The reactions of alkylamino substituted phosphines with I2 and (Ph2Se2I2)2: Structural features of alkylamino phosphonium cations

Article abstract of DOI:10.1039/b713640d

The reactions of the tris-dialkylamino phosphines (Et₂N) ₃P and (ⁿPr₂N)₃P, and the pyrrolidinyl substituted phosphines (C₄H₈N)₃P and ^tBuP(NC₄H₈)₂, with I₂ and (Ph₂Se₂I₂)₂, have been reported. The reactions with diiodine lead to the formation of [R ₃PI]I adducts, which are essentially ionic, but show a tendency to display long, soft-soft, II interactions in the solid state. The crystal structures of [(Et₂N)₃PI]I, (1), [(ⁿPr ₂N)₃PI]I, (2), and [(C₄H₈N) ₃PI]I, (3), have all been determined, and display II interactions varying between 3.5170(6) and 3.6389(14) . The analogous reactions with (Ph₂Se₂I₂)₂ lead to the formation of phenylseleno-phosphonium salts, [R₃PSePh]I. The structures of [(C₄H₈N)₃PSePh]I, (6) and [(C₄H₈N)₂^tBuPSePh] I, (7), have been determined and do not display any soft-soft interactions between the selenium and iodine atoms. All of the phosphonium salts represent examples of structures containing tris-dialkylamino phosphine fragments which show no "special" nitrogen atom, i.e. all three nitrogen atoms are planar. This type of arrangement is usually observed when a C₃ symmetric conformation is observed, (which is the case for 1 and 2), but not for the (C₄H₈N)₃P adducts 3 and 6, where the conformation is closer to C_s, although the nitrogen atoms are still essentially planar. The P-N bonds in all the compounds reported herein are short, ranging between 1.599(12) and 1.643(12) , and are consistent with the previously reported short P-N bonds in phosphonium salts featuring tris-dialkylamino substituted phosphines. The Royal Society of Chemistry.

Full text of DOI:10.1039/b713640d

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PAPER
www.rsc.org/dalton | Dalton Transactions
The reactions of alkylamino substituted phosphines with I2 and (Ph2Se2I2)2:
structural features of alkylamino phosphonium cations†‡
Nicholas A. Barnes, Stephen M. Godfrey,* Ruth T. A. Halton, Imrana Mushtaq and Robin G. Pritchard
Received 5th September 2007, Accepted 22nd November 2007
First published as an Advance Article on the web 8th January 2008
DOI: 10.1039/b713640d
The reactions of the tris-dialkylamino phosphines (Et2N)3P and (nPr2N)3P, and the pyrrolidinyl
substituted phosphines (C4H8N)3P and tBuP(NC4H8)2, with I2 and (Ph2Se2I2)2, have been reported. The
reactions with diiodine lead to the formation of [R3PI]I adducts, which are essentially ionic, but show a
tendency to display long, soft–soft, I · · · I interactions in the solid state. The crystal structures of
[(Et2N)3PI]I, (1), [(nPr2N)3PI]I, (2), and [(C4H8N)3PI]I, (3), have all been determined, and display I · · · I
˚
interactions varying between 3.5170(6) and 3.6389(14) A. The analogous reactions with (Ph2Se2I2)2 lead
to the formation of phenylseleno-phosphonium salts, [R3PSePh]I. The structures of [(C4H8N)3PSePh]I,
t
(6) and [(C4H8N)2 BuPSePh] I, (7), have been determined and do not display any soft–soft interactions
between the selenium and iodine atoms. All of the phosphonium salts represent examples of structures
containing tris-dialkylamino phosphine fragments which show no “special” nitrogen atom, i.e. all three
nitrogen atoms are planar. This type of arrangement is usually observed when a C3 symmetric
conformation is observed, (which is the case for 1 and 2), but not for the (C4H8N)3P adducts 3 and 6,
where the conformation is closer to Cs, although the nitrogen atoms are still essentially planar. The
˚
P–N bonds in all the compounds reported herein are short, ranging between 1.599(12) A and
˚
1.643(12) A, and are consistent with the previously reported short P–N bonds in phosphonium salts
featuring tris-dialkylamino substituted phosphines.
Introduction
Tris-dialkylamino substituted phosphines, (R2N)3P, are in general,
strong r-donors, and, as a consequence, these ligands have
found application in metal complexes possessing catalytic activity
in systems such as Suzuki couplings of aryl chlorides1 and
hydroformylation of 1-hexene.2
The high basicity of these phosphines is a consequence of
donation of electron density from the lone pair on the nitrogen
atoms to the central phosphorus.3–4 This results in a considerable
shortening of the P–N bonds in these systems, which generally vary
5,6
˚
between 1.68 and 1.73 A. The different conformations adopted
Fig. 1 (a) C3 conformation of (R2N)3P, (b) Cs conformation of (R2N)3P,
by (R2N)3P compounds have been the subject of considerable
study, with early reports7 suggesting adoption of a propeller-
like C3 conformation, as shown in Fig. 1a. However, structural
studies of (Me2N)3P,5 (morpholino)3P and (piperidino)3P,6 show
a preference for the Cs conformation shown in Fig. 1b. In these
structures there are two planar nitrogen atoms (sp2 hybridized),
whilst the third nitrogen exhibits significant pyramidalisation. This
nitrogen atom has been termed the “special nitrogen” by Husebye,8
and the angles around the atom are typically 330–350◦, in contrast
to the planar nitrogens, where the angles are close to 360◦. The
P–N bonds to the planar nitrogens are considerably shorter than
to the special nitrogen, e.g. in the structure of (Me2N)3P where P–
with special nitrogen denoted N*.
˚
N(planar): 1.681(3) to 1.699(3) A, compared to P–N(pyramidal):
5
˚
1.729(3) to 1.732(3) A.
The Cs conformation is observed in the majority of compounds
and complexes containing tris-dialkylamino substituted phos-
phines, and adoption of this conformation has also been shown
to be a general phenomenon for almost all (R2N)3E containing
compounds where E = a group 14 or 15 element from the second
or higher row.5 The origin of the strong preference for the Cs
conformation over the C3 is not fully understood, as stabilization
from anomeric effects from the orthogonal lone pairs on the planar
nitrogen atoms would seem to favour the C3 conformation.9,10
Steric effects may be partially responsible, however, as calculations
on (H2N)3P also predict a Cs conformation.5
School of Chemistry, University of Manchester, Oxford Road, Manchester,
UK M13 9PL. E-mail: stephen.m.godfrey@manchester.ac.uk; Fax: +44
(0)161 200 4559; Tel: +44 (0)161 200 4525
† The HTML version of this article has been enhanced with colour images.
‡ CCDC reference numbers 659625–659629. For crystallographic data in
CIF or other electronic format see DOI: 10.1039/b713640d
Semi-empirical MO calculations have shown that the Cs and C3
conformations in (Me2N)3P are close in energy,11 and a number
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of structures with C3 symmetric (R2N)3P groups are known.
These are most commonly observed where an electronegative
element is bound to phosphorus, as for example in compounds
featuring (Me2N)3PO fragments.12 In these structures no special
nitrogen is observed, and all three nitrogen atoms exhibit a
planar geometry. The preference for the C3 conformation in
many (R2N)3PO systems contrasts with analogous phosphine
chalcogenide structures of the heavier chalcogens (S, Se, Te),8,13–15
where Cs conformations are observed, although variations in P–
N bond lengths are not as pronounced as in the free (R2N)3P
structures.5,6 The conformation observed (C3 vs. Cs) appears to be
related to the ability of the phosphorus atom to accept electron
density from the nitrogen lone pairs. In the case of the phosphine
oxide systems the presence of the electronegative oxygen atom
reduces electron density at phosphorus, resulting in reduction in
all three P–N bond lengths, and adoption of the C3 conformation.
A structural determination of tris-(morpholino)phosphine oxide,
[O(C2H4)2N]3PO,16 however, illustrates that the donating power of
the R groups can have an effect on the conformation observed,
as this compound adopts a Cs conformation, in contrast to
(Me2N)3PO systems.
Cationic phosphonium salts of tris-dialkylamino phosphines
are also capable of stabilizing the C3 conformation. We have
reported the structures of a series of [(Me2N)3PX]I compounds,
(X = Cl, Cl0.5Br0.5, I, CN, SePh),17,18 in which the (Me2N)3P groups
all adopt a C3 conformation, irrespective of the large differences
in the electronegativity and size of X in this series. This suggests
that the positive charge residing on the phosphorus atom in these
cationic compounds is sufficient to favour the C3 conformation.
The P–N bond lengths in the compounds are all very short,
Results and discussion
The phosphines (Et2N)3P, (nPr2N)3P, (C4H8N)3P, and
t
(C4H8N)2 BuP were reacted in a 1 : 1 ratio with I2 and “PhSeI”
to yield R3PI2 or R3PSe(Ph)I adducts, as shown in Scheme 1.
Scheme 1 Reactions of alkylamino-substituted phosphines with I2 and
(Ph2Se2I2)2.
Reactions of alkylamino phosphines with diiodine
Spectroscopic features of [R3PI]I adducts. The reactions
of (Et2N)3P, (nPr2N)3P and (C4H8N)3P with diiodine yield
cream/pale yellow coloured powders 1 to 3, respectively. In
t
contrast, the material obtained from the reaction of (C4H8N)2 BuP
with I2 was an intractable brown oil, which was shown by 31P{ H}
1
NMR spectroscopy to exhibit a number of peaks between 20
and 80 ppm. Efforts to recrystallise a pure sample from the oil
were unsuccessful, despite repeated attempts. The 31P{ H} NMR
1
spectra of the adducts 1 to 3 display peaks between 3.6 and
16.1 ppm, similar to chemical shifts reported for other [R3PI]+
cationic species.17,28 The formation of ionic salts in solution is
consistent with the tendency of R3PI2 compounds containing
˚
ranging between 1.551(14) and 1.631(7) A. Other structural data
highly basic phosphines to ionise in CDCl3.17,28–30 The 31P{ H}
1
n
n
for cationic [(R2N)3PX]+ systems (R = Me, Et, Pr, Bu) show
that adoption of the C3 conformation seems to be a general phe-
nomenon of these salts.19–22 In contrast, the series of compounds [p-
(NO2)C6H4P(NR2)3]ClO4 show a structural variation depending
on the NR groups.23 When NR = piperidine a C3 conformation
is observed, but when NR = morpholine the conformation
changes to Cs, which is consistent with the Cs conformation
seen for [O(C2H4)2N]3PO.16 The lower basicity of the morpholino
group appears to “tip the balance” between C3 and Cs confor-
mations.
NMR spectra of 1 to 3 were monitored over several days, as we
have previously observed that [(Me2N)3PX]+ cationic species react
with chlorinated solvents to yield [(Me2N)3PCl]+. This reaction
was particularly facile when X = I.17 However, the 31P{ H} NMR
1
spectra of 1 to 3 display no change in CDCl3 solution over
many days, suggesting that these compounds are more stable in
chlorinated solvents than the analogous [(Me2N)3PI]+ species.
Structural features of [R3PI]I adducts. Crystals of 1, 2 and 3
were grown from layered dichloromethane : diethyl ether solutions
of the compounds, and despite the use of chlorinated solvents, we
observed no formation of the related chlorophosphonium anions,
unlike the related [(Me2N)3PI]+ cationic species, which converts to
[(Me2N)3PCl]+ when recrystallised from dichloromethane.17 This
is consistent with the observations that the iodophosphonium
These observations suggest that the conformation adopted by
cationic phosphonium systems may also be dependent on the
basicity of the alkylamino groups, and it was therefore of interest
to study the structures of [(R2N)3PX]+ compounds featuring dif-
ferent tris-alkylamino phosphines. The products formed from the
reactions of tertiary phosphines with halogens, or pseudohalogens
such as (Ph2Se2I2)2, frequently adopt ionic [R3PX]X phosphonium
salt structures, especially with highly basic phosphines.17,18,24,25
To this end we now report the reactions of (Et2N)3P, (nPr2N)3P
and (C4H8N)3P with diiodine and (Ph2Se2I2)2 (which is capable
of acting as a “PhSeI” source). We also report the analogous
1
species persist in the 31P{ H} NMR spectra of 1 to 3, and suggests
that the larger steric bulk of these phosphines prevents reaction
of the iodophosphonium cation with the chlorinated solvent. The
molecular structures of 1, 2 and 3 are shown in Fig. 2, 3 and 4,
respectively, along with selected bond lengths and angles.
The structures of [(Et2N)3PI]I 1, (monoclinic, P21), and
reactions with (C4H8N)2 BuP. This ligand has been reported by
[(nPr2N)3PI]I 2, (monoclinic, Cc), consist of cation/anion pairs,
t
˚
˚
Woollins and co-workers to exhibit even greater basicity than
(C4H8N)3P,26,27 since it is suggested that the third pyrrolidine group
in (C4H8N)3P (that containing the pyramidal nitrogen), is not able
to act as an electron donating group. Replacement of this group
by the highly donating tBu group yields a highly basic phosphine,
with additional steric bulk.
linked by I · · · I interactions of 3.6168(4) A and 3.6389(14) A,
respectively. In the case of 2 the interaction is to an I− anion from a
neighbouring molecule. These I · · · I interactions are considerably
longer than typically observed in the solid-state structures of
R3PI2 compounds (see Table 1), but still lie within the sum of
the van der Waals radii for two iodine atoms, 3.96 A. The
35
˚
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Fig. 3 Molecular structure of [(nPr2N)3PI]I, 2. Thermal ellipsoids are
Fig. 2 Molecular structure of [(Et2N)3PI]I, 1. Thermal ellipsoids are
shown at the 30% probability level. Hydrogen atoms are omitted for clarity.
shown at the 30% probability level. Hydrogen atoms are omitted for clarity.
◦
˚
Selected bond lengths [A] and angles [ ]: P(1)–I(1): 2.455(4), I(1) · · · I(2_2):
3.6389(14), P(1)–N(1): 1.599(12), P(1)–N(2): 1.643(12), P(1)–N(3):
1.613(11), P(1)–I(1) · · · I(2_2): 161.12(9), I(1)–P(1)–N(1): 106.4(5), I(1)–
P(1)–N(2): 109.6(5), I(1)–P(1)–N(3): 108.7(4), N(1)–P(1)–N(2): 108.5(6),
N(1)–P(1)–N(3): 111.5(6), N(2)–P(1)–N(3): 112.0(6), P(1)–N(1)–C(1):
125.5(10), P(1)–N(1)–C(4): 120.1(10), C(1)–N(1)–C(4): 114.4(12),
P(1)–N(2)–C(7): 113.2(9), P(1)–N(2)–C(10): 128.8(11), C(7)–N(2)–C(10):
118.0(12), P(1)–N(3)–C(13): 123.0(10), P(1)–N(3)–C(16): 120.4(9),
C(13)–N(3)–C(16): 116.1(12).
◦
˚
Selected bond lengths [A] and angles [ ]: P(1)–I(1): 2.4730(8), I(1) · · · I(2):
3.6168(4), P(1)–N(1): 1.602(3), P(1)–N(2): 1.641(4), P(1)–N(3): 1.625(3),
P(1)–I(1) · · · I(2): 171.97(2), I(1)–P(1)–N(1): 107.92(13), I(1)–P(1)–N(2):
106.70(15), I(1)–P(1)–N(3): 109.94(9), N(1)–P(1)–N(2): 111.32(18), N(1)–
P(1)–N(3): 111.03(18), N(2)–P(1)–N(3): 109.81(19), P(1)–N(1)–C(1):
122.8(3), P(1)–N(1)–C(3): 122.3(3), C(1)–N(1)–C(3): 114.7(3), P(1)–
N(2)–C(5): 122.3(3), P(1)–N(2)–C(7): 118.6(3), C(5)–N(2)–C(7): 119.1(3),
P(1)–N(3)–C(9): 118.8(3), P(1)–N(3)–C(11): 123.8(3), C(9)–N(3)–C(11):
115.7(3).
lated directly from the structures reported here using the method
of Mu¨ller and Mingos,36 the values obtained being 173.8◦ for
(Et2N)3P in 1, 195.7◦ for (nPr2N)3P in 2, and 166.8◦ for (C4H8N)3P
in 3. These value◦s are all much larger than the range observed for
(Me2N)3P (155.7 to 160.3◦), in the four independent [(Me2N)3PI]+
cations in the structure of [{(Me2N)3PI}I]6.CH3CN.17 The order of
steric bulk for these alkylamino phosphines is therefore (nPr2N)3P
ꢀ (Et2N)3P > (C4H8N)3P > (Me2N)3P in the series of [(R2N)3PI]+
cations.
structure of [(C4H8N)3PI]I 3, (monoclinic, P21/n), also consists
˚
of a cation/anion pair linked by an I · · · I contact of 3.5170(6) A,
which is somewhat shorter than 1 or 2, and the I · · · I distance
observed in the structure of [{(Me2N)3PI}I]6·CH3CN, I · · · I:
17
˚
3.6378(14) A. Compound 3 also displays a slightly shorter P–
˚
˚
I bond, 2.4303(17) A, compared to the P–I bonds of 2.4730(8) A
˚
in 1, and 2.455(4) A in 2. It seems unlikely that these variations are
due to electronic effects, and are probably due to the greater steric
bulk of the (R2N)3P (R = Et, nPr) compounds, compared with the
(C4H8N)3P system. The crystallographic cone angles were calcu-
The long I · · · I interactions suggest that 1 to 3 are best con-
sidered as ionic in the solid-state, although all three compounds
Table 1 Comparison of P–I and I–I bonds in R3PI2 structures
˚
˚
Compound
P–I/A
I–I/A
Ref.
a
(Mecarb)iPr2PI2
2.5978(14)
2.5523(12)
2.481(4)
2.461(2)
2.482(1)
2.409(2)/2.420(2)
2.410(2)
2.4303(17)
2.4730(8)
3.021(1)
3.0727(4)
3.161(2)
3.326(1)
3.3394(5)
31
25
32
29
33
(o-CH3C6H4)3PI2,
Ph3PI2
tBu3PI2
[2,4,6-(MeO)3C6H2]3PI2
iPr3PI2
Me2PhPI2
3.383(1)/3.372(1) 34
3.408(2)
3.5170(6)
3.6168(4)
28
[(C4H8N)3PI]I, 3
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17
[(Et2N)3PI]I, 1
[{(Me2N)3PI}I]6·CH3CN 2.427(3)–2.448(5)b 3.6378(14)
[(nPr2N)3PI]I, 2
2.455(4)
3.6389(14)
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a (Mecarb) = 1-(2-Me-1,2-C2B10H10). b Value for P–I in cation interacting with an I− is 2.427(3) A.
˚
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one of the R2N groups is twisted slightly more than the other
two, although this is much more noticeable for 1 than for 2.
A comparison with the structure of [{(Me2N)3PI}I]6·CH3CN,
(which contains four independent cations, three of which have
crystallographically imposed C3 symmetry), shows that this ar-
rangement is also observed here, with I–P–N–C torsion angles
of 115.8(12), 136.0(12) and 129.4(12)◦ observed for the cation
where the C3 symmetry is not crystallographically imposed.17 The
torsion angles fall in the range (115–136◦) observed for other C3
symmetric [(Me2N)3PX]+ cationic systems.17–18 These observations
contrast with the data available for (R2N)3P (R = Et, nPr), which
have both been assigned Cs symmetric conformations from UV
photoelectron spectroscopic studies.4 The structures of 1 and 2
show some variation in the P–N bond lengths, with two of the
P–N bonds falling within the range typically observed for C3
symmetric phosphonium cations, and one being rather longer,
˚
e.g. P–N: 1.602(3), 1.641(4) and 1.625(3) A for 1, and P–N:
˚
1.599(12), 1.643(12) and 1.613(11) A for 2. The P–N bonds are still
comparable in magnitude to those in other C3 symmetric systems
containing these phosphines, such as [(Et2N)3PF][Mes3VF], P–N:
37
1.595(4) to 1.601(4) A, and [(nPr2N)3PI]I3, P–N: 1.592(12) to
˚
38
˚
1.612(12) A. An examination of the angles around the nitrogen
Fig. 4 Molecular structure of [(C4H8N)3PI]I, 3. Thermal ellipsoids are
atoms shows that whilst one of the P–N bonds is longer than
expected in the structures of both 1 and 2, the angles around these
nitrogen atoms are still close to 360◦ (359.9◦ for 1, 360.0◦ for 2), as
are the angles around the other two nitrogen atoms (359.8◦, 358.3◦
for 1, 360.0◦, 359.6◦ for 2), and therefore all nitrogens are planar.
These cations therefore exhibit a C3 conformation, but display a
small elongation of one of the three P–N bonds, presumably to
help reduce steric congestion.
In contrast, the [(C4H8N)3PI]+ cation in the structure of 3
does not adopt a C3 conformation. An examination of the I–
P–N–C torsion angles (see Table 2), shows that the confor-
mation is closer to Cs, with torsion angles: I(1)–P(1)–N(1)–
C(4): −162.7(4)◦, I(1)–P(1)–N(2)–C(5): −88.2(5)◦, I(1)–P(1)–
N(3)–C(9): −143.3(6)◦. One of the rings, that containing N(2),
is twisted to a greater degree than the others, but despite this the
nitrogen atom does not show the features usually associated with
a “special” nitrogen. The angles around N(2) are slightly distorted
away from planar, adding up to 353.5◦, whilst the angles around
the other two nitrogens are closer to planar, 358.4◦ and 358.5◦.
shown at the 30% probability level. Hydrogen atoms are omitted for clarity.
◦
˚
Selected bond lengths [A] and angles [ ]: P(1)–I(1): 2.4303(17), I(1) · · · I(2):
3.5170(6), P(1)–N(1): 1.608(5), P(1)–N(2): 1.617(5), P(1)–N(3): 1.610(5),
P(1)–I(1) · · · I(2): 167.97(4), I(1)–P(1)–N(1): 107.0(2), I(1)–P(1)–
N(2): 112.2(2), I(1)–P(1)–N(3): 107.8(2), N(1)–P(1)–N(2): 111.8(3),
N(1)–P(1)–N(3): 112.3(3), N(2)–P(1)–N(3): 105.7(3), P(1)–N(1)–C(1):
126.6(4), P(1)–N(1)–C(4): 120.7(4), C(1)–N(1)–C(4): 111.1(5), P(1)–N(2)–
C(5): 122.3(4), P(1)–N(2)–C(8): 121.4(4), C(5)–N(2)–C(8): 109.7(5),
P(1)–N(3)–C(9): 126.6(5), P(1)–N(3)–C(12): 121.5(4), C(9)–N(3)–C(12):
110.3(5).
still display very weak soft–soft interactions between the two
iodine atoms. The linear nature of this type of interaction is
retained in [{(Me2N)3PI}I]6·CH3CN, where the P–I–I angle is
175.08(8)◦,17 however, the P–I–I angles in the structures of 1 to 3
display considerable deviation from linearity, e.g. 171.97(2)◦ for 1,
161.12(9)◦ for 2, and 167.97(4)◦ for 3. There is a direct correlation
between the steric bulk of the phosphine and the deviation away
from linearity, with the very bulky [(nPr2N)3PI]I, 2, showing the
greatest distortion.
The (R2N)3P groups in the cations of 1 and 2 exhibit a
slightly distorted C3 conformation, with I–P–N–C torsion angles
of −133.5(3), −137.6(3) and −115.1(2)◦ in 1, and 132.2(11),
124.8(12) and 134.2(10)◦ in 2, (see Table 2). In both structures
˚
However, all three P–N bonds are short, P(1)–N(1): 1.608(5) A,
˚
˚
P(1)–N(2): 1.617(5) A, P(1)–N(3): 1.610(6) A. The tighter torsion
angle to one of the pyrrolidine rings is likely to be due to the less
flexible nature of the cyclic amino group, resulting in (C4H8N)3P
being less able to accommodate a C3 conformation than the
straight chain (R2N)3P (R = Et, nPr) groups.
Table 2 Comparison of X–P–N–C torsion angles in a series of alkylamino phosphonium cations
Compound
X–P–N–C Torsion anglea/◦
Ref.
[(Et2N)3PI]I, 1
−133.5(3), −137.6(3), −115.1(2)
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17
[(nPr2N)3PI]I, 2
132.2(11), 124.8(12), 134.2(10)
[(C4H8N)3PI]I, 3
−162.7(4), −88.2(5), −143.3(6)
[(C4H8N)3PSePh]I, 6
76.2(9), 153.6(9), 162.2(8)
[{(Me2N)3PI}I]6·CH3CN b
115.8(12), 136.0(12), 129.4(12) (cation 1); 116.1(10) (cation 2)c;
−124.1(10) (cation 3)c; −128.7(10) (cation 4)c
a X = I in most cases, but Se in compound 6. b Contains four different cations. c These cations have crystallographically imposed C3 symmetry.
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Reactions of alkylamino phosphines with (Ph2Se2I2)2. We have
previously reported that R3PSe(Ph)X (X = Br, I) adducts are
formed when tertiary phosphines are reacted with Ph4Se4Br4,39
or (Ph2Se2I2)2.18,24–25 These adducts exhibit structural isomerism,
and can exist either as charge-transfer (CT) adducts (featuring
a linear P–Se–X motif), or as ionic phenylseleno-phosphonium
salts. The type of adduct formed is mainly dependent on the
properties of the R groups on the phosphine, although we have
identified adducts with four types of behaviour. Type I adducts
are charge-transfer adducts, (10-Se-3), such as Ph3PSe(Ph)I,
contain significant double bond character.42 For example, the m(P–
Se) band for (Et2N)3PSe is 553 cm−1, decreasing to 530 cm−1 in
(Et2N)3PSeI2,42 but is much lower (481 cm−1) in (Et2N)3PSe(Ph)I,
4. Therefore, the P–Se bonds in the adducts reported here are best
considered as single bonds.
Structural features of [R3PSePh]I adducts. Attempts to grow
crystals of the adducts 4 and 5 were unsuccessful after repeated
attempts, although crystals suitable for X-ray diffraction were
obtained for 6 and 7. Crystals of [(C4H8N)3PSePh]I, 6, (mono-
clinic, P21/c) were grown from dichloromethane/diethyl ether.
The molecular structure is shown in Fig. 5, along with selected
bond lengths and angles.
which display relatively strong Se–X bonds, for example Se–I:
24
˚
3.2564(5) A for Ph3PSe(Ph)I. These adducts do not ionise in
solution to give phenylseleno-phosphonium salts, and instead
display fluxional behaviour. Type II adducts are formed with more
basic phosphines, and lie close to the CT/ionic borderline. They
retain the CT motif in the solid-state, but with long Se–X bonds,
25
˚
[for example Se–I: 3.4885(8)–3.5313(14) A in Ph2MePSe(Ph)I],
but ionise in solution. Type III adducts are essentially ionic,
both in the solid-state and solution, but often feature weak soft–
soft Se · · · X interactions in the solid-state, e.g. in the structure
of [(Me2N)3PSePh]I, which displays a weak, non-linear, Se · · · I
18
˚
interaction of 3.825(1) A. Type IV adducts are those which
are also ionic, but where the structural isomerism is dictated
additionally by steric effects, for example in bulky systems
such as [(o-OCH3C6H4)3PSePh]I·CH2Cl2, which is ionic in the
1
solid-state and solution.25 The 31P{ H} NMR spectra of these
1
ionic phenylseleno-phosphonium salts display J(SeP) coupling
constants varying between 412 Hz and 497 Hz.25,39 These values
are consistent with other phosphonium species containing single
P–Se bonds.40 The alkylamino phosphines (Et2N)3P, (nPr2N)3P
and (C4H8N)3P should yield ionic adducts when reacted with
(Ph2Se2I2)2 due to their high basicity, but unlike [(Me2N)3PSePh]I
may not display any weak Se · · · I interactions due to greater steric
hindrance.
Spectroscopic features of [R3PSePh]I adducts. The phosphines
(Et2N)3P, (nPr2N)3P, (C4H8N)3P and (C4H8N)2 BuP were reacted
t
Fig. 5 Molecular structure of [(C4H8N)3PSePh]I, 6. Thermal ellipsoids
are shown at the 30% probability level. Hydrogen atoms are omit-
with (Ph2Se2I2)2 to yield cream coloured solids 4 to 7, respectively,
see Scheme 1. The adducts formed from these reactions were
characterised by multinuclear NMR and Raman spectroscopy.
◦
˚
ted for clarity. Selected bond lengths [A] and angles [ ]: P(1)–Se(1):
2.233(4), P(1)–N(1): 1.609(10), P(1)–N(2): 1.601(9), P(1)–N(3): 1.608(10),
Se(1)–C(13): 1.947(14), P(1)–Se(1)–C(13): 95.8(4), Se(1)–P(1)–N(1):
114.4(4), Se(1)–P(1)–N(2): 110.3(4), Se(1)–P(1)–N(3): 102.0(4), N(1)–
P(1)–N(2): 106.7(5), N(1)–P(1)–N(3): 112.2(5), N(2)–P(1)–N(3): 111.3(5),
P(1)–N(1)–C(1): 120.0(8), P(1)–N(1)–C(4): 126.3(8), C(1)–N(1)–C(4):
109.3(9), P(1)–N(2)–C(5): 120.4(8), P(1)–N(2)–C(8): 125.2(8), C(5)–
N(2)–C(8): 110.6(8), P(1)–N(3)–C(9): 120.1(8), P(1)–N(3)–C(12): 127.8(8),
C(9)–N(3)–C(12): 109.5(9).
1
The 31P{ H} NMR spectra exhibit sharp peaks between 40.2
and 76.5 ppm, with attendant selenium satellites. The 1J(SeP)
coupling constants vary between 473 and 497 Hz, with higher
n
values being observed for the (R2N)3P (R = Et, Pr) derivatives
4 and 5 [1J(SeP) = 494–497 Hz], compared with the pyrrolidine
substituted adducts 6 and 7, [1J(SeP) = 473–479 Hz]. The chemical
shifts and coupling constants for 4 and 5 are identical to those
n
observed for the analogous [(R2N)3PSePh]Br (R = Et, Pr) salts
The structure of 6 is confirmed as an ionic phenylseleno-
phosphonium salt, as suggested by the NMR spectroscopic data.
1
previously reported.39 The 77Se{ H} NMR spectra of 4 to 7 display
˚
doublets between 273.1 and 329.8 ppm, consistent with pre-
vious observations for [R3PSePh]X phenylseleno-phosphonium
salts.25,39
The P–Se bond in 6 is 2.233(4) A, which is consistent with the
18
˚
˚
P–Se bonds of 2.250(1) A in [(Me2N)3PSePh]I, and 2.241(5) A in
[(o-OCH3C6H4)3PSePh]I.CH2Cl2.25 In contrast to the structure of
[(Me2N)3PSePh]I there are no Se · · · I interactions in 6, the closest
The Raman spectra of 4, 6 and 7 display peaks attributable
to m(P–Se) between 469 and 484 cm−1. We could not obtain
satisfactory Raman data for 5 due to decomposition in the
laser beam. The m(P–Se) bands in these [R3PSePh]I adducts are
˚
approach being 5.521 A. This is likely to be due to the greater steric
bulk of (C4H8N)3P compared to (Me2N)3P, as the crystallographic
cone angle of (C4H8N)3P in 6 is 172.8◦, which is much larger than
the cone angles of 155–160◦ observed for the four independent
[(Me2N)3PI]+ cations in [{(Me2N)3PI}I]6·CH3CN.17 The P–N bond
=
observed at lower wavenumbers than both m(P Se) bands for
tertiary phosphine selenides,41 and also m(P–Se) bands in halogen
˚
lengths in 6 vary between 1.601(9) and 1.608(10) A, and angles
adducts of phosphine selenides, R3PSeI2, where the P–Se bonds
1350 | Dalton Trans., 2008, 1346–1354
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around each of the nitrogen atoms are close to planar, varying
between 355.6◦ and 357.3◦. Although the structure displays all the
features of a C3 system (short P–N bonds, planar geometries at all
three nitrogen atoms), the Se–P–N–C torsion angles vary, Se(1)–
P(1)–N(1)–C(1): 76.2(9)◦, Se(1)–P(1)–N(2)–C(8): 153.6(9)◦ and
Se(1)–P(1)–N(3)–C(9): 162.2(9)◦, and the conformation is closer
to Cs, as was also observed for 3. Taken together, the structural
data for 3 and 6 suggest that tris-(pyrrolidinyl)phosphine is too
rigid to adopt a C3 conformation in phosphonium systems.
The P–N bond lengths and cone angles observed for (C4H8N)3P
in the structures of both 3 and 6 are considerably different than
observed for this ligand in metal complexes. For example, the
is considerably larger than the reported estimate for the Tolman
cone angle of this phosphine (157◦).27
The structure of 7 shows similar features to those of 6, and
˚
exhibits a P–Se bond of 2.2556(11) A, which is similar to the P–
˚
Se bond of 2.233(4) A in 6, and also to the P–Se bonds in other
[R3PSePh]X structures.18,25,39 The structure of 7 also displays no
˚
Se · · · I interactions, the closest approach being 5.642 A. In this
respect both 6 and 7 are examples of type IV R3PSe(Ph)I adducts,
which are ionic, and too sterically demanding for soft–soft
interactions to feature in the crystal packing of either compound.
In this respect, the phenylseleno-phosphonium salts differ from
the iodophosphonium salts, which retain long I · · · I contacts even
in extremely bulky systems. The P–N bonds in 7 are 1.619(3) and
cone angle in cis-[PtCl2{P(NC4H8)3}2] is 122◦, with P–N bond
26,27
˚
˚
lengths varying between 1.63(1) and 1.68(1) A.
Despite these
1.626(3) A, and are consistent with the short P–N bonds observed
differences, the angles around the nitrogen atoms in this platinum
complex are 356–360◦, and thus all planar. The related trans-
[RhCl(CO){P(NC4H8)3}2] does display pyramidal distortion at
one nitrogen atom in each (C4H8N)3P ligand,43 suggesting that
steric and crystal packing effects may also play some part in the
conformations adopted in metal complexes of (C4H8N)3P.
for all the phosphonium salts reported here. The bulky tBu group
is located anti to the SePh group along the P–Se bond, and the
greater steric demand of this group is reflected in the opening up of
the two N–P–C angles, N(1)–P(1)–C(11): 111.86(18)◦ and N(6)–
P(1)–C(11): 112.10(19)◦, compared to the N–P–N angle, N(1)–
P(1)–N(6): 107.39(18)◦.
t
A crop of colourless crystals of [(C4H8N)2 BuPSePh]I, 7,
(monoclinic, P21/c) were grown from dichloromethane/diethyl
ether. The molecular structure of 7 is shown in Fig. 6 along with
selected bond lengths and angles.
Conclusions
The reactions of a series of tris-alkylamino phosphines with
diiodine and phenylselenenyl iodide have been undertaken. When
(Et2N)3P, (nPr2N)3P and (C4H8N)3P are reacted with diiodine a
series of iodophosphonium iodides, [R3PI]I, are formed, which
display weak, soft–soft, I · · · I contacts in the solid-state ranging
˚
between 3.5170(6) and 3.6389(14) A. The P–I–I angles exhibit
considerably more deviation (161–172◦) from the usual linear
P–I–I geometry observed for R3PI2 compounds. The reactions
t
of (Et2N)3P, (nPr2N)3P, (C4H8N)3P and (C4H8N)2 BuP with
(Ph2Se2I2)2 lead to the formation of phenylseleno-phosphonium
salts, [R3PSePh]I. The structures of [(C4H8N)3PSePh]I, 6, and
t
[(C4H8N)2 BuPSePh]I, 7, are ionic, and (in contrast to the diiodide
analogues) show no interactions between the soft selenium and
iodine atoms. The structures of the iodophosphonium salts
[(Et2N)3PI]I, 1, and [(nPr2N)3PI]I, 2, feature the alkylamino
phosphines in a conformation close to C3, with all three nitrogen
atoms planar, and no evidence in either case of a pyramidally
distorted “special” nitrogen. The short P–N bonds in 1 and
2 are consistent with the P–N bonds in related [(Me2N)3PX]I
salts,17 and show that the bulkier (Et2N)3P and (nPr2N)3P are
also able to display C3 symmetric structures. In contrast, the
adducts [(C4H8N)3PI]I, 3, and [(C4H8N)3PSePh]I, 6, both feature
the (C4H8N)3P group in a conformation closer to Cs. Although
the Cs conformation is observed for the (C4H8N)3P adducts 3
and 6, no “special” nitrogen is observed, and all three nitrogen
atoms are planar. The P–N bonds in both of these compounds
are short, and of comparable magnitude to the P–N bonds in
the C3 symmetric structures reported herein. Compounds 3 and 6
thus show all the features of a C3 symmetric system, but unlike the
straight-chain (Et2N)3P and (nPr2N)3P, the cyclic (C4H8N)3P is less
flexible and adopts the Cs conformation. The related phenylseleno-
t
Fig. 6 Molecular structure of [(C4H8N)2 BuPSePh]I, 7. Thermal el-
lipsoids are shown at the 30% probability level. Hydrogen atoms
◦
˚
are omitted for clarity. Selected bond lengths [A] and angles [ ]:
Se(1)–P(1): 2.2556(11), Se(1)–C(15): 1.929(4), P(1)–N(1): 1.619(3), P(1)–
N(6): 1.626(3), P(1)–C(11): 1.842(4), P(1)–Se(1)–C(15): 99.34(12),
Se(1)–P(1)–N(1): 113.97(13), Se(1)–P(1)–N(6): 108.37(13), Se(1)–P(1)–
C(11): 103.19(14), N(1)–P(1)–N(6): 107.39(18), N(1)–P(1)–C(11):
111.86(18), N(6)–P(1)–C(11): 112.10(19), P(1)–N(1)–C(2): 121.7(3),
P(1)–N(1)–C(5): 123.2(3), C(2)–N(1)–C(5): 109.5(4), P(1)–N(6)–C(7):
123.8(3), P(1)–N(6)–C(10): 126.0(3), C(7)–N(6)–C(10): 109.3(3).
t
The structure of 7 is confirmed as a phenylseleno-phosphonium
phosphonium salt, [(C4H8N)2 BuPSePh]I, 7, also displays planar
salt, and represents the first crystallographically characterised
nitrogen atoms and short P–N bonds. The bulkiness of these
phosphines is shown by a comparison of the crystallographically
determined cone angles, the order of size being (nPr2N)3P [195.7◦
t
compound containing the (C4H8N)2 BuP ligand. The crystallo-
◦
t
graphic cone angle for (C4H8N)2 BuP is calculated at 177.4 , which
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◦
in 2] ꢀ (C4H8N)2 BuP [177.4 in 7] > (Et2N)3P [173.8◦ in 1] >
scan method, using the SORTAV program.46 Non-hydrogen atoms
were refined with anisotropic thermal parameters, except for
atom N(2) in 2 which was refined isotropically, as the atom was
becoming an oblate spheroid. All hydrogen atoms were modelled
in ideal positions. All thermal ellipsoid plots were generated using
ORTEP-3 for Windows.47
t
(C4H8N)3P [172.8◦ in 6/166.8◦ in 3].
Experimental
Reagents and physical measurements
CCDC reference numbers 659625–659629.
For crystallographic data in CIF or other electronic format see
DOI: 10.1039/b713640d
The compounds synthesised herein are air and moisture sensitive,
therefore strict anhydrous and anaerobic conditions were used
throughout their synthesis. Diethyl ether was purchased commer-
cially (BDH) and freshly distilled from sodium/benzophenone
ketyl before use. Diiodine, (Et2N)3P, (nPr2N)3P and (C4H8N)3P
were all purchased commercially (Aldrich) and used as received.
(Ph2Se2I2)2,44 and tBuP(NC4H8)2,27 were prepared by the literature
methods. Elemental analyses were performed by the University
of Manchester Chemistry Departmental Microanalytical service.
Raman spectra were recorded as solid samples on a Nicolet-Nexus
Synthetic details
Synthesis of diiodine adducts. Compounds 1 to 3 were prepared
by reacting the alkylamino phosphine with diiodine in a 1 : 1 ratio,
the synthesis of 1 being typical:
Synthesis of (Et2N)3PI2, 1. To a rotaflo tube containing 40 cm3
of freshly distilled anhydrous diethyl ether was added 0.820
g/0.908 cm3 (0.0033 moles) of (Et2N)3P in an inert atmosphere
glove box. The tube was removed from the glove box and one
equivalent of diiodine (0.842 g, 0.0033 moles) was added under
a stream of dry nitrogen. Rapid decolourisation of the iodine
occurred with the immediate formation of a cream coloured solid.
The reaction was allowed to stir for ca. two days, after which time
the solid was isolated using standard Schlenk techniques. The solid
was dried for 2 h under vacuum and then transferred to pre-dried
argon filled ampoules. Characterising data for 1 to 3 is given below:
1
combined FT-IR/FT-Raman spectrometer. 1H and 13C{ H}
NMR spectra were recorded on a Bruker DPX400 spectrometer
1
operating at 399.9 and 100.6 MHz, respectively. 31P{ H} and
1
77Se{ H} NMR spectra were recorded on a Bruker DPX200
spectrometer operating at 81.8 and 38.2 MHz, respectively. Peak
positions are quoted relative to external TMS (1H/13C), 85%
H3PO4 (31P), and Me2Se (77Se), using the high frequency positive
convention throughout.
Crystallographic details
Details of the structural analysis for compounds 1, 2, 3, 6 and
7 are summarised in Table 3. Diffraction data were recorded
on a Nonius j-CCD four-circle diffractometer using graphite-
(Et2N)3PI2, 1. Yield = 72.6%. Cream solid. Calculated for
C12H30N3I2P: C, 28.7; H, 6.0; N, 8.4; I, 50.7; Found: C, 28.6; H,
1
6.1; N, 8.2; I, 50.5. H NMR (CDCl3): 0.97 [t, 18H, NCH2CH3,
monochromated Mo-Ka radiation (k = 0.71073 A), at 150(2)
3J(HH) = 7.5 Hz], 2.96 [dq, 12H, NCH2, 3J(PH) = 6.2 Hz,
˚
1
K. Structural data were solved by direct methods, with full-
matrix least squares refinement on F2 using the SHELX-97
program.45 Absorption corrections were applied by the multi-
3J(HH) = 7.5 Hz]. 13C{ H} NMR (CDCl3): 12.2 [d, NCH2CH3,
2
1
3J(PC) = 2.0 Hz], 40.6 [d, NCH2, J(PC) = 2.6 Hz]. 31P{ H}
NMR (CDCl3): 14.5 [s]. Raman (cm−1): 2966, 2931, 1450, 1371,
Table 3 Crystallographic parameters for compounds 1, 2, 3, 6 and 7
[(Et2N)3PI]I, 1
[(nPr2N)3PI]I, 2
[(C4H8N)3PI]I, 3
[(C4H8N)3PSePh]I, 6 [tBu(C4H8N)2PSePh]I, 7
Empirical formula
FW
Colour, habit
Crystal system
Space group
Crystal size/mm
Unit cell dimensions
C12H30I2N3P
501.16
Colourless, needle Colourless, needle
Monoclinic
P21 (no. 4)
C18H42I2N3P
585.32
C12H24I2N3P
495.11
Colourless, prism
Monoclinic
C18H29IN3PSe
524.27
Colourless, block
Monoclinic
C18H30IN2PSe
511.27
Colourless, block
Monoclinic
Monoclinic
Cc (no. 9)
P21/n (no. 14)
P21/c (no. 14)
P21/c (no. 14)
0.12 × 0.14 × 0.18 0.10 × 0.10 × 0.20
0.05 × 0.10 × 0.10
0.07 × 0.13 × 0.14
0.15 × 0.15 × 0.10
˚
˚
˚
˚
˚
a = 7.9120(2) A
a = 16.5326(4) A
a = 8.7268(4) A
a = 9.093(3) A
a = 12.8871(2) A
˚
˚
˚
˚
˚
b = 13.7750(3) A
b = 9.4427(2) A
b = 21.6107(9) A
b = 11.540(6) A
b = 8.1610(2) A
b = 94.703(1)◦
b = 101.214(1)◦
b = 91.655(2)◦
b = 95.386(13)◦
b = 91.058(1)◦
˚
˚
˚
˚
˚
c = 8.5280(3) A
c = 16.7970(5) A
c = 9.3212(4) A
c = 19.803(7) A
c = 19.7450(4) A
3
˚
Volume/A
926.32(4)
150(2)
2
2572.16(11)
150(2)
4
1757.17(13)
150(2)
4
2068.8(15)
150(2)
4
2076.26(7)
150(2)
4
T/K
Z
D
calcd/mg m−3
1.797
0.71073
3.473
488
3.38 to 26.49
1.512
0.71073
2.513
1168
3.16 to 26.49
1.872
0.71073
3.661
952
3.24 to 26.50
1.683
0.71073
3.390
1040
3.19 to 26.00
1.636
0.71073
3.374
1016
2.62 to 27.40
˚
k/A
l(Mo-Ka)/mm−1
F(000)
h range/◦
No. of reflections
Rint
7267 (1965 unique) 12 181 (2648 unique) 14 127 (3496 unique) 13 098 (3046 unique) 22 758 (4701 unique)
0.067
0.045
0.0520
0.067
0.0848
R1/wR2
0.0495/0.1059
0.0617/0.1175
3.095 and −1.705
1.152
0.0560/0.1284
0.0735/0.1445
1.997 and −1.306
1.117
0.0451/0.0912
0.0719/0.1039
1.160 and −0.837
1.060
0.0728/0.1825
0.1264/0.2204
2.785 and −1.255
0.955
0.0466/0.0613
0.0865/0.0709
0.736 and −0.626
1.063
R1/wR2 (all data)
Largest diff. peak and hole/e A
Goodness of fit
−3
˚
1352 | Dalton Trans., 2008, 1346–1354
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©

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1338, 1198, 1145, 1078, 1057, 1024, 974, 947, 924, 798, 638, 451,
303, 231, 173.
[(C4H8N)3PSePh]I, 6. Yield = 55.9%. Cream solid, Calculated
for C18H29N3PSeI: C, 41.2; H, 5.5; N, 8.0; I, 24.2; Found: C,
1
40.9; H, 5.4; N, 7.8; I, 24.1. H NMR (CDCl3): 1.81 [t, 12H,
(nPr2N)3PI2, 2. Yield = 64.2%. Pale yellow solid. Calculated
for C18H42N3I2P: C, 36.9; H, 7.2; N, 7.2; I, 43.4; Found: C, 36.6; H,
7.1; N, 7.4; I, 43.1. 1H NMR (CDCl3): 0.99 [t, 18H, CH3,3J(HH) =
3
3
NCH2CH2, J(HH) = 6.5 Hz], 3.17 [dt, 12H, NCH2, J(HH) =
3
6.5 Hz, J(PH) = 5.0 Hz], 7.28–7.36 [m, 2H, Ph], 7.37–7.43 [m,
1H, Ph], 7.51–7.58 [m, 2H, Ph]. 13C{ H} NMR (CDCl3): 26.6
1
1
7.3 Hz], 1.68 [m, 12H, CH2CH3], 3.03 [m, 12H, NCH2]. 13C{ H}
3
2
[d, NCH2CH2, J(PC) = 8.7 Hz], 49.2 [d, NCH2CH2, J(PC) =
NMR (CDCl3): 11.7 [s, CH3], 20.6 [d, CH2CH3, 3J(PC) = 2.7 Hz],
2
2.9 Hz], 119.3 [d, Ph, J(PC) = 7.7 Hz], 130.8 [d, Ph, J(PC) =
2
1
48.6 [d, NCH2, J(PC) = 3.5 Hz]. 31P{ H} NMR (CDCl3): 16.1
[s]. Raman (cm−1): 2968, 2925, 2877, 2736, 1444, 1367, 1279, 1190,
1107, 1032, 1012, 901, 871, 792, 739, 712, 463, 428, 258, 154.
1.9 Hz], 131.4 [d, Ph, J(PC) = 2.9 Hz], 137.6 [d, Ph, J(PC) =
3.9 Hz]. 31P{ H} NMR (CDCl3): 40.2 [s, 1J(SeP) = 473 Hz].
1
77Se{ H} NMR (CDCl3): 295.4 [d, J(SeP) = 473 Hz]. Raman
(cm−1): 3041, 2976, 2925, 2891, 2875, 1571, 1483, 1456, 1321, 1244,
1155, 1097, 1063, 1016, 997, 916, 858, 731, 669, 611, 569, 484, 307,
260, 233, 210.
1
1
(C4H8N)3PI2, 3. Yield = 78.8%. Pale yellow solid. Calculated
for C12H24N3I2P: C, 29.1; H, 4.9; N, 8.5; I, 51.3; Found: C, 29.3; H,
5.1; N, 8.4; I, 51.0. 1H NMR (CDCl3): 1.91 [m, 12H, NCH2CH2,
3J(HH) = 6.5 Hz, 4J(PH) = 3.0 Hz], 3.16 [m, 12H, NCH2,
t
1
3J(HH) = 6.5 Hz, 3J(PH) = 5.0 Hz]. 13C{ H} NMR (CDCl3): 26.3
[(C4H8N)2 BuPSePh]I, 7. Yield = 71.7%. Cream solid, mp
108–115 ◦C, Calculated for C18H30N2PSeI: C, 42.3; H, 5.9; N,
5.5; I, 24.8: P, 6.1; Found: C, 42.3; H, 5.9; N, 5.9; I, 24.8: P, 6.1. 1H
NMR (CDCl3): 1.37 [d, 9H, C(CH3)3], 1.72 [m, 8H, NCH2CH2],
3.22 [m, 8H, NCH2], 7.26–7.48 [m, 3H, Ph], 7.64–7.70 [m, 2H,
3
2
[d, NCH2CH2, J(PC) = 8.7 Hz], 49.8 [d, NCH2CH2, J(PC) =
3.9 Hz]. 31P{ H} NMR (CDCl3): 3.6 [s]. Raman (cm−1): 2970,
1
2925, 2875, 1483, 1458, 1350, 1248, 1130, 1078, 1024, 912, 850,
735, 328, 208, 156.
1
1
Ph]. 31P{ H} NMR (CDCl3): 76.5 [s, 1J(SeP) = 479 Hz]. 77Se{ H}
NMR (CDCl3): 273.1 [d, 1J(SeP) = 479 Hz]. Raman (cm−1): 3042,
2967, 2891, 2870, 1568, 1460, 1205, 1174, 1151, 1012, 993, 920,
808, 623, 469, 307, 263, 160, 133.
Synthesis of (Ph2Se2I2)2 adducts
Compounds 4 to 7 were prepared by reacting the alkylamino
phosphine with (Ph2Se2I2)2 in a 4 : 1 ratio (i.e. one “PhSeI”
equivalent for one R3P equivalent), the synthesis of 4 being typical:
Acknowledgements
Synthesis of [(Et2N)3PSePh]I, 4. To a rotaflo tube containing
40 cm3 of freshly distilled anhydrous diethyl ether was added
0.763 g/0.845 cm3 (0.0031 moles) of (Et2N)3P, and (0.873 g,
0.0007 moles) of (Ph2Se2I2)2 in an inert atmosphere glove box.
The deep burgundy colour of the (Ph2Se2I2)2 rapidly vanished with
formation of a cream coloured solid. The reaction was allowed to
stir for ca. two days, after which time the solid was isolated using
standard Schlenk techniques, dried for 2 h in vacuo and transferred
to pre-dried argon filled ampoules. Characterising data for 4 to 7
is given below:
The authors would like to thank Professor Derek Woollins
(University of St. Andrews) for a sample of tBuP(NC4H8)2. We are
also grateful to EPSRC for a research studentship (RTAH), and
also for funding the departmental FT IR-Raman facility (Grant
No: GR/M30135), NMR facility (Grant No: GR/L52246), and
X-ray facility (Research Initiative Grant).
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