Studies on the structure behavior of triphenyldichlorophosphorane in different solvents

Article abstract of DOI:10.1016/j.saa.2005.05.003

Triphenyldichlorophosporane, which was prepared according to Appel reaction, was an efficient reagent for alkyl halide synthesis by virtue of having two replaceable groups on "pentavalent" phosphorus. The reaction of triphenylphosphine with hexachloroethane was investigated in different solvents and ³¹P NMR traced the processes of these reactions. As results, it was found that there was similar high coordinated phosphorus species formed in aromatic solvents and in ring ether type solvents, which had large ¹J_P-C (about 140 Hz) according to ¹³C NMR experiments. It is indicated that, for some solvent such as benzene or dioxane, solvent molecules might be locked in the high coordinated phosphorus compounds, which in turn would affect the triphenyl groups situated at the equatorial position.

Full text of DOI:10.1016/j.saa.2005.05.003

Spectrochimica Acta Part A 63 (2006) 192–195
Studies on the structure behavior of triphenyldichlorophosphorane in
different solvents
Qiang Yina, Yong Yea, Guo Tangb, Yu-Fen Zhaoa,b,∗
a
The Key Laboratory of Bioorganic Phosphorus Chemistry & Chemical Biology, Ministry of Education, Department of Chemistry,
Tsinghua University, Beijing 100084, PR China
The Key Laboratory of Chemical Biology of Fujian Province, Department of Chemistry, Xiamen University, Xiamen 361005, Fujian, PR China
b
Received 20 March 2005; accepted 7 May 2005
Abstract
Triphenyldichlorophosporane, which was prepared according to Appel reaction, was an efficient reagent for alkyl halide synthesis by virtue
of having two replaceable groups on “pentavalent” phosphorus. The reaction of triphenylphosphine with hexachloroethane was investigated
in different solvents and 31P NMR traced the processes of these reactions. As results, it was found that there was similar high coordinated
phosphorus species formed in aromatic solvents and in ring ether type solvents, which had large 1JP–C (about 140 Hz) according to 13C NMR
experiments. It is indicated that, for some solvent such as benzene or dioxane, solvent molecules might be locked in the high coordinated
phosphorus compounds, which in turn would affect the triphenyl groups situated at the equatorial position.
© 2005 Elsevier B.V. All rights reserved.
Keywords: 31P NMR; Triphenyldichlorophosporane; 13C NMR; High coordinated phosphorus
1. Introduction
2. Experimental
In 5-mm NMR tube, hexchloroethane (59 mg,
Triphenyldichlorophosporanes were efficient reagents for
alkyl halide synthesis by virtue of having two replaceable
groups on “pentavalent” phosphorus [1–3]. Therefore, they
had also been used as peptide synthesis reagents [4–7]. Many
methods had been developed during the last years [7]. Appel
and Willms [3] have prepared triphenyldichlorophosporane
efficiently according to an easy reaction of triphenylphos-
phine with hexachloroehtane. Arylhalogenophosphoranes
are of considerable interest since various alternative struc-
tures are possible. The configurations of these compounds
might be present as trigonal bipyramids, as found for PF5, or
ionic structures as in the ionic form of PCl5. In addition, they
could also exist as the phosphonium salts. In this paper, the
products from the reaction of Ph3P with C2Cl6 were investi-
gated in various polar and nonpolar solvents.
a
0.25 mmol)andtriphenylphosphine(66 mg, 0.25 mmol)were
mixed in solvent (0.5 mL), such as dioxane, benzene, toluene,
acetonitrile and chloroform under dry Argon atmosphere.
The mixture was stranded overnight. 31P NMR spectra were
recorded with a Brucker NMR at 200 MHz in each interval as
shown in Figs. 1–4. All 13C NMR spectra were recorded with
a JEOL operating at 300 MHz. Chemical shifts are reported
relative to 85% phosphoric acid as an external standard. All
spectra were recorded both in the presence or absence of the
external standard at 25 ◦C.
3. Results and discussion
3.1. Dynamics and chemical Shift
Wiley and Stine had investigated the structures of triph-
enyldichlorophosphorane obtained by adding chlorine to
triphenylphosphine [1]. They suggested that in acteonitrile
∗
Corresponding author. Tel.: +86 10 6277 2259; fax: +86 10 6278 1695.
E-mail addresses: yinq03@mails.tsinghua.edu.cn (Q. Yin),
yfzhao@mail.tsinghua.edu.cn (Y.-F. Zhao).
1386-1425/$ – see front matter © 2005 Elsevier B.V. All rights reserved.
doi:10.1016/j.saa.2005.05.003

Q. Yin et al. / Spectrochimica Acta Part A 63 (2006) 192–195
193
Fig. 1. The stack 31P NMR spectrum of the mixture of triphenylphosphane
and hexachloroethane in dry dioxane.
Fig. 4. The stack 31P NMR spectrum of the mixture of triphenylphosphane
and hexachloroethane in dry CDCl3.
vents, was dependent on the ratios of chlorine to phos-
phine. In this paper, according to Appel’s method, the triph-
enyldichlorophosphorane was obtained from the results of
hexachloroethane with triphenylphosphine in equalmocular
under dry argon in different solvents at 25 ◦C. The process
was traced by 31P NMR spectroscopy as shown on Figs. 1–4.
Starting material triphenylphosphine (about −5 ppm) was
decreasing, while the products were found with the appear-
ance of new peaks in different solvents. Resonances in the
range δ = 25–60 ppm have been reported for Ph3PO in vari-
ous hydrogen-donating solvents (due to the presence of trace
water) [13].
As for the half-life, the reaction velocity is as follows:
CH2Cl2 > dioxane > C6H6 > CDCl3 > THF
> toluene > pentafluorchlorobenzene
Fig. 2. The stack 31P NMR spectrum of the mixture of triphenylphosphane
and hexachloroethane in dry benzene.
From Fig. 5, it was found that in different solvents, the
products gave different chemical shifts reflected different
structures, such as ionic forms or non-ionic forms. It seems
that in polar solvents, such as CH3CN, CDCl3, CH2Cl2
there was equilibrium between the nonpolar penta-coordinate
phosphorane 1 (31P NMR about −40 ppm) the ionic species
2 (31P NMR about 20–60 ppm or the complex 3 structures as
shown in Eq. (A):
2R3PX2 ꢀ 2R3PX+X− ꢀ R3PX R3PX−
(A)
1
2
3
Denney et al. [8] reported that the 31P NMR chemi-
cal shifts of several phenylchlorophosphoranes in polar sol-
Fig. 3. The stack 31P NMR spectrum of the mixture of triphenylphosphane
and hexachloroethane in dry toluene.
Fig. 5. Relationship between solvent dipole moment and 31P NMR chemical
shift of the products from triphenylphosphinewith hexachloroethane.

194
Q. Yin et al. / Spectrochimica Acta Part A 63 (2006) 192–195
and 1,2-dichloroethane and DME (ethylene glycol dimethyl
ether), the products gave low field chemical shifts at 65
to 25 ppm. While in benzene and dioxane types solvents,
the products produced had much higher chemical shifts at
−44.84 to −42.18 ppm.
From the high field chemical shifts, it is indicated that
the products could be the five-coordinate geometry like the
known molecules, such as MePh2PF2 (δ − 43.2), Ph3PF2
(δ − 58.1) and (C6F5)3PCl2 (δ − 110) [9,10]. At first glance,
it seems that the structure of the products is dependent on
the solvents present. Namely, in polar solvent gave the polar
products and in nonpolar solvents gave nonpolar products.
However, it is controversial for THF versus CH2Cl2 with
dipole moment 5.7 and 3.8, respectively (Fig. 5). In THF, the
products are high coordinate phosphorus compound, while
in CH2Cl2 the products are ionic forms.
Fig. 6. Aromatic rings on the compound 6.
In most benzene type solution, in general, the penta-
coordinate products were observed. In order to analyze their
1
3.2. JP–C coupling constant
structures deeply, 13C NMR and JP–C were compared to
1
To elucidate the structure further, the 1JP–C coupling con-
stants are also investigated. It is worth noting that in ben-
zene and dioxane, for the phenyl carbon directly bonded
each other for different solvents.
For example, in benzene and dioxane, the carbons C1 bond
to phosphorus showed a chemical shift at 137 and 141.2 ppm,
respectively (Table 1), which were 16.7 and 21 ppm down
field shift than the products in acetonitrile. At first glance, it
seems controversial, since the 31P NMR showed that in ben-
zene and dioxane, there was about 100 ppm up field shifts
observed than those in acetonitrile, which is due to penta-
coordinate phosphorus was crowed with high electron den-
sity. How to explain these particular effects? These results
might be due to the benzene molecule situated near the api-
cal position, which could results into the C1 experience the
de-shielding effect.
For the product in dioxane, similar phenomena were also
observed as in benzene. While for the linear ether DME
(ethylene glycol dimethyl ether), the soft skeleton could not
stabilize the penta-covalents phosphorus structures. There-
fore, the product is anionic species with 31P NMR shift at
25 ppm.
1
to phosphorous, the JP–C is 145 and 144 Hz, respectively,
which was larger than that in acetonitrile by almost 50 Hz.
In other words, there was about 50% increment on the 1JP–C
of the triphenyldichlorophosphane in benzene and dioxane
(Table 1). What is the structure factor to regulate the 1JP–C
?
Among the five molecular orbits in penta-coordinate phos-
phorus structures, the three ones in the equatorial positions
will be composed of more “s” character than those in the api-
cal positions. Therefore, the groups in the equatorial positions
will have larger coupling constants than those in the api-
cal positions [11,12]. Consequently, the three phenyl groups
adjacent to phosphorus in the product molecule (Fig. 6)
obtained from the reaction in benzene and dioxane could be
locked in the equatorial positions.
It is known that phosphorus atom has high oxygen atom
affinity. It is expected that dioxane, THF and 4-methyl-
morpholine can stabilize the penta-coordinate phosphorus
structure. Therefore, benzene and dioxane types of solvents
might participate into the high coordinate phosphorus struc-
ture. However, for the linear ether DME (ethylene glycol
dimethyl ether), even in the presence of oxygen atom, there
is no penta-coordinate phosphorus structure.
Table 1
NMR data of triphenyldichlorophosphane in different solvents
Entry
Solvent
31P NMR
chemical
13C NMR chemical shift
(ppm) and coupling
constant (Hz)
shift (ppm)
a
CH3CN
60.87
−44.84
−42.18
120.3 (d, JP–C1 = 97.4)
133.5 (d, JP–C2 = 13.0)
130.8 (d, JP–C3 = 14.4)
137.0 (d, JP–C4 = 3.0)
4. Conclusion
The reaction of triphenylphosphine with hex-
achloroethane was investigated in different solvents. It
was found that in actronitrile, the product showed the 31P
NMR shifts at 60.87 ppm; however, in benzene and ring
ether dioxane and THF, the products showed the 31P NMR
shifts at −44.84 and −42.18 ppm, respectively. The large
coupling constant (1JP–C, about 145 Hz) indicates that in
high coordinate phosphors compounds the three phenyl
b
c
Benzene
137.0 (d, JP–C1 = 145.2)
126.3 (d, JP–C2 = 3.6)
126.0 (d, JP–C3 = 13.0)
123.9 (d, JP–C4 = 18.0)
1,4-Dioxane
141.2 (d, JP–C1 = 143.8)
131.4 (d, JP–C2 = 3.6)
130.7 (d, JP–C3 = 12.3)
128.8 (d, JP–C4 = 18.1)

Q. Yin et al. / Spectrochimica Acta Part A 63 (2006) 192–195
195
groups were constrained in the equatorial positions as the
result of solvent effects.
[6] G.A. Wiley, W.R. Stine, Tetrahedron Lett. 8 (1967) 2321.
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(c) A. Wells, Synth. Commun. 24 (1994) 1715;
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18 (1988) 285;
Acknowledgements
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The authors wish to acknowledge the financial support
from the National Natural Science Foundation of China, No.
20132020, the National Science and Technology Commit-
tee of China, Chinese National Ministry of Education and
Tsinghua University
[8] (a) D.B. Denney, D.Z. Denney, B.C. Chang, J. Am. Chem. Soc. 90
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