Synthesis of N-aryl-substituted iminophosphoranes and NMR spectroscopic investigation of their acid-base properties in acetonitrile

Article abstract of DOI:10.1039/b003575k

A series of RN=P(Pyrr)₃ iminophosphoranes (P₁ phosphazenes), where R is amino-, a-naphthyl- or substituted phenyl group, is prepared by the Kirsanov reaction and characterized by FT NMR and other properties. The ΔpK_a-value

Full text of DOI:10.1039/b003575k

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Synthesis of N-aryl-substituted iminophosphoranes and NMR
spectroscopic investigation of their acid–base properties in
acetonitrile
1
Toomas Rodima,a Vahur Mäemetsb and Ilmar Koppel*a
a Institute of Chemical Physics, University of Tartu, Jakobi 2, Tartu, Estonia, 51014.
Tel.: ϩ372-7375263; Fax: ϩ372-7375264; E-mail: ilmar@chem.ut.ee
b Centre of Scientific Competence, University of Tartu, Jakobi 2, Tartu, Estonia, 51014
Received (in Cambridge, UK) 4th May 2000, Accepted 15th June 2000
Published on the Web 26th July 2000
A series of RN᎐P(Pyrr) iminophosphoranes (P phosphazenes), where R is amino-, α-naphthyl- or substituted
᎐
3
1
phenyl group, is prepared by the Kirsanov reaction and characterized by FT NMR and other properties. The
∆pK -values of the 12 different synthesized phosphazenes and C H N᎐P(NMe ) are determined in acetonitrile
᎐
a
6
5
2 3
relative to the reference bases using 13C NMR spectroscopy. The obtained pKa-values are compared with the
corresponding values of RNH2 amines. The pKa-values of the synthesized phosphazenes in acetonitrile range
from 14.6 to 26.8 pKa units.
Introduction
Results and discussion
The alkylphosphazenes (A) and some other classes of novel
Syntheses
There are two general methods for direct preparation of
N-substituted iminophosphoranes. These are the Staudinger
reaction of alkyl or aryl azides with tertiary phosphines and
the route based on the Kirsanov reaction between phosphorus
chlorides and amines.5 In the present work we synthesized the
(monomeric) phosphazenes (P1) by the Kirsanov reaction
according to Schemes 1 and 2.
non-ionic bases are known to be very strong uncharged bases.1,2
The basicity of MeN᎐P(NMe ) , which is a rather weak base,
᎐
2
3
is comparable with or even higher than the basicity of cyclic
or acyclic alkylated amidine and guanidine bases like 1,8-
diazabicyclo[5.4.0]undec-7-ene (DBU), 1,5-diazabicyclo[4.3.0]-
non-5-ene (DBN), 1,5,7-triazabicyclo[4.4.0]dec-5-ene (TBD),
1,1,3,3-tetramethylguanidine (TMG), pentamethylguanidine
(PMG), etc. The relatively high basicity of the latter type of
compounds as compared with the alkylamines arises primarily
from the very extensive delocalization of the cationic charge in
their protonated forms. This is contributed to by the resonance
interactions and in several cases is also due to the intra-
molecular chelation between protonation site and neighboring
lone-pair-carrying groups.3 In acetonitrile, for most of the
alkylphosphazenes the pKa is within the range 26–47 pKa-
units.1,2a At the same time, in acetonitrile the basicity range
from 18 to 26 pKa units is relatively scarcely covered by the
basicity ladder (except for the substituted 1,1,3,3-tetramethyl-
2-phenylguanidines measured by Leffek et al.3d which partially
cover that region). The analogous problem exists in the
case of DMSO solutions where the corresponding basicity
interval between aliphatic amines (pKa < 11) and phosphazenes
(pKa > 15) is not tightly covered.4 To extend the basicity scale
of phosphazenes in acetonitrile towards the lower pKa-values
in the present work we synthesized α-naphthyl- and a series of
substituted [2,4-(NO2)2-, 4-Cl-2-NO2-, 2,6-Cl2-, 2,5-Cl2-, 2-Cl-,
4-Br-, H-, 4-MeO- and 4-Me2N-substituted phenyl]tripyrrol-
idinophosphazenes (B) and determined their ∆pKa-values in
acetonitrile by 13C NMR spectroscopic methods using reference
Scheme 1
Scheme 2
The Cl atoms in intermediate 7 are reactive and can be
readily replaced by such nucleophiles as C6H5MgBr, H2O,
C6H5ONa, amines, etc. Usually the aryl-substituted compounds
7 are crystalline dimeric compounds such as the diazadiphos-
compounds with suitable pK -values. Also, C H N᎐P(NMe )
᎐
a
6
5
2 3
and H NN᎐P(Pyrr) were synthesized and their pKa-values
᎐
2
3
were determined.
DOI: 10.1039/b003575k
J. Chem. Soc., Perkin Trans. 1, 2000, 2637–2644
This journal is © The Royal Society of Chemistry 2000
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Table 1 The δC-values of the C1 (δC1) and C4 (δC4) carbons of the
phosphazene phenyl substituent and their differences [δC(b) Ϫ δC(s)] for
the free phosphazene bases and their HPF6 or HClO4 salts in
acetonitrile
phetidines 14. According to Zhmurova and Kirsanov6 the
conversion of 14 to the monomer occurs at room temperature
in 1,4-dioxane and in polar solvents. This is not the case
in benzene solution. However, both forms 7 and 14 can be used
Compound
δC1
δC4
1
153.7
141.6
12.1
146.2
134.9
11.3
146.3
132.6
13.7
151.0
136.4
14.6
149.7
135.0
14.7
150.0
135.6
14.4
153.1
138.5
14.6
153.4
138.9
14.5
134.8
143.0
Ϫ8.2
117.6
128.9
Ϫ11.3
117.8
130.8
Ϫ13.0
116.2
127.2
Ϫ11.0
116.9
127.6
Ϫ10.7
115.5
126.7
Ϫ11.2
107.2
117.0
Ϫ9.8
116.4
125.0
Ϫ8.6
151.8
158.3
Ϫ6.5
143.8
149.6
Ϫ5.8
116.8
125.5
Ϫ8.7
1ؒHPF6
δC(b) Ϫ δC(s)
2
2ؒHPF6
δC(b) Ϫ δC(s)
3
3ؒHPF6
δC(b) Ϫ δC(s)
4
4ؒHPF6
δC(b) Ϫ δC(s)
5
5ؒHPF6
δC(b) Ϫ δC(s)
6
6ؒHPF6
δC(b) Ϫ δC(s)
8
8ؒHPF6
δC(b) Ϫ δC(s)
9
9ؒHPF6
δC(b) Ϫ δC(s)
10
10ؒHPF6
δC(b) Ϫ δC(s)
11
for the preparation of other phosphazenes by replacing the
chlorine atoms with e.g., with amino groups. The process of
substitution of Cl atoms of the chlorophosphazenes is mainly
controlled by the properties of its imino substituents and by
the amine used for the substitution reaction. For example, if
R is a sterically hindered alkyl group1 then dimethylamine,
isopropylamine and pyrrolidine are capable of replacing all
three chlorine atoms in 7. In the case of C6H5SO2 as the
R-group, Me2NH permits complete substitution (the mono-
and di-substituted products were not formed), Et2NH replaces
only two chlorine atoms and Me2NCH2NMe2 15 introduces
two dimethylamino groups.7,8 At the same time, reaction of
15 with 14 leads to replacement of only one chlorine atom
of the PCl3 group with -NMe2. Attempted isolation of di- and
tri-substituted compounds was not successful.8
In the present study we found that pyrrolidine reacts readily
with intermediates 7 according to Scheme 1 if the R-group is
α-naphthyl or a phenyl which carries electron-withdrawing sub-
stituents. Exploiting this fact we obtained compounds 1–6 as
free bases with moderate yields. The attempt to obtain com-
pounds 9–11 by an analogous method failed as efforts to isolate
them from the reaction mixture were unsuccessful. So, it seems
that in intermediates 7 the electrophilicity of the phosphorus
atom with an electron-donating group such as C6H5-, 4-MeO-
C6H4- and 4-Me2NC6H4 is not sufficient for the substitution
of the attached chlorine atoms by pyrrolidine. Compounds
8–12 were readily synthesized according to Scheme 2, but in
the course of the preparation (except for 12) the solvent was
changed from CH2Cl2 to THF.
147.0
130.8
16.2
145.0
127.0
18.0
153.0
138.8
14.2
11ؒHClO4
δC(b) Ϫ δC(s)
16
16ؒHPF6
δC(b) Ϫ δC(s)
analogous to that for the anilines where the transformation of
aniline to its salt causes similar effects for the aniline C1 and C4
carbons.9 This indicates that the center of basicity is the imino
group of the phosphazene molecule. Another observation
is that usually the P–C, P–H as well as the H–H spin–spin
coupling constants are larger for phosphazenes than for their
salts. In pairs of a phosphazene base and its HPF6 or HClO4
salt the δH-values of aromatic protons are larger for phos-
phazenes. The δC- and δH-values of the pyrrolidines were rela-
tively insensitive to variations in the R-group. For pyrrolidines
some increase in the δH-values and a small but systematic
change in the δC-values (for >N-CH2-CH2- an increase, for
>N-CH2-CH2- a decrease) accompanied the transformation
from neutral phosphazene to the phosphazene HPF6 or HClO4
salt.
For the pKa measurements of the phosphazenes in acetonitrile
the HPF6 (or HClO4) salts of compounds 1–6, 8–12 and
C H N᎐P(NMe ) 16 were prepared. Details of all synthetic
᎐
6
5
2 3
and analytical procedures alongside other measured param-
eters can be found in the Experimental.
NMR spectra of phosphazenes
The complete list of 13C NMR chemical shifts (δC) and 1H
chemical shifts (δH) for phosphazenes and their salts is pre-
sented in the Experimental. The most important values from
a viewpoint of ∆pKa calculations are collected in Table 1. As
one can see, the difference in chemical shifts for the C1 carbon
of phosphazene and its HPF6 or HClO4 salt ranges from 11 to
18 ppm and for the C4 carbon from 6 to 13 ppm. This is quite
remarkable and reduces the error introduced into the ∆pKa
calculations by the specific effects of the NMR method. These
are the local microscopic magnetic fields, which are dependent
on the molecule’s structure and its adjacent neighbors, thereby
manipulating the observable chemical-shift value of atoms used
in ∆pKa calculations as well as the overall inaccuracy of the
chemical-shift-determination procedure. The large difference in
the δC-values for phosphazene and its salt allows one to perform
the ∆pKa calculations with acceptable results at phosphazene-
indicator pKa differences up to one pKa unit. Comparison
of the δC-values for phenyl-substituted phosphazenes and α-
naphthylphosphazene shows that the transformation of the
phosphazene from neutral base to HPF6 or HClO4 salt causes a
decrease of the C1 chemical shift and an increase of the C4
chemical shift for the aromatic ring. This phenomenon is
pKa determination
The equilibrium acidity measurements for the determination of
pKas of various classes of compounds in different solvents are
used widely and a large number of these values are collected
into reviews.4,10
However, there are very few data available for N-phenyl-
substituted iminophosphoranes. Yurchenko has measured by
potentiometric titration the pKa of 16 and some other analo-
gous imino(amino)phosphazenes in nitromethane.11 Using the
indicator bases with known pKa-values as reference compounds
the ∆pKa-values of phosphazenes were calculated from 13C (1H)
NMR spectral data of mixtures of the phosphazene with indi-
cator base in acetonitrile. Depending on the type of indicator
base and its pKa relative to that of the measured phosphazene
the mixture of two compounds was made where the phospha-
zene was in the base form and the indicator in the acid form, or
vice versa.
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Table 2 The calculated ∆pKa- and pKa-values for phosphazenes in acetonitrile
Phosphazene
(R substituent)
pKa of
∆pKa of
phosphazene
pKa of
phosphazene
Average pKa of
phosphazene
Indicator
indicator11
1 [2,4(NO2)2C6H3]
Lutidine
Collidine
EA
TEA
EA
TEA
EA
13.99
14.38
17.53
18.45
17.53
18.45
17.53
19.58
21.6; 20.3b
20.12
21.6; 20.3b
20.6
20.7
23.3
23.3
24.3
23.3
24.3
25.97
20.12
21.6; 20.3a
20.7
0.67
0.05
Ϫ0.06
Ϫ0.32
0.29
Ϫ0.58
0.45
0.18
Ϫ0.33
Ϫ0.22
0.37
0.35
0.68
Ϫ0.68
0.01
Ϫ0.87
0.64
Ϫ0.44
0.86
0.78
14.7
14.4
17.5
18.1
17.8
17.9
18.0
14.5
2 (4-Cl-2-NO2C6H3)
3 (2,6-Cl2C6H3)
17.5
18.0
4 (2,5-Cl2C6H3)
5 (2-ClC6H4)
17.9
19.8
Pyrrolidine
MMSa
DAB
19.8
21.3; 20.0b
19.9
6 (α-Naphthyl)
8 (4-BrC6H4)
MMSa
PhTMG
C6H5CO2Ha
TMG
22.0; 20.7b
21.0
20.7b
21.0
21.4
22.6
23.3
23.5
23.9
23.9
26.8
9 (C6H5)
10 (4-MeOC6H4)
22.6
23.4
TMG
DBU
TMG
DBU
11 (4-Me2NC6H4)
23.9
12 (H2N)
TBD
26.8
20.9
16 C6H5N᎐P(NMe2)3
DAB
20.9
᎐
MMSa
C6H5CO2Ha
0.47
0.36
22.1; 20.8a
21.1
a Carboxylic acids which tend to form strong hydrogen bonds and various associates. The pKa-values obtained on the basis of those indicators are
excluded from the calculation of the average pKa-value for phosphazene. b The pKa-value for MMS obtained in the present work using pyrrolidine as
the reference base and the pKa of the phosphazene calculated on the basis of it.
The indicators (Ind) used were of different types. TBD, DBU,
TMG, 1,1,3,3-tetramethyl-2-phenylguanidine (PhTMG), 1,4-
diaminobutane (DAB), triethylamine (TEA), pyrrolidine, 2-
aminoethanol (EA), 2,6-dimethylpyridine (lutidine) and 2,4,6-
trimethylpyridine (collidine) as neutral bases were added to
the phosphazene HPF6 salt solution to give the equilibrium (1).
determination of the [P1ؒHPF6]/[P1] and [Ind]/[IndؒHPF6], etc.,
quotients. The investigated phosphazenes were mainly phenyl-
substituted ones where the δC- as well the δH-values of the
phenylic substituent atoms in the base and salt forms are
significantly different. The chemical shifts of C1 and C4 of the
aromatic ring, as the most sensitive carbon atoms to the phos-
phazene protonation, were used for the ∆pKa calculation. Both
these shifts give approximately identical ∆pKa-values for the
phosphazene. Only in some cases was the difference up to the
0.1 pKa units. Although the primary data used for the ∆pKa
calculations were δC-values of phosphazene and indicator, in
some cases the δH-values of the indicator compounds and
phosphazene aromatic substituent were used as additional data
in calculations. That was done if the usage or evaluation of the
indicator δC shifts was impossible when they were not suf-
ficiently sensitive to the protonation–deprotonation process, or
when the scatter of ∆pKa-values obtained using δC shifts was
relatively large. On the NMR time-scale, there is a fast exchange
and/or conversion between different species in any phos-
phazene–indicator mixture and the spectral lines of the indi-
vidual species shown in equations (1) and (2) are not directly
observable. However, the well defined and identifiable lines at
the weighted average chemical shifts for mixtures of phospha-
zene base with its salt form and for indicator base form with
its protonated form are observable. Therefore, knowing the
chemical shifts of individual species, their concentrations in
equations (3) and (4) can be calculated on the basis of
equations (5) and (6). For the phosphazene the calculation
was performed according to equation (5). P1s denotes the
Ϫ
P1HϩؒPF6Ϫ ϩ Ind
P1 ϩ IndHϩؒPF6
(1)
Monomethyl succinate (methyl hydrogen succinate) (MMS)
and benzoic acid (C6H5CO2H) as neutral weak protonic acids
were added to the phosphazene solution to give the equilibrium
(2).
P1 ϩ IndH
P1Hϩ ϩ IndϪ
(2)
The calculation of the ∆pKa-value of the phosphazene
relative to the used indicator compound pKa was performed on
the basis of equations (3) and/or (4). In the case of phos-
phazene HPF6 salts (P1ؒHPF6) and TBD, DBU, DAB, TMG,
PhTMG, TEA, lutidine, pyrrolidine, collidine or EA (Ind),
equation (3) holds.
∆pKa = lg([P1ؒHPF6][Ind]/[IndؒHPF6][P1])
(3)
In the case of a neutral phosphazene and MMS or
C6H5CO2H (IndH), then equation (4) applies.
∆pKa = Ϫlg([P1][IndH]/[P1Hϩ] [IndϪ])
(4)
In these equations, P1 denotes phosphazene. As could be
seen, in calculations of the ∆pKa the concentrations rather than
activities are used. This approach is based on the assumption
that the activity coefficient ratios for P1, Ind, IndH and their
respective protonated or deprotonated forms are constants. For
determination of the ∆pKa the solutions of phosphazenes and
their protonated forms (HPF6 or HClO4 salts), and indicators
and their protonated or deprotonated forms, in acetonitrile
were prepared and the corresponding 1H and 13C NMR spectra
were recorded. These spectra were used for the determination
of chemical shifts of the individual species contributing to the
observable average chemical-shift values in phosphazene–
indicator mixtures. Obtained chemical shifts were used for
[P1]/[P1s] = |δ Ϫ δP1s|/|δP1 Ϫ δ|
(5)
phosphazene salt form and [P1] ϩ [P1s] is equal to the total
amount of the phosphazene in solution. For the indicator the
calculation was performed according to equation (6).
[Ind]/[IndH] = |δ Ϫ δInd|/|δIndH Ϫ δ|
(6)
Chemical shifts of the species were obtained from the corre-
sponding 13C NMR spectra. Obtained ∆pKa-values and pKa-
values of the indicators used are presented in Table 2.
J. Chem. Soc., Perkin Trans. 1, 2000, 2637–2644
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and has a slope which is close to unity [pK (᎐yrr ) =
᎐
a
3
0.97ؒpKa(RNH2) ϩ 17.90]. This value of the slope confirms
that solvent-specific interactions have no large effect on the
measured pKa-values of the phosphazenes or that these effects
are cancelled out.14 A satisfactory correlation coefficient
(R2 = 0.96) of this correlation with pKa-values in polar solvents
where the ion pairing is much less probable than in the case
of acetonitrile in the present study supports the quite small
significance of solvent-specific effects.
There are only a few literature pKa-values for anilines in
acetonitrile available.10 However, a similar correlation between
pKa-values of these compounds exists and is observable in
Fig. 1. An analogous correlation is found between pKa-
values of s-C H N᎐P(CH CH ) C H phosphazenes and the
᎐
6
5
2
3
2
6
5
corresponding anilines in nitromethane.15
The analysis of the pKa-values of anilines in water and in
acetonitrile and of those for phosphazenes in acetonitrile
reveals that the transfer of anilines from water to acetonitrile
increases their basicity by approximately 5 pKa units and that
substitution of the hydrogens of the aniline (amine) amino
Fig. 1 The dependence between pKas of phosphazenes and corre-
sponding amines (RNH2).11 The numbering of points corresponds to
Table 2.
group by the ᎐P(Pyrr) group increases the basicity approxi-
mately by 10–12 pKa units.
᎐
3
Comparison of pKa-values
It is seen from Table 2 that the obtained pKa-values for the
phosphazenes obtained using different indicators differ some-
what from each other. Those differences were usually not larger
than was the precision of the ∆pKa determinations, which by
repeated measurements was better than 0.2 pKa units. How-
ever, there were some noticeable deviations from the overall
picture. The obscure region was the range from 19 to 22 pKa
units, which includes the phosphazenes 4–6 and 8. The pKa-
values for 5 obtained using MMS, pyrrolidine and TMG
differed considerably. If we used for MMS the literature12 pKa-
value, 21.6, and for pyrrolidine the corresponding value, 19.58,
then the calculated pKa-values for 5 are correspondingly 21.3
and 19.8, i.e., the difference is 1.5 pKa units. This is a much
larger difference than could be introduced only by experimental
error. To solve this inconsistency we compared the basicities of
MMS and pyrrolidine with each other in their mixture and
found that their apparent ∆pKa is ≈0.7–0.8 pKa units. Compared
with their ∆pKa-value obtained using the literature pKa-
values our ∆pKa-value is significantly lower and incomparable
with it within experimental error. We feel that the literature pKa
of pyrrolidine seems to be closer to its actual value than does
the corresponding value for MMS. This opinion is based on a
comparison of the obtained pKa-values for the phosphazenes
(3–5 and 16) using different indicators (EA, TEA, pyrrolidine,
PhTMG and MMS). The usage for MMS of the pKa-value
20.3 instead of 21.6 reduces the scatter of pKa-values for 5 and
16 obtained using different indicators. Therefore, we assume
that the conjugate anion of MMS is actually not as strong a
base, i.e. its apparent pKa is lower than its literature pKa-value.12
In Table 2 are shown pKa-values for 5, 6 and 16 calculated on
the basis of the both MMS pKa-values (21.6 and 20.3). The
average phosphazene pKa-values for them in Table 2 and the
corresponding values in Fig. 1 are calculated without the ∆pKa
data obtained using MMS and C6H5CO2H as indicators.
It is necessary to keep in mind that, in principle, the obtained
∆pKa-values are rather quantities for the equilibrium where,
besides ions, the solution contains some ion-pairs, and, corre-
spondingly, can contain some contribution from specific
solvation effects.13 In particular this can be the situation in the
case of carboxylic acids used as indicators. Therefore the
obtained ∆pKa-values should be considered as apparent values
for the phosphazenes. However, the calculated pKa-values are
not only of qualitative importance reflecting whether the
indicator used or the phosphazene measured was a stronger
base. Their quantitative value is observable by plotting them
versus basicities of amines in water (Fig. 1). The correlation
of pKa-values of phosphazenes in acetonitrile with the corres-
ponding values of anilines (amines) in water10 is rather good
Experimental
General procedures
The standard 1D H and proton-decoupled 13C NMR spectra
1
were recorded on a Bruker AC-200 NMR spectrometer at 200
MHz and 50 MHz, correspondingly. Solutions were prepared
and sealed off in 5 mm NMR tubes. The concentration of
measured solutions was 0.11–0.12 M. Chemical shifts were
determined relative to TMS as internal standard. Nondeuter-
ated acetonitrile was used as solvent and the preparations were
performed under dry nitrogen. J-Values are in Hz. C, H,
N elemental analysis was done on a Perkin-Elmer Analyzer
2400 ser. II, or a Perkin-Elmer Elemental Analyzer 240. Mps
(uncorrected) were determined on a Gallenkamp mp apparatus
with a digital thermometer (SG 95/09/223). Ion exchangers
used were APA-8π (Reachim) or Dowex Monosphere 550 A,
the strongly basic anion-exchange resins (ClϪ form). The
exchange of anions for ClϪ was performed by means of a
column with MeOH as solvent.
Materials
NaBF4, NaBPh4 (Fluka), KOMe (Merck), DAB (Ferak Berlin),
2,5-dichloroaniline, 70% aq. EtNH2 and 60% aq. HPF6
(Aldrich) were commercial products and were used without
additional purification. CH2Cl2 (Merck), CCl4 (Reakhim)
were distilled from P2O5 and stored on NaOH. Pyrrolidine
(Merck) was distilled and stored on molecular sieves 4 Å. Et3N
(Reakhim) was distilled and stored on NaOH. THF and
benzene were distilled from LiAlH4. Aniline and 4-(dimethyl-
amino)aniline were distilled from Zn powder, α-naphthylamine,
p-anisidine (all Reakhim), and 4-bromoaniline (Fluka) were
recrystallized from an ethanol–water mixture. 2,6-Dichloro-
aniline, 4-chloro-2-nitroaniline and MMS were synthesized by
standard procedures. PhTMG3d and C H N᎐P(NMe ) 16 2d
᎐
6
5
2 3
were prepared as described in the literature. Anhydrous hydra-
zine was prepared from hydrazine hydrate (Reakhim). Romil
Super Purity MeCN was used for spectral measurements. The
reaction conditions (and therefore the isolated yields) for all
synthesized phosphazene compounds were not optimized.
(2,4-Dinitrophenylimino)tripyrrolidinophosphorane
1
(Scheme 1). To a solution of 10 mmol of (2,4-dinitrophenyl-
imino)phosphorus() trichloride6 [7, R = 2,4-(NO2)2C6H3] in 15
ml of THF at Ϫ50 ЊC was added 60 mmol of pyrrolidine in 5 ml
of THF under N2. The mixture was stirred and the temperature
was allowed to warm to ambient, and the mixture was left
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overnight. Settled pyrrolidineؒHCl salt was filtered off and the
solvent removed at reduced pressure. To the residue, 3.5 g of a
brown viscous mass, was added 20 ml of 70% aq. EtNH2. Light
yellow crystals were precipitated, and were recrystallized from
70% aq. EtNH2.1 Product 1 was dried under high vacuum to
give 1 (2.7 g, 63%), mp 97.1–97.4 ЊC; δH 1.83 (12H, m, NCH2-
CH2), 3.16 (12H, dt, 3JH-H 6.6, 3JP-H 3.8, NCH2CH2), 6.87 (1H,
d, 3JH-H 9.4, Ar 6-H), 7.96 (1H, dd, 3JH-H 9.4, 4JH-H 2.9, Ar 5-H),
C-6), 127.3 (Ar C-3), 128.9 (Ar C-4), 134.9 (2JP-C 2.4, Ar C-1),
137.3 (Ar C-5), 138.9 (3JP-C 8.8, Ar C-2) [Calc. for C18H28-
F6ClN5O2P2 (M: 557.82): C, 38.76; H, 5.06; N, 12.55. Found: C,
38.44; H, 4.95; N, 12.04%].
(2,6-Dichlorophenylimino)tripyrrolidinophosphorane
3
(Scheme 1). To 15.6 mmol of 2,6-dichloroaniline solution in
17 ml of CCl4 was added 15.6 mmol of PCl5. HCl was evolved
and the corresponding salt of 2,6-dichloroaniline settled out.
The mixture was stirred, heated and refluxed until the HCl
evolution ceased. The cooled solution was filtered and solvent
was removed in vacuo (eventually 80 ЊC/3 mmHg). The light
yellow oil (3 g, 10 mmol), raw (2,6-dichlorophenylimino)-
phosphorus() trichloride (7, R = 2,6-Cl2C6H3), was dissolved
in 40 ml of dry benzene. A solution of 5.2 g of pyrrolidine in 10
ml of benzene was added. The mixture was stirred and refluxed
for 1 h, stored at 5 ЊC for 36 h, after which the settled pyr-
rolidineؒHCl salt was filtered off. The solvent was removed at
reduced pressure. The thick residue was treated with 70% aq.
EtNH2 (≈10 ml) and the precipitate was separated by suction.
For recrystallization it was dissolved in warm 70% aq. EtNH2
(≈120 ml) and the warm solution was filtered. Precipitated crys-
tals were collected by suction, washed with dil. aq. EtNH2 and
dried under high vacuum to give white crystals (2.2 g, 35%); mp
79.8–81.0 ЊC; δH 1.75 (12H, m, NCH2CH2), 3.18 (12H, dt, 3JH-H
4
8.36 (1H, t, JH-H = 5JP-H = 2.9, Ar 3-H); δC 27.0 (3JP-C 8.0,
NCH2CH2), 47.6 (2JP-C 4.2, NCH2CH2), 121.9 (4JP-C 2.1, Ar
C-3), 123.8 (3JP-C 10.1, Ar C-6), 127.7 (Ar C-5), 134.8 (Ar C-4),
143.4 (3JP-C 28.0, Ar C-2), 153.7 (2JP-C 6.8, Ar C-1) [Calc. for
C18H27N6O4P (M: 422.40): C, 51.18; H, 6.44; N, 19.89. Found:
C, 51.25; H, 6.65; N, 19.33%].
1ؒHPF6. To 1.28 mmol of 1 in 5 ml of MeOH was added 10
ml of 0.6 M HCl (6 mmol, excess). The solution was filtered and
a calculated amount of 30% HPF6 was added. The pale crystals
were collected by suction filter, washed successively with water
and cold MeOH and dried in vacuo: mp 199–205 ЊC; δH 1.9
(12H, overlapped by the solvent, NCH2CH2), 3.34 (12H, dt,
3
3
3JH-H 6.8, JP-H 3.7, NCH2CH2), 7.47 (1H, dd, JH-H 9.3, Ar
3
4
6-H), 8.46 (1H, dd, JH-H 9.3, JH-H 2.7, Ar 5-H), 9.03 (1H,
4
5
2
dd, JH-H 2.7, JP-H 1.5, Ar 3-H), 9.1 (1H, br d, JP-H 9.8, NH);
δC 26.9 (3JP-C 8.7, NCH2CH2), 48.8 (2JP-C 5.1, NCH2CH2), 121.4
(3JP-C 3.1, Ar C-6), 123.9 (Ar C-3), 131.7 (Ar C-5), 137.1 (3JP-C
9.3, Ar C-2), 141.6 (2JP-C 3.1, Ar C-1), 143.0 (Ar C-4) [Calc. for
C18H28F6N6O4P2 (M: 568.39): C, 38.04; H, 4.97; N, 14.79.
Found: C, 38.18; H, 4.86; N, 14.39%].
3
3
3
6.6, JP-H 3.4, NCH2CH2), 6.50 (1H, ddd, JH-H 7.6, JH-H 8.1,
6JP-H 1.9, Ar 4-H), 7.15 [2H, dd, 3JH-H 7.9, 5JP-H 1.4, Ar 3(5)-H];
δC 27.1 (3JP-C 8.2, NCH2CH2), 47.6 (2JP-C 4.5, NCH2CH2), 117.8
(5JP-C 2.4, Ar C-4), 128.7 [Ar C-3(5)], 130.3 [3JP-C 8.9, Ar
C-2(6)], 146.3 (2JP-C 9.7, Ar C-1) [Calc. for C18H27Cl2N4P (M:
401.32): C, 53.87; H, 6.78; N, 13.96. Found: C, 53.79; H, 6.77;
N, 13.84%].
(4-Chloro-2-nitrophenylimino)tripyrrolidinophosphorane
2
(Scheme 1). To 13.1 mmol (2.26 g) of 4-chloro-2-nitroaniline
solution in 10 ml of CCl4 was added 13.1 mmol (2.7 g) of
PCl5 at room temperature. The mixture was heated and refluxed
until the HCl evolution ceased. The solvent was removed. The
residue, raw (4-chloro-2-nitrophenylimino)phosphorus() tri-
chloride (7, R = 4-Cl-2-NO2C6H3), in the form of a pale yellow
solid (2.9 g, 9 mmol), mp 91–93 ЊC was dissolved in 40 ml of
dried benzene and a solution of 4.8 g of pyrrolidine in 10 ml of
benzene was added at room temperature by means of a drop-
ping funnel. The mixture was heated to 50 ЊC and stirred for ca.
1 h. The mixture was cooled to 5 ЊC, pyrrolidineؒHCl salt was
filtered off and the solvent removed at reduced pressure (60 ЊC/
5 mmHg). From the dark brown residue the product 2 was
precipitated by addition of 70% aq. EtNH2. Product 2 was
3ؒHPF6. To a cold methanolic solution of free base 3 the
calculated amount of 60% HPF6 solution was added. The white
precipitate was separated by suction and washed with cold
MeOH. Recrystallization from methanolic solution gave 0.45 g
of nearly colorless crystals; mp 240–244 ЊC; δH 1.83 (12H, m,
NCH2CH2), 3.23 (12H, dt, 3JH-H 6.7, 3JP-H 2.7, NCH2CH2), 6.2
3
3
6
(1H, s, NH), 7.32 (1H, ddd, JH-H 7.1, JH-H 9.0, JP-H 1.5, Ar
4-H), 7.50 [2H, dt, JH-H 7.9, Ar3(5)-H]; δC 26.8 (3JP-C 9.0,
3
NCH2CH2), 48.3 (2JP-C 5.1, NCH2CH2), 130.5 [4JP-C 1.5, Ar
C-3(5)], 130.8 (5JP-C 2.1, Ar C-4), 132.6 (Ar C-1), 136.6 [3JP-C
3.8, ArC-2(6)] [Calc. for C18H28Cl3F6N4O2P2 (M: 547.29):
C, 39.50; H, 5.16; N, 10.24. Found: C, 39.60; H, 5.06; N,
10.08%].
1
recrystallized from 70% aq. EtNH2 and dried under high
vacuum to give yellow crystals (1.7 g, 33%); mp 87.6–87.9 ЊC;
δH 1.80 (12H, m, NCH2CH2), 3.14 (12H, dt, 3JH-H 6.7, 3JP-H 4.0,
NCH2CH2), 6.85 (1H, br d, JH-H 9.0, Ar 6-H), 7.11 (1H, dd,
(2,5-Dichlorophenylimino)tripyrrolidinophosphorane
(Scheme 1). This compound was prepared analogously to
the synthesis of 3. 4.1 of (2,5-dichlorophenylimino)-
4
3
3JH-H 9.0, 4JH-H 2.8, Ar 5-H), 7.46 (1H, br t, 4JH-H 2.8, 5JH-P 2.5,
Ar 3-H); δC 27.0 (3JP-C 7.8, NCH2CH2), 47.6 (2JP-C 4.0,
NCH2CH2), 117.6 (5JP-C 4.2, Ar C-4), 124.3 (4JP-C 1.9, Ar C-3),
126.5 (3JP-C 9.1, Ar C-6), 132.5 (Ar C-5), 145.1 (3JP-C 26, Ar
C-2), 146.2 (2JP-C 7.4, Ar C-1) [Calc. for C18H27ClN5O2P (M:
411.86): C, 52.49; H, 6.61; N, 17.00. Found: C, 52.34; H, 6.57;
N, 16.76%].
g
phosphorus() trichloride (7, R = 2,5-Cl2-C6H3; mp 120.1–
120.4 ЊC) were used for the synthesis. Finally, after purification,
1.6 g of 4 in the form of white crystals were obtained (yield
30.8%); mp 82.7–83.4 ЊC; δH 1.80 (12H, m, NCH2CH2), 3.16
3
3
3
(12H, dt, JH-H 6.6, JP-H 3.9, NCH2CH2), 6.45 (1H, ddd, JH-H
4
6
4
4
8.4, JH-H 2.5, JP-H 0.4, Ar 4-H), 6.72 (1H, dd, JH-H 2.5, JP-H
1.2, Ar 6-H), 7.12 (1H, dd, 3JH-H 8.4, 5JP-H 2.5, Ar 3-H); δC 27.0
(3JP-C 7.7, NCH2CH2), 47.6 (2JP-C 3.9, NCH2CH2), 116.2 (Ar
C-4), 122.4 (3JP-C 8.8, Ar C-6), 126.7 (3JP-C 26.9, Ar C-2), 130.6
(Ar C-3), 132.6 (Ar C-5), 151.0 (2JP-C 7.0, Ar C-1) [Calc. for
C18H27Cl2N4P (M: 401.32): C, 53.87; H, 6.78; N, 13.96. Found:
C, 53.93; H, 6.83; N, 13.86%].
2ؒHPF6. To a methanolic solution of 0.72 g of 2 at Ϫ50 ЊC
was added a calculated amount of 60% HPF6. The yellowish
precipitated salt was filtered off and washed with MeOH. The
salt was dissolved in CHCl3 and reprecipitated by adding
MeOH until turbidity persisted (CHCl3–MeOH ≈1:2). The
mixture was warmed to lose the turbidity and left for crystal-
lization. The pale crystals (0.26 g) were collected by suction,
washed with MeOH and dried in vacuo: mp 214.0–214.4 ЊC;
δH 1.9 (12H, overlapped by solvent, NCH2CH2), 3.30 (12H, dt,
3JH-H 6.7, 3JP-H 3.7, NCH2CH2), 7.31 (1H, d, 3JH-H 9.0, Ar 6-H),
4ؒHPF6. This compound was prepared as described for
3ؒHPF6 with the following parameters: yield 61%; mp 202.5–
3
203 ЊC; δH 1.88 (12H, m, NCH2CH2), 3.27 (12H, dt, JH-H 6.6,
3JP-H 3.6, NCH2CH2), 6.2 (1H, br s, NH) 7.18 (1H, m, Ar 4-H),
7.23 (1H, d, 4JP-H 2.3, Ar 6-H), 7.50 (1H, dd, 3JH-H 8.5, 5JP-H 1.3,
Ar 3-H); δC 26.8 (3JP-C 8.6, NCH2CH2), 48.6 (2JP-C 5.0,
NCH2CH2), 124.1 (3JP-C 2.4, Ar C-6), 127.18 (3JP-C 8.5, Ar C-2),
3
4
4
7.71 (1H, dd, JH-H 9.0, JH-H 2.6, Ar 5-H), 8.28 (1H, dd, JH-H
2.6, JH-P 1.5, Ar 3-H), 8.6 (1H, br, NH); δC 26.9 (3JP-C 8.6,
5
NCH2CH2), 48.7 (2JP-C 5.0, NCH2CH2), 122.9 (3JP-C 2.9, Ar
J. Chem. Soc., Perkin Trans. 1, 2000, 2637–2644
2641

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127.21 (Ar C-4), 132.4 (Ar C-3), 134.2 (Ar C-5), 136.4 (2JP-C 1.9,
The precipitate was dissolved in MeOH and a calculated
Ar C-1).
amount of 60% HPF6 solution was added. The solution (Et2O
and most from MeOH) was drawn up and cooled. The crystals
were filtered off, washed with cold MeOH and dried in vacuo.
80 mg of white crystals of 6ؒHPF6 were obtained, mp 198–
(2-Chlorophenylimino)tripyrrolidinophosphorane
5 (Scheme
1). 11.3 mmol of (2-chlorophenylimino)phosphorus() tri-
chloride6 were slurried in 50 ml of dry benzene, and 71 mmol
of pyrrolidine was added at room temperature by means of a
dropping funnel. The mixture was stirred and warmed to 50 ЊC
and then left to cool. The precipitate of pyrrolidineؒHCl salt
was filtered off, and the solvent was removed. The residue, a
dark viscous oil, was treated with a 25-fold quantity of 70% aq.
EtNH2 and stored at Ϫ15 ЊC for a week. Crystals of 5 were
collected and recrystallized from abundant 70% aq. EtNH21 as
white crystals (1.5 g, 36%), mp 49.3–50.6 ЊC; δH 1.78 (12H, m,
NCH2CH2), 3.16 (12H, dt, 3JH-H 6.6, 3JP-H 4.0, NCH2CH2), 6.45
(1H, dddd, 3JH-H 7.1, 3JH-H 7.8, 4JH-H 1.7, 6JP-H 0.7, Ar 4-H), 6.77
(1H, ddd, 3JH-H 8.1, 4JH-H 1.7, 4JP-H 1.1, Ar 6-H), 6.91 (1H, ddd,
3JH-H 7.1, 3JH-H 8.1, 4JH-H 1.7, Ar 5-H), 7.15 (1H, ddd, 3JH-H 7.8,
4JH-H 1.7, 5JP-H 2.6, Ar 3-H); δC 27.0 (3JP-C 7.6, NCH2CH2), 47.6
(2JP-C 3.8, NCH2CH2), 116.9 (Ar C-4), 123.7 (3JP-C 8.0, Ar C-6),
127.8 (Ar C-5), 128.1 (3JP-C 22, Ar C-2), 130.0 (4JP-C 1.9, Ar C-3),
149.7 (2JP-C 7.8, Ar C-1) [Calc. for C18H28ClN4P (M: 366.83): C,
58.93; H, 7.69; N, 15.27. Found: C, 58.97; H, 7.78; N, 15.21%].
3
202 ЊC; δH 1.81 (12H, m, NCH2CH2), 3.27 (12H, dt, JH-H 6.6,
3JP-H 3.6, NCH2CH2), 6.5 (1H, d, 2JP-H 11.2, NH), 7.34 (1H, br
d, 3JH-H 7.3, ArH), 7.48 (1H, dd, 3JH-H 8.3, 3JH-H 7.3, ArH), 7.63
3
(2H, m, ArH), 7.84 (1H, br d, JH-H 8.3, ArH), 7.96 (1H, m,
ArH), 8.16 (1H, m, ArH); δC 26.8 (3JP-C 8.5, NCH2CH2), 48.5
(2JP-C 4.8, NCH2CH2), 122.6 (3JP-C 3.1, Ar C-2), 123.1 (Ar C),
126.7 (JP-C 1.6, Ar C-4), 127.6 (JP-C 1.2, Ar C), 127.8 (Ar C),
127.9 (Ar C), 129.5 (Ar C), 130.6 (3JP-C 6.9, Ar C-9), 133.3 (Ar
C-10), 135.6 (Ar C-1) [Calc. for C22H32F6N4P2 (M: 528.45): C,
49.62; H, 6.10; N, 10.60. Found: C, 49.96; H, 5.92; N, 10.24%].
(4-Bromoanilino)tripyrrolidinophosphonium tetraphenylborate
8ؒHBPh4 (Scheme 2). The chlorophosphonium salt 13 was
synthesized from 12.5 mmol of PCl5 and 37.4 mmol of pyrrol-
idine in CH2Cl2.1 Et3N was used to eliminate the evolving
HCl. The precipitate of Et3NؒHCl was filtered off and CH2Cl2
replaced with 30 ml of THF. 12.5 mmol of 4-bromoaniline and
then 12.5 mmol of Et3N were added at Ϫ20 ЊC to the solution
after which it was stirred and the temperature was allowed to
rise to ambient. Then the solution was warmed to 50 ЊC and
kept for 30 min at this temperature. Formed Et3NؒHCl was
filtered off and solvent was removed in vacuo. The obtained
dark brown viscous residue was dissolved in MeOH and an
equimolar amount of NaBPh4 as a solution in MeOH was
added. The precipitated 8ؒHBPh4 was filtered off and recrystal-
lized from MeOH–CHCl3 (2:1) to give yellowish crystals (3.1 g,
34%), mp 184.6–186.5 ЊC; δH 1.85 (12H, m, NCH2CH2), 3.20
5ؒHPF6. To a methanolic solution (7.5 ml) of 5 (1.5 g) was
added the calculated amount of 60% HPF6 at Ϫ40 ЊC. The mix-
ture was allowed to warm to ambient temperature, and crystals
of 5ؒHPF6 were collected by suction and recrystallized from
a 2:3 mixture of CHCl3 and MeOH (eventually at Ϫ15 ЊC).
White crystals (0.75 g) were collected; mp 173.7–175.6 ЊC;
δH 1.87 (12H, m, NCH2CH2), 3.26 (12H, dt, 3JH-H 6.6, 3JP-H 3.7,
NCH2CH2), 6.1 (1H, br d, 2JP-H 11, NH), 7.2–7.3 (3H, br m, Ar
4-, 5- and 6-H), 7.5 (1H, br d, 3JH-H 8, Ar 3-H); δC 26.8 (3JP-C 8.5,
NCH2CH2), 48.4 (2JP-C 4.8, NCH2CH2), 124.9 (Ar C-6), 127.6
(Ar C-4), 128.8 (3JP-C 9, Ar C-2), 129.3 (Ar C-5), 131.2 (Ar C-3),
135.0 (2JP-C 1.6, Ar C-1) [Calc. for C18H29ClF6N4P2 (M: 512.79):
C, 42.16; H, 5.70; N, 10.93. Found: C, 42.65; H, 5.64; N,
10.73%].
3
3
3
(12H, dt, JH-H 6.7, JP-H 3.4, NCH2CH2), 6.83 (4H, t, JH-H
+
3
7.1, BPh4 4-H), 6.94 [2H, d, JH-H 8.9, Ar 2(6)-H], 6.99 [8H, t,
+
+
3JH-H 7.1, BPh4 3(5)-H], 7.27 [8H, m, BPh4 2(6)-H], 7.46 [2H,
d, JH-H 8.9, Ar 3(5)-H]; δC 26.9 (3JP-C 8.7, NCH2CH2), 48.4
3
+
(2JP-C 5.2, NCH2CH2), 117.0 (Ar C-4), 122.7 (BPh4 C-4), 122.8
+
[3JP-C 7.0, Ar C-2(6)], 126.5 [2JB-C 2.8, BPh4 C-2(6)], 133.6 [Ar
+
C-3(5)], 136.8 [BPh4 C-3(5)], 138.4 (Ar C-1), 164.9 (1JP-C 49.4,
+
(ꢀ-Naphthylimino)tripyrrolidinophosphorane 6 (Scheme 1).
25 mmol (3.5 g) of α-naphthylamine were dissolved in 20 ml of
CCl4 and 25 mmol (5.2 g) of PCl5 were added. The mixture was
heated at 70 ЊC for ca. 4 h up to the end of evolution of HCl.
The precipitate was filtered off and washed successively with
CCl4, benzene, and diethyl ether. The bluish crystals of (α-
naphthylamino)phosphorus() trichloride (7, R = α-naphthyl)
were dried in vacuo (mp 150–152 ЊC) and 6 mmol of this was
slurried in 60 ml of benzene. The mixture was heated to 80 ЊC
and 40 mmol of pyrrolidine was added by means of a dropping
funnel. The mixture was stirred and kept at 80 ЊC for 4 h and
then cooled. 1,1,2-Trichloroethylene was added and the HCl salt
of pyrrolidine was filtered off. Solvent was removed and to the
dark viscous residue was added 30 ml of 70% aq. EtNH2. The
mixture was left for two days after which the formed crystals
were filtered off, then recrystallized from 40-fold excess of 70%
aq. EtNH2 (eventually at Ϫ15 ЊC) and light beige crystals of 6
were collected (1 g, 44%), mp 81.0–82.5 ЊC; δH 1.78 (12H, m,
NCH2CH2), 3.21 (12H, dt, 3JH-H 6.5, 3JP-H 3.8, NCH2CH2), 6.67
(1H, dt, 3JH-H 7.4, ArH), 7.00 (1H, d, 3JH-H 8.0, ArH), 7.14 (1H,
dt, 3JH-H 7.5, 3JH-H 8.0, ArH), 7.28 (2H, m, ArH), 7.62 (1H, m,
ArH), 8.53 (1H, m, ArH); δC 27.1 (3JP-C 7.6, NCH2CH2), 47.7
(2JP-C 3.8, NCH2CH2), 114.8 (3JP-C 8.3, Ar C-2), 115.5 (Ar C-4),
123.7 (Ar C), 126.0 (Ar C), 126.6 (Ar C), 127.8 (Ar C), 127.9
(JP-C 1.4, Ar C-3), 132.2 (3JP-C 24.1, Ar C-9), 136.2 (4JP-C 2.7, Ar
C-10), 150.0 (2JP-C 4.9, Ar C-1) [Calc. for C22H31N4P (M:
382.49): C, 69.08; H, 8.17; N, 14.65. Found: C, 69.12; H, 8.51;
N, 14.40%].
BPh4 C-1).
(4-Bromophenylimino)tripyrrolidinophosphorane 8. To
a
solution of 8ؒHBPh4 in 10 ml of acetonitrile was added the
calculated amount of 25% methanolic KOMe. The precipi-
tated KBPh4 was filtered off, methanol was removed, and
the obtained residue was extracted with n-hexane. After
evaporation of hexane, white crystals of 8 were obtained,
mp 98.8–99.6 ЊC; δH 1.78 (12H, m, NCH2CH2), 3.13 (12H, dt,
3JH-H 6.5, 3JP-H 3.6, NCH2CH2), 6.55 [2H, d, 3JH-H 8.7, Ar 2(6)-
H], 7.05 [2H, d, JH-H 8.7, Ar 3(5)-H]; δC 27.0 (3JP-C
3
7.9, NCH2CH2), 47.6 (2JP-C 3.8, NCH2CH2), 107.2 (Ar C-4),
125.2 [3JP-C 18.1, Ar C-2(6)], 132.0 [4JP-C 1.0, Ar C-3(5)], 153.1
(2JP-C 2.9, Ar C-1).
8ؒHPF6 was prepared as described above for 5ؒHPF6: mp
191.5–192.6 ЊC; δH 1.89 (12H, m, NCH2CH2), 3.24 (12H, dt,
3
2
3JH-H 6.6, JP-H 3.3, NCH2CH2), 6.5 (1H, br d, JP-H 9.5, NH),
6.97 [2H, d, 3JH-H 8.8, Ar 2(6)-H], 7.48 [2H, d, 3JH-H 8.8, Ar 3(5)-
H]; δC 26.9 (3JP-C 8.8, NCH2CH2), 48.4 (2JP-C 5.1, NCH2CH2),
117.0 (Ar C-4), 122.8 [3JP-C 6.7, Ar C-2(6)], 133.5 [Ar C-3(5)],
138.5 (Ar C-1).
(Phenylimino)tripyrrolidinophosphorane
9
(Scheme 2).
Chlorophosphonium salt 13 was synthesized from 50 mmol of
PCl5 and 150 mmol of pyrrolidine in CH2Cl2.1 Et3N was used
to eliminate the evolving HCl. The precipitate of Et3NؒHCl
was filtered off and CH2Cl2 was replaced with 50 ml of dry
THF. 55 mmol of aniline and 55 mmol of Et3N were added
subsequently to the solution at Ϫ10 ЊC. The mixture was stirred
and its temperature was allowed to rise to ambient after which
it was heated for a short time to 60 ЊC. The mixture was left for
6ؒHPF6. 140 mg of 6 were dissolved in diethyl ether and
6ؒHCl was precipitated by adding an ethereal solution of HCl.
2642
J. Chem. Soc., Perkin Trans. 1, 2000, 2637–2644

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two days and the formed Et3NؒHCl was filtered off. Solvent was
removed in vacuo and the residue was recrystallized twice from
aq. EtNH2.1 Compound 9 was obtained (12 g, 72%), mp 50.8–
51.8 ЊC; δH 1.78 (12H, m, NCH2CH2), 3.14 (12H, dt, 3JH-H 6.5,
3JP-H 3.6, NCH2CH2), 6.48 (1H, t, 3JH-H 7.2, Ar 4-H), 6.63 [2H,
d, JH-H 7.9, Ar 2(6)-H], 6.96 [2H, t, JH-H 7.6, Ar 3(5)-H];
δC 25.4 (3JP-C 7.6, NCH2CH2), 45.9 (2JP-C 3.6, NCH2CH2), 116.4
(Ar C-4), 123.5 [3JP-C 17.5, Ar C-2(6)], 129.4 [Ar C-3(5], 153.4
(2JP-C 2.9, Ar C-1) [Calc. for C19H29N4P (M: 332.38): C, 65.04;
H, 8.79; N, 16.85. Found: C, 64.83; H, 9.20; N, 16.47%].
was filtered off, solvent was removed, and the residue was
extracted with n-hexane. The solvent was removed in vacuo and
10 in form of a yellowish oil, was obtained: δH 1.77 (12H, m,
NCH2CH2), 3.13 (12H, dt, 3JH-H 6.6, 3JP-H 3.8, NCH2CH2), 3.64
(3H, s, OCH3), 6.6 [4H, br s, Ar 2(6)-H and Ar 3(5)-H]; δC 27.0
(3JP-C 7.7, NCH2CH2), 47.6 (2JP-C 4.9, NCH2CH2), 56.2 (OCH3),
115.1 [Ar C-3(5)], 123.9 [3JP-C 16.9, Ar C-2(6)], 147.0 (2JP-C 2.8,
Ar C-1), 151.8 (Ar C-4).
3
3
[4-(Dimethylamino)anilinotripyrrolidinophosphonium]
per-
chlorate 11ؒHClO4 (Scheme 2). The chlorophosphonium salt 13
was prepared from 25 mmol of PCl5 and 75 mmol of pyrrol-
idine in CH2Cl2.1 Et3N was used to eliminate the evolving
HCl. The precipitated Et3NؒHCl was filtered off, and CH2Cl2
removed in vacuo and replaced with 20 ml of THF. 25 mmol
of 4-(dimethylamino)aniline in 10 ml of THF and 25.5 mmol
of Et3N were added subsequently at Ϫ10 ЊC. The mixture was
refluxed for 3 h and left overnight. The formed Et3NؒHCl was
filtered off and solvent was removed in vacuo to give a dark-
brown viscous residue. The obtained product was dissolved in
80 ml of 70% aq. EtNH2 and 25 mmol of NaClO4ؒH2O in 50 ml
of water was added to precipitate 11ؒHClO4. After recrystal-
lization from aq. EtNH2, light pink crystals of 11ؒHClO4
were obtained (4 g, 34%), mp 117.9–118.6 ЊC; δH 1.85 (12H,
9ؒHPF6. 1.5 g of free base 9 were dissolved in 15 ml of 70% aq.
EtNH2 and a calculated amount of 30% HPF6 was added
(pH > 7). The mixture was warmed to 40 ЊC and approximately
2 ml of water were added, the precipitate (≈2.2 g) was collected
by suction, dissolved in 9 ml of MeOH, and the solution was
filtered. To the slightly warmed filtrate were added 5 ml of water
and the solution was left overnight. The formed crystals were
filtered off, washed with dil. MeOH, and dried in vacuo. 1.6 g
of 9ؒHPF6 were obtained, mp 154.0–154.9 ЊC; δH 1.88 (12H, m,
NCH2CH2), 3.23 (12H, dt, 3JH-H 6.7, 3JP-H 3.4, NCH2CH2), 6.4
(1H, s, NH), 7.1 [3H, m, Ar 2(6)-H and 4-H], 7.4 [2H, t, Ar 3(5)-
H]; δC 26.8 (3JP-C 8.5, NCH2CH2), 48.4 (2JP-C 5.1, NCH2CH2),
121.3 [3JP-C 6.4, Ar C-2(6)], 125.0 (Ar C-4), 130.7 [Ar C-3(5)],
138.9 (Ar C-1) [Calc. for C18H30F6N4P2 (M: 478.34): C, 45.20;
H, 6.32; N, 11.71. Found: C, 45.39; H, 6.28; N, 11.66%].
3
m, NCH2CH2), 2.89 (6H, s, NCH3), 3.22 (12H, dt, JH-H 6.6,
2
3JP-H 3.5, NCH2CH2), 6.1 (1H, br d, JP-H 12.2, NH), 6.7 [2H,
3
3
br d, JH-H 9, Ar 3(5)-H], 7.0 [2H, br d, JH-H 9, Ar 2(6)-H];
δC 26.8 (3JP-C 8.5, NCH2CH2), 41.1 (NCH3), 48.3 (2JP-C 4.7,
NCH2CH2), 114.6 [Ar C-3(5)], 125.7 [3JP-C 5.1, Ar C-2(6)], 127.0
(Ar C-1), 149.6 (Ar C-4) [Calc. for C20H35ClN5O4P (M: 475.93):
C, 50.47; H, 8.09; N, 14.71. Found: C, 50.57; H, 7.83; N,
14.52%].
(4-Methoxyanilino)tripyrrolidinophosphonium tetrafluorobor-
ate 10ؒHBF4 (Scheme 2). Chlorophosphonium salt 13 was syn-
thesized from 25 mmol of PCl5 and 75 mmol of pyrrolidine
in CH2Cl2.1 Et3N was used to eliminate the evolving HCl. The
precipitate of Et3NؒHCl was filtered off and solvent CH2Cl2
was replaced with 50 ml of THF. 25 mmol of p-anisidine in
10 ml of THF and 25 mmol of triethylamine were added
subsequently at Ϫ20 ЊC. The temperature of the mixture was
allowed to rise to ambient, after which it was warmed to 65 ЊC
for 4 h, then left overnight. The formed Et3NؒHCl was filtered
off and solvent was removed in vacuo. The residue, 10ؒHCl, was
dissolved in 70% aq. EtNH2, a calculated amount of aq. NaBF4
(as concentrated as possible) was added, and the precipitate of
formed 10ؒHBF4 was filtered off. The following recrystalliza-
tion from aq. EtNH2 yielded 2.1 g (25%) of beige crystals of
10ؒHBF4, mp 164.5–165.7 ЊC; δH 1.86 (12H, m, NCH2CH2),
[4-(Dimethylamino)phenylimino]tripyrrolidinophosphorane
11. A sample of 11 was liberated from intermediate 11ؒHBF4 by
means of KOMe as described earlier in the case of base 10, to
give pink viscous oily phosphazene 11. After storage in a
refrigerator at 5 ЊC the phosphazene 11 afforded yellowish
crystals; δH 1.77 (12H, m, NCH2CH2), 2.71 (6H, s, NCH3), 3.13
(12H, dt, 3JH-H 6.6, 3JP-H 3.8, NCH2CH2), 6.55 [4H, s, Ar 3(5)-H
and Ar 2(6)-H]; δC 27.0 (3JP-C 7.7, NCH2CH2), 42.7 (NCH3),
47.6 (2JP-C 3.5, NCH2CH2), 116.5 [Ar C-3(5)], 123.9 [3JP-C 16.8,
Ar C-2(6)], 143.8 (Ar C-4), 145.0 (2JP-C 2.8, Ar C-1).
3
3
3.22 (12H, dt, JH-H 6.6, JP-H 3.5, NCH2CH2), 3.76 (3H, s,
3
3
OCH3), 6.9 [2H, d, JH-H 9.0, Ar 3(5)-H], 7.0 [2H, d, JH-H 9.0,
Ar 2(6)-H]; δC 26.8 (3JP-C 8.6, NCH2CH2), 48.3 (2JP-C 4.9,
NCH2CH2), 56.3 (OCH3); 115.9 [Ar C-3(5)], 125.0 [3JP-C 5.5,
Ar C-2(6)], 130.9 (Ar C-1), 158.2 (Ar C-4) [Calc. for C19H32-
BF4N4OP (M: 450.20): C, 50.68; H, 7.16; N, 12.40. Found:
C, 50.58; H, 7.51; N, 12.12%].
Hydrazinotripyrrolidinophosphonium
hexafluorophosphate
12ؒHPF6 (Scheme 2). Chlorophosphonium salt 13 was prepared
from 25 mmol of PCl5 and 75 mmol of pyrrolidine in 35 ml
of CH2Cl2.1 Et3N was used to eliminate the evolving HCl.
The precipitated Et3NؒHCl was filtered off and 100 mmol of
hydrazine was added at Ϫ15 ЊC. The mixture was left to warm
to room temperature. Approximately 20 ml of the solvent were
removed by evaporation and the residue was stored at Ϫ15 ЊC
for 24 h. The precipitate of H2NNH2ؒHCl containing some
Et3NؒHCl was filtered off and solvent was removed in vacuo to
give 7 g of a brown viscous residue. This product was dissolved
in 40 ml of 40% aq. EtNH2 and the calculated amount (with
regard to the phosphazene base 12) of 30% HPF6 solution
was added to settle the brownish oil. The aqueous layer was
decanted and the remaining oil was stirred with glass stick
several times with portions of fresh water to give 4.6 g of
yellowish crystals of 12ؒHPF6. Recrystallization of the
product was performed from aq. EtNH2, mp 108.0–109.3 ЊC;
10ؒHPF6. 10ؒHBF4 was dissolved in a small amount of
MeOH and the BF4Ϫ anion was exchanged for ClϪ by means of
a column of strongly basic anion-exchange resin APA–8π using
MeOH as eluent. The solvent was removed and the residue,
10ؒHCl, was dissolved in water. A calculated amount of 15%
HPF6 was added to the aqueous solution, and the precipitated
white crystals of 10ؒHPF6 were recrystallized from aq. MeOH,
mp 135.8–136.1 ЊC; δH 1.86 (12H, m, NCH2CH2), 3.2 (12H, br
3
3
dt, JH-H 6.6, JP-H 3.4, NCH2CH2), 3.8 (3H, br s, OCH3), 6.1
(1H, br d,2JP-H 11.4, NH), 6.9 [2H, br d, 3JH-H 9, Ar 3(5)-H], 7.0
[2H, br d, 3JH-H 9, Ar 2(6)-H]; δC 26.8 (3JP-C 8.5, NCH2CH2), 48.3
(2JP-C 4.8, NCH2CH2), 56.3 (OCH3), 115.9 [Ar C-3(5)], 125.2
[3JP-C 5.5, Ar C-2(6)], 130.8 (Ar C-1), 158.3 (Ar C-4) [Calc. for
C19H32F6N4OP2 (M: 508.43): C, 44.89; H, 6.34; N, 11.02.
Found: C, 45.03; H, 6.35; N, 10.85%].
3
3
δH 1.88 (12H, m, NCH2CH2), 3.21 (12H, dt, JH-H 6.6, JP-H
3
3.9, NCH2CH2) 3.6 (2H, d, JP-H 10.1, NHNH2), 5.4 (1H,
2
d, JP-H 33.6, NHNH2); δC 26.9 (3JP-C 8.1, NCH2CH2), 48.0
(2JP-C 4.2, NCH2CH2) [Calc. for C12H27F6N5P2 (M: 417.32): C,
34.54; H, 6.52; N, 16.78. Found: C, 34.49; H, 6.50; N, 16.74%].
(4-Methoxyphenylimino)tripyrrolidinophosphorane 10. To a
methanolic solution of 10ؒHBF4 was added the calculated
amount of KOMe solution in MeOH. The precipitated KBF4
(Anilino)tris(dimethylamino)phosphonium
hexafluorophos-
phate 16ؒHPF . 0.3 g of C H N᎐P(NMe ) 16 were dissolved in
᎐
6
6
5
2 3
J. Chem. Soc., Perkin Trans. 1, 2000, 2637–2644
2643

View Article Online
O. Guerret, H. Gornitzka, J. B. Cazaux, D. Bigg, F. Palacios and
G. Bertrand. J. Org. Chem., 1999, 64, 3741.
1.5 ml of 70% aq. EtNH2 and 1.4 ml of 30% HPF6 solution were
added with caution. From the obtained slightly alkaline solu-
tion the formed white precipitate was filtered off, washed with
water, and then dissolved in methanol to give a slightly turbid
solution of 16ؒHPF6. The solution was filtered and methanol
removed to give 0.35 g of product in the form of white crystals
which had no sharp mp (melted between 92 and 106 ЊC): δH 2.72
(18H, d, JP-H 10.1, NCH3), 7.06 [2H, d, JH-H 8.2, Ar 2(6)-H],
7.16 (1H, t, 3JH-H 7.6, Ar 4-H), 7.37 [2H, t, 3JH-H(av) 7.9, Ar 3(5)-
H]; δC 37.6 (2JP-C 4.9, NCH3), 122.3 [3JP-C 6.0, Ar C-2(6)], 125.5
(Ar C-4), 130.8 [Ar C-3(5)], 138.8 (Ar C-1) [Calc. for
C12H24F6N4P2 (M: 400.28): C, 36.01; H, 6.04; N, 13.99. Found:
C, 36.10; H, 6.06; N, 13.60%].
3 (a) K. Wozniak, E. D. Raczynska and B. Korybut-Daskiewicz,
Isr. J. Chem., 1999, 39, 245; (b) E. D. Raczynska, M. Decouzon,
J.-F. Gal, P. C. Maria, K. Wozniak, R. Kurg and S. V. Carias, Trends
Org. Chem., 1998, 7, 95; (c) E. D. Raczynska, P. C. Maria, J.-F. Gal
and M. Decouzon, J. Phys. Org. Chem., 1994, 7, 725; (d) K. T.
Leffek, P. Pruszynski and K. Thanapaalasingham, Can. J. Chem.,
1989, 67, 590.
4 (a) I. A. Koppel, J. B. Koppel, L. I. Muuga and V. O. Pihl, Org.
React., 1988, 25, 131; (b) K. Izutsu, Acid-base Dissociation
Constants in Dipolar Aprotic Solvents, IUPAC Chemical Data Series
No. 35, Blackwell Scientific, Oxford, 1990; (c) F. G. Bordwell, Acc.
Chem Res., 1988, 21, 456.
5 A. W. Johnson, Ylides and Imines of Phosphorus., J. Wiley & Sons,
New York, Chichester, Brisbane, Toronto, Singapore, 1993, ch. 13.
6 I. N. Zhmurova and A. V. Kirsanov, J. Gen. Chem. (USSR) (Engl.
Transl.), 1960, 30, 3018.
7 A. V. Kirsanov and N. G. Feshchenko, Zh. Obshch. Khim., 1959, 29,
4085.
3
3
Acknowledgements
This work was supported by grants 3366, 3370, 1867, 3992
from the Estonian Science Foundation and from the German
Government (BMFT X-112.4). We extend our gratitude to
Professor Dr R. Schwesinger for valuable advice and sug-
gestions regarding the manuscript.
8 M. V. Shevchenko and V. P. Kukhar, J. Gen. Chem. (USSR) (Engl.
Transl.), 1986, 56, 73.
9 H.-O. Kalinowski, S. Berger and S. Braun, 13C-NMR-Spektroskopie,
Georg Thieme Verlag, Stuttgart, New York, 1984.
10 (a) Tables of Rate and Equilibrium Constants of Heterolytic Organic
Reactions, ed. V. A. Palm, Moscow, 1976, vol. 2 (I); (b) Tables of
Rate and Equilibrium Constants of Heterolytic Organic Reactions,
ed. V. A. Palm, Moscow, 1976, vol. 1 (I); (c) Tables of Rate
and Equilibrium Constants of Heterolytic Organic Reactions, ed.
V. A. Palm, Tartu, 1985, Supplementary vol. I (3–5) (d) Tables of
Rate and Equilibrium Constants of Heterolytic Organic Reactions,
ed. V. A. Palm, Tartu, 1984, Supplementary vol. I (1, 2).
11 (a) R. I. Yurchenko and I. N. Zhmurova, Zh. Obshch. Khim., 1973,
43, 2635; (b) R. I. Yurchenko, I. N. Zhmurova and A. I. Sedlov,
J. Gen. Chem. (USSR) (Engl. Transl.), 1975, 45, 1705.
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