Stereochemically inactive lone pairs in phosphorus(iii) compounds: The characterisation of some derivatives with the 2,5-(CF3) 2C6H3 (Ar) substituent and their complexation behaviour towards Pt(ii) species

Article abstract of DOI:10.1039/c0dt01313g

Some new phosphorus(iii) derivatives Ar₂PX (X = Br, Cl, F or H), ArPX₂ (X = Br or Cl), Ar₃P and Ar^tBuPCl, with the 2,5-bis(trifluoromethyl)phenyl (Ar) substituent on phosphorus, have been prepared, and characterised by ³¹P and ¹⁹F NMR solution-state spectroscopy. The complexing ability of Ar₂PX, Ar ₃P and Ar^tBuPCl towards the dimeric platinum(ii) complexes [PtY(μ-Y)(PEt₃)]₂ (Y = Cl or Br, the latter for X = Br only) has also been investigated. Single-crystal X-ray diffraction studies at low temperature have been carried out for Ar₃P, Ar₂PCl and the hydrolysis or oxidation products Ar₂P(H)OH and Ar ₂P(O)OH. The structures of Ar₃P and Ar₂PCl are particularly interesting as in each compound the geometry around P is approximately octahedral. In Ar₃P there are three short contacts to fluorine as well as the three bonded C atoms for both of the independent molecules in the unit cell. For Ar₂PCl there are two short P-F contacts, and the octahedron is completed by a weak P-P interaction to a neighbouring molecule. In both instances the lone pair on the P(iii) centre appears to be stereochemically inactive, and does not play a significant role in the structure.

Full text of DOI:10.1039/c0dt01313g

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PAPER
Stereochemically inactive lone pairs in phosphorus(III) compounds: the
characterisation of some derivatives with the 2,5-(CF3)2C6H3 (Ar) substituent
and their complexation behaviour towards Pt(II) species†
Victoria L. Capel,a Keith B. Dillon,*a Andre´s E. Goeta,a Judith A. K. Howard,a Philippa K. Monks,a
Michael R. Probert,a Helena J. Shepherda,b and Natalia V. Zorinaa
Received 30th September 2010, Accepted 21st December 2010
DOI: 10.1039/c0dt01313g
Some new phosphorus(III) derivatives Ar2PX (X = Br, Cl, F or H), ArPX2 (X = Br or Cl), Ar3P and
ArtBuPCl, with the 2,5-bis(trifluoromethyl)phenyl (Ar) substituent on phosphorus, have been prepared,
and characterised by 31P and 19F NMR solution-state spectroscopy. The complexing ability of Ar2PX,
Ar3P and ArtBuPCl towards the dimeric platinum(II) complexes [PtY(m-Y)(PEt3)]2 (Y = Cl or Br, the
latter for X = Br only) has also been investigated. Single-crystal X-ray diffraction studies at low
temperature have been carried out for Ar3P, Ar2PCl and the hydrolysis or oxidation products
Ar2P(H)OH and Ar2P(O)OH. The structures of Ar3P and Ar2PCl are particularly interesting as in each
compound the geometry around P is approximately octahedral. In Ar3P there are three short contacts
to fluorine as well as the three bonded C atoms for both of the independent molecules in the unit cell.
For Ar2PCl there are two short P–F contacts, and the octahedron is completed by a weak P–P
interaction to a neighbouring molecule. In both instances the lone pair on the P(III) centre appears to be
stereochemically inactive, and does not play a significant role in the structure.
derivatives, and often a mixture of products. Only one of the two
possible lithiated compounds has the steric protection afforded
Introduction
The bulky electron-withdrawing ligand 2,4,6-(CF3)3C6H2 (flu-
by two ortho-CF3 groups, although both have the same electron-
oromes) has been used extensively in recent years to sta-
withdrawing substituents. Separation of products can then be
bilise both main group and transition metal species,1 including
difficult or impossible.
phosphorus compounds, some of which have been structurally
For comparison purposes, we decided to attempt the prepa-
characterised.2–15 The combination of steric bulk in the ortho-
ration of some 2,5-(CF3)2C6H3 compounds of phosphorus, via
positions and the electron-withdrawing ability of the –CF3 sub-
lithiation of 1,4-bis(trifluoromethyl)benzene, ArH. The advantage
stituents enables many derivatives to be isolated which would be
is that all four non-substituted positions on the aromatic ring are
thermodynamically unstable, but are stabilised kinetically. This
equivalent in ArH, so there is only one possible monolithiated
stability often seems to be enhanced by secondary short contacts
derivative, ArLi. This ligand will provide only one ortho-CF3
group, of course, like the 2,4-substituted compounds mentioned
above, but will similarly possess two electron-withdrawing sub-
stituents. It thus provides much less steric protection than the 2,6-
or 2,4,6-derivatives, but should have similar electronic properties.
This ligand has so far been very little utilised. The only previous
between the central element and one or more fluorines of the
ortho-CF3 groups.12,15 Less work has been carried out using the 2,6-
(CF3)2C6H3 group, for good reasons.14,16–20 While this ligand, too,
is strongly electron-withdrawing and has bulky ortho-substituents,
synthesis of its derivatives is usually accomplished via lithiation of
the hydrocarbon precursor 1,3-bis(trifluoromethyl)benzene. The
report of phosphorus compounds containing this substituent
problem is that lithiation occurs in two positions, either between
which have been structurally characterised is a very recent one, in
the two –CF3 groups, giving the desired 2,6-(CF3)C6H3 species, or
which two zwitterionic species with Ar as one of the substituents
on a phosphonium centre have been described.21 There are also
only two articles where the ligand has been attached to metals
in structurally-characterised complexes, either as ArH in the
p-complex [Cr(ArH)2],22 or with the Ar group directly bound
to platinum in [ArPtCl(dtBupm)], where dtBupm = bis(di-t-
butylphosphino)methane.23
ortho to one but meta to the second, leading to the isomeric 2,4-
aChemistry Department, University of Durham, South Road, Durham, UK.
DH1 3LE. E-mail: k.b.dillon@durham.ac.uk; Fax: +44 (0)191 384 4737;
Tel: +44 (0)191 334 2092
bCurrently at: Laboratoire de Chimie de Coordination, 205, route de
Narbonne, 31077-Toulouse cedex 04, France
We report the synthesis and characterisation in solution by
31P and 19F NMR spectroscopy of the compounds Ar2PCl (1),
† CCDC reference numbers 795645–795648. For crystallographic data in
CIF or other electronic format see DOI: 10.1039/c0dt01313g
1808 | Dalton Trans., 2011, 40, 1808–1816
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Table 1 31P NMR data for Phosphorus(III) derivatives with the 2,5-(CF3)2C6H3 (Ar) substituent
31
Compound
Number
d P, ppm
d
19F (ortho CF3), ppm
d
19F (para CF3), ppm
d
19F, ppm
4JP–F, Hz
1JP–F, Hz
1JP–H, Hz
Ar2PCl
ArPCl2
Ar3P
Ar2PBr
ArPBr2
Ar2PF
1
2
67.6
-58.0
-56.8
-58.9
-58.0
-57.3
-57.9
-61.0
-55.2
-58.5
-58.0
-64.5
-64.3
-64.9
-64.0
-64.6
-64.4
-65.0
-63.7
-64.0
-63.7
—
—
—
—
—
-189.4
—
—
—
—
66
84
55
66
86
64
39
71
8
—
—
—
—
—
930
—
—
—
—
—
—
—
—
—
—
228
—
550
—
151.2
-16.4
56.9
140.8
145.1
-47.5
97.7
3
4
5
6
Ar2PH
7
ArtBuPCl
Ar2P(O)H
Ar2P(O)(OH)*
8
9
8.8
14.9
10
nr
nr = not resolved. 31P NMR spectrum showed a singlet and the 19F NMR spectrum showed two 1 : 1 singlets.
ArPCl2 (2), Ar3P (3), Ar2PBr (4), ArPBr2 (5), Ar2PF (6), Ar2PH (7),
ArtBuPCl (8), and the hydrolysis or oxidation products Ar2P(O)H
(9) and Ar2P(O)OH (10). The monosubstituted phosphanes
ArPX2 are only present as minor components in solutions formed
by the action of ArLi on PX3, even from equimolar proportions
of the reagents, although they may be readily recognised from
were clearly established). Ar2PCl (1), Ar3P (3), Ar2P(O)H (9) and
Ar2P(O)OH (10) have been fully characterised by single-crystal
X-ray diffraction at low temperature.
Results and discussion
their characteristic NMR coupling patterns (quartets in their 31
P
(a) Synthesis of new phosphorus derivatives
4
spectra and doublets in their 19F spectra, due to JP–F coupling.)
It seems evident that ArLi reacts more readily with ArPX2 than
it does with PX3, leading to the ready formation of Ar2PX. The
complexing behaviour of Ar2PX, ArtBuPCl and Ar3P towards the
dimeric platinum(II) complexes [PtY(m-Y)(PEt3)]2 has also been
investigated (Y = Cl in all instances except for X = Br, where Y
is also Br to avoid any complications from halogen exchange).
In general monomeric trans-[PtY2L(PEt3)] complexes are formed
initially as the kinetic products, though isolation after some time
and partial characterisation by single-crystal X-ray diffraction of
the product where L = Ar2PCl, Y = Cl have shown that the cis-
isomer may eventually be formed as the more thermodynamically
stable product (although the crystals were not of sufficiently good
quality to make the detailed results publishable the connectivities
1,4-Bis(trifluoromethyl)benzene ArH was treated with n-BuLi at
-78◦ C to form the lithiated derivative ArLi. This was then reacted
separately in situ with PX3 (X = Cl or Br) or tBuPCl2, Scheme 1.
In the reaction with the phosphorus trihalides, there was always
more of the disubstituted species Ar2PX formed than of ArPX2
as shown by 31P NMR spectroscopy, whether a 1 : 1 or 1 : 2 molar
ratio of PX3 to ArLi was used. Some Ar3P (3) was also present.
The yield of Ar3P was increased by adding PX3 dropwise to the
cooled ArLi solution, rather than by adding a solution of ArLi to
PX3, thus keeping ArLi in excess relative to PX3 during the early
stages of reaction. The results suggested strongly that ArPX2 is
more reactive towards ArLi than is PX3. 31P and 19F NMR data
for the new phosphorus species prepared are shown in Table 1.
Scheme 1 Reactions of ArLi with PCl3, PBr3 and tBuPCl2.
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Table 2 31P NMR data for Pt(II) complexes synthesised containing phosphorus(III) derivatives with the 2,5-(CF3)2C6H3 (Ar) substituent
trans-[PtX2 (LA)(PBEt3)]
31P
19F
d PA, d PB,
d ortho CF3, d para CF3,
Number
LA
=
X = ppm
ppm 1JPt–PA, Hz 1JPt–PB, Hz 2JP–P, Hz
d
19F, ppm ppm
ppm
1JP–F, Hz 4JP–F, Hz
11
12
13
14
15
16
Ar2PCl
Ar3P
Ar2PBr
Ar2PF
Ar2PH
ArtBuPCl
Cl
Cl
Br
Cl
Cl
Cl
91.9
43.6
72.1
17.8 2694
15.7 ~2400
11.5 2523
2748
2847
2678
2570
2985
2754
565
488
563
567
420
529
—
—
—
-152.5
—
—
-55.9
-63.8
—
—
—
1009
—
6
-54.9
-58.7
-60.3
-52.3
-63.6
-64.3
-65.0
-63.8
5
nr
8
146.5 17.4 3088
16.3 2806
-6.2
112.0 13.6 2466
—
19
nr = not resolved.
t
In the reaction of ArLi with BuPCl2, no evidence was found
(b) Complexation behaviour
t
for formation of the tertiary phosphane Ar2 BuP, irrespective of
These experiments were carried out on an NMR tube scale, by
adding a solution of the chloro-dimer trans-[PtCl(m-Cl)(PEt3)]2
in a 1 : 2 molar ratio to a solution of the appropriate phosphane
Ar2PX (X = Cl, F or H), ArtBuPCl or Ar3P at room temperature
(Scheme 3). Trans-complexes were formed in each case, confirmed
the sequence of addition, probably because of too much steric
hindrance around the central phosphorus atom.
Ar2PF (6) and Ar2PH (7) were synthesised from Ar2PCl in
solution by the action of SbF3 and Bu3SnH respectively, Scheme 2.
The products could be readily recognised by the 1J coupling
between P and F or H, Table 1. When a solution from an
ArLi – PCl3 reaction was layered with hexane and left to stand
for some time in a crystal tube, crystals eventually formed that
were suitable for X-ray diffraction (Section c). These proved to
be of the hydrolysis product Ar2P(O)H (9), rather than Ar2PCl
or Ar3P. Crystals of Ar2PCl (1) and Ar3P (3) were obtained by
alternative procedures (experimental section). A sample of Ar2PF
solution was exposed to air, and produced crystals of the oxidised
and hydrolysed compound, Ar2P(O)OH (10). NMR data for these
species are included in Table 1.
2
by the 31P NMR spectra which showed the expected large JP–P
(488–567 Hz, Table 2) between the inequivalent phosphorus
1
ligands. The JPt–P values were also as expected, between 2300
and 3100 Hz (Table 2).
In a solution containing both Ar2PCl and Ar3P the chlorophos-
phane appeared to react preferentially with the platinum(II)
starting material, with Ar3P remaining largely unaffected. It
proved possible to obtain reaction between Ar3P and the chloro-
dimer when no Ar2PCl was present, even though some of the
unreacted ligand still remained in solution. As a result of line
1
broadening it was difficult to obtain a value of JPtP for the
Ar3P ligand, though this was estimated as ca. 2400 Hz. For
Ar2PBr the corresponding reaction was carried out with the
24
bromo-dimer trans-[PtBr(m-Br)(PEt3)]2
(Scheme 3), to avoid
any complications from halogen exchange. A trans-complex was
again produced (Table 2). Reaction of Ar3P with the bromo-
dimer was also attempted, in the expectation that the Pt–Br bonds
would be more labile, but surprisingly no reaction was apparent
from the NMR spectra, with both starting materials remaining in
solution. This behaviour is discussed further in section (c), where
the molecular structure of Ar3P at low temperature is considered.
An interesting observation in trans-[PtCl2(PEt3)(Ar2PH)] (15), is
that the proton-coupled 31P NMR spectrum showed an apparent
triplet for the resonance of the Ar2PH ligand, J 420 Hz, instead
1
of the expected doublet of doublets. This result implies that JPH
and 2JPP are virtually identical, leading to accidental equivalence.
1
A value of 420 Hz for JPH in a Pt(II) complex of a secondary
phosphane is entirely reasonable; for example, PMes2H gives
1JPH values between 361 and 430 Hz in a range of Pt(II)
complexes.25
Scheme 2 Synthesis of Ar2PF and Ar2PH from Ar2PCl.
Scheme 3 Synthesis of Pt(II) complexes from trans-[PtY(m-Y)(PEt3)]2.
1810 | Dalton Trans., 2011, 40, 1808–1816
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Table 3 Selected bond lengths and angles for compounds (1), (3), (9) and (10)
Compound
Ar2PCl(1)
Ar3P(3)
Ar2P(O)(H) (9)
Ar2P(O)(OH) (10)
P-C1A
P-C1B
P-C1C
1.858(3)
1.858(3)
—
1.847(3)
1.855(3)
1.854(3)
1.825(2)
1.819(2)
—
1.818(2)
1.816(2)
—
P-Cl1
P-O1
P-O2
2.0681(12)
—
—
101.61(13)
—
—
101.12(10)
97.26(10)
—
—
—
—
—
—
—
—
—
—
1.4835(13)
—
111.28(7)
—
—
—
—
113.44(7)
—
111.56(7)
—
—
1.5034(17)
1.5401(17)
112.96(10)
—
—
—
C1A-P-C1B
C1A-P-C1C
C1B-P-C1C
C1A-P-Cl1
C1B-P-Cl1
C1A-P-O1
C1A-P-O2
C1B-P-O1
C1B-P-O2
O1-P-O2
101.51(12)
101.08(12)
100.91(13)
—
—
—
—
—
—
—
—
109.07(10)
106.30(9)
108.45(10)
106.65(10)
113.49(10)
Table 4 Shortest P ◊ ◊ ◊ F contacts in each Ar ligand for compounds (1),
(3), (9) and (10)
The formation of trans-complexes by these phosphanes with
electron-withdrawing aromatic substituents parallels behaviour
previously observed for ligands L such as PPhx(C6F5)3-x (x =
0, 1 or 2), where reaction with the chloro-dimer in refluxing
acetone led to trans-[PtCl2L(PEt3)].26 Similarly, reaction of the
dimer with L’ = PPhx(C6H3F2-2,6)3-x (x = 0, 1 or 2) on gentle heating
in acetone yielded the trans-isomers; the complexes [PtCl2L’2]
were also found to have trans-configurations.27 All the com-
plexes [PtCl2L2], where L = PPh2(C6H4CF3-2), PPh2(C6H4C6F13-
2), PPh2(C6H4C6F13-3), P(C6H4C6F13-4)3 or P(C6H4C6F13-4)2(2-
C6H4C6F13-2), prepared in refluxing dichloromethane (DCM), had
trans-configurations.28 Both cis- and trans-complexes were found
for [PtCl2{P(C6H4C6F13-4)3}(PEt3)] and [PtCl2{P(C6H4C6F13-
4)3}2], after preparation by refluxing in DCM, and in-
deed the isomers of the latter complex co-crystallised.28 For
[PtCl2{PPh2(C6H4C6F13-4)}2] and [PtCl2{PPh(C6H4C6F13)2-4}2]
only cis-isomers were found under similar conditions.28 Hence
normally there is a marked preference for formation of the trans-
complex with one or two strongly electron-withdrawing aromatic
substituents on a phosphane ligand, which is the kinetic reaction
product. Interestingly, in the present work when a few crystals
were isolated from the Ar2PCl reaction after some time, they
were discovered to be of the cis-complex (Section c), even though
only the trans-complex had been observed in solution, and had
remained stable over a minimum of a two-week period. This result
indicates that slow conversion to the thermodynamically more
stable cis-isomer is feasible in some cases in solution (Scheme 3).
Mild preparative conditions were generally used here, which would
again favour formation of the kinetic product in the initial stages.
˚
Compound
P ◊ ◊ ◊ F contact distance (A)
Ar2PCl (1)
2.7092 (21)
2.8419(18)
2.9040 (18)
2.896(1)
3.0111 (22)
2.9232(18)
2.9369 (18)
2.968(1)
—
Ar3P1 (3)
2.9677 (19)
2.9423 (17)
—
Ar3P2
Ar2P(O)(H) (9)
Ar2P(O)(OH) (10)
2.9248 (15)
3.0094 (16)
—
Fig. 1 The molecular structure of Ar2PCl (1) showing the numbering
scheme for the key atoms. Atomic Displacement Parameters (ADPs) are
drawn at 50% probability.
appears to be stereochemically inactive. The angles between trans-
groups in the octahedron are Cl1-P1-F7A1 = 173.13, C1A-P1-
F7B1 = 172.46 and P1¢-P1-C1B = 165.78◦ respectively. Examples
of stereochemically inactive lone pairs in Group 15 octahedral
3- 31
species are known for Sb(III) and Bi(III), in [Sb2Cl11]5-,30 SbBr6
,
3- 32,33
BiCl6
,
and [Bi2Cl11]5-,34,35 but to the best of our knowledge
(c) X-ray crystallography
this is the first such report for a P(III) compound.
The molecular structure of Ar2PCl (1) is shown in Fig. 1; selected
bond lengths and angles are listed in Table 3. The most striking
feature of this structure is the short P–P distance, compared
The molecular structure of Ar3P (3) also demonstrates slightly
distorted octahedral coordination about P, as shown in Fig. 3. In
this structure there is no P–P interaction, however, the octahedral
geometry arising from three P–C bonds and three short P–F
interactions to ortho-CF3 groups. Selected bond distances and
angles are given in Table 3, while the shortest P–F contact distances
are listed in Table 4. There are two independent molecules in
the asymmetric unit, with very similar structures. The angles
with the sum of the van der Waals radii,28 of 3.19 A between
˚
two adjacent molecules, completing approximately octahedral
coordination about P (Fig. 2). This arises from one P–Cl and
two P–C bonds, and two short P–F contacts to ortho-CF3
groups (Fig. 1 and Table 4). The lone pair on phosphorus thus
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Table 5 Experimental data from crystallographic studies of compounds (1), (3), (9) and (10)
Identification code
(1)
(3)
(9)
(10)
Compound
Ar2PCl
C16H6F12PCl
492.63
Ar3P
C24H9F18P
670.28
Ar2P(O)(H)
C16H7F12OP
474.19
120(2) K
Orthorhombic
Pbca
16.1273(3),
8.2646(2),
25.3157(5)
90,
90,
90
3374.22(12)
8
1.867
Ar2P(O)(OH)
C32H14O4F24P2
980.37
120(2) K
Monoclinic
Empirical formula
Formula weight
Temperature
120(2) K
Triclinic
100(2) K
Triclinic
Crystal system
¯
¯
Space group
P1
P1
P21/c
˚
a/A
8.400(2),
9.9017(6),
14.8952(9),
18.3713(11)
100.382(1),
93.644(1),
108.896(1)
2499.8(3)
12.8361(6),
16.8192(8),
8.1211(4)
90,
˚
b/A
10.220(3),
11.474(3)
72.765(3),
72.896(3),
78.100(3)
891.4(4)
˚
c/A
a (◦)
b (◦)
g (◦)
99.455(1),
90
1729.47(14)
2
1.883
0.296
3
˚
Volume/A
Z
2
4
r
calc/mg mm-3
1.835
0.425
484
1.781
0.259
1320
m/mm-1
F(000)
0.296
1872
968
Crystal size/mm
Theta range for data collection
Index ranges
0.18 ¥ 0.13 ¥ 0.09
1.92 to 30.22◦
-11 £ h £ 11,
-14 £ k £ 14,
-15 £ l £ 16
9022
0.19 ¥ 0.17 ¥ 0.11
1.14 to 26.38◦
-12 £ h £ 12,
-18 £ k £ 18,
-22 £ l £ 22
21478
0.32 ¥ 0.28 ¥ 0.21
1.61 to 29.50◦
-22 £ h £ 22,
-11 £ k £ 11,
-35 £ l £ 35
41514
0.2 ¥ 0.18 ¥ 0.17
1.61 to 28.27◦
-17 £ h £ 17,
-21 £ k £ 22,
-10 £ l £ 10
16428
Reflections collected
Independent reflections
4696
10178
4694
4265
[R(int) = 0.0429]
4696/54/272
1.029
[R(int) = 0.0403]
10178/0/775
1.028
[R(int) = 0.0207]
4964/1/299
1.070
[R(int) = 0.0271]
4265/54/290
1.065
Data/restraints/parameters
Goodness-of-fit on F2
Final R indices [I > 2s(I)]
R1 = 0.0591,
wR2 = 0.1085
R1 = 0.1108,
wR2 = 0.1253
0.663/- 0.582
R1 = 0.0507,
wR2 = 0.1052
R1 = 0.0820,
wR2 = 0.1162
0.640/- 0.480
R1 = 0.0406,
wR2 = 0.1079
R1 = 0.0433,
wR2 = 0.1100
0.607/- 0.388
R1 = 0.0461,
wR2 = 0.1120
R1 = 0.0559,
wR2 = 0.1180
0.702/- 0.801
Final R indices
[all data]
Largest diff. peak/hole (e A )
-3
˚
Fig. 2 Ar2PCl dimer illustrating the octahedral coordination of the P
atoms, completed by the P–P intermolecular bond. ADPs are drawn at
50% probability.
Fig. 3 The molecular structure of Ar3P (3), showing the numbering
scheme for the key atoms. ADPs are drawn at 50% probability.
between trans-groups about P1 range from 169.16 – 171.76◦, and
those about P2 from 169.37 – 173.15◦, with the lone pair again
stereochemically inactive. In section (b) it was noted that Ar3P
(3) reacts only to a limited extent with the platinum chloro-dimer
trans-[PtCl(m-Cl)(PEt3)]2, and not at all with its bromo-analogue,
although the electronegative ligands on P would be expected to
favour coordination. This behaviour may thus be attributed to the
unavailability of a directed lone pair in (3). Ar2PCl (1) did react
more readily than Ar3P with the chloro-dimer (section (b)), so a
possible explanation could be the scission of the P–P interaction in
solution, breaking up the y-octahedral structure and facilitating
coordination to a transition metal. There will also be more steric
hindrance to complex formation by Ar3P than by Ar2PCl, because
of the three ortho-CF3 groups in the former. This factor seems
unlikely to predominate, however, since [2,4,6-(CF3)3C6H2]2PCl,
with four ortho-CF3 groups, reacts readily with the platinum
chloro-dimer.
Compound (9), Ar2P(O)H, exists in the phosphorus(V) form
in the solid state with a P–H bond, Fig. 4. The P O bond
˚
length of 1.4835(13) A may be compared with recent literature
36
37
38
˚
˚
˚
values of 1.476(3) A, 1.4819(19) A and 1.4894(15) A in
1812 | Dalton Trans., 2011, 40, 1808–1816
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or two o-CF3 groups on the aromatic ring.12,15,17 The distance of
˚
2.7092(21) A in Ar2PCl thus lies towards the shorter end of the
normal range.
As mentioned earlier a few crystals were isolated from the reac-
tion of Ar2PCl with trans-[PtCl(m-Cl)(PEt3)]2. The crystals showed
signs of twinning and disorder, making the results unsuitable for
publication, although the connectivities were confirmed. These
showed that the cis-isomer of [PtCl2(Ar2PCl)(PEt3)] had formed,
suggesting that this is the thermodynamic product, as expected.
Conclusions
Several phosphorus(III) derivatives containing the 2,5-(CF3)2C6H3
(Ar) substituent have been successfully prepared, four of which
have been fully characterised by single-crystal X-ray diffraction
at low temperature. Two of these structures, for Ar2PCl (1) and
Ar3P (3), are particularly interesting, since in each case the
phosphorus has an approximately octahedral geometry, and the P
lone pair appears to be stereochemically inactive. Ar3P (3) proved
reluctant to react with the platinum(II) species, possibly arising
from this enclosed pseudo-octahedral environment. Ar2PCl (1)
reacted readily with trans-[PtCl(m-Cl)(PEt3)]2, suggesting that the
P–P interaction found in the solid state may break up in solution,
giving a geometry more receptive to coordination to a transition
metal.
Fig. 4 The molecular structure of Ar2P(O)(H) (9), showing the numbering
scheme for the key atoms. ADPs are drawn at 50% probability.
other compounds of this type. There is an H-bonding interaction
between H1P on P1 and the oxygen atom O1A of an adjacent
˚
molecule, at a distance of 2.868(10) A; the P–H–O bond angle is
149.8(11)◦.
The oxidation product (10), Ar2P(O)OH, (Fig. 5) shows only a
small difference in the phosphorus-oxygen bond lengths (Table 3),
˚
with the nominal double bond at 1.5034(17) A and the P-OH
˚
bond at 1.5401(17) A. This again compares well with recent
39
˚
literature data for similar acids, e.g. 1.5053(14) and 1.5584(15) A,
1.4851(19) and 1.561(3) A, 1.502 and 1.524 A,41 and 1.503(1) and
40
˚
˚
1.532(1) A respectively.42 It forms strongly H-bonded symmetrical
dimers between the P-OH group in one molecule and the P
group in an adjacent molecule (and vice versa). The O–O distance
˚
Other ArP(III) derivatives reacted with dimeric platinum(II)
species to form the trans-complexes in solution as the kinetic
products, although the few crystals isolated from the Ar2PCl
reaction proved to be of the more thermodynamically stable cis-
isomer.
O
˚
˚
of 2.479 A compares well with that of 2.497(2) A in the H-bonded
dimer of the isomeric acid [2,4-(CF3)2C6H3]2P(O)OH,42 and with
˚
similar O–O distances between 2.441(3) and 2.554(3) A in other
recent structure determinations for compounds of this type.40,41
Experimental
All manipulations, including NMR sample preparation, were
carried out either under an inert atmosphere of dry nitrogen or
in vacuo, using standard Schlenk line or glovebox techniques.
Chemicals of the best available commercial grade were used, in
general without further purification. All solvents, unless otherwise
stated were dried prior to use. The 31P NMR spectra of all
phosphorus-containing starting materials were recorded, to verify
that no major impurities were present. 31P NMR spectra were
obtained on Varian Mercury 200, Varian Unity 300, Mercury 400
or Inova 500 Fourier-transform spectrometers at 80.96, 121.40,
161.91 or 202.3 MHz, respectively; chemical shifts are referenced
to 85% H3PO4, with the high frequency direction taken as
positive. 19F spectra were recorded on Varian Mercury 200 or
Mercury 400 at 188.18 and 376.34 MHz, respectively; chemical
shifts are referenced to external CFCl3, with the high frequency
direction taken as positive. Microanalyses were performed by the
microanalytical services of the Department of Chemistry, Durham
University.
Fig. 5 The molecular structure of Ar2P(O)(OH) (10) showing the
numbering scheme for key atoms. ADPs are drawn at 50% probability.
All of the new structures have P–F contacts at distances appre-
ciably shorter than the sum of the van der Waals radii,29 as shown
in Table 4. These contacts clearly play a crucial role in determining
the geometry in (1) and (3), and apparently the chemical reactivity
in (3) in particular, as discussed above, while compounds (9)
and (10) also have some comparatively short P–F interactions.
Synthesis of ArLi
The shortest P–F contacts reported to an ortho-CF3 group are
at 2.554(2) and 2.562(11) A in a phosphenium salt, while P–F
BuLi (9.2 ml; 23 mmols) was added dropwise to a solution of 1,4-
bis(trifluoromethyl) benzene (4 ml; 26 mmol) in Et2O (30 ml) at
-78 ◦C. The solution was allowed to warm to room temperature
slowly.
18
˚
˚
distances of between 2.843 and 3.250 A have been ascertained
previously in several other arylphosphorus compounds with one
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Synthesis of Ar2PCl (1)
Synthesis of ArtBuPCl (8)
ArLi solution (as prepared above) was added dropwise to a
solution of PCl3 (1 ml; 12 mmols) in Et2O (30 ml) at -78 ◦C. The
solution was allowed to warm to room temperature and left to
stir for 18 h. Following filtration to remove LiCl, the solution was
concentrated and then cooled to afford large colourless crystals.
(Found: C 39.20% H 1.30% N 0.00% C16H6ClF12P requires C
39.01% H 1.23% N 0.00%). 31P (121.40 MHz, CDCl3): d 67.6 ppm
ArLi solution (19 ml, 2.6 mmols) was added dropwise to a solution
◦
t
of BuPCl2 (0.142 g; 2.6 mmols) in Et2O (20 ml) at -78 C. The
solution was allowed to warm to room temperature and left to
stir for 18 h. Following filtration to remove LiCl, the solution was
concentrated. 31P (161.9 MHz, CDCl3): d 97.7 ppm (q, 4JP–F = 71
4
Hz). 19F (376.34 MHz, CDCl3): d -55.2 ppm (d, JP–F = 71 Hz,
ortho-CF3), d -63.7 ppm (s, para-CF3). Quantitative conversion of
(sept, JP–F = 66 Hz). 19F (376.34 MHz, CDCl3): d -58.0 ppm (d,
ArLi to ArtBuPCl was observed from 31P NMR spectra.
4
4JP–F = 66 Hz, ortho-CF3), d -64.5 ppm (s, para-CF3). 78% yield
from 31P NMR spectra.
Isolation of Ar2P(O)H (9)
A solution from one of the ArLi-PCl3 reactions was layered with
hexane and place in a crystal tube. White crystals suitable for
X-ray analysis eventually formed, proved to be of the hydrolysis
product Ar2P(O)H, presumably formed by ready rearrangement
of Ar2P(OH). This compound was also prepared from Ar2PCl
by adding reagent grade DCM and leaving the mixture to stand
until conversion was complete. Found: C 40.29% H 1.50% N
Synthesis of Ar3P (3)
PCl3 (1 ml; 12 mmols) was added dropwise to a solution of
ArLi (as prepared above) at -78 ◦C. The solution was allowed
to warm to room temperature and left to stir for 18 h. Following
filtration to remove LiCl, the solution was concentrated and then
cooled to afford large colourless crystals. (Found: C 42.85% H
1.38% N 0.00% C24H9F18P requires C 43.01% H 1.35% N 0.00%).
31P (121.40 MHz, CDCl3): d -16.4 ppm (10 line multiplet). 19F
(376.34 MHz, CDCl3): d -58.9 ppm (d, 4JP–F = 55 Hz, ortho-CF3),
d -64.9 ppm (s, para-CF3); m/z (EI) 670 (100%, M+) and 319
(89%, M+ - Ar - 2CF3); m.p. 111–113 ◦C; Isolated yield: 65%.
1
0.00% C16H7F12OP requires C 40.53% H 1.49% N 0.00%. 31P { H}
(161.9 MHz, CDCl3): d 8.8 ppm (sept). 31P (161.9 MHz, CDCl3):
d 8.8 ppm (d of sept, 1JP–H = 550 Hz). 19F (376.34 MHz, CDCl3): d
-58.5 ppm (d, 4JP–F = 8 Hz, ortho-CF3), d -64.0 ppm (s, para-CF3).
m/z (EI) 474 (20%, M+), 405 (100%, M+ - CF3) and 144 (70%,
C6H3CF3); m.p. 96–100 ◦C.
Isolation of Ar2P(O)(OH) (10)
Synthesis of Ar2PBr (4)
A solution of Ar2PF was exposed to air. Crystals were isolated
after some time and X-ray analysis showed that these were
Ar2P(O)(OH). Found: C 39.02% H 1.99% N 0.00% C16H7F12O2P
ArLi solution (38 ml, 24 mmols) was added dropwise to a solution
of PBr3 (1.1 ml; 11 mmols) in Et2O (30 ml) at -78 ◦C. The solution
was allowed to warm to room temperature and left to stir for 18 h.
requires C 39.20% H 1.44% N 0.00%. 31P (161.9 MHz, CDCl3): d
The solvent was removed in vacuo, and the product extracted
4
14.9 ppm (s). 19F (376.34 MHz, CDCl3): d -58.0 ppm (d, JP–F
=
4
using DCM. 31P (161.9 MHz, CDCl3): d 56.9 ppm (sept, JP–F
=
64 Hz, ortho-CF3), d -63.7 ppm (s, para-CF3).
66 Hz). 19F (376.34 MHz, CDCl3): d -58.0 ppm (d, 4JP–F = 66 Hz,
ortho-CF3), d -64.0 ppm (s, para-CF3). 58% yield from 31P NMR
spectra.
Synthesis of trans-[PtCl2(Ar2PACl)(PBEt3)] (11)
A solution of trans-[PtCl(m-Cl)(PEt3)]2 (0.0276g; 0.04 mmols) in
CDCl3 was added to Ar2PCl (0.0419g; 0.08 mmols) in a Young’s
NMR tube. 31P (161.9 MHz, CDCl3): dPA 91.9 ppm (d + sats,
Synthesis of Ar2PF (6)
2
1
SbF3 was added to a solution of Ar2PCl (1 : 1 ratio) in DCM. The
solution was stirred and heated to reflux for 24 h. The solution
was filtered to afford a dark orange solution.31P (121.40 MHz,
1JPt–P = 2694 Hz, JP–P = 565 Hz) dPB 17.8 ppm (d + sats, JPt–P
=
2748 Hz, 2JP–P = 565 Hz). 19F (376.34 MHz, CDCl3): d -55.9 ppm
(d, 4JP–F = 6 Hz, ortho-CF3), d -63.8 ppm (s, para-CF3).
CDCl3): d 145.1 ppm (d of sept1JP–F = 930 Hz, JP–F = 64 Hz).
4
19F (376.34 MHz, CDCl3): d -57.9 ppm (d, JP–F = 64 Hz, ortho-
4
Synthesis of trans-[PtCl2(Ar3PA)(PBEt3)] (12)
CF3), d -64.41 ppm (s, para-CF3), d -189.4 ppm (d of sept, 1JP–F
=
A solution of trans-[PtCl(m-Cl)(PEt3)]2 (0.0500g; 0.065 mmols) in
CDCl3 was added to Ar3P (0.0871g; 0.13 mmols) in a Young’s
NMR tube. 31P (161.9 MHz, CDCl3): dPA 43.6 ppm (d + sats,
930 Hz, P-F). From the 31P and 19F NMR spectra, the conversion
of Ar2PCl to Ar2PF appeared to be essentially quantitative.
1JPt–P = ~2400 Hz, 2JP–P = 488 Hz) dPB 15.7 ppm (d + sats, 1JPt–P
2847 Hz, 2JP–P = 488 Hz).
=
Synthesis of Ar2PH (7)
Bu3SnH (0.37 ml, 12 mmols) was added dropwise to a solution of
Ar2PCl (0.5 ml, 12 mmols) at room temperature. The solution was
Synthesis of trans-[PtCl2(Ar2PABr)(PBEt3)] (13)
1
stirred for 4 h to afford a yellow solution. 31P { H} (121.40 MHz,
A solution of trans-[PtCl(m-Cl)(PEt3)]2 (0.0601g; 0.065 mmols) in
CDCl3 was added to Ar2PBr (0.0710g; 0.13 mmols) in a Young’s
NMR tube. 31P (161.9 MHz, CDCl3):): dPA 72.1 ppm (d + sats,
4
CDCl3): d -47.5 ppm (sept, JP–F = 39 Hz). 31P (121.40 MHz,
CDCl3): d -47.5 ppm (d of sept, 1JP–H = 228 Hz, 4JP–F = 39 Hz). 19
F
(376.34 MHz, CDCl3): d -61.0 ppm (d, 4JP–F = 39 Hz, ortho-CF3), d
-65.0 ppm (s, para-CF3). The conversion of Ar2PCl to Ar2PH also
appeared to be quantitative from the 31P and 19F NMR spectra.
1JPt–P = 2523 Hz, JP–P = 563 Hz) dPB 11.5 ppm (d + sats, JPt–P
=
2
1
2678 Hz, 2JP–P = 563 Hz). 19F (376.34 MHz, CDCl3): d -54.9 ppm
(d, 4JP–F = 5 Hz, ortho-CF3), d -63.6 ppm (s, para-CF3).
1814 | Dalton Trans., 2011, 40, 1808–1816
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Synthesis of trans-[PtCl2(Ar2PAF)(PBEt3)] (14)
constrained to those CF3 groups not involved in P–F contacts,
again highlighting the importance of these interactions.
A solution of trans-[Pt(PEt3)Cl(m-Cl)]2 in CDCl3 was added to
Ar2PF (1 : 2 ratio) in a Young’s NMR tube. 31P (121.40 MHz,
1
2
CDCl3): dPA 146.5 ppm (d + sats, JPt–P = 3088 Hz, JP–P = 567
Acknowledgements
Hz) dPB 17.4 ppm (d + sats, 1JPt–P = 2570 Hz, 2JP–P = 567 Hz). 19
F
We would like to thank Dr D. S. Yufit for determining one
of the crystal structures, the EPSRC (UK) for research grant
EP/C536436/1 (MRP), and for a research studentship (HJS),
and the Maria da Grac¸a Memorial Fund/Chemistry Department,
University of Durham (PKM), for financial support.
(376.34 MHz, CDCl3): d -52.3 ppm (d, 4JP–F = 19 Hz, ortho-CF3),
d -63.8 ppm (s, para-CF3).
Synthesis of trans-[PtCl2(Ar2PAH)(PBEt3)] (15)
A solution of trans-[PtCl(m-Cl)(PEt3)]2 (0.0570g; 0.075 mmols) in
CDCl3 was added to Ar2PH (0.15 mmols) in a Young’s NMR tube.
31P (161.9 MHz, CDCl3): dPA -7.6 ppm (d + sats, 1JPt–P = 2362 Hz,
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©