Unusual neutral ligand coordination to arsenic and antimony trifluoride

Article abstract of DOI:10.1039/c1dt10113g

The preparations and spectroscopic characterisation of the hydrolytically unstable As(iii) complexes, [AsF₃(OPR₃)₂] (R = Me or Ph) and [AsF₃{Me₂P(O)CH₂P(O)Me ₂}] are described and represent the first examples of complexes of AsF₃ with neutral ligands. The crystal structure of [AsF ₃{Me₂P(O)CH₂P(O)Me₂}] contains dimers with bridging diphosphine dioxide, but there are also long contacts between the dimers to neighbouring phosphine oxide groups, completing a very distorted six-coordination at arsenic and producing a weakly associated polymer structure. The reaction of AsF₃ with OAsPh₃ affords Ph₃AsF₂, and no arsine oxide complex was formed. Reaction of SbF₃ with OER₃ (R = Me or Ph, E = P or As), Me ₂P(O)CH₂P(O)Me₂ and Ph₂P(O)(CH ₂)_nP(O)Ph₂ (n = 1 or 2) in MeOH produces [SbF₃(OER₃)₂], [SbF₃{Me ₂P(O)CH₂P(O)Me₂}] and [SbF₃{Ph ₂P(O)(CH₂)_nP(O)Ph₂}] respectively. The X-ray structures reveal that the complexes contain square pyramidal SbF ₃O₂ cores with apical F and cis disposed pnictogen oxides. However, whilst [SbF₃(OER₃)₂] (R = Ph: E = P or As; R = Me: E = As) and [SbF₃{Ph₂P(O)CH ₂P(O)Ph₂}] are monomeric, [SbF₃{Me ₂P(O)CH₂P(O)Me₂}] is a dimer with bridging diphosphine dioxides producing a twelve-membered ring, and [SbF ₃{Ph₂P(O)(CH₂)₂P(O)Ph₂}] is a chain polymer with diphosphine dioxide bridges. In the OAsR₃ reactions with SbF₃, R₃AsF₂ are also formed. Notably the Sb-O(P) bonds are shorter than As-O(P), despite the covalent radii (As < Sb), consistent with very weak coordination of the AsF₃. IR and multinuclear (¹H, ¹⁹F and ³¹P) NMR data are reported and discussed. BiF₃ does not react with pnictogen oxide ligands under similar conditions and halide exchange of bismuth chloro complexes with Me₃SnF gave BiF₃.

Full text of DOI:10.1039/c1dt10113g

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PAPER
Unusual neutral ligand coordination to arsenic and antimony trifluoride†
William Levason,a Mark E. Light,*a Seema Maheshwari,a,b Gillian Reid*a and Wenjian Zhanga
Received 19th January 2011, Accepted 14th March 2011
DOI: 10.1039/c1dt10113g
The preparations and spectroscopic characterisation of the hydrolytically unstable As(III) complexes,
[AsF3(OPR3)2] (R = Me or Ph) and [AsF3{Me2P(O)CH2P(O)Me2}] are described and represent the first
examples of complexes of AsF3 with neutral ligands. The crystal structure of [AsF3{Me2P(O)CH2-
P(O)Me2}] contains dimers with bridging diphosphine dioxide, but there are also long contacts between
the dimers to neighbouring phosphine oxide groups, completing a very distorted six-coordination at
arsenic and producing a weakly associated polymer structure. The reaction of AsF3 with OAsPh3
affords Ph3AsF2, and no arsine oxide complex was formed. Reaction of SbF3 with OER3 (R = Me or
Ph, E = P or As), Me2P(O)CH2P(O)Me2 and Ph2P(O)(CH2)nP(O)Ph2 (n = 1 or 2) in MeOH produces
[SbF3(OER3)2], [SbF3{Me2P(O)CH2P(O)Me2}] and [SbF3{Ph2P(O)(CH2)nP(O)Ph2}] respectively. The
X-ray structures reveal that the complexes contain square pyramidal SbF3O2 cores with apical F and cis
disposed pnictogen oxides. However, whilst [SbF3(OER3)2] (R = Ph: E = P or As; R = Me: E = As) and
[SbF3{Ph2P(O)CH2P(O)Ph2}] are monomeric, [SbF3{Me2P(O)CH2P(O)Me2}] is a dimer with bridging
diphosphine dioxides producing a twelve-membered ring, and [SbF3{Ph2P(O)(CH2)2P(O)Ph2}] is a
chain polymer with diphosphine dioxide bridges. In the OAsR3 reactions with SbF3, R3AsF2 are also
formed. Notably the Sb–O(P) bonds are shorter than As–O(P), despite the covalent radii (As < Sb),
consistent with very weak coordination of the AsF3. IR and multinuclear (1H, 19F and 31P) NMR data
are reported and discussed. BiF3 does not react with pnictogen oxide ligands under similar conditions
and halide exchange of bismuth chloro complexes with Me3SnF gave BiF3.
a fluorinating agent (Swarts reagent) for organic and inorganic
Introduction
chloro-compounds;4 arsenic trifluoride also found limited use as
The widely acknowledged renaissance in p-block chemistry over
a fluorinating agent but has been superceded by less corrosive
the last decade has included significant developments in the
and toxic reagents. In contrast, BiF3 is insoluble in common
coordination chemistry of the heavier p-block halides (chlorides,
solvents and inert. The only structurally characterised adducts
of AsF3 functioning as a Lewis acid appear to be [AsF4]-, [As2F7]-
bromides, iodides). In contrast, similar studies of the fluorides are
very limited. Within Group 15, the elements, arsenic, antimony
and bismuth all form trivalent and pentavalent fluorides which
show varying degrees of Lewis acidity. However, they are mostly
also strong fluorinating agents and hence their reactions with
organic ligands can result in fluorination over coordination.1–3
Arsenic trifluoride is a colourless, corrosive liquid at ambient
temperatures and is composed of pyramidal AsF3 molecules in
the solid state. In contrast, SbF3 is a polymeric solid and contains
a distorted six-coordinate antimony environment with three
short and three long Sb–F bonds, whilst BiF3 contains bismuth
in a very distorted nine-coordinate environment.1,2 Antimony
trifluoride is widely used (usually with some added SbCl5) as
and [As4F13]-,5 whilst it behaves as a Lewis base via the As
5
lone pair in [(h -C5H5)Mn(CO)2(AsF3)] and [Au(AsF3)SbF6],6
and as a fluorine donor ligand towards some “naked-” d, f
or s block metal cations.7 SbF3 forms a range of fluoroan-
ions including [SbF4]-, [Sb2F7]-, [Sb3F10]-, [Sb4F13]-, [Sb2F10]4-,
[Sb4F16]4-,3,8–10 but only a few complexes with neutral ligands
have been fully characterised, including [SbF3(crown)] (crown =
15-crown-5, 18-crown-6) and [(SbF3)2(12-crown-4)], all of which
˚
contain pyramidal SbF3 units weakly interacting (~3.0–3.2 A)
with the crown oxygen atoms,11 [SbF3(L)] (L = 12,13-benzo-1,10-
di(azamethyl)-4,7-dioxacyclotetradecane-11,14-dione),12 [SbF3(4-
MeO-C5H4NO)2]13 and two amino acid adducts in which the
amino acid bridges the five-coordinate Sb(III) atoms.14 Bismuth(III)
fluoride also forms fluoroanions with a variety of stoichiometries;
these have high bismuth coordination numbers (8 or 9) and some
behave as fast fluoride ion conductors,3,15 but again there seem to
be no well established examples of neutral ligand complexes.
The heavier trihalides of arsenic, antimony and bismuth, MX3
(M = As, Sb or Bi; X = Cl, Br or I) are modest Lewis acids
aSchool of Chemistry, University of Southampton, Southampton, UK, SO17
1BJ. E-mail: G.Reid@soton.ac.uk; Fax: +44 (0)23 80593781, E-mail:
M.E.Light@soton.ac.uk
bDepartment of Pure and Applied Chemistry, M. D. S. University, Ajmer,
305009, India
† CCDC reference numbers 803403–803408. For crystallographic data in
CIF or other electronic format see DOI: 10.1039/c1dt10113g
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and form complexes with a variety of neutral donor ligands from
Group 15 and 16.3 The structures, although complicated in detail,
are often characterised by the presence of pyramidal MX3 or
dimeric X2M(m-X)2MX2 units with the remaining coordination
sites occupied by weakly bound neutral ligands or bridging
halides. The As, Sb or Bi based lone pairs show varying degrees
of stereochemical activity (often most evident in the case of
antimony); in some cases a vacant vertex site is found (assumed
to be occupied by the lone pair), but in other cases the lone pair
appears inactive and is presumably in the ns orbital. In solution in
non-coordinating solvents, the complexes are typically extensively
dissociated.
Here we report the results of our studies of the reactions of the
AsF3 and SbF3 with a series of (neutral) pnictogen oxides, which
were selected since the hard O-donor groups would be expected
to offer the maximum likelihood of coordination to the Group 15
trifluorides. IR and multinuclear (1H, 19F and 31P) NMR data are
reported for all the new complexes and the crystal structures of
representative examples are reported.
Fig. 1 View of the structure of the [AsF3{Me2P(O)CH2P(O)Me2}]
polymer with atom numbering scheme. Ellipsoids are drawn at the 50%
probability level and H◦atoms are omitted for clarity. Selected bond
˚
lengths (A) and angles ( ): As1–F1 = 1.7414(15), As1–F2 = 1.7562(15),
As1–F3 = 1.7587(15), As1–O1 = 2.5750(17), As1–O2a = 2.6327(17),
As1–O2b = 2.9655(18), P1–O1 = 1.4978(17), P2–O2 = 1.5029(17),
F1–As1–F2 = 92.64(7), F1–As1–F3 = 90.48(7), F2–As1–F3 = 90.98(8),
F1–As1–O1 = 80.68(6), F2–As1–O1 = 80.86(6), F1–As1–O2a = 84.55(7),
F3–As1–O2a = 87.54(7), O1–As1–O2a = 100.13(6), F2–As1–O2b =
83.93(6), F3–As1–O2b
=
79.72(6), O1–As1–O2b
=
108.41(5),
O2a–As1–O2b = 98.57(5). Symmetry operations: a = 1 -x, 1 -y,
-z; b = x, 1 + y, z.
Results and discussion
AsF3 Complexes
a distorted octahedron about the arsenic atoms and lead to a
weakly assembled polymer structure. The sum of the van der
Very moisture sensitive, white powders were obtained from the
reaction of AsF3 with OPPh3, OPMe3 and Me2P(O)CH2P(O)Me2
in anhydrous CH2Cl2 solution. These were identified by microanal-
ysis as [AsF3(OPR3)2] and [AsF3{Me2P(O)CH2P(O)Me2}]. How-
ever, attempts to isolate complexes with Ph2P(O)(CH2)nP(O)Ph2
(n = 1, 2) were unsuccessful (the unreacted ligands being recov-
ered), although in situ 19F and 31P NMR spectroscopic studies
suggested some interaction of AsF3 and Ph2P(O)CH2P(O)Ph2
in CH2Cl2 solution. The complexes are extremely moisture
sensitive especially in solution, losing AsF3 easily. In contrast,
[AsF3(OAsPh3)2] did not form from the reaction of AsF3 with
OAsPh3, which instead produced Ph3AsF2 identified by its IR spec-
˚
Waals radii of As and O is 3.4 A. This very distorted six-
coordination contrasts with the five-coordination found in the
directly analogous [SbF3{Me2P(O)CH2P(O)Me2}] (below). The
As–F(1) bond, which is trans to the long As ◊ ◊ ◊ O, is shorter
˚
˚
(1.741(2) A) than the other two (1.756(2), 1.769(2) A), and the
two shorter As–O bonds disposed cis are 2.575(2) and 2.633(2)
˚
A. Notably, these bonds are longer than the Sb–O bonds in
[SbF3{Me2P(O)CH2P(O)Me2}] despite the smaller covalent radius
˚
˚
of As (1.21 A) compared to Sb (1.41 A), indicating very weak As–
O interactions. The P–O bonds are not significantly different in
the two complexes, and only slightly lengthened from those in
1
trum, the 19F{ H} chemical shift of d = -89.5, and by the unit cell
19
˚
Me2P(O)CH2P(O)Me2 itself (1.489(3), 1.492(3) A). The As–F
of the colourless crystals isolated from the reaction mixture.16–18
Fluorination of arsine oxides by some p-block fluorides (e.g. SiF4)
has been observed previously.19
˚
bonds in solid AsF3 are 1.699(12) to 1.721(10)◦A and in the ga◦s
˚
phase are 1.708 A, with ∠F–As–F 92.9 to 95.5 (solid) or 95.97
(gas).21 The structural data therefore suggest little perturbation of
the AsF3 moiety, and very weak interaction with the phosphine
oxide groups, which mirrors the low stability of these complexes.
The spectroscopic data on the AsF3 complexes are generally
similar to those of the antimony analogues (below), showing IR
spectra with low frequency shifts in the u(P O) vibrations and
strong bands in the region ~580–650 cm-1 assigned as terminal
As–F modes.20 The NMR spectra are consistent with exchanging
SbF3 Complexes
systems and show a single line in the 31P{ H} NMR spectra
White solids formulated as [SbF3(OPR3)2] (R = Me or Ph) and
[SbF3{R2P(O)(CH2)nP(O)R2}] (R = Ph or Me: n = 1; R = Ph: n =
2) were obtained by stirring solutions of anhydrous SbF3 and the
appropriate ligand in anhydrous methanol for several hours. The
reactions did not occur on stirring the ligand with a suspension of
SbF3 in CH2Cl2, andwere incompleteinMeCN solution. Similarly,
[SbF3(OAsR3)2] (R = Me or Ph) were obtained from methanol
solution, although the reactions are less clean. In addition to the
formation of [SbF3(OAsR3)2], variable amounts of R3AsF2 are
also formed, readily identified by their characteristic IR spectra16
and 19F NMR chemical shifts17,22 (R = Ph: d = -89.6; R = Me:
d = -53.6). The R3AsF2 can be removed by careful washing with
n-hexane, or recrystallisation. Attempts to isolate complexes with
softer neutral sulfur ligands, including Ph3PS and MeS(CH2)2SMe,
1
with small positive coordination shifts. In CH2Cl2 solution, AsF3
exhibits a singlet in the 19F{ H} NMR spectra at d = -43.5, and
1
freshly prepared solutions of the complexes each show singlet
resonances in the range d ~-46 to -53, which show only small
temperature drifts on cooling to 190 K. On standing in solution in
CH2Cl2 some decomposition occurs, evidenced by the appearance
of new resonances at lower frequency in the 19F NMR spectra.
Needle crystals of [AsF3{Me2P(O)CH2P(O)Me2}] were ob-
tained directly from the reaction mixture upon cooling, and the
structure (Fig. 1) reveals pyramidal AsF3 units coordinated to
bridging diphosphine dioxides to give a 12-membered ring, but
˚
in addition, there are weak O ◊ ◊ ◊ As (2.966(2) A) contacts from
the diphosphine dioxides of neighbouring rings which complete
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under similar reaction conditions were unsuccessful. This is in
marked contrast to the ready formation of several series of
complexes of the heavier SbX3 (X = Cl, Br or I) with neutral
S- and Se-donor ligands.23–28
In contrast to the AsF3 systems above, the SbF3 phosphine- and
arsine-oxide complexes are mostly white powders or colourless
crystals, not appreciably moisture-sensitive in the solid state, and
modestly soluble in anhydrous CH2Cl2, MeCN or MeOH. Spec-
troscopic data provided limited structural information, and thus
we also undertook X-ray crystal structure analyses for several of
the new complexes, since no literature data exist in this area. In
fact, we find that although the structures with the different ligands
differ in detail, all are based upon a square pyramidal SbF3O2
core with apical F, the “free site” presumably accommodating a
stereochemically active lone pair. A similar SbF5 core geometry is
found in many fluoroantimonate(III) structures.9
Fig. 3 View of the structure of [SbF3(OAsPh3)2] showing the major
component of the disorder, with atom numbering scheme adopted.
The structure of [SbF3(OAsMe3)2] (Fig. 2) shows a discrete
square pyramidal molecule with an apical fluorine (Sb–F(1) =
Ellipsoids are drawn at the 50% probability level and
H
atoms
◦
˚
are omitted for clarity. Selected bond lengths (A) and angles ( ):
Sb1a–F1a = 2.10(2), Sb1a–F2a = 1.96(3), Sb1a–F3a = 1.918(13), Sb1a–
O1 = 2.363(6), Sb1a–O2 = 2.300(5), As1–O1 = 1.666(5), As2–O2 = 1.682(5),
F1a–Sb1a–F2a = 83.5(10), F1a–Sb1a–F3a = 71.8(6), F2a–Sb1a–F3a =
88.2(7), F1a–Sb1a–O1 = 93.4(6), F1a–Sb1a–O2 = 151.2(5), F2a–Sb1a–
˚
1.943(2) A) and the antimony lying below the base plane, which
results in all the angles involving F(1) being < 90◦. The basal Sb–F
˚
bonds are slightly longer (Sb–F = 2.002(2), 2.010(2) A) with the
angle between the cis fluorines (F(2) and F(3)) of 84.69(10)◦. The
Sb–F bond lengths may be compared with the three shortest bond◦s
O1
= 162.0(6), F2a–Sb1a–O2 = 84.7(8), F3a–Sb1a–O1 = 74.0(4),
29
˚
in solid SbF3 (1.94(2)–1.90(2) A). The O–Sb–O angle is 99.9(1)
F3a–Sb1a–O2 = 81.7(8), O2–Sb1a–O1 = 89.8(2).
˚
and d(As–O) = 1.680(3), 1.692(3) A. Crystal structures were also
obtained for [SbF3(OAsPh3)2] and [SbF3(OPPh3)2] and both are
similar square pyramidal monomers with apical fluorine and cis
disposed pnictogen oxides (Fig. 3). Both sets of crystals were
twinned, and while for [SbF3(OAsPh3)2] the pseudo-merohedral
twinning was modelled satisfactorily, this was less successful
for [SbF3(OPPh3)2]‡ (see Experimental Section), hence only the
former is described in detail.
Fig. 2 View of the structure of [SbF3(OAsMe3)2] with atom numbering
Fig. 4 View of the structure of [SbF3{Ph2P(O)CH2P(O)Ph2}] with
scheme. Ellipsoids are drawn at the 50% probability level and H atoms
atom numbering scheme. Ellipsoids are drawn at the 50% probability
◦
˚
are omitted for clarity. Selected bond lengths (A) and angles ( ):
Sb1–F1 = 1.943(2), Sb1–F2 = 2.002(2), Sb1–F3 = 2.010(2), Sb1–O1 =
2.238(3), Sb1–O2 = 2.276(3), As1–O1 = 1.680(3), As2–O2 = 1.692(3),
F1–Sb1–F2 = 83.69(10), F1–Sb1–F3 = 83.83(10), F2–Sb1–F3 = 84.63(10),
F1–Sb1–O1 = 80.07(10), F2–Sb1–O1 = 85.46(10), F1–Sb1–O2 = 80.50(10),
F2–Sb1–O2 = 162.12(11), F3–Sb1–O1 = 161.91(10), F3–Sb1–O2 =
85.42(10), O1–Sb1–O2 = 99.89(10).
˚
level and H atoms are omitted for clarity. Selected bond lengths (A)
and angles (◦): Sb1–F1 = 1.916(3), Sb1–F2 = 1.921(3), Sb1–F3 =
2.018(3), Sb1–O1 = 2.593(3), Sb1–O2 = 2.306(3), P1–O1 = 1.493(4),
P2–O2 = 1.508(4), F1–Sb1–F2 = 90.17(13), F1–Sb1–F3 = 81.68(13),
F2–Sb1–F3 = 88.40(13), F1–Sb1–O1 = 78.27(12), F1–Sb1–O2 = 78.01(12),
F2–Sb1–O1
= 160.21(12), F2–Sb1–O2 = 83.85(13), F3–Sb1–O1 =
105.49(12), F3–Sb1–O2 = 158.20(12), O1–Sb1–O2 = 78.10(11).
mony lies slightly below the basal plane which is distorted
by the wide F3–Sb–O1 angle of 105.49(12)◦. The chloro ana-
logue [SbCl3{Ph2P(O)CH2P(O)Ph2}] is known and is also square
pyramidal,24 but much less distorted. The reasons for the distortion
are unclear; there are no short contacts to neighbouring molecules
and similar distortions are not found in the other structures
reported below.
The structure of [SbF3{Ph2P(O)CH2P(O)Ph2}] (Fig. 4) shows
a very distorted square pyramidal monomer with apical fluo-
ride and a chelating diphosphine dioxide, which is asymmet-
˚
rically coordinated (Sb–O = 2.306(3), 2.593(3) A). The anti-
‡ Crystal of [SbF3(OPPh3)2]: monoclinic, Cc, a = 10.1140(7), b = 32.559(2),
◦
˚
c = 10.8680(7) A, b = 117.732(3) .
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The structure of [SbF3{Me2P(O)CH2P(O)Me2}] also contains a
square pyramidal antimony geometry, but in this case the diphos-
phine dioxides are bridging to give a discrete dimer containing
a twelve-membered ring (Fig. 5). The geometry at antimony
replicates the key features found in [SbF3(OAsR3)2] (above). The
˚
P–O distances (1.507(3) to 1.509(3) A) are only slightly longer than
19
˚
in the ligand itself (1.489(3), 1.492(3) A). The nearest contact to
the open face of the pyramid is an oxygen from a neighbouring
˚
molecule at >4.3 A, which is significantly greater than the sum
˚
of the van der Waals radii (3.6 A); thus the square pyramidal
description seems fully justified.
Fig.
6
View of the part of the polymer structure of
[SbF3{Ph2P(O)(CH2)2P(O)Ph2}] with atom numbering scheme and
showing the coordination environment at antimony. Ellipsoids are
drawn at the 50% probability level and H atoms are omitted for
◦
˚
clarity. Selected bond lengths (A) and angles ( ): Sb1–F1 = 1.906(3),
Sb1–F2 = 1.979(3), Sb1–F3 = 1.952(3), Sb1–O1 = 2.456(3), Sb1–O2 =
2.385(4), P1–O1 = 1.507(4), P2–O2 = 1.504(4), F1–Sb1–F3 = 87.00(13),
F1–Sb1–F2 = 86.50(13), F2–Sb1–F3 = 86.84(13), F1–Sb1–O1 = 77.97(12),
F1–Sb1–O2
=
79.19(13), F2–Sb1–O1
=
83.22(12), F2–Sb1–O2
=
163.43(13), F3–Sb1–O1
=
162.42(13), F3–Sb1–O2
=
84.12(13),
O1–Sb1–O2 = 101.71(12).
are similar to those observed for various fluoroantimonates(III)
in aqueous solution,10 which suggests that the Sb–F are the
dominant interactions. The solution spectra do not reflect the
inequivalent fluorine positions evident in the solid structures.
This indicates either fluxionality in solution, or, more likely, rapid
dissociation/exchange which continues even at low temperatures.
Fig.
5
View of the dimer present in the crystal structure of
[SbF3{Me2P(O)CH2P(O)Me2}] with atom numbering scheme. Ellipsoids
are drawn at the 50% probability level and H ◦atoms are omitted for
˚
clarity. Selected bond lengths (A) and angles ( ): Sb1–F1 = 1.914(2),
Sb1–F2 = 1.970(2), Sb1–F3 = 1.972(2), Sb2–F4 = 1.909(2), Sb2–F5 =
1.964(2), Sb2–F6 = 1.971(2), Sb2–O1 = 2.446(3), Sb1–O4 = 2.416(3),
Sb2–O3 = 2.411(3), Sb2–O2 = 2.455(3), P1–O1 = 1.508(3), P2–O2 =
1.509(3), P3–O3 = 1.508(3), P4–O4 = 1.507(3), F1–Sb1–F2 = 87.46(10),
F1–Sb1–F3 = 85.83(9), F2–Sb1–F3 = 84.53(9), F1–Sb1–O4 = 82.24(9),
F3–Sb1–O4 = 84.07(9), F1–Sb1–O1 = 77.90(9), F2–Sb1–O1 = 82.26(9),
O1–Sb1–O4 = 105.83(9), F4–Sb2–F5 = 85.71(10), F4–Sb2–F6 = 88.72(10),
F5–Sb2–F6 = 85.04(10), F4–Sb2–O3 = 78.81(10), F6–Sb2–O3 = 84.47(10),
F4–Sb2–O2 = 81.61(9), F5–Sb2–O2 = 87.05(9), O2–Sb2–O3 = 100.59(9).
BiF3 Complexes
No reaction occurred on refluxing suspensions of BiF3 in MeOH
or MeCN with the pnictogen oxide ligands. On overnight stirring
of a solution of [BiCl3(OPPh3)3]31 in CH2Cl2 with three equivalents
of Me3SnF, the latter slowly dissolved and then a fine white
precipitate formed. The precipitate was identified as BiF3 by
its IR spectrum. On removing the solvent from the filtrate, a
white solid was obtained which was identified by IR, 1H and
1
A
third
structural
type
is
provided
by
31P{ H} NMR spectroscopy as [Me3SnCl(OPPh3)].32 Reaction of
[SbF3{Ph2P(O)(CH2)2P(O)Ph2}] which also contains square
pyramidal SbF3O2 units, but in this case the diphosphine
dioxide bridges adjacent Sb atoms producing an infinite chain
structure (Fig. 6). The bond lengths and angles parallel those
in the other structures. In all of the pnictogen oxide complexes,
the Sb–O distances are much shorter than those found in
[BiCl3{Ph2P(O)CH2P(O)Ph2}]31 and Me3SnF also produced BiF3.
It is clear therefore that pnictogen oxides do not react directly
with the polymeric BiF3. Also, the neutral ligands do not bind
sufficiently strongly to the Bi(III) centre in molecular complexes
to prevent BiF3 precipitating from chloride/fluoride exchange
reactions. Similar behaviour has been seen in some d-block fluoride
systems.33
11
˚
[SbF3(crown)], which are typically ≥ 3 A, but similar to those in
[SbF3(4-MeO-C5H4NO)2].13
The IR spectra of the phosphine- and arsine-oxide complexes
show the u(PO) and u(AsO) frequencies are too low a frequency
compared to the ligands themselves, and exhibit two or three
strong absorptions in the region ~560–470 cm-1 (Experimental
Section) which we assign to terminal Sb–F bonds.30 The solution
Conclusions
The first examples of Lewis acid complexes of AsF3 with neutral
ligands have been prepared and fully characterised, together
with a series of SbF3 analogues. The results demonstrate that
both AsF3 and SbF3 are modest Lewis acids towards neutral
oxygen donor ligands, but in contrast to the analogues containing
heavier halogens they did not form isolable complexes with softer,
neutral sulfur ligands. Their tendency to behave as fluorinating
agents is illustrated by the formation of F2AsR3 in their reaction
1
31P{ H} NMR spectra each show singlet resonances, with small
high frequency coordination shifts and the spectra are essentially
unchanged on cooling the solutions to 190 K. Similarly, the
1
19F{ H} NMR spectra show singlets in the range ~ -70 to
-80 ppm, again little affected by cooling the solutions. These values
5294 | Dalton Trans., 2011, 40, 5291–5297
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with OAsR3. Although its coordination chemistry has been little
studied prior to this work, we note that AsF3 is highly unusual
in coordinating in three different ways: as a Lewis base via the
lone pair on As,6 as an F-donor ligand via the As-coordinated
fluorides,7 and as a Lewis acid towards appropriate neutral ligands
as established here. It seems likely that with careful choice of
ligand structure, a wider range of complexes may exist, despite
the competition from fluorination reactions. The absence of Lewis
base adducts of BiF3, reflects the inability of the pnictogen oxides
to compete with formation of insoluble polymeric BiF3.
NMR (CD2Cl2/CH2Cl2, 293 K): d = 39.6 (s), (190 K) 43.0 (s). IR
(Nujol): 1135 (s) (P O), 65 3(m), 598 (s), 580 (s) (AsF) cm-1.
[SbF3(OPPh3)2]: SbF3 (0.16 g, 0.9 mmol) was dissolved in
anhydrous MeOH (10 mL) and OPPh3 (0.51 g, 1.8 mmol) in
MeOH (5 mL) was added dropwise and the solution stirred
overnight. On concentration in vacuo a white solid separated out,
which was filtered off, rinsed with n-hexane (5 mL) and dried in
vacuo. Yield: 0.62 g, 90%. Required for C36H30F3O2P2Sb·MeOH
(767.4): C 57.9, H 4.8; found: C 57.8, H 3.8%. 1H NMR
1
(CDCl3, 293 K): d = 7.5–7.7 (m), 4.4 (s) MeOH. 31P{ H} NMR
1
(CD2Cl2/CH2Cl2, 293 K): d = 32.6 (br s); (200 K): 34.1 (s). 19F{ H}
NMR (CD2Cl2/CH2Cl2, 293 K): d = -78.2 (s); (223 K): -79.0 (s);
(183 K): -80.1 (s). IR (Nujol): u = 1141 (vs, br) (P O), 542 (s),
508 (s) (SbF) cm-1.
Experimental section
General: All reactions were conducted using Schlenk, vacuum line
and glove-box techniques and under a dry dinitrogen atmosphere.
Solvents were dried by distillation from magnesium turnings
(MeOH) or CaH2 (MeCN, CH2Cl2). SbF3 and BiF3 were obtained
from Aldrich and used as received. AsF3 was made from As2O3
and HSO3F and purified by distillation under dinitrogen.34 OPMe3
(Strem) was freshly sublimed in vacuo. OPPh3 and OAsPh3
(Aldrich)were heated invacuo. OAsMe3 and R2P(O)(CH2)nP(O)R2
(n = 1 or 2) were made as described.19,35,36 IR spectra were recorded
as Nujol mulls using CsI plates on a Perkin Elmer Spectrum 100
spectrometer, 1H NMR spectra in CDCl3 or CD2Cl2 solutions on
[SbF3(OPMe3)2]: SbF3 (0.19 g, 1.08 mmol) was dissolved in
anhydrous MeOH (10 mL) and OPMe3 (0.20 g, 2.17 mmol) in
MeOH (10 mL) was added dropwise and the solution stirred
overnight. The colourless solution was concentrated to ~ 5 mL
and n-hexane (5 mL) added and the mixture refrigerated. The
white solid which deposited was filtered off, washed with n-hexane
(5 mL) and dried in vacuo. Block crystals were obtained by
layering the filtrate with n-hexane. Yield: 0.35 g, 91%. Required for
C6H18F3O2P2Sb (362.9): C 19.9, H 5.0; found: C 19.4, H 4.9%. 1H
1
NMR (CDCl3, 293 K): d = 1.55 (d, 2JPH = 14 Hz). 31P{ H} NMR
1
(CD2Cl2/CH2Cl2, 293 K): d = 45.5 (s); (200 K): 48.9 (s). 19F{ H}
a Bruker AV300, 31P{ H} and 19F{ H} NMR spectra on a Bruker
DPX400 and referenced to external 85% H3PO4 and CFCl3,
respectively. Microanalytical measurements were performed by
Medac Ltd.
NMR (CD2Cl2/CH2Cl2, 293 K): d = -78.6 (s); (200 K): -79.9 (s).
IR (Nujol): u = 1137 (vs, br) (P O), 556 (s), 542 (s), 507 (s), 489
(m) (SbF) cm-1.
1
1
[SbF3{Me2P(O)CH2P(O)Me2}]: SbF3 (0.24 g, 1.34 mmol) was
dissolved in anhydrous MeOH (10 mL) and Me2P(O)CH2P(O)Me2
(0.23 g, 1.36 mmol) in MeOH (5 mL) was added dropwise and
the solution stirred overnight. On concentration in vacuo a white
solid separated out, which was filtered off, rinsed with n-hexane
(5 mL) and dried in vacuo. Yield: 0.32 g, 68%. Required for
C5H14F3O2P2Sb (346.9): C 17.3, H 4.1; found: C 17.4, H 3.6%.
1H NMR (CDCl3, 293 K): d = 1.73 (d, [12H], 2JPH = 12 Hz), 2.32
[AsF3(OPPh3)2]: A solution of OPPh3 (0.55 g, 1.97 mmol)
in CH2Cl2 (10 mL) was added dropwise to a CH2Cl2 (5 mL)
solution of AsF3 (0.13 g, 0.98 mmol). The colourless reaction
mixture was stirred for 3 h. A white solid was obtained on
concentrating the solution; this was filtered off, washed with
hexane (5 mL) and dried in vacuo. Yield: 0.45 g, 63%. Required for
1
2
C36H30AsF3O2P2· CH2Cl2 (731.0): C 60.0, H 4.3; found: C 59.3, H
4.6%. 1H NMR (CDCl3, 293 K): d = 5.3 (s) CH2Cl2, 7.4–7.7 (m).
(t, [2H] JPH = 12 Hz). 31P{ H} NMR (CD2Cl2/CH2Cl2, 293 K):
2
1
1
1
19F{ H} NMR (CD2Cl2/CH2Cl2, 293 K): d = -51.7 (s), (190 K)
d = 43.5 (s); (200 K): 42.6 (s). 19F{ H} NMR (CD2Cl2/CH2Cl2,
1
-53.0 (s). 31P{ H} NMR (CD2Cl2/CH2Cl2, 293 K): d = 32.0 (s);
293 K): d = -77.8 (s); (200 K): -78.2 (s). IR (Nujol): u = 1144 (vs,
br), 1093 (s) (P O), 556 (s), 513 (s), 484 (s) (SbF) cm-1.
(195 K): 31.3 (s). IR (Nujol): u = 1153 (br), (P O), 610 (m), 585
(m) (AsF) cm-1
[SbF3{Ph2P(O)CH2P(O)Ph2}]: SbF3 (0.18 g, 1.00 mmol) was
dissolved in anhydrous MeOH (10 mL) and Ph2P(O)CH2P(O)Ph2
(0.41 g, 1.00 mmol) in MeOH (10 mL) was added and the solution
stirred overnight. An off-white solid separated out, which was
filtered off, washed with n-hexane and dried in vacuo. Very pale
yellow block crystals were obtained from refrigerating the filtrate.
[AsF3(OPMe3)2]: Was made similarly to the OPPh3 com-
plex, as
a waxy white solid. Yield: 50%. Required for
1
C6H18AsF3O2P2· CH2Cl2 (358.5): C 21.8, H 5.3; found: C 21.6,
2
H 4.6%. 1H NMR (CDCl3, 293 K): d = 1.51 (d, 2JPH = 15 Hz), 5.3
(s) CH2Cl2. 19F{ H} NMR (CD2Cl2, 293 K): d = -52.5, (200 K)
1
1
4
-53.0. 31P{ H} NMR (CD2Cl2/CH2Cl2, 293 K): d = 43.8 (s); (190
Yield: 0.39 g, 66%. Required for C25H22P2O2F3Sb· CH2Cl2 (616.3):
1
K): 44.7 (s). IR (Nujol): u = 1148 (vbr), 1120 (sh) (P O), 610 (sh),
596 (s) (AsF) cm-1.
C 49.2, H 3.7; found: C 49.2, H 3.9%. 1H NMR (CDCl3, 293 K):
d = 3.64 (t, [2H], 2JPH = 12 Hz), 5.3 (s) CH2Cl2, 7.2–7.9 (m, [20H]).
1
[AsF3{Me2P(O)CH2P(O)Me2}]: A solution of AsF3 (0.16 g, 1.2
mmol) in CH2Cl2 (5 mL) was added dropwise to the CH2Cl2 (10
mL) solution of Me2P(O)CH2P(O)Me2 (0.21 g, 1.2 mmol). The
colourless reaction mixture was stirred for 1 h. A white solid along
with some needle shaped crystals were obtained on concentrating
the solution. The solid was filtered off and dried in vacuo. Yield:
0.30 g, 80%. Required for C5H14AsF3P2O2 (302.0): C 20.0, H 4.7;
31P{ H} NMR (CD2Cl2/CH2Cl2, 293 K): d = 28.8 (s); (200 K):
1
29.6 (s). 19F{ H} NMR (CD2Cl2/CH2Cl2, 293 K): d = -74.5 (s);
(200 K): -76.5 (s). IR (Nujol): u = 1156 (vs, br), 1092 (m) (P O),
532 (s), 503 (s) (SbF) cm-1.
[SbF3{Ph2P(O)(CH2)2P(O)Ph2}]: Was made similarly to the
previous complex above, giving a white powder. Yield: 82%.
Colourless block crystals were obtained by layering the filtrate
from the preparation with n-hexane and refrigerating. Required
for C26H24F3O2P2Sb·CH2Cl2 (694.1): C 46.7, H 3.9; found: C 47.7,
1
found: C 20.7, H 5.6%. H NMR (CDCl3, 295 K): d = 1.69 (d,
1
2JPH = 15 Hz, [12H]), 2.34 (t, 2JPH = 12 Hz, [2H]). 19F{ H} NMR
1
1
(CD2Cl2/CH2Cl2, 293 K): d = -46.0 (s); (295 K): -48.5 (s). 31P{ H}
H 4.1%. H NMR (CDCl3, 293 K): d = 2.75 (br,s [4H]), 5.3 (s)
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Table 1 Crystallographic parametersa
[AsF3{Me2P(O)-
[SbF3{Ph2P(O)-
CH2P(O)Ph2}]
[SbF3{Me2P(O)-
CH2P(O)Me2}]
[SbF3{Ph2P(O)-
(CH2)2P(O)Ph2}]
Compound
CH2P(O)Me2}]
[SbF3(OAsMe3)2]
[SbF3(OAsPh3)2]
Formula
M
C5H14AsF3O2P2
300.02
C6H18As2F3O2Sb
450.79
C36H30As2F3O2Sb
823.19
C25H22F3O2P2Sb
595.12
C10H28F6O4P4Sb2
693.70
C26H24F3O2P2Sb
609.14
Crystal system
Triclinic
Monoclinic
P21/c (no. 14)
8.1563(10)
13.546(2)
12.4707(15)
90
97.531(10)
90
1366.0(3)
4
Monoclinic
Cc (no. 9)
10.0551(3)
32.8259(10)
10.7878(3)
90
116.5420(10)
90
3185.43(16)
4
Orthorhombic
P212121 (no. 19)
11.4165(15)
13.335(2)
15.599(2)
90
90
90
2374.7(6)
4
1.341
Monoclinic
P21/c (no. 14)
17.8949(15)
8.4721(10)
16.1193(15)
90
109.908(5)
90
2297.8(4)
4
Triclinic
¯
¯
Space group
P1 (no. 2)
P1 (no. 2)
˚
A (A)
7.7004(10)
8.1617(15)
9.7109(15)
76.455(2)
78.429(2)
65.015(2)
534.22(15)
2
9.7891(15)
11.664(2)
12.503(2)
65.839(10)
77.987(10)
80.634(10)
1269.3(4)
2
˚
B (A)
˚
C (A)
a (◦)
b (◦)
g (◦)
3
˚
U (A )
Z
m(Mo-Ka) (mm-1)
Total no.
3.491
11357
6.840
17429
2.978
13457
2.690
25860
1.256
21763
17960
reflections
Rint
Unique reflections
No. of parameters,
restraints
0.038
2446
122, 0
0.046
3124
133, 0
0.046
5159
398, 2
0.054
5133
299, 0
0.043
5254
235, 0
0.068
5825
307, 0
R1[Io > 2s(Io)]
R1 (all data)
wR2[Io > 2s(Io)]
wR2 (all data)
0.028
0.036
0.054
0.057
0.029
0.037
0.064
0.068
0.041
0.045
0.104
0.108
0.043
0.052
0.078
0.083
0.033
0.041
0.062
0.066
0.059
0.084
0.104
0.115
Common items: T = 120 K; l(Mo-Ka) = 0.71073 A; q(max) = 27.5◦; R1 = RꢀFo|–|Fcꢀ/R|Fo|; wR2 = [Rw(Fo - Fc2)2/R wFo
]
.
a
2
4 1/2
˚
1
CH2Cl2, 7.4–7.9 (m, [20H]). 31P{ H} NMR (CD2Cl2/CH2Cl2, 293
Kappa CCD diffractometer fitted with monochromated Mo-
K): d = 38.6 (s); (200 K): 39.3 (s). 19F{ H} NMR (CD2Cl2/CH2Cl2,
1
˚
Ka radiation (l = 0.71073 A), with the crystals held at 120 K
in a nitrogen gas stream. Structure solution and refinement
were mostly straightforward,37–39 except for [SbF3(OEPh3)2] (E =
As, P). E = As was solved in the non-centrosymmetric space-
group Cc with an absolute structure parameter of 0.076(15). The
coordination sphere about the metal was modelled as disordered
(ca. 35/65) about a pseudo mirror plane located normal to the Sb–
Fax bond just above the metal. Split atom pairs were constrained
to have the same atomic displacement parameters. An initial
(poor) refinement of E = P was obtained with the coordinates
from E = As, subsequent analysis of the most disagreeing Fo/Fc
values38 revealed the twin law [-1 0 0, 0 -1 0, 1 0 1]. Application
of this dramatically improved the agreement indices, but a full
anisotropic refinement free from constraints/restraints was not
possible (indicating the possibility of further additional twinning).
CCDC 803403–803408 contain the supplementary crystallo-
graphic data for this paper. These data can be obtained free of
charge from The Cambridge Crystallographic Data Centre via
www.ccdc.cam.ac.uk/data_request/cif.
293 K): d = -76.8 (s); (200 K): -77.1 (s). IR (Nujol): u = 1146 (vs,
br), 1084 (s) (P O), 534 (s), 501 (s) (SbF) cm-1.
[SbF3(OAsMe3)2]: SbF3 (0.19 g, 1.08 mmol) was dissolved in
anhydrous MeOH (10 mL) and OAsMe3 (0.30 g, 2.2 mmol) in
MeOH (10 mL) was added dropwise and the solution stirred
overnight. The colourless solution was evaporated to dryness,
and treated with CH2Cl2 (5 mL) and n-hexane (5 mL), which
deposited a white solid on stirring. The solid was filtered off,
rinsed with n-hexane and dried in vacuo. Block crystals were
obtained by refrigerating the filtrate. Yield: 0.35 g. Required
for C6H18As2F3O2Sb (450.8): C 16.0, H 4.0; found: C 16.3, H
4.2%. 1H NMR (CDCl3, 293 K): d = 1.64 (s).19F{ H} NMR
1
(CD2Cl2/CH2Cl2, 293 K): d = -70.7 (s); (213 K): -70.0 (br). IR
(Nujol): u = 799 (vs, br) (As O), 554 (s), 515 (s) (SbF) cm-1.
[SbF3(OAsPh3)2]: SbF3 (0.16 g, 0.9 mmol) was dissolved in
anhydrous MeOH (10 mL) and OAsPh3 (0.57 g, 1.8 mmol) in
MeOH (5 mL) was added dropwise and the solution stirred
overnight. On concentration in vacuo a white solid separated out,
which was filtered off, rinsed with n-hexane (5 mL) and dried in
vacuo. Yield: 0.40 g, 60%. Block shaped crystals were obtained
from refrigerating the filtrate. Required for C36H30As2F3O2Sb
(823.2): C 52.5, H 3.8; found: C 50.5, H 4.2%; several different
batches of this compound gave consistently low C analyses,
although spectroscopically the complex appeared pure. 1H NMR
Acknowledgements
We thank the EPSRC (UK) for support and the Commonwealth
Commission for award of a split-site PhD scholarship (S.M.),
Dr M. Webster for assistance with the X-ray crystallography
and J. Burt for experimental assistance.
(CDCl3, 293 K): d = 7.5–7.7 (m). 19F{ H} NMR (CD2Cl2/CH2Cl2,
1
293 K): d = -73.3 (br). IR (Nujol): u = 801 (vs, br) (As O), 542
(s), 508 (s), (SbF) cm-1.
Notes and references
X-Ray Crystallography Details of the crystallographic data
collection and refinement parameters are given in Table 1.
Crystals suitable for single crystal X-ray analysis were obtained
as described above. Data collections used a Bruker-Nonius
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