Tetra­kis[3,5-bis­(trifluoro­meth­yl)phen­yl]silane

Agnew, C.; Dillon, K.B.; Goeta, A.E.; Thompson, A.L.

doi:10.1107/S1600536806017417

organic compounds

CRYSTALLOGRAPHIC
COMMUNICATIONS

ISSN: 2056-9890

Volume 62| Part 6| June 2006| Pages o2344-o2346

https://doi.org/10.1107/S1600536806017417

Tetrakis[3,5-bis(trifluoromethyl)phenyl]silane

Caroline Agnew,^a Keith B. Dillon,^a ^* Andrés E. Goeta ^a and Amber L. Thompson ^a

^aDepartment of Chemistry, University of Durham, South Road, Durham DH1 3LE, England
^*Correspondence e-mail: k.b.dillon@durham.ac.uk

(Received 3 February 2006; accepted 11 May 2006; online 17 May 2006)

The title compound, tetrakis[3,5-bis(trifluoromethyl)phenyl]silane (SiAr′′′₄, C₃₂H₁₂F₂₄Si), is a minor product from the reaction of silicon(IV) bromide with lithiated 1,3-bis(trifluoromethyl)benzene (Ar′H). The structure crystallizes with two half-molecules in the asymmetric unit, with each central Si atom positioned on a twofold axis in a pseudo-tetrahedral environment, with Si—C bond lengths in the range 1.873 (3)–1.879 (3) Å.

Comment

The reactions of silicon(IV) chloride in a 1:2 ratio with lithiated trifluoromethyl-substituted aromatic hydrocarbons are complex and interesting (Buijink et al., 1993 ; Braddock-Wilking et al., 1995 ; Batsanov et al., 2003 ). With lithiated 1,3,5-tris(trifluoromethyl)benzene (ArH), the only product identified was Ar₂SiF₂, which was fully characterized crystallographically (Buijink et al., 1993). This result was subsequently confirmed by Batsanov et al. (2003). Similarly, HSiCl₃ reacts with ArLi to form Ar₂SiHF, again involving chlorine–fluorine exchange; this has also been characterized by single-crystal X-ray diffraction (Braddock-Wilking et al., 1995). With 1,3-bis(trifluoromethyl)benzene, Ar′H, the system is more complicated because there are various lithiation positions (Bartle et al., 1973 ; Batsanov et al., 2002 , 2003; Cornet et al., 2003 ). These are ortho to both CF₃ groups, giving 2,6-bis(trifluoromethyl)phenyl (Ar′) derivatives, ortho to one CF₃ group and para to the other, yielding 2,4-bis(trifluoromethyl)phenyl (Ar′′) species, and, much less likely, meta to both CF₃ groups, giving 3,5-bis(trifluoromethyl)phenyl (Ar′′′) derivatives. An analytical gas–liquid chromatography study, following carboxylation of the organolithium compounds and subsequent esterification with diazomethane, showed ca 60% of the 2,4-isomer, 40% of the 2,6-isomer and less than 1% of a third component, presumed to be the 3,5-isomer (Bartle et al., 1973). With SiCl₄, four of the possible disubstituted products, once F/Cl exchange is taken into account, have been observed spectroscopically, viz. Ar′₂SiCl₂, Ar′₂SiF₂, Ar′′₂SiCl₂ and Ar′′₂SiF₂; two of these, Ar′₂SiF₂ and Ar′′₂SiCl₂, have been characterized by single-crystal X-ray diffraction at 120 K (Batsanov et al., 2003). The results suggested that the F/Cl exchange rate decreased in the order Ar > Ar′ > Ar′′ (Batsanov et al., 2003). It was therefore of considerable interest to extend this work to reactions of silicon(IV) bromide in a 1:2 molar ratio with the lithium derivatives of ArH and Ar′H.

Not surprisingly, the only product observed from SiBr₄ and ArLi was Ar₂SiF₂; Si—Br bonds are weaker than Si—Cl bonds, so facile exchange could reasonably be expected. The ¹⁹F NMR data are given in Table 2, with literature data for comparison (Batsanov et al., 2003). With lithiated Ar′H and SiBr₄, the products Ar′₂SiF₂ (Batsanov et al., 2003), Ar′′₂SiBr₂ and Ar′′₂SiBrF were identified by ¹⁹F NMR solution state spectroscopy (Table 2). The results thus lend support to the idea that halogen exchange is slowest in the Ar′′ species. After the mixture had been left to stand for some time, a few crystals were isolated, and proved to be of the fully substituted silane with no ortho CF₃ groups, i.e. tetrakis[3,5-bis(trifluoromethyl)phenyl]silane. Since there is little or no steric hindrance around silicon, further substitution beyond the disubstituted product is clearly more favourable for 3,5-derivatives than for 2,4- or 2,6-compounds. Nevertheless this product is a surprising one, in view of the work of Bartle et al. (1973).

The compound tetrakis[3,5-bis(trifluoromethyl)phenyl]silane, (I), crystallizes in the monoclinic space group P2/c, with two half molecules in the asymmetric unit and the molecular structure is shown in Fig. 1. Selected bond distances and angles are listed in Table 1. The central Si atom is in a tetrahedral environment, with bond angles around Si between 106.27 (16) and 110.97 (11)°. The Si—C bond lengths are all very similar, between 1.873 (3) and 1.877 (3) Å. The CF₃ groups are all ordered, presumably due to the weak F⋯F interactions (Fig. 2 and Table 1). While this species has not been reported previously, the structurally similar tetrakis[3,5-bis(trifluoromethyl)phenyl]borate ion has been widely used in recent years, since the first report by Nishida et al. (1984 ), as a large lipophilic stable counter-ion for a variety of cationic complexes; it features in 291 structures in the Cambridge Structural Database (November 2004 edition; Allen, 2002 ). The structures of neutral tris[3,5-bis(trifluoromethyl)phenyl]phosphane (Jessop et al., 2002 ) and -arsane (Dietzel & Jansen, 2004 ) have also been described. However, these species were all made directly from 3,5-bis(trifluoromethyl)phenyl-substituted aromatic starting materials.

Figure 1
View of one of the independent molecules of (I)

with selected atoms labelled. Displacement ellipsoids are drawn at the 50% probability level. [Symmetry code for primed and unlabelled atoms: 1 − x, y, ½ − z.] The other molecule is very similar.

Figure 2
Crystal packing in the title compound, viewed down the b axis, showing short intermolecular F⋯F contacts as dashed lines. H atoms have been omitted for clarity.

Experimental

All manipulations of air- and/or moisture-sensitive compounds were performed either under an inert atmosphere of dry nitrogen or in vacuo, using standard Schlenk and cannula techniques, or in a nitrogen-filled glovebox. ¹⁹F NMR spectra were recorded on a Varian Unity 300 Fourier transform spectrometer at 282.2 MHz; chemical shifts were measured relative to external CFCl₃. A solution of SiBr₄ (1.7 ml, 13.5 mmol) in diethyl ether was added dropwise, via a cannula, to a solution of ArLi (8 ml, 27 mmol) in diethyl ether at 195 K [the lithiated solutions of both ArH and Ar'H were prepared as described previously by Batsanov et al. (2002)]. White fumes were evolved. The mixture was allowed to warm to room temperature and stirred for 5 h, giving a pale-yellow oil. The presence of Ar₂SiF₂ as the only major silicon-containing component was confirmed by ¹⁹F NMR solution state spectroscopy (Table 2). Similarly, a solution of SiBr₄ (0.7 ml, 5.6 mmol) in diethyl ether was added slowly, via a cannula, to a solution of lithiated Ar′H (4 ml, 11.3 mmol) in diethyl ether at 195 K. The mixture was allowed to reach room temperature and stirred overnight, giving a pale-brown solution. Analysis by ¹⁹F NMR spectroscopy indicated three main components (Table 2). When the mixture was allowed to stand for some weeks, a few crystals appeared; these were isolated, and analysed by single-crystal X-ray diffraction. As indicated above, they proved to be of tetrakis[3,5-bis(trifluoromethyl)phenyl]silane.

Crystal data

C₃₂H₁₂F₂₄Si
M_r = 880.51
Monoclinic, P 2/c
a = 18.3760 (4) Å
b = 9.5325 (2) Å
c = 18.7776 (4) Å
β = 100.388 (1)°
V = 3235.34 (12) Å³
Z = 4
D_x = 1.808 Mg m⁻³
Mo Kα radiation
μ = 0.24 mm⁻¹
T = 120 (2) K
Block, colourless
0.20 × 0.12 × 0.10 mm

Data collection

Bruker SMART-6000 CCD diffractometer
ω scans
Absorption correction: integration (XPREP in SHELXTL; Sheldrick, 1997b ) T_min = 0.957, T_max = 0.977
28959 measured reflections
7404 independent reflections
5078 reflections with I > 2σ(I)
R_int = 0.040
θ_max = 27.5°

Refinement

Refinement on F²
R[F² > 2σ(F²)] = 0.051
wR(F²) = 0.158
S = 1.02
7404 reflections
515 parameters
H-atom parameters constrained
w = 1/[σ²(F_o²) + (0.0779P)² + 2.8011P] where P = (F_o² + 2F_c²)/3
(Δ/σ)_max < 0.001
Δρ_max = 0.62 e Å⁻³
Δρ_min = −0.37 e Å⁻³

Table 1
Selected geometric parameters (Å, °)

Si1—C11	1.873 (3)
Si1—C31	1.877 (3)
Si2—C41	1.876 (3)
Si2—C21	1.879 (3)

F12⋯F14ⁱ	2.847 (3)
F13⋯F31ⁱⁱ	2.919 (3)
F16⋯F42	2.997 (3)
F16⋯F43	2.848 (3)
F21⋯F44ⁱⁱⁱ	2.861 (3)
F31⋯F41	2.901 (3)
F33⋯F26	2.969 (3)
F33⋯F41	2.852 (3)

C11^iv—Si1—C11	106.27 (16)
C11^iv—Si1—C31^iv	110.63 (11)
C11—Si1—C31^iv	110.97 (11)
C11^iv—Si1—C31	110.97 (11)
C11—Si1—C31	110.63 (11)
C31^iv—Si1—C31	107.40 (16)
C41^v—Si2—C41	105.22 (16)
C41^v—Si2—C21	111.80 (11)
C41—Si2—C21	110.87 (11)
C41^v—Si2—C21^v	110.87 (11)
C41—Si2—C21^v	111.80 (11)
C21—Si2—C21^v	106.39 (16)
Symmetry codes: (i) $[-x+1, y, -z+{\script{1\over 2}}]$ ; (ii) $[-x, y, -z+{\script{1\over 2}}]$ ;. (iii) -x+1, -y, -z+1; (iv) -x+1, -y+1, -z+1; (v) $[x, -y+1, z-{\script{1\over 2}}]$ .

Table 2
¹⁹F NMR (p.p.m., Hz) data for reaction products

Group	No. of Fs	δ ¹⁹F	⁵J_FF	δ ¹⁹F^a	⁵J_FF^a
Ar₂SiF₂
o-CF₃	12	−57.7	t, 12.4	−57.3	t, 12.8
p-CF₃	6	−63.8	s	−64.2	s
Si—F	2	−125.7	m, NR^b	−124.5	m, 12.8
Ar′₂SiF₂
o-CF₃	12	−57.5	t, 12.8	−57.5	t, 12.3
Si—F	2	−125.4	m, 12.8	−125.5	m, 12.5
Ar′′₂SiBr₂
o-CF₃	6	−57.6	s
p-CF₃	6	−64.5	s
Ar′′₂SiBrF
o-CF₃	6	−59.6	d, 12.8
p-CF₃	6	−64.6	s
Si—F	1	−158.4	m, 12.8
Notes: (a) literature data from Batsanov et al. (2003); (b) not resolved.

All H atoms were positioned geometrically (C—H = 0.95 Å) and refined using a riding model with U_iso(H) = 1.2U_eq(C).

Data collection: SMART-NT (Bruker, 2000 ); cell refinement: SMART-NT; data reduction: SAINT-NT (Bruker, 2000); program(s) used to solve structure: SHELXS97 (Sheldrick, 1997a ); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997a); molecular graphics: SHELXTL (Sheldrick, 1997b); software used to prepare material for publication: SHELXTL.

Supporting information

Crystal structure: contains datablocks I, global. DOI: https://doi.org/10.1107/S1600536806017417/rn2003sup1.cif

Structure factors: contains datablock I. DOI: https://doi.org/10.1107/S1600536806017417/rn2003Isup2.hkl

Computing details top

Data collection: SMART-NT (Bruker, 2000); cell refinement: SMART-NT; data reduction: SAINT-NT (Bruker, 2000); program(s) used to solve structure: SHELXS97 (Sheldrick, 1997a); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997a); molecular graphics: SHELXTL (Sheldrick, 1997b); software used to prepare material for publication: SHELXTL.

Tetrakis[3,5-bis(trifluoromethyl)phenyl]silane top

Crystal data top

C₃₂H₁₂F₂₄Si	F(000) = 1736
M_r = 880.51	D_x = 1.808 Mg m⁻³
Monoclinic, P2/c	Melting point: not measured K
Hall symbol: -P 2yc	Mo Kα radiation, λ = 0.71073 Å
a = 18.3760 (4) Å	Cell parameters from 5856 reflections
b = 9.5325 (2) Å	θ = 2.4–26.8°
c = 18.7776 (4) Å	µ = 0.24 mm⁻¹
β = 100.388 (1)°	T = 120 K
V = 3235.34 (12) Å³	Block, colourless
Z = 4	0.20 × 0.12 × 0.10 mm

Data collection top

Bruker SMART-6000 CCD diffractometer	7404 independent reflections
Radiation source: fine-focus sealed tube	5078 reflections with I > 2σ(I)
Graphite monochromator	R_int = 0.040
Detector resolution: 8 pixels mm^-1	θ_max = 27.5°, θ_min = 1.1°
ω scans	h = −23→23
Absorption correction: integration (XPREP in SHELXTL; Sheldrick, 1997b)	k = −12→12
T_min = 0.957, T_max = 0.977	l = −24→24
28959 measured reflections

Refinement top

Refinement on F²	Primary atom site location: structure-invariant direct methods
Least-squares matrix: full	Secondary atom site location: difference Fourier map
R[F² > 2σ(F²)] = 0.051	Hydrogen site location: inferred from neighbouring sites
wR(F²) = 0.158	H-atom parameters constrained
S = 1.02	w = 1/[σ²(F_o²) + (0.0779P)² + 2.8011P] where P = (F_o² + 2F_c²)/3
7404 reflections	(Δ/σ)_max < 0.001
515 parameters	Δρ_max = 0.62 e Å⁻³
0 restraints	Δρ_min = −0.37 e Å⁻³

Special details top

Experimental. The data collection nominally covered full sphere of reciprocal Space, by a combination of 5 sets of ω scans each set at different φ and/or 2θ angles and each scan (15 s exposure) covering 0.3° in ω. Crystal to detector distance 5.81 cm.

Geometry. All e.s.d.'s (except the e.s.d. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell e.s.d.'s are taken into account individually in the estimation of e.s.d.'s in distances, angles and torsion angles; correlations between e.s.d.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell e.s.d.'s is used for estimating e.s.d.'s involving l.s. planes.

Refinement. Refinement of F² against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F², conventional R-factors R are based on F, with F set to zero for negative F². The threshold expression of F² > σ(F²) is used only for calculating R-factors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F² are statistically about twice as large as those based on F, and R- factors based on ALL data will be even larger.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å²) top

	x	y	z	U_iso*/U_eq
Si1	0.5000	0.51518 (10)	0.2500	0.0226 (2)
C11	0.50382 (15)	0.3973 (3)	0.33037 (14)	0.0265 (5)
C12	0.55556 (16)	0.2873 (3)	0.33934 (15)	0.0306 (6)
H12	0.5873	0.2748	0.3051	0.037*
C13	0.56073 (16)	0.1963 (3)	0.39802 (15)	0.0324 (6)
C14	0.51587 (17)	0.2136 (3)	0.44805 (15)	0.0328 (6)
H14	0.5202	0.1519	0.4883	0.039*
C15	0.46426 (17)	0.3205 (3)	0.44026 (15)	0.0332 (6)
C16	0.45809 (16)	0.4127 (3)	0.38142 (15)	0.0307 (6)
H16	0.4225	0.4860	0.3763	0.037*
C17	0.61350 (19)	0.0747 (3)	0.40342 (16)	0.0399 (7)
F11	0.67404 (11)	0.1038 (2)	0.37646 (12)	0.0562 (5)
F12	0.58198 (12)	−0.03549 (18)	0.36466 (11)	0.0524 (5)
F13	0.63480 (14)	0.0299 (2)	0.47074 (11)	0.0641 (6)
C18	0.4136 (2)	0.3379 (3)	0.49352 (18)	0.0446 (7)
F14	0.44268 (14)	0.2839 (2)	0.55899 (11)	0.0691 (7)
F15	0.34864 (13)	0.2778 (3)	0.47187 (14)	0.0729 (7)
F16	0.40028 (11)	0.4729 (2)	0.50652 (10)	0.0485 (5)
C31	0.41640 (14)	0.6318 (3)	0.23931 (13)	0.0242 (5)
C32	0.41887 (14)	0.7540 (3)	0.28073 (14)	0.0269 (5)
H32	0.4625	0.7763	0.3143	0.032*
C33	0.35807 (15)	0.8435 (3)	0.27335 (14)	0.0281 (5)
C34	0.29410 (15)	0.8129 (3)	0.22503 (15)	0.0295 (6)
H34	0.2528	0.8743	0.2200	0.035*
C35	0.29090 (14)	0.6912 (3)	0.18393 (14)	0.0289 (6)
C36	0.35160 (14)	0.6021 (3)	0.19073 (14)	0.0267 (5)
H36	0.3488	0.5198	0.1618	0.032*
C37	0.36451 (17)	0.9769 (3)	0.31688 (16)	0.0369 (6)
F31	0.40129 (10)	0.95860 (18)	0.38421 (9)	0.0418 (4)
F32	0.40239 (13)	1.07538 (18)	0.28782 (11)	0.0561 (6)
F33	0.29914 (11)	1.0315 (2)	0.32191 (12)	0.0571 (5)
C38	0.22219 (17)	0.6590 (3)	0.13071 (18)	0.0421 (7)
F34	0.21457 (13)	0.7411 (3)	0.07311 (13)	0.0871 (9)
F35	0.16130 (10)	0.6791 (2)	0.15935 (13)	0.0622 (6)
F36	0.21858 (11)	0.5268 (2)	0.10818 (13)	0.0665 (7)
Si2	0.0000	0.85198 (10)	0.2500	0.0226 (2)
C21	0.06268 (14)	0.9701 (3)	0.20832 (14)	0.0263 (5)
C22	0.06995 (15)	0.9610 (3)	0.13596 (14)	0.0274 (5)
H22	0.0441	0.8899	0.1062	0.033*
C23	0.11462 (15)	1.0547 (3)	0.10653 (14)	0.0292 (6)
C24	0.15327 (15)	1.1580 (3)	0.14924 (15)	0.0314 (6)
H24	0.1842	1.2209	0.1291	0.038*
C25	0.14687 (15)	1.1696 (3)	0.22082 (15)	0.0306 (6)
C26	0.10142 (15)	1.0782 (3)	0.25045 (15)	0.0294 (6)
H26	0.0964	1.0887	0.2996	0.035*
C27	0.11787 (18)	1.0511 (3)	0.02752 (16)	0.0382 (7)
F21	0.08780 (13)	0.9363 (2)	−0.00568 (10)	0.0557 (5)
F22	0.07939 (13)	1.1592 (2)	−0.00753 (10)	0.0579 (5)
F23	0.18555 (11)	1.0634 (3)	0.01409 (11)	0.0633 (6)
C28	0.18495 (18)	1.2886 (3)	0.26534 (17)	0.0392 (7)
F24	0.14555 (13)	1.40746 (18)	0.25369 (11)	0.0576 (6)
F25	0.25153 (11)	1.3164 (2)	0.24927 (12)	0.0593 (6)
F26	0.19520 (11)	1.26399 (19)	0.33628 (9)	0.0465 (4)
C41	0.05500 (15)	0.7325 (3)	0.31883 (13)	0.0257 (5)
C42	0.13058 (14)	0.7488 (3)	0.34453 (13)	0.0281 (5)
H42	0.1561	0.8258	0.3284	0.034*
C43	0.16907 (15)	0.6534 (3)	0.39354 (14)	0.0305 (6)
C44	0.13299 (16)	0.5395 (3)	0.41750 (14)	0.0312 (6)
H44	0.1594	0.4748	0.4511	0.037*
C45	0.05818 (15)	0.5215 (3)	0.39184 (14)	0.0284 (5)
C46	0.01943 (15)	0.6164 (3)	0.34351 (14)	0.0273 (5)
H46	−0.0320	0.6029	0.3268	0.033*
C47	0.25038 (17)	0.6700 (4)	0.41920 (16)	0.0394 (7)
F41	0.27414 (10)	0.7993 (2)	0.41015 (11)	0.0542 (5)
F42	0.28932 (11)	0.5855 (2)	0.38304 (12)	0.0609 (6)
F43	0.27010 (10)	0.6407 (2)	0.49010 (10)	0.0556 (5)
C48	0.01947 (17)	0.3948 (3)	0.41478 (16)	0.0373 (7)
F44	0.04750 (12)	0.3538 (2)	0.48211 (11)	0.0567 (6)
F45	−0.05241 (11)	0.41571 (19)	0.41221 (11)	0.0502 (5)
F46	0.02479 (12)	0.28522 (19)	0.37153 (12)	0.0571 (5)

Atomic displacement parameters (Å²) top

	U¹¹	U²²	U³³	U¹²	U¹³	U²³
Si1	0.0238 (5)	0.0191 (4)	0.0240 (5)	0.000	0.0023 (4)	0.000
C11	0.0300 (13)	0.0216 (12)	0.0261 (12)	−0.0028 (10)	0.0002 (10)	−0.0013 (10)
C12	0.0342 (14)	0.0259 (13)	0.0300 (13)	−0.0013 (11)	0.0012 (11)	−0.0003 (10)
C13	0.0395 (16)	0.0231 (12)	0.0316 (14)	−0.0008 (11)	−0.0016 (12)	−0.0017 (10)
C14	0.0438 (16)	0.0243 (13)	0.0288 (13)	−0.0022 (12)	0.0025 (12)	0.0009 (10)
C15	0.0393 (16)	0.0307 (14)	0.0294 (13)	−0.0026 (12)	0.0055 (12)	−0.0002 (11)
C16	0.0343 (15)	0.0251 (13)	0.0324 (14)	−0.0010 (11)	0.0054 (12)	0.0007 (11)
C17	0.0497 (19)	0.0342 (15)	0.0338 (15)	0.0078 (13)	0.0023 (13)	0.0045 (12)
F11	0.0446 (11)	0.0508 (12)	0.0728 (14)	0.0135 (9)	0.0097 (10)	0.0108 (10)
F12	0.0702 (14)	0.0297 (9)	0.0570 (12)	0.0055 (9)	0.0110 (10)	−0.0044 (8)
F13	0.0912 (17)	0.0581 (13)	0.0391 (10)	0.0369 (12)	0.0015 (10)	0.0116 (9)
C18	0.054 (2)	0.0382 (16)	0.0433 (17)	0.0010 (15)	0.0127 (15)	0.0105 (14)
F14	0.0957 (18)	0.0727 (15)	0.0466 (11)	0.0325 (13)	0.0336 (12)	0.0274 (11)
F15	0.0619 (14)	0.0767 (16)	0.0898 (17)	−0.0275 (12)	0.0391 (13)	−0.0178 (13)
F16	0.0595 (12)	0.0453 (10)	0.0436 (10)	0.0083 (9)	0.0168 (9)	0.0003 (8)
C31	0.0252 (13)	0.0226 (12)	0.0253 (12)	−0.0013 (10)	0.0061 (10)	0.0036 (9)
C32	0.0273 (13)	0.0240 (12)	0.0286 (12)	−0.0010 (10)	0.0029 (10)	0.0010 (10)
C33	0.0325 (14)	0.0245 (12)	0.0286 (13)	0.0011 (11)	0.0088 (11)	0.0015 (10)
C34	0.0284 (13)	0.0261 (12)	0.0347 (14)	0.0045 (11)	0.0077 (11)	0.0031 (11)
C35	0.0239 (13)	0.0306 (13)	0.0318 (13)	0.0025 (10)	0.0043 (11)	0.0002 (11)
C36	0.0270 (13)	0.0238 (12)	0.0291 (13)	−0.0005 (10)	0.0046 (10)	−0.0012 (10)
C37	0.0422 (17)	0.0294 (14)	0.0390 (16)	0.0031 (12)	0.0065 (13)	−0.0023 (12)
F31	0.0523 (11)	0.0376 (9)	0.0345 (9)	0.0000 (8)	0.0052 (8)	−0.0085 (7)
F32	0.0899 (16)	0.0301 (9)	0.0505 (11)	−0.0173 (10)	0.0182 (11)	−0.0029 (8)
F33	0.0523 (12)	0.0458 (11)	0.0707 (14)	0.0176 (9)	0.0041 (10)	−0.0218 (10)
C38	0.0303 (15)	0.0437 (17)	0.0491 (18)	0.0064 (13)	−0.0014 (13)	−0.0071 (14)
F34	0.0638 (15)	0.124 (2)	0.0598 (14)	−0.0178 (15)	−0.0259 (12)	0.0330 (15)
F35	0.0242 (9)	0.0650 (13)	0.0958 (17)	−0.0018 (9)	0.0061 (10)	−0.0259 (12)
F36	0.0408 (11)	0.0643 (13)	0.0837 (15)	0.0096 (10)	−0.0173 (10)	−0.0399 (12)
Si2	0.0253 (5)	0.0212 (4)	0.0210 (4)	0.000	0.0033 (4)	0.000
C21	0.0250 (13)	0.0247 (12)	0.0290 (13)	0.0038 (10)	0.0046 (10)	0.0030 (10)
C22	0.0278 (13)	0.0264 (12)	0.0274 (12)	0.0003 (10)	0.0034 (10)	0.0001 (10)
C23	0.0297 (14)	0.0271 (13)	0.0303 (13)	0.0012 (11)	0.0044 (11)	0.0009 (10)
C24	0.0285 (14)	0.0273 (13)	0.0388 (15)	0.0006 (11)	0.0070 (12)	0.0033 (11)
C25	0.0314 (14)	0.0243 (13)	0.0348 (14)	0.0017 (11)	0.0023 (11)	−0.0014 (11)
C26	0.0309 (14)	0.0259 (13)	0.0317 (14)	0.0009 (11)	0.0059 (11)	0.0003 (10)
C27	0.0433 (17)	0.0391 (16)	0.0336 (15)	−0.0081 (13)	0.0103 (13)	−0.0016 (12)
F21	0.0835 (15)	0.0508 (11)	0.0351 (10)	−0.0203 (11)	0.0170 (10)	−0.0103 (8)
F22	0.0821 (15)	0.0550 (12)	0.0359 (10)	0.0079 (11)	0.0083 (10)	0.0104 (9)
F23	0.0449 (12)	0.1063 (18)	0.0417 (11)	−0.0164 (12)	0.0161 (9)	−0.0057 (11)
C28	0.0448 (17)	0.0297 (14)	0.0427 (17)	−0.0048 (13)	0.0066 (14)	−0.0036 (12)
F24	0.0805 (15)	0.0269 (9)	0.0592 (12)	0.0046 (9)	−0.0041 (11)	−0.0078 (8)
F25	0.0559 (13)	0.0569 (12)	0.0673 (13)	−0.0292 (10)	0.0169 (10)	−0.0174 (10)
F26	0.0570 (11)	0.0397 (10)	0.0393 (10)	−0.0081 (9)	−0.0009 (8)	−0.0093 (8)
C41	0.0301 (13)	0.0250 (12)	0.0221 (11)	0.0009 (10)	0.0048 (10)	−0.0009 (9)
C42	0.0279 (13)	0.0311 (13)	0.0247 (12)	−0.0008 (11)	0.0035 (10)	−0.0012 (10)
C43	0.0291 (14)	0.0348 (14)	0.0268 (13)	0.0007 (11)	0.0028 (11)	−0.0015 (11)
C44	0.0348 (15)	0.0293 (13)	0.0282 (13)	0.0053 (11)	0.0022 (11)	0.0026 (11)
C45	0.0321 (14)	0.0250 (12)	0.0272 (13)	−0.0004 (11)	0.0031 (11)	−0.0005 (10)
C46	0.0265 (13)	0.0266 (12)	0.0277 (12)	0.0003 (10)	0.0022 (10)	0.0001 (10)
C47	0.0313 (15)	0.0528 (18)	0.0327 (15)	0.0047 (14)	0.0024 (12)	0.0040 (13)
F41	0.0339 (10)	0.0646 (13)	0.0612 (12)	−0.0148 (9)	0.0006 (9)	0.0076 (10)
F42	0.0369 (11)	0.0805 (15)	0.0651 (13)	0.0157 (10)	0.0088 (10)	−0.0065 (11)
F43	0.0354 (10)	0.0860 (15)	0.0400 (10)	−0.0051 (10)	−0.0078 (8)	0.0137 (10)
C48	0.0412 (17)	0.0293 (14)	0.0391 (16)	−0.0026 (12)	0.0009 (13)	0.0060 (12)
F44	0.0675 (13)	0.0451 (11)	0.0503 (11)	−0.0140 (10)	−0.0087 (10)	0.0236 (9)
F45	0.0430 (11)	0.0400 (10)	0.0689 (13)	−0.0049 (8)	0.0138 (9)	0.0151 (9)
F46	0.0692 (14)	0.0311 (9)	0.0734 (14)	−0.0123 (9)	0.0190 (11)	−0.0125 (9)

Geometric parameters (Å, º) top

Si1—C11ⁱ	1.873 (3)	Si2—C41ⁱⁱ	1.876 (3)
Si1—C11	1.873 (3)	Si2—C41	1.876 (3)
Si1—C31ⁱ	1.877 (3)	Si2—C21	1.879 (3)
Si1—C31	1.877 (3)	Si2—C21ⁱⁱ	1.879 (3)
C11—C16	1.392 (4)	C21—C22	1.392 (4)
C11—C12	1.406 (4)	C21—C26	1.411 (4)
C12—C13	1.392 (4)	C22—C23	1.393 (4)
C12—H12	0.9500	C22—H22	0.9500
C13—C14	1.367 (4)	C23—C24	1.383 (4)
C13—C17	1.503 (4)	C23—C27	1.496 (4)
C14—C15	1.382 (4)	C24—C25	1.375 (4)
C14—H14	0.9500	C24—H24	0.9500
C15—C16	1.400 (4)	C25—C26	1.391 (4)
C15—C18	1.493 (4)	C25—C28	1.505 (4)
C16—H16	0.9500	C26—H26	0.9500
C17—F13	1.325 (3)	C27—F23	1.318 (4)
C17—F11	1.332 (4)	C27—F21	1.330 (3)
C17—F12	1.348 (4)	C27—F22	1.351 (4)
C18—F15	1.321 (4)	C28—F26	1.332 (4)
C18—F16	1.340 (4)	C28—F25	1.338 (4)
C18—F14	1.351 (4)	C28—F24	1.341 (4)
C31—C36	1.392 (4)	C41—C42	1.394 (4)
C31—C32	1.397 (4)	C41—C46	1.405 (4)
C32—C33	1.393 (4)	C42—C43	1.393 (4)
C32—H32	0.9500	C42—H42	0.9500
C33—C34	1.381 (4)	C43—C44	1.388 (4)
C33—C37	1.505 (4)	C43—C47	1.493 (4)
C34—C35	1.388 (4)	C44—C45	1.383 (4)
C34—H34	0.9500	C44—H44	0.9500
C35—C36	1.390 (4)	C45—C46	1.385 (4)
C35—C38	1.494 (4)	C45—C48	1.503 (4)
C36—H36	0.9500	C46—H46	0.9500
C37—F33	1.328 (4)	C47—F41	1.329 (4)
C37—F31	1.333 (3)	C47—F42	1.340 (4)
C37—F32	1.342 (4)	C47—F43	1.344 (3)
C38—F34	1.322 (4)	C48—F45	1.328 (4)
C38—F36	1.327 (4)	C48—F44	1.335 (3)
C38—F35	1.340 (4)	C48—F46	1.338 (4)

F12···F14ⁱⁱⁱ	2.847 (3)	F21···F44^v	2.861 (3)
F13···F31^iv	2.919 (3)	F31···F41	2.901 (3)
F16···F42	2.997 (3)	F33···F26	2.969 (3)
F16···F43	2.848 (3)	F33···F41	2.852 (3)

C11ⁱ—Si1—C11	106.27 (16)	C41ⁱⁱ—Si2—C41	105.22 (16)
C11ⁱ—Si1—C31ⁱ	110.63 (11)	C41ⁱⁱ—Si2—C21	111.80 (11)
C11—Si1—C31ⁱ	110.97 (11)	C41—Si2—C21	110.87 (11)
C11ⁱ—Si1—C31	110.97 (11)	C41ⁱⁱ—Si2—C21ⁱⁱ	110.87 (11)
C11—Si1—C31	110.63 (11)	C41—Si2—C21ⁱⁱ	111.80 (11)
C31ⁱ—Si1—C31	107.40 (16)	C21—Si2—C21ⁱⁱ	106.39 (16)
C16—C11—C12	118.4 (2)	C22—C21—C26	117.7 (2)
C16—C11—Si1	123.5 (2)	C22—C21—Si2	122.9 (2)
C12—C11—Si1	118.1 (2)	C26—C21—Si2	119.28 (19)
C13—C12—C11	120.5 (3)	C21—C22—C23	121.0 (2)
C13—C12—H12	119.7	C21—C22—H22	119.5
C11—C12—H12	119.7	C23—C22—H22	119.5
C14—C13—C12	120.4 (3)	C24—C23—C22	120.3 (2)
C14—C13—C17	120.6 (3)	C24—C23—C27	118.9 (2)
C12—C13—C17	119.0 (3)	C22—C23—C27	120.7 (2)
C13—C14—C15	120.2 (3)	C25—C24—C23	119.9 (3)
C13—C14—H14	119.9	C25—C24—H24	120.0
C15—C14—H14	119.9	C23—C24—H24	120.0
C14—C15—C16	120.2 (3)	C24—C25—C26	120.3 (3)
C14—C15—C18	120.6 (3)	C24—C25—C28	119.4 (3)
C16—C15—C18	119.2 (3)	C26—C25—C28	120.2 (3)
C11—C16—C15	120.3 (3)	C25—C26—C21	120.8 (2)
C11—C16—H16	119.8	C25—C26—H26	119.6
C15—C16—H16	119.8	C21—C26—H26	119.6
F13—C17—F11	107.8 (3)	F23—C27—F21	108.1 (3)
F13—C17—F12	106.7 (3)	F23—C27—F22	105.5 (2)
F11—C17—F12	105.3 (3)	F21—C27—F22	105.2 (3)
F13—C17—C13	112.9 (3)	F23—C27—C23	113.3 (3)
F11—C17—C13	112.8 (2)	F21—C27—C23	113.3 (2)
F12—C17—C13	110.8 (3)	F22—C27—C23	110.8 (2)
F15—C18—F16	106.7 (3)	F26—C28—F25	106.9 (3)
F15—C18—F14	107.6 (3)	F26—C28—F24	106.7 (2)
F16—C18—F14	104.8 (3)	F25—C28—F24	106.5 (3)
F15—C18—C15	112.6 (3)	F26—C28—C25	113.0 (2)
F16—C18—C15	112.7 (3)	F25—C28—C25	112.1 (2)
F14—C18—C15	112.1 (3)	F24—C28—C25	111.3 (3)
C36—C31—C32	118.2 (2)	C42—C41—C46	117.8 (2)
C36—C31—Si1	122.45 (19)	C42—C41—Si2	123.4 (2)
C32—C31—Si1	119.36 (19)	C46—C41—Si2	118.7 (2)
C33—C32—C31	120.7 (2)	C43—C42—C41	120.8 (2)
C33—C32—H32	119.6	C43—C42—H42	119.6
C31—C32—H32	119.6	C41—C42—H42	119.6
C34—C33—C32	120.6 (2)	C44—C43—C42	120.6 (3)
C34—C33—C37	120.7 (2)	C44—C43—C47	119.1 (3)
C32—C33—C37	118.7 (2)	C42—C43—C47	120.2 (3)
C33—C34—C35	119.2 (2)	C45—C44—C43	119.2 (2)
C33—C34—H34	120.4	C45—C44—H44	120.4
C35—C34—H34	120.4	C43—C44—H44	120.4
C34—C35—C36	120.5 (2)	C44—C45—C46	120.6 (2)
C34—C35—C38	119.3 (2)	C44—C45—C48	119.5 (2)
C36—C35—C38	120.2 (2)	C46—C45—C48	119.9 (2)
C35—C36—C31	120.9 (2)	C45—C46—C41	121.1 (2)
C35—C36—H36	119.6	C45—C46—H46	119.5
C31—C36—H36	119.6	C41—C46—H46	119.5
F33—C37—F31	107.1 (2)	F41—C47—F42	106.0 (3)
F33—C37—F32	107.3 (2)	F41—C47—F43	106.4 (3)
F31—C37—F32	105.4 (2)	F42—C47—F43	107.7 (2)
F33—C37—C33	112.7 (3)	F41—C47—C43	112.9 (3)
F31—C37—C33	112.4 (2)	F42—C47—C43	111.6 (3)
F32—C37—C33	111.5 (2)	F43—C47—C43	111.9 (2)
F34—C38—F36	108.0 (3)	F45—C48—F44	106.8 (3)
F34—C38—F35	105.7 (3)	F45—C48—F46	106.0 (2)
F36—C38—F35	105.4 (3)	F44—C48—F46	106.8 (2)
F34—C38—C35	112.2 (3)	F45—C48—C45	112.8 (2)
F36—C38—C35	113.3 (2)	F44—C48—C45	112.6 (2)
F35—C38—C35	111.6 (3)	F46—C48—C45	111.3 (2)

C11ⁱ—Si1—C11—C16	−130.9 (3)	C41ⁱⁱ—Si2—C21—C22	−4.0 (3)
C31ⁱ—Si1—C11—C16	108.8 (2)	C41—Si2—C21—C22	113.0 (2)
C31—Si1—C11—C16	−10.4 (3)	C21ⁱⁱ—Si2—C21—C22	−125.2 (2)
C11ⁱ—Si1—C11—C12	48.89 (18)	C41ⁱⁱ—Si2—C21—C26	172.4 (2)
C31ⁱ—Si1—C11—C12	−71.4 (2)	C41—Si2—C21—C26	−70.5 (2)
C31—Si1—C11—C12	169.4 (2)	C21ⁱⁱ—Si2—C21—C26	51.23 (18)
C16—C11—C12—C13	−0.1 (4)	C26—C21—C22—C23	0.7 (4)
Si1—C11—C12—C13	−179.9 (2)	Si2—C21—C22—C23	177.2 (2)
C11—C12—C13—C14	−0.5 (4)	C21—C22—C23—C24	0.6 (4)
C11—C12—C13—C17	176.4 (3)	C21—C22—C23—C27	−175.5 (3)
C12—C13—C14—C15	0.9 (4)	C22—C23—C24—C25	−0.8 (4)
C17—C13—C14—C15	−176.0 (3)	C27—C23—C24—C25	175.3 (3)
C13—C14—C15—C16	−0.6 (4)	C23—C24—C25—C26	−0.3 (4)
C13—C14—C15—C18	178.3 (3)	C23—C24—C25—C28	−175.8 (3)
C12—C11—C16—C15	0.3 (4)	C24—C25—C26—C21	1.6 (4)
Si1—C11—C16—C15	−179.9 (2)	C28—C25—C26—C21	177.1 (3)
C14—C15—C16—C11	0.0 (4)	C22—C21—C26—C25	−1.8 (4)
C18—C15—C16—C11	−179.0 (3)	Si2—C21—C26—C25	−178.4 (2)
C14—C13—C17—F13	−27.5 (4)	C24—C23—C27—F23	47.1 (4)
C12—C13—C17—F13	155.6 (3)	C22—C23—C27—F23	−136.7 (3)
C14—C13—C17—F11	−150.0 (3)	C24—C23—C27—F21	170.7 (3)
C12—C13—C17—F11	33.1 (4)	C22—C23—C27—F21	−13.1 (4)
C14—C13—C17—F12	92.2 (3)	C24—C23—C27—F22	−71.3 (3)
C12—C13—C17—F12	−84.7 (3)	C22—C23—C27—F22	104.9 (3)
C14—C15—C18—F15	−95.9 (4)	C24—C25—C28—F26	−159.3 (3)
C16—C15—C18—F15	83.0 (3)	C26—C25—C28—F26	25.2 (4)
C14—C15—C18—F16	143.4 (3)	C24—C25—C28—F25	−38.4 (4)
C16—C15—C18—F16	−37.7 (4)	C26—C25—C28—F25	146.1 (3)
C14—C15—C18—F14	25.5 (4)	C24—C25—C28—F24	80.7 (3)
C16—C15—C18—F14	−155.6 (3)	C26—C25—C28—F24	−94.7 (3)
C11ⁱ—Si1—C31—C36	18.9 (2)	C41ⁱⁱ—Si2—C41—C42	132.2 (2)
C11—Si1—C31—C36	−98.8 (2)	C21—Si2—C41—C42	11.1 (3)
C31ⁱ—Si1—C31—C36	140.0 (2)	C21ⁱⁱ—Si2—C41—C42	−107.4 (2)
C11ⁱ—Si1—C31—C32	−160.32 (19)	C41ⁱⁱ—Si2—C41—C46	−44.69 (17)
C11—Si1—C31—C32	82.0 (2)	C21—Si2—C41—C46	−165.72 (19)
C31ⁱ—Si1—C31—C32	−39.28 (17)	C21ⁱⁱ—Si2—C41—C46	75.7 (2)
C36—C31—C32—C33	−0.1 (4)	C46—C41—C42—C43	−0.5 (4)
Si1—C31—C32—C33	179.19 (19)	Si2—C41—C42—C43	−177.4 (2)
C31—C32—C33—C34	0.1 (4)	C41—C42—C43—C44	0.4 (4)
C31—C32—C33—C37	−177.5 (2)	C41—C42—C43—C47	178.4 (2)
C32—C33—C34—C35	0.3 (4)	C42—C43—C44—C45	0.3 (4)
C37—C33—C34—C35	177.8 (2)	C47—C43—C44—C45	−177.8 (3)
C33—C34—C35—C36	−0.7 (4)	C43—C44—C45—C46	−0.7 (4)
C33—C34—C35—C38	−179.0 (3)	C43—C44—C45—C48	177.1 (3)
C34—C35—C36—C31	0.8 (4)	C44—C45—C46—C41	0.6 (4)
C38—C35—C36—C31	179.0 (3)	C48—C45—C46—C41	−177.3 (2)
C32—C31—C36—C35	−0.3 (4)	C42—C41—C46—C45	0.1 (4)
Si1—C31—C36—C35	−179.6 (2)	Si2—C41—C46—C45	177.1 (2)
C34—C33—C37—F33	20.9 (4)	C44—C43—C47—F41	−161.8 (3)
C32—C33—C37—F33	−161.5 (2)	C42—C43—C47—F41	20.1 (4)
C34—C33—C37—F31	142.1 (3)	C44—C43—C47—F42	79.0 (3)
C32—C33—C37—F31	−40.3 (4)	C42—C43—C47—F42	−99.1 (3)
C34—C33—C37—F32	−99.8 (3)	C44—C43—C47—F43	−41.7 (4)
C32—C33—C37—F32	77.8 (3)	C42—C43—C47—F43	140.2 (3)
C34—C35—C38—F34	72.9 (4)	C44—C45—C48—F45	154.3 (3)
C36—C35—C38—F34	−105.4 (3)	C46—C45—C48—F45	−27.9 (4)
C34—C35—C38—F36	−164.4 (3)	C44—C45—C48—F44	33.2 (4)
C36—C35—C38—F36	17.3 (4)	C46—C45—C48—F44	−148.9 (3)
C34—C35—C38—F35	−45.5 (4)	C44—C45—C48—F46	−86.7 (3)
C36—C35—C38—F35	136.2 (3)	C46—C45—C48—F46	91.2 (3)

Symmetry codes: (i) −x+1, y, −z+1/2; (ii) −x, y, −z+1/2; (iii) −x+1, −y, −z+1; (iv) −x+1, −y+1, −z+1; (v) x, −y+1, z−1/2.

¹⁹F NMR (p.p.m., Hz) data for reaction products top

Group	No. of Fs	δ ¹⁹F	⁵J_FF	δ ¹⁹F^a	⁵J_FF^a
Ar₂SiF₂
o-CF₃	12	-57.7	t, 12.4	-57.3	t, 12.8
p-CF₃	6	-63.8	s	-64.2	s
Si—F	2	-125.7	m, NR^b	-124.5	m, 12.8
Ar'₂SiF₂
o-CF₃	12	-57.5	t, 12.8	-57.5	t, 12.3
Si—F	2	-125.4	m, 12.8	-125.5	m, 12.5
Ar''₂SiBr₂
o-CF₃	6	-57.6	s
p-CF₃	6	-64.5	s
Ar''₂SiBrF
o-CF₃	6	-59.6	d, 12.8
p-CF₃	6	-64.6	s
Si—F	1	-158.4	m, 12.8

Notes: (a) literature data from Batsanov et al. (2003); (b) not resolved.

Acknowledgements

The authors thank the EPSRC for a postgraduate fellowship (ALT) and A. Hickman for technical assistance in isolating the crystalline product.

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