Substituent effects on the 31P NMR chemical shifts of arylphosphorothionates

Article abstract of DOI:10.1016/j.tet.2005.12.053

Six tris(aryloxy)phosphorothionates substituted in the para position of the aromatic rings were synthesized and studied by ³¹P NMR, X-ray diffraction techniques and ab initio calculations at a RHF/6-31G** level of theory, in order to find the main structural factors associated with the δ³¹P in these compounds. As the electron-withdrawing (EW) ability of the substituents was increased, an 'abnormal' shielding effect on δ³¹P of the arylphosphorothionates was observed. The analyses of the geometrical properties obtained through both experimental and theoretical methods showed that a propeller-type conformation is preferred for the arylphosphorothionates, except in the case of the tris(O-4-methylphenyl) phosphorothionate, since one of the aromatic rings is not rotated in the same direction as the other two in the solid state. The main features associated with the δ³¹P NMR of compounds 1-6 were a decrease of the averaged O-P-O angle and mainly the shortening of the PS bond length, which is consistent with an increase of the thiophosphoryl bond order as δ³¹P values go upfield. On the other hand, comparison of the experimental and calculated bond lengths and bond angles involving α bonded atoms to phosphorus of the six compounds suggested that stereoelectronic interactions of the type n_πO-σ*_PS, n_πO- σ*_P-OAr and n_πS-σ* _P-OAr could be present in the arylphosphorothionates 1-6.

Full text of DOI:10.1016/j.tet.2005.12.053

Tetrahedron 62 (2006) 2520–2528
3
1
Substituent effects on the P NMR chemical shifts
of arylphosphorothionates
a,
a
*
Francisco M. Goycoolea, Denisse Zepeda-Rivera,
a
Javier Hern a´ ndez,
Josu e´ Ju a´ rez-Onofre, Karla Mart ´ı nez, Jaime Lizardi, Magali Salas-Reyes,
a
a
a
b,†
b
B a´ rbara Gordillo, Carlos Vel a´ zquez-Contreras, Oscar Garc ´ı a-Barradas,
c
d
d
Samuel Cruz-S a´ nchez and Zaira Dom ´ı nguez
d,
*
a
Centro de Investigaci o´ n en Alimentaci o´ n y Desarrollo A.C. Apartado Postal 1735, Hermosillo, Son., M e´ xico
Departamento de Qu ´ı mica, Centro de Investigaci o´ n y de Estudios Avanzados del Instituto Polit e´ cnico Nacional,
Apartado Postal 14-740 M e´ xico, D.F., M e´ xico
b
c
Departamento de Ciencias Qu ´ı mico Biol o´ gicas, Universidad de Sonora, C.P. 83000, Hermosillo Son., M e´ xico
d
Unidad de Servicios de Apoyo en Resoluci o´ n Anal ´ı tica, Universidad Veracruzana, Apartado Postal 575, Xalapa, Ver., M e´ xico
Received 20 September 2005; revised 16 December 2005; accepted 21 December 2005
Available online 19 January 2006
3
1
Abstract—Six tris(aryloxy)phosphorothionates substituted in the para position of the aromatic rings were synthesized and studied by
NMR, X-ray diffraction techniques and ab initio calculations at a RHF/6-31G** level of theory, in order to find the main structural factors
P
3
associated with the d P in these compounds. As the electron-withdrawing (EW) ability of the substituents was increased, an ‘abnormal’
1
3
1
shielding effect on d P of the arylphosphorothionates was observed. The analyses of the geometrical properties obtained through both
experimental and theoretical methods showed that a propeller-type conformation is preferred for the arylphosphorothionates, except in the
case of the tris(O-4-methylphenyl)phosphorothionate, since one of the aromatic rings is not rotated in the same direction as the other two in
3
1
the solid state. The main features associated with the d P NMR of compounds 1–6 were a decrease of the averaged O–P–O angle and mainly
3
1
the shortening of the P]S bond length, which is consistent with an increase of the thiophosphoryl bond order as d P values go upfield. On
the other hand, comparison of the experimental and calculated bond lengths and bond angles involving a bonded atoms to phosphorus of the
six compounds suggested that stereoelectronic interactions of the type n O-s*
p
, n O-s*
p
and n S-s*
p
could be present in the
P]S
P-OAr
P-OAr
arylphosphorothionates 1–6.
q 2005 Elsevier Ltd. All rights reserved.
1
. Introduction
the effect that an electron withdrawing (EW) or electron
releasing (ER) group in the para position of the ring has on
3
1
During the last three decades, numerous groups have been
interested in understanding the factors that contribute to the
the P chemical shift, seems related to the type of
phosphorylated function present in the molecule and/or to
the electronegativity of the a-atoms directly linked to
3
d P chemical shift of organophosphorus compounds. In
1
1
2
i
this context, many correlations between chemical shifts and
phosphorus. However, these two factors cannot always be
separated so as to understand their behavior. For instance, it
has been reported that an increase in the EW power of the
2
molecular structure have been performed. Among them
one of the most known is the relationship found by
3
Gorenstein between the P NMR chemical shift of cyclic
1
31
para substituent causes a deshielding of the P signal in
5
N-aryltriphenylphospha-l -azenes
2
a
2m
and acyclic phosphate esters and OPO bond angles. In the
case of organic phosphorus compounds with aromatic rings,
and O-aryl diethyl-
phosphinates, whereas the opposite behavior is observed
in aryldihexylphosphates.
2
e
2
j
31
Keywords: P NMR; Ab initio; Back-bonding; Propeller-type confor-
mation; X-ray crystal structures; Arylphosphorothionates.
In spite of their commercial importance, few reports dealing
3
with the correlation between P chemical shift and the
1
*
Corresponding authors. Tel.: C52 66 26 89 24 00x364; fax: C52
66 22 80 04 21 (J.H.); tel.: C52 22 88 4189 00x13552; fax: C52 22 88
3
structure of thiophosphoryl compounds have appeared. For
4189 17 (Z.D.);
instance, the phosphorothionates have been applied world-
wide as insecticides but also as motor and transmission oil
e-mail addresses: jahernan@cascabel.ciad.mx; zdominguez@uv.mx
Present address: Unidad de Servicios de Apoyo en Resoluci o´ n Anal ´ı tica,
Universidad Veracruzana, Apartado Postal 575, Xalapa, Ver., M e´ xico.
4
†
5
additive, plasticizer, antioxidant and lubricant of magnetic
0040–4020/$ - see front matter q 2005 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tet.2005.12.053

J. Hern a´ ndez et al. / Tetrahedron 62 (2006) 2520–2528
2521
6
recording materials. Reported in this work is the study of
31
Table 1. P chemical shifts of p-X-arylphosphorothionates 1–6
3
1
the electronic effect that EW and ER groups exert on the
chemical shift of the arylphosphorothionates shown in
P
Compound
1
2
3
4
5
6
31
3
1
Figure 1. The d P of the six compounds are correlated with
d
P (ppm) 56.56
54.92
53.71
53.81
50.47
50.09
the Hammett constants (s ) within the context of LFER
p
7
theory. We analyzed thoroughly the experimental and
Five of the six compounds were solids, only tris(O-4-
methoxyphenyl)phosphorothionate (compound 1) resulted
a colorless oil. We were able to get crystals with quality
enough for an X-ray diffraction study of compounds 2, 3,
theoretical structural parameters obtained through X-ray
diffraction techniques of the resulting crystalline com-
pounds and from the ab initio calculations of the complete
series in order to find the principal structural features that
4
and 5. The ORTEP drawings of them are shown in
3
1
determine the d P of arylphosphorothionates.
Figures 2–5. Data collection and refinement parameters,
bond lengths and bond angles are provided in Tables 2–4.
Compounds 2, 4 and 5 crystallized in the monoclinic
system, the space group found was P2 /n, in the cases of
1
2 and 4 and P2 /c for compound 5. On the other hand,
1
S
P
Compound
X
X
O
O
X
1
2
3
4
5
6
OMe
Me
H
Cl
CN
NO2
O
compound 3 crystallized in the non-centrosymetric space
group P2 2 2 of the orthorhombic system.
1
1 1
X
Figure 1.
2. Results
The synthesis of arylphosphorothionates has been described
5
,6,8
before by several authors.
Treatment of thiophosphoryl
chloride with 3 equiv of the corresponding substituted phenol
is a one-step synthetic route to prepare triaryl phosphorothio-
nates. However, phase transfer catalysts are needed due to the
low reactivity of PSCl with phenols, even under forcing
3
8
c
conditions. In this work, the synthesis of arylphosphor-
othionates1–6 was accomplished as summarized in Scheme 1.
The use of THF as solvent in the first step of the synthesis
contributes to increase the solubility of the corresponding
phosphites, makingeasier its extraction (by filtration) from the
triethylammonium chloride, produced during the reaction.
Then, the phosphites were reacted with sulfur in toluene under
reflux to produce the corresponding arylphosphorothionates.
The desired products were purified from the crude of the
reaction by chromatographic column.
Figure 2. ORTEP drawing of tris(O-4-methylphenyl)phosphorothionate (2).
S8
THF
PCl3 + 3HOAr
P(OAr)3
S=P(OAr)3
Et N
toluene
reflux
3
Scheme 1.
The structures of the synthesized compounds were
3
1
1
13
confirmed from the P, H, C NMR spectra and EI
3
1
mass spectrometry. The P chemical shifts of the six
arylphosphorothionates are given in Table 1. Homogeneous
K1
solutions with the same concentration (0.03 mol L ) of
3
1
compounds 1–6 were prepared, and their corresponding
NMR spectra were acquired in CDCl at 25 8C. The
P
3
Figure 3. ORTEP drawing of tris(O-phenyl)phosphorothionate (3).
3
1
reproducibility of the P chemical shifts was evaluated
through repeated measurements under similar conditions,
and resulted better than G0.01 ppm. The effect of the
Geometry optimization of the six compounds was carried
out at a RHF 6-31G** level of theory. The vibrational
frequencies were computed for each molecule to charac-
terize them as true minima. No imaginary frequencies were
found. The RHF method and the 6-31G** basis set have
3
1
concentration on P chemical shift was measured for
compound 5. Only a small shielding of the signal
(
increased from 0.03 to 0.14 mol L
0.042 ppm) was observed when the concentration was
K1
9
.
been used before succesfully to describe related molecules.

2522
J. Hern a´ ndez et al. / Tetrahedron 62 (2006) 2520–2528
Figure 4. ORTEP drawing of tris(O-4-chlorophenyl)phosphorothionate (4).
The numerical results from our theoretical analyses are
shown in Tables 5 and 6.
data obtained with X-ray diffraction techniques for some of
these heterocyclic compounds, it was observed a shortening
of the P–Oendocyclic bonds of the 1,3,2-dioxaphosphorinane
ring as the EW power of the substituent increases, in
agreement with the presence of the known n O-s* and
P-OAr
3. Discussion
p
npO-s*P]S hyperconjugative interactions acting on the
axial and equatorial thiophosphates, respectively, but also
with the possible transfer of charge density by endocyclic
oxygen atoms to phosphorus (Fig. 7).
3
1
.1. Substituent effect on d P NMR
3
3
The P chemical shift for the six compounds reported here
1
(
(
‘
Table 1) is distributed between 50.09 (XZNO ) and 56.56
2
31
In spite of the structural differences between the cyclic
thiophosphates and the arylphosphorothionates 1–6, it is
interesting to note that the presence of an EW group in the
XZOMe) ppm. The d P of compounds 1–6 show an
abnormal’ shielding effect when the EW power of the
substituent increases. A plot of Hammett s constant versus
p
3
1
3
d P gives a straight line, whose slope is K5.66 with a
1
aromatic ring causes the same shielding effect on the
P
1
0
chemical shift in both kind of systems, which reveals that in
addition to the transfer of charge density from the
endocyclic oxygen atoms toward phosphorus nucleus
proposed for the anancomeric dioxaphosphorinanes there
are other structural and electronic factors that could
contribute to observe the same behavior in the cyclic and
acyclic thiophosphates.
correlation coefficient of 0.974 (Fig. 6).
In analogy to these results, recently it was reported a similar
reversible correlation between the Hammett s constant and
p
3
the P NMR signals of the anancomeric axial and
1
5
equatorial 2-p-X-aryloxy-2-thio-1,3,2l -dioxaphosphori-
3
e
nanes (XZEW or ER groups). Through the structural
Figure 5. ORTEP drawing of tris(O-4-cyanophenyl)phosphorothionate (5).

J. Hern a´ ndez et al. / Tetrahedron 62 (2006) 2520–2528
2523
a
Table 2. X-ray crystal data for arylphosphorothionates 2, 3, 4 and 5
2
3
4
5
Formula
FW
Crystal system
Space group
Crystal size (mm )
C
21
H
21
O
3
PS
C
18
H
15
342.33
O
3
PS
C
445.66
Monoclinic
P2(1)/n
0.7!0.5!0.5
Mo Ka
0.71073
11.243(2)
17.469(4)
11.279 (2)
90.00
118.85(3)
90.00
1940.3(7)
4
54.98
1.526
0.678
9153
4446
2911
18
H
12
C
l3
O
3
PS
C
21 12 3 3
H N O PS
384.41
417.37
Monoclinic
P1 21/c 1
0.75!0.45!0.45
Mo Ka
0.71073
8.8272(3)
18.5137(5)
12.6684(5)
90.00
91.7030(10)
90.00
2069.41(12)
4
55.02
1.340
0.260
8793
4704
3064
0.0499
0.1180
0.0881
0.1374
1.014
Monoclinic
P 1 21/n 1
0.392!0.28!0.28
Mo Ka
0.71073
10.161(4)
12.68(14)
15.753(6)
90.00
97.93 (3)
90.00
2010.2(13)
4
54.98
1.270
0.258
2553
2433
2316
0.0556
0.1178
0.0587
Orthorhombic
P 2(1)2(1)2(1)
0.4!0.4!0.4
Mo Ka
0.71073
7.941(2)
13.183(3)
16.133(3)
90.00
90.00
90.00
1688.9(7)
4
55.24
1.346
0.297
2234
2234
1374
0.0295
0.0789
0.0822
0.0954
1.016
3
Radiation
Wavelength (A)
˚
˚
a (A)
˚
b (A)
˚
c (A)
a
b
g
3
˚
V (A )
Z
2qmax(8)
K3
D
calcd (Mg m
)
K1
Absortion coefficient (mm
No. of reflections collected
No. of independent reflection
No. of observed reflections
R1[FO4s(F)]
WR2
R1 (all data)
WR2
GOF on F2
Max. shift for final cycle of least
squares D/s
Max. peak in final difference
syntheses (e/A )
Max. difference hole (e/A )
)
0.0534
0.1334
0.0881
0.1446
1.034
0.1197
1.096
0.000
0.001
0.003
0.000
0.234
0.201
0.534
0.248
3
˚
3
˚
K0.263
K0.224
K0.355
K0.272
a
Standard deviations are in parentheses.
a
˚
Table 3. Selected bond lengths (A) for arylphosphorothionates 2–5
P]S
P–O1
P–O2
P–O3
O1–C
O2–C
O3–C
2
3
4
5
1.8987(16)
1.8981(12)
1.8968(10)
1.8888(8)
1.572(3)
1.567(2)
1.579(2)
1.5704(16)
1.581(3)
1.579(2)
1.5862(19)
1.5869(17)
1.575(3)
1.578(2)
1.5908(18)
1.5811(16)
1.412(4)
1.414(3)
1.418(3)
1.402(3)
1.414(4)
1.399(4)
1.401(3)
1.394(3)
1.414(4)
1.406(3)
1.418(3)
1.403(3)
a
Standard deviations are in parentheses.
a
Table 4. Selected bond angles (q) in degree for arylphosphorothionates 2–5
O1PO2
O2PO3
O3PO1
SPO1
SPO2
SPO3
2
3
4
5
106.23(15)
100.05(12)
100.48(10)
100.60(9)
100.98(15)
99.14(12)
99.85(10)
99.06(9)
100.78(15)
101.30(12)
99.95(10)
99.06(9)
111.91(12)
117.01(10)
118.04(8)
117.51(7)
17.03(12)
118.02(9)
117.78(8)
117.93(7)
117.98(11)
117.98(9)
117.36(8)
117.64(7)
a
Standard deviations are in parentheses.
Table 5. Selected calculated parameters of arylphosphorothionates 1–6
RHF 6-31G**
˚
(A)
Bond
Lengths
a
P–O
Bond
OPO
Angles
OPO
(Degrees)
OPO
a
P]S
O–C
1
2
3
4
5
6
1.918
1.918
1.916
1.914
1.910
1.909
1.584
1.584
1.584
1.585
1.586
1.586
1.388
1.386
1.386
1.384
1.381
1.379
100.78
100.76
100.72
100.61
100.46
100.40
100.78
100.76
100.73
100.61
100.48
100.40
100.78
100.76
100.74
100.61
100.48
100.40
a
The calculated P–O1, P–O2 and P–O3 bond lengths were identical in each case, an only one value is reported. It was the same case for C–O1, C–O2
and C–O3.

2524
J. Hern a´ ndez et al. / Tetrahedron 62 (2006) 2520–2528
Table 6. Calculated natural charges on heteroatoms of arylphosphorothio-
nates 1–6
The averaged O–P–O bond angles found for compounds 2,
, 4 and 5 are 102.66, 100.16, 100.09 and 99.578,
3
a
respectively. As can be observed, it is clear that this
parameter reaches its greater value when the para
substituent at the aromatic ring is an ER group and the
smallest one when X is an EW group. In addition, the
compounds 3 and 4 have almost the same averaged O–P–O
bond angle, and it is interesting that the chemical shifts of
both compounds have very close values (53.71 ppm for 3
and 53.81 ppm for 4).
Compound
S
P
O
1
2
3
4
5
6
K0.677
K0.675
K0.670
K0.658
K0.643
K0.635
2.360
2.359
2.356
2.349
2.340
2.336
K0.917
K0.917
K0.917
K0.914
K0.913
K0.912
a
As the calculated molecules have a C
3
symmetry, O1, O2 and O3 are
equivalent into each molecule, and as a consequence, the natural charges
too.
A similar behavior was found from the analysis of
calculated O–P–O bond angles (Table 5). Since the
geometry optimization of the six compounds gave in all
the cases the same conformation, important changes
between the averaged O–P–O bond angles of the six
arylphosphorothionates were not found. However, as the
EW power of the para substituent decreases, the averaged
O–P–O angle is opened very slightly, from 100.40 degrees
in compound 6 to 100.78 in compound 1. A plot of the
5
5
5
5
5
5
5
5
7
6
5
4
3
2
1
0
3
1
averaged O–P–O angle against P chemical shift gave an
acceptable correlation (the correlation coefficient was
0
.947) (Fig. 8), showing that even a minimum difference
in the OPO angle might also be correlated succesfully to the
shielding effect observed for this kind of compound.
5
7
–
0.4
–0.2
0.0
0.2
0.4
0.6
0.8
sp
56
31
P
Figure 6. Relationship between the calculated s
p
and the experimental
5
5
5
5
5
5
5
4
3
2
1
0
NMR chemical shift for arylphosphorothionates 1–6 (correlation coeffi-
cientZ0.974, slopeZK5.66).
(a)
EW
(b)
O
P
S
P
O
O
S
O
EW
O
O
1
00.4
100.5
100.6
100.7
100.8
Calculated (averaged) O–P–O angle (degrees)
Figure 7.
Figure 8. Relationship between the calculated O–P–O bond angle and the
31
experimental P NMR chemical shift for arylphosphorothionates 1–6
correlation coefficientZ0.946, slopeZ14.80).
(
3
.2. Structural analysis
Three of the four arylphosphorothionates analyzed by X-ray
diffraction techniques have almost a propeller-type confor-
On the other hand, although significant variations of the
P]S bond length were not observed among the X-ray
diffraction data of compounds 2, 3 and 4 [the difference
between the bond lengths are less than 2.7 s(O99%
confidence level )], when the para substituent is a strong
EW group (XZCN in compound 5) the P]S bond length
˚
become significantly shorter [1.8888(8) A in 5 against
1
1
mation in solid state, since the three OAr groups are
rotated more or less in one direction, except in the case of
the compound 2, as can be visualized in the ORTEP
drawings (Figs. 2–5). The optimized geometries of the six
compounds gave also molecular propellers, but in this case
1
2
all of them have C symmetry, therefore the three OAr
3
groups of each structure were equivalent among them.
1.8987(16), 1.8981(12) and 1.8968(10) in 2, 3 and 4,
respectively (see Table 3)]. This result supports the idea that
a participation of sulfur in the transference of the charge
density towards the phosphorus atom exists in the arylphos-
phorothionates when EW substituents are bonded to them.
RHF calculations reinforce the experimental observation,
the calculated P]S bond length (Table 5) is distributed
The analysis of all the O–P–O bond angles found for the
crystalline compounds 2–5 (Table 4), reveals that in most of
them this angle is of around 1008, only O1–P–O2 in
compound 2 is considerably more opened [106.238 (15)].

J. Hern a´ ndez et al. / Tetrahedron 62 (2006) 2520–2528
2525
˚
between 1.918 (compounds 1 and 2) and 1.909 A,
data are in agreement with the theoretical data reported
before by Kuivalainen in the study of a series of O,O-
(
compound 6). In addition, the linear regression of
3
1
3a
dialkyl O-aryl phosphorothionates. The presence of EW
calculated P]S bond length against the experimental d P
chemical shift correlates satisfactorily, as can be visualized
from Figure 9 (coefficient of correlation was 0.9634). The
result suggests an increasing thiophosphoryl bond order as
groups on the aromatic rings of arylphosphorothionates
lead to a decrease of the positive charge on phosphorus,
accompanied also by a decreasing of the net charge on
sulfur and oxygen atoms and the shortening of the P]S
bond length, whereas the ER groups produce a slight
shortening of the P–O bond length. As can be assumed,
structures I and IV must be favored over the other two
when X is an EW group, whereas II and III should have
important contributions when X is an ER group.
3
1
d P values go upfield, which is in agreement with an effect
of back-bonding from sulfur to phosphorus atom.
3
a,e
5
5
5
5
5
5
5
5
7
6
5
4
3
2
1
0
S
P
S
P
ArO
O
X
ArO
O
X
OAr
I
OAr
II
S
P
S
P
1
.908
1.910
1.912
1.914
1.916
1.918
ArO
O
X
ArO
O
X
Calculated P=S bond length
OAr
IV
OAr
III
Figure 9. Relationship between the calculated P]S bond length and the
experimental P NMR chemical shift for arylphosphorothionates 1–6
correlation coefficientZ0.964, slopeZ621.70).
31
Scheme 2.
(
Nevertheless those significant differences among the
averaged P–O bond lengths of compounds 2, 3, 4 and 5
The plot of natural charges on phosphorus and sulfur
1
3
atoms against experimental
P chemical shift of
˚
1.576, 1.575, 1.585 and 1.579 A, respectively) were not
(
observed in solid state. The fact that P–O1 bond length is
shorter than P–O2 and P–O3 in compounds 3, 4 and 5
compounds 1–6 gave good correlation coefficients
(0.955 and 0.954, respectively) (Figs. 10 and 11),
however an analogous plot of natural charges at oxygen
˚
1.567(2) against 1.579(2) and 1.578(2) A in 3, 1.579 (2)
31
[
against 1.5862 (19) and 1.5908 (18) A in 4 and 1.5704
atoms against d P was not satisfactory (the correlation
coefficient was 0.7), which suggests a minor participation
of the aryl oxygen atoms to the ‘abnormal’ shielding of
˚
˚
16) against 1.5869 (17) and 1.5811 (16) A in 5] is
(
consistent with the presence of at least a n O-s* or
3
the P chemical shift observed experimentally.
1
p
P-OAr
npO-s*P]S interaction per molecule in solid state, as it
has been proposed for analogous phosphorus containing
1
3
compounds. The changes in the calculated geometrical
parameters of these systems also could be related to
57
9
a,b
the existence of stereoelectronic interactions
of the
5
5
5
6
5
4
npO-s*P]S type, for example, since an increase of the ER
power of the para substituent at the aromatic rings
produces a slight shortening of the calculated averaged
˚
P–O bond lengths (from 1.584 A in compounds 1–3 to
˚
.586 A in compound 6) accompanied by a lengthening of
1
the P]S bond distance, as it was discussed above.
53
52
However, a plot of the calculated averaged P–O bond
lengths against the experimental d P did not give a linear
relationship.
3
1
5
5
1
0
The electronic effect of the para substituent (X) on
arylphosphorothionates 1–6 can be summarized by the
canonical structures I–IV (Scheme 2). Natural charges
evaluated to the RHF 6-31G** level of theory (Table 6)
are well described by these resonance structures. The
charges at S are ca. K0.7 and those at P are ca. C2.4,
whereas the calculated charges at O are ca. K0.9. These
2
.335 2.340 2.345 2.350 2.355 2.360 2.365
Natural charges on phosphorus
Figure 10. Relationship between the natural charge on phosphorus atom
and the experimental P NMR chemical shift for arylphosphorothionates
1–6 (correlation coefficientZ0.955, slopeZ238.16).
31

2526
J. Hern a´ ndez et al. / Tetrahedron 62 (2006) 2520–2528
syringe-septum and cannula techniques. THF and toluene
5
5
5
5
5
5
5
5
7
6
5
4
3
2
1
0
were of reagent grade and were dried and distilled
immediately before use from sodium/benzophenone.
Triethylamine was dried and distilled from LiAlH4.
Products were purified by flash column chromatography
on silica gel 230–400 mesh using as eluent mixtures of
AcOEt/hexanes. Yields are given for isolated products.
AcOEt/hexanes or CH Cl /hexanes mixtures were used
2
2
for recrystallization of 2–5. Crystallographic work was
performed in the difractometers Enraf-Nonius CAD-4 and
14
Kappa CCDC. Data collection: CAD-4 and Kappa CCDC
1
Software. Cell refinement: CAD-4 and Kappa CCDC
5
1
Software. Data reduction WinGX. The structures were
6
1
resolved by direct methods with SHELXS97 and refined
7
1
with SHELXL97. Molecular graphics: Diamond and
8
19
2
0
–
0.68
–0.67
–0.66
–0.65
–0.64
–0.63
dihedral angles: PARST 95. Crystallographic Data Center
and the deposition numbers are: CCDC 284418 for
compound 2, CCDC 284416 for 3, CCDC 284415 for
compound 4 and CCDC 284417 for 5. Ab initio calculations
Natural charge on sulfur atom
Figure 11. Relationship between the natural charge on sulfur atom and the
experimental P NMR chemical shift for arylphosphorothionates 1–6
correlation coefficientZ0.954, slopeZK137.89).
3
1
2
1
were performed employing the Gaussian 98 program.
(
4
. Conclusion
5.1. General procedure for the synthesis of compounds
–6
1
3
1
The P chemical shifts of a series of p-X-arylphos-
phorothionates 1–6 are analyzed in terms of the electronic
effect of the p-substituent. As the electronwithdrawing
In a three-necked 500 mL flask, fitted with dropping funnel,
stir bar and rubber septa, were placed 34.2 mmol of p-X
(
EW) power of the X substituent increases, an ‘abnormal’
phenol, 5.28 mL of Et
THF. Then 1.57 g of PCl
3
N (37.9 mmol) and 200 mL of dry
(11.4 mmol) were added via
3
1
shielding on the P NMR signal is observed, which is
expressed in the reversible correlation between the
Hammett constant s and d P. The detailed analyses of
the experimental and theoretical structural parameters of the
six arylphosphorothionates, obtained through X-ray diffrac-
tion techniques and ab initio calculations showed that the
features associated with the shielding of the P NMR signal
of the arylphosphorothionates are the decreasing of the
O–P–O averaged angle and the shortening of the P]S bond
length. An increase of the thiophosphoryl bond order as a
result of the back-bonding effect from sulfur toward the
phosphorus atom is observed for arylphosphorothionate
substituted with EW groups. Additionally, the changes
observed in the experimental and theoretical structural
parameters could be related to the presence of stereo-
3
syringe. The reaction mixture was stirred at room
temperature for 24 h then, the resultant triethylammonium
chloride was filtered off through a filter tipped cannula. The
solid was washed two times with 15 mL of dry THF
collecting the filtrate in a round-bottomed flask. The solvent
was removed under reduced pressure to dryness to give the
intermediate p-X-phenyl phosphite in w80% yield as a
thick oil, which was used in subsequent reaction without
further purification.
3
1
p
3
1
In a round-bottomed 100 mL flask, fitted with a reflux
condenser, stir bar and rubber septa, were placed 0.36 g
(11.4 mmol) of elemental sulfur. A solution of the p-X-
phenylphosphite (11.4 mmol) in dry toluene (80 mL) was
added to the flask and the resulting suspension was stirred
under reflux in an oil bath for 24 h. After cooling, the
unreacted sulfur was filtered off and the suspension was
concentrated under vaccum. The residue was washed with
an aqueous solution of 10% sodium bicarbonate. The
product was extracted with methylene chloride and the
organic layer dried over sodium sulfate. The solvent was
removed in a rotary evaporator and the oily residue was
chromatographed on silica gel using hexanes/ethyl acetate
as eluent.
electronic interactions of the type n O-s*
p
, and n O-
p
P]S
s*P-OAr, as has been proposed before for analogous systems.
Further efforts in the theoretical study of this kind of
compound are currently underway, and will be reported
soon.
5. Experimental
1
13
31
Melting points are uncorrected. The H, C and P spectra
were recorded on a Bruker AVANCE 400 spectrometer
operating at 400 MHz at a probe temperature of 25.0 8C.
Bruker MSL-200 spectrometer operating at 50.32 MHz and
Varian Mercury Plus (300 MHz) spectrometers, respect-
8
f
5.1.1. Tris(O-4-methoxyphenyl)phosphorothionate (1).
According to the general procedure described above, 4.25 g
(34.2 mmol) of p-MeO-phenol was treated with 1.57 g
(11.4 mmol) of PCl and 4.7 mL (34.2 mmol) of Et N. The
ively, using deuterated CDCl as solvent. Phosphorus NMR
3
3
3
spectra are reported in ppm downfield (C) from 85%
H PO used as external standard. Mass spectra were
measured on Varian Saturn Star 3400 CX spectrometer
using electron impact (El) at 70 eV. The reactions were
performed under an atmosphere of nitrogen in oven-dried
glassware. Solvents and solutions were transferred by
resulting 3.64 g of phosphite (9.1 mmol) were reacted with
0.3 g (9.1 mmol) of elemental sulfur. Flash chromatography
(hexanes/ethyl acetate 80:20) gave 3.1 g (80%) of a
3
4
1
3
colorless oil. H NMR d 3.79 (s, 9H), 6.86 (d, JHHZ
3
4
9.0 Hz, 6H), 7.13 (dd, J Z9.0 Hz, JHPZ1.7 Hz, 6H),
HH
1
RMN C d 55.48 (s, OCH ), 114.57 (s, C ), 121.76 (d,
3
3
m

J. Hern a´ ndez et al. / Tetrahedron 62 (2006) 2520–2528
2527
3
2
3
13
J Z3.9 Hz, C ), 144.24 (d, J Z8.1 Hz, C ), 157.09
1.4 Hz, 6H), 7.73 (d, J Z8.6 Hz, 6H), C NMR d 110.37
CP
o
CP
i
HH
3
s, C ), RMN P d 56.56; MS (EI) m/z 432, 401, 309, 123.
1
3
(
Anal. Calcd for C H O PS: C 58.33, H 4.89, S 7.42.
(s, C ), 117.58 (s, CN), 122.05 (d, J Z5.2 Hz, C ), 134.25
p
p
CP
31
o
2
(s, C ), 152.99 (d, J Z7.4 Hz, C ), P NMR d 50.47. MS
2
1
21
6
m CP i
Found: C 58.80, H 4.68, S 7.14.
(EI) m/z 417, 315, 299, 118, 102. Anal. Calcd for
C H N O PS: N 10.07, C 60.43, H 2.90, S 7.68. Found:
N 10.19, C 60.80, H 2.43, S 8.02.
2
1 12 3 3
8
a,8d
5.1.2. Tris(O-4-methylphenyl)phosphorothionate (2).
According to the general procedure described above, 3.53 g
8
a,8e
(
(
34.2 mmol) of p-Me-phenol were treated with 1.57 g
11.4 mmol) of PCl3 and 4.7 mL (34.2 mmol) of Et N.
5.1.6. Tris(O-4-nitrophenyl)phosphorothionate (6).
According to the general procedure described above,
3
The resulting 3.53 g (10.0 mmol) of phosphite were reacted
with 0.3 g (10.0 mmol) of elemental sulfur. Flash chromato-
graphy (hexanes/ethyl acetate 95:5) gave 3.27 g (85%) of a
4.06 g (34.2 mmol) of p-nitrophenol were treated with
1.57 g (11.4 mmol) of PCl
Et N. The resulting 2.57 g of phosphite were reacted with
and 4.7 mL (34.2 mmol) of
3
3
white solid. Recrystallization from a mixture hexanes–
CHCl (90/10) gave colorless crystals (mp 89–90 8C). H
0.18 g (5.7 mmol) of elemental sulfur. Flash chromato-
graphy (hexanes/ethyl acetate 60:40) gave 0.81 g (30%)
of colorless needles. Recrystallization from a mixture
hexanes–ethyl acetate (80/20) gave ligth yellow crystals
1
3
3
4
NMR d 2.26 (s, 9H), 7.03 (dd, J Z8.7 Hz, JHPZ1.2 Hz,
HH
3
13
6
H), 7.07 (d, J Z8.7 Hz, 6H), RMN C d 20.75 (s,
HH
2
1
3
CH ), 148.55 (d, J Z8.3 Hz, C ), 135.20 (s, C ), 120.44
(mp 175.0—175.1 8C) H NMR d 7.43 (dd, JHHZ9.0 Hz,
3
3
CP
i
p
31
4 3 13
(
d, J Z4.4 Hz, C ), 130.09 (s, C ), RMN P d 54.92. MS
JHPZ1.5 Hz, 6H), 8.35 (d, JHHZ9.0 Hz, 6H), C NMR d
3
CP
o
m
(
C H O PS: C 65.61, H 5.51, S 8.34. Found: C 65.15, H
EI) m/z 384 (100), 293, 277, 107, 91. Anal. Calcd for
121.83 (d, JCPZ4.3 Hz, C
o
), 125.86 (s, C
m
), d 145.80
(s, C ), 154.30 (d, JCPZ7.4 Hz, C ), P NMR d 50.09.
p i
2
31
2
1 21 3
5
.03, S 8.41.
MS (EI) m/z 477, 355, 339, 138, 122. Anal. Calcd for
C H N O PS: N 8.80, C 45.29, H 2.53, S 6.72. Found: N
8.74, C 45.38, H 2.11, S 6.95.
1
8 12 3 9
5
,8d
5
ing to the general procedure described above, 3.2 g
.1.3. Tris(O-phenyl)phosphorothionate (3).
Accord-
(
(
34.2 mmol) of phenol were treated with 1.57 g
11.4 mmol) of PCl3 and 4.7 mL (34.2 mmol) of Et N.
6. Supplementary material
3
The resulting 2.83 g (9.1 mmol) of phosphite were reacted
with 0.3 g (9.1 mmol) of elemental sulfur. Flash chroma-
tography (hexanes/ethyl acetate 98:2) gave 2.74 g (88%)
of colorless needles. Recrystallization from a mixture of
hexanes–ethyl acetate (80/20) gave colorless crystals (mp
Crystallographic data for the structural analysis have been
deposited at the Cambridge Crystallographic Data Centre,
CCDC.
1
3
5
3–54 8C). H NMR d 7.14 (m, 3H), 7.16 (d, JHHZ8.3 Hz,
3 13
6
H), 7.29 (d, JHHZ8.3 Hz, 6H), C NMR d 121.13 (d,
Acknowledgements
3
J Z4.4 Hz, C ), 125.68 (s, C ), 129.67 (s, C ), 150.69 (d,
CP
o
p
m
2
31
We thank CONACyT (Me
30137-E) and Dr. Gabiel Merino for his comments. The
help of Ma. Teresa Corte
´z Picasso and Geiser Cu e´ llar of the
´
xico) for financial support (Grant
J Z7.7 Hz, C ), P NMR d 53.71. MS (EI) m/z 342
CP
i
(
H 4.42, S 9.37. Found: C 62.94, H 3.89, S 9.68.
100), 265, 249, 93. Anal. Calcd for C H O PS: C 63.15,
18 15 3
Departamento de Qu ´ı mica of CINVESTAV-IPN to obtain
the elemental analyses is greatly appreciated.
8
a
5
According to the general procedure described above,
.1.4. Tris(O-4-chlorophenyl)phosphorothionate (4).
4
1
.39 g (34.2 mmol) of p-chlorophenol were treated with
.57 g (11.4 mmol) of PCl and 4.7 mL (34.2 mmol) of
References and notes
3
Et N. The resulting 3.6 g (8.7 mmol) of phosphite were
3
reacted with 0.27 g (8.7 mmol) of elemental sulfur. Flash
chromatography (hexanes/ethyl acetate 80:20) gave 3.87 g
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76%) of colorless crystals (mp 80–82 8C). H NMR d 7.15
(
(
3
4
3
dd, J Z9.1 Hz, J Z2.0 Hz, 6H), 7.34 (dd, JHHZ
HH HP
5 13 2
9
4
1
4
2
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c
5
According to the general procedure described above,
.1.5. Tris(O-4-cyanophenyl)phosphorothionate (5).
4
.06 g (34.2 mmol) of p-cyanophenol were treated with
1
Et N. The resulting 3.86 g (10.0 mmol) of phosphite were
.57 g (11.4 mmol) of PCl and 4.7 mL (34.2 mmol) of
3
3
reacted with 0.32 g (10.0 mmol) of elemental sulfur. Flash
chromatography (hexanes/ethyl acetate 80:20) gave 3.27 g
(
of hexanes–ethyl acetate (80/20) gave colorless crystals (mp
85%) of colorless needles. Recrystallization from a mixture
1
3
4
1
55–156 8C). H NMR d 7.34 (dd, J Z8.6 Hz, JHPZ
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1