The identification of some new antimony(III) compounds containing fluoroxyl ligands by 19F solution-state NMR spectroscopy: Crystal and molecular structure of Ar′Ar″2Sb (Ar′ = 2,6-(CF3)2C6H3; Ar″ = 2,4-(CF3)2C6H3)

Article abstract of DOI:10.1016/j.ica.2004.09.041

Reaction between 2,6-(CF₃)₂C₆H ₃Li (Ar′Li) and/or 2,4-(CF₃)₂C ₆H₃Li (Ar″Li) and SbCl₃ has afforded a series of new antimony(III) derivatives, which have all been identified in solution by ¹⁹F NMR spectroscopy. The unusual compound Ar′Ar″₂Sb has been isolated, and its crystal and molecular structures determined by single-crystal X-ray diffraction. Ar′Ar″₂Sb is only the second example of a compound containing three fluoroxyl ligands to be structurally characterised.

Full text of DOI:10.1016/j.ica.2004.09.041

Inorganica Chimica Acta 358 (2005) 844–848
www.elsevier.com/locate/ica
Note
The identification of some new antimony(III) compounds containing
19
fluoroxyl ligands by F solution-state NMR spectroscopy:
crystal and molecular structure of Ar0Ar200Sb
(Ar0 = 2,6-(CF3)2C6H3; Ar00 = 2,4-(CF3)2C6H3)
*
Stephanie M. Cornet, Keith B. Dillon , Andres E. Goeta
´
´
Chemistry Department, University of Durham, South Road, Durham DH1 3LE, UK
Received 6 May 2004; accepted 22 September 2004
Available online 22 October 2004
Abstract
Reaction between 2,6-(CF3)2C6H3Li (Ar0Li) and/or 2,4-(CF3)2C6H3Li (Ar00Li) and SbCl3 has afforded a series of new anti-
mony(III) derivatives, which have all been identified in solution by 19F NMR spectroscopy. The unusual compound Ar0Ar200Sb
has been isolated, and its crystal and molecular structures determined by single-crystal X-ray diffraction. Ar0Ar200Sb is only the second
example of a compound containing three fluoroxyl ligands to be structurally characterised.
ꢀ 2004 Elsevier B.V. All rights reserved.
Keywords: Antimony(III); Fluoroxyl; 19F NMR; Crystal structure
1. Introduction
Only three Sb(III) compounds containing the fluoro-
mes ligand are known: ArSbCl2 [2,4,5], Ar2SbCl [2,5]
and Ar2SbOSO2CF3 [5], and to date no other antimony
species containing Ar0 or Ar00 have been mentioned in
the literature. Bismuth has proved large enough to be
able to bear three aryl rings with o-CF3 substituents,
and Ar3Bi has been structurally characterised, as well
as Ar2BiCl [3]. Such a molecule has not been prepared
with any other group 15 element.
The chemistry of the ligand 2,4,6-(CF3)3C6H2 (fluoro-
mes = Ar) is nowadays well known, due to extensive
studies of its ability to stabilise low-coordinate com-
pounds of both main group elements and transition met-
als [1–18]. The ‘‘fluoroxyl’’ ligand 2,6-(CF3)2C6H3 (Ar0)
has similar properties, but its chemistry has been much
less explored, due to complications occurring during
the lithiation process, giving rise to a mixture of two
lithium derivatives, 2,6-(CF3)2C6H3Li (Ar0Li) and 2,4-
(CF3)2C6H3Li (Ar00Li). We have in recent years under-
taken an extensive study of a series of group 13 (B), 14
(Si, Ge, Sn) and 15 (P, As) derivatives with Ar, Ar0
and/or Ar00 ligands [2,7–17].
To extend our knowledge of the group 15 series, reac-
tions between SbCl3 and Ar0Li/Ar00Li have been carried
out. The synthesis and characterisation by 19F solution-
state NMR spectroscopy of new antimony species
Ar0SbCl2 ð1Þ; Ar00SbCl2 ð2Þ; Ar0 SbCl ð3Þ; Ar00SbCl ð4Þ;
2
2
and Ar0Ar020Sb ð5Þ are described. The crystal and molec-
ular structures of Ar0Ar200Sb ð5Þ have been determined at
120 K. Following Ar030B [15], 5 is only the second main-
group derivative containing three fluoroxyl ligands to be
structurally characterised by single-crystal X-ray
diffraction.
*
Corresponding author. Tel.: +44 191 3342092; fax: +44 191
3844737.
E-mail address: k.b.dillon@durham.ac.uk (K.B. Dillon).
0020-1693/$ - see front matter ꢀ 2004 Elsevier B.V. All rights reserved.
doi:10.1016/j.ica.2004.09.041

S.M. Cornet et al. / Inorganica Chimica Acta 358 (2005) 844–848
845
Table 2
d
2. Results and discussion
13C (ppm) for Ar0Ar020Sb
Carbon
d (ppm)
J (Hz)
The chloro-derivatives were synthesised by reaction
of antimony trichloride with a mixture of the lithiated
products Ar0Li/Ar00Li, prepared as described previously
[14–17].
A
B
C
D
E
F
G
H
I
139.9
142.8
132.1
130.4
139.9
124.5
128.9
128.0
137.6
123.1
136.7
123.5
124.1
broad singlet
broad singlet, double intensity
2
q, JC–F 33.4
3
q, JC–F 5.9
s
q, JC–F 275.8
1
2.1. Synthesis and solution-state NMR spectroscopy
s
s
The Ar0Li/Ar00Li mixture was added to a solution of
SbCl3 in hexanes at room temperature in a 2:1 molecular
ratio. Solution-state 19F NMR spectroscopy showed a
mixture of five different products, which was separated
by distillation under reduced pressure (0.01 Torr). These
2
q, JC–F 31.5
m
q, JC–F 31.5
J
2
K
L
M
1
q, JC–F 275.8
1
q, JC–F 275.8
were identified as Ar0SbCl2 ð1Þ; Ar00SbCl2 ð2Þ; Ar0
2
SbCl ð3Þ; Ar020SbCl ð4Þ; and Ar0Ar020Sb ð5Þ. The spectra
show some characteristic signals of the fluoroxyl ligands:
a singlet at around ꢀ54 ppm for the o-CF3 groups of the
Ar0 ring, a resonance at about ꢀ58.5 ppm corresponding
to the o-CF3 group of the Ar00 ligands and one near ꢀ63
ppm for the para-trifluoromethyl group. Table 1 lists the
19F NMR data for all new compounds. The chemical
shifts are similar to those found in ArSbCl2 [4] and
Ar2SbCl [5].
M
CF3
I
J
H
G
L
F3C
K
F3C
B
In order to investigate the rotation of the aromatic
rings around their Sb–C axes in Ar0Ar200Sb ð5Þ, variable
temperature 19F NMR spectra were recorded at ꢀ50
and 100 ꢁC, but no change was observed within this tem-
perature range. Restricted rotation might occur at a
lower temperature, but due to solvent restrictions, it
was not possible to run a spectrum below that recorded
at ꢀ50 ꢁC. The 13C NMR spectrum of 5 was also re-
corded at ambient temperature; the results and assign-
ments are given in Table 2, following the lettering
scheme shown in Fig. 1.
F
F3C
Sb
C
A
D
CF3
CF3
C
E
F
D
Fig. 1. Lettering scheme for Ar0Ar200Sb.
[5]. The molecule crystallises in the monoclinic space
group, C2/c, with Z = 8. The Sb atom exhibits trigonal
pyramidal geometry, with C–Sb–C angles of
92.46(10)ꢁ, 95.26(11)ꢁ and 108.31(10)ꢁ (average 98.68ꢁ).
This range (ꢁ16ꢁ) is probably due to the unsymmetrical
character of Ar0Ar200Sb and the presence of bulky CF3
groups in the ortho position, leading to short Sbꢂ ꢂ ꢂF
contacts between some of these fluorines and the central
Sb atom. Three intramolecular interactions are observed
(Table 3), one from an o-CF3 group from each of the
aryl substituents, with Sbꢂ ꢂ ꢂF distances less than 3.03
2.2. X-ray crystallography
Crystals of Ar0Ar200Sb were obtained by recrystallisa-
tion from dichloromethane. The structure was deter-
mined at 120 K and is shown in Fig. 2. Selected bond
distances and angles are listed in Table 3, together with
some structural data for Ar2SbCl and Ar2SbOSO2CF3
Table 1
d
19F (ppm) for new Sb(III) compounds
˚
A, appreciably shorter than the sum of the van der
˚
Waals radii of 3.74 A [19]. These values are similar to
Compounds
d (ppm)
Ar0SbCl2 (1)
Ar00SbCl2 (2)
ꢀ53.2 (s, 6F, o-CF3)
ꢀ54.9 (s, 3F, o-CF3)
ꢀ63.6 (s, 3F, p-CF3)
ꢀ55.1 (s, 12F, o-CF3)
ꢀ58.4 (s, 6F, o-CF3)
ꢀ63.7 (s, 6F, p-CF3)
ꢀ55.5 (s, 6F, o-CF3 in Ar0)
ꢀ58.4 (s, 6F, o-CF3 in Ar00)
ꢀ63.6 (s, 6F, p-CF3)
those found in Ar2SbCl and Ar2SbOSO2CF3 [5]. The
C–Sb–C bond angles for other triaryl antimony(III)
compounds described in the literature are usually more
symmetrical. Those in Mes3Sb, with two independent
molecules in the unit cell, range from 103.63ꢁ to
106.41ꢁ (average 105.3ꢁ) [20], while in the p-tolyl com-
pound they are all identical at 97.3(1)ꢁ [21]. Two crystal-
line forms of the o-tolyl analogue have been reported,
Ar02SbCl ð3Þ
Ar020SbCl ð4Þ
Ar0Ar020SbCl ð5Þ

846
S.M. Cornet et al. / Inorganica Chimica Acta 358 (2005) 844–848
tortion is present in other tris(aryl) compounds of group
15 elements with substituents in ortho positions, e.g.
113.2ꢁ and 126.7ꢁ in tris(2,6-dimethylphenyl)stibine
[24], and 115ꢁ and 126ꢁ in trimesitylbismuthane [25,26].
The geometry at the antimony atom (sum of the
bond angles at Sb: 296.03ꢁ) is comparable to that ob-
served in Ar2SbCl [5] and Ar2SbOSO2CF3 [5] (where
the sums of the bonds angles at Sb are 296.7ꢁ and
287.8ꢁ, respectively). While the average Sb–C distance,
˚
˚
2.204 A, falls within the limits of 2.03–2.25 A found in
related organoantimony structures [5,21–24,27,28], two
of the Sb–C bonds (Sb(1)–C(21) 2.184(3) and Sb(1)–
˚
C(11) 2.194(3) A) are shorter than those found in
Ar2SbCl and Ar2SbOSO2CF3 [5]. This is due to the
smaller steric demand of the Ar00 groups (only one o-
CF3 group) in comparison with the Ar substituents.
˚
The third Sb–C bond (Sb(1)–C(1) 2.234(3) A) is longer,
and the distance is comparable to those found in
Ar2SbCl and Ar2SbOSO2CF3 (respectively, 2.25 and
˚
2.23 A), due to the presence of trifluoromethyl groups
in the ortho position. It is noteworthy that the average
Sb–C distance in tris(2,6-dimethylphenyl)stibine is
Fig. 2. Molecular structure of Ar0Ar200Sb ð5Þ.
˚
2.190 A [24], and 2.183 A in the trimesityl analogue
˚
[20]. Sb–C distances are longer than in Ph3Sb (average
with values of 96.7–97.1ꢁ (average 96.9ꢁ) for the triclinic
form, and 97.0–97.7ꢁ (average 97.4ꢁ) for the monoclinic
polymorph [22]. For the phenyl derivative, which also
has two independent molecules per unit cell, these range
from 95.1ꢁ to 98.0ꢁ (average 96.3ꢁ) [23]. Interestingly,
the compound (2,6-Me2C6H3)3Sb has a less symmetrical
structure, with C–Sb–C angles of 98.7(2)ꢁ, 106.0(2)ꢁ and
109.5(2)ꢁ (average 104.7ꢁ) [24], a range of ca. 11ꢁ. The
loss of pseudosymmetry in this molecule was attributed
to intramolecular steric effects, though it is not then
clear why the mesityl derivative should be more symmet-
rical, since both have all ortho-positions occupied by
methyl groups. Long-range Fꢂ ꢂ ꢂSb contacts are obvi-
ously not possible in these systems, although H bonding
from H to Sb could be envisaged.
˚
2.155 A) [23], probably as a result of steric interactions
with the o-CH3 groups.
3. Experimental
All manipulations, including NMR sample prepara-
tion, were carried out under either an inert atmosphere
of dry nitrogen or in vacuo, using standard Schlenk pro-
cedures or a glovebox. 19F NMR spectra were recorded
on a Varian Mercury 200, Varian VXR 400 or Varian
Inova 500 Fourier-transform spectrometer at 188.18,
376.35 and 470.26 MHz, respectively. Chemicals
shifts were measured relative to external CFCl3, with
the higher frequency direction taken as positive. 13C
NMR spectra were recorded on the Varian VXR instru-
ment at 100.57 MHz; shifts are quoted relative to TMS.
In compound 5, there is an inequality of valence an-
gles Sb–C–C at the ipso carbons C(1), C(11) and C(21)
(the mean values are 118.0ꢁ and 125.4ꢁ). The same dis-
Table 3
0
00
˚
Selected bond distances (A) and bond angles (ꢁ) for Ar Ar2Sb ð5Þ, Ar2SbCl and Ar2SbOSO2CF3
Ar2SbCl
Ar0Ar020Sb
SbAr2OSO2CF3
˚
Bond distance (A)
Sb(1)–C(21)
Sb(1)–C(11)
Sb(1)–C(1)
2.184(3)
2.194(3)
2.234(3)
2.911
Sb(1)–C(1)
Sb(1)–C(10)
2.22(3)
2.25(3)
Sb(1)–C(1)
Sb(1)–C(10)
2.21(1)
2.23(1)
Sb(1)–F(3)
Sb(1)–F(9)
Sb(1)–F(15)
3.024
2.889
Bond angle (ꢁ)
C(21)–Sb(1)–C(11)
C(21)–Sb(1)–C(1)
C(11)–Sb(1)–C(1)
95.26(11)
108.31(10)
92.46(10)
C(1)–Sb(1)–Cl
C(10)–Sb(1)–Cl
C(1)–Sb(1)–C(10)
101.3(9)
88.4(9)
107.0(12)
C(1)–Sb(1)–O
C(10)–Sb(1)–O
C(1)–Sb(1)–C(10)
94.8(4)
87.7(4)
105.3(4)

S.M. Cornet et al. / Inorganica Chimica Acta 358 (2005) 844–848
847
Microanalyses were performed by the microanalytical
services of the Department of Chemistry, University of
Durham.
ppm; Ar0Ar00 Sb: d ꢀ55.5 (s, 6F, o-CF3 in Ar0), ꢀ58.4
2
(s, 6F, o-CF3 in Ar00), ꢀ63.6 (s, 6F, p-CF3) ppm.
3.2. X-ray crystallography
3.1. Syntheses
The single crystal structure determination was carried
out from data collected at 120 K, using graphite mono-
Lithiation reactions were carried out as described
previously. Warning: It is important in these reactions
to keep a slight excess of the hydrocarbon (Ar0H) to
n-butyllithium at all times, to avoid any attack on the
CF3 group and possible explosive formation of LiF.
Ar0SbCl2 ð1Þ=Ar00SbCl2 ð2Þ; Ar20 SbCl ð3Þ=Ar020SbCl
ð4Þ; and Ar0Ar200Sb ð5Þ: A solution of Ar0Li/Ar00Li (100
ml, 127 mmol) was added slowly to a solution of SbCl3
in hexanes/Et2O at room temperature. A precipitate of
LiCl formed. The solution was stirred for 5 h. The solu-
tion was filtered and the solvents and excess SbCl3 were
removed under vacuum, leaving a brown oil, which was
distilled under reduced pressure (0.02 Torr): fractions
were collected at 95 ꢁC (orange oil, Ar0SbCl2/Ar00SbCl2),
and 120 ꢁC (yellow sticky oil). The latter yellow oil was
dissolved in hexanes and left in the freezer overnight. A
white solid formed, which was filtered off and washed
twice with CH2Cl2 ðAr0 SbCl=Ar00SbClÞ. Solvents were
˚
chromated Mo Ka radiation (k = 0.71073 A) on a Bru-
ker SMART-1K CCD detector diffractometer equipped
with a Cryostream N2 flow cooling device [29]. A series
of narrow x-scans (0.3ꢁ) was performed at several / set-
tings in such a way as to cover a sphere of data to a max-
˚
imum resolution of 0.75 A. Cell parameters were
determined and refined using the SMART software [30],
and raw frame data were integrated using the SAINT
program [31]. The structure was solved using direct
methods and refined by full-matrix least-squares on F2
using SHELXTL [32]. Relevant parameters for data col-
lection and structure solution are given in Table 4.
Acknowledgements
We thank EPSRC for the award of a studentship (to
S.M.C.), and A.M. Kenwright, C.F. Heffernan and I.H.
McKeag for assistance in recording some of the NMR
spectra.
2
2
removed from the filtered yellow solution leaving a
sticky solid, which was recrystallised from dichloro-
methane, giving white crystals of Ar0Ar200Sb.
Elemental Anal. Calc. for C24H9F18Sb (761.06): C,
37.88; H, 1.19. Found: C, 37.72; H, 1.19%.
Appendix A. Supplementary material
19F NMR (CDCl3): Ar0SbCl2: d ꢀ53.2 (s, 6F, o-CF3)
ppm; Ar00SbCl2: d ꢀ54.9 (s, 3F, o-CF3), ꢀ63.6 (s, 3F, p-
CF3) ppm; Ar02SbCl: d ꢀ55.1 (s, 12F, o-CF3) ppm;
Crystallographic data for the structural analysis have
been deposited with the Cambridge Crystallographic
Data Centre, CCDC reference number 233083. Copies
of this information may be obtained free of charge from
The Director, CCDC, 12 Union Road, Cambridge CB2
1EZ, UK (fax: +44 1223 336 033; e-mail: deposit@ccdc.-
cam.ac.uk or www: www.ccdc.cam.ac.uk). Supplemen-
tary data associated with this article can be found, in
the online version at doi:10.1016/j.ica.2004.09.041.
Ar00 SbCl: d ꢀ58.4 (s, 6F, o-CF3), ꢀ63.7 (s, 6F, p-CF3)
2
Table 4
Crystallographic data
Empirical formula
Crystal system
Space group
C24H9F18Sb
monoclinic
C2/c
Crystal size (mm)
T (K)
0.05 · 0.16 · 0.20
120(2)
˚
a (A)
18.370(1)
13.807(1)
20.791(2)
104.439(4)
5106.4(7)
8
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