New look into the synthesis of polyhalogenoarylphosphanes

Article abstract of DOI:10.1080/10426500802531677

The present study shows new aspects of the synthesis of polyhalogenoarylphosphanes. The sterically hindered anions Ph(R)P-Y- (1a-c, Y = O, lone pair; R = Ph, But) have been used to show the complexity of the reaction between phosphorus nucleophiles and hexahalogenobenzenes or 9-bromofluorene (E3). The Ph(Bu^t)P-O-(1a) anion reacts with hexachlorobenzene (E1), hexafluorobenzene (E2), or E3 to give Ph(R)P(O)X (4a-c, X = F, Cl, Br) with the release of the corresponding carbanion as a nucleofuge, followed by side reactions. In contrast, the lithium phosphides Ph(R)PLi (1b,c) react with hexahalogenobenzenes to give the corresponding diphosphanes 5a,b as the main product and traces of P-arylated products, i.e., Ph(R)P-C₆X ₅ (10a,b, X = Cl, F). Unexpectedly, Ph(Bu^t)PLi (1b) reacts with an excess of 9-bromofluorene to give only halogenophosphane Ph(Bu ^t)P-X. Taylor & Francis Group, LLC.

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Phosphorus, Sulfur, and Silicon
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New Look into the Synthesis of
Polyhalogenoarylphosphanes
Jacek E. Nycz a
a Department of Organic Chemistry , Institute of
Chemistry, University of Silesia , Katowice, Poland
Published online: 21 Sep 2009.
To cite this article: Jacek E. Nycz (2009) New Look into the Synthesis of
Polyhalogenoarylphosphanes, Phosphorus, Sulfur, and Silicon and the Related
Elements, 184:10, 2605-2612, DOI: 10.1080/10426500802531677
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Phosphorus, Sulfur, and Silicon, 184:2605–2612, 2009
Copyright © Taylor & Francis Group, LLC
ISSN: 1042-6507 print / 1563-5325 online
DOI: 10.1080/10426500802531677
New Look into the Synthesis of
Polyhalogenoarylphosphanes
Jacek E. Nycz
Department of Organic Chemistry, Institute of Chemistry,
University of Silesia, Katowice, Poland
The present study shows new aspects of the synthesis of polyhalogenoarylphos-
phanes. The sterically hindered anions Ph(R)P-Y− (1a–c, Y = O, lone pair; R = Ph,
But) have been used to show the complexity of the reaction between phosphorus nu-
cleophiles and hexahalogenobenzenes or 9-bromofluorene (E3). The Ph(But)P-O−
(1a) anion reacts with hexachlorobenzene (E1), hexafluorobenzene (E2), or E3 to
give Ph(R)P(O)X (4a–c, X = F, Cl, Br) with the release of the corresponding car-
banion as a nucleofuge, followed by side reactions. In contrast, the lithium phos-
phides Ph(R)PLi (1b,c) react with hexahalogenobenzenes to give the corresponding
diphosphanes 5a,b as the main product and traces of P-arylated products, i.e.,
Ph(R)P-C6X5 (10a,b, X = Cl, F). Unexpectedly, Ph(But)PLi (1b) reacts with an
excess of 9-bromofluorene to give only halogenophosphane Ph(But)P-X.
Keywords Halogen–metal exchange; halogenobenzene; polyhalogenoarylphosphane;
single-electron transfer (SET)
INTRODUCTION
The preparation of polyhalogenoarylphosphanes using phosphorus nu-
cleophiles through various synthetic routes is well reported in the lit-
erature.1,2 In these articles, the authors postulated that this transfor-
mation had the characteristics of a nucleophilic aromatic substitution.
Neutral silyl and stannyl derivatives of three-coordinated phosphorus
nucleophiles are convenient reagents, clearly giving the target products
without side products.1 On the other hand, negatively charged three-
coordinate phosphorus nucleophiles possess a different reactivity.2
Bardin et al.3 reported the reaction of p-RꢀC6F4Br with
tris(diethylamino)phosphane in the presence of R3MX (Scheme 1).
Received 23 September 2008; accepted 7 October 2008.
This article is dedicated to Dr. Andrey Protchenko.
Address correspondence to Jacek E. Nycz, Department of Organic Chemistry, Institute
of Chemistry, University of Silesia, ul. Szkolna 9, 40–007, Katowice, Poland. E-mail:
jnycz@us.edu.pl
2605

2606
J. E. Nycz
SCHEME 1
p-RꢀC6F4MR3 was isolated with more than 50% yield, and the halo-
genated phosphorus nucleophile (Et2N)3PXBr was obtained as the sec-
ond product. It was observed that bromide or chloride was more easily
taken off than fluoride. It was suggested that the rate-determining step
was the cleavage of the ArF-X bond (X = halogen). Furthermore, no P-
arylated product was identified. However, arylated silyl, germyl, and
stannyl products were isolated, which could confirm the intermediate
formation of an aryl anion, i.e., p-RꢀC6F4−, in the reaction mixture.
4a,b
´
Rachon and colleagues
postulated the possibility of the halogen
transfer through a halophilic substitution in the reaction between the
>P-O− ambident phosphorus nucleophile and the C-Br bond of the
benzyl bromide. The >P-O− nucleophile attacks the C-Br bond of benzyl
bromide by the soft phosphorus atom, giving >P(O)-Br. The first step
of removing the halogen atom by the negatively charged phosphorus
nucleophile could be a halogen–metal exchange type reaction, as first
reported by Jones and Gilman.5
Bunnett6 and Russell & Hershberger7 showed that dialkyl phosphate
anions participate in aromatic as well as in aliphatic SRN1 processes. In
contrast to the observations made by both authors, the current study
demonstrates the formation of a phosphorus–halogen bond.
The reaction between negatively charged three-coordinated phos-
phorus nucleophiles and polychlorinated aromatic hydrocarbon com-
pounds seems to occur in a different manner than a nucleophilic aro-
matic substitution. Experiments were performed in order to explore
these unresolved issues.
RESULTS AND DISCUSSION
To look deeper into the reaction between phosphorus nucleophiles and
hexahalogenobenzenes, negatively charged nucleophiles with steric
hindrance at the phosphorus atom were chosen, i.e., Ph(R)P-Y− (1a–
c, Y = O, lone pair; R = But, Ph). Bulky carbon substituents should
slow down side reactions for steric and electronic reasons. Moreover,
such reagents should demonstrate higher nucleophilicity than neutral
nucleophile or analogue compounds, which possess alkoxy or aryloxy

The Synthesis of Polyhalogenoarylphosphanes
2607
substituents at the phosphorus atom. Hexachlorobenzene (E1), hex-
afluorobenzene (E2), and 9-bromofluorene (E3) were chosen as elec-
trophiles. Compound E3 was chosen because it is much more sus-
ceptible to nucleophilic substitution than halogenoaryls. To compare
the reactivity of various three-coordinate phosphorus nucleophiles to-
wards hexahalogenated benzenes, a reaction between the potassium
salt of tert-butylphenylphosphine oxide (1a) with E1 was performed.
The conversion was unambiguous and gave a halogenated phospho-
rus product, namely tert-butylphenylphosphinic acid chloride (4a) with
81% yield, as well as pentachlorobenzene (7b) with 41% yield, 1,2,4,5-
tetrachlorobenzene (7a) with 6% yield, and traces of decachlorobiphenyl
(7c) (Scheme 2). The final products suggest that the three-coordinate
phosp−horus atom attacked E1 at the chlorine atom to give 4a and
C6Cl5 as a leaving group with a characteristic deep violet color. Sub-
sequently the C6Cl5− anion participates in side reactions, probably via
single electron transfer (SET), to give 7c or 7a. Similar results were
obtained in the reaction between 1a and E2. No P-arylated product was
observed among the final products.
SCHEME 2
The reaction between C6X6 (X = halogen) and negatively charged
three-coordinated phosphorus nucleophiles results in the formation of
products with a phosphorus halogen bond, such as Ph(But)P(O)-X (4a,b,
X = Cl, F).
A comparison of nucleophilic substitution at the benzyl and aro-
matic carbon atoms was made by reacting 1a with E3. The neg-
atively charged three-coordinate phosphorus nucleophile 1a should
easily undergo a nucleophilic substitution with benzyl bromide. How-
ever in the case of the related 9-bromofluorene (E3), the phospho-
rus atom attacks the bromine atom of the C-Br bond to give tert-
butylphenylphosphinic acid bromide (4c) and fluorenyl anion as a
leaving group, which subsequently participates in a SET reaction to

2608
J. E. Nycz
form 9,9ꢀ-bifluorenyl (9). In fact the reaction produced 4c with 39%
yield and tert-butylphenylphosphine oxide (3a) with 37% yield, 9 with
82% yield, and fluorine (8) with 6% yield (Scheme 3). It is important
to note that the phosphorus compounds were isolated in similar molar
amounts. Dimerization products such as 9 or 7c indirectly confirm the
presence of an aryl anion in the reaction mixture and a single-electron
transfer (SET) mechanism operating. The above observations further
´
support the halophilic substitution mechanism reported by Rachon and
colleagues.4a,b
SCHEME 3
The lithium salts of tert-butylphenylphosphane (1b) and
diphenylphosphane (1c) show a very different reactivity towards
E1 and E2. The corresponding diphosphanes [1,2-di-tert-butyl-1,2-
diphenyldiphosphane (5) (mixture of meso and rac isomer in a 7:1 ra-
tio) or 1,1,2,2-tetraphenyldiphosphane (5c)] and traces of P-arylated
products [i.e., tert-butylphenyl(pentafluorophenyl)phosphane (10a) or
diphenyl(pentachlorophenyl)phosphane (10b)] were identified among
the final products (Scheme 4). These results demonstrate the differ-
ent type of reactivity of the nucleophiles 1b and 1c. It is possible
that both nucleophiles participate in the transfer of electrons to the
hexahalogenobenzenes, as is postulated by Bunnett6 and Russell &
Hershberger.7
SCHEME 4

The Synthesis of Polyhalogenoarylphosphanes
2609
Compared to 1a (shown in Scheme 2), 1b possesses stronger nucle-
ophilicity, which, however, did not go thorough a mechanism to gener-
ate tert-butylphenyl(9-fluorenyl)phosphane when reacted with excess
of E3 that was treated as an analogue of benzyl bromide. Similarly to
1a, 1b exclusively gave tert-butylbromophenylphosphane (4d) (Scheme
3), without any P-arylated product or diphosphane 5a,b observed.
1
Compound 4d was conveniently identified by 31P{ H} NMR spec-
troscopy. In analogy to the previous experiments, compounds with phos-
phorus halogen bonds, i.e., 4d and 9 (Scheme 3), were observed. Using
an excess of 9-bromofluorene (5 equiv.) allowed us to avoid side reac-
tions between the nucleophile 1b and the newly produced 4d. The pres-
ence of the bromophosphane 4d was fully confirmed by an independent
reaction between 5a,b and bromine.
CONCLUSION
The direct reactions between negatively charged three-coordinated
phosphorus nucleophiles such as Ph(But)P-O− with hexahalogenoben-
zenes or 9-bromofluorene result in the formation of halogenated phos-
phorus products such as Ph(But)P(O)X (4, X = F, Cl, Br) and corre-
sponding carbanions, which subsequently participate in side reactions.
The presented results suggest that instead of an SNAr mechanism, the
dehalogenation reaction occurs through a halophilic substitution (or
halogen–metal exchange) by a single-electron transfer (SET) mecha-
nism. No P-arylated products were observed in the reaction with the
potassium salt of tert-butylphenylphosphine oxide (1a). Similarly, in
the reaction with the excess of 9-bromofluorene (1c) exclusively gave
4d without any P-arylated products. In contrast, 1b and 1c reacted
with an excess of E1 or E2 gave the diphosphanes 5a,b (as a mix-
ture of meso and rac isomer), and 5c, respectively, as well as traces of
the P-arylated products 10a or 10b, which suggest in this case a SRN
1
processes.
EXPERIMENTAL
All experiments were carried out in an atmosphere of dry argon, us-
ing Schlenk techniques. Solvents were dried by usual methods (ben-
zene and THF over benzophenone ketyl, CHCl3 over P2O5, hexane
over sodium–potassium alloy), distilled, and degassed. Chromatogra-
phy was carried out on silica gel 60 (0.15–0.3 mm) Machery Nagel. For
GC/MS, a Gas Chromatograph 5890 Seriess II with MSD 9772 SERIES
(GC-MS) with autosampler (Hewlett-Packard) was used. NMR spectra

2610
J. E. Nycz
were obtained with a Varian Gemini 500 instrument operating at 500
MHz (1H) and at 202.4 MHz (31P). All J values are given in Hz. 31P NMR
1
spectra were obtained using broadband H decoupling, and chemical
shifts are reported relative to 85% H3PO4 as external standard. Mass
spectra were obtained with a MASPEC II system [II32/99D9] in EI
mode and, where necessary, the liquid SIMS technique was applied.
Reagents 1a–c were generated according to procedures described in
the literature.9a,b
Reaction of Potassium Salt of 1a with E1, E2, and E3
Potassium (0.39 g, 10 mmol) was dissolved in a mixture composed of
liquid ammonia (25 mL) and THF (25 mL). The reaction mixture was
stirred to complete dissolution of the metal. After cooling to –78◦C, 4a
(1.08 g, 5 mmol) in THF (5 mL) was added, and the reaction mixture
was stirred at –78◦C for additional 30 min. Then E1, E2, or E3 (5 mmol)
in THF (40 mL) was added, and immediately a violet (in the case of E3
a red) color appeared. After 3 h, NH4Cl (1.5 g) was added, and the
ammonia was evaporated at 10 mm Hg. The residue was poured into
a mixture of toluene and aqueous KHSO4 solution (25 mL). The water
layer was extracted with toluene, and the combined organic phase was
dried over MgSO4. The solvent was evaporated, and the product was
purified by crystallization and chromatography.
Products from the Reaction of 1a with E1
7a: 0.060 g (0.3 mmol, 6%), tr = 6.75 min, GC/MS: (EI) M+ 216;
7b: 0.514 g (2.0 mmol, 41%), tr = 7.90 min, GC/MS: (EI) M+ 250; 7c:
(traces), tr = 15.16 min, GC/MS: (EI) M+ 430; 4a: (CHCl3) 0.877 g (4.0
1
3
mmol, 81%); H NMR (CDCl3): δ = 1.15 (d, JPH = 19 Hz, 9H, But),
7.10–7.77 (m, 5H, arom-H); 31P{ H} NMR (C6D6): δ = 72.2.8,9
1
Products from the Reaction of 1a with E2
tert-Butylphenylphosphinic acid fluoride (4b): 0.651 g (3.2
3
mmol, 65%); 1H NMR (CDCl3): δ = 1.23 (d, JPH = 17 Hz, 9H,
1
But), 7.55–7.83 (m, 5H, arom-H); 31P{ H} NMR (C6D6): δ = 61.4 (d,
1JPF = 1052 Hz);10 1,2-di-tert-butyl-1,2-diphenyldiphosphane 1,2-
dioxide (6a,b): (CHCl3:MeOH = 50:1); 6a: 0.130 g (0.4 mmol, 14%);
mpmeso = 205◦C; 1H NMR (CDCl3): δmeso = 0.98 (d, 3JPH = 16 Hz, 18H,
1
But), 7.40–8.45 (m, 10H, arom-H); 31P{ H} NMR (CDCl3): δmeso = 39.8;
MS: (SIMS) M+ 362; 6b: 0.061 g (0.1 mmol, 7%); mprac = 192–193◦C;
1H NMR (CDCl3): δrac = 1.38 (d, 3JPH = 17 Hz, 18H, But), 7.00–7.80 (m,
1
10H, arom-H); 31P{ H} NMR (CDCl3): δrac = 50.7; MS: (SIMS) M+ 362;8
tert-butylphenylphosphinic acid (2): (traces), mp = 155–156◦C; 1H

The Synthesis of Polyhalogenoarylphosphanes
2611
3
NMR (CDCl3): δ = 0.93 (d, JPH = 15 Hz, 9H, But), 6.93–7.57 (m, 5H,
arom-H), 11.0 (s, 1H, OH); 31P NMR (CDCl3): δ = 52.0.8
Products from the Reaction of 1a with E3
8: (hexane) 0.045 g (0.3 mmol, 6%); mp 116–118◦C; 1H NMR (CDCl3):
δ = 3.93 (s, 2H, CH2), 7.28–7.50 (m, 4H, arom-H), 7.56 (d, J = 7.2 Hz,
2H, arom-H), 7.82 (d, J = 7.5 Hz, 2H, arom-H); 9: (hexane) 0.677 g
1
(2.0 mmol, 82%); mp 248–249◦C; H NMR (CDCl3): δ = 4.60 (s, 2H,
CH), 6.86 (d. J = 7.0 Hz, 4H, arom-H), 7.00 (t, J = 7.4 Hz, 4H, arom-
H), 7.18 (t, J = 7.5 Hz, 4H, arom-H), 7.48 (d, J = 7.7 Hz, 4H, arom-
H); 2c: (CHCl3:MeOH = 50:1), (Kugelrohr, 136◦C/0.5 mm Hg), 0.509
1
3
g (1.9 mmol, 39%); H NMR (CDCl3): δ = 1.03 (d, JPH = 16 Hz, 9H,
But), 7.10–7.77 (m, 5H, arom-H); 31P{ H} NMR (CDCl3): δ = 73.5.8 3a:
1
1
(CHCl3:MeOH = 50:1), 0.337 g (2.0 mmol, 37%), H NMR (CDCl3): δ
= 1.13 (d, JPH = 15 Hz, 9H, But), 6.70 (d, JPH = 440 Hz, 1H, PH),
3
6.83–7.67 (m, 5H, arom-H); 31P NMR (CDCl3): δ = 46.0 (d, JPH = 440
Hz).9b
Synthesis of tert-Butylbromophenylphosphine (4d)
To freshly prepared potassium naphthalenide (5 mmol) in 25 mL of
THF at –78◦C, tert-butylphenylchlorophosphane (4f) (1.003 g, 5 mmol)
in THF (5 mL) was added. The reaction mixture was stirred until the
disappearance of the green color. After 3 h at r.t., a sample of the
1
reaction mixture was taken, C6D6 was added, and the 31P{ H} NMR
1
spectrum was recorded. The 31P{ H} NMR spectrum of the reaction
mixture showed two resonance lines attributable to 1,2-di-tert-butyl-
1,2-diphenyldiphosphane (5a,b) (δ = 2.9 and –3.5 ppm). The solution
of 5a,b was treated with bromine (0.80 g, 5 mmol), and after 3 h a
sample of the reaction mixture was analyzed by 31P NMR. The spectrum
showed a resonance line attributable to 4d (δ = 109.9 ppm).
Reaction of 1b,c with E1, E2, or E3
tert-Butylphenylphosphane (3b) or diphenylphosphane (3c) (5 mmol)
was dissolved in THF (20 mL). The solution was cooled to –78◦C, and
BuLi (2.2 mL, 2.5 M) in hexane was added. The reaction mixture was
stirred at r.t. for 1 h, followed by the addition of E1, E2, or E3 (25 mmol)
in THF (45 mL). After 3 h, a sample of the reaction mixture was taken,
1
C6D6 was added, and the 31P{ H} NMR spectrum was recorded (for the
identified products see below). To fully confirm the identity of 4d both
samples, that from the reaction mixture and that from an independent

2612
J. E. Nycz
1
synthesis, were mixed together and the 31P{ H} NMR spectrum was
recorded. It showed the presence of only one signal at δ = 109.9 ppm.
In the case of E2 resonance lines attributable to 5a,b (δ = 2.9 and –3.5
ppm) and to 10a (δ = 1.6, m, P-C6F5) were observed. In the case of E1,
the 31P NMR spectrum showed resonance lines attributable to 5c (δ
3
= –15.1 ppm) and to 10b (δ = 10.7, quintet, JPH = 7.3 Hz, P-C6H5).
Subsequently, dry air was passed through the reaction mixture in both
experiments, which was then poured into a mixture of toluene and
aqueous KHSO4. The water layer was extracted with toluene (20 mL),
and the combined organic phase was dried over MgSO4. The solvent
was evaporated, and the product was purified by crystallization and
chromatography.
Products from the Reaction of 1b with E3
4c: 1.018 g (4.0 mmol, 78%); (Kugelrohr, 136◦C/0.5 mm Hg); 1H NMR
(CDCl3): δ = 1.03 (d, 3JPH = 16 Hz, 9H, But), 7.10–7.77 (m, 5H, arom-H),
31P NMR (CDCl3): δ = 73.5.8
Products from the Reaction of 1b with E2
6a: 0.471 g (1.3 mmol, 51%); 6b: 0.181 g (0.5 mmol, 19%).
Products from the Reaction of 1c with E1
Tetraphenyldiphosphane P,Pꢀ-dioxide (6c): 1.126 g (2.8 mmol,
56%), mp = 168–169◦C; 1H NMR (CDCl3/DMSO): δ = 6.90–6.99 (m, 6H,
1
arom-H), 7.81–7.85 (m, 4H, arom-H), 31P{ H} NMR (CDCl3/DMSO):
δ = 24.9.8
REFERENCES
[1] (a) L. I. Goryunov, J. Grobe, V. D. Shteingarts, B. Krebs, A. Lindemann, E.-U.
Wu¨rthwein, and Ch. Mueck-Lichtenfeld, Chem. Eur. J., 6, 4612 (2000) (b) Y. A.
Veits, E. B. Neganova, and I. P. Beleskaya, Russ. J. Org. Chem., 33, 1351 (1997).
[2] W. Boenigk and G. Ha¨gele, Chem. Ber., 117, 2287 (1984).
[3] V. V. Bardin, L. N. Aparina, L. S. Pressman, and G. G. Furin, Izv. Akad. Nauk SSSR,
Ser. Khim., 2153 (1989).
[4] (a) L. Dembkowski, D. Witt, and J. Rachon, Phosphorus, Sulfur, and Silicon, 127,
143 (1997) (b) D. Witt and J. Rachon, Phosphorus, Sulfur, and Silicon, 108, 169
(1996).
[5] R. G. Jones and H. Gilman, Org. React., 6, 339 (1951).
[6] J. F. Bunnett, Acc. Chem. Res., 11, 413 (1978).
[7] G. A. Russell and J. Hershberger, J. Chem. Comun., 216 (1980).
[8] J. E. Nycz and R. Musiol, Heteroatom Chem., 17, 310 (2006).
[9] (a) M. Stankiewicz, J. Nycz, and J. Rachon, Heteroatom Chem., 13, 330 (2002) (b) J.
Nycz and J. Rachon, Phosphorus, Sulfur, and Silicon, 161, 39 (2000).
[10] A. Łopusinski, Phosphorus, Sulfur, and Silicon, 45, 137 (1989).