Addition of perfluorooctyl iodide to alkenes. Catalysis by triphenylphosphane

Article abstract of DOI:10.1016/S0040-4020(02)00254-5

Triphenylphosphane catalyses the addition of perfluorooctyl iodide to linear and cyclic olefines.

Full text of DOI:10.1016/S0040-4020(02)00254-5

TETRAHEDRON
Pergamon
Tetrahedron 58 02002) 4061±4065
Addition of per¯uorooctyl iodide to alkenes.
Catalysis by triphenylphosphane
Maria Lumbierres, Marcial Moreno-ManÄasp and Adelina Vallribera
Á
Department of Chemistry, Universitat Autonoma de Barcelona, Cerdanyola de Valles, 08193 Barcelona, Spain
Received 4 October 2001; revised 4 January 2002; accepted 16 January 2002
AbstractÐTriphenylphosphane catalyses the addition of per¯uorooctyl iodide to linear and cyclic ole®nes. q 2002 Elsevier Science Ltd.
All rights reserved.
1. Introduction
reaction is a typical free-radical chain reaction, featuring
an initiation stepleading to the generation of the Rf radical
06) followed by propagation steps.2,3 Customarily radical-
anion 6a is believed to be an intermediate in the generation
Per and poly¯uorinated organic compounds have excep-
tional theoretical and practical interest.1 The addition of
per¯uoroalkyl iodides to ole®ns is one of the more useful
reactions aimed at the preparation of compounds heavily
loaded with ¯uorine atoms 0see 01) in Scheme 1).2 The
Â
of free radical 6. However, Saveant and co-workers have
shown that electron transfer to Rf2I and carbon±iodine
bond cleavage are concerted processes leading directly to
6 and iodide anion.4 Radical 7 can take alternative pathways
as, for example, capturing a hydrogen atom from a suitable
donor to afford directly the iodine-free compounds 4.5 In
general compounds 4 are prepared from 3 in an independent
reduction step.
The addition of per¯uoroalkyl iodides to ole®ns is mechan-
istically related to the so-called Kharasch reaction, the
addition of carbon tetrachloride and other polychlorinated
compounds to alkenes 0see 02), Scheme 1).6
Pioneer work by Brace on the addition of per¯uoroalkyl
iodides to ole®ns was performed under a typical free-radical
initiator,
azobisisobutyronitrile,2
whereas
initial
examples of the Kharasch reactions were performed
under diacyl peroxides initiation.6 However, ruthenium0II)
chloride tris-0triphenylphosphane) 01) has emerged as a
very useful catalyst for such a reaction,7 which occurs
by a non-chain sequence involving free-radical inter-
mediates.7e Moreover, Grubb's ruthenium carbene and
other ruthenium complexes are also active in the Kharasch
reaction.8
We were surprised by the fact that, in spite of the close
mechanistic relationshipbetween both reactions, no
examples have been disclosed on the use of 1 as catalyst
for the addition of per¯uoroalkyl iodides to ole®ns.
However, this addition has been induced or catalyzed by
many low-valent metal or transition metal species as well
as by other non-metallic sources of radicals, excellent
summaries of methods being available.3
Scheme 1. General features of the addition of per¯uoroalkyl iodides or
tetrachloromethane to ole®ns.
Keywords: poly¯uorinated ole®nes; catalysis; triphenylphosphane; free
radical.
p
Corresponding author. Tel.: 134-935811254; fax: 134-935811265;
e-mail: marcial.moreno@uab.es
0040±4020/02/$ - see front matter q 2002 Elsevier Science Ltd. All rights reserved.
PII: S0040-4020002)00254-5

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M. Lumbierres et al. / Tetrahedron 58 ,2002) 4061±4065
2. Results
stereochemistry, and 10d as a mixture of diastereoisomers.
Using a 18% of catalyst 2 the yield of 10c increased to 57%
working at room temperature for 72 h. Diole®n 9g posses a
problem. It is known that diallyl ether reacts to afford a
cyclic tetrahydrofuran derivative by trapping the inter-
mediate secondary radical by the second double bond to
afford a primary radical by an 5-exo-trig cyclization
0see 01), Scheme 3).10b In our case trapping the intermediate
radical would imply either the formation of a secondary
radical in a cyclopentane ring by a disfavored 5-endo-trig
cyclization step0see 02), Scheme 3) or the formation of a
four-membered ring by a favored 4-exo-trig cyclization
0see 03), Scheme 3). However, no cyclization took place.
Instead, formation of 10g occurred. The low yield of the
reaction can be attributed to the use of a defect of 9g to
favor reaction of both ole®ns. Monitoring of the reaction
revealed the saturation of one double bond while the second
one was still present. Prolonged reaction time led to the
formation of both diastereoisomers 10g as the only detected
reaction products.
At this point we decided to explore the use of the ruthenium
derivative 1. We have recently found that triphenyl-
phosphane 02) is the actual catalyst in the putative catalysis
by 1 or by RuH20PPh3)4 for the non-radical conjugate
additions of b-dicarbonyl compounds.9 Our initial studies
on the addition of per¯uorooctyl iodide 08) to ole®ns
catalyzed by 1 were run in parallel with experiments in
which only triphenylphosphane 2 was introduced as
possible catalyst. To our relative surprise, we immediately
realized that 2 catalyzes the addition of 8 to ole®ns
0Scheme 2). A closer scrutiny of the literature revealed
also that catalysis by 2 is not without precedent.10 However,
we decided to study further the potential of 2 as catalyst as
well as to look at some mechanistic aspects of its behavior.
Our results are in Scheme 2. Monosubstituted ole®ns react
at room temperature with 8 in the presence of only 5% molar
2. Thus, 10-undecenoic acid 09b) and 1-octene 09f) afford
10b and 10f in good to excellent yields. A 1,1-disubstituted
ole®n 09e) was also active and afforded 10e in useful yield.
An open chain 1,2-disubstituted ole®n: trans-4-octene, as
well as 1H,1H,2H-per¯uoro-1-decene, vinyl acetate, and
isopropenyl acetate were sluggish and gave no useful
reactions. However, cyclic ole®ns were active enough to
afford preparatively useful results. Thus, norbornene 09a)
gave an excellent yield of 02RS,3SR)-2-iodo-3-per¯uoro-
octylnorbornane, 10a. trans-Stereochemistry for 10a was
determined by 2D-COSY and 2D-NOESY NMR experi-
ments. This was the only isolated isomer. Monocyclic
ole®ns such as cyclopentene and cyclohexene were less
reactive, affording 10c as one diastereoisomer of unknown
Reactions with styrene and with 1,3-cyclohexadiene failed.
It seems that intermediate benzylic and allylic radicals 7 are
too stable to progress according to the equations of Scheme
1. Only in one case, working under catalysis by ruthenium
species 1 we could isolate minor amounts of compound 11
0Scheme 3). This exempli®es another possible pathway for
radicals 7, namely, reaction with a second ole®n initiating a
polymerization pathway. In any case, the reaction with
styrene was erratic and it was given up. The reaction of
9a with 8 in the presence of one equivalent of distilled
styrene did not progress, styrene acting as a radical trap,
probably at the level of radical 6. The same reaction is
Scheme 2. All reactions were performed in acetonitrile at room temperature in the presence of 5% molar 2. For 10a±f 2.5-fold molar excess of ole®n was used.
For 10g, fourfold molar excess of 8 was used.

M. Lumbierres et al. / Tetrahedron 58 ,2002) 4061±4065
4063
Scheme 3.
also stopped in the presence of 1,3-dinitrobenzene, probably
by direct electron transfer from 2 to dinitrobenzene.
and carbon tetrachloride or carbon tetrabromide did not
take place under triphenylphosphane catalysis, in the
presence and in the absence of acetonitrile. Therefore,
ruthenium species are truly catalysts for the Kharasch reac-
tion. However, phosphorus centered radicals have recently
been suggested as intermediates in a Kharasch reaction.23
The simultaneous presence of triphenylphosphane 02) and
alkyl iodides 10 makes it possible, in principle, the forma-
tion of phosphonium salts. However, a mixture of 10f and 2
in benzene did not give reaction at room temperature or at
re¯ux for 144 h 031P NMR monitoring). More important, the
reaction of 8 with 9f was reproduced in the NMR probe in
CD3CN solvent; 31P NMR monitoring showed that 2 was the
only signi®cant phosphorus species detectable 0d ca.
30.6 ppm), only triphenylphosphane oxide 0d ca. 4.1 ppm)
appeared slowly as a result of the spurious oxidation of 2.
This is an indication that electron transfer from 2 to 8 is the
slow stepof the catalytic cycle.
4. Experimental
4.1. '2RS,3SR)-2-Iodo-3-per¯uorooctylnorbornane
'10a): typical procedure
A mixture of triphenylphosphane 2 00.092 g, 0.4 mmol),
norbornene 9a 01.644 g, 17.5 mmol), per¯uorooctyl iodide
8 01.85 mL, 7.0 mmol), and acetonitrile 02.1 mL) was
magnetically stirred under argon atmosphere for 48 h. The
mixture was evaporated to afford a white solid residue,
which was passed through a column of silica gel with aceto-
nitrile as eluent to afford 10a 04.25 g, 95%), mp35±36 8C
0Lit.24 mp40±42 8C); IR 0KBr) 2964, 2873, 1202, 1151,
Electron transfer from 2 implies the formation of the
radical-cation 12. This species has been invoked in a
number of occasions: in electron transfer to tetracyano-
quinodimethane,11 in the photochemical decomposition of
phosphonium salts,12,13 and in the dediazoniation of arene-
diazonium salts with triphenylphosphane.14
1
995 cm21; H NMR 0CDCl3, 500 MHz) d 1.30±1.35 0m,
2H), 1.60±1.71 0m, 3H), 1.87±1.92 0m, 1H), 2.37±2.44
0dt, Jˆ11.6 and 3.9 Hz, 1H), 2.44 0s, 1H), 2.49 0s, 1H),
4.31±4.32 0m, 1H, CHI); 13C NMR 0CDCl3, 62.9 MHz) d
25.9, 27.4, 29.7, 35.0, 37.9, 44.6, 55.7 0t, Jˆ20 Hz, CHCF2),
109.8±123.0 0C8F17); MS 0m/z) 513 0M2I, 100), 115 028),
77 020), 67 025), 41 035).
3. Conclusion
Triphenylphosphane is an ef®cient catalyst for additions of
per¯uoroalkyl iodides to ole®ns. Molar percentage of
catalysts, temperature, and extraction procedures have
been improved with respect to the previously reported.10
In some cases it has been shown that the putative catalytic
action of transition metal complexes is really due to
phosphane stabilizing ligands.9,15±18 This rises a question
on the contribution of triphenylphosphane to the proposed
catalytic activity of tetrakis0triphenylphosphane)palladium,
Pd0PPh3)4 in the additions of per¯uoroalkyl iodides to
ole®ns,19±21 since it is known that Pd0PPh3)4 is, in solution,
in equilibrium with Pd0PPh3)42n and nPPh3.22
4.1.1. 12,12,13,13,14,14,15,15,16,16,17,17,18,18,19,19,19-
Heptadeca¯uoro-10-iodononadecanoic acid, 10b. Acid
10b precipitated out after 70 h reaction. It was ®ltered and
recrystallized from acetonitrile to afford 3.81 g 075%) of
pure compound: mp 65±688C 0Lit.25 mp70±71 8C); IR
0KBr) 3500±2500, 2928, 2853, 1703, 1202, 1148 cm21
;
1H NMR 0CDCl3, 250 MHz) d 1.24±1.40 0m, 10H), 1.63±
1.69 0m, 2H), 1.76±1.87 0m, 2H), 2.37 0t, Jˆ7.0 Hz, 2H),
2.70±3.03 0m, 2H, CH2±CF2), 4.32±4.38 0m, 1H, CHI); 13
C
NMR 0CDCl3, 62.9 MHz) d 21.2, 25.0, 28.8, 29.3, 29.5,
29.5, 29.9, 34.4, 40.7, 42.1 0t, Jˆ21 Hz, CH2±CF2),
106.8±119.8 0C8F17), 180.4.
Moreover, we performed complementary experiments
which showed that Kharasch reactions between 1-octene

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M. Lumbierres et al. / Tetrahedron 58 ,2002) 4061±4065
4.1.2. 1-Iodo-2-per¯uorooctylcyclopentane, 10c. This
compound was liquid. Attempted distillation at
4.1.6. 1,1,1,2,2,3,3,4,4,5,5,6,6,7,7,8,8,15,15,16,16,17,17,
18,18,19,19,20,20,21,21,22,22,22-tetratria¯uoro-10-13-
diododocosane, 10g. For preparation of this compound
molar ratio 9g:8 was 1:4. After evaporation the formed
solid was washed with HFE7100, then with hot acetonitrile,
and ®ltered while hot to afford 10g 01.425 g, 17%) as a
mixture of diastereoisomers: mp90±91 8C 0from aceto-
a
0.2 mmHg failed. The liquid was treated with per¯uoro-
octane and the precipitate 0phosphorus compounds) was
®ltered off and washed with more per¯uorooctane. The
¯uorinated solvent phase was evaporated and the residue
was pure 10c 01.57 g, 36%): IR 0®lm) 2971, 1206,
1
1149 cm21; H NMR 0CDCl3, 500 MHz) d 1.82±1.87 0m,
nitrile); IR 0KBr) 1202, 1149 cm21 1H NMR 0CDCl3,
;
2H), 1.93±2.06 0m, 2H), 2.12±2.24 0m, 2H), 3.21±3.27 0m,
1H, CH±CF2), 4.52±4.53 0m, 1H, CH±CI); 13C NMR
0CDCl3, 62.9 MHz) d 18.4, 25.3, 26.3, 41.1, 54.0 0t,
Jˆ21 Hz, CH±CF2), 106.1±124.7 0C8F17); MS 0m/z) 487
0M2I, 70), 467 0100), 117 021), 67 059), 41 022). Anal.
Calcd for C13H8F17I: C, 25.43; H, 1.31; found: C, 25.37;
H, 1.31.
250 MHz) d 1.99±2.27 0m, 4H), 2.75±3.06 0m, 4H,
CH2-CF2), 4.37±4.41 0m, 2H, CHI); 13C NMR 0CDCl3,
62.9 MHz) d 17.2, 17.5, 40.4, 42.1 0t, Jˆ22 Hz, CH2±
CF2), 42.3 0t, Jˆ21 Hz, CH2±CF2), 110±130 0C8F17);
Anal. Calcd for C22H10F34I2: C, 22.51; H, 0.86; found: C,
22.55; H, 0.75.
4.1.3. 1-Iodo-2-per¯uorooctylcyclohexane, 10d. This
compound is a mixture of diastereoisomers 065:35). After
evaporation, the liquid residue was treated with cold
per¯uorooctane 0ice bath), the formed solid phase 02 plus
triphenylphosphane oxide) was ®ltered off, and the solvent
was evaporated, then the residue was distilled 0758C/
0.26 mmHg) to afford pure 10d 00.92 g, 21%): IR 0®lm)
Acknowledgements
Financial support from DGESIC 0Project PB98-0902) and
CIRIT±Generalitat de Catalunya 0Projects SGR98-0056
and SGR2000-0062, and predoctoral scholarship to M. L.)
is gratefully acknowledged.
1
2945, 2867, 1452, 1327, 1202, 1149, 964 cm21; H NMR
0CDCl3, 250 MHz) d 1.37±1.97 0m, 8H), 2.21±2.26 0m, 1H,
CH±CF2, major diastereoisomer), 2.64±2.78 0m, 1H, CH±
CF2, minor diastereoisomer), 4.72 0m, 1H, CHI, major
diastereoisomer), 4.98±4.99 0m, 1H, CHI, minor diastereo-
isomer); 13C NMR 0CDCl3, 62.9 MHz) d 21.3, 21.8, 22.0,
22.7, 25.2, 27.3 0t, Jˆ4 Hz), 34.7, 37.4, 44.6 0t, Jˆ21 Hz,
CH±CF2, major diastereoisomer), 45.2 0t, Jˆ20 Hz,
CH±CF2, minor diastereoisomer, 103.4±124.6 0C8F17);
MS 0m/z) 501 0M2I, 9), 131 040), 81 0100), 41 095). Anal.
Calcd for C14H10F17I: C, 26.77; H, 1.60; found: C, 26.60; H,
1.64.
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