph
Ph
Ph
Ph
Ph
Ph
AcO
Py
1 (1 : 0.15)
2 (1 : 0.12)
2
1
1
1
3(1 : 0.4)
4
5
(bpy)NiBr2
(bpy)NiBr2
(bpy)NiBr2
(pybox)NiBr2
(tpy)NiBr2
NiBr2
(bpy)NiBr2
(tpy)NiBr2
(bpy)NiBr2
(bpy)NiBr2
DMF
DMF
CH3CN
DMF
DMF
70%
49%
58%
34%
46%
14%
51%
48%
61%
72%
H(CF2)6Br
H(CF2)6I
C6F13I
C6F13I
C6F13I
H(CF2)6Br
H(CF2)6I
C6F13I
DMF: pyridine (9 : 1)
DMF
DMF
DMF
DMF
9
10
Py
Ph
(CF3)2CF(CF2)I
6 (1 : 0.8)
a Compound number, diastereomeric ratio is given in parenthesis (meso: dl).
electrocatalytic fluoroalkylation, to manipulate the dimer/
monomer formation and to explore the possible reaction path-
ways.
Aiming to identify optimum reaction conditions and to broaden
the scope of the electrocatalytic method, a set of experiments with
various catalysts, olefins and fluoroalkyl halides was performed
(Table 1). Several nickel complexes with alpha-diimines were used
(Fig. 1) as catalysts.
catalyzed cross-coupling reaction with alkyl iodides proceeds
much better than with bromides.
For all of the products listed in Table 1, there are two chirality
centers and therefore two diastereomers (meso and dl) can be
expected. Indeed, in several cases (e.g., for compound 1) there
are two sets of signals clearly seen for some nuclei in NMR
spectra (1H, 13C and 19F, see ESI†) with intensities at ca. 1 : 0.12–
19
0.8 (Entry 1, Table 1). A combination of 1D (1H, 1H{ F},
1
1
13C, 19F) and 2D (COSY H-1H, HSQC/HMBC H-13C) NMR
methods19–21 allowed straightforward establishment of key pieces
of the chain up to C3 carbon (e.g., for compound 2, Fig. 2).
Unfortunately, a large quantity of vicinal fluorine atoms with
strong spin–spin couplings to more remote fluorine bearing
carbons (C4–C6) leads to dramatic diminishing of their intensities,
and therefore no signals were assigned in 13C NMR spectra for
these carbons. Proton–fluorine and fluorine–fluorine correlation
NMR experiments21 were particularly helpful in this case. Namely,
2D HETCOR/HOESY 1H–19F methods reveal connectivity up to
fluorine at C3, then 2D COSY 19F–19F experiments let us follow
along the perfluorinated chain and then, in the case of 2–5, to reach
1
the “end” protons (H8) by 2D HETCOR H–19F correlations.
Thus half of the chain can be revealed unambiguously. Moreover
for nitrogen containing compounds (4, 5) 1H–15N HMBC spectra
were useful to determine pyridine moiety. Finally, taking into
account valence rules and intermoiety 1H–13C HMBC correlations
(3–5), two halves were linked into the whole molecule via the C1–
C1¢ bond.
An almost perfect correlation of the calculated (GIAO
B3LYP/6-31G(d)//B3LYP/6-31G(d), (see ESI†)22–23 versus ex-
perimental 13C and 19F chemical shifts (R2 = 0.99 and 0.98,
respectively for carbon and fluorine) provides additional support
for the validity of the above conclusion on the structure.
The various NMR technique results are consistent with the
X-ray single crystal diffraction data for compounds 4, 5 and 6.
The crystals contain meso-forms, with molecules located in special
positions, the inversion center being in the middle of the central
Fig. 1 Ligands selected for catalytic purposes (bpy = 2,2¢-bipyridine;
tpy = 2,2¢: 6¢,2¢¢-terpyridine; pybox = (S,S)-2,6-Bis(4-phenyl-2-oxazolin-
2-yl)-pyridine).
From Table 1, it is clear that (bpy)NiBr2 is the most effective
catalyst for electrocatalytic fluoroalkylation. Nevertheless, the
tridentate complexes of pybox and tpy afforded considerable
yields of the reaction products. 6-H-perfluoroiodohexane (Entries
3 and 8) could be used in place of perfluoroiodohexane and,
due to the presence of the terminal hydrogen atom in the
fluoroalkyl chain, enables convenient recognition of products
1
by H NMR spectroscopy. Gratifyingly, experiments with 6-H-
perfluorobromohexane (Entries 2 and 7) provided decent yields
compared to fluoroalkyl iodides though it is known that nickel
166 | Dalton Trans., 2012, 41, 165–172
This journal is
The Royal Society of Chemistry 2012
©

View Article Online
Fig. 2 1H and 19F spectra with principal homo (19F–F) and hetero-correlations (1H–19F) for compound 2 (characteristic signals of the second diastereomer
are marked with *).
monomeric product whereby a hydrogen atom is incorporated
into the final structure. Use of NH4ClO4 and a mixture of solvents
DMF : MeOH as a hydrogen source did not yield monomer
formation, however, the addition of tributyltin hydride provided
monomer in 52% yield (Scheme 1). Since the reaction outlined
in Scheme 1 generates a single site of chirality, future work will
involve exploring the possibility of doing the olefin perfluoroalky-
lations enantioselectively.
Scheme 1 Electrocatalytic fluoroalkylation with tributyltin hydride.
Information regarding the electrogeneration of active nickel
complexes in the presence of fluoroorganic halides was obtained by
cyclic voltammetry techniques. While the electrochemical behavior
of (bpy)NiBr2 is well documented,24–26 it has not yet been described
for the analogous dibromide complexes of tpy and pybox. The
first reduction wave potentials in DMF were found to shift
towards less cathodic values for the LNiBr2 series when bpy was
replaced with either tpy or pybox (see Table 2 and ESI†). For
Fig. 3 ORTEP drawings of compound (5) and (6) with 50% probability
displacement ellipsoids of non-H atoms.
Table 2 Reduction potentials (V, vs. Ag/AgNO3) of selected nickel
complexes in DMF
C–C bond (Fig. 3). Molecular structure of both compounds is
Compound
1st reduction
2nd reduction
similar: all sp3 carbon atoms form transoid chains with aromatic
pyridine rings being perpendicular to its plane.
(bpy)NiBr2
(tpy)NiBr2
(pybox)NiBr2
1.52
1.32
1.37
2.32
1.86
1.74
We sought to expand upon the success of the dimerization
reactions and develop a complementary method to prepare the
This journal is
The Royal Society of Chemistry 2012
Dalton Trans., 2012, 41, 165–172 | 167
©

View Article Online
the complex with bpy the first two-electron (Ni2+/Ni0) reduction
wave is reversible, while for complexes with tpy and pybox the
process is characterized by two one-electron reversible transfers
(Ni2+/Ni1+/Ni0), i.e., is by two successive reduction stages.
The cyclic voltammograms of nickel complexes with selected
ligands in the presence of increasing amounts of RFX substrates
demonstrate significant changes for each complex. Fig. 4 shows
that in the presence of perfluoroalkyl halide the first reduction
wave for (bpy)NiBr2 decreases by half upon addition of excess of
C6F12HBr, and moreover the wave is no longer reversible. Further
addition of substrate results in only a minor increase of the first
wave current.
Fig. 4 Cyclic voltammograms of (bpy)NiBr2 (0.01 mol dm-3) in the
presence of increasing quantities of C6F12HBr. Ratios of (bpy)NiBr2 to
RFBr are 1 : 0 (red); 1 : 3(blue); 1 : 6 (violet); 1 : 12 (dark blue); 1 : 30 (black).
One interpretation of these data is that the current decrease for
the reduction peak of the NiII/Ni0 bpy catalyst (Fig. 4) is connected
with a rapid reaction of RFX with initially generated [(bpy)Ni]+,
the latter catalytically reacting with perfluoroalkyl halide on a time
scale that is much faster than the reduction of NiI to Ni0. The NiI
species is proposed to react with RFX to generate a transient NiIII
species according to the below equation (Scheme 2).
Fig. 5 Cyclic voltammograms of (tpy)NiBr2 (top) (0.01 mol dm-3) and
(pybox)NiBr2 (bottom) (0.01 mol dm-3) in the presence of increasing
quantities of C6F13I. Ratios of complexes to RFI are 1 : 0 (red); 1 : 3 (blue);
1 : 6 (violet); 1 : 12 (dark blue); 1 : 30 (black).
reduction of NiIIL complex to NiIL followed by an oxidation
by the fluoroorganic halide to regenerate NiIIL. In the case of
the bipyridine complex, a NiI species may further be generated
by a comproportionation reaction between Ni0 and NiII. The
perfluoroalkyl radicals produced by these redox events react with
a-methylstyrene to form an addition product which undergoes
either dimerization process or forms the monomer product under
the treatment of tributyltin hydride. An alternative and more
complex mechanism would involve coordination of the olefinic
substrate. Further experiments to unambiguously rule out this
step are necessary.
Scheme 2
The s-complex (bpy)NiRFBrX should be reduced at the same
24,27
or more cathodic potentials as for (bpy)NiBr2
This explains
the fact that the electrocatalytic regeneration of initial (bpy)NiBr2
is not observed at its reduction potential. Therefore it appears
likely that catalysis occurs through the NiIbpy active form. In the
case of the substrate C6F13I, the reduction waves of substrate and
(bpy)NiBr2 are much closer to each other, thus making the analysis
of the CV extremely difficult (see ESI†).
The cyclic voltammograms of (tpy)NiBr2 and the (pybox)NiBr2
complexes are shown in Fig. 5. The addition of C6F13I substrate
increases the current of the first reduction waves in both complexes,
suggesting that NiI species are the active forms of the catalyst.
The cyclic voltammetry and preparative electrolysis data give
experimental support to the reactions highlighted in Scheme 3.
The proposed mechanism of the processes involves electrochemical
3
Conclusions
Within the framework of the current contribution several de-
ductions can be made. Firstly, we have developed an efficient
electrocatalytic fluoroalkylation technique which was tested with
various olefins, fluoroalkyl halides and nickel catalysts. The
products derived from addition-dimerization process bear two
olefin and fluoroalkyl moieties and contain two stereocenters.
168 | Dalton Trans., 2012, 41, 165–172
This journal is
The Royal Society of Chemistry 2012
©

View Article Online
Scheme 3 Proposed reaction sequence in the electrocatalytic fluoroalkylation of a-methylstyrene using (tpy)NiBr2.
Therefore, two diastereomers are obtained which have been
characterized by NMR spectroscopy and X-ray crystallography.
Interestingly, the branching nature of the fluoroalkyl halides
affects the diastereomeric ratio (Table 1, entries 1 and 10).
Secondly, it was revealed that (bpy)NiBr2 is the most effective
catalyst of the studied reactions. Furthermore, we were able to
control whether addition of perfluoroalkyl radicals occurs with
dimer or monomer formation. The electrochemical behavior of
three nickel complexes was studied towards fluoroalkyl halides in
electroreductive conditions which allows to suggest the plausible
reaction scheme where NiIL is a key intermediate and the active
catalyst form. Thus, some key aspects of a mechanistic under-
standing of electrocatalytic fluoroalkylation have been delineated,
and further investigation and optimization of these processes is
ongoing.
COLLECT,28 cell refinement with Dirax/lsq,29 and data reduction
with EvalCCD30 for structures 4 and 5, while for structure 6
programs APEX2 and SAINT (Bruker, 2004) were used. Each
structure was solved by direct methods using SHELXS-97.31
Multi-scan empirical absorption corrections were applied to all
data sets using the program SADABS.32 All structures were refined
and extended with SHELXL-97.31 Carbon-bound hydrogen atoms
were included in idealised positions and refined using a riding
model.
Specific refinement details follow below (Table 3).
4.2 General procedures
All reactions were carried out under dry argon atmosphere.
All solvents employed were purified and dried prior to use.
N,N-Dimethylformamide was purified by double fractiona-
tion distillation over melting potash. Perfluoroiodohexane, 6-
H-perfluorobromohexane, 6-H-perfluoroiodohexane and perflu-
oroiodoisopentane were purchased from P&M Invest and used
without further purification. a-Methylstyrene, vinyl acetate and
vinyl pyridine were procured from Acros Organics. Tetra-
butylammonium tetrafluoroborate was purchased from Aldrich
and recrystallized from diethylether. (Bpy)NiBr2 was prepared
according to a previously reported procedure,33 (tpy)NiBr2
and (pybox)NiBr2 were obtained utilizing the same procedure.
4
Experimental
4.1 X-ray structure determination
Structures of 4 and 5 were collected on a Nonius Kappa
CCD and the structure 6 on a Bruker AXS Kappa APEX II
diffractometer with w and j scans. The diffractometers employed
graphite-monochromated Mo-Ka radiation generated from a
˚
sealed tube (0.71073 A). Data collections were undertaken with
Table 3 Crystallographic data for 4, 5 and 6
Compound reference
4
5
6
Chemical formula
Formula mass
C26H16F24N2
812.41
Monoclinic
16.091(1)
5.905(1)
16.645(1)
90.00
110.047(5)
90.00
1485.7(3)
198(2)
P21/n
2
24975
2732
0.0392
0.0390
0.0966
0.0571
C26H14F26N2
848.39
Triclinic
C28H20F22
774.44
Monoclinic
12.266(6)
22.489(2)
10.538(5)
90.00
Crystal system
˚
a/A
5.4351(3)
9.9164(4)
14.5715(6)
83.270(4)
80.137(4)
86.720(4)
767.86(6)
198(2)
˚
b/A
˚
c/A
a (◦)
b (◦)
g (◦)
95.81(1)
90.00
3
˚
Unit cell volume/A
T/K
Space group
2892(3)
150(2)
Pc
¯
P1
No. of formula units per unit cell, Z
No. of reflections measured
No. of independent reflections
Rint
Final R1 values (I > 2s(I))
Final wR(F2) values (I > 2s(I))
Final R1 values (all data)
Final wR(F2) values (all data)
1
4
15277
2814
0.0179
0.0364
0.1032
0.0446
0.1089
30248
11902
0.0927
0.0796
0.1813
0.1328
0.2091
0.1058
This journal is
The Royal Society of Chemistry 2012
Dalton Trans., 2012, 41, 165–172 | 169
©

View Article Online
Preparative electrolyses were performed by means of the direct
current source B5–49 in thermostatically controlled cylindrical
divided 100 mL electrolyser (a three-electrode cell). Platinum
with surface areas of 20 cm2 was used as a cathode; platinum
rod was used as the anode. The working electrode potential
was determined using reference electrode Ag/AgNO3. During
electrolysis, the electrolyte was stirred with a magnetic stirrer. The
saturated solution of Et4NBF4 in DMF was used as analyte, and
the anode compartment was separated by ceramic membrane. IR
spectra of the compounds were recorded on an FTIR spectrometer
“Vector 22” (Bruker) in the 400–4000 cm-1 range. Solid samples
were prepared as KBr pellets. Mass spectra were recorded in EI
mode using ThermoQuest TRACE MS.
269.43 Hz, at C3), -123.09 (4F, at C5), -124.41 (4F, at C6), -125.04
(4F, at C4), -126.63 (4F, at C7). 13C NMR (100.6 MHz, C6D6):
d = 21.19 (CH3), 34.89 (C2), 46.88 (C1), 141.09(C9). Characteristic
signals for second diastereomer: 1H NMR (400 MHz, C6D6): d =
2.28 and 2.57 (m, 4H, CH2). 19F NMR (376.5 MHz, C6D6): d =
-108.68 (ABq, 4F, DnAB = 3266.18 Hz, JAB = 270.35 Hz, at C3).
IR (KBr,n, c#xX_CYR_HEX_43c;-1): 1144, 1208, 1237 (C–F),
1602 (C C aromatic), 3069 (HC ). EIMS, m/z: 437.0 [1/2 M]+.
Anal. Calc: C, 41.19; H, 2.29; F, 56.52. Found: C, 41.28; H, 2.45.
4.4.2 2,3-Dimethyl-2,3-diphenyl-1,4-bis(6-H-perfluorohexyl)-
butane (2). A solution for electrolysis was prepared by mix-
ing 0.576 g (1.5 mmol) (bpy)NiBr2, 5.86 g (15 mmol) 6-H-
perfluorobromohexane and 1.81 g (15 mmol) a-methylstyrene in
DMF (100 ml). Electrolysis was carried out in an electrochemical
cell with separation of anode and cathode compartments at
ambient temperature under argon atmosphere at the potential
of a working electrode -1.5 V. The amounts of electricity
passed through the electrolyte were 2F per one mole of 6-
H-perfluorobromohexane (824 mA h). After completing the
electrolysis, the solution was washed with distilled water (150 ml)
and extracted with benzene (3 ¥ 100 ml). The organic layer was
dried over magnesium sulfate and filtered. The residual solution
was concentrated under reduced pressure and left overnight, then
the white solid precipitated from the mixture, filtered, washed with
hexane and dried in vacuo to give 2,3-dimethyl-2,3-diphenyl-1,4-
bis(6-H-perfluorohexyl)butane. Yield 3.2 g (51%) (diastereomeric
ratio 1 : 0.12). 1H NMR (400 MHz, C6D6): d = 1.35(s, 6H, CH3),
4.3 NMR experiments
NMR investigation was carried out in the NMR department
(A. E. Arbuzov Institute of Organic and Physical Chemistry) of
the Federal Collective Spectral Analysis Center for physical and
chemical investigations of structure, properties and composition
of matter and materials. NMR experiments were carried out
with Bruker spectrometers AVANCE-400 (400.1 MHz (1H), 376.5
MHz (19F), 100.6 MHz (13C)) and AVANCE-600 (600.1 MHz
(1H), 150.9 MHz (13C), 60.8 MHz (15N)) equipped with a pulsed
gradient unit capable of producing magnetic field pulse gradients
in the z-direction of 53.5 G cm-1. All spectra were acquired
in a 5 mm gradient inverse broad band probehead. Chemical
shifts are reported in the d (ppm) scale relative to the residual
1H and 13C signal of C6D6, to external C6F6 (-164.9 ppm) for
19F NMR spectra and to external CH3CN (235.50 ppm) for
15N NMR spectra. Chemical shifts were calculated within the
DFT framework using a hybrid exchange–correlation functional,
B3LYP, at the 6-31G(d) level as implemented in Gaussian 98.34
Full geometry optimizations were done at the ab initio RHF/6-
31G level. All data were referred to TMS (1H and 13C) chemical
shifts that were calculated under the same conditions.
2.17 and 3.13 (m, 4H, CH2), 4.94 (tt, 2H, 2JHF = 51.58 Hz, 3JHF
=
5.28 Hz), 6.96–7.07 (m, 10H, C6H5). 19F NMR (376.5 MHz, C6D6):
d = -106.94 (ABq, 4F, DnAB = 2818.58 Hz, JAB = 268.85 Hz, at
C3), -121.61 (4F, at C5), -123.41 (4F, at C6), -123.6 (4F, at C4),
-129.41 (4F, at C7), -136.86 (4F, at C8). 13C NMR (100.6 MHz,
C6D6): d = 21.22 (CH3), 34.97 (C2), 46.88 (C1), 107.93 (C7), 119.56
(C3), 141.29 (C8). Characteristic signals for second diastereomer:
1H NMR (400 MHz, C6D6): d = 2.43 and 2.71(m, 4H, CH2). 19
F
NMR (376.5 MHz, C6D6): d = -107.18 (ABq, 4F, DnAB = 3272.82
Hz, JAB = 271.34 Hz, at C3). IR (KBr, n, c#xX_CYR_HEX_43c;-1):
1145, 1208, 1238 (C–F), 1600 (C C), 3071 (HC ). EIMS, m/z:
419.0 [1/2 M]+. Anal. Calc.: C, 42.96; H, 2.62; F, 54.41. Found: C,
42.58; H, 2.51.
4.4 Electrosynthesis
4.4.1 2,3-Dimethyl-2,3-diphenyl-1,4-bis(perfluorohexyl)butane
(1). A solution for electrolysis was prepared by mixing 0.317 g
(0.85 mmol) (bpy)NiBr2, 3.79 g (8.5 mmol) perfluoroiodohexane
and 1 g (8.5 mmol) a-methylstyrene in DMF (70 ml). Electrolysis
was carried out in an electrochemical cell with separation of
anode and cathode compartments at ambient temperature under
argon atmosphere at the potential of a working electrode -1.5 V.
The amount of electricity passed through the electrolyte were
2F per one mole of perfluoroiodohexane (454 mA h). After
completing the electrolysis, the solution was washed with distilled
water (100 ml) and extracted with benzene (3 ¥ 100 ml). The
organic layer was dried over magnesium sulfate and filtered.
The residual solution was concentrated under reduced pressure
and left overnight, then the white solid precipitated from the
mixture, filtered, washed with hexane and dried in vacuo to give
2,3-dimethyl-2,3-diphenyl-1,4-bis(perfluorohexyl)butane. Yield
4.4.3 2,3-Diacetoxy-1,4-bis(6-H-perfluorohexyl)butane
A solution for electrolysis was prepared by mixing 0.209
(0.56 mmol) (bpy)NiBr2, 2.39 (5.6 mmol) 6-H-
(3).
g
g
perfluorobromohexane and 0.48 g (5.6 mmol) vinyl acetate in
DMF (70 ml). Electrolysis was carried out in an electrochemical
cell with separation of anode and cathode compartments at
ambient temperature under argon atmosphere at the potential
of a working electrode -1.5 V. Electrolysis was carried out in
an electrochemical cell with separation of anode and cathode
compartments at ambient temperature under argon atmosphere
at the potential of a working electrode -1.2 V. The amount
of electricity passed through the electrolyte were 2 F per
one mole of 6-H-perfluorobromohexane (300 mA h). After
completing the electrolysis, the solution was washed with distilled
water (100 ml) and extracted with benzene (3 ¥ 100 ml). The
organic layer was dried over magnesium sulfate, filtered and
concentrated under reduced pressure. Residue was purified by
column chromatography (SiO; hexane:EtOAc, 9 : 1) to afford
1
2.6 g (70%) (diastereomeric ratio 1 : 0.15). H NMR (400 MHz,
C6D6): d = 1.33 (s, 6H, CH3), 2.13 and 3.11 (m, 4H, CH2),
7.07–6.95 (m, 10H, C6H5). 19F NMR (376.5 MHz, C6D6): d =
-82.56 (s, 6H, CF3), -108.45 (ABq, 4F, DnAB = 2793.58 Hz, JAB
170 | Dalton Trans., 2012, 41, 165–172
=
This journal is
The Royal Society of Chemistry 2012
©

View Article Online
2,3-diacetoxy-1,4-bis(6-H-perfluorohexyl)butane as an oily
liquid. Yield 1.107g. (51%) (diastereomeric ratio 1 : 0.4). 1H NMR
(400 MHz, C6D6): d = 1.64 (s, 6H, 2CH3), 2.27 (m, 4H, 2CH2),
ether, dried in vacuo to give 2.578 g (64%) of 2,3-dipyridyl-1,4-
1
bis(perfluorohexyl)butane. H NMR (600 MHz, C6D6): d = 2.09
3
and 3.12 (m, 4H, 2CH2), 3.76 (d, 2H, JHH = 9.2 Hz, 2CH), 6.53
2
3
3
5.1 (tt, 2H, JHF = 51.6 Hz, JHF = 4.6 Hz), 5.65 (d, 2H, JHH
=
(m, 2H, at C12), 6.65 (m, 2H, at C14), 6.92 (m, 2H, at C13), 8.41
(m, 2H, at C11). 19F NMR (376.5 MHz, C6D6): d = -80.96 (6F,
at C8), -112.01 (ABq, 4F, DnAB = 871.29 Hz, JAB = 269.63 Hz,
at C3), -121.72 (4F, at C5), -122.81 (4F, at C6), -123.32 (4F, at
C4), -126.01 (4F, at C7). 13C NMR (150.9 MHz, C6D6): d = 33.75
(CH2), 45.23 (CH), 122.28 (C12), 124.81 (C14), 136.28 (C13), 150.33
(C11), 160.34 (C9). IR (KBr, n, cm-1): 1141, 1204, 1238 (CF2), 1365
(CF3), 1625–1460 (pyridine), 3080 (CF2–H). EIMS, m/z: 424 [1/2
M]+. Anal. Calc: C 36.81; H 1.66; F 58.23; N 3,30. Found: C
36.59; H 1.58; N 3,33.
9.2 Hz, 2CH). 19F NMR (376.5 MHz, C6D6): d = -112.49 (ABq,
4F, D nAB = 187.56 Hz, JAB = 271.67 Hz, at C3), -121.7 (4F, at
C5), -123.02 (4F, at C6), -123.25 (4F, at C4), -129.16 (4F, at C7),
-136.74 (4F, at C8). 13C NMR (100.6 MHz, C6D6): d = 19.9 (CH3),
31.28 (C2), 66.69 (C1), 107.97 (C8), 111.26 (C6), 117.8 (C3), 169.06
(C O). Characteristic signals for second diastereomer: 1H NMR
(400 MHz, C6D6): d = 1.6 (s, 6H, 2CH3), 2.07 (m, 4H, 2CH2), 5.56
(d, 2H, 3JHH = 9.87 Hz, 2CH). 19F NMR (376.5 MHz, C6D6): d =
-113.02 (ABq, 4F, D nAB = 198.88 Hz, JAB = 273.51 Hz, at C3). IR
(KBr, n, c#xX_CYR_HEX_43c;-1): 1142, 1207, 1235 (C–F), 1760
(C O). EIMS, m/z: 773.93 [M]+. Anal. Calc.: C, 31.02; H, 1.82;
F, 58.89; O, 8.27. Found: C, 30.73; H, 1.75.
4.4.6 2,3-Dimethyl-2,3-diphenyl-1,4-bis(perfluoroisopentyl)-
butane (6). The electrochemical cell was loaded with 0.1827
g (0.488 mmol) of (bpy)NiBr2, 1.93 g (4.88 mmol) of 6-H-
perfluoroiodohexane and 0.576 g (4.88 mmol) of a-methylstyrene
in DMF (40 ml). The amounts of electricity passed through the
electrolyte were 2 F per one mole of 6-H-perfluoroiodohexane
(260 mA h). Electrolysis was carried out in an electrochemical cell
with separation of anode and cathode compartments at ambient
temperature under argon atmosphere at the potential of a working
electrode -1.5 V. After completing the electrolysis, the solution
was washed with saturated ammonium chloride (3 ¥ 50 ml) and
extracted with benzene (3 ¥ 50 ml). The organic layer was dried
over magnesium sulfate, filtered and solvent evaporated on a
rotary evaporator. The residue was dried overnight on the Shlenk-
line and yielded 1.36 g (72%) of 2,3-dimethyl-2,3-diphenyl-1,4-
4.4.4 2,3-Dipyridyl-1,4-bis(6-H-perfluorohexyl)butane
(4).
The electrochemical cell was charged with 0.201 g (0.535 mmol)
of (tpy)NiBr2, 2.29 g (5.35 mmol) of 6-H-perfluoroiodohexane
and 0.563 g (5.35 mmol) 2-vinylpyridine and DMF (50 ml) was
added. Electrolysis was carried out in the electrochemical cell
with separation of anode and cathode compartments at ambient
temperature under argon atmosphere at the potential of a working
electrode -1.3 V. The amounts of electricity passed through the
electrolyte were 2 F per one mole of 6-H-perfluoroiodohexane
(574 mA h). After completing the electrolysis, the reaction
mixture was washed with saturated ammonium chloride (3 ¥
60 ml) and extracted with benzene (3 ¥ 70 ml). After separation,
the organic layer was dried over magnesium sulfate and then the
solvent was removed. The crystalline residue was washed with
diethyl ether, dried in vacuo to give 1.04 g (48%) 2,3-dipyridyl-
1
bis(perfluoroisopentyl)butane as a light-brown solid. H NMR
(400 MHz, C6D6): d = 1.34 (s, 6H, CH3), 2.13 and 3.12 (m, 4H,
CH2), 7.06–6. 94 (m, 10H, C6H5). 19F NMR (376.5 MHz, C6D6):
d = -71.88 (s, 12F, 2CF3), -106.64 (ABq, 4F, DnAB = 2759.13
Hz, JAB = 262.58 Hz, at C3), -116.28 (4 F at C4), -185.45 (2 F
at C5). 13C NMR (100.6 MHz, C6D6): d = 21.13 (CH3), 35.03
(C2), 46.95 (C1), 120.8 (C3), 141.03 (C8). Characteristic signals for
1
1,4-bis(perfluorohexyl)butane. H NMR (400 MHz, C6D6): d =
3
2.13 and 3.16 (m, 4H, 2CH2), 3.79 (d, 2H, JHH = 9.8 Hz, 2CH),
4.92 (tt, 2H, 2JHF = 51.8 Hz, 3JHF = 5.05 Hz), 6.54 (m, 2H, at C12),
6.68 (m, 2H, at C14), 6.93 (m, 2H, at C13), 8.43 (m, 2H, at C11). 19
F
1
NMR (376.5 MHz, C6D6): d = -113.6 (ABq, 4F, DnAB = 877.136
Hz, JAB = 269.05 Hz, at C3), -123.37 (4F, at C5), -125.02 (4F,
at C6), -125.24 (4F, at C4), -130.98 (4F, at C7), -138.35 (4F, at
C8). 13C NMR (100.6 MHz, C6D6): d = 33.78 (CH2), 45.26 (CH),
122.25 (C12), 124.82 (C14), 134.25 (C13), 150.34 (C11), 160.3 (C9).
IR (KBr, n, cm-1): 1140, 1203, 1239 (CF2), 1625–1480 (pyridine),
3080 (CF2-H). EIMS, m/z: 406 [1/2 M]+. Anal. Calc.: C, 38.44;
H, 1.99; F, 56.13; N, 3,45. Found: C,38.11; H, 1.81; F, 56.25; N,
3,44.
second diastereomer: H NMR (400 MHz, C6D6): d = 2.31 and
2.56 (m, 4H, CH2). 19F NMR (376.5 MHz, C6D6): d = -106.87
(ABq, 4F, DnAB = 3304.21 Hz, JAB = 269.02 Hz, at C3). IR (KBr, n,
c#xX_CYR_HEX_43c;-1): 1144, 1208, 1237 (C–F), 1602 (C
C
aromatic), 3069 (HC ). EIMS, m/z: 387.0 [1/2 M]+. Anal. Calc:
C, 43.43; H, 2.60; F, 53.97. Found: C, 42.87; H, 2.55.
4.4.7 1-(6H-Perfluorohexyl)-2-phenyl-propane (7). The elec-
trochemical cell was charged with 0.373 g (0.995 mmol) of
(tpy)NiBr2 and purged with argon, then an anhydrous DMF
was added via cannula and kept stirring until all precipi-
tate was dissolved. After that 2.127 g (4.975 mmol) of 6-H-
perfluoroiodohexane, 0.588 g (4.975 mmol) of a-methylstyrene
and 1.738 g (5.97 mmol) of tributyl tin hydride were added via
syringe. Electrolysis was carried out in the electrochemical cell
with separation of anode and cathode compartments at ambient
temperature under argon atmosphere at the potential of a working
electrode -1.3 V. The amount of electricity passed through the
electrolyte was 2 F per one mole of 6-H-perfluoroiodohexane
(255 mA h). After completing the electrolysis, the solution was
washed with saturated ammonium chloride (3 ¥ 50 ml) and
extracted with diethyl ether (3 ¥ 50 ml). The organic layer was
dried over magnesium sulfate, filtered and evaporated on rotary
evaporator. Residue was purified by column chromatography (SiO;
4.4.5 2,3-Dipyridyl-1,4-bis(perfluorohexyl)butane (5). The
electrochemical cell was charged with 0.356 g (0.95 mmol)
(bpy)NiBr2, 4.237 g (9.5 mmol) of perfluoroiodohexane and
1.001 g (9.5 mmol) of 2-vinylpyridine and DMF (60 ml) was
added. Electrolysis was carried out in the electrochemical cell
with separation of anode and cathode compartments at ambient
temperature under argon atmosphere at the potential of a working
electrode -1.5 V. The amount of electricity passed through the
electrolyte were 2 F per one mole of perfluoroiodohexane (510 mA
h). After completing the electrolysis, the reaction mixture was
washed with saturated ammonium chloride (3 ¥ 60 ml) and
extracted with benzene (3 ¥ 800 ml). After separation, the organic
layer was dried over magnesium sulfate and then the solvent
was removed, the crystalline residue was washed with diethyl
This journal is
The Royal Society of Chemistry 2012
Dalton Trans., 2012, 41, 165–172 | 171
©

View Article Online
hexane : CHCl3, 1 : 2) to give 1-(6H-perfluorohexyl)-2-phenyl-
propane as a colorless oily liquid. Yield 1.087 g (52%). 1H NMR
(400 MHz, C6D6): d = 1.36(s, 3H, CH3), 2.15 and 3.16 (m, 2H,
11 Y. Kobayashi, K. Yamamoto and I. Kumadaki, Tetrahedron Lett., 1979,
20, 4071.
12 G. G. Dubinina, H. Furutachi and D. A. Vicic, J. Am. Chem. Soc.,
2008, 130, 8600.
13 V. A. Soloshonok, Enantiocontrolled synthesis of fluoro-organic com-
poundsWiley: Chichester, 1999.
2
3
CH2), 3.42 (m, 1H, CH), 4.97 (tt, 1H, JHF = 51.63 Hz, JHF
=
5.34 Hz), 6.96–7.07 (m, 5H, C6H5). 13C NMR (100.6 MHz, C6D6):
d = 21.32 (CH3), 34.71 (CH2), 47.04 (CH), 107.95 (CF2H), 119.73
(CF2CH2), 140.87 (C10). IR (KBr, n, cm-1): 1136, 1212, 1243 (C–F),
1615 (C C), 3080 (HC ). EIMS, m/z: 420 [M]+. Anal. Calc.: C,
42.87; H, 2.88; F, 54.25. Found: C 42.38; H 2.49
14 K. Iseki, Tetrahedron, 1998, 54, 13887.
15 G. Resnati, Tetrahedron, 1993, 49, 9385.
16 P. Bravo and G. Resnati, Tetrahedron: Asymmetry, 1990, 1,
661.
17 T. Hayashi and V. A. Soloshonok, Tetrahedron: Asymmetry, 1994, 5,
1091.
18 D. Y. Mikhaylov, Y. H. Budnikova, T. V. Gryaznova, D. B. Krivolapov,
I. A. Litvinov, D. A. Vicic and O. G. Sinyashin, J. Organomet. Chem.,
2009, 694, 3840.
4.5 Cyclic voltammetry
Cyclic voltammograms of all complexes have been recorded in
DMF with 0.01 mol dm-3 substrate concentration, Bu4NBF4 was
used as a supporting electrolyte (0.1 mol dm-3) and a glassy
carbon electrode as a working electrode (8 mm2), the auxiliary
electrode was a platinum rod. All potentials are referenced
against the Ag/AgNO3, 10-2 M in MeCN. All complexes show
a reversible redox process on the first peak potential, which
was established to correspond to a one electron reduction by
controlled-potential coulometry (two-electron for bpy complex).
Cyclic voltammograms registration was performed with BASi
Epsilon potentiostate (USA). Scan rate was 100 mV s-1.
19 A. E. Derome, Modern NMR Techniques for Chemistry Research,
Pergamon, 1988.
20 Atta-ur-Rahman, One and Two Dimensional NMR Spectroscopy,
Elsevier: Amsterdam, 1989.
21 J. Battiste and R. A. Newmark, Prog. Nucl. Magn. Reson. Spectrosc.,
2006, 48, 1.
22 Sh. Latypov, A. Balandina, M. Boccalini, A. Matteucci, K. Usachev
and S. Chimichi, Eur. J. Org. Chem., 2008, 27, 4640.
23 Sh. K Latypov, A. V. Kozlov, E. Hey-Hawkins, A. S. Balueva, A.
A. Karasik and O. G. Sinyashin, J. Phys. Chem. A, 2010, 114,
2588.
24 Y. H. Budnikova, J. Perichon, D. G. Yakhvarov, Y. M. Kargin and O.
G. Sinyashin, J. Organomet. Chem., 2001, 630, 185.
25 C. Cannes, E. Labbe, M. Durandetti, M. Devaud and J.-Y. Ne´de´lec, J.
Electroanal. Chem., 1996, 412, 85.
26 D. G. Yakhvarov, D. I. Tazeev, O. G. Sinyashin, G. Giambastiani,
C. Bianchini, A. M. Segarra, P. Lo¨nnecke and E. Hey-Hawkins,
Polyhedron, 2006, 25, 1607.
27 A. Klein, Y. H. Budnikova and O. G. Sinyashin, J. Organomet. Chem.,
2007, 692, 3156.
28 BV Nonius, Delft, The Netherlands, 1998.
29 A. J. M. Duisenberg, J. Appl. Crystallogr., 1992, 25, 92.
30 A. J. M. Duisenberg, L. M. J. Kroon-Batenburg and A. M. M. Schreurs,
J. Appl. Crystallogr., 2003, 36, 220.
Acknowledgements
This work was supported by the RFBR grants 10-03-00335 and 09-
03-00123-a. OK is thankful to DFG grant KN240/16-1. D.A.V.
thanks the Office of Basic Energy Sciences of the U. S. Department
of Energy (DE-FG02-07ER15885).
31 G. M. Sheldrick, Acta Crystallogr., Sect. A: Found. Crystallogr., 2008,
64, 112.
32 G. M. Sheldrick, SADABS: Empirical Absorption and Correction
Software, University of Go¨ttingen, Institut fu¨r Anorganische Chemie
der Universita¨t, Tammanstrasse 4, D-3400 Go¨ttingen, Germany, 1999-
2003.
Notes and references
1 J.-A. Ma and D. Cahard, J. Fluorine Chem., 2007, 128, 975.
2 R. Filler and Y. L. Kobayashi, Organoflourine Compounds in Medicinal
Chemistry and Biologiocal Applications. ed.; Elsevier: Amsterdam,
1993.
3 R. E. Banks, B. E. Smart, and J. C. Tatlow, Organoflourine chemistry:
Principles and Commercial Applications., ed.: Plenium Press: New York,
1994.
4 J.-A. Ma and D. Cahard, Chem. Rev., 2004, 104, 6119.
5 C. F. Smith, E. J. Soloski and C. Tamborski, J. Fluorine Chem., 1974,
4, 35.
33 M. Troupel, Y. Rollin, O. Sock, G. Meyer and J. Perichon, Nouv. J.
Chim., 1986, 10, 593.
34 M. J. Frisch, G. W. Trucks, H. B. Schlegel, G. E. Scuseria, M. A.
Robb, J. R. Cheeseman, V. G. Zakrzewski, J. A. Montgomery, R. E.
Stratmann, J. C. Burant, S. Dapprich, J. M. Millam, A. D. Daniels, K.
N. Kudin, M. C. Strain, O. Farkas, J. Tomasi, V. Barone, M. Cossi, R.
Cammi, B. Mennucci, C. Pomelli, C. Adamo, S. Clifford, J. Ochterski,
G. A. Petersson, P. Y. Ayala, Q. Cui, K. Morokuma, D. K. Malick,
A. D. Rabuck, K. Raghavachari, J. B. Foresman, J. Cioslowski, J. V.
Ortiz, B. B. Stefanov, G. Liu, A. Liashenko, P. Piskorz, I. Komaromi,
R. Gomperts, R. L. Martin, D. J. Fox, T. Keith, M. A. Al-Laham, C.
Y. Peng, A. Nanayakkara, C. Gonzalez, M. Challacombe, P. M. W.
Gill, B. Johnson, W. Chen, M. W. Wong, J. L. Andres, C. Gonzalez,
M. Head-Gordon, E. S. Replogle and J. A. Pople, Gaussian 98, revision
A.3; Gaussian, Inc.: Pittsburgh, PA, 1998.
6 D. D. Denson, C. F. Smith and C. Tambroski, J. Fluorine Chem., 1973,
3, 247.
7 S. S. Dua, R. D. Howells and H. Gilman, J. Fluorine Chem., 1974, 4,
409.
8 E. K. S Liu, Inorg. Chem., 1980, 19, 266.
9 R. Mietchen, C. Hager and M. Hein, Synthesis, 1997, 2, 159.
10 A. A. Kolomeitsev, A. A. Kadyrov, J. Szczepkowska-Sztolman, M.
Milewska, H. Koroniak, G. Bissky, J. A. Barten and G.-V. Roeschen-
thaler, Tetrahedron Lett., 2003, 44, 8273.
172 | Dalton Trans., 2012, 41, 165–172
This journal is
The Royal Society of Chemistry 2012
©