Synthesis and characterization of bis(2,4,6-tris(trifluoromethyl)phenyl) derivatives of arsenic and antimony: X-ray crystal structures of As(RF)2Cl, Sb(RF)2Cl, and Sb(RF)2OSO2CF3

Article abstract of DOI:10.1021/om990768w

Bis(2,4,6-tris(trifluoromethyl)phenyl)chloropnictines, Pn(R_F)₂Cl (Pn = As, Sb) have been synthesized by the reaction of 2 equiv of R_FLi with PnCI₃ to provide a homologous series. The crystal structures, elemental analyses, and spectral data confirm the introduction of two R_F substituents onto the pnictogen center. Sb(R_F)₂Cl reacts quantitatively with silver triflate or trimethylsilyl triflate to give Sb(R_F)₂OSO₂CF₃, while As(R_F)₂Cl does not react with either triflate reagent. The solid-state structure of Sb(R_F)₂OSO₂CF₃ reveals a covalent Sb-O interaction, indicating that, in contrast to the observations for dicoordinate group 14 element derivatives, the fluoromethyl substituents of R_F are not sufficiently basic to preclude coordination of the weakly basic anion at the cationic stibenium center.

Full text of DOI:10.1021/om990768w

152
Organometallics 2000, 19, 152-155
Syn th esis a n d Ch a r a cter iza tion of
Bis(2,4,6-tr is(tr iflu or om eth yl)p h en yl) Der iva tives of
Ar sen ic a n d An tim on y: X-r a y Cr ysta l Str u ctu r es of
As(RF )2Cl, Sb(RF )2Cl, a n d Sb(RF )2OSO2CF 3
Neil Burford,*,† Charles L. B. Macdonald, Daren J . LeBlanc, and
T. Stanley Cameron*
Department of Chemistry, Dalhousie University, Halifax, Nova Scotia, Canada B3H 4J 3
Received September 30, 1999
Bis(2,4,6-tris(trifluoromethyl)phenyl)chloropnictines, Pn(RF)2Cl (Pn ) As, Sb) have been
synthesized by the reaction of 2 equiv of RFLi with PnCl3 to provide a homologous series.
The crystal structures, elemental analyses, and spectral data confirm the introduction of
two RF substituents onto the pnictogen center. Sb(RF)2Cl reacts quantitatively with silver
triflate or trimethylsilyl triflate to give Sb(RF)2OSO2CF3, while As(RF)2Cl does not react with
either triflate reagent. The solid-state structure of Sb(RF)2OSO2CF3 reveals a covalent Sb-O
interaction, indicating that, in contrast to the observations for dicoordinate group 14 element
derivatives, the fluoromethyl substituents of RF are not sufficiently basic to preclude
coordination of the weakly basic anion at the cationic stibenium center.
In tr od u ction
natively unsaturated cations of the pnictogen elements
(specifically, pnictenium environments, R2Pn+), which
are isovalent with the group 14 carbenoids.9-12 RF
substitution of pnictogen centers has been spectroscopi-
cally confirmed for Pn(RF)Cl2 (Pn ) P, As)13,14 and
P(RF)2Cl,15 and crystal structures have been reported
for RFNPnRF (Pn ) P,10 As14), RFPPRF,13 RFP(Se)PRF,16
(C6F5NPRF)2,17 and Bi(RF)2Cl and Bi(RF)318 (see also (RF-
NPnCl)2 (Pn ) P, As)10). Despite the steric restrictions,
the recent synthesis and crystal structure of the phos-
phide [Ph3PMe]+[P(RF)2]- 15 demonstrates that multi-
substitution is not restricted to the larger bismuth
nucleus.18 We now report the preparation and charac-
terization of Pn(RF)2Cl (Pn ) As, Sb), thus completing
the Pn(RF)2Cl (Pn ) P, As, Sb, Bi) homologous series.
In addition, we show that the triflate derivative Sb(RF)2-
OSO2CF3 involves a covalent Sb-O interaction rather
than a stibenium cation.
The structure, stability, and reactivity of a molecule
are governed, in part, by the size and shape of periph-
eral substituents. Large bulky hydrocarbon substituents
have a dramatic effect on the relative thermodynamic
stability of a system1 and may also render a site un-
reactive by virtue of the imposed steric shield. Smaller
fluorinated substituents impart thermodynamic stabil-
ity without inhibiting reactivity.2 In particular, the
estimated steric bulk of the 2,4,6-tris(trifluoromethyl)-
phenyl substituent (RF)3 is between those of “mesityl”
(2,4,6-trimethylphenyl (mes)) and 2,4,6-tris(isopropyl)-
phenyl (tip), but the electron-withdrawing effect of RF
and coordinative interactions by the ortho CF3 moieties
allow for the isolation of structural arrangements that
are unstable with the larger substituents tip and “super
mesityl” (2,4,6-tris(tert-butyl)phenyl (mes*)).4 Notable
examples include air- and moisture-stable monomeric
triarylgallium5 and -indium6 compounds, a rare diin-
dane,6 and compounds containing dicoordinate indium,7
thallium,8 germanium,9,10 tin,11 and lead.12
Exp er im en ta l Section
Gen er a l P r oced u r es. Diethyl ether was obtained from
ACP Chemicals Inc., hexane from Van Waters & Rogers,
These observations prompted us to examine the appli-
cation of RF substitution to the stabilization of coordi-
(10) Ahlemann, J . T.; Roesky, H. W.; Murugavel, R.; Parisini, E.;
Noltemeyer, M.; Schmidt, H. G.; Mu¨ller, O.; Herbst-Irmer, R.; Mark-
ovskii, L. N.; Shermolovich, Y. G. Chem. Ber./ Recl. 1997, 130, 1113-
1121.
† E-mail: burford@is.dal.ca.
(1) Burford, N.; Clyburne, J . A. C.; Chan, M. S. W. Inorg. Chem.
1997, 36, 3204-3206.
(11) Gru¨tzmacher, H.; Pritzkow, H.; Edelmann, F. T. Organometal-
lics 1991, 10, 23-25.
(2) Plenio, H. Chem. Rev. 1997, 97, 3363-3384.
(3) Bondi, A. J . Phys. Chem. 1964, 68, 441-451.
(4) Edelmann, F. T. Comments Inorg. Chem. 1992, 12, 259-284.
(5) Schluter, R. D.; Isom, H. S.; Cowley, A. H.; Atwood, D. A.; J ones,
R. A.; Oblich, F.; Corbelin, S.; Lagow, R. J . Organometallics 1994, 13,
4058-4063.
(12) Brooker, S.; Buijink, J . K.; Edelmann, F. T. Organometallics
1991, 10, 25-26.
(13) Scholz, M.; Roesky, H. W.; Stalke, D.; Keller, K.; Edelmann, F.
T. J . Organomet. Chem. 1989, 366, 73-85.
(14) Ahlemann, J . T.; Ku¨nzel, A.; Roesky, H. W.; Noltemeyer, M.;
Markovski, L.; Schmidt, H. G. Inorg. Chem. 1996, 35, 6644-6645.
(15) Davidson, M. G.; Dillon, K. B.; Howard, J . A. K.; Lamb, S.;
Roden, M. D. J . Organomet. Chem. 1998, 550, 481-484.
(16) Voelker, H.; Pieper, U.; Roesky, H. W.; Sheldrick, G. M. Z.
Naturforsch. 1994, 49B, 255-257.
(6) Schluter, R. D.; Cowley, A. H.; Atwood, D. A.; J ones, R. A.; Bond,
M. R.; Carrano, C. J . J . Am. Chem. Soc. 1993, 115, 2070-2071.
(7) Scholz, M.; Noltemeyer, M.; Roesky, H. W. Angew. Chem., Int.
Ed. Engl. 1989, 28, 1383-1384.
(8) Roesky, H. W.; Scholz, M.; Noltemeyer, M.; Edelmann, F. T.
Inorg. Chem. 1989, 28, 3829-3830.
(9) Bender, J . E., IV; Banaszak Holl, M. M.; Kampf, J . W. Organo-
metallics 1997, 16, 2743-2745.
(17) Lu¨bben, T.; Roesky, H. W.; Gornitzka, H.; Steiner, A.; Stalke,
D. Eur. J . Solid State Inorg. Chem. 1995, 32, 121-130.
(18) Whitmire, K. H.; Labahn, D.; Roesky, H. W.; Noltemeyer, M.;
Sheldrick, G. M. J . Organomet. Chem. 1991, 402, 55-66.
10.1021/om990768w CCC: $19.00 © 2000 American Chemical Society
Publication on Web 12/16/1999

Bis(2,4,6-tris(trifluoromethyl)phenyl)chloropnictines
Organometallics, Vol. 19, No. 2, 2000 153
1
arsenic(III) chloride from Kodak Chemicals, and silver triflate
from Fisher Scientific. All other chemicals and reagents were
obtained from Aldrich Chemical Co. 1,3,5-Tris(trifluorometh-
yl)benzene and n-butyllithium (1.6 M in hexane) were used
as received. Phosphorus(III) chloride and arsenic(III) chloride
were degassed and distilled in vacuo prior to use. Antimony-
(III) chloride was sublimed twice in vacuo prior to use. Diethyl
ether was dried over sodium with benzophenone, n-hexane was
dried over CaH2, and CD2Cl2 was dried over P2O5 and CaH2.
All solvents were stored in evacuated bulbs. Solids were
handled in nitrogen-filled gloveboxes (Vacuum Atmospheres
or Innovative Technologies), and liquids were manipulated in
a nitrogen-filled glovebag. Reactions were performed in sealed
reactors,19 which were flame-dried under vacuum before use.
Melting points were recorded on a Fisher-J ohns apparatus and
are uncorrected. Elemental analyses were performed by Beller
Laboratories, Go¨ttingen, Germany. Infrared spectra were
recorded as Nujol mulls on CsI plates with use of a Nicolet
510P FT-IR spectrometer. Raman spectra were recorded, on
neat powdered samples sealed under nitrogen in melting point
tubes, using a Bruker RFS 100 spectrometer. NMR spectra
were recorded on a Bruker AC-250 Fourier transform spec-
trometer with spectrometer frequencies of 250.133 MHz for
1H, 62.896 MHz for 13C, 101.256 MHz for 31P, and 235.361 MHz
for 19F. NMR samples were flame-sealed in 5 mm Pyrex tubes.
All chemical shifts are reported in ppm relative to an external
standard (TMS for 1H and 13C, 85% H3PO4 for 31P, CFCl3 for
19F). Crystalline samples were obtained by distilling solvent
in vacuo (static) from the solution compartment by placing the
adjoining compartment in a cool stream of water or over liquid
nitrogen. Crystals were washed with cool solvent by cold spot
back-distillation.
Vibr a tion a l Sp ectr a for P (RF )2Cl (1). 1 was prepared by
the method of Davidson et al.15 IR (cm-1): 3106 w, 2727 w,
1845 w, 1626 m, 1577 w, 1278 s, 1196 s, 1172 s(sh), 1155 s(sh),
1133 s, 1086 s, 1039 m, 929 w(sh), 915 m, 860 m, 833 m, 754
m, 737 w, 704 m, 700 m, 686 s, 668 m, 564 w, 527 m, 506 w,
478 w, 434 m, 356 w. Raman (cm-1; 225 mW (poor scatterer)):
3093 m, 1665 w, 1627 s, 1374 s, 1262 w, 1154 w, 1121 w, 1035
s, 740 s, 527 w, 507 w, 472 w, 437 w, 300 m, 261 m, 212 w,
158 s, 114 m.
P r ep a r a tion a n d Ch a r a cter iza tion of P n (RF )2Cl (P n
) As (2), Sb (3)). In a typical reaction, an excess of nBuLi
(1.6 M in hexane) was slowly added through a septum to a
stirred, cooled (0 °C) solution of RFH in diethyl ether (50 mL)
under nitrogen. After 3-4 h at room temperature, the dark
orange solution was added over a period of 15 min to a stirred
solution of PnCl3 in diethyl ether (30 mL), producing a yellow
solution and a white precipitate (LiCl). The reaction mixture
was frozen, the reactor was evacuated, and the suspension was
stirred for 2 days at room temperature. Crystalline material
was obtained from the filtered solution as described in the
general procedures.
1J C-F ) 277.0 Hz, p-CF3),123.4 (q, J C-F ) 276.1 Hz, o-CF3),
128.7 (s(br), Cm), 133.3 (q, 2J C-F ) 34.8 Hz, Co), 136.3 (q, 2J C-F
) 34.5 Hz, Cp), 147.5 (s, Ci); 19F, -54.5 (s, 12F), -63.9 (s, 6F).
Sb(RF )2Cl (3) was prepared from RFH (1.3 g, 4.7 mmol) and
SbCl3 (0.53 g, 2.3 mmol). Large, hexagon-shaped, pale yellow
crystals were obtained: yield 0.69 g, 0.96 mmol, 41%; mp 112-
113 °C. Anal. Calcd: C, 30.05; H, 0.56; Cl, 4.93. Found: C,
30.23; H, 0.67; Cl, 4.86. IR (cm-1): 3096 w, 3083 w, 1844 w,
1623 s, 1577 m, 1559 w, 1419 w, 1279 s, 1200 s, 1129 s, 1109
s, 1082 s(sh), 1015 w(sh), 930 m, 915 s, 852 s, 837 m, 742 m,
691 s(sh), 684 s, 670 s, 560 w, 432 m, 408 w, 401 w(sh), 366 w,
351 s, 302 w. Raman (cm-1; 166 mW (poor scatterer)): 3084
m, 1624 m, 1383 m, 1261 w, 1157 w, 1014 w, 854 w, 738 s,
691 w, 581 w, 451 w, 434 w, 367 w, 349 s, 304 m, 262 s, 211
w, 184 m, 155 s, 126 s, 101 s. NMR (δ; CD2Cl2): 1H, 8.22 (s);
13C, 122.8 (q, 1J C-F ) 272.8 Hz, p-CF3), 124.1 (q, 1J C-F ) 276.1
2
Hz, o-CF3), 128.3 (s(br), Cm), 133.9 (q, J C-F ) 34.8 Hz, Co),
137.8 (q, J C-F ) 32.9 Hz, Cp), 151.9 (s(br), Ci); 19F -55.3 (s,
2
12F), -63.9 (s, 6F).
P r ep a r a tion a n d Ch a r a cter iza tion of Sb(RF )2OSO2CF 3
(4). Sb(RF)2Cl (0.25 g, 0.34 mmol) and AgOSO2CF3 (0.10 g, 0.37
mmol) were combined in hexane (10 mL), and the mixture was
stirred for 3 days with exclusion of light. The resultant yellow
suspension was filtered through a fine, sintered-glass filter to
give a clear yellow solution, from which pale, yellow, diamond-
shaped crystals of Sb(RF)2OSO2CF3 (4) were obtained; yield
0.04 g, 0.05 mmol, 14%; mp 126-127 °C. Anal. Calcd: C, 27.40;
H, 0.48. Found: C, 27.36; H, 0.56. IR (cm-1): 3105 w, 3087 w,
2726 w, 1625 w, 1578 w, 1377 s, 1280 s, 1268 s(sh), 1238 m(sh),
1220 s(sh), 1198 s, 1171 s, 1183 s(sh), 1152 s(sh), 1140 s, 1084
m, 1077 m, 1013 w, 942 m(sh), 932 s, 916 s, 852 m, 836 w, 767
w, 742 m, 693 m, 685 m, 672 w, 628 m, 603 w, 571 w, 559 w,
537 w, 515 w, 431 w, 408 w, 384 w, 366 w. Raman (cm-1; 110
mW (poor scatterer)): 3090 m, 1862 w(br), 1796 w(br), 1626
m, 1384 m, 1264 w, 1238 w, 1085 w, 1042 w(br), 1018 m, 931
w, 856 w, 767 m, 739 w, 693 w, 574 w, 456 w, 434 w, 306 m,
262 s, 212 m, 184 m, 157 s. NMR (δ; CD2Cl2): 1H, 8.32 (s);
13C, 124.1 (q, J C-F ) 276.1 Hz, o-CF3) and 128.9 (s(br), Cm);
1
19F, -55.7 (s(br, 33 Hz in CD2Cl2 and 26 Hz in hexane), 12F),
-64.0 (s, 6F), -77.3 (s, 3F).
X-r a y Cr ysta llogr a p h y. Crystals were obtained as de-
scribed above, except for 2a , which was grown from a reaction
mixture containing silver triflate. Details of the crystal
structure determinations are summarized in Table 1. For each
of these structures, there was severe disorder among the para
CF3 groups. Restraints were necessary for the refinement of
the disordered CF3 groups, and their positional and displace-
ment parameters are unreliable.
For 2a , unit cell determination and data collection were
performed, with graphite-monochromated radiation (Mo KR,
λ ) 0.710 73 Å) and 1° rotations on Φ scans, on a Nonius
KappaCCD diffractometer. Data reduction, including Lorentz,
polarization, and absorption corrections, was performed with
the DENZO-SMN software package,20 whereas structure solu-
tion and refinement were performed with the SHELX-9721 and
SHELXTL22 software packages. All non-hydrogen atoms were
refined anisotropically, whereas the hydrogen atoms, which
were located from a difference map, were refined with a
common isotropic displacement parameter. The hydrogen
atoms were constrained to ride on their attached carbon atoms,
but the coordinates were allowed to vary and the C-H bond
distances were restrained to be equal.
As(RF )2Cl (2) was prepared from RFH (4.88 g, 17.3 mmol)
and AsCl3 (1.5 g, 8.3 mmol). The crude yellow solid was
sublimed at 75 °C under dynamic vacuum to yield a white
solid, which was recrystallized from hexane to give colorless,
needle-shaped crystals: yield 0.72 g, 1.1 mmol, 13%; mp 98-
100 °C. Anal. Calcd: C, 32.14; H, 0.60; Cl, 5.27. Found: C,
32.20; H, 0.70; Cl, 5.12. IR (cm-1): 3377 vw(br), 3100 w, 3087
w(sh), 2727 w, 2671 w(br), 2279 w(br), 1844 w, 1668 w, 1624
m, 1581 w, 1341 m(sh), 1279 s, 1207 s(sh), 1195 s, 1153 s, 1125
s, 1085 s, 1039 m, 930 w(sh), 916 s, 891 w(sh), 857 m, 836 m,
792 w(br), 747 m, 736 w, 695 m, 692 m(sh), 685 s, 671 m, 652
For 2b, 3, and 4, unit cell determination and data collection
were performed, with graphite-monochromated radiation (Mo
KR, λ ) 0.710 73 Å for 2b and 4, Cu KR, λ ) 1.541 78 Å for 3)
and ω-2θ scans, on a Rigaku AFC5R diffractometer. Data
w(sh), 562 w, 435 w, 424 w, 417 w, 408 w, 387 m. Raman (cm-1
;
225 mW (poor scatterer)): 3089 m, 1665 w, 1625 s, 1588 m,
1022 m, 857 w, 739 s, 461 w, 388 s, 304 m, 260 s, 217 w, 193
w, 158 s, 110 m. NMR (δ; CD2Cl2): 1H, 8.10 (s); 13C, 122.6 (q,
(20) Nonius, B. V. Denzo-SMN; Delft, Holland, 1997.
(21) Sheldrick, G. M. SHELX-97 (version 97-2); University of
Go¨ttingen, Go¨ttingen, Germany, 1997.
(19) Burford, N.; Mu¨ller, J .; Parks, T. M. J . Chem. Educ. 1994, 71,
807-809.
(22) Sheldrick, G. M. SHELXTL (version 5.03); Siemens Analytical
Xray Instruments Inc., Madison, WI, 1994.

154 Organometallics, Vol. 19, No. 2, 2000
Burford et al.
Ta ble 1. Su m m a r y of th e Cr ysta l Da ta , Da ta Collection , a n d Refin em en t Con d ition s for As(RF )2Cl (2a ,b),
Sb(RF )2Cl (3), a n d Sb(RF )2OSO2CF 3 (4)
2a
2b
3
4
empirical formula
fw
C
18H4AsClF18
C18H4AsClF18
672.58
C18H4ClF18Sb
719.41
C19H4F21O3SSb
833.03
672.58
cryst syst
space group
a (Å)
b (Å)
c (Å)
orthorhombic
P212121
8.6646(2)
9.69650(10)
25.4076(6)
90
monoclinic
P21/a
8.705(9)
30.38(1)
8.167(4)
90
91.53(6)
90
2159(2), 4
2.069
monoclinic
P21/c
8.296(2)
30.430(7)
8.779(3)
90
94.030(3)
90
2211(1), 4
2.161
orthorhombic
P212121
16.172(4)
17.758(2)
9.119(1)
90
R (deg)
â (deg)
90
90
90
90
γ (deg)
V (Å3), Z
2134.65(7), 4
2.093
0.710 73
1.880, 1296
0.30 × 0.25 × 0.15
colorless, plate
Nonius KappaCCD
1° rotations on Φ
130(2)
2618.8(6), 4
2.113
Dcalcd (Mg m-3
λ (Å)
)
0.710 73
1.859, 1296
0.40 × 0.30 × 0.20
colorless, prism
Rigaku AFC5R
ω/2θ
1.541 78
12.518, 1368
0.30 × 0.13 × 0.11
light yellow, needle
Rigaku AFC5R
ω/2θ
0.710 73
1.304, 1592
0.50 × 0.40 × 0.40
colorless, block
Rigaku AFC5R
ω/2θ
µ (mm-1), F(000)
cryst size (mm3)
cryst color, habit
diffractometer
scan type
temp (K)
296(1)
296(1)
296(1)
abs cor
multiscan
0.766-0.602
16157
ψ-scan
ψ-scan
ψ-scan
transmissn factors
no. of data collected
no. of unique data
no. of obsd data, criterion
1.000-0.615
1.000-0.640
1.000-0.966
4082
3825
803, I > 3σI
0.109, 50.2
206
3953
3874
4287
4287
4353
3925, I > 2σI
0.074, 52.74
402
1022, I > 2σI
0.0740, 126.9
238
1840, I > 3σI
R
int, 2θmax (deg)
-, 60.0
no of refined params
refinement on
368
F
F2
F
F2
R1,a wR2 (obsd data)
R1,a wR2 (all data)
R,b Rw (obsd data)
Sc
0.0334, 0.0775
0.0403, 0.0822
0.0550, 0.220
-, 0.2793
0.067, 0.073
1.73
0.043, 0.044
1.40
1.062
1.00
abs structure param
0.002(10)
0.451, -0.463
-
-0.018(4)
0.72, -0.43
final ∆F map (e Å-3
)
0.53, -0.40
0.630, -0.950
a
2
b
R1 ) ∑(||Fo| - |Fc||)/∑|Fo|; wR2 ) {∑[w(Fo - Fc2)2]/∑[w(Fo2)2]}1/2
.
R ) ∑(||Fo| - |Fc||)/∑|Fo|; Rw ) [∑w(|Fo| - |Fc|)2/∑w(Fo2)]1/2
.
c S )
[∑w(Fo - Fc2)]2/(n - p)]1/2 for 2a and 3 and S ) [∑w(|Fo| - |Fc|)2/(n - p)]1/2 for 2b and 4; n ) number of data and p ) number of refined
2
parameters.
reduction (including Lorentz, polarization, and absorption
corrections), structure solution, and refinement were per-
formed with use of the teXsan crystallographic software
package,23 with the exception of compound 3, which was
refined with SHELXL-97.21 Some non-hydrogen atoms were
refined anisotropically, while the rest were refined isotropi-
cally. Hydrogen atoms were included at calculated positions
but were not refined.
Resu lts a n d Discu ssion
Reaction of 2 equiv of RFLi, prepared in situ, with
PnCl3 (Pn ) As, Sb) in diethyl ether gives As(RF)2Cl (2)
F igu r e 1. Solid-state structure of As(RF)2Cl (2a ) drawn
and Sb(RF)2Cl (3), respectively, which, together with the
with 50% probability displacement ellipsoids. Selected bond
previously reported Pn(RF)2Cl (Pn ) P, Bi)15,18 com-
lengths (Å) and angles (deg) for 2a : As1-Cl1 ) 2.1920-
pounds, completes the Pn(RF)2Cl (Pn ) P, As, Sb, Bi)
(12), As1-C1 ) 2.023(4), As1-C10 ) 2.016(4); C1-As1-
homologous series. Compound 2 was isolated as color-
Cl1 ) 00.57(12), C10-As1-Cl1 ) 92.04(11), C1-As1-C10
) 107.53(16). Selected bond lengths (Å) and angles (deg)
for Sb(RF)2Cl (3) (structure not shown): Sb1-Cl1 ) 2.358-
(11), Sb1-C1 ) 2.22(3), Sb1-C10 ) 2.25(3); C1-Sb1-Cl1
) 101.3(9), C10-Sb1-Cl1 ) 88.4(9), C1-Sb1-C10 )
107.0(12).
(2a , 2.1920(12) Å; 2b, 2.181(9) Å; cf. AsPh2Cl, 2.26(2)
Å,24 10-chloro-5,10-dihydrophenarsazine, 2.301(4),25 2.270
Å,26 10-chlorophenothiarsenin, 2.241(1) Å27) and other
less, needle-shaped crystals after multiple purification
steps to remove As(RF)Cl2 and AsnBuxClx-3. It crystal-
lizes in both orthorhombic (P212121; 2a ) and monoclinic
(P21/a; 2b) space groups, with essentially identical
molecular structures (the structure of 2a is shown in
Figure 1). In both structures, the As-Cl bond length
(24) Trotter, J . Can. J . Chem. 1962, 40, 1590-1593.
(25) Camerman, A.; Trotter, J . J . Chem. Soc. 1965, 730-738.
(26) Fukuyo, M.; Nakatsu, K.; Shimada, A. Bull. Chem. Soc. J pn.
1966, 39, 1614-1615.
(27) Pennington, W. T.; Cordes, A. W.; Graham, J . C.; J ung, Y. W.
Acta Crystallogr. 1983, C39, 712-714.
(23) teXsan for Windows; Molecular Structure Corp., The Wood-
lands, TX, 1997.

Bis(2,4,6-tris(trifluoromethyl)phenyl)chloropnictines
Organometallics, Vol. 19, No. 2, 2000 155
Pb-O bond observed in the isovalent carbenoid complex
(RFS)2Pb-THF31 (Pb-O, 2.495(10) Å; sum of covalent
radii, 2.20 Å) and those calculated for other carbenoid
complexes.32 In addition, the S-O bond length distinc-
tion (1.40(1), 1.41(1) Å; S-O(Sb) 1.513(9) Å) in the
triflate moiety of 4 confirms the covalency of the Sb-O
interaction (anionic triflate moieties typically exhibit
nearly equal S-O bond lengths of 1.42-1.47 Å). The
C-Sb-C angle in 4 is 1.7° smaller than in the chlorine
precursor, implicating slight steric strain imposed by
the triflate ligand over that of chlorine; however, a
substantial increase in pyramidalization is evident
(sums of the bond angles at Sb: 4, 287.8°; 3, 296.7°).
The geometry of the Sb atom is similar to those observed
in SbPh2OAc (sums of the bond angles at Sb: 270.8 and
268.9°)33 or Ph2SbOSbPh2 (sums of the bond angles at
Sb: 283.0 and 283.4°).34 Compound 4 also exhibits five
intermolecular Sb-F contacts in the range of 2.733(8)-
3.131(7) Å.
F igu r e 2. Solid-state structure of Sb(RF)2OSO2CF3 (4)
drawn with 50% probability displacement ellipsoids for the
anisotropically refined atoms. Selected bond lengths (Å)
and angles (deg) for 4: Sb1-O1 ) 2.082(8), Sb1-C1 ) 2.21-
(1), Sb1-C10 ) 2.23(1), S1-O1 ) 1.513(9), S1-O2 ) 1.40-
(1), S1-O3 ) 1.41(1), S1-C19 ) 1.66(2); O1-Sb1-C1 )
94.8(4), O1-Sb1-C10 ) 87.7(4), C1-Sb1-C10 ) 105.3-
(4), O2-S1-O1 ) 114.6(6), O3-S1-O1 ) 109.9(6), O1-
S1-C19 ) 100.6(8), O2-S1-O3 ) 119.2(7), O2-S1-C19
) 111(1), O3-S1-C19 ) 99(1), S1-O1-Sb1 ) 124.0(5).
Con clu sion s
Synthetic procedures and characterization data are
provided for the arsenic and antimony derivatives of Pn-
(RF)2Cl to complete the homologous series (Pn ) P, As,
Sb, Bi). In contrast to As(RF)2Cl, the chlorine site of the
stibine is accessible for metathesis with silver triflate
to give Sb(RF)2OSO2CF3, the solid-state structure of
which reveals a covalent Sb-O interaction. Therefore,
in contrast to the observations for dicoordinate group
14 element derivatives, the fluoromethyl substituents
of RF are not sufficiently basic to preclude coordination
of the weakly basic anion at the cationic stibenium
center. RF may be more effective at stabilizing carbenoid
anions such as [(RF)2M]- for M ) B, Al, Ga, In, and Tl,
which have been highlighted as interesting synthetic
targets on the basis of ab initio studies.35
structural features are normal. Sb(RF)2Cl (3) is struc-
turally similar to 2 and also structurally normal (Sb-
Cl, 2.358(11) Å; cf. (biphenyl-2,2′-diyl)antimony chloride,
2.423(2) Å,28 10-chlorophenothiantimonin, 2.390(2) Å29).
Noteworthy features of these structures are secondary
Pn-F contacts (2.823(2)-3.143(3) Å for 2a , 2.83(2)-
3.14(2) Å for 2b and 2.80(2)-3.11(2) Å for 3) beyond the
primary tricoordinate pnictogen coordination sphere,
typical of RF compounds. Comparison of FT-IR and FT-
Raman spectra of Pn(RF)2Cl derivatives18 reveal impor-
tant similarities enabling tentative assignment of the
Pn-Cl stretching frequencies, which are distinct in the
region of 500-250 cm-1. IR: P-Cl, 434 cm-1; As-Cl,
387 cm-1; Sb-Cl, 351 cm-1; Bi-Cl, 305 cm-1. Raman:
Ack n ow led gm en t. We thank the Natural Sciences
and Engineering Research Council of Canada and the
Killam Trust for funding, the Atlantic Regional Mag-
netic Resonance Centre for the use of instrumentation,
and Dr. Alan Lough of the University of Toronto for
collecting the X-ray data for 2a .
P-Cl, 437 cm-1; As-Cl, 388 cm-1; Sb-Cl, 349 cm-1
.
Reactions of Pn(RF)2Cl derivatives (Pn ) As, Sb) with
AgOSO2CF3 or Me3Si-OSO2CF3 in hydrocarbon sol-
vents were examined by 19F NMR spectroscopy. No
reaction was observed for Pn ) As, perhaps due to the
steric restrictions imposed by RF ligands (kinetic) or an
increase in ligand strain relative to the chloride (ther-
modynamic) resulting from metathesis. In contrast, the
larger antimony nucleus facilitates the quantitative
reaction to give Sb(RF)2OSO2CF3 (4). The broad 19F
NMR signal assigned to the ortho CF3 fluorine atoms
of 4 is indicative of the increased crowding at the Sb
center, relative to 3; moreover, the assigned Sb-Cl
stretch in the IR spectrum of 3 is absent in the spectrum
of 4. X-ray crystallographic analysis of 4 (Figure 2)
reveals an Sb-O bond distance (2.082(8) Å) close to the
sum of the covalent radii (2.07 Å),30 in contrast to the
Su p p or tin g In for m a tion Ava ila ble: Thermal ellipsoid
diagrams of 2b and 3 and tables of crystallographic data,
atomic coordinates, isotropic and anisotropic displacement
parameters, and bond lengths and angles. This material is
available free of charge via the Internet at http://pubs.acs.org.
OM990768W
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