Formation and crystal structure of 4,4'-oxybis(2,6-bis(dimethylamino)-4 H-1,3,5,4-thiadiazaphosphinine 4-Oxide)

Article abstract of DOI:10.1080/10426507.2014.883623

The reaction of P₄S₁₀ with dimethyl cyanamide as solvent yields a complex mixture of products, from which the new compound 4,4′-oxybis(2,6-bis(dimethylamino)-4H-1,3,5,4-thiadiazaphosphinine 4-oxide) (1) was isolated. In this pyrophosphate derivative, the phosphorus atoms are part of the, otherwise rarely encountered, 1,3,5,4-thiadiaza-phosphinine ring. The molecular structure of the new compound was elucidated by single-crystal X-ray diffraction, showing an almost planar thiadiazaphosphinine ring and a cis-like arrangement of the heterocycles at the two phosphorus atoms.

Full text of DOI:10.1080/10426507.2014.883623

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Phosphorus, Sulfur, and Silicon and the
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Formation and Crystal
Structure of 4,4'-Oxybis(2,6-
bis(dimethylamino)-4H-1,3,5,4-
thiadiazaphosphinine 4-Oxide)
Stefanie Schönbergera, Amra Blumea & Konstantin Karaghiosoffa
a Department of Chemistry, Ludwig-Maximilian University of Munich,
Butenandtstrasse 5-13, 81377, Munich, Germany
Accepted author version posted online: 30 Apr 2014.Published
online: 04 Aug 2014.
To cite this article: Stefanie Schönberger, Amra Blume & Konstantin Karaghiosoff (2014) Formation
and Crystal Structure of 4,4'-Oxybis(2,6-bis(dimethylamino)-4H-1,3,5,4-thiadiazaphosphinine
4-Oxide), Phosphorus, Sulfur, and Silicon and the Related Elements, 189:7-8, 1226-1236, DOI:
10.1080/10426507.2014.883623
To link to this article: http://dx.doi.org/10.1080/10426507.2014.883623
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Phosphorus, Sulfur, and Silicon, 189:1226–1236, 2014
Copyright ꢀC Taylor & Francis Group, LLC
ISSN: 1042-6507 print / 1563-5325 online
DOI: 10.1080/10426507.2014.883623
FORMATION AND CRYSTAL STRUCTURE OF
4,4ꢀ-OXYBIS(2,6-BIS(DIMETHYLAMINO)-4H-1,3,5,4-
THIADIAZAPHOSPHININE
4-OXIDE)
Stefanie Scho¨nberger, Amra Blume, and Konstantin
Karaghiosoff
Department of Chemistry, Ludwig-Maximilian University of Munich,
Butenandtstrasse 5-13 81377, Munich, Germany
GRAPHICAL ABSTRACT
Abstract The reaction of P4S10 with dimethyl cyanamide as solvent yields a complex mixture
of products, from which the new compound 4,4ꢁ-oxybis(2,6-bis(dimethylamino)-4H-1,3,5,4-
thiadiazaphosphinine 4-oxide) (1) was isolated. In this pyrophosphate derivative, the phospho-
rus atoms are part of the, otherwise rarely encountered, 1,3,5,4-thiadiaza-phosphinine ring.
The molecular structure of the new compound was elucidated by single-crystal X-ray diffrac-
tion, showing an almost planar thiadiazaphosphinine ring and a cis-like arrangement of the
heterocycles at the two phosphorus atoms.
Keywords Phosphorus(V) sulfide; dimethyl cyanamide; synthesis; crystal structure;
thiadiazaphosphinine ; phosphoric acid anhydride
INTRODUCTION
The reaction of P4S10 withnitrogen-containingnucleophiles represents a challenge for
chemists since several years. Roesky et al.1 investigated the nucleophilic attack of different
Received 5 November 2013; accepted 17 December 2013.
This paper is dedicated to Professor Louis D. Quin on the occasion of his 86th birthday.
Address correspondence to Prof. Konstantin Karaghiosoff, Department of Chemistry, Ludwig-Maximilian
University of Munich, Butenandtstrasse 5-13, 81377, Munich, Germany. E-mail: klk@cup.uni-muenchen.de
Color versions of one or more of the figures in the article can be found online at www.tandfonline.com/gpss.
1226

A NEW 1,3,5,4-THIADIAZAPHOSPHININE
1227
Table 1 Comparison of 31P NMR shifts and coupling constants for 2, 3, P4S9 and P4S10 (for comparison)
Compound
δ(P1) (ppm)
δ(P2) (ppm)
2JPP (Hz)
P4S9N− (2)1
67.8
67
67.6
64.6
52.0
56.1
32.8
30
32.8
48.8
44.2
—
21.5
21
21.5
96.3
30.5
—
P4S8(NC(S)Ph)2 (3)2
P4S10 + 2 PhCN3
4
α-P4S9
5
β-P4S9
4
P4S10
anions on P4S10 already in 1970. Mainly, alkali metal salts of cyanide, azide, and thio-
cyanate were allowed to react with phosphorus(V) sulfide in acetonitrile. The reaction with
[(n-C3H7)4N][(N3)2PS2] in MeCN yielded a white precipitate, which was characterized us-
ing IR- and 31P NMR spectroscopy. The 31P NMR spectrum of this compound showed two
triplets of equal intensity (Table 1). For its structure, a P4S10 motive with one endocyclic
sulfur being substituted by a nitrogen atom, resulting in the (n-C3H7)4N+ salt of the anion
P4S9N− (I) was proposed (Figure 1).
Eight years later, Retuert et al.2 observed nearly identical 31P NMR signals, when
they investigated a suspension of P4S10 in PhCN. They claimed the structure of the orange
crystalline product, resulting from this reaction, to be a neutral P4S10 adamantane-like cage,
with two exocyclic sulfur atoms being substituted by N–CS–C6H5 groups (Figure 2).
Neels and coworkers3 tried to answer the question, to which of the above-mentioned
compounds the observed 31P NMR shift can be assigned. For the formation of the product,
acetonitrile was used as solvent, so it is likely, that it is generally formed by reaction of
P4S10 with nitriles. They reproduced the synthesis of Retuert and isolated crystals of the
3,5-diphenyl-l,2,4-dithiazolium salt of 2 and determined the structure using single-crystal
X-ray diffraction.
In the course of our investigations on the reactivity of P4S10, we took a closer look at
the influence of different nitrogen-containing basic solvents on its reaction behavior.
RESULTS AND DISCUSSION
P4S10 was dissolved in benzonitrile or propionitrile on prolonged heating. 31P NMR
spectra of the reaction solutions showed the formation of complex mixtures of products. In
both cases, also 31P NMR signals indicating the presence of compound 2 were observed.
This was also the case, when pyridine and 2,2ꢁ-bipyridine was added to the solution.
Figure 1 Structure of the P4S9N− anion (2) by Roesky.1

¨
1228
S. SCHONBERGER ET AL.
Figure 2 Structure of P4S8(NC(S)C6H5) (3) by Retuert.2
The reaction of P4S10 with dimethyl cyanamide resulted in the isolation of an unex-
pected product. Refluxing P4S10 in dimethyl cyanamide yields a brown reaction solution.
Here, also a complex mixture of different products could be observed in the 31P NMR.
From this solution, a small amount of colorless crystals could be obtained. The product
was identified by single-crystal X-ray diffraction as the novel compound 4,4ꢁ-oxybis(2,6-
bis(dimethylamino)-4H-1,3,5,4-thiadiazaphosphinine 4-oxide) (1) (Figure 3).
In the literature, only one compound has been reported, containing a 1,3,5,4-
thiadiazaphosphinine ring, which has been characterized in terms of single-crystal X-ray
diffraction. Woollins et al.6 described the formation of the P-ferrocenyl-substituted 2,6-
bis(dimethylamino)-1,3,5,4-thiadiazaphosphorine-4-sulfide (5) in good yield together with
small amounts of the thiocyanate (6) from the reaction of the corresponding ferrocenyl
perthiophosphonic acid anhydride (4) with an excess of dimethyl cyanamide as shown in
Scheme 1.
Compound 1 crystallizes in the orthorhombic space group Pbcn with four formula
units in the unit cell. Half of the molecule is symmetry generated, so it adopts perfect
twofold symmetry. Figure 4 shows the molecular structure and selected atom distances and
bond angles are listed.
The terminal N–C entities of two dimethyl cyanamide molecules are connected by a
phosphorus atom at the nitrogen end and by a sulfur atom at the carbon end of the former CN
group, forming a 1,3,5,4-thiadiazaphosphinine ring. In contrast to the thiadiazaphosphinine
ring in 5, which adopts a distorted boat conformation,6 the phosphinine ring in 1 deviates
onlyslightly fromplanarity withvalues of thetorsionangles withinthe ringbetween −3.9(4)
and 1.1(5)◦. A comparison of atom distances and bond angles of the thiadiazaphosphinine
ring in 1 and 5 is presented in Table 2.
What attracts attention is that the bond lengths found in 1 and 5 are all in about the
same range. The P–N bond distances in 1 are in the range, expected for P–N single bonds and
are slightly shorter compared with those in 5. The C–S bond lengths in both compounds are
practically equal. The endocyclic C–N bond lengths within the ring of 1 and 5 correspond
to double bonds. The exocyclic C–N distances to the dimethylamino groups are clearly
Figure 3 Chemical structure of 4,4ꢁ-oxybis(2,6-bis(dimethylamino)-4H-1,3,5,4-thiadiazaphosphinine 4-oxide)
(1).

A NEW 1,3,5,4-THIADIAZAPHOSPHININE
1229
Scheme 1 Synthesis of compound 5.6
shortened compared with C–N single bonds. Together with the coplanarity of the methyl
groups, this indicates a delocalization of the nitrogen lone pair as shown in Scheme 2.
For a discussion of the structural parameters of the diphosphate moiety, the closely
related pyrophosphate derivative 78 and the diphosphoric tetraamides 8,9–11 912 (Figure 5)
Figure 4 Molecular structure of 1 (two different viewing directions). Thermal ellipsoids are set at 50% prob-
ability level. Hydrogen atoms are omitted for clarity. Symmetry operation: i = 1−x, y, 0.5−z. Selected atom
distances (Å) and bond angles (◦) (standard uncertainties are given in brackets): P1–O1 1.496(2), P1–O2
1.607(2), P1–N1/P1–N2 1.626(3)/1.617(3), N1–C1/N2–C2 1.273(4)/1.295(4), S1–C1/S1–C2 1.786(3)/1.774(3),
C1–N4/C2–N3 1.348(4)/1.342(4); O1–P1–O2 108.0(2), P1–O2–P1i 134.2(2), O1–P1–N1 123.9(2), O1–P1–N2
113.6(2), O2–P1–N1 105.2(2), O2–P1–N2 104.5(2).

¨
S. SCHONBERGER ET AL.
1230
Table 2 Comparison of atom distances (Å) and bond angles (◦) within the thiadiaza-phosphinine ring in com-
pounds 1 and 56 and standard values compiled by Allen7
1a
5a
Ref.7
P–N
N–C
1.626(3)/1.617(3)
1.273(4)/1.295(4)
1.348(4)/1.342(4)
1.786(3)/1.774(3)
111.7(2)
125.6(3)/126.4(3)
126.8(3)/127.1(3)
102.2(2)
1.648(6)/1.664(4)
1.289(6)/1.290(6)
1.365(6)/1.335(6)
1.788(5)/1.771(5)
108.2(2)
122.6(4)/121.0(4)
125.4(5)/127.3(4)
101.0(2)
1.652(24)
1.279(8)
1.419(17)
1.712(13)
C–NMe2
C–S
N–P–N
P–N–C
N–C–S
C–S–C
aStandard uncertainties are given in brackets.
Scheme 2 Mesomerism in the 1,3,5,4-thiadiazaphosphinine rings of 1.
can be consulted for comparative reasons. In the bridging O–P–O–P–O entity, the bond
lengths between phosphorus and the terminal oxygen atoms (1.496(2) Å) are shorter as
compared with the P–O distance to the bridging oxygen atom (1.607(2) Å) as was to be
expected. Both values are in good accordance with those of 1.444–1.497 Å and 1.591–1.627
Å, respectively, reported for compounds 7–9.8–12 The P–O–P angle (134.2(2)◦) is smaller
compared to that observed in 7, probably as consequence of the bulkier substituents of
the latter. The value of 1, however, fits well to those found in the tetraamides 8 and 9
(125.1–133.8◦).9–12
The three-dimensional buildup of the structure is affected by several intra- and inter-
molecular interactions. An overview can be found in Table 3.
One would expect the two thiadiazaphosphinine rings in 1 to be oriented trans to each
other as they are rather bulky. However, a cis orientation of the two phosphinine rings is
observed. A similar arrangement in the solid state is found for the triazaphosphinine rings
in 7.8 The observed orientation is most probably caused by three different electrostatic
interactions in the molecular unit (Figure 6).
Hydrogen bonds between H3A and N3, as well as between H6A and N2 are observed
within one asymmetric unit. The donor–acceptor distances are with 2.717(5) and 2.715(5) Å
Table 3 Intra- and intermolecular interactions in 1 (van der Waals radii [Å]: H: 1.20; C: 1.70; N: 1.55; O: 1.52)13
D–H···A
d(D–H) (Å)
d(H···A) (Å)
d(D ···A) (Å)
< D–H···A (◦)
C3–H3A···N3
C6–H6A···N2
C3–H3C···N5i
C3ii–H3Bii ···O1
0.98(1)
0.98(1)
0.98(1)
0.98(1)
2.37(1)
2.47(1)
2.58(1)
2.31(1)
2.717(5)
2.715(5)
3.492(6)
3.260(5)
100(1)
94(1)
155(1)
165(1)
Symmetry codes: i = 1−x, y, 0.5−z; ii = 1.5−x, 0,5−y, z. Standard uncertainties are given in brackets.

A NEW 1,3,5,4-THIADIAZAPHOSPHININE
1231
Figure 5 Structurally characterized diphosphoric tetraamides.8–12
well below the sum of the van der Waals radii of carbon and nitrogen (3.25 Å). These are
rather strong interactions and have therefore a great influence on the structure, prohibiting
rotation of the methyl groups. This allows the heterocycles to move closer together. The
interaction between H3C and N5 connects both rings with a D···A distance of 3.492(6) Å.
This electrostatic interaction is rather weak but nevertheless results in the rings being kept
together.
In the crystal of 1, one molecule is connected to four others via C3–H3B···O1
interactions (Figure 7). The contact of the carbon to the acceptor oxygen atom has a D···A
distance of 3.260(5) Å and the D–H···A angle of 164.6(3)◦.
These intermolecular interactions lead to the formation of chains along the c-axis
(Figure 8, upper picture). The molecules are further interconnected to form layers perpen-
dicular to the direction of propagation of these chains (Figure 8, lower picture).
Possible Mechanism of Formation
Regarding the formation mechanism of compound 1, we can only speculate
(Scheme 3). Obviously, traces of water are responsible for the presence of the oxygen
atoms.

¨
1232
S. SCHONBERGER ET AL.
Figure 6 C–H···N interactions in 1.
The compound may have formed from the reactive species (I). This species is anal-
ogous to the bis(pyridine) adduct of P2S5,14 which is known to be stable and isolatable.
In contrast, I contains a reactive –C N bond, which undergoes cyclization with one of
the terminal sulfur atoms, yielding the intermediate II. A similar intermediate has been
considered for the formation of the thiadiazaphosphinine ring in 5.6 This species reacts
further with more dimethyl cyanamide, which is formally inserted into the P–S bond of
the four-membered ring in II yielding III. In the presence of water, III is converted to the
isolated product 1.
Figure 7 C–H···O interactions, connecting the molecules in 1. Symmetry operation: ii = 1.5−x, 0,5−y, z.

A NEW 1,3,5,4-THIADIAZAPHOSPHININE
1233
Figure 8 Layers perpendicular and chains along the c-axis in 1.
CONCLUSION
Here, the new pyrophosphate derivative 4,4ꢁ-oxybis(2,6-bis(dimethylamino)-4H-
1,3,5,4-thiadiazaphosphinine 4-oxide) (1) is presented. Its unexpected formation in the
course of the reaction of P4S10 and dimethyl cyanamide shows the variable reactivity of
P4S10 depending on the nitrogen base employed. Compound 1 is the second representative
with a 1,3,5,4-thiadiazaphosphinine ring, which could be characterized using single-crystal
X-ray diffraction. The presence of a planar thiadiazaphosphinine ring in 1, in contrast to
the boat conformation in 5, points to a structurally flexible ring system. The conformation
of 1 is mainly influenced by electrostatic C–H···N and C–H···O interactions. These intra-
and intermolecular hydrogen bonds lead to a layered arrangement in the crystal.
EXPERIMENTAL
Dimethyl cyanamide was obtained from Sigma–Aldrich Inc. and used as supplied
without further purification. P4S10 was commercially obtained (Riedel-de Ha¨en) and was

¨
1234
S. SCHONBERGER ET AL.
Scheme 3 Proposed mechanism for the formation of 1.
purified by extraction with CS2 before use. 31P NMR spectra were recorded using a Jeol
EX 400 Eclipse instrument operating at 161.997 MHz. Chemical shifts are referred to 85%
H3PO4 as external standard. All spectra were measured, if not mentioned otherwise, at
25 ◦C.
X-ray Crystallography. An Oxford XCalibur3 diffractometer equipped with a CCD
area detector was employed for data collection using Mo-Kα radiation (λ = 0.71073 Å). The
structures were solved using direct methods (SIR2004)15 and refined by full-matrix least-
squares on F2 (SHELXL-97).16 All non-hydrogen atoms were refined anisotropically. The
hydrogen atoms were located in difference Fourier maps and placed with a C–H distance
of 0.98 Å for C–H bonds. Intra- and intermolecular contacts were analyzed with DIA-
MOND (Version 3.2i), thermal ellipsoids are drawn at the 50% probability level. Selected
crystallographic data and refinement details for the structure determination of compound
1 are summarized in Table 4. CCDC 966235 contains the supplementary crystallographic
data for compound 1. These data can be obtained free of charge from The Cambridge
Crystallographic Data Centre via www.ccdc.cam.ac.uk/data request/cif.
Reaction of P4S10 with Benzonitrile and Propionitrile
P4S10 (0.25 mmol, 111 mg) in 1.5 mL of benzonitrile was heated to 120◦C for 3 h,
when a dark yellow solution was obtained. The 31P NMR spectrum of the reaction solution
showed the signals of an A2×2 spin system as main product (86%): δA = 68.9, δX = 33.9,
JAX = 21.5 Hz.
Similarly, P4S10 (0.27 mmol, 121 mg) in propionitrile (1.5 mL) was heated to 100◦C
for 4 h. After cooling to ambient temperature, the remaining P4S10 was separated by
filtration. The 31P NMR spectrum of the dark yellow filtrate showed a series of signals in

A NEW 1,3,5,4-THIADIAZAPHOSPHININE
1235
Table 4 Crystallographic and refinement data for 1
1
Empirical formula
Formula mass
T (K)
C12H24N8O3P2S2
454.45
173(2)
Crystal size (mm)
Crystal description
Crystal system
Space group
a (Å)
b (Å)
c (Å)
V (Å3)
0.4 × 0.35 × 0.05
Colorless block
Orthorhombic
Pbcn
11.4631(8)
12.4813(8)
14.0977(11)
2017.0(2)
4
Z
ρcalc (g/cm−3
)
1.497
0.454
μ (mm−1
)
F(000)
952
θ range (◦)
4.17–26.00
−14 ≤ h ≤ 14
−15 ≤ k ≤ 15
−17 ≤ l ≤ 13
9648
Index ranges
Reflns. collected
Reflns. obsd.
Reflns. unique
R (int)
1233
1952
0.0920
R1, wR2 (2σ data)
R1, wR2 (all data)
GOOF on F2
0.0519, 0.1024
0.0983, 0.1218
0.997
Large diff. peak/hole (e/Å)
0.333/−0.260
the range of δ = 155–20 ppm and with a relative intensity of 38% the signals of an A2X2
spin system: δA = 70.2, δX = 34.4, JAX = 21.5 Hz.
Reaction of P4S10 with Dimethyl Cyanamide
P4S10 (0.37 mmol, 168 mg) was refluxed for 3 h of dimethyl cyanamide (1.5 mL)
yielding a dark yellow solution. The 31P NMR spectrum of the reaction solution indicated
the presence of a complex mixture of products and displayed main signals at δ = 64.8, 61.1,
18.2, 16.9, and 11.6 ppm. After 7 days, a small amount of colorless block-shaped crystals
of 1 were obtained from the solution.
ACKNOWLEDGMENTS
The authors thank Prof. T. M. Klapo¨tke, Department of Chemistry, Ludwig-
Maximilian University, for the generous allocation of diffractometer time and for his
continuous support.
FUNDING
Financial support by the Department of Chemistry, Ludwig-Maximilian University,
is gratefully acknowledged.

¨
S. SCHONBERGER ET AL.
1236
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