Syntheses of Diphenylaminodiazidophosphane and Diphenylaminofluoroazidophosphane

Article abstract of DOI:10.1021/acs.inorgchem.5b02097

Diphenylaminodiazidophosphane (C₆H₅)₂NP(N₃)₂ was synthesized from the corresponding dihalides (C₆H₅)₂NPX₂ (X = F, Cl) and (CH₃)₃SiN

Full text of DOI:10.1021/acs.inorgchem.5b02097

Article
pubs.acs.org/IC
Syntheses of Diphenylaminodiazidophosphane and
Diphenylaminofluoroazidophosphane
William W. Wilson,*,† Andrew J. Clough,† Ralf Haiges,† Martin Rahm,‡ and Karl O. Christe*,†
†Loker Hydrocarbon Research Institute, 837 Bloom Walk, LHI 106, Department of Chemistry, University of Southern California, Los
Angeles, California 90089-1661, United States
‡Baker Laboratory, Cornell University, Ithaca, New York 14853-1301, United States
S
* Supporting Information
ABSTRACT: Diphenylaminodiazidophosphane (C6H5)2NP-
(N3)2 was synthesized from the corresponding dihalides
(C6H5)2NPX2 (X = F, Cl) and (CH3)3SiN3, and was
characterized by vibrational and multinuclear NMR spectros-
copy. The intermediate compound (C6H5)2NPF(N3) was also
observed by NMR spectroscopy in solution. Some physical
properties and reactions of all these compounds are discussed.
lium species [(2-diazidophosphino)-4,5-dimethyl-1,3-bis(1-
methylethyl)-1H-imidazolium cation] has been identified via
its X-ray crystal structure and fully characterized spectroscopi-
cally as its triflate salt,14 although it slowly decomposes even at
−31 °C. Another more recent publication describes the Raman,
IR, multinuclear NMR spectra, and crystal structure of the [(2-
diazidophosphino)-4,5-dichloro-1,3-bis(2,6-methylethyl-phe-
nyl)-1H-imidazolium cation] as its triflate salt15 which is stable
at −40 °C, but tends to decompose slowly upon warming to
room temperature.
1. INTRODUCTION
The amount of research into azide-containing compounds has
increased rapidly over the past decade, due largely to advances
in the field of highly energetic high nitrogen materials, and
many novel main group azides have been synthesized, including
several of phosphorus. Phosphorus triazide had been reported,
and its vibrational spectra and 31P NMR spectrum had been
given,1 but later work brought most of these data into question
when the rapid thermal decomposition of P(N3)3 in solution
near room temperature and new 31P NMR data were
published.2,3 Otherwise, apart from photoelectron spectra,4
only some computational results have been reported for
phosphorus triazide.5,6 Later it was reported that P(N3)3 was
In contrast to the amount of research conducted on P(III)-
azido compounds, there has been considerable research on
phosphorus(V)-azido compounds. Although phosphorus pen-
taazide was previously reported in 1975,1 this claim was
7
reacted with N3− in an attempt to generate P(N3)4 ; however,
−
subsequently retracted.16
A
31P NMR study on several mixed
there was no experimental evidence offered that either P(N3)3
phosphorus(V)-chloro-azido species [P(V)Cl(5‑n)(N3)n, n = 4,
−
or P(N3)4 was present.
3, 2] in pyridine solution, however, has been reported.17 The
Several phosphorus(III) monoazides are also known:
(CF3)2P(N3), which decomposes between 0 °C and ambient
temperature and sometimes unexpectedly even at −196 °C;8
(C6H5)2P(N3), which decomposes explosively at ∼14 °C;9
F2P(N3) is unstable and occasionally explodes at 25 °C;10 and
Cl2P(N3) and Br2P(N3), both of which decompose slowly at 35
°C.2,3 With respect to ionic monoazido-P(III) species, it is
worth noting that no evidence was found for the PF3(N3)−
anion in an NMR study.11 On the other hand, there has been a
crystal structure reported for the monoazido-P(III) cationic
−
existence of the P(N3)6 anion was initially described in 1967
as its P(C6H5)4+ salt18 and has been extended from alkali metal
16
cations such as Na+ to the polynitrogen N5+ cation,19 and the
[(C6H5)3PNP(C6H5)3]+ cation,20 for example. Various
mixed phosphorus(V)-chloro-fluoro-azido anions
[PClxFy(N3)z−, x + y + z = 6] in CH2Cl2 solutions have also
been described.11,21,22 The formation of many P(V)-azido
+
cations has been reported including P(N3)4 and the mixed
23
+
−
P(N3)n(CH3)4‑n (n = 3, 2, 1) SbCl6 compounds, as well as
P(N3)n(C6H5)4‑n+ (n = 3, 2, 1) SbCl6− salts24 for which various
properties have been described.
+
−
species, [(CH3)3Si]2NPN3 , as its GaCl4 salt which is
only stable up to −40 °C.12
Additional compounds have been made where three azido
groups are attached to a P(V) atom, i.e., the long known
OP(N3)3 and SP(N3)3 compounds which have recently had
their crystal structures determined.25 Whereas the mixed
OPF(N3)2, OPF2(N3), and SPF2(N3) compounds have been
More relevant to this work, much less is known about P(III)-
diazido compounds. There is a brief report on two very
unstable compounds, (C6H5)P(N3)2, which starts to decom-
pose before its preparative reaction is complete, and
(Me3C6H2)P(N3)2, which is only stable for a few hours in
solution,13 and the room temperature stable [(t-Bu)3C6H2]P-
(N3)2, which was characterized by X-ray crystallography.13 In
addition, a phosphorus(III) diazido tetra-substituted-imidazo-
Received: September 10, 2015
Published: November 25, 2015
© 2015 American Chemical Society
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known since 1972,10 OPF(N3)2 has only recently been
investigated via photolytic and thermal decomposition.26
Other phosphorus(V)-azido compounds such as SP[N
PRPh2]2(N3) and SP[NPRPh2](N3)2 have been re-
ported,27 as have several cyclic P−N phosphorus-azido
RR′(P−N)m(N3)n species.28−30
vacuum distillation in a short-path-length apparatus. The yield
of this clear, colorless liquid was again improved, in this case to
86% as compared to the literature report of 78%.34 The
compound’s identity was verified via vibrational and NMR
spectroscopy which showed no impurites, vide infra.
Initially, the synthesis of (C6H5)2NP(N3)2 was attempted by
reacting (C6H5)2NPCl2 with NaN3 in acetonitrile, as shown in
reaction 3, a method which has been known to result in Cl/N3
exchange in many other systems.
Whereas several structural studies on certain M(III)(N3)3/
M(III)(N3)4− and M(V)(N3)5/M(V)(N3)6− systems, [M = As,
Sb, Bi] have been reported [refs 31, 7, and 32 (and references
therein)], none have been found for either P(N3)3 or any
−
(C6H5)2NPCl2 + 2NaN3
P(N3)4 compounds.
CH3CN
Many covalent azido compounds have a reputation for being
unpredictably unstable with respect to sudden decompositions
(as described above), but even these can be handled safely
using appropriate precautions and techniques. This is true
primarily because the N3 group is highly endothermic with a
positive heat of formation,33 which explains why azido
compounds have found use in propellants and explosive
formulations. The purpose of this work, however, was the
preparation and characterization of diphenylaminodiazidophos-
phane, thereby contributing to the understanding of the
relatively poorly known class of diazidophosphanes.
⎯⎯⎯⎯⎯⎯→⎯ (C6H5)2NP(N3)2 + 2NaCl
(3)
However, this approach resulted in only a very small amount
of (C6H5)2NP(N3)2 as determined by NMR spectroscopy.
Even in the presence of CsF as a catalyst, which has often been
used in other similar systems, reaction 4 progressed only slowly
to give (C6H5)2NP(N3)2 over extended periods of time.
(C6H5)2NPCl2 + 2NaN3
CH3CN
⎯⎯⎯⎯⎯⎯→⎯ (C6H5)2NP(N3)2 + 2NaCl
(4)
CsF
The thermal instability at ambient temperature and low
volatility at lower temperatures of (C6H5)2NP(N3)2, however,
did not allow its isolation and separation from the NaCl
byproduct, either by filtration in acetonitrile, or by distillation
either at ambient temperature under a nitrogen atmosphere or
at lower temperatures in vacuo. The greatest drawback in the
generation of (C6H5)2NP(N3)2 by this method was the
exceedingly long time that was required for the reaction to
go to completion.
A superior method for the preparation of (C6H5)2NP(N3)2
involved the generation of a volatile byproduct which could be
more easily removed in vacuo along with the solvent from the
desired less volatile product. Therefore, (C6H5)2NPF2 was
reacted instead with (CH3)3SiN3 in CH3CN. Initial efforts
using the neat reagents resulted in a very slow reaction, but
when a small amount of CsF was added as a catalyst, the
reaction in CH3CN solution proceeded much more rapidly as
shown in reaction 5.
2. RESULTS AND DISCUSSION
Both of the two dihalide compounds, (C6H5)2NPCl2 and
(C6H5)2NPF2,34 are thermally stable to at least 100 °C, and it
was expected that the corresponding diazide compound could
also be isolated. (C6H5)2NPCl2 was first considered as a
precursor for the preparation of (C6H5)2NP(N3)2. Although
the (C6H5)2NPCl2 compound had been previously reported,34
its synthesis has been improved in this study.
2.1. Syntheses of (C6H5)2NPCl2, (C6H5)2NPF2, and
(C6H5)2NP(N3)2. The synthesis of (C6H5)2NPCl2 was con-
ducted in benzene according to reaction 1 under strictly
anhydrous conditions after it was discovered that moisture
hydrolyzes not only the PCl3 starting material, but also the
desired (C6H5)2NPCl2, which probably affected the initial
purity and yields in the past studies.34
PCl3 + (C6H5)2NH + xs N(C2H5)3
C6H6
⎯⎯⎯⎯→ (C6H5)2NPCl2 + NH(C2H5)3Cl
(1)
(C6H5)2NPF + 2(CH3)3SiN3
2
CH3CN
After vacuum distillation of the crude product at 135 °C and
collection of the final product at 25 °C, the isolated yield was
increased to over 74% compared to the previously reported
55%. In this work the vibrational and NMR spectra of the clear,
colorless, viscous liquid (C6H5)2NPCl2 were recorded and
showed no evidence of any impurities, vide infra. When it was
discovered that this material was not suitable for the direct
synthesis and isolation of pure (C6H5)2NP(N3)2, the
(C6H5)2NPCl2 reagent was replaced by (C6H5)2NPF2.
The (C6H5)2NPF2 was prepared under anhydrous conditions
in acetonitrile according to reaction 2 as reported in the
literature:34
⎯⎯⎯⎯⎯⎯→⎯ (C6H5)2NP(N3)2 + 2(CH3)3SiF
(5)
CsF
A low temperature NMR study as a function of time revealed
that reaction 5 was complete in a matter of only a few hours.
When the volatile (CH3)3SiF and CH3CN solvent were
pumped off at temperatures between −20 and −30 °C, the
poorly soluble CsF catalyst settled to the bottom of the reactor,
and the clear colorless (C6H5)2NP(N3)2 was easily cannulated
from the small amount of CsF to give a pure product.
2.2. Raman Spectroscopic Results. Raman spectroscopy
at −60 °C was used to characterize (C6H5)2NP(N3)2 (Figure
1). The Raman spectra at 20 °C of (C6H5)2NPF2 and
(C6H5)2NPCl2 were also recorded for comparison (Figures 2
and 3).
Although vibrational data have been published for P(N3)3
and P(N3)5,1 the former are questionable, and those for the
latter must be discounted in view of the subsequent 31P NMR
data and chemical analyses.2,3 According to previous low level
HF/6-31+G* calculations for phosphorus triazide, P(N3)3,6 the
in-phase and out-of-phase antisymmetric N3 stretching
CH3CN
(C6H5)2NPCl2 + 2NaF ⎯⎯⎯⎯⎯⎯→⎯ (C6H5)2NPF + 2NaCl
2
(2)
The (C6H5)2NPF2 product is a somewhat less viscous
material than the (C6H5)2NPCl2 starting material and has a
higher vapor pressure at room temperature, requiring its
collection at a temperature of −22 °C well below its melting
point of 11 °C to avoid large losses of the material upon
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complete list of the experimental and calculated vibrational
frequencies for these three compounds can be found in the
accompanying Supporting Information Table S1.
Experimentally, the presence of the azido groups in
(C6H5)2NP(N3)2 can be easily seen in the Raman spectrum
from the νas in-phase and νas out-of-phase stretching modes
which occur, respectively, at 2136 and 2119 cm−1 (Figure 1),
and which are absent in the analogous difluoro- and dichloro-
compounds. This conclusion is clearly supported by the
calculated values for the diazido-compound (Table 1). Similar
bands for the N3 group have been observed for the in-phase
and out-of-phase antisymmetric N3 stretching vibrations of
As(N3)3 at 2128 and 2103 cm−1, respectively, and of Sb(N3)3 at
2123 and 2079 cm−1, respectively.35 In the case of (C6H5)2NP-
(N3)2 a relatively broad band was observed at 1257 cm−1
characteristic for the symmetric N3 stretching vibration.
Although there are bands in the Raman spectra for
(C6H5)2NPF2 and (C6H5)2NPCl2 in this same region, the
band at 1257 cm−1 has a comparatively larger intensity than
those in the other spectra. The frequency of 1257 cm−1
compares well with similar bands found at 1257, 1244/37
cm−1 and 1263, 1248 cm−1 for As(N3)3 and Sb(N3)3,
respectively.35
Figure 1. Raman spectrum of (C6H5)2NP(N3)2 recorded in a thin-
walled Teflon FEP tube at −60 °C. Bands for the Teflon FEP tube are
designated with *.
Several other bands were observed in the (C6H5)2NP(N3)2
spectrum that could be assigned with confidence to modes not
predominantly associated with the (C6H5)2N group. (1) Of the
three expected N3 bending frequencies, only two modes, the δ
N3 in-phase/out-of-plane and δ N3 in-phase/in-plane vibrations
(coupled with a P−N stretching band) at 550 and 509 cm−1,
respectively, were observed in agreement with those previously
reported for As(N3)3.35 A third mode, the δ N3 out-of-phase/
in-plane vibration, at ∼639 cm−1 was calculated to be too low
an intensity to be observed. (2) Four P−N stretching vibrations
involving only the P-[N(N2)]2 group were expected. One
calculated band at 678 cm−1 was not observed because of an
overlap at ∼702 cm−1 with a much stronger differently assigned
band (see below). A second closely calculated band at 639 cm−1
was simply not observed because of extremely weak intensity.
On the other hand, two other calculated bands at 530 and 492
cm−1 were observed at 533 and 509 cm−1, respectively, (albeit
the latter is coupled with an N3 bending vibration as stated
above). (3) A number of other predicted frequencies
containing a contribution from the P−N stretching mode of
the PN(C6H5)2 group coupled with other vibrations [such as δ
N3, δsciss N3, or δsciss NC2] of the molecule could be matched
with experimental bands. Some calculated couplings of this P−
N mode with other modes in the molecule, however, were not
observed due to low calculated intensities, and are listed in
Table S1 of the Supporting Information. (4) One particular
vibration (the νs (C6H5)2N−P−[N(N2)]2 skeletal mode
involving the P atom with the amido-N and the two azido-N
atoms) could be unambiguously assigned to the band at 702
cm−1. Also, the δsciss PX2 (X = F, N3, Cl) modes were found at
400, 282, and 191 cm−1, respectively. The rest of the N3
deformations and N−P−N skeletal deformation modes were
calculated to be very weak and are presumably hidden
underneath other (C6H5)2N group bands.
Figure 2. Raman spectrum of (C6H5)2NPF2 recorded in a Pyrex tube
at 20 °C.
Figure 3. Raman spectrum of (C6H5)2NPCl2 recorded in a Pyrex tube
at 20 °C.
vibrations and the symmetric N3 stretching vibrations were
predicted to occur at 2520 and 2558 cm−1 and at 1338 and
1378 cm−1, respectively.
Some selected Raman data calculated using configuration 1
(see below in section 2.3) are listed together with the
experimental data in Table 1 for (C6H5)2NP(N3)2, along with
experimental data for (C6H5)2NPF2 and (C6H5)2NPCl2. A
The symmetric and antisymmetric stretching vibrations for
the PF2 group in the Raman spectrum of (C6H5)2NPF2 were
observed at 809 and 761 cm−1. These frequencies are lower (as
expected) than those found for the P−F stretching frequencies
36,37
in liquid PF3 at 890 and 840 cm−1
and at 893.2 and 858.4
cm−1 in gaseous PF3.38 Raman frequencies for the PF2 group
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Table 1. Selected Experimental and Calculated Raman Data for (C6H5)2NPX2 Compounds, [X = Cl, F, and N3]
a
Experimental Raman frequencies in cm−1 with intensities (in parentheses) in arbitrary units normalized to the most intense band in each spectrum
b
set at 100.0; ol = overlap, br = broad, sh = shoulder, n.o. = not observed. Calculated Raman frequencies are given in cm−1 with intensities (in
c
parentheses) in Å4 amu−1. A scaling factor of 0.96 was used. Raman bands for the Teflon FEP sample container were found in the (C6H5)2NP(N3)2
spectrum at 1384 cm−1 (3.4), 1303 cm−1 (3.7,sh), 1226 cm−1 (6.2,sh), 735 cm−1 (12.2), 611 cm−1 (4.0), 570 cm−1 (3.7), 388 cm−1 (2.6), and 292
cm−1 (2.0) but are not listed.
have been reported for PF2Cl at 857 and 829 cm−1 and for
PF2Br at 853 and 825 cm−1.39,40 Raman bands for solid PF2I at
−197 °C have been observed at 862 and 807 cm−1,41 whereas
infrared frequencies for the PF2 group in Ar matrix isolated
PF2I at 4.2 K were found at 843 and 835 cm−1.42 The infrared
spectrum of the Ar matrix isolated radical •PF2 showed bands at
839.3 and 834.0 cm−1.42 Infrared frequencies for the
antisymmetric and symmetric PF2 group in matrix isolated
PF2H were found at 839.7 and 827.0 cm−1, respectively.42 The
lowering of the PF2 frequencies in (C6H5)2NPF2 can be
ascribed to the relatively strong electron-donating effect of the
(C6H5)2N ligand as compared to the more electron-with-
drawing halogens in PF2X, where X = F, Cl, Br, and I. The
assignment of a band found at 400 cm−1 for (C6H5)2NPF2 can
reasonably be made to the PF2 scissoring mode. This
assignment is in accord with bands at 411, 391, and 365
cm−1 in PF2Cl, PF2Br, and PF2I, respectively.39−43
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For (C6H5)2NPCl2 the symmetric and antisymmetric PCl2
stretching modes are assigned to 495 and 472 cm−1,
respectively. Values of 515 and 504 cm−1 in the vapor phase
Raman38 as well as 507 and 493 cm−1 in the vapor phase IR
spectra44 have been reported for PCl3. For liquid PFCl2, the
symmetric and antisymmetric PCl2 stretching vibrations are
found at 522 and 498 cm−1, respectively.39 Similar frequencies
around 521 cm−1 were observed in the infrared spectrum of
gaseous PFCl2.45 For the Ar matrix isolated •PCl2 radical,
frequencies at 525 and 452 cm−1 have been reported, although
the assignments have been reversed for the symmetric and
antisymmetric PCl2 vibrations in the literature.46 The bending
vibration for PCl2 in (C6H5)2NPCl2 was found at 191 cm−1,
comparable to that found for PFCl2 at 199 and 200 cm−1.39,43,45
The assignments for the symmetric and antisymmetric
stretching frequencies depend on the PX2 bond angle where
a crossing of the symmetric and antisymmetric vibrational
frequencies occurs at a bond angle of roughly 90°.47 It does not
seem very likely that the PF2 or PCl2 angle would be
significantly greater than 90° in which case the antisymmetric
stretching mode could begin to be lower in frequency than the
symmetric one. Although two N3 groups are not exactly
comparable to two Cl atoms, the computational calculations
conducted in this study (see below) indicate that the Nazido−P−
temperature within the limits of the computational method.
This is not unexpected for a molecule in which the azido
groups are fluxional32 and can rotate with low barriers about the
phosphorus−nitrogen bonds.
Overall the calculated bond distances between the
phosphorus atom and each of the two nitrogenazido atoms are
similar for each of the configurations 1−3 with values of 1.75
0.01 Å for one of the bonds and 1.79 0.02 Å for the second.
In comparison, the bond lengths between the phosphorus and
the nitrogenamido atoms were all shorter at 1.71 0.01 Å for all
three isomers. The specific P−Nazido bond lengths, Nα−Nβ−Nγ
lengths and angles, as well as bond lengths and angles for the
C2NP fragment of configuration 1 can be found in Table S5 in
the Supporting Information. The just mentioned calculated
bond length values compare favorably with crystallographic
studies for a number of phosphorus−azido bond lengths in the
range 1.673−1.753 Å, whether they are for phosphorus(III)−
azido groups present in a cation,12,14,15 covalent P(V)−azido
molecules,25,27 or cyclic P(V)N−azido compounds.28−30 The
calculated nitrogenazido−phosphorus−nitrogenazido bond angles
for the three (C6H5)2NP(N3)2 configurations showed more
variation with a value of 90.5° for configuration 1 and values of
97.8° and 95.5° for configurations 2 and 3, respectively. These
values can be compared with experimental X-ray structure
values between 96.4° and 113.4°.12,14,15,25,27−30
The calculated vibrational frequencies of configuration 1,
however, had the best match with the experimental Raman
values. Additionally, the calculations showed that the C2NP
fragment was essentially planar for configuration 1 with the sum
of the C2NP angles being 359.7°. (The corresponding sums for
the C2NP angles for configurations 2 and 3 were 359.6° and
359.8°, respectively, which again show the structural similarities
of the C2NP fragment for all three configurations.) This finding
is consistent with X-ray results for (CH3)2NPF2 and
(CH3)2NPCl2 where the sums of the C2NP angles were
found to be 360.0(10)° and 359.9(4)°, respectively.49,50 This
results in a virtually planar C2NP fragment in which the central
nitrogen atom is located only 0.053 Å above the plane defined
by the two carbons and the phosphorus atom. The significantly
shorter nitrogenamido−phosphorus bond when compared to the
longer nitrogenazido−phosphorus bonds indicates that some
partial double bond character is responsible for the near
planarity of the C2NP fragment.
Nazido bond angle is 90.5°, thus making assignments other than
those given here rather unlikely.
2.3. Computational Results. As a part of this research,
(C6H5)2NP(N3)2 was studied computationally via Gaussian 09,
Revision A.02 at the B3LYP/6-311+G(d,p) level of theory,48
and three main conformations were identified as minima on the
potential energy surface at 298 K. The preferred configuration
is shown in Figure 4. The only major differences among the
three structures are in the orientations of the two azido groups
with respect to each other on the pseudotetrahedral
coordinated phosphorus atom. The predicted Gibbs energy
difference between the highest and lowest energy conforma-
tions is only 1.6 kcal/mol, which implies that the three
calculated structures have virtually the same energy at room
2.4. NMR Spectroscopic Results. Further characterization
of (C6H5)2NP(N3)2 was accomplished via multinuclear NMR
spectroscopy. The primary nucleus used for the investigation
was 31P. An initial report1 for the chemical shift of the related
P(N3)3 compound resulted in a value for what was later
determined to be a decomposition product. A corrected value
of 134.6 ppm for P(N3)3 was subsequently reported.2,3 For
ClP(N3)2 its 31P chemical shift has been measured not only in
the following solvents CH2Cl2, C6H5NO2, and CS2, but also in
CH3CN where a value of 149.1 ppm was found.3 The 31P NMR
data have previously been published for (C6H5)2NPF2 (in
1
CH3CN) as 131.0 ppm (triplet) with J(31P−19F) = 1239 Hz,
and for (C6H5)2NPCl2 (without solvent) as 148.0 ppm
(singlet).34 For (C6H5)2NPF2 its 19F NMR resonance was
Figure 4. Calculated structure of configuration 1 for (C6H5)2NP(N3)2
at the B3LYP/6-311G(p,d) level of theory.48 Selected bond distances
[Å]: P24−N1 1.715, P24−N25 1.757, P24−N26 1.782. Selected bond
angles [deg]: N25−P24−N26 90.49, N1−P24−N25 101.16, N1−
P24−N26 105.14. Angles [deg] between planes: C2−C13−N1 and
C13−N1−P24 174.58; C2−N1−P24 and N1−P24−C13 173.99;
C13−N1−C2 and N1−C2−P24 173.83. Distance [Å]: N1 above
plane C2−C13−P24 0.053.
1
also found at −63.7 ppm (doublet) with J(19F−31P) = 1241
Hz.34
In the present work, data for (C6H5)2NPCl2, (C6H5)2NPF2,
and(C6H5)2NP(N3)2 were recorded either in CD2Cl2, CDCl3,
CD3CN, or CH3CN solutions or as neat liquids at variable
temperatures. For neat (C6H5)2NPCl2, a singlet 31P resonance
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was found with a value of 148.9 ppm, consistent with the
published value,34 whereas in CH3CN a singlet at 149.4 ppm
was observed. In the case of (C6H5)2NPF2, the 31P NMR
spectrum showed a triplet in CD2Cl2 at 131.8 ppm with
1J(31P−19F) = 1237 Hz, whereas the 19F spectrum showed a
1
doublet at −63.3 ppm with J(19F−31P) = 1237 Hz which was
again consistent with the literature.34
For (C6H5)2NP(N3)2, a singlet 31P NMR resonance was
observed in CD3CN at 113.2 ppm. Additionally, three 14N
NMR signals at −144.8, −176.7, and −296.0 ppm were found
in CD3CN. The first 14N signal can be attributed to the central
Nβ atom in the N3 group, whereas the second signal is
characteristic of the terminal Nγ, and the third weak, broad
signal is due to the Nα atom bonded to P. These 14N
resonances can be favorably compared with those found in
other covalently bonded azido groups to elements such as As
(−145.3, −175.9, and −290 ppm for As(N3)3),35,51 and Sb
(−136.2, −172.3, and −324.5 ppm for Sb(N3)3).35 The
chemical shift for the N atom in the diphenylamino group
was expected to be in the region −330 to −350 ppm52 but was
either too weak and/or too broad to be observed.
The reaction between (C6H5)2NPF2 and (CH3)3SiN3 with a
small amount of CsF as a catalyst in CD3CN was followed by
31P and 19F NMR spectroscopy in an experiment where the
reactants were combined at −196 °C and the temperature was
increased gradually inside the NMR spectrometer. In this
experiment the formation of (C6H5)2NP(N3)2 was first
observed at a temperature of −30 °C and slowly increased
over 1 h. As expected, the reaction rate to produce
(C6H5)2NP(N3)2 increased with time and rising temperatures
from −20 °C, to 0 °C, and up to 20 °C when decomposition
began to be observed. At 25 °C, decomposition products were
noticeable as some insoluble material appeared in the bottom of
the NMR tube. At the end of the experiment the triplet in the
31P spectra due to (C6H5)2NPF2 had completely disappeared
while the singlet for (C6H5)2NP(N3)2 dominated the spectrum.
These results can be seen in Figure 5.
Figure 5. Temperature dependent 31P NMR spectra of the reaction of
(C6H5)2NPF2 with excess (CH3)3SiN3 in CD3CN solution in the
presence of a catalytic amount of CsF to yield (C6H5)2NP(N3)2 at
varying temperatures over time. Resonances marked with * are due to
an unstable unidentified decomposition product occurring at temper-
atures at or above 20 °C.
2.5. Identification of (C6H5)2NPF(N3). During the course
of this variable temperature experiment, a new weak doublet in
the 31P spectra gradually grew in at 135.5 ppm with 1J(31P−19F)
= 1147 Hz. The intensity of this doublet stayed relatively
constant over time until the end of the experiment when these
resonances disappeared together with the triplet due to
(C6H5)2NPF2. The presence of a new doublet can be seen in
Figure 6 showing the 31P NMR spectrum taken after 1 h of
reaction at 20 °C. This new species was confirmed in the 19F
NMR spectrum which showed a doublet at −89.2 ppm with a
Figure 6. 31P NMR spectrum of the (C6H5)2NPF(N3) intermediate at
20 °C in CD3CN upon warm-up from −30 °C from the reaction of
(C6H5)2NPF2 with excess (CH3)3SiN3 in the presence of a catalytic
amount of CsF. The resonance marked with an asterisk is an unstable
unidentified decomposition product which forms at temperatures ≥20
°C.
1
coupling constant J(19F−31P) = 1105 Hz. Given that this new
doublet in the 31P spectrum occurred in the range of those for
(C6H5)2NPF2 and (C6H5)2NP(N3)2 and taken together with its
eventual disappearance when all of the (C6H5)2NPF2 was
consumed in its reaction with excess (CH3)3SiN3, this species
can be assigned to the reaction intermediate (C6H5)2NPF(N3).
The results of the 31P and 14N experiments are combined in
Table 2.
intermediate compound (C6H5)2NPF(N3) has been shown to
be formed in the system of (C6H5)2NPF2 and excess
(CH3)3SiN3 in acetonitrile at low temperatures and has been
found to be stable to about 20 °C.
4. EXPERIMENTAL SECTION
3. CONCLUSIONS
Caution! The handling of all azides should be done with great respect due
to their potentially dangerous properties. All manipulations and reactions
should be conducted with appropriate safety measures such as behind
shields or barricades in a fume hood with protective clothing such as safety
glasses, face shields, leather gloves, and leather suits and ear plugs.
Infrared spectra were recorded on a Midac Model M FTIR
spectrometer in the range 4000−400 cm−1 with samples either as a
The novel diazidophosphane, (C6H5)2NP(N3)2, has been
synthesized and characterized by its 31P and 14N NMR spectra.
Furthermore, Raman spectra of the various (C6H5)2NPX2 (X =
F, Cl, N3) compounds have all been recorded for the first time
with vibrational assignments for these compounds. The
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Table 2. Selected Experimental and Literature 31P and 19F NMR Values for (C6H5)2NPX2 (X = Cl, F, N3) and Related
Compounds
compd
δ
31P, ppm
δ
19F, ppm
δ
14N, ppm
1J(PF), Hz
ref
PF3 (neat, −90 °C)
97.0
143.0
219.4
138
−34.0
−65.3
1403
1197
53−56
56, 57
58, 59
13
Me2NPF2 (neat, room temp)
PCl3 (neat, room temp)
(1,3,5-Me3C6H5)P(N3)2 (CH3CN)
P(N3)3 (CH3CN)
134.6
131.0
148.0
131.8
148.9
149.4
113.2
3
Ph2NPF2 (CH3CN)
−63.7
−63.8
1239
1237
34
Ph2NPCl2 (neat)
34
Ph2NPF2 (CD3CN)
this work
this work
this work
this work
this work
this work
this work
Ph2NPCl2 (neat, room temp)
Ph2NPCl2 (CD3CN)
Ph2NP(N3)2 (CD3CN)
−144.8 (Nβ)
−176.7 (Nγ)
−296.0 (Nα)
Ph2NPF(N3) (CD3CN)
135.5
−89.2
1147
liquid film or a finely ground powder between two AgCl windows in a
Barnes Engineering Co. Econo Press. Raman spectra were recorded on
a Bruker Equinox 55 FT-RA spectrometer using a Nd:YAG laser at
1064 cm−1 in the range between 4000 and 80 cm−1 using either 5 mm
o.d. Pyrex J. Young NMR tubes or 9 mm o.d. Teflon-FEP tubes fitted
with stainless steel valves as sample containers which were pretreated
before use with (CH3)3SiN3 and thoroughly pumped out. NMR data
33.270g, 196.60 mmol), and benzene (150 mL) over 30 min with
stirring at room temperature. The mixture was stirred for an additional
17 h, resulting in a golden-brown solution with a white precipitate.
This mixture was then refluxed under GN2 at 80 °C for 4.5 h, after
which time the solution had turned murky red-brown in color. After
the mixture had been cooled to 0 °C overnight and the precipitate had
settled out, the liquid phase was separated from the precipitate using
GN2-pressurized Schlenk cannula techniques. The volatile benzene
and triethylamine were pumped off from the wine-red material at
room temperature, resulting in 53.197 g of crude product. Diethyl
ether (200 mL) was added to the crude product, and the mixture was
cooled to −30 °C which resulted in the appearance of an additional
white precipitate. The liquid phase was separated again from the
precipitate using GN2-pressurized cannula techniques at −30 °C, and
the ether was pumped off, first at −30 °C and then gradually as the
mixture was warmed to around 100 °C. Lastly, the mixture was
distilled at 130−135 °C in a short-path-length distillation apparatus
where the final product was collected at 25 °C as a clear, colorless,
viscous liquid. Theoretical mass expected for 196.61 mmol
1
for H, 14N, 19F, and 31P were recorded on either a Varian VNMRS-
400 or a Varian VNMRS-500 spectrometer, and for 14N on a Bruker
AMX-500 spectrometer. The NMR solvents (CDCl3 and CD3CN)
were from Cambridge Isotope Laboratories and were used as received.
1H NMR spectra were referenced to Si(CH3)4, 14N spectra to
CH3NO2, 19F to CFCl3, and 31P to 85% H3PO4. Geometries and
vibrational frequencies and intensities were calculated for three
conformers of (C6H5)2NP(N3)2 using Gaussian09, Revision A.02, at
the B3LYP/6-311+G(p,d) level of theory.48 The frequency analyses
confirmed that all structures were local minima on the potential energy
surface with the lowest energy conformer differing by ≤1.6 kcal/mol
from the other two.
(C6H5)2NPCl2 = 53.104 g; experimental mass (C6H5)2NPCl2
=
The phosphorus trichloride (99%) and diphenylamine (99%), both
from Sigma-Aldrich, Inc., and triethylamine from Mallinckrodt (OR
grade, bp 88−90 °C) were used as received. Sodium fluoride was
obtained from Mallinckrodt (Analytical grade) and heated to 650 °C
in a stream of GN2 (gaseous nitrogen) in order to ensure that it was
completely anhydrous, and checked for the absence of NaHF2 and
H2O by infrared and Raman spectroscopy before being stored in a
drybox prior to use. Cesium fluoride was obtained from KBI
Chemicals and fused at >700 °C under GN2 and then finely ground
in a drybox. Sodium azide (99.99+%) from Sigma-Aldrich was heated
in vacuo at 120 °C overnight to remove any traces of moisture.
Benzene (DriSolv) and anhydrous ethyl ether (DriSolv) were both
used as received from EMD. Acetonitrile (DriSolv) was either used as
received from EMD or was further dried by storage over P2O5.
Perdeuterated acetonitrile, CD3CN (99.8% D), was obtained from
Cambridge Isotope Laboratories and used as an NMR solvent for
1
39.345 g (yield = 74.1%). Raman spectra and 31P, 13C, and H NMR
spectra confirmed the product to be pure (C6H5)2NPCl2.
4.2. Diphenylaminodifluorophosphane, (C6H5)2NPF2. Diphe-
nylaminodichlorophosphane (15.445 g, 57.18 mmol) was added in the
drybox to a 500 mL flask, followed by the addition inside the glovebag
of acetonitrile (150 mL) and dried NaF (14.181 g, 337.74 mmol)
similar to the literature method34 except for strict avoidance of
moisture. The reaction mixture was then refluxed at 95 °C under a
GN2 atmosphere for 5 h. After cooling the mixture to room
temperature, the liquid phase was cannulated using Schlenk techniques
under a GN2 atmosphere into a separate dry 500 mL Pyrex vessel, and
the solvent was pumped off at ambient temperature. Finally, the crude
product (12.368 g) was distilled in vacuo into a dry short-path-length
vacuum distillation apparatus. The crude product was then heated at
45 °C, and a white solid product was collected in a trap at −25 °C
under a high vacuum. Upon warming to 20 °C, the solid product
melted to a clear colorless liquid having sufficient vapor pressure to
allow it to pass through a trap at −6 °C. Theoretical mass expected for
57.18 mmol = 13.562 g; experimental mass of (C6H5)2NPF2 = 11.640
g (yield = 85.8%). Raman spectra and 31P, 19F, 14N, 13C, and 1H NMR
spectra confirmed the product to be pure (C6H5)2NPF2.
1
several H, 14N, 19F, and 31P NMR experiments. Liquid reagents and
solvents were transferred to reaction vessels or J. Young NMR tubes
inside a GN2 purged glovebag, or on a Pyrex glass vacuum line using
high vacuum or standard Schlenk line techniques. All the other
reagents were handled inside the dry N2 atmosphere of a D. L. Herring
drybox.
4.1. Diphenylaminodichlorophosphane, (C6H5)2NPCl2. In a
method similar to that reported in the literature,34 except with the
essential precaution of preventing any water vapor from entering into
the reaction apparatus, phosphorus trichloride (26.863 g, 196.61
mmol) and benzene (100 mL) were added inside a GN2 purged
glovebag to a three-necked 500 mL flask. This was followed by the
dropwise addition (under a GN2 atmosphere) of a preformed solution
of triethylamine (55 mL, 40 g, 395 mmol), diphenylamine (50 mL,
4.3. Diphenylaminodiazidophosphane, (C6H5)2NP(N3)2. Di-
phenylaminodifluorophosphane (0.534 g, 2.11 mmol) and finely
powdered CsF (0.0206 g, 0.135 mmol) as a catalyst were loaded inside
the drybox into a preconditioned (with trimethylsilylazide) Teflon
ampule equipped with a stainless steel valve. Next, CD3CN
(approximately 10 mL) was added to the Teflon ampule on the
Pyrex vacuum line at −196 °C. After the mixture was warmed to room
temperature and the reactants were homogenized, the ampule was
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recooled to −196 °C, and excess trimethylsilylazide (3.538 mmol) was
added at −196 °C on the Pyrex vacuum line. The mixture was kept at
−30 °C for 2 days with occasional agitation. Raman spectroscopy at
−30 °C revealed that the reaction had not gone to completion.
Eventually, the temperature was raised to 0 °C, then briefly to 20 °C,
and then to 25 °C until there was no more evidence via 31P NMR
spectroscopy of any remaining diphenylaminodifluorophosphane. The
liquid products from the reaction mixture were cannulated from the
insoluble CsF catalyst into a separate Teflon ampule at −30 °C, after
which the excess trimethylsilylazide and the solvent were pumped off
between −30 and −20 °C resulting in a clear, viscous/semisolid
material. Raman spectra of the final product showed only bands due to
(C6H5)2NP(N3)2.
(12) Hering, C.; Schulz, A.; Villinger, A. Angew. Chem., Int. Ed. 2012,
51, 6241−6245.
(13) Cowley, A. H.; Gabbai, F.; Schluter, R.; Atwood, D. J. Am. Chem.
Soc. 1992, 114, 3142−3144.
(14) Weigand, J. J.; Feldmann, K. O.; Henne, F. D. J. Am. Chem. Soc.
2010, 132, 16321−16323.
(15) Henne, F. D.; Dickschat, A. T.; Hennersdorf, F.; Feldmann, K.
O.; Weigand, J. J. Inorg. Chem. 2015, 54, 6849−6861.
(16) Volgnandt, P.; Schmidt, A. Z. Anorg. Allg. Chem. 1976, 425,
189−192.
(17) Dillon, K. B.; Platt, A. W. G.; Waddington, T. C. J. Chem. Soc.,
Dalton Trans. 1981, 2292−2295.
(18) Roesky, H. W. Angew. Chem., Int. Ed. Engl. 1967, 6, 637.
(19) Haiges, R.; Schneider, S.; Schroer, T.; Christe, K. O. Angew.
Chem., Int. Ed. 2004, 43, 4919−4924.
ASSOCIATED CONTENT
* Supporting Information
The Supporting Information is available free of charge on the
ACS Publications website at DOI: 10.1021/acs.inorg-
chem.5b02097.
■
(20) Portius, R.; Fowler, P. W.; Adams, H.; Todorova, T. Z. Inorg.
Chem. 2008, 47, 12004−12009.
S
(21) Dillon, K. B.; Platt, A. W. G.; Waddington, T. C. J. Chem. Soc.,
Chem. Commun. 1979, 889.
(22) Dillon, K. B.; Platt, A. W. G. J. Chem. Soc., Dalton Trans. 1983,
1159−1164.
Tables of Raman data, XYZ coordinates, and bond
lengths and angles (PDF)
(23) Schmidt, A. Chem. Ber. 1970, 103, 3923−3927.
(24) Bruder, W.; Schmidt, A. Chem. Ber. 1973, 106, 3812−3816.
(25) Zeng, X.; Bernhardt, E.; Beckers, H.; Willner, H. Inorg. Chem.
2011, 50, 11235−11241.
AUTHOR INFORMATION
■
Corresponding Authors
*E-mail: wwwilson@usc.edu.
*E-mail: kchriste@usc.edu.
(26) Li, D.; Li, H.; Zhu, B.; Zeng, X.; Willner, H.; Beckers, H.;
Neuhaus, P.; Grote, D.; Sander, W. Phys. Chem. Chem. Phys. 2015, 17,
6433−6439.
Notes
(27) Gotz, N.; Herler, S.; Mayer, P.; Schulz, A.; Villinger, A.;
̈
Weigand, J. J. Eur. J. Inorg. Chem. 2006, 2006, 2051−2057.
The authors declare no competing financial interest.
(28) Aubauer, C.; Klapotke, T. M.; Noth, H.; Schulz, A.; Suter, M.;
̈
̈
Weigand, J. Chem. Commun. 2000, 2491−2492.
ACKNOWLEDGMENTS
■
(29) Aubauer, C.; Karaghiosoff, K.; Klapotke, T. M.; Kramer, G.;
̈
This work was performed with support from the following
agencies with their corresponding grant numbers: National
Science Foundation, CHE0956635; the Air Force Office of
Scientific Research, FA95501010357; the Office of Naval
Research, N000141210543 and N000141210555; and the
Defense Threat Reduction Agency, HDTRA10810036. Com-
putational work at the University of Southern California was
supported by the University of Southern California Center for
High-Performance Computing and Communications. Helpful
discussions with Allan Kershaw, Director of NMR Instrumen-
tation at USC, are gratefully acknowledged.
Schulz, A. Z. Anorg. Allg. Chem. 2001, 627, 2547−2552.
(30) Muralidharan, K.; Omotowa, B. A.; Twamley, B.; Piekarski, C.;
Shreeve, J. M. Chem. Commun. 2005, 5193−5195.
(31) Haiges, R.; Rahm, M.; Dixon, D. A.; Garner, E. B., III; Christe,
K. O. Inorg. Chem. 2012, 51, 1127−1141.
(32) Haiges, R.; Rahm, M.; Christe, K. O. Inorg. Chem. 2013, 52,
402−414.
(33) JANAF Themochemical Tables; Vol. 5, N3(g), 12-31-1970.
(34) Falius, H.; Babin, M. Z. Anorg. Allg. Chem. 1976, 420, 65−73.
(35) Haiges, R.; Vij, A.; Boatz, J. A.; Schneider, S.; Schroer, T.;
Gerken, M.; Christe, K. O. Chem. - Eur. J. 2004, 10, 508−517.
(36) Yost, D. M.; Anderson, T. F. J. Chem. Phys. 1934, 2, 624−627.
(37) Wilson, M. K.; Polo, S. R. J. Chem. Phys. 1952, 20, 1716−1719.
(38) Clark, R. J. H.; Rippon, D. M. J. Mol. Spectrosc. 1974, 52, 58−71.
DEDICATION
In memory of Prof. Dr. Reinhard Schmutzler.
■
(39) Muller, A.; Niecke, E.; Krebs, B.; Glemser, O. Z. Naturforsch., B:
̈
J. Chem. Sci. 1968, 23B, 588−594.
REFERENCES
(40) Muller, A.; Koniger, F.; Cyvin, S. J.; Fadini, A. Spectrochim. Acta
̈
̈
■
267.
1973, 29A, 219−228.
(1) Buder, W.; Schmidt, A. Z. Anorg. Allg. Chem. 1975, 415, 263−
(41) Dean, C. R. S.; Finch, A.; Gates, P. N. J. Chem. Soc., Dalton
Trans. 1972, 1384−1387.
(2) Dillon, K. B.; Platt, A. W. G.; Waddington, T. C. Inorg. Nucl.
Chem. Lett. 1978, 14, 511−513.
(42) Burdett, J. K.; Hodges, L.; Dunning, V.; Current, J. H. J. Phys.
Chem. 1970, 74, 4053−4059.
(3) Dillon, K. B.; Platt, A. W. G.; Waddington, T. C. J. Chem. Soc.,
Dalton Trans. 1980, 1036−1041.
(43) Delwaulle, M. L.; Francois, F. J. Chim. Physique 1949, 46, 87−
97.
(4) Zeng, X.; Wang, W.; Liu, F.; Ge, M.; Sun, Z.; Wang, D. Eur. J.
Inorg. Chem. 2006, 2006, 416−421.
(44) Davis, P. W.; Oetjen, R. A. J. Mol. Spectrosc. 1958, 2, 253−258.
(45) Muller, A.; Niecke, E.; Glemser, O. Z. Anorg. Allg. Chem. 1967,
̈
(5) Wang, L.; Warburton, P. L.; Mezey, P. G. J. Phys. Chem. A 2005,
109, 1125−1130.
350, 256−262.
(46) Andrews, L.; Frederick, D. L. J. Phys. Chem. 1969, 73, 2774−
(6) Klapotke, T. M.; Schulz, A. Main Group Metal Chemistry 1997,
̈
2778.
20, 325−338.
(47) Weidlein, J.; Muller, U.; Dehnicke, K. Schwingungsspektroskopie,
̈
(7) Schulz, A.; Villinger, A. Chem. - Eur. J. 2012, 18, 2902−2911.
(8) Tesi, G.; Haber, C. P.; Douglas, C. M. Proc. Chem. Soc. (London)
1960, 219−220.
Eine Einfuhrung; Georg Thieme Verlag: Stuttgart, 1982; pp 52−54.
̈
(48) Frisch, M. J.; Trucks, G. W.; Schlegel, H. B.; Scuseria, G. E.;
Robb, M. A.; Cheeseman, J. R.; Scalmani, G.; Barone, V.; Mennucci,
B.; Petersson, G. A.; Nakatsuji, H.; Caricato, M.; Li, X.; Hratchian, H.
P.; Izmaylov, A. F.; Bloino, J.; Zheng, G.; Sonnenberg, J. L.; Hada, M.;
Ehara, M.; Toyota, K.; Fukuda, R.; Hasegawa, J.; Ishida, M.; Nakajima,
(9) Paciorek, K. L.; Kratzer, R. Inorg. Chem. 1964, 3, 594−595.
(10) O'Neill, S. R.; Shreeve, J. M. Inorg. Chem. 1972, 11, 1629−1631.
(11) Chevrier, P. J.; Brownstein, S. J. Inorg. Nucl. Chem. 1980, 42,
1397−1405.
11866
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Inorg. Chem. 2015, 54, 11859−11867

Inorganic Chemistry
Article
T.; Honda, Y.; Kitao, O.; Nakai, H.; Vreven, T.; Montgomery, J. A., Jr.;
Peralta, J. E.; Ogliaro, F.; Bearpark, M.; Heyd, J. J.; Brothers, E.; Kudin,
K. N.; Staroverov, V. N.; Kobayashi, R.; Normand, J.; Raghavachari, K.;
Rendell, A.; Burant, J. C.; Iyengar, S. S.; Tomasi, J.; Cossi, M.; Rega,
N.; Millam, J. M.; Klene, M.; Knox, J. E.; Cross, J. B.; Bakken, V.;
Adamo, C.; Jaramillo, J.; Gomperts, R.; Stratmann, R. E.; Yazyev, O.;
Austin, A. J.; Cammi, R.; Pomelli, C.; Ochterski, J. W.; Martin, R. L.;
Morokuma, K.; Zakrzewski, V. G.; Voth, G. A.; Salvador, P.;
̈
Dannenberg, J. J.; Dapprich, S.; Daniels, A. D.; Farkas, O.;
Foresman, J. B.; Ortiz, J. V.; Cioslowski, J.; Fox, D. J. Gaussian 09,
Revision A.02; Gaussian, Inc.: Wallingford, CT, 2009.
(49) Morris, E. D., Jr; Nordman, C. E. Inorg. Chem. 1969, 8, 1673−
1676.
(50) Mitzel, N. W. J. Chem. Soc., Dalton Trans. 1998, 3239−3242.
(51) Geissler, P.; Klapotke, T. M.; Kroth, H.-J. Spectrochim. Acta, Part
̈
A 1995, 51A, 1075−1078.
(52) Witanowski, M.; Stefaniak, L.; Webb, G. A. Annual Reports on
NMR Spectroscopy; Webb, G. A., Ed.;Academic Press: London, 1992;
pp 113, 124, and 131.
(53) Gutowsky, H. S.; McCall, D. W.; Slichter, C. P. J. Chem. Phys.
1953, 21, 279−292.
(54) Gutowsky, H. S.; McCall, D. W. J. Chem. Phys. 1954, 22, 162−
164.
(55) Holmes, R. R.; Gallagher, W. P. Inorg. Chem. 1963, 2, 433−437.
(56) Reddy, G. S.; Schmutzler, R. Z. Naturforsch., B: J. Chem. Sci.
1965, 20b, 104−109.
(57) Schmutzler, R. Inorg. Chem. 1964, 3, 415−421.
(58) Muller, N.; Lauterbur, P. C.; Goldenson, J. J. Am. Chem. Soc.
1956, 78, 3557−3561.
(59) Van Wazer, J. R.; Callis, C. F.; Shoolery, J. N.; Jones, R. C. J. Am.
Chem. Soc. 1956, 78, 5715−5726.
11867
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