Electrocatalytic fluoroalkylation of olefins

Article abstract of DOI:10.1016/j.jorganchem.2009.08.015

An efficient nickel-catalyzed method devoted to the direct addition of perfluoroalkyl halides (I, Br) to α-methylstyrene is described. This procedure allows for synthesis of compounds resulting from addition-dimerization in good yields.

Full text of DOI:10.1016/j.jorganchem.2009.08.015

Journal of Organometallic Chemistry 694 (2009) 3840–3843
Contents lists available at ScienceDirect
Journal of Organometallic Chemistry
journal homepage: www.elsevier.com/locate/jorganchem
Communication
Electrocatalytic fluoroalkylation of olefins
a
a
a
b
D.Y. Mikhaylov a, Y.H. Budnikova a, , T.V. Gryaznova , D.V. Krivolapov , I.A. Litvinov , D.A. Vicic ,
*
O.G. Sinyashin a
a A.E. Arbuzov Institute of Organic and Physical Chemistry, Kazan Scientific Center of Russian Academy of Sciences, 8, Arbuzov Str., 420088 Kazan, Russian Federation
b Department of Chemistry, University of Hawaii, 2545 McCarthy Mall, Honolulu, HI 96822, USA
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 28 May 2009
Received in revised form 10 August 2009
Accepted 11 August 2009
Available online 15 August 2009
An efficient nickel-catalyzed method devoted to the direct addition of perfluoroalkyl halides (I, Br) to a-
methylstyrene is described. This procedure allows for synthesis of compounds resulting from addition-
dimerization in good yields.
Ó 2009 Elsevier B.V. All rights reserved.
Keywords:
Nickel complexes
Electrosynthesis
Fluoroalkylation
Olefin
1. Introduction
increasingly important in the medicinal, materials, and agricultural
fields [10–12], yet their chemical syntheses remain problematic. In
The conjugate addition of organometallic reagents to electron-
deficient olefins is a powerful method for formation of new car-
bon–carbon bonds, yielding Michael adducts which represent
useful synthons to further organic transformations [1]. Moreover,
such methodology can be expanded to include the addition of rad-
fact, while there has been many advances in incorporating the sim-
plest fluoroalkyl group (trifluoromethyl) stoichiometrically into or-
ganic electrophiles [13–22], only two catalytic processes have ever
been reported [23,24]. Moreover, most of the catalytic and stoichi-
ometric processes employ expensive sources of the fluoroalkyl
group, limiting their use in a large-scale process. The goal of the
work presented was to demonstrate the proof-in-principle that
selective additions of inexpensive perfluoroalkyl synthons to ole-
fins can occur electrocatalytically under mild conditions.
ical substrates to a,b-unsaturated compounds , and in many cases
these radical additions proceed enantioselectively [2]. The most
commonly used methods to generate radicals for olefin addition
chemistry involve the oxidation of trialkylboranes [2], oxidation
of organozinc reagents [3], and the reduction of alkyl halides by
low valent metal complexes [4]. The last of these methods can be
made catalytic in metal complex upon the introduction of a chem-
ical reducing agent [4] or by electrochemical means [5,6]. Some of
the metals capable of generating organic radicals for olefin addi-
tion chemistry via electrocatalytic reduction are [Ni(tet a)]2+ [5],
CoBr2(py)x [7,8], NiBr2(py)x [9] (tet a = 5,5,7,12,12,14-hexa-
methyl-1,4,-8, 11-tetra-azacyclotetradecan; py = pyridine).
With a few exceptions [4,7], most of the substrates used in rad-
ical olefin addition chemistry are unfunctionalized, thereby limit-
ing the scope of the methodology. In efforts to further expand
the scope we set out to explore the possibility of using electro-
chemical methods to add perfluoroalkyl radicals across double
bonds to generate new functionalized fluorocarbons. This class of
substrates was chosen because fluoroalkyl moieties are becoming
2. Results and discussion
The electrochemical reduction of Ni(II) to Ni(0) complexes is a
key stage in many electrocatalytic reactions involving
a-organo-
nickel complexes [25–28], so NiBr2bpy (bpy = bipyridine) was tar-
geted for use in coupling fluoroalkyl halides and olefins. We have
discovered that the joint electrolysis of NiBr2bpy and fluoroalkyl
halides (RfX, X = I, Br) in dimethylformamide in the presence of
a-methylstyrene in cathode compartment of electrolizer (potential
kept at ꢀ1.2 V vs. SCE to regenerate Ni(0)) yields new organic prod-
ucts in which the perfluoroalkyl group has added to the olefin sub-
strate (Eq. (1)). The course of the reaction was followed by
combined gas chromatography mass-spectrometry. The reactions
can be run at 10 mol% nickel catalyst to afford product in moderate
yields. Interestingly, the end-product is a dimer, bearing two per-
fluoroalkyl and two olefin synthons, unlike all previously described
cases of electrocatalytic additions to olefins [1,5,7–9,25].
* Corresponding author. Tel.: +7 9172931629; fax: +7 8432732253.
E-mail address: yulia@iopc.knc.ru (Y.H. Budnikova).
0022-328X/$ - see front matter Ó 2009 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2009.08.015

D.Y. Mikhaylov et al. / Journal of Organometallic Chemistry 694 (2009) 3840–3843
3841
are underway to unravel more mechanistic features of these unu-
sual addition reactions.
N
N
NiBr2
ð2Þ
ð1Þ
Ph
Ph
Rf
+
RfX
Rf
2e per RfX
DMF
Ph
RfX = C6F13
I
3. Conclusion
or H(CF2)6Br
The new method reported herein allows for the introduction of
inexpensive perfluoroalkyl synthons with long Rf chains to olefins.
This work is the first time that dimer formation occurs under elec-
trocatalytic conditions. Further investigations in this area will
hopefully afford ways to control monomer/dimer formation as well
as stereochemistry of the resulting addition products.
The structure of 2,3-dimethyl-2,3-diphenyl-1,4-bis(perflu-
orohexyl)butane (1) and 2,3-dimethyl-2,3-diphenyl-1,4-bis(6-H-
perfluorohexyl)butane (2) were confirmed by X-ray analysis
(Fig. 1). Both molecules are located on a special position at the cen-
ter of symmetry in the asymmetric unit cell, affording two frag-
ments bearing chiral centers. Due to coincidence of molecular
centers with the centers of inversion, each molecule is the meso
form.
4. Experimental
Several possible reaction mechanisms must be considered,
including traditional organometallic mechanisms involving oxida-
tive addition and reductive elimination as well as traditional radi-
cal chain mechanisms. We can, however, note several important
features of the addition reactions. First, no reaction occurs in the
absence of a nickel catalyst. Second, the use of NH4ClO4 as a proton
source does not result in monomer formation, inconsistent with a
mechanism like that shown in Eq. (2), which has literature prece-
dence [5,29–31]. Finally, a control experiment demonstrates that
reduction of RfX at the electrode in the absence of nickel and the
presence of olefin does not result in olefin addition products or
Rf dimerization according to gas chromatography. Further studies
4.1. X-ray analysis
Data were collected on a Bruker Smart Apex II CCD diffractom-
eter using graphite monochromated Mo Ka (0.71073 Å) radiation.
Details concerning data collection and refinement are given in
Table 1. Data were corrected for absorption using SADABS [32] pro-
gram. All non-hydrogen atoms were refined anisotropically. The
hydrogen atoms were calculated and refined as riding atoms. Data
collection images were indexed, integrates, and scaled using the
APEX2 data reduction package [33]. Structure solution and refine-
ment SIR [34], SHELXL97 [35], WINGX [36] program. Pictures were gen-
erated with ORTEP3 for Windows [37]. In molecules 1 and 2
Fig. 1. Molecular structure of ,3-dimethyl-2,3-diphenyl-1,4-bis(perfluorohexyl)butane (1) and 2,3-dimethyl-2,3-diphenyl-1,4-bis(6-H-perfluorohexyl)butane (2). Disordered
atoms were omitted for clarity, thermal ellipsoids drawn at 30% probability.

3842
D.Y. Mikhaylov et al. / Journal of Organometallic Chemistry 694 (2009) 3840–3843
Table 1
Crystallographic data for 1 and 2.
Compound
1
2
Empirical formula
Formula weight
C30H20F26
874.46
C30H22F24
838.48
Crystal color/habitus
Colorless/prism
Colorless/prism
Unit cell dimensions
a (Å)
b (Å)
c (Å)
14.9307(16)
11.1647(12)
10.3937(11)
14.984(7)
11.052(6)
10.416(5)
b (°)
103.548(1)
1684.4(3)
1.724
0.201
103.958(7)
1674(1)
1.663
0.191
V (nm3)
Density (calcd) (Mg mꢀ3
)
Absorption coefficient (mmꢀ1
)
F(0 0 0)
868
836
h Range for data collection (°)
Index ranges
Reflections collected
2.30–26.0
2.32–26.0
ꢀ18 6 h 6 17, ꢀ13 6 k 6 13, ꢀ12 6 l 6 12
ꢀ18 6 h 6 18, ꢀ13 6 k 6 13, ꢀ12 6 l 6 12
12 447
12 397
Independent reflections
Restraints/parameters
Goodness of fit (GOF) on F2
3302 [Rint = 0.0217]
109/373
1.241
3277 [Rint = 0.0356]
68/349
1.028
Final R indices [I > 2
R indices (all data)
r
(I)]
R1 = 0.0775, wR2 = 0.2128
R1 = 0.1033, wR2 = 0.2353
0.588/ꢀ0.386
R1 = 0.0724, wR2 = 0.1991
R1 = 0.1335, wR2 = 0.2485
0.400/ꢀ0.296
Largest difference in peak/hole (e Åꢀ3
)
Temperature 293 K, wavelength
0.10 ꢂ 0.10 ꢂ 0.10; Z 2 (molecule in special position).
k
0.71073 pm, crystal system monoclinic, space group P21/c; crystal size (mm). Compound 1. 0.30 ꢂ 0.20 ꢂ 0.20. Compound 2.
fluorine atoms of fluoroalkyl substituents are disordered in crystals
one mole of perfluoroiodohexane (454 mA h). After completing
the electrolysis, the solution was washed with distilled water
(100 ml) and extracted with benzene (3ꢁ ꢂ 100 ml). The organic
layer was dried over magnesium sulfate and filtered. The residual
solution was concentrated under reduced pressure and left over-
night, then the white solid precipitated from the mixture, filtered
and dried in vacuo to give 2,3-dimethyl-2,3-diphenyl-1,4-bis(per-
fluorohexyl)butane. Yield 2.6 g (70%). m.p.: 160–162 °C. 1H NMR
(400 Hz, C6D6): d = 1.45 and 1.46 (two s, 6H, CH3), 2.25 and 3.23
and were refined with occupancy 0.598(0.402) for
1 and
0.537(0.463) for 2, respectively.
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 fractionation distilla-
tion over melting potash. Perfluoroiodohexane and 6-H-perfluo-
robromohexane were purchased from P&M Invest and used
(m, 4H, CH2), 7.07–7.19 (m, 10H, C6H5). IR (KBr, m
, cmꢀ1): 1144,
1208, 1237 (C–F), 1602 (C@C aromatic), 3069 (HC@). EIMS, m/z
(rel. intensity): 437.0 (1/2M+). Anal. Calc.: C, 41.19; H, 2.29; F,
56.52. Found: C, 41.28; H, 2.45%.
without further purification.
a-Methylstyrene was procured from
Acros Organics. Tetrabutylammonium tetrafluoroborate was pur-
chased from Aldrich and recrystallized from diethylether. NiBr2bpy
were prepared according reported procedure [26]. Preparative
electrolyses were performed by means of the direct current source
B5-49 in thermostatically controlled cylindrical divided 40 ml elec-
trolyser (a three-electrode cell). Platinum with surface areas of
20 cm2 was used as a cathode. The working electrode potential
was determined using reference electrode SCE. During electrolysis,
the electrolyte was stirred with a magnetic stirrer. The saturated
solution of Et4NBF4 in DMA was used as anolyte, and the anode
compartment was separated by ceramic membrane. The 1H NMR
spectra were recorded on a Bruker MSL-400 (400 MHz). IR spectra
of the compounds were recorded on a FTIR spectrometer ‘‘Vector
22’’ (Bruker) in the 400–4000 cmꢀ1 range. Solid samples were pre-
pared as KBr pellets. Mass spectra were recorded in EI mode using
ThermoQuest TRACE MS.
4.3.2. Electrosynthesis of 2,3-dimethyl-2,3-diphenyl-1,4-bis(6-H-
perfluorohexyl)butane
A solution for electrolysis was prepared by mixing 0.576 g
(1.5 mmol) NiBr2bpy, 5.86 g (15 mmol) 6-H-perfluorobromohex-
ane and 1.81 g (15 mmol) a-methylstyrene in DMF (100 ml). Elec-
trolysis was carried out in an electrochemical cell with separation
of anode and cathode compartments at ambient temperature un-
der argon atmosphere at the potential of a working electrode
ꢀ1.2 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 ꢂ 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 mix-
ture, filtered and dried in vacuo to give 2,3-dimethyl-2,3-diphenyl-
1,4-bis(6-H-perfluorohexyl)butane. Yield 3.2 g (49.6%). 1H NMR
(400 Hz, C6D6): d = 1.34 and 1.35 (two s, 6H, CH3), 2.17 and 3.13
4.3. Preparative electrolyses
4.3.1. Electrosynthesis of 2,3-dimethyl-2,3-diphenyl-1,4-
bis(perfluorohexyl)butane
A solution for electrolysis was prepared by mixing 0.317 g
(0.85 mmol) NiBr2bpy, 7.54 g (16 mmol) perfluoroiodohexane and
2
3
(m, 4H, CH2), 4.94 (tt, 2H, JHF 51.62 Hz, JHF 5.12 Hz), 6.96–7.07
(m, 10H, C6H5). IR (KBr, m
, cmꢀ1): 1145, 1208, 1238 (C–F), 1600
(C@C), 3071 (HC@). EIMS, m/z: 419.0 (1/2M+). Anal. Calc.: C,
42.96; H, 2.62; F, 54.41. Found: C, 42.58; H, 2.51%.
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 ꢀ1.2 V. The
amounts of electricity passed through the electrolyte were 2F per
Acknowledgement
This work was supported by the RFBR grant N 07-03–00213.

D.Y. Mikhaylov et al. / Journal of Organometallic Chemistry 694 (2009) 3840–3843
[15] Y. Chang, C. Cai, Chin. Chem. Lett. 16 (2005) 1313.
3843
Appendix A. Supplementary material
[16] Y. Chang, C. Cai, Chem. Lett. 34 (2005) 1440.
[17] Y. Chang, C. Cai, Tetrahedron Lett. 46 (2005) 3161.
[18] Q. Chen, J. Duan, Tetrahedron Lett. 34 (1993) 4241.
[19] Y. Kobayashi, I. Kumadaki, S. Sato, N. Hara, E. Chikami, Chem. Pharm. Bull. 18
(1970) 2334.
[20] B.R. Langlois, N. Roques, J. Fluorine Chem. 128 (2007) 1318.
[21] C. Liu, Q.-Y. Chen, Eur. J. Org. Chem. (2005).
[22] M. Schlosser, Angew. Chem., Int. Ed. 45 (2006) 5432.
[23] T. Kitazume, N. Ishikawa, Chem. Lett. (1982) 137.
[24] M. Oishi, H. Kondo, H. Amii, Chem. Commun. (Cambridge, United Kingdom)
(2009) 1909.
CCDC 720933 and 720934 contain the supplementary crystallo-
graphic data for this paper. These data can be obtained free of
charge from The Cambridge Crystallographic Data Centre via
www.ccdc.cam.ac.uk/data_request/cif. Supplementary data associ-
ated with this article can be found, in the online version, at
doi:10.1016/j.jorganchem.2009.08.015.
[25] J.-Y. Nedelec, J. Perichon, M. Troupel, in: E. Steckhan (Ed.), Topics in Current
Chemistry, vol. 185, Springer-Verlag, Berlin, 1997, p. 141.
[26] A. Klein, Y.H. Budnikova, O.G. Sinyashin, J. Organomet. Chem. 692 (2007)
3156–3166.
[27] Y.H. Budnikova, J. Perichon, D.G. Yakhvarov, Y.M. Kargin, O.G. Sinyashin, J.
Organomet. Chem. 630 (2001) 185.
References
[1] P. Perlmutter, Conjugate Addition Reactions in Organic Synthesis, Pergamon
Press, Oxford, 1992.
[2] M.P. Sibi, S. Manyem, J. Zimmerman, Chem. Rev. 103 (2003) 3263.
[3] K.-I. Yamada, M. Maekawa, T. Akindele, M. Nakano, Y. Yamamoto, K. Tomioka, J.
Org. Chem. 73 (2008) 9535.
[28] A. Jutand, Chem. Rev. 108 (2008) 2300.
[29] S. Ozaki, H. Matsushita, H. Ohmori, J. Chem. Soc., Chem. Commun. (1992) 1120.
[30] S. Ozaki, H. Matsushita, H. Ohmori, J. Chem. Soc., Perkin Trans. 1 (1993) 2339.
[31] S. Ozaki, I. Horiguchi, H. Matsushita, H. Ohmori, Tetrahedron Lett. 35 (1994)
725.
[4] H. Gong, R.S. Andrews, J.L. Zuccarello, S.J. Lee, M.R. Gagne, Org. Lett. 11 (2009)
879.
[5] S. Ozaki, H. Matsushita, H. Ohmori, J. Chem. Soc., Perkin Trans. 1 (1993) 649.
[6] C. Gosden, D. Pletcher, J. Organomet. Chem. 186 (1980) 401.
[7] P. Gomes, C. Gosmini, J. Perichon, J. Org. Chem. 68 (2003) 1142.
[8] P. Gomes, O. Buriez, E. Labbe, C. Gosmini, J. Perichon, J. Electroanal. Chem. 562
(2004) 255–260.
[32] G.M. Sheldrik, SADABS
, Program for Empirical X-ray Absorption Correction,
Bruker-Nonius, 1990–2004.
[33] APEX2 (Version 2.1), SAINTPLUS. Data Reduction and Correction Program (Version
7.31A), Bruker Advanced X-ray Solutions, BrukerAXS Inc., Madison, Wisconsin,
USA, 2006.
[34] A. Altomare, G. Cascarano, C. Giacovazzo, D. Viterbo, Acta Crystallogr., Sect. A
47 (1991) 744.
[9] S. Condon-Gueugnot, E. Leonel, J.-Y. Nedelec, J. Perichon, J. Org. Chem. 60
(1995) 7684.
[10] R. Filler, Y.L. Kobayashi (Eds.), Organoflourine Compounds in Medicinal
Chemistry and Biological Applications, Elsevier, Amsterdam, 1993.
[11] R.E. Banks, B.E. Smart, J.C. Tatlow (Eds.), Organoflourine chemistry: Principles
and Commercial Applications, Plenum Press, New York, 1994.
[12] J.-A. Ma, D. Cahard, Chem. Rev. 104 (2004) 6119–6146.
[13] G.G. Dubinina, H. Furutachi, D.A. Vicic, J. Am. Chem. Soc. 130 (2008) 8600.
[14] G.G. Dubinina, J. Ogikubo, D.A. Vicic, Organometallics 27 (2008) 6233.
[35] G.M. Sheldrick, SHELXL97
A Computer Program for Crystal Structure
Determination, University for Göttingen, 1997.
[36] L.J. Farrugia, J. Appl. Crystallogr. 32 (1999) 837.
[37] L.J. Farrugia, Appl. Crystallogr. 30 (1997) 565.