Synthesis of phosphonium salts - Phosphine structure and inorganic salts effects

Article abstract of DOI:10.1080/10426500701545950

Solvent-free reactions of 2- and 3-halopyridines with PPh3, PBu3, and PCy3 were studied under conventional heating, as well as under microwave irradiation. No difference was observed in the reaction course between classical and microwave reactions. 2-Bromopyridine gave quantitative yields of 2-pyridyltriphenylphosphonium bromide within few minutes at 190C. Equimolar amounts of some inorganic salts (LiPF6, LiOTf, LiBr, NaPF6, KPF6) were necessary for the reactions of the other 2-halopyridines. 3-Halopyridines did not react with PPh3 even in the presence of LiPF6. Their reactions with PCy3 in the presence of LiPF6 resulted in the quantitative formation of dicyclohexylphosphine oxide.

Full text of DOI:10.1080/10426500701545950

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Synthesis of Phosphonium
Salts—Phosphine Structure and
Inorganic Salts Effects
Mária Mečiarová a , Štefan Toma a , André Loupy b &
Branislav Horváth c
a Department of Organic Chemistry, Faculty of
Natural Sciences, Comenius University, Bratislava,
Slovakia
b Laboratoire des Réactions Sélectives sur Supports,
Université de Paris-Sud, Institut de Chimie
Moléculaire et des Matériaux d'Orsay, Orsay, France
c Institute of Chemistry, Faculty of Natural Sciences,
Comenius University, Bratislava, Slovakia
Published online: 20 Feb 2008.
To cite this article: Mária Mečiarová , Štefan Toma , André Loupy & Branislav Horváth
(2007): Synthesis of Phosphonium Salts—Phosphine Structure and Inorganic Salts
Effects, Phosphorus, Sulfur, and Silicon and the Related Elements, 183:1, 21-33
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Phosphorus, Sulfur, and Silicon, 183:21–33, 2008
Copyright © Taylor & Francis Group, LLC
ISSN: 1042-6507 print / 1563-5325 online
DOI: 10.1080/10426500701545950
Synthesis of Phosphonium Salts—Phosphine Structure
and Inorganic Salts Effects
1
1
2
ˇ
´
´
ˇ
´
´
Maria Meciarova, Stefan Toma, Andre Loupy,
3
and Branislav Horvath
1Department of Organic Chemistry, Faculty of Natural Sciences,
Comenius University, Bratislava, Slovakia
2Laboratoire des Re´actions Se´lectives sur Supports, Universite´ de
Paris-Sud, Institut de Chimie Mole´culaire et des Mate´riaux d’Orsay,
Orsay, France
3Institute of Chemistry, Faculty of Natural Sciences, Comenius
University, Bratislava, Slovakia
Solvent-free reactions of 2- and 3-halopyridines with PPh3 , PBu3 , and PCy3 were
studied under conventional heating, as well as under microwave irradiation. No
difference was observed in the reaction course between classical and microwave reac-
tions. 2-Bromopyridine gave quantitative yields of 2-pyridyltriphenylphosphonium
bromide within few minutes at 190◦C. Equimolar amounts of some inorganic salts
(LiPF6 , LiOTf, LiBr, NaPF6 , KPF6 ) were necessary for the reactions of the other
2-halopyridines. 3-Halopyridines did not react with PPh3 even in the presence of
LiPF6 . Their reactions with PCy3 in the presence of LiPF6 resulted in the quanti-
tative formation of dicyclohexylphosphine oxide.
Keywords Phosphonium salts; inorganic salt effects; phosphine structure effects;
halopyridines; SNAr mechanism; microwave irradiation
INTRODUCTION
In our previous work,1 we examined the reactions of neutral (PhCH2Cl
and PhCH2Br) and ionic (PhCH2N+Me3Cl−) benzylating agents with
phosphines. We have found that the effect of microwave irradia-
tion on these reactions depended essentially on the leaving group.
Received January 12, 2007; accepted June 29, 2007.
This work was carried out under the auspices of COST D32 project No. 0010/04 and
Slovak grant agency VTP grant No. 1012/2003. NMR measurements were performed on
the equipment supported by the Slovak State Program Project No. 2003SP200280203.
ˇ
Address correspondence to Stefan Toma, Department of Organic Chemistry, Fac-
ulty of Natural Sciences, Comenius University, SK-842 15 Bratislava, Slovakia. E-mail:
toma@fns.uniba.sk
21

22
M. Mecˇiarova´ et al.
Rather poor acceleration of the reaction was observed with benzyl bro-
mide, more pronounced with benzyl chloride and high with benzyl tri-
alkylammonium salts. The solvent-free reaction of tributylphosphine
with PhCH2N+Me3Cl− occurred only under microwave irradiation. Mi-
crowave reaction with PBu3 (100◦C, 10 min) gave PhCH2P+Bu3Cl−
quantitatively.
Solid-liquid phase transfer catalysis coupled with microwave irradia-
tion was shown to be an efficient method for SNAr reaction of quinoline
and pyridine halides with potassium methoxide or phenoxide.2,3 Mi-
crowave acceleration of the reaction was observed for phenoxylation.4
These earlier results, as well as the fact that there was just one paper
published on the reactions of halopyridines with triphenylphosphine,5
prompted us to study SNAr reactions of pyridine halides with sev-
eral phosphines (PPh3, PBu3, and PCy3) under solvent-free condi-
tions, both under classical heating, as well as under microwave
irradiation.
RESULTS AND DISCUSSION
We started our work with the study of reactions of 2-halopyridines with
triphenylphosphine (PPh3) (Scheme 1). Reactions were carried out with
equimolar quantities of reactants at the same temperature both under
thermal heating, as well as under microwave irradiation. In the case
of the classical experiment, a flask containing the reaction mixture
was immersed into the pre-heated oil bath. The results are given in
Table I.
SCHEME 1 Reactions of 2-halopyridines 1a–d with triphenylphosphine.

Synthesis of Phosphonium Salts
23
TABLE I Reactions of 2-Halopyridines with Triphenylphosphine
Under Classical Heating (CH) or Microwave Irradiation (MWI)
Yield %
X
Temperature ◦
C
Time min
Product
CH
0a
7
52
35
88
97
95
68
MWI
F
120
160
160
190
190
190
190
190
120
120
30
10
15
20
30
120
—
2b
2c
2c
2c
2c
2c
2d
0a
10
53
38
93
95
95
73
Cl
Br
Br
Br
Br
Br
I
aOnly starting materials were detected in the reaction mixture.
Quantitative yields of 2c were obtained from the reaction with 2-
bromopyridine 1c after 20 min at 190◦C. 2-Iodopyridine 1d gave 73%
and 68% of 2d by CH or MWI under similar conditions (2 h at 190◦C),
respectively. On the other hand, 2-chloropyridine 1b gave only a small
amount (7–10%) of the product 2c. 2-Fluoropyridine 1a did not react
under these conditions and only the starting materials were recovered.
The sequence of reactivity according to halide nature is not the clas-
sical one (Br > I ꢀ Cl, F). It is not the one we could expect from normal
SNAr mechanism, where the first step (I) is usually rate-determining6
(Scheme 2).
SCHEME 2 The two-step SNAr mechanism (addition-elimination).
Other mechanisms have been proposed: a radical mechanism SRN
17 (Scheme 3) and an aryne (here dehydropyridine) mechanism
(Scheme 4). The aryne mechanism involves HX β-elimination and sub-
sequent phosphine / HX addition, leading to the formation of two
regioisomers.6
The aryne mechanism was excluded because no Diels-Alder cy-
cloadduct was observed when anthracene was added to the reaction
mixture in the case of the experiment with 2-bromopyridine.

24
M. Mecˇiarova´ et al.
SCHEME 3 The SRN1 radical mechanism (elimination-addition).
SCHEME 4 The aryne mechanism.
It was described that addition of inorganic salts can substantially
affect the course of different reactions.8 For that reason, we next stud-
ied the consequence of addition of various inorganic salts to the reac-
tion mixture. We hoped that addition of salts can enhance the reaction
rate and that could gave us a hint on the reaction mechanism. Essen-
tially, alkaline salts were added and their effects could be important
and indicative of the mechanism concerned: either negative if step (I)
or positive if step (II) is the rate-determining step (Scheme 2).8 There-
fore, equivalent amounts of Li, Na, or K salts containing either halide
anions (which also facilitate the halide exchange with halopyridine) or
non-nucleophilic anions such as PF−6 or OTf− were added to the reaction
mixture (Scheme 5). The results are given in Table II.
Reaction of 2-fluoropyridine 1a with PPh3 now proceeded efficiently
with the assistance of LiBr (62–67%), LiPF6 (72–76%) or NaPF6 (74–
78%). No reaction was induced by LiCl. 2-Chloropyridine 1b gave the
corresponding phosphonium salts in moderate to very good yields in the
presence of lithium salts (LiBr, LiI, LiPF6, LiOTf) and with the assis-
tance of NaPF6 and KPF6. Addition of LiCl to the reaction mixture of
chloropyridine 1b and PPh3 did not affect the reaction course and only
very low yields of 2b (6 and 10%, respectively) were isolated after clas-
sical as well as microwave reaction. Addition of LiPF6 to the reaction
mixture of 2-bromopyridine 1c and PPh3 resulted in the formation of
2-pyridyltriphenylphosphonium hexafluorophosphate 2e in high yields
(70–84%). It becomes evident that Li and Na salts have important ef-
fects that allow high yields of the products. These effects appeared to

Synthesis of Phosphonium Salts
25
SCHEME 5 Reactions of 2-halopyridines 1a–d with triphenylphosphine in the
presence of various inorganic salts.
be consistent with the intervention of Li+ or Na+ions to promote elec-
trophilic assistance to C X bond breaking in the second step of the SNAr
mechanism (Figure 1). When adding LiBr or LiI, one can also expect
a halide exchange to produce 2-bromo (or -iodo) pyridine, which would
be more reactive under these conditions. On the contrary, the halide
exchange induced by addition of LiCl in the case of fluoropyridine 1a
would result in the formation of a less reactive chloro compound 1c.
We next examined reactions of the 3-halopyridines 3b,c, which are
usually much less reactive than their 2-regioisomers, under conven-
tional heating and under microwave irradiation. No similar reaction
was described in the literature. Unfortunately, no reaction occurred re-
gardless of the conditions applied and only the starting materials were
recovered. Even addition of LiPF6 resulted only in 7−9% yields of 4 for
the reactions of 3-chloro- as well as 3-bromopyridine (Scheme 6).
These results suggest that the mechanism operating here is the SNAr
mechanism, where the rate-determining step involves the elimination
of the leaving group under electrophilic assistance by the alkaline
FIGURE 1 Electrophilic assistance by Li+ in the second step of SN Ar mecha-
nism.

26
M. Mecˇiarova´ et al.
SCHEME 6 Reactions of 3-halopyridines 3b, c with triphenylphosphine in the
presence of LiPF6.
cation. Control experiments carried out in the presence of hydroquinone
as radical scavenger, which did not induce any change in the yields,
thus precluding a radical mechanism. We performed also experiments
in the presence of anthracene (reactant for trapping possible “aryne”
intermediate in Diels-Alder reaction), but no cycloaddition product was
observed, which excluded the elimination-addition mechanism. Such
mechanism can be excluded also by the fact that just one regioisomer
of the product was isolated in each case.
TABLE II Reactions of 2-Halopyridines 1a–d with
Triphenylphosphine in the Presence of Inorganic Salts Under CH
or MWI
Yield %
X
Salt
Y
Temperature ◦
C
Time h
Product
CH
0a
MWI
F
F
F
F
—
—
Br
PF6
PF6
Cl
—
Cl
Br
I
PF6
OTf
PF6
PF6
—
120
120
120
120
120
160
160
160
160
160
160
160
160
160
180
180
2
2
2
2
2
2
2
2
2
—
2c
2e
2e
—
2b
2b
2c
2d
2e
2f
2e
2e
2c
2e
2e
0a
67
72
74
0a
10
10
71
60
88
37
82
31
53
70
84
LiBr
LiPF6
NaPF6
LiCl
—
LiCl
LiBr
LiI
LiPF6
LiOTf
NaPF6
KPF6
—
62
76
78
F
0a
7
6
Cl
Cl
Cl
Cl
Cl
Cl
Cl
Cl
Br
Br
Br
67
64
82
40
82
29
52
70
86
5 min
2
2
2
0.5
0.25
0.5
LiPF6
LiPF6
PF6
PF6
aOnly starting materials were recovered from the reaction mixture.

Synthesis of Phosphonium Salts
27
Next the reaction of tricyclohexylphosphine (PCy3) with 2-
halopyridines was studied. Even with 2-bromopyridine no reaction was
observed. Instead decomposition of PCy3 or side-products takes place
and only black tarry materials were isolated from the reactions at high
temperature (190◦C). Performing the reaction of 2-halopyridines with
PCy3 in the presence of LiPF6 at lower temperatures (100 and 120◦C,
respectively) gave dicyclohexylphosphine oxide 5 as the only product in
high yields (89–96%).
Presumably 5 is formed by a competing reaction of tricyclohexylphos-
phine with oxygen. To investigate this hypothesis the following exper-
iments were performed: Heating of PCy3 with LiPF6 in air (2 h at
120◦C) without any halopyridines gave quantitative amounts of dicy-
clohexylphosphine oxide 5. No oxidation was observed, when we heated
PCy3 (2 h at 120◦C) without LiPF6 and only unreacted starting material
was detected (1H NMR) in the product mixture. Performing the reaction
of 2-bromopyridine with PCy3 in the presence of LiPF6 at 120 ◦C under
a nitrogen atmosphere gave only traces of dicyclohexylphosphine oxide
5 as the only product. These experiments confirmed our hypothesis and
a plausible reaction path is shown in Scheme 7. We observed no differ-
ence between the course of classically heated reactions and microwave
reactions.
SCHEME 7 Proposed reaction path for the formation of dicyclohexylphosphine
oxide 5.
Finally, we checked the reactivity of 2- and 3-halopyridines with
tributylphosphine (PBu3) under conventional heating as well as un-
der microwave irradiation (Schemes 8 and 9). 2-Halopyridines showed
no reaction with PBu3. Only the starting materials and some uniden-
tified products resulting from the thermal decomposition of PBu3 were
detected by TLC in the reaction mixtures. Addition of LiPF6 to the re-
action mixture resulted in isolation of 2-chloro-N-butylpyridinium hex-
afluorophosphate (24–28%) and 2-bromo-N-butylpyridinium hexafluo-
rophosphate (10%). 2-Fluoropyridine did not react even in the presence
of LiPF6.
In contrast to the reaction with PPh3, 2-chloropyridine 1b did not
react with PBu3 in the presence of LiBr, NaPF6 or LiOTf. Starting ma-
terials and some products of decomposition were detected (TLC) in the

28
M. Mecˇiarova´ et al.
SCHEME 8 Reactions of 2-halopyridines 1a–c with tributylphosphine in the
presence of LiPF6.
SCHEME 9 Reactions of 3-halopyridines 3a–d with tributylphosphine in the
presence of LiPF6.
reaction mixture under both conventional and microwave conditions.
Only unreacted starting material was detected (1H NMR) after heating
of 2-bromopyridine 1c with PBu3 in the presence of LiPF6 at 150◦C (4 h)
under inert atmosphere.
The isolation of a pyridine alkylation product in the presence of
LiPF6 can be explained by the higher thermodynamic stability of N-
butylpyridinium PF6 salt compared to its bromide salt. On the other
hand the bromide anion has reasonable nucleophilicity and can dealky-
late an N-butylpyridinium salt (1-bromobutane can be formed). 3-
Chloro-, 3-bromo-, and 3-iodopyridines reacted with PBu3 in the pres-
ence of LiPF6 to give 3-halo-N-butylpyridinium hexafluorophosphate in
low (9−11%) yields. No reaction of PBu3 with 3-fluoropyridine was ob-
served (Scheme 9). The low yields of N-alkylation products observed
in the reaction with 3-chloro, 3-bromo- and 3-iodopyridines can be
explained by the lower nucleophilicity of the nitrogen atom owing to

Synthesis of Phosphonium Salts
29
the –I effect of the halogen atom located at position 3 of the pyridine
ring.
Under our experimental conditions (open systems exposed to air)
the formation of trialkylphosphine oxides was feasible. Triphenylphos-
phine is less nucleophilic than trialkylphosphines and therefore less
susceptible to attack by oxygen. Probably tributylphosphine oxide acts
as an alkylating agent enabling N-alkylation of pyridine to occur. In
the case of tricyclohexylphosphine, owing to steric constraints alkyla-
tion appears less probable, allowing a competitive elimination process
to occur to give cyclohexene and dicyclohexylphosphine oxide 5.
CONCLUSION
Nucleophilic substitutions of 2-halopyridines with triphenylphosphine
proceeded straightforward in the case of 2-bromo- and 2-iodopyridine
and comparable results were achieved in experiments with and without
MW irradiation. No effect of microwave irradiation was observed. Reac-
tivity of 2-fluoro- and 2-chloropyridines was strongly enhanced by addi-
tion of lithium salts and especially with LiBr or LiPF6 a specific Li effect
was observed. 2-Halopyridines behaved very differently in the reactions
with tributylphosphine and tricyclohexylphosphine. These phosphines
can undergo reaction with atmospheric oxygen to form corresponding
trialkylphosphine oxides. Tributylphosphine oxide in turn could act as
an alkylating agent forming N-butylpyridinium salts, especially when
LiPF6 was present. Tricyclohexylphosphine oxide is rather bulky and
therefore no alkylation of pyridine was observed. Instead it underwent
cyclohexene elimination and dicyclohexylphosphine oxide was isolated
in quantitative yield.
EXPERIMENTAL
NMR spectra were recorded on a Varian Gemini 2000 spectrometer op-
erating at 300 MHz (1H), 75 MHz (13C) and 121.5 MHz (31P). Tetram-
ethylsilane was used as an internal standard (1H, 13C) and H3PO4 (85%)
was used as an external standard (31P). Melting points were deter-
mined on a Kofler apparatus. The elemental analyses were recorded
on a Carlo-Erba instrument. Halopyridines, phosphines and inorganic
salts were purchased in reagent grade (Aldrich, Acros Organics, Fluka,
Merck, Janssen Chimica, Avocado) and used without further purifica-
tion. All microwave experiments were carried out in a monomode re-
actor SynthewaveꢀR 402 from Prolabo (France).9 The temperature was
measured by IR detection, which indicates the surface temperature af-
ter previous calibration of emissivity in each case using an optical fiber

30
M. Mecˇiarova´ et al.
inside the reaction mixture. The reactions were conducted using a cylin-
der tube in Pyrex under mechanical stirring to allow homogeneity in
the temperature.
General Microwave Procedure
A homogeneous mixture of the halopyridine (10 mmol), the phosphine
(10 mmol) and the inorganic salt (10 mmol) was irradiated in the
SynthewaveꢀR 402 MW reactor for the times and temperatures indicated
in Tables I and II. After cooling down to room temperature, the solid
material was dissolved in a mixture of dichloromethane (50 mL) and
water (50 mL). The organic phase was separated, extracted twice with
water (50 mL) to remove inorganic salts and then dried over anhydrous
magnesium sulfate. Dichloromethane was evaporated under reduced
pressure and the solid residue was washed with diethyl ether (100 mL)
to remove unreacted starting materials. The products thus obtained
were analytically pure. When the reactions were performed without an
inorganic salt, the solid material after irradiation was washed directly
with diethyl ether and the products were analyzed by 1H, 13C, and 31
spectroscopy.
P
General Procedure under Conventional Heating
The experiments were carried out in a thermostated oil bath at the
same temperature, in identical reaction vessels, for the same time and
with similar profiles of raising the temperature as for the microwave
experiments (Tables I and II). The treatment of the reaction mixture
and the analysis of the products were identical to those described in the
microwave procedure.
2-Pyridyltriphenylphosphonium Chloride (2b)
Colorless solid, m.p. 250−253◦C, lit.5 254−256◦C; 1H NMR (CDCl3):
δ 7.68−7.91 (m, 16H, Ar H), 8.02−8.06 (m, 1H, pyridine H), 8.40−8.42
(m, 1H, pyridine H), 9.00−9.02 (m, 1H, pyridine H); 13C NMR
(CDCl3): δ 117.3 (d, J = 88.4 Hz, C-i), 129.0 (d, J = 3.7 Hz, C5-pyridine),
130.9 (d, J = 13.0 Hz, C-m), 132.6 (d, J = 24.7 Hz, C3-pyridine), 134.9 (d,
J = 10.2 Hz, C-o), 136.0 (d, J = 3.1 Hz, C-p), 139.6 (d, J = 10.5 Hz, C4-
pyridine), 144,3 (d, J = 119.6 Hz, C2-pyridine), 152.7 (d, J = 19.5 Hz,
C6-pyridine); 31P NMR (CDCl3): δ 15.6.
2-Pyridyltriphenylphosphonium Bromide (2c)
Colorless solid, m.p. 271−274◦C, lit.5 272−274◦C; 1H NMR (CDCl3):
δ 7.67−7.93 (m, 16H, Ar H), 8.06−8.10 (m, 1H, pyridine H), 8.38−8.47

Synthesis of Phosphonium Salts
31
(m, 1H, pyridine H), 9.00−9.01 (m, 1H, pyridine H); 13C NMR
(CDCl3): δ 117.3 (d, J = 88.4 Hz, C-i), 129.0 (d, J = 3.8 Hz, C5-pyridine),
130.9 (d, J = 12.6 Hz, C-m), 132.6 (d, J = 24.7 Hz, C3-pyridine), 134.9
(d, J = 9.8 Hz, C-o), 136.0 (d, J = 2.8 Hz, C p), 139.5 (d, J = 10.5 Hz,
C4-pyridine), 144,5 (d, J = 119.9 Hz, C2-pyridine), 152.7 (d, J = 19.5
Hz, C6-pyridine); 31P NMR (CDCl3): δ 15.6.
2-Pyridyltriphenylphosphonium Iodide (2d)
Colorless solid, m.p. 289−292◦C; 1H NMR (CDCl3): δ 7.69−7.93
(m, 16H, Ar−H), 8.09−8.14 (m, 1H, pyridine−H), 8.32−8.47 (m, 1H,
pyridine H), 8.99−9.00 (m, 1H, pyridine H); 13C NMR (CDCl3): δ 117.2
(d, J = 88.4 Hz, C i), 128.8 (d, J = 3.4 Hz, C5-pyridine), 130.9 (d,
J = 13.0 Hz, C-m), 132.7 (d, J = 24.7 Hz, C3-pyridine), 134.9 (d, J =
10.0 Hz, C-o), 135.9 (d, J = 2.8 Hz, C-p), 139.5 (d, J = 10.5 Hz, C4-
pyridine), 144,5 (d, J = 119.6 Hz, C2-pyridine), 152.7 (d, J = 19.4 Hz,
C6-pyridine); 31P NMR (CDCl3): δ 15.6.
2-Pyridyltriphenylphosphonium Hexafluorophosphate (2e)
Colorless solid, m.p. 314–317◦C; 1H NMR (DMSO): δ 7.74–7.99 (m, 17
H, Ar H), 8.16–8.22 (m, 1H, pyridine H), 9.08–9.09 (m, 1H, pyridine-
H); 13C NMR (DMSO): δ 117.2 (d, J = 88.2 Hz, C-i), 128.4 (d, J = 3.4
Hz, C5-pyridine), 130.3 (d, J = 12.8 Hz, C-m), 132.1 (d, J = 24.4 Hz, C3-
pyridine), 134.7 (d, J = 10.5 Hz, C-o), 135.3 (d, J = 2.9 Hz, C p), 138.4
(d, J = 10.5 Hz, C4-pyridine), 144,2 (d, J = 119.7 Hz, C2-pyridine),
152.3 (d, J = 19.3 Hz, C6-pyridine); 31P NMR (DMSO): δ -143.0 (PF6−),
16.5.
2-Pyridyltriphenylphosphonium Triflate (2f)
Colorless solid, m.p. 256−259◦C; 1H NMR (CDCl3): δ 7.66−7.91
(m, 16H, Ar H), 7.94−7.98 (m, 1H, pyridine H), 8.18−8.27 (m, 1H,
pyridine H), 8.98−8.99 (m, 1H, pyridine H); 13C NMR (CDCl3): δ 117.4
(d, J = 88.3 Hz, C-i), 128.8 (d, J = 3.8 Hz, C5-pyridine), 130.8 (d,
J = 13.0 Hz, C-m), 132.6 (d, J = 24.5 Hz, C3-pyridine), 134.9 (d, J =
10.2 Hz, C-o), 135.9 (d, J = 3.1 Hz, C p), 139.2 (d, J = 10.5 Hz, C4-
pyridine), 144,8 (d, J = 119.9 Hz, C2-pyridine), 152.6 (d, J = 19.4 Hz,
C6-pyridine); 31P NMR (CDCl3): δ 15.7.
3-Pyridyltriphenylphosphonium Hexafluorophosphate (4)
Colorless solid, m.p. 316−319◦C; 1H NMR (DMSO): δ 7.55−8.01
(m, 16H, Ar H), 8.18−8.28 (m, 1H, pyridine H), 8.86−8.89 (m, 1H,
pyridine−H), 9.06−9.12 (m, 1H, pyridine H); 13C NMR (DMSO): δ
114.9 (d, J = 84.2 Hz, C3-pyridine), 116.9 (d, J = 89.3 Hz, C-i), 125.0

32
M. Mecˇiarova´ et al.
(d, J = 9.4 Hz, C5-pyridine), 130.5 (d, J = 12.8 Hz, C-m), 134.7 (d,
J = 10.8 Hz, C-o), 135.6 (d, J = 2.8 Hz, C p), 142.6 (d, J = 8.8 Hz,
C4-pyridine), 153,8 (d, J = 11.9 Hz, C2-pyridine), 155.3 (d, J = 2.2 Hz,
C6-pyridine); 31P NMR (DMSO): δ -143.0 (PF−6 ), 21.5.
Dicyclohexylphosphine Oxide (5)
1
Colorless solid, m.p. 233−236◦C; H NMR (CDCl3): δ 1.28−1.83 (m,
12H, CH2), 1.92−2.01 (m, 8H, CH2), 2.40−2.58 (m, 2H, PCH), 5.62 (ddd,
J = 467.7 Hz, 7.4 Hz, 3.8 Hz, 1H, PH); 13C NMR (CDCl3): δ 25.3 (d, J =
1.0 Hz, C-4), 26.4 (d, J = 12.7 Hz, C-2), 28.1 (d, J = 3.5 Hz, C-3), 28.4
(d, J = 36.8 Hz, C-1); 31P NMR (CDCl3): δ 29.1.
2-Chloro-N-butylpyridinium Hexafluorophosphate (6b)
1
Colorless solid, m.p. 59−62◦C; H NMR (DMSO): δ 0.94 (t, J = 7.4
Hz, 3H, CH3), 1.35−1.42 (m, 2H, CH2), 1.82−1.90 (m, 2H, CH2), 4.70
(t, J = 8.0 Hz, 2H, NCH2), 8.10−8.16 (m, 1H, pyridine H), 8.39 (dd,
J = 8.3 Hz, 1.2 Hz, 1H, pyridine H), 8.58−8.64 (m, 1H, pyridine H),
9.19 (dd, J = 6.2 Hz, 1.5 Hz, 1H, pyridine H); 13C NMR (DMSO): δ 13.3
18.8, 30.8, 59.5, 126.5, 130.3, 147.2, 147.2, 147.6; 31P NMR (DMSO): δ
–144.2 (septet, J = 713 Hz).
2-Bromo-N-butylpyridinium Hexafluorophosphate (6c)
Colorless solid, m.p. 76−78◦C; 1H NMR (DMSO): δ 0.95 (t, J = 7.2 Hz,
3H, CH3), 1.35−1.43 (m, 2H, CH2), 1.82−1.90 (m, 2H, CH2), 4.72 (t,
J = 7.8 Hz, 2H, NCH2), 8.12−8.17 (m, 1H, pyridine H), 8.42−8.54 (m,
2H, pyridine H), 9.23 (dd, J= 6.2 Hz, 1.5 Hz, 1H, pyridine−H); 13C
NMR (DMSO): δ 13.3, 18.8, 31.0, 62.0, 127.0, 134.3, 138.2, 146.2, 148.0;
31P NMR (DMSO): δ –144.2 (septet, J = 713 Hz).
3-Chloro-N-butylpyridinium H◦exafluorophosphate (7b)
1
Colorless solid, m.p. 116−119 C; H NMR (DMSO): δ 0.92 (t, J =
7.5 Hz, 3H, CH3), 1.27−1.35 (m, 2H, CH2), 1.89−1.94 (m, 2H, CH2),
4.60 (t, J = 7.4 Hz, 2H, CH2), 8.17−8.22 (m, 1H, pyridine H), 8.78 (d,
J = 8.4 Hz, 1H, pyridine H), 9.08 (d, J = 6.0 Hz, 1H, pyridine−H), 9.47
(s, 1H, pyridine H); 13C NMR (DMSO): δ 13.3, 18.8, 32.4, 61.1, 128.7,
134.1, 143.6, 144.2, 145.1; 31P NMR (DMSO): δ –144.2 (septet, J = 712
Hz).
3-Bromo-N-butylpyridinium Hexafluorophosphate (7c)
Colorless solid, m.p. 94−95◦C; 1H NMR (DMSO): δ 0.92 (t, J = 7.4 Hz,
3H, CH3), 1.27−1.34 (m, 2H, CH2), 1.86−1.94 (m, 2H, CH2), 4.56 (t,
J = 7.5 Hz, 2H, CH2), 8.11 (t, J = 7.4 Hz, 1H, pyridine H), 8.88 (d,
J = 8.4 Hz, 1H, pyridine H), 9.11 (d, J = 6.0 Hz, 1H, pyridine H),

Synthesis of Phosphonium Salts
33
9.51 (s, 1H, pyridine H); 13C NMR (DMSO): δ 13.3, 18.8, 32.5, 61.0,
122.1, 128.8, 143.8, 146.0, 147.8; 31P NMR (DMSO): δ –144.2 (septet,
J = 712 Hz).
3-Iodo-N-butylpyridinium Hexafluorophosphate (7d)
Colorless solid, m.p. 101−103◦C; 1H NMR (DMSO): δ 0.92 (t, J = 7.4
Hz, 3H, CH3), 1.26−1.33 (m, 2H, CH2), 1.87−1.91 (m, 2H, CH2), 4.52 (t,
J = 7.1 Hz, 2H, CH2), 7.93 (t, J = 6.9 Hz, 1H, pyridine H), 8.96 (d, J =
7.8 Hz, 1H, pyridine H), 9.09 (d, J = 5.4 Hz, 1H, pyridine H), 9.48 (s,
1H, pyridine H); 13C NMR (DMSO): δ 13.3, 18.8, 32.6, 60.6, 95.5, 128.6,
143.7, 150.0, 153.0; 31P NMR (DMSO): δ – 144.2 (septet, J = 712 Hz).
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