Reaction of tertiary phosphine selenides, R3PSe (R = Me2N, Et2N or C6H11), with dibromine. The first reported examples of 1:1 addition

Article abstract of DOI:10.1039/a807892k

The R₃PSeBr₂ compounds (R = Me₂N, Et₂N or C₆H₁₁) have been prepared and characterised by ³¹P-{H} and infrared spectroscopy. The compounds R₃PSeBr₂ (R = Me

Full text of DOI:10.1039/a807892k

View Article Online / Journal Homepage / Table of Contents for this issue
Reaction of tertiary phosphine selenides, R3PSe (R ؍ Me2N, Et2N
or C6H11), with dibromine. The first reported examples of 1:1
addition
Stephen M. Godfrey, Sheena L. Jackson, Charles A. McAuliffe and Robin G. Pritchard
Department of Chemistry, University of Manchester Institute of Science and Technology,
Manchester, UK M60 1QD
Received 12th October 1998, Accepted 26th October 1998
The R3PSeBr2 compounds (R = Me2N, Et2N or C6H11) have been prepared and characterised by 31P-{H} and infrared
spectroscopy. The compounds R3PSeBr2 (R = Me2N or C6H11) have also been crystallographically characterised. In
contrast to the analogous diiodo compounds R3PSeI2 (which have a molecular Ψ-tetrahedral charge-transfer
structure, R3PSeI–I), the R3PSeBr2 compounds adopt Ψ-trigonal bipyramids at the selenium centre (taking account
of the stereochemically active lone pairs). The crystal structure of (Me2N)3PSeBr2 exhibits very different d(Se–Br),
2.602(2) and 2.544(2) Å. This phenomenon is reasoned to be due to the fact that both staggered and eclipsed Se–Br
bonds are observed in the structure. The crystal structure of (C6H11)3PSeBr2 shows two crystallographically
independent molecules in the asymmetric unit, d(Se–Br) being identical in one molecule, 2.568(3) and 2.566(3) Å, but
significantly different in the second molecule, 2.591(3) and 2.556(3) Å. A possible explanation for this is the presence
of a close non-bonded Br ؒ ؒ ؒ Br contact in this second (C6H11)3PSeBr2 molecule. The compounds R3PSeBr2
(R = Me2N or C6H11) both exhibit P–Se bonds typical of those expected for single bonds, 2.262(2) and 2.263(2)
average, respectively, again in contrast to the analogous diiodo compounds, R3PSeI2, in which significant P–Se double
bond character was retained. The 31P-{H} NMR and infrared spectroscopic data for R3PSeBr2 (R = Me2N, Et2N or
C6H11) are discussed with respect to those of the parent tertiary phosphine selenide, R3PSe.
an analogous phenomenon being observed by us5 for the
compound Ph3PSeI2, in which significant retention of
Introduction
The nature of compounds formed between tertiary phosphine
selenides and dihalogens has received only limited study.
Spectroscopic studies by Zingaro and Meyers1,2 concerning the
reaction of Ph3PSe with diiodine or iodine monobromide
point to the formation of a stable 1:1 adduct of formula Ph3P-
SeX2 (X2 = I2 or IBr). In contrast, the stoichiometric reaction
of diiodine with triphenylphosphine sulfide produced an
unexpected compound of formula 2Ph3PSؒ3I2. An X-ray crys-
tallographic study of this molecule,3 the first reported crystallo-
graphic study of a compound formed from the interaction of
R3PS with dihalogens, revealed an interesting dimeric structure
where two Ph3PSI2 moieties are linked into pairs by a diiodine
molecule. The d(I–I) for the I2 is significantly lengthened
[2.85(1) Å compared to d(I–I) for solid diiodine, 2.71(1) Å],
indicating that electron density is being donated to the σ* anti-
bonding orbitals of the diiodine by the two Ph3PSI2 moieties.
The d(I–I) between the terminal iodide atoms on the Ph3PSI2
moieties and the diiodine molecule are 3.57(1) Å, constituting
long but significant I–I interactions when compared to the van
der Waals radius for two iodine atoms (4.3 Å). From this obser-
vation, and the fact that lengthening of the d(I–I) for the di-
iodine molecule is observed, it would appear that the donor
power of Ph3PS towards diiodine is not sufficiently strong to
form a stable 1:1 adduct3 and that a further Ph3PS moiety and
a diiodine molecule are required to form a stable adduct.
phosphorus–selenium double bond character is observed. In
fact the structural features of Ph3PSI2 are generally very similar
to those exhibited by Ph3PSeI2. One notable difference between
Ph3PEI2 (E = S or Se) is the difference in iodine–iodine bond
lengths, d(I–I) for Ph3PSI2 and Ph3PSeI2 being 2.823(1) and
2.881(3) Å respectively. These differences reflect the fact that the
selenium atom in Ph3PSe is a better donor towards diiodine
than the sulfur atom in Ph3PS, as expected. Nevertheless, des-
pite the poorer donor ability of Ph3PS towards diiodine it is still
able to form a 1:1 complex, Ph3PSI2, which is contrary to the
conclusions of previous workers.
Until recently, no X-ray crystallographic data were available
for any tertiary phosphine selenide dihalogen compounds, how-
ever in 1996 we5 investigated the structural nature of the di-
iodide adducts, R3PSeI2 (R = Ph, Me2N or Et2N). All such
compounds were shown to be charge-transfer, R3PSe–I–I, com-
plexes. The d(I–I) was found to be dependent on R, 2.881(2),
2.962(2) (average) and 2.985(2) Å, for Ph3PSeI2, (Me2N)3PSeI2
and (Et2N)3PSeI2, respectively. These observations clearly illus-
trate that d(I–I) is sensitive to the basicity of the parent ter-
tiary phosphine,4 despite the fact that the R groups are bound
to the phosphorus atom and not to the donor selenium atom.5
There are no reports concerning the reaction of any tertiary
phosphine selenide with the lighter halogens.
We are currently engaged in a study of the interaction of
organogroup 15 and 16 donor atoms with dihalogens. We have
found that the nature of the products formed are dependent on
three variables: the organo substituents resident on the Group
15 or 16 donor atom, the donor atom itself, and the dihalogen
employed. For example, triphenylarsine–diiodine is a molecular
charge transfer compound Ph3As–I–I, whereas triphenylarsine
dibromide is trigonal bipyramidal.6 Our studies on the analo-
gous Group 16 systems, R2SeX2, have similarly shown that
However, very recently Bricklebank and co-workers4
reported the single crystal structure of the 1:1 adduct Ph3PSI2,
clearly illustrating that triphenylphosphine sulfide is able to
form a charge-transfer complex with diiodine. The crystal struc-
ture reveals approximately tetrahedral geometry for the phos-
phorus atom and Ψ-tetrahedral geometry for the sulfur atom;
d(P–S) for the complex, 1.998(2) Å, is rather short suggesting
some retention of phosphorus–sulfur double bond character,
J. Chem. Soc., Dalton Trans., 1998, 4201–4204
4201

View Article Online
Table 1 Analytical and 31P-{H} NMR and infrared spectroscopic data for the compounds R3PSe and R3PSeBr2 (R = Me2N, Et2N or C6H11)
% Elemental analysis: Found (Calc.)
Compound
Colour
C
H
N
Br
δ(31P-{H})a
ν(P–Se)/cmϪ1
(Me2N)3PSe
(Me2N)3PSeBr2
(Et2N)3PSe
(Et2N)3PSeBr2
(C6H11)3PSeb
(C6H11)3PSeBr2
White
Yellow
White
Yellow
White
Yellow
29.6(29.8)
17.7(17.9)
43.8(44.1)
29.8(29.6)
60.4(60.2)
41.5(41.6)
7.4(7.4)
17.2(17.4)
10.1(10.4)
12.8(12.9)
7.0(7.2)
—
—
83.2
66.1
77.1
66.1
59.0
56.7
530
504
553
517
550
517
4.2(4.5)
9.4(9.2)
29.8(29.6)
9.0(9.2)
6.5(6.4)
40.4(39.8)
—
32.8(32.9)
—
—
30.4(30.8)
a Shifts recorded in CDCl3 solution, relative to concentrated phosphoric acid as standard. b Selenium analysis 22.2(22.0)%.
Table 2 Selected bond lengths (Å) and angles (Њ) for (Me2N)3PSeBr2
Me2SeI2 adopts a molecular three-co-ordinate charge-transfer
structure, Me2Se–I–I, whereas the adducts with the lighter
halogens (Cl, Br) adopt a Ψ-trigonal bipyramidal structure.7
Finally, we have also shown that the solvent of preparation for
these compounds is of importance; for example, we treated
equimolar quantities of triphenylphosphine and dichlorine in
dichloromethane solution and crystallographically character-
ised8 the product as the solvated dinuclear ionic species [Ph3P-
Cl ؒ ؒ ؒ Cl ؒ ؒ ؒ ClPPh3]Clؒ2CH2Cl2; however, the same reaction
performed in diethyl ether solution produces the non-solvated
molecular trigonal bipyramidal species, Ph3PCl2.9 We were,
therefore, interested structurally to characterise the products
formed from the reaction of tertiary phosphine selenides and
dibromine, for three reasons: first, there are no reports concern-
ing such reactions,5 secondly to determine if changes in the R
groups on a given tertiary phosphine selenide affect the nature
of any product(s) formed upon reaction with dibromine and
finally to investigate whether tertiary phosphine selenide–
dibromine compounds adopt a structure analogous to that of
the corresponding diiodine compounds, viz. the charge transfer
structure, R3PSeX–X, or whether a different structure would be
revealed.
Br(1)–Se(1)
Br(2)–Se(1)
2.602(2)
2.544(2)
Se(1)–P(1)
2.262(2)
P(1)–Se(1)–Br(2)
P(1)–Se(1)–Br(1)
Br(2)–Se(1)–Br(1) 174.60(6)
95.46(8)
89.83(8)
N(1)–P(1)–Se(1)
N(3)–P(1)–Se(1)
N(2)–P(1)–Se(1)
107.4(3)
108.9(3)
113.7(3)
Results and discussion
Fig. 1 Crystal structure of (Me2N)3PSeBr2.
Analytical and spectroscopic data for the tertiary phosphine
selenides, and their 1:1 addition compounds with dibromine,
are displayed in Table 1. The tertiary phosphine selenides were
easily prepared from the direct reaction of tertiary phosphine
with elemental selenium at room temperature (r.t.) in diethyl
ether according to literature methods.10 The reaction time was
approximately 1 d to yield quantitatively the air stable R3PSe
compound which was isolated by filtration. After drying under
vacuum for ca. 1 d, the tertiary phosphine selenides were
treated with dibromine in a 1:1 stoichiometric ratio under
anhydrous conditions according to eqn. (1).
for analysis by single crystal X-ray diffraction. The structure of
(Me2N)3PSeBr2 is illustrated in Fig. 1, and selected bond
lengths and angles are given in Table 2. This represents the first
report of a tertiary phosphine selenide–dibromine compound
and clearly establishes that R3PSeX2 (X = Br or I) compounds
are geometrically dependent on X at the selenium centre. In
(Me2N)3PSeBr2 the geometry at selenium is T-shaped or
approximately trigonal bipyramidal (taking account of the
stereochemically active lone pairs on the selenium atom,
VSEPR model). In contrast, we previously reported5 the crystal
structure of (Me2N)3PSeI–I, which exhibited a charge-transfer
structure, i.e. containing a lengthened but unbroken I–I bond
and bent or approximately tetrahedral geometry for the selen-
ium atom (again taking account of the stereochemically active
lone pairs on the selenium centre, VSEPR model). It was also
noted for (Me2N)3PSeI2 that significant phosphorus–selenium
double bond character was retained, d(P–Se) = 2.180(7) Å com-
pared to 2.24(1) Å for a typical phosphorus–selenium single
bond. In contrast, for (Me2N)3PSeBr2, it would appear that
any P–Se double bond character formally present in the parent
tertiary phosphine selenide is destroyed, since for this com-
pound d(P–Se), 2.262(2) Å, falls within the range expected for a
P–Se single bond. Another feature of (Me2N)3PSeBr2 worthy of
note is the large difference in the two Se–Br distances, 2.602(2)
and 2.544(2) Å. A closer inspection of the structure offers a
possible explanation. One of the Se–Br bonds almost eclipses
an NMe2 group [N(2)–P(1)–Se(1)–Br(2) Ϫ13.3Њ]; the effect of
this is that the N(2)–P(1)–Se(1) and P(1)–Se(1)–Br(2) angles are
opened up to 113.7 and 95.5Њ respectively compared to the
angles associated with the staggered Se–Br bond; N(1)–P(1)–
N2, ca. 2 d
(1)
R3PSe ϩ Br2
R3PSeBr2
Et2O, r.t.
(R = Me2N, Et2N or C6H11)
All of the compounds were isolated in quantitative yield. In
direct contrast to the analogous diiodo compounds, R3PSeI2
(R = Me2N, Et2N or Ph), which were found to be stable towards
air and moisture,5 the dibromo compounds, R3PSeBr2,
described herein proved to be quite sensitive to moisture,
decomposing in less than an hour if exposed to the atmosphere.
Consequently anaerobic conditions were adhered to through-
out (see Experimental section). This observation alone perhaps
suggests a different solid-state structure for R3PSeBr2 com-
pounds compared to R3PSeI2. In order to investigate this
possibility, we decided crystallographically to characterise
(Me2N)3PSeBr2. Recrystallisation of this yellow powder from
diethyl ether–dichloromethane (1:1) solution at 50 ЊC pro-
duced a large quantity of yellow-orange crystals on standing at
room temperature for ca. 3 d. From these a crystal was chosen
4202
J. Chem. Soc., Dalton Trans., 1998, 4201–4204

View Article Online
Table 3 Selected bond lengths (Å) and angles (Њ) for (C6H11)3PSeBr2
Although no compound of formula R3PSeBr2 has previously
been reported, a few related R2SeBr2 compounds have been
studied by single crystal X-ray diffraction.7,11,12 The Se–Br bond
lengths for these compounds are similar to or a little shorter
than those in the R3PSeBr2 compounds described herein [e.g.
d (Se–Br) for Me2SeBr2 = 2.546(4) and 2.551(4) Å].7 The change
in structure of R3PSeX2 compounds (X = Br or I) from a
molecular charge-transfer structure, R3PSeI–I, to a Ψ-trigonal
bipyramidal structure, R3PSeBr2, upon changing the halogen
complements studies concerning organogroup 15 and 16
dihalogen adducts previously reported. For example, Me2SeI2 is
a charge-transfer compound, Me2SeI–I, whereas Me2SeBr2 is
Ψ-trigonal bipyramidal.7 Similarly Ph3AsI2 adopts the charge-
transfer structure but Ph3AsBr2 is trigonal bipyramidal.6
The loss of double bond character for the R3PSe compounds
upon reaction with dibromine is clearly illustrated from their
infrared spectra, a shift to lower energy of 25–30 cmϪ1 being
observed for the compounds R3PSe after reaction with dibro-
mine, Table 1. The 31P-{H} NMR results indicate that δ values
for R3PSe are shifted upfield upon reaction with dibromine,
although the effect is slight for (C6H11)3PSe and (C6H11)3PSeBr2
(δ 59.0 and 56.7, respectively).
Br(1)–Se(1)
Br(2)–Se(1)
Br(3)–Se(2)
2.568(3)
2.566(3)
2.591(3)
Br(4)–Se(2)
Se(1)–P(2)
Se(2)–P(1)
2.556(3)
2.271(6)
2.254(6)
P(2)–Se(1)–Br(2)
P(2)–Se(1)–Br(1)
Br(2)–Se(1)–Br(1) 169.1(1)
94.5(1)
95.6(1)
P(1)–Se(2)–Br(4)
P(1)–Se(2)–Br(3)
Br(4)–Se(2)–Br(3) 169.2(1)
95.3(1)
94.8(1)
Conclusion
The synthesis and characterisation of R3PSeBr2 (R = Me2N,
Et2N or C6H11) is reported for the first time. The solid state
structure of these materials is revealed to be T-shaped or Ψ-
trigonal bipyramidal which is in contrast to that of the analo-
gous R3PSeI2, previously reported,5 which are charge-transfer
species, R3PSeI–I, and contain bent or Ψ-tetrahedral selenium
atoms (both geometries take account of the stereochemically
active lone pairs present at the selenium centre). The geo-
metrical dependence of the selenium atom in R3PSeX2 upon X
(X = Br or I) is therefore clearly established. It has previously
been shown that reaction of R3PSe with I2 results in the charge-
transfer adduct R3PSeI–I in which the parent tertiary phos-
phine selenide retains significant phosphorus–selenium double
bond character (the P–Se bond distances being intermediate
Fig. 2 Crystal structure of (C6H11)3PSeBr2 (two independent mol-
ecules are present in the asymmetric unit, hydrogen atoms are omitted
for clarity).
Se(1)–Br(1) 46.6, N(1)–P(1)–Se(1) 10.7.4, P(1)–Se(1)–Br(1)
89.8Њ. Consequently a significant shortening of the sterically
congested Se(1)–Br(2) bond is observed, 2.544(2) Å, compared
to the staggered Se(1)–Br(1) bond, 2.602(2) Å.
In order to compare the structural features of (MeN)3PSeBr2
with those of another R3PSeBr2 compound, we decided crystal-
lographically to characterise (C6H11)3PSeBr2. Single crystals of
this material were grown in an identical way to that described
for (Me2N)3PSeBr2. The crystal structure of (C6H11)3PSeBr2
is illustrated in Fig. 2. Selected bond lengths and angles are
displayed in Table 3. In common with (Me2N)3PSeBr2,
(C6H11)3PSeBr2 also adopts a T-shape or Ψ-trigonal bipyram-
idal geometry for the selenium atoms (two crystallographically
independent molecules are present in the asymmetric unit). The
phosphorus–selenium distances again fall within the range
expected for single bonds, 2.271(6) and 2.254(6) Å, with no
evidence for any retention of double bond character. The
selenium–bromine bond distances for (C6H11)3PSeBr2 show less
variation compared to those exhibited by (Me2N)3PSeBr2. In
one molecule of (C6H11)3PSeBr2, d(Se–Br) are identical,
2.568(3) and 2.566(3) Å, however a significant difference is
observed in the second molecule [d(Se–Br) = 2.591(3) and
2.556(3) Å]. Again a closer look at the crystal structure provides
a possible explanation.
The asymmetric unit of (C6H11)3PSeBr2 is composed of two
molecules related by a non-crystallographic inversion centre,
each molecule being bisected by an approximate mirror plane
through the phosphorus and selenium atoms as well as one of
the cyclohexyl rings. Despite the similarity between the two
molecules, their crystal packing differs considerably, with one
molecule exhibiting a relatively short Br ؒ ؒ ؒ Br non-bonded
contact [Br(4) ؒ ؒ ؒ Br(4Ј) 3.615(3) Å; where Ј denotes Ϫx, 1 Ϫ y,
1 Ϫ z; van der Waals radius for two bromine atoms = 3.9 Å].
This phenomenon, which is not observed in the other molecule
of (C6H11)3PSeBr2 (which exhibits identical Se–Br bonds), may
be responsible for the asymmetric Se–Br bonds illustrated in
this molecule of (C6H11)3PSeBr2.
between typical single P–Se and double P᎐Se bond lengths).
᎐
This phenomenon is not observed for R3PSeBr2, the P–Se bond
lengths falling in the range expected for a typical P–Se single
bond. The 31P-{H} NMR and infrared data for the compounds
are also described, the first such data on a compound of
formula R3PSeBr2, the latter illustrating the downfield shift
of ν(P–Se) upon co-ordination of dibromine, as expected.
The 31P-{H} NMR resonances illustrate a downfield shift for
R3PSeBr2 compared to the parent R3PSe for a given R group.
Experimental
The compounds R3PSe were easily prepared from the direct
reaction of commercially obtained R3P (R = Me2N, Et2N or
C6H11) (Aldrich) and elemental selenium. Reaction time was
approximately 1 d. The dibromine adducts, R3PSeBr2, are mois-
ture sensitive, consequently strictly anaerobic and anhydrous
conditions were employed for their synthesis. Any subsequent
manipulations were carried out inside a Vacuum Atmospheres
HE-493 glove-box. Diethyl ether (BDH) was dried by stand-
ing over sodium wire for ca. 1 d, refluxed over CaH2 in an
inert atmosphere and distilled directly into the reaction vessel.
Anhydrous CH2Cl2 was obtained commercially and used as
received, as was dibromine.
The R3PSeBr2 compounds described were synthesized in the
same way, that of (C6H11)3PSeBr2 being typical. Tricyclohexyl-
phosphine selenide (2.00 g, 5.57 mmol) was suspended in Et2O
(ca. 75 cm3) and subsequently dibromine (0.89 g, 0.29 cm3, 5.57
mmol) was added. After ca. 2 d the resultant yellow solid was
isolated using standard Schlenk techniques. The solids were
J. Chem. Soc., Dalton Trans., 1998, 4201–4204
4203

View Article Online
Table 4 Crystal data and details of refinement for R3PSeBr2 (R =
CAD4 diffractometer employing graphite-monochromated
Mo-Kα radiation (λ = 0.71069 Å) and ω–2θ scans. Both struc-
tures were solved by direct methods. Unit-cell dimensions were
derived from the setting angles of 25 accurately centred reflec-
tions. Lorentz-polarisation corrections were applied. Details of
the X-ray measurements and subsequent structure determin-
ations are presented in Table 4. Hydrogen atoms were confined
to chemically reasonable positions. Neutral atom scattering
factors were taken from ref. 13, anomalous dispersion effects
from ref. 14. The structure determinations were performed
using SHELXS 8615a and the refinement based on F2 by using
SHELXL 9315b crystallographic software packages.
Me2N or C6H11)
(Me2N)3PSeBr2
C6H18Br2N3PSe
(C6H11)3PSeBr2
C36H66Br4P2Se2
Formula
M
401.98
1038.39
Monoclinic
P21/n (no. 14)
12.432(5)
18.716(7)
17.788(6)
96.86(3)
4109(3)
146(2)
Crystal system
Space group
a/Å
b/Å
c/Å
Monoclinic
P21/n (no. 14)
8.151(1)
13.585(2)
12.619(3)
97.90(2)
1384.1(4)
293(2)
β/Њ
U/Å3
CCDC reference number 186/1216.
T/K
Z
4
4
Dc/g cmϪ3
1.929
1.678
Acknowledgements
We are grateful to the EPSRC for a research studentship to
S. L. J.
F(000)
776
85.71
0.63, 0.93
2080
57.91
0.72, 0.98
µ/cmϪ1
Maximum, minimum
transmission
Crystal size/mm
Maximum 2θ/Њ
Total data measured
No. unique reflections
No. observed reflections
[I > 2.00σ(I)]
No. parameters
Largest difference peak and
hole/e Å3
0.3 × 0.1 × 0.1
49.92
2596
2424
1500
[R(int) 0.073]
122
1.027 and Ϫ1.012
0.35 × 0.3 × 0.25
50.0
5959
5307
1869
[R(int) 0.081]
217
References
1 R. A. Zingaro and E. A. Meyers, Inorg. Chem., 1962, 4, 771.
2 R. A. Zingaro, Inorg. Chem., 1963, 5, 192.
3 W. W. Schweikert and E. A. Meyers, J. Phys. Chem., 1968, 5, 1561.
4 D. C. Apperley, N. Bricklebank, S. L. Burns, D. E. Hibb, M. B.
Hursthouse and K. M. A. Malik, J. Chem. Soc., Dalton Trans.,
1998, 1289.
0.678 and Ϫ0.657
Final R indices [I > 2σ(I)]
(all data)
0.0659, 0.1685
0.1208, 0.1947
0.0842, 0.1154
0.2611, 0.1641
5 S. M. Godfrey, S. L. Jackson, C. A. McAuliffe and R. G. Pritchard,
J. Chem. Soc., Dalton Trans., 1996, 4499.
6 N. Bricklebank, S. M. Godfrey, C. A. McAuliffe, R. G. Pritchard
and J. M. Moreno, J. Chem. Soc., Dalton Trans., 1995, 3873.
7 S. M. Godfrey, C. A. McAuliffe, R. G. Pritchard and S. Sarwar,
J. Chem. Soc., Dalton Trans., 1997, 1031.
8 S. M. Godfrey, C. A. McAuliffe, R. G. Pritchard and J. M. Sheffield,
Chem. Commun., 1996, 2521.
9 S. M. Godfrey, C. A. McAuliffe, R. G. Pritchard and J. M. Sheffield,
Chem. Commun., 1998, 921.
10 W. Tefteller and R. A. Zingaro, Inorg. Chem., 1966, 5, 2151; D. W.
Allen and B. F. Taylor, J. Chem. Soc., Dalton Trans., 1982, 51.
11 J. D. McCullough and G. Hamburger, J. Am. Chem. Soc., 1941, 63,
303.
then transferred to predried argon-filled ampoules which were
flame sealed.
Elemental analyses were performed by the analytical lab-
oratory of this department. The 31P-{H} NMR spectra were
recorded as CDCl3 solutions on a Bruker AC200 high
resolution multiprobe spectrometer relative to concentrated
phosphoric acid as standard, infrared spectra on a Nicolet 5PC
Fourier transform spectrometer.
12 S. Akabori, Y. Takanohashi, S. Aoki and S. Sato, J. Chem. Soc.,
Perkin Trans. 1, 1991 3121.
Crystallography
13 International Tables for X-Ray Crystallography, Kynoch Press,
Birmingham, 1974, vol. 4, Table 2.2A.
14 International Tables For X-Ray Crystallography, Kynoch Press,
Birmingham, 1974, vol. 4, Table 2.3.1.
15 G. M. Sheldrick, (a) SHELXS 86, University of Göttingen, 1986;
(b) SHELXL 93, University of Göttingen, 1993.
Crystals of (Me2N)3PSeBr2 were mounted in Lindemann tubes
under an atmosphere of dry argon. Crystals of (C6H11)3PSeBr2
were submerged in an inert oil under anaerobic conditions and
a suitable one was chosen by examination under the micro-
scope. The crystal, with its protective coating of oil, was then
mounted on a glass fibre and transferred to the diffractometer
and cooled to 146(2) K in the cold gas stream derived from
liquid nitrogen. All measurements were performed on a MAC3
Paper 8/07892K
4204
J. Chem. Soc., Dalton Trans., 1998, 4201–4204