Substituent effects on 31P NMR chemical shifts and 1J P-Se of triarylselenophosphates

Article abstract of DOI:10.1080/10426500902953979

The effect of electron-withdrawing (EW) and electron-releasing (ER) substituents on the 31P NMR chemical shifts and the structural parameters of a series of tris-(p-X-aryl)selenophosphates is reported in this article. Similarly to O-aryl phosphates and O-aryl thiophosphates, EW groups attached to aromatic rings induce a shielding effect on the 31P NMR signal. After a detailed experimental and theoretical analysis, we confirmed that the selenium atom is the main part responsible for the charge density transfer toward phosphorus through a back-bonding effect. The obtained 1JP-Se values for the complete series agree with this observation. Supplemental materials are available for this article. Go to the publisher's online edition of Phosphorus, Sulfur, and Silicon and the Related Elements to view the free supplemental file.

Full text of DOI:10.1080/10426500902953979

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Substituent Effects on 31P NMR
Chemical Shifts and 1JP–Se of
triarylselenophosphates
Zaira Domínguez a , Javier Hernández a , Lorena Silva-Gutiérrez b
Magali Salas-Reyes a , Mario Sánchez c & Gabriel Merino c
,
a Unidad de Servicios de Apoyo en Resolución Analítica , Universidad
Veracruzana , Xalapa, México
b Centro de Investigación en Alimentación y Desarrollo A.C. ,
Hermosillo, México
c Departamento de Química , Universidad de Guanajuato ,
Guanajuato, México
Published online: 23 Mar 2010.
To cite this article: Zaira Domínguez , Javier Hernández , Lorena Silva-Gutiérrez , Magali Salas-
Reyes , Mario Sánchez & Gabriel Merino (2010) Substituent Effects on 31P NMR Chemical Shifts and
1JP–Se of triarylselenophosphates, Phosphorus, Sulfur, and Silicon and the Related Elements, 185:4,
772-784, DOI: 10.1080/10426500902953979
To link to this article: http://dx.doi.org/10.1080/10426500902953979
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Phosphorus, Sulfur, and Silicon, 185:772–784, 2010
Copyright ꢀC Taylor & Francis Group, LLC
ISSN: 1042-6507 print / 1563-5325 online
DOI: 10.1080/10426500902953979
SUBSTITUENT EFFECTS ON 31P NMR CHEMICAL SHIFTS
AND 1JP–Se OF TRIARYLSELENOPHOSPHATES
Zaira Dom´ınguez,1 Javier Herna´ndez,1 Lorena Silva-Gutie´rrez,2
Magali Salas-Reyes,1 Mario Sa´nchez,3 and Gabriel Merino3
1Unidad de Servicios de Apoyo en Resolucio´n Anal´ıtica, Universidad Veracruzana,
Xalapa, Me´xico
2Centro de Investigacio´n en Alimentacio´n y Desarrollo A.C., Hermosillo, Me´xico
3Departamento de Qu´ımica, Universidad de Guanajuato, Guanajuato, Me´xico
The effect of electron-withdrawing (EW) and electron-releasing (ER) substituents on
the 31P NMR chemical shifts and the structural parameters of a series of tris-(p-X-
aryl)selenophosphates is reported in this article. Similarly to O-aryl phosphates and O-aryl
thiophosphates, EW groups attached to aromatic rings induce a shielding effect on the 31
P
NMR signal. After a detailed experimental and theoretical analysis, we confirmed that the
selenium atom is the main part responsible for the charge density transfer toward phospho-
rus through a back-bonding effect. The obtained 1JP-Se values for the complete series agree
with this observation.
Supplemental materials are available for this article. Go to the publisher’s online edition of
Phosphorus, Sulfur, and Silicon and the Related Elements to view the free supplemental
file.
Keywords DFT calculations; 31P NMR; selenophosphates; solvent effect
INTRODUCTION
Phosphates, and their sulfur analogues, are systems with relevant biological and com-
mercial importance. While the phosphate group is a fundamental part of several molecules
of biological relevance, such as ATP,1 the thiophosphoryl group is a primary component of
insecticides applied worldwide.2 In contrast, the chemistry of selenophosphates has been
Received 6 February 2009; accepted 6 April 2009.
We thank Dr. Barbara Gordillo from Cinvestav for the facilities provided during the collection of the
diffraction data and Dr. Oscar Garc´ıa-Barradas for the acquisition of the NMR spectra. The help of Karla Martinez
Robinson, Ma. Teresa Corte´z Picasso, and Geiser Cue´llar in obtaining the elemental analyses and the mass spectra
is also greatly appreciated. We thank Ariana Teissier and Maryel Contreras for cheerful discussion. The authors
are grateful for financial support from Conacyt (Grant 57892). M.S. acknowledges Conacyt for the postdoctoral
fellowship.
Address correspondence to Dr. Javier Herna´ndez, Unidad de Servicios de Apoyo en Resolucio´n Anal´ıtica,
Universidad Veracruzana, Apartado Postal 575, Xalapa, Ver., Me´xico. E-mail: javmartinez@uv.mx and Dr. Gabriel
Merino, Departamento de Qu´ımica, Universidad de Guanajuato, Noria Alta s/n, Guanajuato, Gto., 36050, Me´xico.
E-mail: gmerino@quijote.ugto.mx
772

SUBSTITUENT EFFECTS ON TRIARYLSELENOPHOSPHATES
773
X
X
S
P
O
O
P
O
O
O
O
S
Figure 1 Hyperconjugate interactions at the anancomeric 2-p-X-aryloxy-2-thio-1,3,2λ5-dioxaphosphorinanes.
less studied.3,4 Recently the discovery of two eukaryotic enzymes, type I iodothyronine
5ꢁ-deiodinase and mammalian thioredoxin reductase, emphasized the biological impor-
tance of the selenophosphate group.5,6
The 31P NMR chemical shift is a very sensitive parameter for monitoring structural
changes of organophosphorus compounds. Several correlations between 31P chemical shifts
and molecular structure have been found.7–19 For instance, the effect of the electron-
withdrawing (EW) groups at the para position of the phenyl rings on the 31P chemical
shift of O-aryl phosphates13,14 and O-aryl thiophosphates has been analyzed by several
authors.16–19 Interestingly, an “abnormal” shielding effect of the 31P NMR signal was found
when the electron-withdrawing (EW) power of the substituent was increased in these types
of compounds.
Theoretical and experimental results have suggested that the π bond character of
the O–P and S–P bonds is related to the shielding of the δ31P in O-aryl chalcogenphos-
phates. However, other parameters could be involved. Recently, we found that, the P–O
endocyclic bond lengths of the anancomeric axial and equatorial 2-p-X-aryloxy-2-thio-
1,3,2λ5-dioxaphosphorinanes in the solid state become shorter as the EW power of the
substituent X increases.18 This effect was explained by the presence of the nπ O→σ∗
P-OAr
and nπ O→σ∗ hyperconjugative interactions (Figure 1), but also an electron transfer
P-S
from the endocyclic oxygen atoms to the phosphorus atom could be involved.
In a subsequent study, we found that tris(p-X-aryloxy)phosphorothionates (TAPTs)
prefer a propeller-type conformation.17 This geometrical arrangement allows interactions
between the oxygen lone pairs and polar bonds that keep an antiperiplanar disposition.
As shown in Figure 2, there is a lone pair at each oxygen atom with an antiperiplanar
disposition to the P–S bond, whereas the other occupied orbital is antiperiplanar respect to
their contiguous P–OAr bonds. The X-ray diffraction data show that one of the three P–O
bonds is significantly shorter than the other two bonds (the difference is higher than 2.76 σ).
At least three of the four reported crystalline structures show this trend, which suggests
S
Ar
P
Ar
O
O
Ar
O
Figure 2 TAPTs adopted conformation.

´
774
Z. DOMINGUEZ ET AL.
Se
X
X
O
P
O
X
1 = OMe
2 = Me
3 = H
O
4 = Cl
5 = CN
6 = NO2
X
Figure 3 Studied selenophosphates in this article.
the existence of the hyperconjugative interactions, similar to those described before for
analogous systems.
The electronic substituent effect on the 31P chemical shift, in terms of its structure, is
an attractive problem. Clearly, a complete analysis should include the bonding properties of
the α-bonded atoms to phosphorus, as well as the possible stereoelectronic interactions that
play an important role on structure and conformation. In this article, we report a detailed
analysis of the substitution effect on 31P NMR chemical shift and 1JP-Se coupling constant
of tris-(p-X-aryl)selenophosphates (Figure 3). This NMR study is supported by density
functional theory (DFT) calculations, which provide insight into the electronic effect of the
para-substituent on the structure.
RESULTS AND DISCUSSION
The synthesis of arylselenophosphates 1–6 was achieved by adding elemental se-
lenium to a triarylphosphite solution in refluxing toluene, using the same methodology
described for the preparation of the phosphorothionate analogues.17 The synthesis of the
six compounds was confirmed by 1H, 13C, and 31P NMR spectra; EI mass spectroscopy; and
elemental analysis. All compounds reported here are solids. However, we only obtained
crystals of suitable quality for 2, 3, 4, and 5. The isomorphism of the previously reported
four crystalline phosphorothionates17 offers us an opportunity to compare experimental
structural parameters for each pair of chalcogenphosphates in the solid state. The ORTEP
drawings of compounds 2, 3, 4, and 5 are shown in Figure 4. Selected bond lengths, bond
angles, data collection, and refinement parameters are provided in Tables I and II. Com-
pounds 2, 4, and 5 were crystallized in the monoclinic system. While the space group for 2
and 4 is P21/n, in the case of compound 5 it corresponds to P21/c. Finally, compound 3 was
crystallized in the non-centrosymmetric space group P212121 of the orthorhombic system.
Several authors have found that trimethyl chalcogenphosphates (O-P(OMe)3, S-
P(OMe)3, and Se-P(OMe)3) adopt at least three different conformers, usually addressed
in terms of their overall symmetry as C3, C1, and Cs.3,4,20–22 The triarylselenophosphates
structures reported in this article seem to have a similar behavior. Three of the four com-
pounds analyzed by X-ray diffraction adopted a conformation with an almost C3 symmetry,
whereas compound 2 preferred a conformation with a C1 symmetry in the solid state (see
Figure 4).

SUBSTITUENT EFFECTS ON TRIARYLSELENOPHOSPHATES
775
Figure 4 ORTEP drawing of tris(p-X-aryl)selenophosphates 2–5.
One may speculate that triarylselenophosphates 1–6 present more than one confor-
mation in solution, depending on the dielectric constant. Obviously, these facts may have
an effect on the 31P chemical shift and on the 1JP-Se coupling constant of compounds 1–6.
Taking this into account, we acquired the 31P NMR spectra of the six compounds employing
solvents with distinct dielectric constants: CCl4, C6D6, CDCl3, CO(CD3)2, CD3OD, and
(CD3)2SO.
Table I Selected bond lengths (Å) and bond angles (◦) for arylselenophosphates 2–5a
2
3
4
5
P–Se
P–O1
P–O2
P–O3
O1–C
O2–C
O3–C
O1PO2
O2PO3
O3PO1
SePO1
SePO2
SePO3
2.0520(14)
1.577(3)
1.578(3)
1.587(3)
1.425(5)
2.0522(8)
1.5746(19)
1.584(2)
1.579(2)
1.416(3)
2.0451(10)
1.586(2)
1.586(3)
1.587(2)
1.408(4)
2.0397(10)
1.573(2)
1.589(3)
1.586(2)
1.403(4)
1.396(4)
1.406(4)
100.60(9)
99.06(9)
99.06(9)
1.421(5)
1.405(5)
1.415(4)
1.409(3)
1.414(4)
1.414(4)
100.65(16)
100.83(18)
106.11(18)
111.89(14)
118.63(13)
116.73(13)
100.09(11)
99.42(11)
101.39(11)
117.18(9)
117.66(8)
117.85(8)
100.48(10)
99.85(10)
99.95(10)
117.18(9)
117.66(8)
117.85(8)
117.51(7)
117.93(7)
117.64(7)
aStandard deviations are in parentheses.

´
776
Z. DOMINGUEZ ET AL.
Table II X-ray crystal data for arylselenophosphates 2, 3, 4, and 5a
2
3
4
5
Formula
FW
Crystal system
Space group
Crystal size (mm3)
Radiation
Wavelength (Å)
a (Å)
b (Å)
c (Å)
α
C21H21O3PSe
431.33
Monoclinic
P21/n
C18H15O3PSe
389.33
Orthorhombic
P212121
C18H12Cl3O3PSe C21H12N3O3PSe
492.56
Monoclinic
P21/n
464.27
Monoclinic
P21/c
0.125 × 0.3 × 0.6 0.62 × 0.5 × 0.5 0.5 × 0.5 × 0.25 0.5 × 0.32 × 0.25
MoKα
0.71073
10.185(5)
12.726(4)
15.779(5)
90.00
MoKα
0.71073
7.8399(2)
13.5557(3)
16.1392(4)
90.00
MoKα
0.71073
11.1932(2)
17.5004(4)
11.3704 (4)
90.00
MoKα
0.71073
9.0132(2)
18.2540(5)
12.6938(3)
90.00
β
97.65 (4)
90.00
2026.9(14)
4
53.96
1.41
1.948
4872
4411
1473
0.0422
0.015
0.1908
0.0401
1.122
90.00
90.00
1715.20(7)
4
55.00
1.507
2.293
16860
3909
3021
0.0351
0.0576
0.0592
0.0646
1.151
118.1300(1)
90.00
1964.21(9)
4
55.04
1.666
2.416
13165
91.8290(10)
90.00
2087.41(9)
4
54.98
1.477
1.902
13805
γ
V (Å3)
Z
2θmax(◦)
Dcalc (Mg m−3
)
Absortion coefficient (mm−1
No. of reflections collected
)
No. of independent reflection
No. of observed reflections
R1[F>4σ(F)]
WR2
R1 (all data)
4474
2907
4763
3018
0.0477
0.0950
0.0896
0.1120
1.093
0.0510
0.0853
0.1010
0.1024
1.071
WR2
GOF on F2
Max. shift for final cycle of
least squares /σ
Max. Peak in final difference
syntheses (e/Å3)
0.0062
0.000
0.001
0.001
0.33
0.177
0.328
0.290
Max. Difference hole (e/Å3)
−0.33
−0.199
−0.348
−0.289
aStandard deviations are in parentheses.
31P NMR Analysis
The 31P chemical shifts of triarylselenophosphates are given in Table III, and their
corresponding phosphorus–selenium coupling constants are in parentheses. Homogeneous
Table III 31P Chemical shifts of p-X-arylselenophosphates 1–6
1
2
3
4
5
6
CCl4
C6D6
CDCl3
CO(CD3)2
CD3OD
DMSO
62.36 (1017)
63.41 (1019)
62.37 (1007)
62.40 (1014)
62.64 (1012)
62.23 (1007)
59.90 (1023)
60.99 (1023)
60.20 (1010)
60.07 (1018)
60.31 (1016)
60.08 (1012)
58.69 (1029)
59.53 (1028)
58.84 (1016)
59.09 (1022)
59.44 (1023)
59.13 (1016)
59.90 (1032)
60.16 (1034)
59.82 (1025)
60.20 (1028)
60.58 (1029)
60.18 (1021)
55.93 (a)
55.53 (a)
56.40 (1046)
56.22 (1042)
56.85 (1041)
57.19 (a)
55.83 (1049)
55.92 (1045)
56.47 (1044)
56.86 (a)
56.97 (1034)
55.49 (1036)
aIt was not observed due to the low solubility of the compound.

SUBSTITUENT EFFECTS ON TRIARYLSELENOPHOSPHATES
777
solutions with the same concentration (0.05 mol·L−1) of compounds 1–6 were prepared in
each solvent. Because 5 and 6 have a very low solubility in CCl4 and CD3OD, it was not
possible to distinguish 1JP-Se from the noise of the corresponding spectra. The 31P chemical
shift reproducibility was evaluated through repeated experiments under similar conditions,
and resulted in better than 0.01 ppm.
As can be observed from Table III, the 31P chemical shift of the six selenophos-
phates shows an “abnormal” shielding effect in the selected solvents when the electron-
withdrawing power of the substituent increases. The phosphorus–selenium coupling con-
stants found for 1–6 are between 1007–1049 Hz, which belong to typical values for
phosphorus–selenium “double” bonds coupling constants,23,24 and they turn greater when
the para-substituents are strong EW groups (CN or NO2). The 1JP-Se values in the series of
compounds reported here are consistent with (1) an increase of the π character of the P-Se
bond, and (2) the electron transfer from the chalcogen toward the phosphorus atom as an
effect of the EW power of the substituent at the aromatic rings.
The linear fittings between Hammett constant σ2p5 vs 31P chemical shifts and 1JP-Se of
compounds 1–6 are shown in Figures 5 and 6, respectively. A simple analysis of the plots
reveals that the substituent effect on δ31P has almost the same trend and does not depend
on the solvent employed in the measurements. Only benzene induces a slight deshielding
effect on the 31P NMR signal of compounds 1 (X = OMe) and 2 (X = Me), which could
be explained in terms of an aromatic solvent induced shift (ASIS) on the electronically rich
systems.26
From Figure 6, it is clear that σp constants have a better correlation with the
phosphorus–selenium coupling constants (obtained from the six different solvents) than
Figure 5 Relationship between the Hammett constant σp and the experimental 31P NMR chemical shift for
triarylselenophosphates 1–6.

´
Z. DOMINGUEZ ET AL.
778
1
Figure 6 Relationship between the Hammett constant σp and the experimental JP-Se coupling constant for
triarylselenophosphates 1–6.
the one obtained with the 31P chemical shifts. This agrees with the strong effect of the
1
para-substituent on the phosphorus–selenium bond. In addition, the values of JP-Se in
compounds 1–6 are slightly greater when the spectra were acquired in C6D6. In contrast,
the 1JP-Se coupling constants observed in d6-DMSO, for five of the six compounds of the se-
ries, reached some of the smallest values. However, a linear relationship between dielectric
constants of the six employed solvents in the analysis and 1JP-Se was not found.
Since the substituent effect on the δ31P of triarylselenophosphates remains almost
the same, even if the dielectric constant is dramatically changed, we concluded that the
structural features related to the abnormal shielding effect of the 31P NMR signal of the
series 1–6 are not very different between the six solvents.
Structural Analysis
As mentioned above, three of the four triarylselenophosphates analyzed by X-ray
diffraction techniques (3, 4, and 5) have a similar propeller conformation. In contrast,
compound 2 adopts a different conformation in the solid state with a C1 local symmetry
(Figure 4). It is interesting that the isomorphous triarylphosphorothionates reported before
have exactly the same conformation in the solid state as their analogous 2–5, which reveals
that a change in the nature of the phosphorus–chalcogen bonding does not have a strong
influence in the conformation into the crystalline cell.
There is not a significant variation between the P-Se bond lengths found for compound
´
2 and 3 (2.052 Å). However, when the substituent at the para position of the aromatic ring
´
is an EW group, as Cl or CN, the P-Se bond length becomes slightly shorter (2.045 Å and
´
2.040 Å, in each case). This result agrees with the observed magnitude trend of the 1JP-Se
coupling constant discussed before, supporting the idea that the selenium atom is involved

SUBSTITUENT EFFECTS ON TRIARYLSELENOPHOSPHATES
779
in the charge transfer toward phosphorous when EW groups are attached to the aromatic
ring.
The analysis of the averaged P–O bond lengths of compounds 2, 3, 4, and 5 (1.581,
´
1.579, 1.586, and 1.583 Å, respectively) reveals that there is not an appreciable variation
among them. In addition, contrary to the experimental data obtained for the triarylphospho-
rothionates, significant variations among the three P–O bond lengths for each molecule of
triarylselenophosphate were not found, except for compound 5, where P–O1 bond length
´
is shorter than P–O2 and P–O3 (1.573, 1.589, and 1.586 Å). The shortening of one of the
three P–O bond lengths observed in most of arylphosphorothionates reported before was
attributed to the presence of at least one nπ O-σ∗P-OAr or nπ O-σ∗P-S interaction per molecule
in the solid state. However, from the experimental results, it is not clear that the analogous
interactions exist for the reported crystalline triarylselenophosphates.
On the other hand, most of the O–P–O angles are approximately 100◦ for the crys-
talline compounds 2–5 (Table II). Only O1–P–O3, in compound 2, is considerably larger
(106.1◦) as a consequence of its particular conformation. The averaged O–P–O bond angles
found for compounds 2, 3, 4, and 5 are 102.5, 100.3, 100.1, and 99.6 degrees, respectively.
As it can be observed, the angle value is larger when the para-substituent at the aromatic
ring is an electron releasing (ER) group.
DFT Calculations
The structures of triarylselenophosphates have been optimized without geometry
restrictions at the B3LYP/6-31+G(d,p) level.
It is easier to find trends if other electron-withdrawing (EW) and/or electron-releasing
(ER) groups are included in the analysis. Of course, this exercise is easy to do in silico.
We have chosen to study two extra EW groups (−F and −Br) and one more ER group
(−NH2) for our purpose. Some general trends are identified from the results summarized in
Table S1 (available online in the Supplemental Materials):
1. The P–O bond lengths are longer for those molecules containing an EW group.
2. The P–Se and C–O distances are shorter for those arylselenophosphates containing a
p-EW substituent.
3. There is a linear correlation between the P–Se bond distance and the δDFT(31P), but it is
necessary to separate the EW to the ER groups (see Figure S1, Supplemental Materials).
4. The presence of an EW group induces a larger electron transfer from Se→P, and the
immediate consequence is the stronger shielding on the observed 31P NMR signal.
CONCLUSIONS
Analogous to the O-aryl phosphates and O-aryl thiophosphates studied in a previous
contribution,17 EW groups attached to the para position of the aromatic rings induce a
shielding effect on the 31P NMR signal of a series of tris-(p-X-aryl)selenophosphates. After
a detailed analysis of experimental and calculated structural data and also of 1JP-Se values
of the complete series, we confirmed that the presence of an EW group induces a larger
electron transfer from Se→P and the immediate consequence is a stronger shielding on the
observed 31P NMR signal. The electronic effect of the substituent observed in both NMR
parameters (31P and 1JP-Se) does not suffer appreciable changes if the dielectric constant of
the media is changed.

´
Z. DOMINGUEZ ET AL.
780
EXPERIMENTAL
The 1H, 13C, and 31P spectra were recorded on a Varian Mercury Plus spectrometer
operating at 300 MHz at a probe temperature of 25◦C. Phosphorus NMR spectra are
reported in ppm downfield (+) from 85% H3PO4 used as external standard. Mass spectra
were measured on a Hewlett Packard 5989A spectrometer and on a Varian Saturn Star
3400 CX spectrometer using electron impact (EI) at 70 eV. The reactions were performed
under an atmosphere of nitrogen in oven-dried glassware. Solvents and solutions were
transferred by syringe-septum and cannula techniques. THF and toluene were of reagent
grade and were dried and distilled immediately before use from sodium/benzophenone.
Triethylamine was dried and distilled from LiAlH4. The products were purified by flash
column chromatography on silica gel 230–400 mesh using mixtures of AcOEt/hexanes as
eluent. Yields are given for isolated products. AcOEt/hexanes or CH2Cl2/hexanes mixtures
were used for recrystallization of all compounds.
Crystallographic work, data collection, and cell refinement was performed in the
Enraf-Nonius CAD-4 and Kappa CCDC diffractometers.27,28 The data reduction was per-
formed in WinGX.29 The structures were resolved by direct methods with SHELXS97 and
refined with SHELXL97.30 Molecular graphics (diamond and dihedral angles) were created
using PARST 95.31,32 Crystallographic Data Center and the deposition numbers are CCDC
642423 for compound 2, CCDC 642424 for 3, CCDC 642425 for 5, and CCDC 642426
for 4.
General Procedure for the Synthesis of Compounds 1–6
In a three-necked 500 mL flask, fitted with a dropping funnel, stir bar, and rubber
septa, p-X phenol (34.2 mmol), PCl3 (1.57 g, 11.4 mmol), and dry THF (200 mL) were
placed. Then Et3N (4.7 mL, 34.2 mmol) was added via syringe. The reaction mixture
was stirred at room temperature for 24 h. Then the resulting triethylammonium chloride
was filtered off through a filter tipped cannula. The solid was washed with dry THF (2 ×
15 mL) and 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 as thick
oil, which was used in subsequent reaction without further purification.
In a round-bottomed 100 mL flask, fitted with a reflux condenser, stir bar, and
rubber septa, elemental selenium (0.9 g, 11.4 mmol) was placed. A solution of the p-X-
phenylphosphite 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 selenium was
filtered off, and the suspension was concentrated under vacuum. The residue was washed
with an aqueous solution of 10% sodium bicarbonate (30 mL). The product was extracted
with methylene chloride, and the organic layer was 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.
Tri s( O-4-methoxyphenyl)phosphoroselenoate (1). According to the general
procedure described above, p-MeO-phenol (4.25 g, 34.2 mmol) was treated with of PCl3
(1.57 g, 11.4 mmol) and Et3N (4.7 mL, 34.2 mmol). The resulting phosphite (3.65 g,
7.6 mmol) was reacted with elemental selenium (0.90 g, 11.4 mmol). Flash chromatography
1
(hexanes:ethyl acetate, 98:2) gave 1.1 g (25%) of a white solid. Mp 51–52◦C. H NMR
(300 MHz, CDCl3, 25◦C, TMS): δ = 3.79 (s, 9H; OCH3), 6.87 (d, 3J(HH) = 9.0 Hz, 6H;
CH), 7.14 (dd, 3J(HH) = 9.0 Hz, 4J(HP) = 1.8 Hz, 6H; CH), 13C NMR (75.5 MHz, CDCl3,

SUBSTITUENT EFFECTS ON TRIARYLSELENOPHOSPHATES
781
25◦C, TMS): δ = 55.89 (s, OCH3), 114.79 (d, 4J(CP) = 1.7 Hz, Cm), 122.47 (d, 3J (CP) =
4.3 Hz, Co), 144.40 (d, 2J(CP) = 8.0 Hz, Ci), 157.36 (d, 5J(CP) = 2.0 Hz, Cp), 31P NMR
(121.5 MHz, CDCl3, 25◦C, H3PO4): δ = 62.37 (s, 1J(PSe77) = 1007 Hz); MS (70 eV, EI):
m/z (%): 480 (71) [M+], 123 (100) [CH3OC6H4O+]; elemental analysis: calcd. (%) for
C21H21O6PSe: C 52.62 H 4.42; found: C 52.66 H 4.44.
Tri s( O-4-methylphenyl)phosphoroselenoate (2). According to the general
procedure described above, p-Me-phenol (3.53 g 34.2 mmol) was treated with PCl3 (1.57 g,
11.4 mmol) and Et3N (4.7 mL, 34.2 mmol). The resulting phosphite (3.19 g, 9.0 mmol) was
reacted with elemental selenium (0.9 g, 11.4 mmol). Flash chromatography (hexanes:ethyl
acetate, 98:2) gave 1.97 g (51%) of a white solid. Recrystallization from a solution of
1
hexanes/ethyl acetate (9:1) gave colorless crystals. Mp 108–109◦C. H NMR (300 MHz,
7
3
CDCl3, 25◦C, TMS): δ = 2.33 (d, J(PH) = 1.6 Hz, 9H), 7.12 (dd, J(HH) = 8.9 Hz,
4J(HP) = 1.6 Hz, 6H), 7.16 (d, 3J(HH) = 8.9 Hz, 6H), 13C NMR (75.5 MHz, CDCl3, 25◦C,
TMS): δ = 20.94 (s, CH3), 121.00 (d, 3J(CP) = 4.9 Hz, Co), 130.04 (d, 4J(CP) = 1.1 Hz,
Cm), 135.32 (d, 5J(CP) = 2.1 Hz, Cp), 148.42 (d, 2J(CP) = 9.2 Hz, Ci), 31P NMR (121.5
MHz, CDCl3, 25◦C, H3PO4): δ = 60.20 (s, 1J(PSe77) = 1010 Hz). MS (70 eV, EI): m/z (%):
432 (100) [M+], 342 (20) [M+-C7H7], 107 (14) [M+-C7H7O], 91 (61) [C7H7+]; elemental
analysis: calcd. (%) for C21H21O3PSe: C 58.48, H 4.91; found: C 58.26, H 5.05.
Tri s( O-phenyl)phosphoroselenoate (3). According to the general procedure
described above, phenol (3.2 g, 34.2 mmol) was treated with PCl3 (1.57 g, 11.4 mmol)
and Et3N (4.7 mL, 34.2 mmol). The resulting phosphite (2.8 g, 9.0 mmol) was reacted
with elemental selenium (0.9 g, 11.4 mmol). Flash chromatography (hexanes:ethyl ac-
etate, 98:2) gave 2.6 g (74%) of colorless needles. Recrystallization from a solution of
1
hexanes:ethyl acetate (98:2) gave colorless crystals. Mp 73–74◦C; H NMR (300 MHz,
CDCl3, 25◦C, TMS): δ = 7.23 (m, 3H), 7.25 (m, 6H), 7.38 (dd, 3J(HH) = 8.9, 3J(HH) =
3
6.2 Hz, 6H), 13C NMR (75.5 MHz, CDCl3, 25◦C, TMS): δ = 121.31 (d, J(CP) = 5.1
5
4
Hz, Co), 125.76 (d, J(CP) = 2.0 Hz, Cp), 129.60 (d, J(CP) = 1.7 Hz, Cm), 150.53 (d,
2J(CP) = 7.7 Hz, Ci), 31P NMR (121.5 MHz, CDCl3, 25◦C, H3PO4): δ = 58.84 (s,
1J(PSe77) = 1016 Hz); MS (70 eV, EI): m/z (%): 390 (100) [M+], 313 (15) [M+-C6H5], 77
(58) [C6H5+]; elemental analysis: calcd. (%) for C18H15O3PSe: C 55.54, H 3.88; found: C
55.39, H 3.87.
Tri s( O-4-chlorophenyl) phosphoroselenoate (4). According to the general
procedure described above, p-chlorophenol (4.39 g, 34.2 mmol) was treated with PCl3
(1.57 g, 11.4 mmol) and Et3N (4.7 mL, 34.2 mmol). The resulting phosphite (3.77 g, 9.1
mmol) was reacted with elemental selenium (0.91 g, 11.4 mmol). Flash chromatography
1
(hexanes:ethyl acetate, 80:20) gave 2.36 g (53%) of colorless crystals. Mp 87–88◦C. H
NMR (300 MHz, CDCl3, 25◦C, TMS): δ = 7.35 (dd, 3J(HH) = 9.1 Hz, 4J(HP) = 1.8 Hz,
3
6H), 7.16 (dd, J(HH) = 9.1 Hz, 4J(HP) = 2.0 Hz, 6H), 13C NMR (75.5 MHz, CDCl3,
25◦C, TMS): δ = 122.62 (d, 3J(CP) = 4.9 Hz, Co), 129.78 (d, 4J(CP) = 2.0 Hz, Cm), 131.55
(d, 5J(CP) = 2.6 Hz, Cp), 148.68 (d, 2J(CP) = 7.7 Hz, Ci), 31P NMR (121.5 MHz, CDCl3,
25◦C, H3PO4): δ = 59.82 (s, 1J(PSe77) = 1025 Hz). MS (70 eV, EI): m/z (%): 493 (100)
[M+], 365 (11) [M+-ClC6H4O], 127 (18) [ClC6H4O+]; elemental analysis: calcd. (%) for
C18H12Cl3O3PSe: C 43.89, H 2.46. Found: C 43.55, H 2.13.
Tri s( O-4-cyanophenyl) phosphoroselenoate (5). According to the general
procedure described above, p-cyanophenol (4.06 g, 34.2 mmol) was treated with PCl3
(1.57 g, 11.4 mmol) and Et3N (4.7 mL, 34.2 mmol). The resulting phosphite 3.55 g
(9.2 mmol) was reacted with elemental selenium (0.9 g, 11.4 mmol). Flash

´
Z. DOMINGUEZ ET AL.
782
chromatography (hexanes:ethyl acetate, 7:3) gave 1.16 g (28%) of colorless nee-
dles. Recrystallization from hexanes/ethyl acetate mixture (80/20) gave colorless crystals
1
3
Mp 174–175◦C. H NMR (300 MHz, CDCl3, 25◦C, TMS): δ = 7.36 (dd, J(HH) = 8.5
Hz, 4J(HP) = 1.6 Hz, 6H), 7.74 (d, 3J(HH) = 8.5 Hz, 6H), 13C NMR (75.5 MHz, CDCl3,
25◦C, TMS): δ 110.64 (d, 5J(CP) = 2.0 Hz, Cp), 117.60 (s, CN), 122.30 (d, 3J(CP) = 5.1
Hz, Co), 134.16 (d, J(CP) = 1.7 Hz, Cm), 152.84 (d, J(CP) = 7.4 Hz, Ci), 31P NMR
4
2
(121.5 MHz, CDCl3, 25◦C, H3PO4): δ = 56.22 (s, J(PSe77) = 1042 Hz). MS (70 eV,
1
EI): m/z (%): 465 (89) [M+], 347 (30) [M+ -OC6H4CN], 102 (25) [C6H4CN+]; elemental
analysis: calcd. (%) for C21H12N3O3PSe: C 54.33, H 2.61. Found: C 53.96, H 2.42.
Tri s( O-4-nitrophenyl) phosphoroselenoate (6). According to the general pro-
cedure described above, p-nitrophenol (4.06 g, 34.2 mmol) was treated with PCl3 (1.57 g,
11.4 mmol) and Et3N (4.7 mL, 34.2 mmol). The resulting phosphite (1.52 g, 3.4 mmol) was
reacted with elemental selenium (0.9 g, 11.4 mmol). Flash chromatography (hexanes:ethyl
acetate, 7:3) gave 1.19 g (66.5%) of colorless crystals. Mp 170–171◦C. H NMR (300
1
MHz, CDCl3, 25◦C, TMS): δ = 7.43 (dd, 3J(HH) = 9.0 Hz, 4J(HP) = 1.6 Hz, 6H), 8.34
(d, J(HH) = 9.0 Hz, 6H), 13C NMR (75.5 MHz, CDCl3, 25◦C, TMS): δ = 122.07 (d,
3
3J(CP) = 5.1 Hz, Co), 125.79 (d, 4J(CP) = 1.7 Hz, Cm), δ 145.72 (d, 5J(CP) = 2.4 Hz, Cp),
154.14 (d, 2JCP = 7.2 Hz, Ci), 31P NMR (121.5 MHz, CDCl3, 25◦C, H3PO4): δ = 55.92 (s,
1J(PSe77) = 1045 Hz). MS (70 eV, EI): m/z (%): 525(100) [M+],; elemental analysis: calcd.
(%) for C18H12N3O9PSe: C 41.24, H 2.31, N 8.02. Found: C 41.20, H 2.05, N 7.86.
COMPUTATIONAL DETAILS
The geometry optimizations and electronic structure calculations were performed
using Gaussian 98.33 Structures were optimized using Becke’s exchange (B),34 Lee, Yang,
and Parr (LYP) correlation,35 and within the hybrid functional (B3LYP) approach, as
implemented in Gaussian. All calculations were done using the 6-31+G(d,p) basis set.36
Every stationary point on the potential energy surface was characterized by a harmonic
analysis using the same theoretical methodology as the one used in the optimization.
The natural population analysis was employed to calculate the atomic charges.37 NMR
chemical shifts were computed using gauge including atomic orbitals (GIAO)38 at B3LYP/6-
31+G(d,p). The calculated chemical shieldings were converted to chemical shifts using the
following Equation:
δDFTP(X) = σDFT(PH3) − σDFT(X) − 266.1
suggested by van Wullen,39 where X denotes the molecule for which we calculate the
31P chemical shift, and 266.1 ppm is the difference between the absolute experimental
chemical shielding of PH3 (594.5 ppm) and 85% H3PO4 (328.4 ppm) at 300 K.40 The
chemical shielding of PH3 calculated at the B3LYP/6-31+G(d,p) is 591.3 ppm.
See the Supplemental Materials available online for the complete computational
details.
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