Synthesis and oligomerization of cyclodiphosph(V)azene adducts

Article abstract of DOI:10.1002/ejic.201301012

The reaction of R¹R²PCl (R¹ = Me, Ph; R² = Ph, oTol) with N,N′-bis(trimethylsilyl)sulfur diimide in the presence of GaCl₃ yields Lewis acid/base adducts of the corresponding cyclodiphosph(V)azenes: [M

Full text of DOI:10.1002/ejic.201301012

FULL PAPER
DOI:10.1002/ejic.201301012
Synthesis and Oligomerization of Cyclodiphosph(V)azene
Adducts
CLUSTER
ISSUE
Martin Bendle,[a] Rene Kuzora,[b] Ian Manners,*[a] Paul Rupar,[a]
Axel Schulz,*[b,c] and Alexander Villinger[b]
Keywords: Adducts / Bonding / Cyclodiphosphazenes / Phosphorus / Polymerization / Polyphosphazenes / Structure
elucidation
The reaction of R1R2PCl (R1 = Me, Ph; R2 = Ph, oTol) with
N,NЈ-bis(trimethylsilyl)sulfur diimide in the presence of
GaCl3 yields Lewis acid/base adducts of the corresponding
cyclodiphosph(V)azenes: [MePhPN]2·(GaCl3)2, [Me(dmp)-
PN]2·(GaCl3)2 (dmp = 2,6-dimethylphenyl), and [Ph(oTol)-
PN]2·(GaCl3)2. The same synthetic protocol was applied for
the model compound Ph2AsCl. All isolated products were
characterized spectroscopically and by single-crystal X-ray
diffraction studies. Their ability to form oligomers/polymers
induced by abstraction of the Lewis acid was investigated
with the model compounds [MePhPN]2·(GaCl3)2 and
[Ph2PN]2·(GaCl3)2.
Introduction
Polyphosphazene derivatives are the largest class of inor-
ganic macromolecules, and their importance in industrial
applications is defined by their broad range of proper-
ties.[1,2] The preparation of the most significant starting ma-
terial for synthesizing these macromolecules dates back to
1834, when Liebig and Wöhler isolated the cyclic hexa-
chlorotriphosphazene (PNCl2)3 from the reaction of phos-
phorus pentachloride and ammonium chloride.[3] Over the
last five decades, myriads of cyclotriphosph(V)azenes, tet-
raphosph(V)azenes, and polyphosph(V)azenes were pre-
pared,[4] but only a few members of the cyclodiphosph(V)
azene class have been synthesized and fully characterized
(Scheme 1).[5] The first cyclodiphosph(V)azene was re-
ported by Bertrand, Majoral, and co-workers, who intro-
duced the photolysis of phosphorus azides as a method to
prepare the first “heterocyclobutadiene” in 1984.[5a] Only
recently, Bertrand reported on the isolation of the monomer
R2PN, a formal nitridophosphane(V).[6]
Scheme 1. Structurally characterized cyclodiphosph(V)azenes.
ter = 2,6-bis(2,4,6-trimethylphenyl)phenyl, Mes* = 2,4,6-tri-tert-
butylphenyl, Cp* = pentamethylcyclopentadiene.[5a–5c]
Hitherto, three synthetic routes to cyclodiphosph(V)-
azenes are known, and all require azides as a reagent; the
formation of the cyclodiphosph(V)azenes proceeds under
release of molecular nitrogen.[4] Only a few years ago, a
novel synthetic route to cyclodiphosph(V)azenes was re-
ported by Schulz et al.[7] In a reaction of chlorophosphanes
with N,NЈ-bis(trimethylsilyl)sulfur diimide, Me3Si–NSN–
SiMe3, the elimination of Me3SiCl and S8 is triggered by
Lewis acids such as AlCl3 and GaCl3, and the diadducts of
the corresponding cyclodiphosph(V)azenes, [Ph2PN]2·
(GaCl3)2 (1), [Ph2PN]2·(AlCl3)2, and [PhClPN]2·(AlCl3)2,
were isolated and fully characterized (Scheme 2).
[a] School of Chemistry, University of Bristol,
Bristol BS8 1TS, England
E-mail: Ian.Manners@bristol.ac.uk
http://www.bris.ac.uk/chemistry/people/ian-manners/
[b] Universität Rostock, Institut für Chemie,
Albert-Einstein-Str. 3a, 18059 Rostock, Germany
E-mail: Axel.Schulz@uni-rostock.de
Scheme 2. Synthesis of adducts of cyclodiphosph(V)azenes. R1
=
R2 = Ph, E = Ga, Al; R1 = Ph, R2 = Cl, E = Al;[7] R1 = Me, R2
= Ph or dmp, E = Ga; R1 = Ph, R2 = oTol, E = Ga.
http://www.schulz.chemie.uni-rostock.de/
[c] Leibniz-Institut für Katalyse e.V. an der Universität Rostock,
Albert-Einstein-Str. 29a, 18059 Rostock, Germany
Supporting information for this article is available on the
WWW under http://dx.doi.org/10.1002/ejic.201301012.
Herein we report on the synthesis and characterization of
diadducts of cyclodiphosph(V)azenes [MePhPN]2·(GaCl3)2
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(2), [Me(dmp)PN]2·(GaCl3)2 (3), and [Ph(oTol)PN]2· tween the coordination complex R1R2(Cl)P·GaCl3 (II) and
(GaCl3)2 (4) and polymerization attempts by utilizing the diphosphorus cation [R1R2(Cl)P–PR1R2]+ (IV,
[Ph2PN]2·(GaCl3)2 (1) and [PhMePN]2·(GaCl3)2 (2) as Scheme 3). Burford et al. investigated the reaction of chlor-
model compounds.
o(dialkyl/diaryl)phosphanes with gallium trichloride in a
systematic NMR spectroscopy study and described the
presence of different species related by equilibrium in solu-
tion depending on the substituent at the phosphorus atom
and the reaction stoichiometry.[10] In this context, further
investigations according to the herein deployed chlorophos-
phanes were made.
Results and Discussion
Synthesis of Cyclodiphosphadiazene
Lewis acid catalyzed cyclization reactions have been in-
tensively studied in phosphorus–nitrogen chemistry.[8] For
instance, in the synthesis of triazadiphospholes, (Me3Si)2N–
P2N3, GaCl3 as a Lewis acid triggers the elimination of
Me3SiCl from N,NЈ,NЈ-dichloro[tris(trimethylsilyl)hydraz-
ino]phosphane prior to the cyclization step.[8a] A similar
concept of Lewis acid catalysis was used for the preparation
of cyclodiphosph(V)azene adducts.
Starting at a low temperature of –50 °C, a stirred solu-
tion of GaCl3 in dichloromethane was slowly combined
with a solution of chlorophosphane, R1R2PCl, in dichloro-
methane and then with N,NЈ-bis(trimethylsilyl)sulfur di-
imide, Me3Si–NSN–SiMe3 (Scheme 2). The obtained solu-
tion was slowly warmed to ambient temperature over a
period of 4 h. At a temperature of about –10 °C, a white
precipitate was observed, which was identified as the corre-
sponding cyclodiphosph(V)azene adduct and isolated in
moderate yield. By increasing the steric demand of the chlo-
rophosphanes, we observed a slightly higher yield in the
synthesis of the cyclodiphosph(V)azene adducts. Chloro-
phosphanes with oversized bulky groups gave no reaction
with the sulfur diimide, as stable Lewis acid/base adducts
were formed (e.g., tBu2PCl·GaCl3, see below).
Scheme 3. Equilibrium in solution of the reaction of R1R2PCl and
GaCl3.
The reaction with the sulfur diimide only occurs if the
equilibrium lies on the side of the [R1R2(Cl)P–PR1R2]+ cat-
ion (IV). It can be assumed that the cationic phosphorus
atom attacks a nitrogen atom of N,NЈ-bis(trimethylsilyl)-
sulfur diimide, and according to the overall reaction, sulfur
and Me3SiCl are eliminated.[11] The Lewis acid adducts of
phosphanes II are not able to react with the sulfur diimide.
The equilibrium of an equimolar reaction of MePhPCl
and GaCl3 in solution observed by 31P NMR spectroscopy
is shown in Figure 1. For the phosphanylphosphonium cat-
ion [MePh(Cl)P–PMePh]+, a total of four doublets results
owing to the presence of two conformational isomers in a
ratio of 4:5; the resonances for conformer 1 have chemical
shifts of δ(31P) = 85.6 and –16.1 ppm (1JP,P = 355 Hz), and
the resonances for conformer 2 have chemical shifts of
δ(31P) = 84.2 and –20.9 ppm (1JP,P = 355 Hz) {cf. [Ph2(Cl)-
The main product in the reaction of MePhPCl[9] and
Me3Si–NSN–SiMe3 in the presence of GaCl3 was the trans
isomer of cyclodiphosphadiazene, trans-2, which was de-
tected by 31P NMR spectroscopy as a singlet at δ(31P) =
84.8 ppm (Scheme 2). The cis isomer (cis-2) was also gener-
ated in small amounts (ca. 2%), as shown by a singlet reso-
nance at δ(31P) = 85.8 ppm. Compound 2 (98% trans, 2%
cis isomer) has a decomposition temperature of 314 °C [cf.
(Ph2PN)2(GaCl3)2, Tdec = 370 °C].[7] The reaction of
chloro(2,6-dimethylphenyl)methylphosphane yielded only
cis-3. Only one singlet was detected at δ(31P) = 88.9 ppm.
Compound 3 has a decomposition temperature of 325 °C,
which is slightly higher than that of 2. Compound 4 with
oTol/Ph groups was detected by 31P NMR spectroscopy at
δ(31P) = 74.9 ppm as the cis isomer, and it has a decomposi-
tion temperature of 365 °C.
1
P–PPh2]+: δ = 73 and 1 ppm, JP,P = 393 Hz; [Me2(Cl)-
1
P–PMe2]+: δ = 96 and –28 ppm, JP,P = 311 Hz}.[10] The
singlet resonance of the observed MePhPCl·GaCl3 donor–
acceptor complex is observed at δ(31P) = 45.6 ppm, which
is the typical range for such complexes [cf. Ph2(Cl)P·GaCl3:
δ = 41 ppm; Me2(Cl)P·GaCl3: δ = 57 ppm].[10] In addition,
a very small, very broad resonance is observed at δ =
55 ppm, which could not be assigned.
The monophosphonium cationic species [MePhP]+ (III)
and uncoordinated MePhPCl (I) are not observed. The ra-
Mechanistic Study of Cyclodiphosphadiazene Formation
The reaction mechanism is not completely understood, tio of observed species IV/II according to inserted
but in the absence of GaCl3, no reaction of chlorophos- MePhPCl is ca. 8:1. By increasing the steric bulk of the
phanes with N,NЈ-bis(trimethylsilyl)sulfur diimide occurs at substituent on the chlorophosphane, the formation of
low and ambient temperatures.
GaCl3 complex II was favored. Substitution of the phenyl
Presumably, in the first step of the reaction, GaCl3 reacts group by a 2,6-dimethylphenyl group (dmp) decreased the
with chlorophosphane (I) to develop an equilibrium be- ratio of the phosphanylphosphonium cation [Me(dmp)(Cl)
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Figure 1. 31P NMR spectrum of an equimolar reaction of MePhPCl with GaCl3.
P–PMe(dmp)]+ to the coordination complex Me(dmp)(Cl)
In an equimolar reaction of gallium trichloride with the
P·GaCl3 according to the inserted chlorophosphane to chlorophosphane, free Lewis acid is always present in solu-
nearly 2:1. As an additional effect, one isomer of the di- tion if the equilibrium is on side of phosphanylphosphon-
phosphorus cation was promoted with a new ratio of 2:1. ium cation IV. In this case, the formation of an additional
In the case of the oTol/Ph compound, the cation/adduct adduct after the addition of N,NЈ-bis(trimethylsilyl)sulfur
ratio decreased to below 1:1. The formation of the phos- diimide is implicated.[12] This leads to stretching of the Si–
phane–gallium trichloride adduct was clearly favored, and N and S–N bonds of the GaCl3-coordinated N atom, which
the ratio of the isomers is nearly equal. By using chloro- probably favors a reaction with the diphosphorus cation
phosphanes with sterically more demanding substituents and the formation of the cyclodiphosph(V)azene adduct.
such as the tert-butyl group, the equilibrium of an equi-
molar reaction with GaCl3 lies far to the chlorophosphane–
Reaction of Ph2AsCl with Bis(trimethylsilyl)sulfur Diimide
gallium trichloride adduct. In this case, only one broad sin-
glet with a chemical shift of δ = 102.4 ppm is observed for
tBu2PCl·(GaCl3) (5; Table 1; Supporting Information, Fig-
ure S1).
In concurrent investigations, the synthesis of an arsenic-
analogous cyclodiarsa(V)azene adduct was attempted in a
reaction with Ph2AsCl.[13] In contrast to Ph2PCl, the arsen-
ic compound was able to react with bis(trimethylsilyl)-
sulfur diimide in the absence of gallium trichloride under
the formation of bis(diphenylarsanyl)sulfur diimide (6).[14]
Several attempts to obtain a defined reaction with the sulfur
diimide and gallium trichloride always led to a yellow oil
without any trace amount of a cyclodiars(V)azene adduct
or any other defined product. However, it was possible to
isolate small crystals during one reaction, which were iden-
tified by single-crystal X-ray diffraction to be Ph2As–
N=S=N–SiMe3·GaCl3 (7; Supporting Information, Fig-
ure S2). The formation of a cyclodiars(V)azene adduct was
not observed, as no sulfur was eliminated in this case. Nev-
ertheless, characterization of 7 could give further insight
into the reaction mechanism of the cyclodiphosph(V)-
azenes, as the analogous phosphorus compound could be
expected as an intermediate.
Table 1. 31P NMR spectroscopic data and assignments for reaction
mixtures R1R2(Cl)P and GaCl3 (1:1).
R1/R2
δ [ppm] (J [Hz])
δ [ppm] (rel. int.[a] [%])
[R1R2(Cl)P–R1R2P]+
R1R2(Cl)P–GaCl3
Me/Me[b]
Ph/Ph[b]
Me/Ph[c]
96 (311), –28 (311)
73 (393), 1 (391)
85.6 (355), –16.1 (355) 45.6 (ca. 5)
84.2 (355), –20.9 (355)
83.0 (395), –9.2 (395)
80.4 (405), –10.9 (405)
73.6 (397), –0.8 (397)
72.0 (404), –7.4(404)
–
57 (Ͻ5)
41 (Ͻ10)
Me/dmp[c]
oTol/Ph[c]
tBu/tBu
34.3 (ca. 10)
38.5 (ca. 25)
102.4 (100)
[a] Relative integration with respect to the principal signal given.
[b] No fractional digits available, taken from ref.[10] [c] Two isomers
of phosphanylphosphonium cation were observed.
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Structure Elucidation
acts intramolecularly with a hydrogen atom of an adjacent
methyl group. The distance of the intermolecular Cl···H
contact is about 2.87 Å.
Single-crystal X-ray structure analysis was carried out for
cyclodiphosph(V)azene adducts trans-2, cis-2, 3, and 4.
Crystallographic details are listed in Tables 3 and 4.
Furthermore, the structures of 5 and 7 are discussed briefly.
For (Ph2AsN)2S (6), a new polymorph was found.[13,14b]
In general, the metrical parameters of the P2N2 ring sys-
tem of all considered cyclodiphosph(V)azene adducts are
similar to those of [Ph2PN]2·(GaCl3)2 (1, Table 2).[7] The
P2N2 ring is distorted with two slightly different P–N bond
lengths between 1.65 and 1.67 Å, which is substantially
shorter than the sum of the covalent radii for a P–N bond
[Σrcov(N–P) = 1.8 Å, Σrcov(N=P) = 1.6 Å],[15] which indi-
cates partial double-bond character. The Ga–N bond
length of 1.92–1.94 Å is in the typical range found for other
GaCl3 adducts [cf. 1.978(3) Å in triazadiphosphole and
1.965(2) Å in (Me3Si–N)2S·GaCl3].[8a,12,16]
Although cis-2 was isolated in very small amounts
(Ͻ3%), it was possible to obtain single crystals for X-ray
structure analysis. Compound cis-2 crystallizes as colorless
thin plates in the orthorhombic Pbca space group with four
units per cell (Figure 3). The P2N2 ring is nearly planar
[ЄNPPN = 178.95(2)°]. The GaCl3 moieties are found in
an ecliptic conformation and are nearly in plane with the
ring system (ЄN2–P1–N1–Ga1 = 178.71°). In contrast to
trans-2, no significant intermolecular Cl···H interactions are
found, but intramolecular Cl···H interactions do exist. Cl1
is in contact with a hydrogen atom of a methyl group C1
(dCl···H = 2.87 Å), and Cl3 interacts with an aryl hydrogen
atom of one phenyl group (dCl···H = 2.75 Å). Owing to this
interaction, the phenyl groups are more strongly twisted
towards the GaCl3 moieties than they are in trans-2.
Table 2. Selected bond lengths [Å] and angles [°] for 1, trans-2, cis-
2, 3, and 4.
1[7]
trans-2
cis-2
3·CH2Cl2 4
P1–N1
P1–N2
P2–N1
P2–N2
Ga1–N1
Ga2–N2
N2–P1–N1 88.7(2)
N2–P2–N1 88.7(2)
P2–N1–P1
P2–N2–P1
ЄNPPN
1.680(4) 1.663(2) 1.673(3) 1.666(2) 1.672(2)
1.671(3) 1.667(2) 1.654(3) 1.678(2) 1.673(2)
1.680(4) 1.663(2) 1.661(3) 1.679(2) 1.672(2)
1.671(3) 1.667(2) 1.667(4) 1.668(2) 1.673(2)
1.937(4) 1.927(2) 1.924(3) 1.934(2) 1.945(2)
1.937(4) 1.927(2) 1.923(3) 1.934(2) 1.945(2)
88.3(1)
88.3(1)
91.7(1)
91.7(1)
180
89.2(1)
88.67(8) 88.37(9)
89.10(1) 88.58(8) 88.37(9)
90.6(1)
91.1(1)
91.3(2)
91.3(2)
180
91.30(8) 91.54(9)
91.28(8) 91.54(9)
178.9(2) 175.5(1) 175.3(1)
Adduct trans-2 crystallizes from dichloromethane as col-
Figure 3. ORTEP drawing of the molecular structure of cis-2 in the
crystal. Thermal ellipsoids with 50% probability at 173 K.
orless crystal blocks without solvent molecules in the tri-
¯
clinic P1 space group with two units per cell. As depicted
in Figure 2, the P2N2 ring is planar (ЄNPPN = 180°), and
a center of inversion is found in the centroid of the P2N2
ring. Thus, a staggered conformation is found for both
GaCl3 moieties. The GaCl3 groups are not completely in
plane with the PN ring (ЄN1i–P1–N1–Ga1 = 175.3°), and
in each case, one chlorine atom of the GaCl3 moiety inter-
Compound 3 crystallizes in the monoclinic P21/c space
group with four units per cell and a CH2Cl2 solvent mole-
cule in the asymmetric unit (Figure 4). As a result of the
sterically demanding aryl groups, the P2N2 ring loses its
planarity (ЄNPPN = 175.47°), and the GaCl3 moieties are
pushed out of the P2N2 plane (ЄN1–P1–N2–Ga2 =
Figure 2. ORTEP drawing of the molecular structure of trans-2 in
the crystal. Thermal ellipsoids with 50% probability at 173 K.
Figure 4. ORTEP drawing of the molecular structure of 3 in the
crystal. Thermal ellipsoids with 50% probability at 173 K.
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160.16°). Intermolecular and intramolecular Cl···H interac- possible noncyclic monomers.[18] Whereas, in general, the
tions can be observed. The methyl group attached to the formation of tri- and tetramers appears to be thermody-
phosphorus atom has a distance of 2.87 Å to a chlorine namically favored, sterically overcrowded substituents force
atom of an adjacent molecule. The Cl6 atom shows some dimerization. The surprising stability of cyclodiphosph(V)-
intramolecular Cl···H interaction with the aryl methyl azenes was attributed to the high thermodynamic energy
groups with distances of about 2.86 Å.
of the monomer, which prevents dissociation, and to steric
Diaryl compound 4 crystallizes in the tetragonal P421c factors, which hinder polymerization.
space group with four units per cell and one half of a
In the case of (MePhPN)2·(GaCl3)2, the steric demand
CH2Cl2 solvent molecule in the asymmetric unit (Figure 5). of the methyl and phenyl groups is considerably smaller
The P2N2 ring is slightly distorted from planarity (ЄNPPN than that of the isopropylamine, supermesityl, and ter-
= 175.47°). The GaCl3 moieties are found in a staggered phenyl groups that were used for stabilization in the cyclo-
conformation and are nearly in plane with the ring system diphosph(V)azenes synthesized by Bertrand and Majoral et
(ЄN1i–P1–N1–Ga1 = 177.25°). Two intermolecular Cl···H al., Wehmschulte et al., and Niecke et al. (Scheme 1).[5]
interactions of the GaCl3 moieties with the hydrogen atoms However, the ring dimer in, for example, (MePhPN)2·
in the para position to the o-toluene group of adjacent mo- (GaCl3)2, is additionally stabilized by the coordination of
lecules with distances of about 2.76 Å are observed.
the GaCl3 Lewis acid. In the interest of our research, we
investigated the behavior of the (MePhPN)2·(GaCl3)2 (2) di-
adduct towards the abstraction of GaCl3 by using Lewis
bases to answer the question if it was possible to obtain a
soluble polymer from Ph/Me-substituted ring dimers by
ROP. For comparison, (Ph2PN)2·(GaCl3)2 (1) was used as a
model compound.
The reaction of (MePhPN)2·(GaCl3)2 with Lewis bases
[e.g., DMAP = 4-(dimethylamino)pyridine, nBu3P, Et3N]
was finished within seconds. The use of 2 equiv. of DMAP
resulted in quantitative formation of the cyclic (MePhPN)4
tetramer, as observed by 31P NMR spectroscopy (δ = 10.8
and 10.4 ppm) independent of the reaction conditions. As
shown in Scheme 4, four different structural isomers are
possible (Scheme 4).
Figure 5. ORTEP drawing of the molecular structure of 4 in the
crystal. Thermal ellipsoids with 50% probability at 173 K (hydro-
gen atoms omitted for clarity).
Attempted Ring-Opening Polymerization
There are three synthetic strategies to prepare polyorgan-
ophosphazenes (POPs):[1] (1) Preparation of polydichloro-
phosphazene, (NPCl2)n, a polymeric intermediate from
which the large majority of POPs were prepared by nucleo-
philic substitution of the highly reactive chlorine atoms
with carefully selected organic substituents. (2) Use of poly-
condensation processes of substituted phosphoranimines to
obtain already substituted polyorganophosphazenes.
(3) Utilization of ring-opening polymerization (ROP) pro-
cesses of completely or partially substituted cyclophosphaz-
Scheme 4. Isomers of cyclotetraphosph(V)azenes.
On the basis of the fact that the cyclic Me/Ph-substituted
enes to obtain POPs having predictable chemical structures. dimer adduct basically has a trans conformation, the forma-
In 2006, the group of Manners found a new high-yielding tion of the 1,2-alternated and 1,3-alternated cyclic tetramer
synthetic route to high-molecular-weight poly(alkyl/aryl)- was not unexpected. According to 31P NMR spectroscopy,
phosphazenes [RPhPN]n (R = Me, Ph) by employing phos- the formation of the 1,3-alternated isomer was slightly pre-
phites (RO)3P at ambient temperature.[1a,17]
In the synthesis of cyclodiphosph(V)azene diadducts, was not verifiable (Scheme 5).
ferred. Any formation of the cone or partial cone isomers
GaCl3 as the Lewis acid has two assignments: (1) to trigger
Wisian-Neilson et al. reported first about the formation
the elimination of Me3SiCl and (2) to help in the kinetic and characterization of all four diastereoisomers of meth-
stabilization of the dimeric form of the cyclophosph(V)- yl(phenyl)tetracyclophosphazene,[19] but for the isolation of
azene. Early calculations by Ahlrichs and Schiffer indicated each of the four structural isomers, an extensive isolation
that the dimer is by far the most stable compound of all the route was necessary. Starting with 20.0 g of pure trans-
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= 6.3 ppm is related to the cyclic tetramer.[20] Furthermore,
the linear dimer, tetramer, and hexamer are detectable (Fig-
ure 6).
The linear dimer exhibits two doublets at δ = 28.3 and
2
25.5 ppm with JP,P = 9.7 Hz. Another pattern with four
Scheme 5. General reaction of cyclodiphosph(V)azenes with Lewis resonances fits to the linear tetrameric species: two doublets
at δ = 28.6 (2JP,P = 9.4 Hz) and 24.7 ppm (2JP,P = 8.7 Hz)
bases depending on R = Me, Ph.
for the terminal phosphorus atom and two doublets of dou-
blets for the interior phosphorus atom at δ = 5.0 (2JP,P
=
=
2
2
6.6 Hz, JP,P = 9.4 Hz) and 1.6 ppm (2JP,P = 6.6 Hz, JP,P
[Me(Ph)PN]3 heated at 250 °C for 6 d, a 2:1 ratio of trimers
to tetramers was obtained. The isolation of each compound
required several column chromatography steps, and by ex-
ploiting the different solubilities of the isomers, all of them
were obtained in very moderate yields.
8.7 Hz). In addition, the 31P NMR spectrum exhibited six
resonances for the linear hexamer appearing at δ = 26.1
(2JP,P = 11.7 Hz) and 23.9 ppm (2JP,P = 9.4 Hz) for the ter-
minal phosphorus atom. For their adjacent phosphorus
atom, two doublets of doublets appear at δ = 2.3 (2JP,P
=
By using just 1 equiv. of Lewis base (DMAP or nBu3P),
another species in addition to the starting material and the
cyclic tetramer was observed. An interpretation of the 31P
NMR spectrum was not clearly definable, but a tentative
assignment of the linear tetrameric compound by four
(DMAP-stabilized species) and five (nBu3P-stabilized spe-
cies) new 31P NMR signals was possible. A second equiva-
lent of Lewis base always led to the quantitative formation
of the cyclic tetramer.
More interesting results were obtained from the reactions
of the model compound, (Ph2PN)2·(GaCl3)2 (1), with
nBu3P or DMAP as the Lewis base. By abstracting GaCl3
with 2 equiv. of nBu3P, the cyclic tetramer (δ = 6.4 ppm)
2
2
6.6 Hz, JP,P = 11.7 Hz) and 1.0 ppm (2JP,P = 5.7 Hz, JP,P
= 9.4 Hz). The two resonances for the interior phosphorus
atoms are given as another doublet of doublets at δ = –2.5
2
(2JP,P = 6.6 Hz, JP,P = 10.9 Hz) and –3.0 ppm (2JP,P
=
5.7 Hz, 2JP,P = 10.9 Hz). The occurrence of the linear dimer,
tetramer, and hexamer species besides the cyclic tetramer
was additionally confirmed by ESI mass spectrometry (Fig-
ure 7). Furthermore, the linear octamer was detected at m/z
= 1630.42 (exact mass 1629.43), which was not verifiable
by NMR spectroscopy. Notably, owing to the ESI process,
DMAP and GaCl3 were replaced by Cl and NH3 groups.
In general, the formation of the Ph/Me- and Ph/Ph-sub-
and another species were detected by 31P NMR spec- stituted polymeric species was not possible by starting with
troscopy. This other species was identified as the linear tet- cyclodiphosphazene diadducts. This may be a consequence
ramer with a GaCl3 (Lewis acid) molecule and an nBu3P of two factors: (1) Owing to the poor solubility of the cyclo-
(Lewis base) molecule at each side. A pattern of five reso- diphosphazene diadducts in nearly all of the solvents, the
nances with a triplet at δ = 1.9 ppm (2JP,P = 7.9 Hz), a abstraction of the GaCl3 Lewis acid is rather slow. There-
3
doublet of triplets at δ = 9.6 ppm (2JP,P = 7.9 Hz, JP,P
=
fore, the concentration of the uncoordinated cyclodiphos-
19.0 Hz), a doublet at δ = 17.1 ppm (2JP,P = 7.9 Hz), a phazene may be too low to favor polymer formation.
doublet of doublets at δ = 17.2 ppm (1JP,P = 15.7 Hz, JP,P (2) During the polymerization reaction, the Lewis acid and
2
= 19.0 Hz), and another doublet of duplets at δ = 37.6 ppm the Lewis base may coordinate to the intermediates and
3
(1JP,P = 15.7, JP,P = 19.0 Hz) appears.
hinder further polymerization. Additionally, the Ph/Me di-
In the reaction of (Ph2PN)2·(GaCl3)2 with 2 equiv. of mer favors the formation of cyclic tetramers if an equimolar
DMAP, the formation of several species was observed by amount or even an excess amount of the Lewis base is used.
31P NMR spectroscopy. A singlet with a chemical shift of δ In all of our polymerization attempts for the Ph/Me-substi-
Figure 6. 31P NMR spectrum of the reaction of (Ph2PN)2·(GaCl3)2 with DMAP (2 equiv.).
Eur. J. Inorg. Chem. 2014, 1735–1744
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Figure 7. MS (ESI) of the end product of the reaction of (Ph2PN)2·(GaCl3)2 with DMAP (2 equiv.).
dard Schlenk or dry-box techniques. Dichloromethane was purified
according to a literature procedure, dried with P4O10, and freshly
distilled prior to use.[21] N,NЈ-Bis(trimethylsilyl)sulfur diimide was
tuted compound, no sign of polymer or chains longer than
the tetramer were obtained. In contrast, the Ph/Ph dimer
appears to form both linear and cyclic products indepen-
dently from the amount of Lewis base used. The formation
of linear species is favored, which is in contrast to the Ph/
Me-substituted cyclic dimers, and at least the linear octa-
mer is formed. Unfortunately, the high-molecular-weight
Ph/Ph-substituted polymer is insoluble and difficult to char-
acterize, but no material consistent with its formation was
noted during the attempted polymerization reactions.
prepared according to
a
modified literature procedure.[22]
MePhPCl, (dmp)PhPCl, and oTolPhPCl were prepared according
to literature procedures.[23] tBu2PCl (99%, Fluka) was freshly dis-
tilled prior to use. GaCl3 (99.99%, Sigma–Aldrich) was used as
received. Ph2AsCl was prepared according to a literature pro-
cedure.[24] Information about the attempted synthesis of cyclodi-
ars(V)azene adducts and the polymerization attempts can be found
in the Supporting Information. 31P{1H}, 13C{1H}, 13C DEPT, and
1H NMR spectra were obtained with Bruker Avance 250, 300, and
500 or JEOL Lambda 300 and Eclipse 300 spectrometers and were
referenced internally to the deuterated solvent (13C, CD2Cl2:
δreference = 54 ppm) or to protic impurities in the deuterated solvent
(1H, CDHCl2: δreference = 5.31 ppm). The IR spectra were recorded
Conclusions
We presented new derivatives of cyclodiphosph(V)azenes
from the reaction of chlorophosphanes with N,NЈ-bis(tri- with a Nicolet 380 FTIR with a Smart Orbit ATR device. Raman
spectra were recorded with a Bruker Vertex 70 FTIR with RAM
II FT-Raman module equipped with an Nd:YAG laser (1064 nm)
or with a Kaiser Optical Systems RXN1-785 nm. ESI mass spectra
were recorded with a Bruker Daltonics Apex IV Fourier transform
ion cyclotron resonance mass spectrometer, and EI and CI mass
spectrometry were carried out with a VG Analytical AutoSpec mass
spectrometer or a Finnigan MAT 95-XP from Thermo Electron.
CHN analyses were performed with an Analysator Flash EA 1112
from Thermo Quest or a C/H/N/S-Mikronalysator TruSpec-932
from Leco. Melting points were recorded with an EZ-Melt, Stan-
methylsilyl)sulfur diimide, Me3Si–NSN–SiMe3, triggered by
the action of GaCl3. The steric influence of the substituent
at the phosphane was discussed as well as the necessity for
the formation of an [R1R2(Cl)P–PR1R2]+ cation for this
type of reaction. The heavier Ph2AsCl congener reacted
with Me3Si–NSN–SiMe3 in the presence of GaCl3 to give
Ph2As–N=S=N–SiMe3·GaCl3. In contrast to the phos-
phorus species, the elimination of S8 was not observed.
Furthermore, Ph/Me- and Ph/Ph-substituted compounds 1
and 2 were investigated with respect to their ring-opening ford Research Systems, with a heating rate of 20 °Cmin–1 (clearing-
points are reported). Differential scanning calorimetry (DSC) was
performed with a DSC 823e from Mettler-Toledo with a heating
rate of 5 °Cmin–1.
polymerization. This led mainly to the cyclic tetramer (for
1) and at most to the linear octamer species (for 2). Studies
of the polymerization behavior of more soluble analogues
of Lewis acid stabilized cyclodiphosph(V)azenes would be
a worthwhile subject for future work.
X-ray Structure Determination: X-ray-quality crystals of all com-
pounds were selected in Kel-F-oil (Riedel–de Haën) or Fomblin
YR-1800 perfluoroether (Alfa Aesar) at ambient temperature. The
samples were cooled to 173(2) K during measurement. The data
was collected with a Bruker Kappa Apex-II CCD diffractometer
by using graphite-monochromated Mo-Kα radiation (λ = 0.71073).
The structures were solved by direct methods (SHELXS-97)[25] and
refined by full-matrix least-squares procedures (SHELXL-97).[26]
Experimental Section
General Information: All manipulations were carried out under
oxygen- and moisture-free conditions under argon by using stan-
Eur. J. Inorg. Chem. 2014, 1735–1744
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Table 3. Crystallographic details of 1, trans-2, cis-2, 3, and 4.
cis-2 trans-2
3·CH2Cl2
4·0.5CH2Cl2
Empirical formula
Formula mass
Color
Crystal system
Space group
a [Å]
b [Å]
c [Å]
α [°]
β [°]
C14H16Cl6Ga2N2P2 C14H16Cl6Ga2N2P2 C18H24Cl6Ga2N2P2·CH2Cl2 C26H24Cl6Ga2N2P2·0.5CH2Cl2
626.37
626.37
colorless
orthorhombic
Pbca
14.8995(5)
9.2766(3)
16.6902(6)
90
90
90
2306.9(1)
4
767.40
colorless
monoclinic
P21/c
11.433(5)
12.642(6)
20.859(8)
90
98.90(1)
90
2979 (2)
4
821.02
colorless
triclinic
P1
colorless
tetragonal
P421c
13.2711(2)
13.2711(2)
18.2860(5)
90
¯
¯
8.758(5)
9.837(6)
14.936(9)
80.659(1)
75.957(1)
72.74(2)
1186.5(1)
2
90
90
γ [°]
V [Å3]
3220.57(1)
4
Z
ρcalcd..[ gcm–3]
1.753
3.084
0.71073
173(2)
19049
5406
1.804
3.173
0.71073
173(2)
12987
3056
1.711
2.648
0.71073
173(2)
23298
8634
1.693
2.375
0.71073
173(2)
16744
3888
μ [mm–1]
λ(Mo-Kα) [Å]
T [K]
Measured reflections
Independent reflections
Reflections with IϾ2σ(I)
Rint.
3340
0.0492
616
2362
0.0331
1232
6997
0.0288
1528
3444
0.0391
1636
F(000)
R1 {R[F2 Ͼ 2σ(F2)]}
wR2 (all data)
GooF
0.0374
0.0707
0.933
0.0349
0.0980
1.059
0.0285
0.0702
1.049
0.0261
0.0580
1.008
185
Parameters
237
120
314
Table 4. Crystallographic details of 5, 6, and 7.
5
6
7
Empirical formula
Formula mass
Color
Crystal system
Space group
a [Å]
b [Å]
c [Å]
α [°]
β [°]
C8H18Cl4GaP
356.71
colorless
monoclinic
P21/n
9.0310(4)
15.2834(8)
10.7635(5)
90
90.589(2)
90
1485.55(1)
4
C24H20As2N2S
518.32
yellow
monoclinic
C2/c
18.2635(6)
5.8395(2)
20.8645(6)
90
105.9440(1)
90
2139.59(1)
4
C15H19AsCl3GaN2SSi
538.46
yellow
triclinic
¯
P1
9.7832(5)
11.2660(6)
11.6349(6)
68.767(3)
83.625(3)
66.190(3)
1092.65(1)
2
γ [°]
V [Å3]
Z
ρcalcd..[ gcm–3]
1.595
2.646
1.609
3.234
1.637
3.280
μ [mm–1]
λ(Mo-Kα) [Å]
T [K]
Measured reflections
Independent reflections
Reflections with IϾ2σ(I)
Rint.
0.71073
173(2)
17811
4304
4003
0.0181
720
0.0188
0.0472
1.049
0.71073
173(2)
13595
3822
2990
0.0278
1040
0.0286
0.0613
1.031
0.71073
173(2)
26886
7310
4423
0.0614
536
0.0406
0.0788
0.991
F(000)
R1 {R[F2 Ͼ 2σ(F2)]}
wR2 (F2)
GooF
Parameters
133
132
220
Semiempirical absorption corrections were applied (SADABS).[27]
All non-hydrogen atoms were refined anisotropically; hydrogen
atoms were included in the refinement at calculated positions by
using a riding model (Tables 3 and 4). CCDC-955010 (for cis-2),
paper. These data can be obtained free of charge from The Cam-
bridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/
data_request/cif.
-955009 (for trans-2), -955011 (for 3·CH2Cl2), -955012 (for General Synthesis of Cyclodiphosph(V)azenes Adducts: The corre-
4·0.5CH2Cl2), -955012 (for 5), -955013 (for 6), and -955015 (for 7) sponding chlorophosphane (2.0 mmol) was added slowly by syringe
contain the supplementary crystallographic data for this
to a solution of GaCl3 (2.0 mmol) in CH2Cl2 (10 mL) at –50 °C.
Eur. J. Inorg. Chem. 2014, 1735–1744
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The resulting mixture was stirred at this temperature for 15 min,
and then pure N,NЈ-bis(trimethylsilyl)sulfur diimide (1.0 mmol)
was added dropwise. The resulting mixture was slowly warmed to
ambient temperature over 4 h whilst stirring, and a white precipi-
tate formed. The resulting suspension was concentrated and fil-
tered, and the colorless precipitate was washed several times with
small amounts of CH2Cl2. For further purification, the crude prod-
uct was recrystallized from CH2Cl2.
1385 (w), 1312 (w), 1288 (w), 1278 (w), 1265 (w), 1199 (w), 1188
(w), 1167 (w), 1138 (m), 1107 (m), 1084 (m), 1051 (w), 1028 (w),
999 (w), 958 (s), 869 (vs), 836 (m), 810 (m), 761 (m), 746 (s), 739
(s), 714 (m), 703 (m), 681 (s), 669 (m), 628 (w), 612 (w), 569 (s)
cm–1. Raman: ν = (500 mW, 25 °C, 250 scans): 3061(4), 2928 (1),
˜
1585(8), 1441 (1), 1393 (1), 1202 (1), 1167 (1), 1136 (1), 1113 (3),
1086 (1), 1051 (4), 1026 (2), 999 (6), 814 (1), 629 (2), 614 (1), 557
(1), 399 (1), 359 (6), 334 (1), 224 (4), 185 (1), 116 (6), 101 (10) cm–1.
Crystals suitable for X-ray crystallographic analysis were obtained
by cooling a saturated CH2Cl2 solution of 4 to –40 °C.
(MePhPN)2(GaCl3)2 (2): Yield: 0.16 mmol, 16%. M.p. 315 °C
(dec.). C14H16Cl6Ga2N2P2 (626.40): calcd. C 26.84, H 2.57, N 4.47;
found C 26.34, H 2.69, N 4.22. 31P{1H} NMR (121.5 MHz,
CD2Cl2, 25 °C): δ = 84.8 ppm. 1H NMR (300 MHz, CD2Cl2,
25 °C): δ = 2.90 [d, 2J(1H-31P) = 14.0 Hz, 6 H, CH3], 7.81 (m, 4 H,
o-H), 7.98 (t, J = 7.35 Hz, 2 H, p-H), 8.11 (m, 4 H, m-H) ppm. IR
Synthesis of tBu2PCl(GaCl3) (5): Bis(tert-butyl)chlorophosphane
(0.180 g, 1.0 mmol) was added slowly by syringe to a solution of
GaCl3 (0.176 g, 1.0 mmol) in CH2Cl2 (10 mL) at –30 °C. The re-
sulting mixture was stirred at this temperature for 15 min and
warmed to ambient temperature. The solvent was removed, and the
resulting colorless residue was dried in vacuo to yield 5 (0.350 g,
0.99 mmol, 99%). For further purification, the product was recrys-
tallized from CH2Cl2. M.p. 176 °C (dec.). C8H18Cl4GaP (356.74):
calcd. C 26.93, H 5.09; found C 26.66, H 5.27. 31P{1H} NMR
(202.5 MHz, CD2Cl2, 25 °C): δ = 101.4 (br.) ppm. 1H NMR
(500 MHz, CD2Cl2, 25 °C): δ = 1.56 [d, 3J(1H,31P) = 17.8 Hz, 18
H] ppm. 13C NMR (125.7 MHz, CD2Cl2, 25 °C): δ = 27.9 [d,
2J(13C,31P) = 4.5 Hz, 6 C, (CH)3C], 41.6 [s, 2 C, (CH)3C] ppm. IR
(ATR, 25 °C, 32 scans): ν = 3068 (w), 2991 (w), 2908 (m), 1810
˜
(w), 1588 (m), 1552 (w), 1487 (w), 1438 (s), 1387 (w), 1339 (w),
1312 (m), 1298 (m), 1164 (w), 1120 (s), 1003 (vs), 908 (vs), 840 (s),
825 (s), 767 (m), 740 (vs), 730 (s), 680 (s), 573 (s) cm–1. Raman
(100 mW, 25 °C, 302 scans): ν = 3073 (4), 2998 (2), 2984 (5), 1586
˜
(5), 1398 (1), 1190 (1), 1166 (1), 1119 (2), 1027 (2), 999 (10), 616
(2), 568 (2), 400 (2), 361 (5), 246 (2), 170 (2), 135 (2), 115 (4) cm–1.
MS (EI, 70 eV): m/z (%) = 46(15), 51(13), 57(12), 69(16), 71(17),
77(37) [C6H5]+, 78(20), 91 (38), 109(12), 121(13), 122(32), 123(12),
124(15), 125(10), 136(14), 138(42), 139(51), 140(16),183(18),
199(19), 201(13), 215(95), 216(29), 260(10), 261(91), 262(16),
276(67) [(MePhPN)2 + 2 H]2+, 277(55), 278(10), 291(12), 305(36),
319 (20), 320 (78), 321(17), 359(11) 379(48), 381(57), 383(12),
395(58), 396(13), 397(58), 398(10), 399(16), 415(72), 416(14),
417(100), 418(17), 419(41), 430(24), 432(30), 434(13), 459(15)
461(20). Crystals suitable for X-ray crystallographic analysis were
obtained by cooling a saturated CH2Cl2 solution of 2 to –40 °C.
(ATR, 25 °C, 32 scans): ν = 2967 (w), 2942 (w), 2897 (w), 2869 (w),
˜
2395 (w), 1464 (s), 1398 (w), 1373 (s), 1169 (m), 1069 (w), 1023
(m), 940 (m), 935 (m), 898 (w), 798 (m), 717 (w), 621 (m), 592 (s),
560 (s) cm–1. MS (CI+, isobutane): m/z (%) =183 (30), 181 (100)
[tBu2PCl + H]+, 145 (5) [tBu2P]+. Crystals suitable for X-ray crys-
tallographic analysis were obtained by cooling a saturated CH2Cl2
solution of 5 to –40 °C.
Supporting Information (see footnote on the first page of this arti-
cle): Experimental details, structure elucidation, synthesis and reac-
tions, and polymerization attempts.
[Me(dmp)PN]2(GaCl3)2 (3): Yield: 0.25 mmol, 25%. M.p. 326 °C
(dec.). C18H24Cl6Ga2N2P2 (682.51): calcd. C 31.68, H 3.54, N 4.10;
found C 31.48, H 3.68, N 3.39. 31P{1H} NMR (121.5 MHz,
CD2Cl2, 25 °C): δ = 88.9 ppm. 1H NMR (300 MHz, CD2Cl2,
Acknowledgments
2
25 °C): δ = 2.94 [d, J(1H,31P) = 13.3 Hz, 6 H, P-CH3], 2.88 [s, 12
H, C6H3-(CH3)2], 7.58 (t, J = 7.86 Hz, 2 H, p-H), 7.60 (m, 4 H, m-
Financial support by the Deutsche Forschungsgemeinschaft
(DFG) (SCHU 1170/8-1) is gratefully acknowledged.
H) ppm. IR (ATR, 25 °C, 32 scans): ν = 3068 (w), 3011 (w), 2992
˜
(w), 2922 (w), 1588 (m), 1566 (w), 1454 (s), 1392 (m), 1377 (w),
1301 (m), 1251 (w), 1243 (w), 1173 (m), 1138 (m), 1060 (s), 1024
(m), 978 (vs), 909 (s), 898 (vs), 883 (vs), 817 (s), 787 (s), 779 (s),
737 (s), 709 (m) 578 (m), 534 (m) cm–1. Raman (1500 mW, 25 °C,
[1] a) T. J. Taylor, A. Presa Soto, K. Huynh, A. J. Lough, A. C.
Swain, N. C. Norman, C. A. Russell, I. Manners, Macromole-
cules 2010, 43, 7446–7252; b) H. R. Allcock, Chemistry and
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c) R. H. Neilson, P. Wisian-Neilson, Chem. Rev. 1988, 88, 541–
562; d) G. D’Halliun, R. De Jaeger, J. P. Chambrette, P. Potin,
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García-Alonso, P. Gómez-Elipe, J. Ignacio Fidalgo, J. L.
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500 scans): ν = 3060 (4), 3014 (3), 2993 (5), 2942 (7), 2924 (8), 1588
˜
(6), 1458 (1), 1385 (3), 1244 (5), 1174 (1), 1068 (7), 785 (1), 532 (8),
400 (3), 364 (10), 209 (1), 147 (1), 125 (2) cm–1. MS (EI, 70 eV):
m/z (%) = 67(1), 257(1), 330(5) [(dmpMePN)2 + 2 H+]2+, 331(2),
361(2), 376(5), 377(3), 451(14), 452(3), 453(13), 454(3), 455(3),
469(26), 470(5), 471(34), 472(7), 473(13), 474(2), 475(1), 487(5),
488(2), 489(8), 490(2), 491(3), 515(72), 516(17), 517(100), 518(22),
519(31), 520(9), 521(6), 522(1), 893(1). Crystals suitable for X-ray
crystallographic analysis were obtained by cooling a saturated
CH2Cl2 solution of 3 to –40 °C.
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[Ph(oTol)PN]2(GaCl3)2 (4): Yield: 0.52 mmol, 52%. M.p. 365 °C
(dec.). C26H24Cl6Ga2N2P2 (778.59): calcd. C 40.1, H 3.11, N 3.60;
found C 39.62, H 3.33, N 3.43. 31P{1H} NMR (202.5 MHz,
CD2Cl2, 25 °C): δ = 74.9 ppm. 1H NMR (500 MHz, CD2Cl2,
25 °C): δ = 2.28 [s, 6 H, C6H4-(CH3)], 7.47 [m, 2 H, C6H4-(CH3)],
7.49 [m, 2 H, C6H4-(CH3)], 7.72 (m, 4 H, o-H, C6H5), 7.81 (t, J =
7.6 Hz, 2 H, p-H, C6H5), 7.95 [t, J = 7.6 Hz, 2 H, p-H, C6H4-
(CH3)], 8.08 (m, 4 H, m-H, C6H5), 8.19 [m, 2 H, C6H4-(CH3)] ppm.
IR (ATR, 25 °C, 32 scans): ν = 3083 (w), 3059 (w), 2980 (w), 1951
˜
[6] F. Dielmann, O. Back, M. Henry-Ellinger, P. Jerabek, G.
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[9] Interestingly, freshly distilled MePhPCl was allowed to stand
for several weeks, which resulted in the formation of a small
amount of colorless crystals. These crystals were identified as
[PhMe2P–PMePh]Cl by single-crystal X-ray diffraction. Full
crystallographic details can be found in the Supporting Infor-
mation.
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[13] Further information can be found in the Supporting Infor-
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Received: August 5, 2013
Published Online: September 19, 2013
[15] a) Sum of covalent radii: r(P) = 1.1 and r(N) = 0.7; b) H.
Wiberg, Lehrbuch der Anorganischen Chemie, 102. Aufl., Walter
de Gruyter, Berlin, 2007, Anhang IV.
Eur. J. Inorg. Chem. 2014, 1735–1744
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