Dependence of the long-range phosphorus-hydrogen coupling constantnJP-H (n = 3, 6, 7) on the bond order between phosphorus and its substituents: Preparation and spectroscopic characterization of several phosphoramidates

Article abstract of DOI:10.1002/mrc.928

The examination of spectra of a selected series of phosphoramidates showed that, in addition to a double bond, whenever there are one or two partial multiple bonds in the molecule the long-range coupling constant, such as ⁶J_P-H,

Full text of DOI:10.1002/mrc.928

MAGNETIC RESONANCE IN CHEMISTRY
Magn. Reson. Chem. 2001; 39: 684–688
Dependence of the long-range phosphorus–hydrogen
coupling constant nJP–H (n = 3, 6, 7) on the bond order
between phosphorus and its substituents: preparation
and spectroscopic characterization of several
phosphoramidates
Khodayar Gholivand,∗ Said Ghadimi, Hossein Naderimanesh and Akbar Forouzanfar
Department of Chemistry, Tarbiat Modarres University, PO Box 14155-4838, Tehran, Iran
Received 20 March 2001; Revised 13 July 2001; Accepted 13 July 2001
The examination of spectra of a selected series of phosphoramidates showed that, in addition to a double
bond, whenever there are one or two partial multiple bonds in the molecule the long-range coupling
constant, such as 6JP–H, 7JP–H and 3JP–H, either disappears or at least reduces. In particular, the experimental
data indicate the unexpected effect of a partial multiple bond between phosphorus and fluorine in 7JP–H and
3JP–H. The preparation of the compounds p-CH3C6H4NHP(O)Cl2 (II), p-CH3C6H4NHP(O)(Cl)OC6H4CH3-
p (XIV), m-CH3C6H4NHP(O)(Cl)OC6H4CH3-p (XV), m-CH3C6H4NHP(O)(Cl)OC6H4CH3-m (XVI) and the
rigid molecule CH3C6H3(NH)2P(O)Cl (XVII) are described and they are characterized by 1H, 13C, 31P NMR,
IR spectroscopy and elemental analysis. Copyright  2001 John Wiley & Sons, Ltd.
KEYWORDS: long-range coupling constant; phosphoramidate
spin–spin coupling,16 and among them is the hyperconju-
gation mechanism that was first suggested by Bersohn23
in 1962. On the basis of this mechanism, Khaleeludin and
Scott15 interpreted the long-range coupling in methylben-
zylphosphonium salt. The authors indicated that the positive
charge induced on the methylene group by the electroposi-
tive phosphorus atom could be distributed around the ring
and that the methyl groups could then interact with the ‘pos-
itive holes’ by hyperconjugation. The interaction decreases
in the order of para > ortho > meta.16 Allen et al.24 and Gulick
et al.25 have, in fact, rationalized the coupling constant in
a series of semiquinone phosphate radicals in terms of a
hyperconjugative mechanism.
Griffin and Gordon found two inconsistencies in the sug-
gested model. (1) If the inductive-hyperconjugation model
is important in methylbenzylphosphorus compounds, it
should be even more important in the tolylphosphorus
derivatives, in which the phosphorus atom is attached
directly to the ꢀ-system, and parallel behavior should be
observed in the long-range coupling constants of the two
systems.16 (2) This model would indicate that the magni-
tude of the coupling constant should reflect the inductive
strength of the phosphorus substituent. Finally, Griffin and
Gordon observed that there exists a long-range coupling in
tris-p-tolylphosphonic dichloride,16 which provides evidence
against the importance of hyperconjugation as a mecha-
nism for putting ꢀ-character into the phosphorus–carbon
bond.
INTRODUCTION
Phosphorus nuclear magnetic resonance (NMR) is playing an
ever-increasing role in structural characterization and qual-
itative identification of different phosphorus compounds.1
The correlation between the 31P NMR chemical shifts and
the structure of some of the organophosphorus pesticides is
reported by Ross and Biros.2 Griffin,3 Stothers and Robinson4
and Berry et al.5 have reported the correlation between the
hybridization state of the phosphorus atom with proton
shift and spin–spin coupling constant JP–H, which was inter-
preted by Hendrickson et al.6 The influence of benzene on
the 1H NMR spectra of mononuclear phosphorus(V) amides
and dimethylamino cyclotriphosphazatrienes is described by
Keat and Shaw.7 Several other publications have described
the short- and long-range JP–H in phosphorus compounds3–22
and four- and five-bond coupling constants (4JP–H 5JP–H
, )
in allylic and homoallylic phosphorus compounds.11,13,14,19,22
The observations of five, six, and seven bond couplings in iso-
meric methylbenzylphosphonium salts have been reported
by Khaleeludin and Scott15 and Gordon and Griffin14,16 and
some other studies have reported 3JP–H spin–spin coupling
too.6,16
In the above-mentioned studies, several models have
been put forward to explain the mechanism of long-range
ŁCorrespondence to: K. Gholivand, Department of Chemistry,
Tarbiat Modarres University, PO Box 14155-4838, Tehran, Iran.
E-mail: gholi kh@net1cs.modares.ac.ir
DOI: 10.1002/mrc.928
Copyright  2001 John Wiley & Sons, Ltd.

Long-range (P, H) coupling 685
An alternative mechanism for long-range coupling was
introduced by Fisher, Hirshfelder and Taylor in Ref. [15].
Their model indicates that the phosphorus atom lies over the
inner circumference of the aromatic ring, and thus over the ꢀ
orbital in benzylphosphorus compounds.16 This model also
showed some shortcomings that were pointed out by Griffin
and Gordon.
Finally, Griffin and Gordon suggested an angle-
dependent model for interpretation of long-range coupling.15
This model described the relationship of the long-range JP–H
to the angle between the carbon–phosphorus bond and the
plane of the ꢀ-electron system in compounds a and b, with
for C7H8Cl2NOP: C, 37.5; H, 3.54; N, 6.25. Found: C, 37.37;
H, 3.41; N, 5.98%.
IR spectrum (KBr, cmꢀ1): 3160 (s), 3020 (m), 2920 (m),
1297 (sh), 1252 (s), 1001 (w), 774 (s), 706 (s), 546 (s). 1H NMR
2
(CDCl3): υ D 2.29 (s), 7.1–7.2 (m), 7.45 (d, JP–H D 11.5 Hz);
3
13C NMR (CDCl3): υ D 20.8 (s), 121.7 (d, JP–C D 7.8 Hz),
5
2
130.1 (s), 133.6 (d, JP–C D 1.5 Hz), 135.1 (d, JP–C D 1.5 Hz);
31P NMR (CDCl3): υ D 10.8 (s).
N-4-Methylphenylphosphoramidochloridic acid
4-methylphenyl ester,
p-CH3C6H4NHP(O)(Cl)OC6H4CH3-p (XIV)
A mixture of 5.62 g (25 mmol) phosphordichloridic acid 4-
methylphenyl ester and 50 ml dried benzene was placed in a
100 ml flask. A solution of 3.59 g (25 mmol) p-toluidine and
3.95 g (25 mmol) pyridine in small portions was added to the
°
JP–H reaching a minimum at an angle of 0 .
+
P
C6H5
C6H5
C6H5
C6H5
+
P
°
flask at 0 C. The mixture was stirred at room temperature for
2–3 days. After filtration of the pyridinium salt, the solvent
was distilled in vacuum. The residue remaining was purified
by column chromatography (silica gel: n-hexane/acetic acid
ethyl ester 1 : 1–1 : 5) and after removal of the solvent in vacuo
a white powder was obtained. Anal. Calc. for C14H15ClNO2P:
C, 56.86; H, 5.11; N, 4.73. Found: C, 56.13; H, 4.98; N, 4.40%.
IR spectrum (KBr, cmꢀ1): 3135 (s), 3050 (m), 2920 (m),
1309 (m), 1309 (w), 1257 (s), 1163 (s), 1015 (m), 814 (s),
H3C
H3C
a
b
6J = 0.9 Hz
7J = 0.4 Hz
In the present study we have put forward our experimen-
tal observations and tried to suggest a different mechanism
1
690 (w), 558 (s). H NMR (CDCl3): υ D 2.30 (s), 7.1–7.2 (m),
for the long-range spin–spin coupling constant JP–H
.
2
7.28 (d, JP–H D 8.35 Hz); 13C NMR (CDCl3): υ D 20.7 (s),
3
3
20.8 (s), 120.0 (d, JP–C D 7.4 Hz), 120.3 (d, JP–C D 4.9 Hz),
129.9 (s), 130.4 (s), 133.3 (s), 135.0 (s), 135.8 (s), 147.6 (d,
2JP–C D 8.7 Hz); 31P NMR (CDCl3): υ=6.21 (s).
EXPERIMENTAL
1H and 13C NMR spectra were recorded on a JEOL-JUM-
EX 80 and Bruker (Avance DRS) 500 spectrometers and 19F,
and 31P NMR spectra on Bruker AC-80 and Bruker 500
spectrometers. 1H and 13C, 19F, and 31P chemical shifts
were determined relative to TMS, CFCl3 and 85% H3PO4
respectively as external standards. Infrared (IR) spectra
were recorded on a Shimadzu model IR-60 spectrometer.
Elemental analysis was also performed, using a Heraeus
CHN-O-RAPID elemental analysis.
N-3-Methylphenylphosphoramidochloridic acid
4-methylphenyl ester,
m-CH3C6H4NHP(O)(Cl)OC6H4CH3-p (XV)
Compound XV was prepared in the same way as XIV by
using m-toluidine instead of p-toluidine. Anal. Calc. for
C14H15ClNO2P: C, 56.86; H, 5.11; N, 4.73. Found: C, 56.75;
H, 5.19; N, 4.68%.
IR spectrum (KBr, cmꢀ1): 3155 (s), 3040 (m), 2940 (m),
1285 (m), 1268 (s), 1166 (s), 1019 (s), 810 (s), 773 (s), 691 (s),
1
Materials
551 (s). H NMR (CDCl3): υ D 2.26 (s), 2.29 (s), 6.8–7.2 (m),
2
7.78 (d, JP–H D 8.9 Hz); 13C NMR (CDCl3): υ D 20.8 (s),
n-Hexane and acetic acid ethyl ester were distilled; the
other chemicals were used without further purification and
obtained from the following companies: p-cresol 97% (Fluka),
pyridine 99% (Aldrich), p-toluidine 98%, m-toluidine 98%,
triethylamine 99%, 4-ethylphenylenediamine 98%, phospho-
rylchloride supra pure, benzene pure analyse (Merck). Phos-
phordichloridic acid 4-methylphenylester (I) was prepared
as described in the literature.26 Compounds IV and V,27
and VI, VII, VIII and IX28 were prepared and synthesized
according to the reported methods.
3
3
21.5 (s), 116.6 (d, JP–C D 7.7 Hz), 121.3 (d, JP–C D 5.5 Hz),
5
124.4 (s), 129.2 (s), 130.5 (s), 135.8 (d, JP–C D 1.6 Hz),
137.8 (s), 139.3 (s), 147.7 (d, JP–C D 8.55 Hz); 31P NMR
2
(CDCl3): υ D 6.23 (s).
N-3-Methylphenylphosphoramidochloridic acid
3-methylphenyl ester,
m-CH3C6H4NHP(O)(Cl)OC6H4CH3-m (XVI)
A solution of 3.59 g (25 mmol) m-toluidine and 3.95 g
°
(25 mmol) pyridine was added at ꢀ5 C to a mixture of
4-Methylphenylphosphoramidicdichloride.
p-CH3C6H4NHP(O)Cl2 (II)
A mixture of 5.36 g (50 mmol) p-toluidine and 5.06 g
(50 mmol) triethylamine was added in small portions to
a stirred solution of 7.67 g (50 mmol) phosphorylchloride
5.62 g (25 mmol) phosphordichloridic acid 3-methylphenyl
ester and 200 ml benzene in small portions. The mixture was
stirred at room temperature for 2 days. After filtration of the
pyridinium salt, the solvent was removed in vacuum and
the product was purified by column chromatography [silica
gel; n-hexane/acetic acid ethyl ester (1 : 5)]. Anal. Calc. for
C14H15ClNO2P: C, 56.86; H, 5.11; N, 4.73. Found: C, 57.28;
H, 4.98; N, 4.40%.
°
in 50 ml acetonitrile at ꢀ10 C. After 0.5 h the mixture
was filtered and the solvent was distilled off in vacuum
and compound II was obtained (yield 70%). Anal. Calc.
Copyright  2001 John Wiley & Sons, Ltd.
Magn. Reson. Chem. 2001; 39: 684–688

686
K. Gholivand et al.
IR spectrum (KBr, cmꢀ1): 3145 (s), 3025 (m), 2915 (m),
1292 (m), 1248 (s), 1142 (s), 1014 (s), 777 (s), 693 (s), 558 (m).
hydrogen in the terminal methyl. Finally, we selected the
rigid molecule XVII in Table 1 to investigate the Griffin and
Gordon model (angular dependency). The 1H NMR spectra
of these compounds showed a singlet for the terminal methyl
connected to the phenol ring.
1H NMR (CDCl3): υ D 2.23 (s), 2.33 (s), 6.91–7.24 (m);
3
13C NMR (CDCl3): υ D 21.3 (s), 21.5 (s), 116.7 (d, JP–C
D
5
3
7.3 Hz), 117.4 (d, JP–C D 1.4 Hz), 120.3 (d, JP–C D 6.7 Hz),
3
121.1 (d, JP–C D 5.0 Hz), 124.6 (s), 126.9 (s), 129.2 (s),
2
129.5 (s), 137.5 (s), 139.4 (s), 140.4 (s), 149.8 (d, JP–C
8.6 Hz); 31P NMR (CDCl3): υ D 5.52 (s).
D
DISCUSSION
The 1H NMR spectra of selected compounds (Table 1)
revealed that there is long-range coupling in I and III but
only a singlet of terminal methyl in compound II. This could
be related to oxygen and its para-elements, such as NH, CH2
and CR2,31 mainly due to the lack of partial multiple bonds
with phosphorus for O, CH2 and CR2 (R D Alkyl).
N,Nꢀ-(3-methyl)phenylenediamidophosphoryl-
chloridate, CH3C6H3(NH)2P(O)Cl (XVII)
A mixture of 7.5 g (50 mmol) phosphorylchloride and 12.0 g
(100 mmol) 4-methyl-1,2-phenylenediamine in 40 ml ben-
°
zene was stirred at 25 C for 1.5 h. The solvent was removed
in vacuum and the residue was collected. Purification of the
product from amine-hydrochloride was obtained by recrys-
tallization in methanol/ethylacetate (1 : 2) (yield 30%). Anal.
Calc. for C7H8ClN2OP: C, 41.50; H, 3.96; N, 13.81. Found:
C, 42.10; H, 4.11; N, 13.58%.
δ−
O
O
P
δ+
N
P
N
CH3
CH3
H
IR spectrum: (KBr, cmꢀ1): 3340 (vw), 3050 (sh), 2810 (vs),
2570 (vs), 1528 (s), 1217 (s), 1140 (ms), 806 (ms), 564 (ms),
492 (w), 438 (ms). 1H NMR (CD3CN); υ D 2.45 (s), 3.64 (d,
A
B
2JP–NH D 11.3 Hz), 3.66 (d, 2JP–NH D 11.2 Hz), 6.75 (d, 2JH–H
D
The mesomery B of compound II could be the main
7.6 Hz), 6.84 (s), 7.41 (d, 2JH–H D 7.8 Hz); 13C NMR (CD3OD);
υ D 19.55 (s), 121.98 (s), 124.72 (s), 124.81 (s), 126.83 (s),
129.19 (s), 140.76 (s); 31P NMR (CD3OD); υ D ꢀ11.69 (s).
7
reason for lack of JP–H. To follow this up we considered
molecules with general formula R1R2NP(O)(X)OC6H4CH3.
The main focus was on substitution of R1, R2 and X D F,
7
Cl and their effects on the long-range coupling JP–H. Com-
pounds IV, VI, VIII, X with phosphorus atoms bonded to
RESULTS
sp3-hybridized atoms showed long-range coupling between
7
phosphorus and terminal methyl of p-cresol with JP–H
D
The observed chemical shifts and coupling constants of
selected molecules are listed in Table 1. The 1H NMR spectra
of compounds I, II and III in Table 1, of general formula
Cl2P(O)XC6H4CH3-p (where X D O, NH, and CH2 or CR2),
show different behavior. Molecules I and III have long-range
couplings between phosphorus and the terminal methyl,
7JP–HꢁIꢂ D 1.98 Hz, 7JP–HꢁIIIꢂ D 2.6 Hz, but no coupling
was observed in molecule II. Compounds IV, VI, VII
and X were the molecules selected next for this study.
1.2–1.5 Hz. This coupling is consistent with hyperconjuga-
tion and the Fisher–Hirshfelder–Taylor (F.H.T.) model. The
1H NMR of homologous fluoride compounds V, VII and IX
(Table 1), showed only a singlet with no split in the 1H NMR
peaks. Among the possible explanations for such an exciting
CH3
δ−
CH3
O
7
The presence of a long-range coupling constant JP–H has
O
H3C
δ+
N
P
H3C
H3C
been shown in all of the phosphorylchloride derivatives, i.e.
7JP–H D 1.2 Hz, 1.2 Hz, 1.5 Hz and 1.2 Hz for compounds
IV, VI, VIII and X respectively, and we did not observe a
seven-bond interaction between phosphorus and hydrogen
of the terminal methyl in the phosphorylfluoride derivatives.
Only a sharp singlet was observed in 1H NMR spectra
for the compounds V, VII and IX. In addition, we have
N
H
P
N
N
H
NH
H3C
NH
CH3
CH3
I
II
1
also examined the H NMR spectra of compounds XI, XII
and XIII containing the groups (CH3)2NP(O)(NHC6H4R)2,
with R D CH3; see Table 1. These compounds have more
than five-, six- or seven-bonds between phosphorus and
para atoms. The 1H NMR spectra showed a sharp singlet
for the terminal methyl in the aniline system and no
coupling constants of JP–H (VII), JP–H (XII) and JP–H (XI)
were observed. The final molecules selected were XIV, XV
and XVI; see Table 1. These molecules have p-cresol and
substituted aniline groups. The 1H NMR spectra showed
a sharp singlet for the terminal methyl connected to the
phenol ring and aniline system. Again we did not observe
six- and seven-bond interactions between phosphorus and
CH3
CH3
δ−
δ−
O
O
H3C
H3C
H3C
H3C
δ+
N
P
P
N
N
N
H
5
6
7
δ +N
NH
CH3
CH3
III
IV
Copyright  2001 John Wiley & Sons, Ltd.
Magn. Reson. Chem. 2001; 39: 684–688

Long-range (P, H) coupling 687
Table 1. Long-range coupling constants
6
No.
Compound
3JP−H 5JP−H JP−H 7JP−H
Ref.
a
Cl2P(O)O
CH3
I
−
1.98 (d)
−
a
Cl2P(O)NH
CH3
II
III
−
s
−
Cl2P(O)C
CH3
3
−
2.6 (d)
16
27
27
28
28
28
28
29
30
30
(CH3)2NP(O)(Cl)O
(CH3)2NP(O)(F)O
CH3
CH3
IV
V
13.7
10.99
13.4
10.73
mult.
mult.
mult.
10.11
9.89
1.2 (d)
s
(CH3)(C6H5CH2)NP(O)(Cl)O
(CH3)(C6H5CH2)NP(O)(F)O
(C6H5CH2)2NP(O)(Cl)O
CH3
CH3
VI
VII
VIII
IX
X
1.2 (d)
s
CH3
1.5 (d)
(C6H5CH2)2NP(O)(F)O
CH3
s
[(CH3)2CHCH2]2NP(O)(Cl)O
CH3
1.2 (d)
(CH3)2NP(O) NH
(CH3)2NP(O) NH
CH3
2
XI
XII
s
s
−
2
CH3
(CH3)2NP(O) NH
XIII
10.33
s
−
30
2
H3C
a
p-CH3C6H4NHP(O)(Cl)O
m-CH3C6H4NHP(O)(Cl)O
m-CH3C6H4NHP(O)(Cl)O
CH3
−
XIV
XV
−
−
−
s
s
−
a
CH3
−
s
s
a
XVI
−
CH3
H
N
a
−
−
s
s
ClP(O)
XVII
N
H
CH3
a This work.
observation could be the fluorine behavior, which has been
noticed by Robinson and Lavery.32
multiple bonds between phosphorus and fluorine is the
major cause of coupling constant reduction in fluorine
compounds.
We previously reported that substitution of a strong
electron-releasing group, such as p-cresol, with chlorine in
To check the influence of the type of bonding on the 3JP–H
we selected (CH3)2NP(O)R2 compounds and measured 3JP–H
,
,
3
the molecule (CH3)2NP(O)Cl2 will shift its JP–H from 15.8
to 13.7 Hz for molecule IV and the replacement of the other
chlorine by fluorine will reduce it further to 10 Hz in molecule
V; see Table 1.
These findings support the early suggestion by a number
of workers32–37 that perhaps the formation of partial
5JP–H, 6JP–H and 7JP–H (with R D p-toluidine (XI), m-toluidine
(XII), o-toluidine (XIII); see Table 1). To our surprise, we did
not observe any 5JP–H, 6JP–H or 7JP–H in these compounds, and
they only showed a singlet for terminal methyl connected to
the benzyl ring and a strong reduction in 3JP–H in comparison
Copyright  2001 John Wiley & Sons, Ltd.
Magn. Reson. Chem. 2001; 39: 684–688

688
K. Gholivand et al.
with (CH3)2NP(O)Cl2. This change can again be related to
formation of a partial multiple bond between phosphorus
and the aniline group and would soften the P–N(CH3)2 bond:
suggest that, in addition to a double bond, whenever there
is a partial multiple bond or two partial multiple bonds in
6
the molecule than the long-range couplings, such as JP–H
,
7
3
To evaluate the JP–H connectivity, we designed
7JP–H and JP–H either disappear or at least reduce. This
could perhaps be due to the perturbation in phosphorus
hybridization in comparison with phosphorylchloride or
with phosphorylchloride derivatives with three single bonds.
and selected p-CH3C6H4NHP(O)(Cl)OC6H4CH3-p (XIV),
m-CH3C6H4NHP(O)(Cl)OC6H4CH3-p (XV) and m-CH3C6H4
NHP(O)(Cl)OC6H4CH3-m (XVI), Table 1, and measured
their coupling constants. 1H NMR spectra of these
compounds showed only a singlet for the methyl group
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6
7
connected to the phenol ring and no JP–H and JP–H. The
only difference between compounds IV, VI, VIII and X with
7JP–H D 1.2–1.5 Hz and XIV and XV with zero 7JP–H is their
amine substitution. In compounds IV, VI, VIII and X, the
nitrogen atom is bonded to an sp3-hybridized carbon atom
and in XIV and XV compounds the N atom is bonded to
an sp2-hybridized carbon. In compounds XIV and XV the
partial multiple bond of P–N is supported by the aromatic
ring attached to the nitrogen atom. Therefore, we should not
expect any long-range spin–spin coupling of 7JP–H, 6JP–H and
5JP–H in compounds II, XI, XII and XIII, and this coincides
exactly with our observations. Considering Table 1, all of
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7
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XII, XIII, XIV and XV. In molecule XVII, we only observed
a singlet for terminal CH3 and this is contradictory to the
Griffin and Gordon model. This can again be explained
by formation of a partial multiple bond in this molecule.
Both N–H groups of XVII are acidic, and undergo a proton
exchange with moisture in CD3CN. However, the rates of
exchange are expected to be different for these N–H groups.
Thus, we attribute the intensity difference of the NH proton
signals in the 1H NMR spectrum to the acidity difference of
these groups. Finally, to conclude our observation, we can
Copyright  2001 John Wiley & Sons, Ltd.
Magn. Reson. Chem. 2001; 39: 684–688