Novel small organo-P-S/Se heterocycles

Article abstract of DOI:10.1039/b107214e

Oxidative addition of elemental sulfur and selenium to cyclomonocarbatetraphosphines (PhP)₄CR₂ (R = H, Me) afforded novel five- and four-membered heterocycles PhP(E)CH₂PhP(E)E₂(E = S, Se) and PhP(Se)CMe₂

Full text of DOI:10.1039/b107214e

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Novel small organo-P–S/Se heterocycles
Petr Kilian, Alexandra M. Z. Slawin and J. Derek Woollins*
Department of Chemistry, University of St. Andrews, Fife, UK KY16 9ST.
E-mail: jdw3@st-andrews.ac.uk
Received (in Cambridge, UK) 9th August 2001, Accepted 25th September 2001
First published as an Advance Article on the web 18th October 2001
Oxidative addition of elemental sulfur and selenium to
cyclomonocarbatetraphosphines (PhP)4CR2 (R = H, Me)
afforded novel five- and four-membered heterocycles
PhP(E)CH2PhP(E)E2 (E
PhP(Se)Se.
The internal bond lengths in 1 are comparable to those in 9. The
envelope shape however accounts to significant changes in
internal bond angles, the P–C–P angle as well as PSSP dihedral
angle are substantially decreased in 1 [P–C–P angle in 1
114.47(9)°; 119.6(4)° in 9; PSSP dihedral angle in 1 49.48(3)°;
54.8(1)° in 9]. Also the S(3)–P(1)–C(2) and S(4)–P(2)–C(8)
angles of 115° are decreased due to lower steric hindrance of
phenyl vs. supermesityl substituent in 9 (corresponding angles
126°). The shortest intermolecular contacts in 1 are 3.47 Å
[S(2)…S(3)], which is less than twice the van der Waals radius
for sulfur (3.70 Å).
= S, Se) and PhP(Se)CMe2-
Although the chemistry of cyclophosphines (RAP)n (RA = alkyl,
aryl; n = 3–6) has been studied extensively, tetraphospholanes
(RAP)4CR2 have received less attention, despite their ease of
access from cyclophosphines.1 Due to the stability of the
endocyclic P–C bond they are a valuable source of PhPCR2PPh
moiety as shown herein for oxidative addition reactions with
elemental sulfur and selenium (Scheme 1). Four- and five-
membered heterocycles described here represent only the third
known heterocycle with the atomic sequence PCPSe (and the
first X-ray structure determination reported), whilst the hetero-
cyclic sequence PCPSeSe is the first example. The parallels in
S chemistry are also scarce; PCPS rings were prepared using
low-coordinate phosphorus starting compounds such as diphos-
phaallene,2 phosphanylidene3 and thioxophosphane with phos-
phonium ylide.4 The only known heterocyclic compound with
the PCPSS atomic sequence, 9, has been isolated in low yield as
a side product in the reaction of sulfur and diphosphaallene with
stabilizing bulky supermesityl side groups.2a Partially sulfur
oxidised derivatives (PhP)4CH2S and (PhP)4CH2S2 were ob-
tained from the reaction of (PhP)4CH2 with lower molar
amounts of sulfur.5
The 31P{1H} NMR spectrum of 1 (in CDCl3) shows a singlet
at d 80.3. A minor singlet (ca. 4% intensity) with a very similar
shift of d 80.9 has been also observed in the spectrum, belonging
to a less energetically favourable conformation or cis-isomer of
1. The 1H NMR spectrum of 1 contains multiplets for the phenyl
ring protons and a triplet for the CH2 group [d 3.9, 2J(HP) 9.9
Hz]. These spectral data are in a very good agreement with those
reported for 9 [dP 87.6, dH(CH2) 3.96, 2J(HP) 9.6 Hz].2a
Treatment of (PhP)4CH2 with 9 equivalents of grey selenium
in boiling toluene, hot filtration to remove insoluble 6 and
unreacted selenium, concentration of the filtrate in vacuo and
cooling afforded the orange crystalline solid 2 in 94% yield
(Scheme 1). The minor impurities, heterocycles 7 and 8, can be
removed by recrystallisation from hot toluene.8
Our aim was to obtain thermodynamically stable products,
thus all the reactions were performed in refluxing toluene
(under N2). Treatment of (PhP)4CH2 with 8 equivalents of
sulfur and a catalytic amount of DBU, followed by fractional
crystallisation afforded colourless crystals of 1 in a moderate
yield (40%, Scheme 1).6
Crystallographic analysis7 reveals 2 to be almost isostructural
with 1 (Fig. 1). The central heterocycle has again envelope
Crystallographic analysis of 1 (Fig. 1)7 reveals the formation
of a five–membered PCPSS heterocycle with a trans-geometry
of exocyclic phenyl and sulfur substituents. The central
heterocycle has an envelope shape, with S(2) atom lying 1.1 Å
out of the plane defined by the other ring atoms (mean deviation
of this plane is 0.04 Å), which is in contrast to the half-chair
conformation found in the only known PCPSS heterocycle 9.2a
Fig. 1 Molecular structure of 1 (E = S) and 2 (E = Se). H atoms omitted
for clarity. Selected bond lengths (Å) and angles (°) for 1 and 2 (values in
square brackets): P(1)–C(1) 1.839(2) [1.830(7)], P(2)–C(1) 1.839(2)
[1.839(6)], P(1)–E(1) 2.1160(7) [2.249(2)], P(2)–E(2) 2.1095(7) [2.247(2)],
E(1)–E(2) 2.0667(7) [2.338(1)], P(1)–C(2) 1.810(2) [1.809(7)], P(2)–C(8)
1.810(2) [1.828(8)], P(1)–E(3) 1.9394(7) [2.100(2)], P(2)–E(4) 1.9419(7)
[2.100(2)], P(1)–C(1)–P(2) 114.47(9) [116.7(4)], P(1)–E(1)–E(2) 97.07(3)
[93.40(6)], P(2)–E(2)–E(1) 95.73(3) [91.97(6)], E(1)–P(1)–C(1) 102.71(6)
[105.2(2)], E(2)–P(2)–C(1) 100.90(6) [102.7(2)], C(2)–P(1)–E(3)
114.86(6) [114.0(2)], C(8)–P(2)–E(4) 114.78(7) [114.0(2)], E(1)–P(1)–
E(3) 107.16(3) [106.82(9)], E(2)–P(2)–E(4) 107.77(3) [107.91(9)].
Scheme 1
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Chem. Commun., 2001, 2288–2289
This journal is © The Royal Society of Chemistry 2001
DOI: 10.1039/b107214e

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conformation, with Se(2) lying 1.27 Å out of plane defined by
other ring atoms (mean deviation of this plane is 0.04 Å). The
PCP angle, P…P distance and PSeSeP torsion angle vary little
from the corresponding values in 1, as expected the ring
dimensions are increased due to larger radii of Se atoms (see e.g.
differences in Se–Se and S–S bond length for 2 and 1), however
Se(3)–P(1)–C(2) and Se(4)–P(2)–C(8) angles (114°) show no
significant change when compared with corresponding angles
in 1. The shortest intermolecular contacts in 2 are 3.48 Å
[Se(2)…Se(3)].
= CH3 protons, X, XA = P) at d 1.3, confirming magnetic
inequivalence of methyl groups protons as a consequence of the
folded geometry of the central heterocycle.
Studies to employ new soluble P–Se heterocycles in our
reagent program for CNO to CNSe transformations are now
underway.
We are grateful to the EPSRC for financial support.
Notes and references
The 31P{1H} NMR spectrum of 2 comprises of a singlet (dP
43, in CDCl3) with symmetric sets of selenium satellites. The
satellite spectrum is generated mainly from two distinct
isotopomers with one 77Se atom in exo- or endo-positions of the
ring, both having an AXXA pattern (A = 77Se, X = P).
Simulation of the satellite spectra enabled determination of all
four P–Se coupling constants9 as well as a homonuclear P–P
coupling [2J(PP) 34.1 Hz].
1 M. Baudler, J. Vesper, P. Junkes and H. Sandmann, Angew. Chem. Int.
Ed. Engl., 1971, 10, 940; M. Baudler, E. Tolls, E. Clef, B. Kloth and D.
Koch, Z. Anorg. Allg. Chem., 1977, 435, 21; Synth. React. Inorg. Met.
Org. Chem., 1977, 7, 253.
2 (a) K. Toyota, Y. Ishikawa, M. Yoshifuji, K. Okada, K. Hosomi and K.
Hirotsu, Chem. Lett., 1991, 2213; (b) K. Toyota, M. Yoshifuji and K.
Hirotsu, Chem. Lett., 1990, 643.
3 N. M. Yousif, Phosphorus, Sulfur Silicon Relat. Elem., 1989, 46, 169.
4 G. Jochem, A. Schmidpeter, F. Kulzer and S. Dick, Chem. Ber., 1995,
128, 1015.
5 M. Baudler, J. Vesper, B. Kloth, D. Koch and H. Sandmann, Z. Anorg.
Allg. Chem., 1977, 431, 39.
By the treatment of (PhP)4CMe2 with 9 equivalents of grey
selenium in the same manner as 2 (including work-up
procedures), orange crystalline 3 has been obtained in 68%
yield (Scheme 1).10 Crystallographic analysis of 3 (Fig. 2)7
reveals that oxidation of (PhP)4CMe2 proceeds surprisingly
with the formation of a four-membered PCPSe ring. The unit
cell contains two independent molecules, in both the central ring
is folded (17 and 28° along the Se…C diagonal) with phenyl
and exocyclic selenium substituents in trans configuration. No
X-ray structure determination of a PCPSe ring has been
reported up to date, the nearest parallels found are PCPS rings,
both thiadiphosphetanes with known X-ray data2b,4 show cis
configuration and folded geometry of the central ring (19.2 and
29.4° along C…S diagonal). Internal P–Se bond lengths in 3
[2.274(2)–2.283(2) Å] are slightly increased with respect to 2
[2.247(2) and 2.249(2) Å] however they are comparable with 6
[2.276(2) and 2.284(2) Å].11 In contrast, the internal P–Se–P
angles in 3 (77.7 and 76.0° for each molecule in the unit cell) are
substantially decreased when compared with corresponding
angle in the planar PSePSe heterocycle 6 (85.5°).11 The shortest
intermolecular contacts in 3 are 3.59 Å [Se(1)…Se(2)].
31P{1H} NMR examination of the mixture after the reaction
did not show any reasonably intense signals at lower field,
assignable to related five-membered heterocycle 10. The
31P{1H} NMR spectrum of 3 comprises of a singlet (dP 52, in
CDCl3) with two symmetric sets of selenium satellites of AXXA
(Seexo) and AX2 (Seendo) pattern (A = 77Se, X = P). The
simulation of the AXXA satellite subspectrum enabled determi-
nation of a homonuclear P–P coupling, whose magnitude is
surprisingly low [2J(PP) < 2 Hz].12 The 1H NMR spectrum of
3 (CDCl3, 25 °C) shows a second-order A3B3XXA pattern (A, B
6
31P{1H} NMR examination of the reaction mixture before recrystallisa-
tion indicated presence of two side products 4 (s, dP 17.3) and 5 (s, dP
29.8). Full spectral and structural characterisation of 5 is the subject of
our continuating studies. Compound 1 is soluble in dichloromethane and
toluene, correct C, H microanalysis were obtained; mp 153–155 °C; MS
(EI, sampled neat) 358 (M+, base peak), 326 (M 2 S), 294 (M 2 2S),
262 (M 2 3S); IR (KBr disc) 769 cm21 (vs, nPNS).
7 Crystal data: for 1: C13H12P2S4, M = 358.41, space group P21/c,
monoclinic, a = 9.8833(6), b = 8.8370(5), c = 18.375(1) Å, b =
94.948(1)°, U = 1598.9(2) Å3, T = 293 K, Z = 4, m(Mo-Ka) = 0.777
mm21, 6688 reflections measured, 2276 unique (Rint = 0.0121) which
were used in all calculations. The final R was 0.0228 for I > 2s(I) and
wR(F2) was 0.0649 for all data. For 2: C13H12P2Se4, M = 546.01,
monoclinic, space group P21/c, a = 10.016(1), b = 8.9836(5), c =
18.677(5) Å, b = 93.687(1)°, U = 1677.2(5) Å3, T = 293 K, Z = 4,
m(Mo-Ka) = 8.924 mm21, 9054 reflections measured, 3481 unique
(Rint = 0.1376) which were used in all calculations. The final R was
0.0632 for I > 2s(I) and wR(F2) was 0.1677 for all data. For 3:
C15H16P2Se3, M = 495.10, orthorhombic, space group Pna21, a =
17.7582(3), b = 27.4561(2), c = 7.1512(1) Å, U = 3486.72(8) Å3, T
=
293 K, Z
=
8, m(Mo-Ka)
=
6.501 mm21, 14916 reflections
0.0522) which were used in all
measured, 4885 unique (Rint
=
calculations. The final R was 0.0347 for I > 2s(I) and wR(F2) was
0.0876 for all data. CCDC reference numbers 169264–169266. See
http://www.rsc.org/suppdata/cc/b1/b107214e/ for crystallographic data
in CIF or other electronic format.
8 The identity of by-products 7 and 8 has been established by single
crystal X-ray structure analyses and NMR, their details together with
their rational syntheses and NMR spectra will be published elsewhere.
Compound 2 is only slightly soluble in cold dichloromethane and
toluene. It is stable under dry nitrogen atmosphere, on exposition to air
it decomposes with deposition of a red selenium. Recrystallised product
gave correct C, H microanalysis; mp decomp. above 180 °C; MS (EI,
sampled neat) 546 (M+), 468 (M 2 Se + 1); IR (KBr disc) 555 cm21 (s,
nPNSe).
1
3
9 Further selected NMR data for 2: J(PSeexo
)
775 Hz, J(PSeexo
) 11
Hz, 1J(PSeendo 342 Hz, 2J(PSeendo
)
)
13 Hz. Magnitudes of 1J(PSe)
coupling constants have been confirmed by measurement of 77Se NMR
spectra of 2; d(77Se) 2114 (d, Seexo) and 494 ppm (d, Seendo); 1H NMR:
d 4.4 [t, CH2, 2J(HP) 9.2 Hz]; 13C{1H} NMR: d 52.2 [t, CH2, 1J(CP)
27.3 Hz].
10 Compound 3 is stable under N2 atmosphere, it is well soluble in
dichloromethane and toluene. Correct C, H microanalysis were ob-
tained; mp 211–214 °C; MS (EI, sampled neat) 496 (M+); IR (KBr disc)
553 cm21 (m, nPNSe).
Fig. 2 Structure of one of the two independent molecules present in unit cell
of 3. H atoms omitted for clarity. Selected bond lengths (Å) and angles (°)
for the molecule with less folded central heterocycle: P(1)–C(1) 1.915(7),
P(2)–C(1) 1.910(6), P(1)–Se(1) 2.279(2), P(2)–Se(1) 2.283(2), P(1)–C(4)
1.825(7), P(2)–C(10) 1.817(7), P(1)–Se(3) 2.096(2), P(2)–Se(2) 2.101(2),
P(1)–C(1)–P(2) 96.9(3), P(1)–Se(1)–P(2) 77.73(7), Se(1)–P(1)–C(1) and
Se(1)–P(2)–C(1) 91.4(2), C(1)–P(1)–Se(3) 114.4(2), C(1)–P(2)–Se(2)
115.1(2), C(1)–P(1)–C(4) 110.2(3), C(1)P(2)–C(10) 108.9(3), C(4)–P(1)–
Se(3) 112.3(2), C(10)–P(2)–Se(2) 113.0(3), Se(1)–P(1)–C(4) 109.0(2),
Se(1)–P(2)–C(10) 107.5(3), Se(1)–P(1)–Se(3) 117.70(9), Se(1)–P(2)–Se(2)
118.74(9), C(2)–C(1)–C(3) 113.2(6). For parameters of second molecule in
the independent unit see crystallographic data in CIF format.
11 P. Bhattacharyya, A. M. Z. Slawin and J. D. Woollins, J. Chem. Soc.
Dalton Trans., 2001, 300.
12 Further selected NMR data for 3: 1J(PSeexo
) ) 243
804 Hz, 1J(PSeendo
Hz, inner lines of AXXA subspectrum were hidden under intensive
central line, prohibiting determination of 3J(PSeexo) coupling. Magni-
1
tudes of J(PSe) coupling constants have been confirmed by measure-
ment of 77Se NMR spectra of 3; d(77Se) 296 (d, Seexo) and 506 (t,
1
Seendo); H NMR: d 1.2–1.5 (m, 2 3 CH3); 13C{1H} NMR: d 63.2 [t,
CP2, 1J(CP) 29.3 Hz], 26.8 (s, 2 3 CH3).
Chem. Commun., 2001, 2288–2289
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