Synthesis and characterisation of four- and six-membered P-Se heterocycles

Article abstract of DOI:10.1039/b517093a

The preparation, spectroscopic characterisation and crystal structures of [FcP(-Se)Se]₂, [FcP(-Se₂)Se]₂ and [PhP(-Se ₂)Se]₂ are reported. Crystallographic data reveal planar four-membered PSePSe and skewed six-membered P₂Se₄ rings, respectively, in all cases with trans arrangement of organic substituents and exo selenium atoms. Whilst stable at room temperature in solid state, NMR data suggest the six-membered rings of both the ferrocenyl and phenyl compounds decompose in the solution with loss of red selenium, forming PSe₂PSe five-membered rings. The Royal Society of Chemistry 2006.

Full text of DOI:10.1039/b517093a

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PAPER
www.rsc.org/dalton | Dalton Transactions
Synthesis and characterisation of four- and six-membered P–Se heterocycles
Sahrah Parveen, Petr Kilian, Alexandra M. Z. Slawin and J. Derek Woollins*
Received 1st December 2005, Accepted 22nd February 2006
First published as an Advance Article on the web 8th March 2006
DOI: 10.1039/b517093a
The preparation, spectroscopic characterisation and crystal structures of [FcP(l-Se)Se]2,
[FcP(l-Se2)Se]2 and [PhP(l-Se2)Se]2 are reported. Crystallographic data reveal planar four-membered
PSePSe and skewed six-membered P2Se4 rings, respectively, in all cases with trans arrangement of
organic substituents and exo selenium atoms. Whilst stable at room temperature in solid state, NMR
data suggest the six-membered rings of both the ferrocenyl and phenyl compounds decompose in the
solution with loss of red selenium, forming PSe2PSe five-membered rings.
Here we report the preparation of [FcP(l-Se)Se]2 5 (Fc =
ferrocenyl), and the selenium-rich six-membered heterocycles
[FcP(l-Se2)Se]2 6 and [PhP(l-Se2)Se]2 8.
Introduction
Amongst the many phosphorus–sulfur heterocycles is 2,4-
bis(p-methoxyphenyl)-1,3,2,4-diathiadiphosphetane 2,4-disulfide
(1, Lawesson’s Reagent) which has been extensively exploited as
a thionation reagent.1–3 In contrast to this thionation reagent, its
selenium analogue has not received as much attention though
compounds of this class are of interest as selenating agents.
Both ourselves and Karaghiosoff et al. have reported a series
of diselenadiphosphetane diselenides,4–10 including 2,4-diphenyl-
1,3,2,4-diselenadiphosphetane 2,4-diselenide 2 (also referred to
as Woollins’ Reagent).11 A handful of reports highlighting the
superior selenating abilities of 212–15 have appeared, though there is
still a need to extend this family of compounds not least to develop
more soluble analogues. Some time ago, we have also reported
a ferrocene analogue of Lawesson Reagent 1, 2,4-diferrocenyl-
1,3,2,4-diathiadiphosphetane 2,4-disulfide, 3.16
Experimental
Unless otherwise stated all manipulations were performed under
an oxygen-free nitrogen atmosphere, using standard Schlenk tech-
niques and glassware. Solvents were dried and stored according to
common procedures. Reagents were obtained from Aldrich and
used without further purification, Na2Se was prepared according
to the literature procedure.17 (PPh)n was prepared from PhPCl2
and Mg.18 Solution-state NMR spectra were recorded using a
JEOL GSX Delta 270 or Bruker Avance 300 spectrometer, solid-
state NMR spectra were obtained at the EPSRC solid-state NMR
service in Durham; IR spectra were recorded using KBr discs on
a Perkin-Elmer System 2000 FT spectrometer. Mass spectra were
recorded by both the National Service in Swansea and University
of St Andrews Mass Spectrometry Service. Microanalyses were
performed by the University of St. Andrews microanalysis service.
FcPCl2 (4)
An adaptation of the literature procedure was used.19 To a flask
containing ferrocene (18.6 g, 0.1 mmol) and aluminium chloride
(13.4 g, 0.1 mmol), in dry n-heptane (200 cm3), dimethylphos-
phoramidous dichloride (14.6 g, 0.1 mmol) in n-heptane (50 cm3)
was added slowly via a pressure equalised dropping funnel. Once
addition was complete the reaction mixture was left to reflux
for 3 h. After heating was ended and whilst still warm, the red
organic layer was decanted to a distillation flask under a nitrogen
atmosphere. Care was taken not to transfer any of the insoluble
dark red material. Volatiles from the organic phase were then
evaporated in vacuo to give an orange–red oil. This oil was further
purified by addition of 100 ml of n-heptane, the insoluble white
solids that precipitated were removed by filtration via a Celite
plug. The solvent was removed under reduced pressure to yield 4 as
orange–red oil. Yield 3.15g (10.9%). NMR(CDCl3): dH (270 MHz)
4.14 (2H, s, Fc substituted ring), 4.27 (5H, s, Fc unsubstituted
ring), 4.59 (2H, s, Fc substituted ring); dP (109.4 MHz) 165.3 (s);
dC (67.9 MHz) 67.9 (s, substituted Fc ring), 69.9 (s, unsubstituted
Fc ring), 71.0 [d, 1J(CP) = 21.8 Hz], 73.2 [d, 2J(CP) = 4.2 Hz].
Department of Chemistry, University of St Andrews, Fife, UK KY16 9ST.
E-mail: jdw3@st-and.ac.uk; Fax: +44-1334-463384
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[FcP(l-Se)Se]2 (5)
1172vs, 1105s, 1020br, 819s, 550vs (mP=Se), 484vs, 450vs; NMR
1
(for numbering of atoms see Scheme 2): 31P{ H} (109.4 MHz) in
4 (1.1 g, 3.8 mmol) dissolved in toluene (10 cm3) was added to
Na2Se (0.48 g, 3.8 mmol) suspended in toluene (15 cm3). To this
mixture was added a portion of grey selenium powder (0.31 g,
3.8 mmol) and the mixture was heated under reflux for 12 h.
After this initial reflux, the mixture was hot-filtered to remove the
sodium chloride by-product formed during the reaction. To the
resulting filtrate a second portion of grey selenium powder (0.06 g,
0.7 mmol) was added and the reaction mixture was heated under
reflux for another 12 h, then the reaction mixture was hot filtered
for a second time, to remove any unreacted selenium. The solvent
from the deep red clear filtrate was then evaporated in vacuo to
give a red powder. Crystals of 4 were obtained by reducing the
solvent volume by a third, and storing the flask under a nitrogen
atmosphere in the fridge. Yield, 1.14 g (40%) C20H18Fe2P2Se4: calc.
C 32.12, H 2.42%; found C 33.25, H 2.39%; mp 192 ◦C (decomp.);
IR (KBr tablet, cm−1): m = 1202vs, 1128s 1106s, 1039s, 1012s, 943vs,
CDCl3 at 298 K d 35.0 (s, with selenium satellites), in CD2Cl2 at
213 K d 35.5 (s, PA), 35.9 (s, PB), each with selenium satellites,
2
2
1
1J(PASeA) = 755.5, J(PASeD) = J(PASeF) = 13.4, J(PASeE) =
1
2
2
1J(PASeC) = 400.3, J(PBSeB) = 757.1, J(PBSeC) = J(PBSeE) =
1
1
14.7, J(PBSeD) = J(PBSeF) = 396.3 Hz. MS (FAB, EI and CI):
all attempts to identify the parent peak were unsuccessful.
=
815m, 584vs (mP Se), 448vs; low solubility of sample prevented
Scheme 2
measurement of solution NMR spectra; solid-state NMR: 31P{ H}
1
(121.4, MHz) diso −16.2 ppm; 13C (75.4, MHz) diso 71.4 (s, Fc
unsubstituted ring), 83.7 (s, Fc substituted ring); MS (FAB, EI, CI
and ES): all attempts to identify the parent peak were unsuccessful,
however low mass peaks that could be identified were at m/z 186
(C10H9Fe) and 157.8 (Se2).
1
Solid state NMR: 31P{ H} (121.4, MHz) diso 35.9 (s), 40.7 ppm
(s);13C (75.4, MHz) diso 71.7 (s, unsubstituted Fc ring), 78.7 ppm
(s, substituted Fc ring).
[FcP(l-Se)Se]2Se (7)
[FcP(l-Se2)Se]2 (6)
A five-membered ring 7 was observed by 31P NMR as a decom-
position product in the solution of 6, however it was not isolated.
NMR (subtracted from the mixture with 6, for numbering of atoms
4 (1.8 g, 6.3 mmol) was dissolved in toluene (30 cm3) before
addition to Na2Se (0.8 g, 6.3 mmol) suspended in toluene (30 cm3).
To this mixture an excess portion of selenium (0.8 g, 10 mmol)
was added and the solution was heated under reflux for 12–14 h.
The reaction mixture was filtered whilst still warm to remove salt
by-products. To the resulting filtrate a second excess portion of
selenium (0.8 g, 10 mmol) was added and the mixture was heated
under reflux for another 12 h. The solution was allowed to cool
enough to handle, then filtered to remove any unreacted selenium.
The deep red filtrate was maintained under a nitrogen atmosphere
and stored in the fridge. From this filtrate dark red prismatic
crystals were isolated by filtration and identified as 6. Yield 2.8 g
(49%). Found C, 29.06; H, 2.0. C20H18Fe2P2Se6 requires C, 29.8;
H, 2.3%; mp 180 ◦C (decomp.); IR (KBr tablet, cm−1): m = 1188s,
1
see Scheme 2): 31P{ H} (109.4 MHz, CDCl3, 298 K): d 49.8 (s) with
77Se satellites, analysis of 77Se subspectra gave, 1J(PASeA) = 758.4 =
1
1
1
1J(PBSeB) = 767.7, J(PASeE) = J(PBSeF) = 427.2, J(PASeC) =
1J(PBSeD) = 366.2, 2J(PAPB) = 28.2 Hz.
[PhP(l-Se2)Se]2 (8)
(PPh)n (mixture of oligomers, n = 4, 5 and 6) [2.0 g, 18.5 mmol
of ‘(PPh)’] and grey selenium powder (4.38 g, 55.5 mmol) in
toluene (40 cm3) were heated under reflux for 12 h. The resulting
suspension was hot-filtered, yielding a red solid (consisting of
major product 2 and unreacted selenium) and a clear red filtrate.
Dark red crystals of 8 precipitated from the filtrate after standing
for several days, they were filtered off, washed with cold toluene
and dried in vacuo. Yield 0.25 g (3.9%). Found C, 21.1; H, 1.1.
C12H10P2Se6 requires C, 20.9, H, 1.5%.; mp 146 ◦C (decomp.).
IR (KBr tablet, cm−1): m = 1433vs, 1081s, 742s, 683m, 527vs
(mP=Se), 483s. NMR (for numbering of atoms see Scheme 2):
1
31P{ H} (121.4 MHz, CD2Cl2) at 298 K d 40.6 (br s) and 43.0
(br s); at 203 K d 41.8 (s, PA) and 44.1 (s, PB) each with
two sets of 77Se satellites, analysis of satellite subspectra (see
Fig. 1) yielded 1J(PASeC) = 430.8, 2J(PASeD) = 2J(PASeF) =
1
1
1
24.7, J(PASeE) = 375.9, J(PASeA) = 764.8, J(PBSeD) = 422.9,
2J(PBSeC) = J(PBSeE) = 26.5, J(PBSeF) = 388.7, J(PBSeB) =
2
1
1
1
765.1 Hz; H (300.1 MHz, CDCl3, 298 K) d 7.55–7.70 (4H, m),
8.20–8.38 (6H, m). 77Se{ H} (57.2 MHz, CD2Cl2, 213 K, for
1
numbering of atoms see Scheme 2) d 570 (dd, SeF), 568 (dd,
SeC), 560 (dd, SeE), 460 (dd, SeD), −21 (d, SeA or SeB), −33 (d,
SeA or SeB). MS (EI+): m/z 612 (Ph2P2Se5), 534 (Ph2P2Se4), 454
(Ph2P2Se3), 426 (PhPSe4), 268 (PhPSe2), all peaks showed correct
isotopic patterns.
Scheme 1
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1
Fig. 2 Analysis of the 77Se satellites in the 31P{ H} NMR spectrum
of 9 (121.5 MHz, CDCl3 solution): (a) spectrum measured at 298 K;
(b) simulated spectrum, intense central line omitted to show the hidden
fine inner lines; * denotes impurity.
2
2J(PASeD) = J(PBSeC) ≈ 8 Hz. Determination of the magnitudes
of all long-range PSe couplings was not possible as the inner lines
of 77Se subspectra were hidden under an intense central line.
Fig. 1 31P{ H} NMR spectra of 8 and 6 (CD2Cl2 solutions): (a) spectrum
1
of 8 measured at 121.5 MHz, 203 K; (b) iteratively simulated spectrum of
Crystallography
1
8; (c) 31P{ H} NMR spectrum of 6 (109.4 MHz, 213 K).
Table 1 list details data collections and refinements, data (Mo ra-
diation) for 5 and 6 were collected at 93 K using a Rigaku MM007
high brilliance RA with Mercury and Saturn70 ccd detectors,
respectively, and for 8 at 293 K using a Bruker SMART (sealed
tube) system. Intensities were corrected for Lorentz-polarisation
and for absorption. The structures were solved by direct methods.
The positions of the hydrogen atoms were idealised. Refinements
were by full-matrix least squares based on F2 using SHELXTL.20
CCDC reference numbers 291575–291577.
[PhP(l-Se)Se]2Se (9)
9 was observed in solution by 31P{ H} NMR spectroscopy as a
1
decomposition product of 8 (Scheme 2), no attempts were made
to isolate it. NMR (subtracted from the mixture with 8, for
numbering of atoms see Scheme 2): 31P{ H} (121.4 MHz, CD2Cl2,
1
298 K) d 59.7 (s) with 77Se satellites, analysis of satellite subspectra
1
1
1
(see Fig. 2) yielded J(PASeC) = J(PBSeD) = 369, J(PASeE) =
For crystallographic data in CIF or other electronic format see
DOI: 10.1039/b517093a
2
1
1
1J(PBSeF) = 433, J(PAPB) = 31, J(PASeA) = J(PBSeB) = 769,
Table 1 Data collection and structural refinement parameters for 5, 6 and 8
Compound
5
6
8
Formula
M
C20H18Fe2P2Se4
747.82
93(2)
Monoclinic
P21/n
6.623(2)
12.720(4)
13.847(5)
90
94.470(12)
90
1162.9(7)
2
7.650
C20H18Fe2P2Se6.C7H8
997.88
93(2)
Triclinic
¯
P1
C12H10P2Se6
689.90
293(2)
Orthorhombic
P212121
6.622(1)
9.9780(1)
28.146(4)
90
90
90
1859.7(5)
4
11.964
T/K
Crystal system
Space group
˚
a/A
9.3608(9)
11.404(1)
14.390(1)
98.515(4)
90.548(5)
94.704(4)
1513.7(2)
2
8.296
2.189
4898 (0.0287)
1.0, 0.4820
0.0361, 0.0790
1.247, −0.995
˚
b/A
˚
c/A
a/◦
b/◦
c /◦
U/A
Z
3
˚
l(Mo-Ka)/mm−1
Dc/Mg m−3
2.136
2.464
Independent reflections (Rint
Max., min. transmission
Final R, Rꢀ
Max., min. Dq/e A
Flack parameter
)
1952 (0.0808)
1.0, 0.7626
0.0520, 0.0716
0.523, −0.644
2641 (0.1927)
1.0, 0.2427
0.0581, 0.0870
0.928, −0.874
0.01(3)
−3
˚
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˚
Results and discussion
distances are 3.1(1) and 3.3(1) A, respectively. These distances are,
as expected, marginally longer than those observed for the sulfur
analogue 3.
The reaction of ferrocene with dimethylphosphoramidous dichlo-
ride and aluminium chloride gives 4 as a red oil in low yield. This
compound has been previously reported by Sallot and Peterson,19
however in their report the compound was only characterised by
IR spectroscopy, here we report the 1H, 13C and 31P NMR data for
4.
Ring system 2 can be obtained by two different procedures;
either oxidation of (PhP)n (n = 4, 5 and 6) with elemental
selenium4 or reaction of PhPCl2 with Na2Se.10 To date, 211 is
the most selenium-rich heterocycle reported from either of these
methods. By minor modification to both of these methods we have
successfully isolated heterocycles which are more selenium rich
(Scheme 1). Here we report on the preparation for 5, 6 and 8 along
with their complete structural and spectroscopic characterisation.
Compound 8 has been briefly mentioned in a previous report from
us.21 Although obtained only as a minor product by synthesis
described here, the amount and purity of 8 was sufficient for its
full structural and spectral characterization.
Compound 6 was prepared following the same general pro-
cedure as 5, however, use of a larger volume of solvent and an
excess of grey selenium resulted in this selenium-rich heterocycle.
The product was isolated as deep red prismatic crystals from
toluene. The 31P{ H} NMR spectrum obtained after dissolving
1
these crystals in CDCl3 consists of a singlet at dP 35.9 with two sets
of 77Se satellites, also present is another singlet at dP 49.8 with its
own 77Se satellites (vide infra). Upon cooling to 213 K (in CD2Cl2)
the singlet at dP 35.5 resolves to two separate singlets at dP 35.5
and 35.9, with the satellites becoming more defined. Analysis of
the satellites confirmed the structure as that of 6, which was further
characterized by IR, solid-state NMR and microanalysis. All
attempts to obtain suitable mass spectra by various methods (EI,
CI, FAB and ES) were unsuccessful. The X-ray crystal structure
(Fig. 4, Table 3) reveals a central six-membered P2Se4 ring that
adopts a skewed chair conformation. Bond lengths and angles
are comparable with other P–Se heterocyclic systems,21 exocyclic
Compound 5 was formed in 40% yield by reaction of equimolar
amounts of 4 and Na2Se with excess of grey selenium powder
in toluene. Microanalysis is in good agreement with theoretical
values but poor solubility in cold solvents prevented measurement
of solution NMR; identification of the parent peak by various
methods of mass spectrometry was not possible. Solid-state 31P
NMR shows a singlet peak at d −16.2 ppm and in the 13C NMR
two peaks are visible which can be assigned to carbons atoms
in the cyclopentadienyl rings of the ferrocene group. The X-ray
crystal structure of 5 (Fig. 3, Table 2) shows that the molecule is
disposed about a crystallographic centre of symmetry; with the
bulky ferrocenyl groups oriented trans to one another; the bond
lengths and angles are normal and are comparable to those in
2 and 3.4,16 Within the four-membered ring the Se–P–Se angle is
94.18(6)◦ and the P–Se–P angle is 85.82(6)◦ whilst the ring P–
˚
=
P Se bonds are 2.094(1) and 2.103(1) A, whilst ring P–Se bond
˚
lengths are 2.254(1) and 2.283(1) A. The transannular P · · · P
˚
bond distance is 4.3(1) A. As was also the case for 5 and 3 the
cyclopentadienyl rings of the ferrocene groups in 6 are eclipsed.
˚
Se bond lengths are 2.2577(2) and 2.2889(2) A and the exocyclic
˚
=
P Se distance is 2.0957(2) A. The cyclopentadienyl rings of the
ferrocene group are eclipsed. The transannular P · · · P and Se · · · Se
Fig. 4 Crystal structure of 6, 3,6-diferrocenyl-1,2,4,5,3,6-tetraselenadi-
phosphorinane 3,6-diselenide; H atoms omitted for clarity.
◦
˚
Table 3 Selected bond lengths (A) and angles ( ) for compounds 6 and 8
6
8
Se(1)–P(1)
P(1)–Se(2)
2.094(1)
2.254(1)
2.298(1)
2.3329(7)
2.103(1)
2.282(1)
2.281(1)
2.3216(7)
2.100(4)
2.253(4)
2.299(4)
2.315(2)
2.099(4)
2.283(5)
2.245(4)
2.322(2)
P(1)–Se(13)
Se(2)–Se(3)
P(11)–Se(11)
P(11)–Se(12)
P(11)–Se(3)
Se(12)–Se(13)
Fig. 3 Crystal structure of 5, 2,4-diferrocenyl-1,3,2,4-diselenadiphos-
phetane 2,4-diselenide; H atoms omitted for clarity.
Se(1)–P(1)–Se(2)
104.98(6)
119.34(6)
106.52(5)
98.10(4)
99.32(4)
108.46(6)
117.78(6)
106.36(5)
97.09(4)
98.47(4)
104.11(6)
116.8(2)
109.1(1)
99.6(1)
102.2(1)
104.8(2)
120.4(2)
105.8(2)
101.3(1)
98.2(1)
Se(1)–P(1)–Se(13)
Se(2)–P(1)–Se(13)
P(1)–Se(2)–Se(3)
P(11)–Se(3)–Se(2)
Se(11)–P(11)–Se(3)
Se(11)–P(11)–Se(12)
Se(3)–P(11)–Se(12)
P(11)–Se(12)–Se(13)
P(1)–Se(13)–Se(12)
◦
˚
Table 2 Selected bond lengths (A) and angles ( ) for compound 5
Se(1)–P(1)
Se(2)–P(1A)
2.096(2)
2.289(2)
Se(2)–P(1)
P(1)–C(1)
2.258(2)
1.754(6)
P(1)–Se(2)–P(1A)
Se(1)–P(1)–Se(2A)
C(1)–P(1)–Se(1)
85.82(6)
115.51(7)
115.8(2)
Se(1)–P(1)–Se(2)
Se(2)–P(1)–Se(2A)
C(1)–P(1)–Se(2)
114.55(8)
94.18(6)
107.0(2)
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Over time it was found that 6 decomposes with the elimination of
red selenium to give the five-membered heterocycle 7. The presence
reported that the six-membered ring in [MeP(l-Se2)Se]2 was
unstable and decomposed to five- and four-membered rings,
[MeP(l-Se)Se]2Se and [MeP(l-Se)Se]2, respectively. Grossmann
et al. reported both solution and solid-state NMR data of two
triselenadiphospholanes [RP(l-Se)Se)2Se (R = Me, Et).23 In line
with our observations (on 6 and 8), the magnitude of long-range
3J(PP) coupling constant was small (3.2 Hz) in [MeP(l-Se2)]Se2.22
1
of this ring was confirmed by analysis of the 31P{ H} NMR
spectra, which showed a sharp singlet at dP 49.8 ppm, with 77Se
satellites (AAꢀX systems for SeA and SeB, other AAꢀX systems for
SeC and SeD, and A2X system for SeE, A and Aꢀ denote phosphorus
nuclei, X denotes 77Se nuclei, for atom numbering see Scheme 2).
This phenomenon was also observed for 8. The room temper-
1
In good agreement with our 31P{ H} spectra of both 7 and 9,
1
ature 31P{ H} spectrum of a solution of 8 taken shortly after its
the NMR signals of (MeP(l-Se)Se)2Se and (EtP(l-Se)Se)2Se23
both appear as singlets in solution, 2J(PP) magnitudes are 34 and
31 Hz, respectively, and also the magnitudes of other short-range
couplings are similar to those found in our compounds. It is worth
noting that the anisochronous nature of the two phosphorus atoms
in 6 and 8 is in contrast to isochronicity of phosphorus atoms in
the related six-membered ring compound (PPh)6 (s, dP −22).24 By
the way of contrast, the five-membered ring compound (PPh)5
shows a very complicated second-order pattern in 31P NMR as all
its phosphorus atoms are anisochronous.
preparation showed three signals: two broad singlets at dP 40.6
and 43.0, belonging to 8, and a sharp singlet at dP 59.7 with
three sets of selenium satellites, belonging to 9 (approx. 4% of
overall integral intensity). On cooling to 203 K, the signals of
8 become sharp singlets and their 77Se satellites become visible
(Fig. 1). The analysis of these confirmed the signals stem from
the six-membered heterocycle 8. The magnitudes of the J(PSe)
1
coupling read from 31P{ H} NMR were in good agreement with
1
these found from 77Se{ H} NMR spectra. Careful analysis reveals
that J(PP) approaches zero in 8, and that the spin systems of
the two phosphorus atoms are independent and the sub-spectra
from each isotopomer are first order (AMX spin systems for
endo selenium atoms, AX spin systems for exo selenium atoms).
Compound 8 was further characterized by 1H NMR, IR, EI-MS
and microanalyses and by X-ray diffraction (Fig. 5, Table 3) which
revealed it to be structurally closely similar to 6.
The new compounds described here illustrate the accessibility of
six-membered selenium-rich heterocycles in addition to the more
familiar four- and five-membered P–Se rings.
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Fig. 5 Crystal structure of 8, 3,6-diphenyl-1,2,4,5,3,6-tetraselenadi-
phosphorinane 3,6-diselenide); H atoms omitted for clarity.
Although significant amount of 8 was recovered as red crystals
from its solution in toluene on cooling, it decomposed partially
in solution to give the five-membered heterocycle 9 and elemental
selenium, which precipitated after a short time as a red film on
the walls of a vial (Scheme 2). The ring contraction process was
accelerated by heating, e.g. the 31P NMR spectrum taken after
short heating of solution 8 in CDCl3 to its boiling point showed
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1
ca. 30% integral intensity of 9. The 31P{ H} NMR spectrum of 9 at
19 G. P. Sollott and W. R. Peterson, Jr., J. Organomet. Chem., 1969, 19,
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room temperature consists of a sharp singlet at dP 59.7 ppm with
three sets of selenium satellites, AAꢀX systems for SeA and SeB,
another AAꢀX systems for SeC and SeD, and A2X system for SeE.
There are only two reports on ring systems closely related to
6–9 in the literature, Hahn and co-workers reported a series of
tetraselenadiphosphorinanes [RP(l-Se2)Se]2 and triselenadiphos-
pholanes [RP(l-Se)Se]2Se (R = Me, Ph, t-Bu).22 Only the basic
31P NMR data of methyl derivatives were listed, Hahn also
20 SHELXTL 6.1, Bruker AXS, Madison, WI, 2001.
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2001, 627, 1269–1278.
24 L. R. Smith and J. L. Mills, J. Am. Chem. Soc., 1976, 98, 3852–3857.
2590 | Dalton Trans., 2006, 2586–2590
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