2,2,6,6-Tetra­kis(biphenyl-2-yl)-4,4,8,8-tetra­methyl­cyclo­tetra­siloxane

Couzijn, E.P.A.; Lutz, M.; Spek, A.L.; Lammertsma, K.

doi:10.1107/S1600536809031961

organic compounds

CRYSTALLOGRAPHIC
COMMUNICATIONS

ISSN: 2056-9890

Volume 65| Part 9| September 2009| Pages o2182-o2183

doi:10.1107/S1600536809031961

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2,2,6,6-Tetrakis(biphenyl-2-yl)-4,4,8,8-tetramethylcyclotetrasiloxane

Erik P. A. Couzijn,^a Martin Lutz,^b Anthony L. Spek ^b ^* and Koop Lammertsma ^a

^aDepartment of Chemistry and Pharmaceutical Sciences, Faculty of Sciences, VU University Amsterdam, De Boelelaan 1083, 1081 HV Amsterdam, The Netherlands, and ^bBijvoet Center for Biomolecular Research, Crystal and Structural Chemistry, Faculty of Science, Utrecht University, Padualaan 8, 3584 CH Utrecht, The Netherlands
^*Correspondence e-mail: a.l.spek@uu.nl

(Received 3 August 2009; accepted 12 August 2009; online 19 August 2009)

The title compound, [–Si(C₁₂H₉)₂OSi(CH₃)₂O–]₂, was obtained unintentionally as the product of an attempted crystallization of caesium bis(biphenyl-2,2′-diyl)fluorosilicate from dimethylformamide. In the crystal, the molecule is located on an inversion center and the siloxane ring adopts a twist-chair conformation with the two dimethyl-substituted Si atoms lying 0.7081 (5) Å out of the plane defined by the two bis(biphenyl-2-yl)-substituted Si atoms and the four O atoms. In each Si(C₁₂H₉)₂ unit, the orientation of one terminal phenyl ring relative to the phenylene ring of the other biphenyl moiety suggests a parallel displaced π–π stacking interaction [centroid distance = 4.2377 (11) Å and dihedral angle = 15.40 (9)°].

Related literature

For general background to stable compounds of pentavalent, anionic silicon bearing five organic substituents, see: Couzijn et al. (2004 , 2006 , 2009 ); Deerenberg et al. (2002 ); de Keijzer et al. (1997 ). For related structures, see: Malinovskii et al. (2007 ); Steinfink et al. (1955 ); Hensen et al. (1997 ). For puckering analysis,, see: Evans & Boeyens (1989 ). Bis(biphenyl-2,2′-diyl)silane was synthesized using a slight modification of a literature procedure (Gilman & Gorsich, 1958 ).

Experimental

Crystal data

C₅₂H₄₈O₄Si₄
M_r = 849.26
Orthorhombic, P b c a
a = 17.3418 (2) Å
b = 14.6488 (2) Å
c = 17.9584 (2) Å
V = 4562.09 (10) Å³
Z = 4
Mo Kα radiation
μ = 0.18 mm⁻¹
T = 110 K
0.30 × 0.12 × 0.03 mm

Data collection

Nonius KappaCCD diffractometer
Absorption correction: none
68467 measured reflections
4317 independent reflections
3247 reflections with I > 2σ(I)
R_int = 0.081

Refinement

R[F² > 2σ(F²)] = 0.036
wR(F²) = 0.097
S = 1.07
4317 reflections
273 parameters
H-atom parameters constrained
Δρ_max = 0.26 e Å⁻³
Δρ_min = −0.33 e Å⁻³

Table 1
Selected geometric parameters (Å, °)

Si1—O1	1.6287 (12)
Si1—O2	1.6290 (13)
Si1—C12	1.8684 (19)
Si1—C11	1.8746 (17)
Si2—O2ⁱ	1.6342 (13)
Si2—O1	1.6347 (12)
Si2—C2	1.8452 (19)
Si2—C1	1.8494 (19)

O1—Si1—O2	109.98 (7)
O2ⁱ—Si2—O1	107.88 (7)
Si1—O1—Si2	141.85 (8)
Si1—O2—Si2ⁱ	142.12 (8)

O1—Si2—O2ⁱ—Si1ⁱ	−74.36 (14)
O2—Si1—O1—Si2	−52.51 (15)
O2ⁱ—Si2—O1—Si1	84.84 (14)
O1—Si1—O2—Si2ⁱ	−37.42 (15)
C11—C61—C71—C81	81.5 (2)
C12—C62—C72—C82	56.1 (3)
Symmetry code: (i) -x+1, -y+1, -z+1.

Data collection: COLLECT (Nonius, 1999 ); cell refinement: HKL-2000 (Otwinowski & Minor, 1997 ); data reduction: HKL-2000 and SORTAV (Blessing, 1997 ); program(s) used to solve structure: SIR97 (Altomare et al., 1999 ); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008 ); molecular graphics: PLATON (Spek, 2009 ); software used to prepare material for publication: manual editing of SHELXL output.

Supporting information

Crystal structure: contains datablocks I, global. DOI: 10.1107/S1600536809031961/vm2002sup1.cif

Structure factors: contains datablock I. DOI: 10.1107/S1600536809031961/vm2002Isup2.hkl

checkCIF report

Comment top

Our research is focused on stable compounds of pentavalent, anionic silicon bearing five organic substituents (Couzijn et al., 2009; Couzijn et al., 2006; Couzijn et al., 2004). Such pentaorganosilicates are commonly proposed as intermediates for nucleophilic substitution reactions on silanes, but were only recently characterized in the condensed phase (e.g., de Keijzer et al., 1997; Deerenberg et al., 2002). In solution, these five-coordinate species undergo intramolecular substituent interchange via Berry pseudorotation and related processes. For a better understanding of the influence of the substituents on the stereomutational barrier, we synthesized bis(biphenyl-2,2'-diyl)fluorosilicate as the caesium and tetramethylammonium salts (Couzijn et al., 2009). While attempting to crystallize these salts, we obtained crystals of the title compound, [–Si(C₁₂H₉)₂OSi(CH₃)₂O–]₂, instead. This siloxane was most probably formed by reaction with silicone grease and adventitious water.

The title compound crystallizes with C_i point group symmetry, adopting a twist-chair conformation of the eight-membered siloxane ring (Fig. 1, Table 1). A ring puckering analysis (Evans & Boeyens, 1989) shows that the out-of-plane displacements in the ring can be described as a linear combination of the E_3g (sin form) and E_3g (cos form) normal modes, respectively, in a ratio of 0.891:0.109. The two bis(biphenyl)-substituted silicon atoms and the four oxygen atoms lie in a plane (RMS deviation 0.025 Å), whereas the two dimethyl-substituted silicon atoms are situated at 0.7081 (5)Å above and below this plane, respectively. Similar arrangements have been reported for octamethyl- (Steinfink et al., 1955) and 2,2,6,6-tetraphenyl-4,4,8,8-tetramethyltetrasiloxane (Malinovskii et al., 2007). Each Si(C₁₂H₉)₂ unit features a parallel displaced π-π stacking interaction between one terminal phenyl ring and the phenylene ring of the other biphenyl moiety. The ring centroids are 4.2377 (11)Å apart and their vector makes an angle of 38.65° with the phenylene plane, while the ring planes make a dihedral angle of 15.40 (9)°.

Related literature top

For general background to stable compounds of pentavalent, anionic silicon bearing five organic substituents, see: Couzijn et al. (2004, 2006, 2009); Deerenberg et al. (2002); de Keijzer et al. (1997). For related structures, see: Malinovskii et al. (2007); Steinfink et al. (1955); Hensen et al. (1997). For puckering analysis,, see: Evans & Boeyens (1989). Bis(biphenyl-2,2'-diyl)silane was synthesized using a slight modification of a literature procedure (Gilman & Gorsich, 1958).

Experimental top

General procedures: dimethylformamide (DMF) was distilled from phenylzinc iodide and stored in a glovebox on 3Å molecular sieves. Commercial caesium fluoride was dried in vacuo at > 373 K. Bis(biphenyl-2,2'-diyl)silane was synthesized from 1,1'-dibromobiphenyl and tetrachlorosilane using a slight modification of a literature procedure (Gilman & Gorsich, 1958).

The title compound was obtained as follows. In the purified nitrogen atmosphere of a glovebox, a flame-dried Schlenk tube was charged with caesium fluoride (71.45 mg, 470 µmol) and bis(biphenyl-2,2'-diyl)silane (73.95 mg, 222 µmol). Anhydrous DMF (3 ml) was added and the mixture was stirred in the glovebox for 2 days. ¹⁹F and ¹H NMR indicated almost quantitative conversion to the desired caesium bis(biphenyl-2,2'-diyl)fluorosilicate (Couzijn et al., 2009). The clear colorless supernate was filtered through glass wool in the glovebox and evaporated on a Schlenk line to afford the crude fluorosilicate as a white solid. Recrystallization of the fluorosilicate from DMF was initially performed by cooling the Schlenk tube in a freezer outside the glovebox. After repeated attempts, colorless blocks were obtained that were shown by X-ray analysis to be the title compound. Recrystallizations of the fluorosilicate using Young-type glassware (closed with a greaseless Teflon tap) in the freezer of a glovebox invariably afforded an amorphous solid.

Computing details top

Data collection: COLLECT (Nonius, 1999); cell refinement: HKL-2000 (Otwinowski & Minor, 1997); data reduction: HKL-2000 (Otwinowski & Minor, 1997) and SORTAV (Blessing, 1997); program(s) used to solve structure: SIR97 (Altomare et al., 1999); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: PLATON (Spek, 2009); software used to prepare material for publication: manual editing of SHELXL output.

Figures top

Fig. 1. Displacement ellipsoid plot of [–Si(C₁₂H₉)₂OSi(CH₃)₂O–]₂ with ellipsoids drawn at the 50% probability level. The parallel displaced π-π stacking interaction is indicated by a dashed line between the ring centroids. Hydrogen atoms are omitted for clarity. Symmetry operation i: 1 - x, 1 - y, 1 - z.

2,2,6,6-Tetrakis(biphenyl-2-yl)-4,4,8,8-tetramethylcyclotetrasiloxane top

Crystal data top

C₅₂H₄₈O₄Si₄	F(000) = 1792
M_r = 849.26	D_x = 1.236 Mg m⁻³
Orthorhombic, Pbca	Mo Kα radiation, λ = 0.71073 Å
Hall symbol: -P 2ac 2ab	Cell parameters from 88729 reflections
a = 17.3418 (2) Å	θ = 1.0–25.7°
b = 14.6488 (2) Å	µ = 0.18 mm⁻¹
c = 17.9584 (2) Å	T = 110 K
V = 4562.09 (10) Å³	Needle, colourless
Z = 4	0.30 × 0.12 × 0.03 mm

Data collection top

Nonius KappaCCD diffractometer	3247 reflections with I > 2σ(I)
Radiation source: rotating anode	R_int = 0.081
Graphite monochromator	θ_max = 25.7°, θ_min = 2.1°
ϕ and ω scans	h = −21→21
68467 measured reflections	k = −17→17
4317 independent reflections	l = −21→21

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)] = 0.036	Hydrogen site location: difference Fourier map
wR(F²) = 0.097	H-atom parameters constrained
S = 1.07	w = 1/[σ²(F_o²) + (0.0428P)² + 1.7858P] where P = (F_o² + 2F_c²)/3
4317 reflections	(Δ/σ)_max = 0.001
273 parameters	Δρ_max = 0.26 e Å⁻³
0 restraints	Δρ_min = −0.33 e Å⁻³

Crystal data top

C₅₂H₄₈O₄Si₄	V = 4562.09 (10) Å³
M_r = 849.26	Z = 4
Orthorhombic, Pbca	Mo Kα radiation
a = 17.3418 (2) Å	µ = 0.18 mm⁻¹
b = 14.6488 (2) Å	T = 110 K
c = 17.9584 (2) Å	0.30 × 0.12 × 0.03 mm

Data collection top

Nonius KappaCCD diffractometer	3247 reflections with I > 2σ(I)
68467 measured reflections	R_int = 0.081
4317 independent reflections

Refinement top

R[F² > 2σ(F²)] = 0.036	0 restraints
wR(F²) = 0.097	H-atom parameters constrained
S = 1.07	Δρ_max = 0.26 e Å⁻³
4317 reflections	Δρ_min = −0.33 e Å⁻³
273 parameters

Special details top

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	0.42728 (3)	0.37257 (3)	0.49618 (3)	0.02364 (14)
Si2	0.41400 (3)	0.57131 (3)	0.44096 (3)	0.02422 (14)
O1	0.42038 (7)	0.45998 (8)	0.44053 (6)	0.0257 (3)
O2	0.49862 (7)	0.38739 (8)	0.55394 (6)	0.0272 (3)
C1	0.35711 (12)	0.60943 (14)	0.52232 (11)	0.0382 (5)
H1A	0.3064	0.5798	0.5215	0.057*
H1B	0.3505	0.6758	0.5203	0.057*
H1C	0.3843	0.5928	0.5682	0.057*
C2	0.37276 (12)	0.60687 (14)	0.35079 (11)	0.0367 (5)
H2A	0.4062	0.5858	0.3103	0.055*
H2B	0.3689	0.6736	0.3492	0.055*
H2C	0.3213	0.5801	0.3450	0.055*
C11	0.45192 (10)	0.27253 (12)	0.43560 (9)	0.0243 (4)
C21	0.46918 (11)	0.28754 (13)	0.36038 (10)	0.0298 (4)
H21	0.4646	0.3475	0.3408	0.036*
C31	0.49264 (11)	0.21768 (13)	0.31368 (10)	0.0332 (5)
H31	0.5034	0.2298	0.2628	0.040*
C41	0.50025 (12)	0.13027 (13)	0.34161 (11)	0.0329 (5)
H41	0.5165	0.0820	0.3100	0.039*
C51	0.48408 (11)	0.11334 (13)	0.41570 (10)	0.0305 (4)
H51	0.4901	0.0533	0.4347	0.037*
C61	0.45917 (10)	0.18265 (12)	0.46293 (10)	0.0240 (4)
C71	0.43948 (10)	0.15854 (11)	0.54194 (10)	0.0252 (4)
C81	0.36294 (11)	0.14336 (12)	0.56199 (10)	0.0307 (4)
H81	0.3233	0.1526	0.5263	0.037*
C91	0.34381 (12)	0.11508 (13)	0.63306 (11)	0.0347 (5)
H91	0.2914	0.1045	0.6457	0.042*
C101	0.40081 (13)	0.10219 (13)	0.68579 (11)	0.0358 (5)
H101	0.3877	0.0827	0.7346	0.043*
C111	0.47717 (12)	0.11785 (13)	0.66701 (10)	0.0342 (5)
H111	0.5165	0.1096	0.7032	0.041*
C121	0.49649 (11)	0.14550 (12)	0.59550 (10)	0.0300 (4)
H121	0.5490	0.1556	0.5830	0.036*
C12	0.33957 (11)	0.36475 (12)	0.55627 (10)	0.0264 (4)
C22	0.35201 (12)	0.35934 (12)	0.63354 (10)	0.0319 (5)
H22	0.4034	0.3554	0.6517	0.038*
C32	0.29145 (13)	0.35950 (13)	0.68412 (11)	0.0386 (5)
H32	0.3015	0.3561	0.7360	0.046*
C42	0.21658 (13)	0.36468 (15)	0.65844 (12)	0.0433 (5)
H42	0.1749	0.3641	0.6927	0.052*
C52	0.20213 (12)	0.37074 (14)	0.58287 (11)	0.0388 (5)
H52	0.1504	0.3745	0.5658	0.047*
C62	0.26242 (11)	0.37139 (12)	0.53110 (10)	0.0298 (4)
C72	0.24184 (11)	0.38291 (13)	0.45090 (11)	0.0299 (4)
C82	0.26624 (11)	0.32206 (13)	0.39587 (10)	0.0328 (5)
H82	0.2966	0.2707	0.4094	0.039*
C92	0.24684 (12)	0.33543 (15)	0.32168 (11)	0.0392 (5)
H92	0.2643	0.2936	0.2850	0.047*
C102	0.20206 (12)	0.40966 (15)	0.30091 (11)	0.0399 (5)
H102	0.1891	0.4190	0.2501	0.048*
C112	0.17661 (12)	0.46966 (15)	0.35464 (11)	0.0392 (5)
H112	0.1457	0.5205	0.3409	0.047*
C122	0.19584 (11)	0.45615 (14)	0.42866 (11)	0.0346 (5)
H122	0.1773	0.4977	0.4651	0.042*

Atomic displacement parameters (Å²) top

	U¹¹	U²²	U³³	U¹²	U¹³	U²³
Si1	0.0279 (3)	0.0196 (3)	0.0235 (3)	−0.0010 (2)	0.0023 (2)	−0.0001 (2)
Si2	0.0271 (3)	0.0214 (3)	0.0241 (3)	0.0024 (2)	0.0005 (2)	0.0006 (2)
O1	0.0306 (7)	0.0207 (6)	0.0258 (6)	−0.0004 (5)	0.0028 (5)	0.0004 (5)
O2	0.0308 (7)	0.0240 (6)	0.0266 (7)	−0.0015 (5)	0.0002 (5)	0.0014 (5)
C1	0.0389 (12)	0.0349 (11)	0.0409 (12)	0.0038 (9)	0.0085 (9)	−0.0055 (9)
C2	0.0380 (12)	0.0349 (11)	0.0370 (11)	−0.0011 (9)	−0.0074 (9)	0.0067 (9)
C11	0.0237 (9)	0.0242 (9)	0.0251 (9)	−0.0016 (8)	−0.0005 (7)	−0.0011 (7)
C21	0.0359 (11)	0.0253 (10)	0.0282 (10)	0.0007 (8)	0.0037 (8)	0.0018 (8)
C31	0.0392 (12)	0.0334 (11)	0.0270 (10)	0.0006 (9)	0.0067 (8)	−0.0029 (8)
C41	0.0392 (12)	0.0278 (10)	0.0317 (10)	0.0028 (9)	0.0079 (9)	−0.0063 (8)
C51	0.0336 (11)	0.0220 (9)	0.0359 (11)	0.0030 (8)	0.0039 (9)	−0.0004 (8)
C61	0.0214 (9)	0.0242 (9)	0.0263 (9)	−0.0010 (7)	0.0000 (7)	0.0001 (7)
C71	0.0314 (10)	0.0155 (8)	0.0286 (10)	0.0006 (7)	0.0010 (8)	−0.0017 (7)
C81	0.0306 (11)	0.0295 (10)	0.0321 (10)	−0.0019 (8)	−0.0002 (8)	−0.0003 (8)
C91	0.0358 (12)	0.0348 (11)	0.0335 (11)	−0.0058 (9)	0.0071 (9)	0.0017 (9)
C101	0.0553 (14)	0.0257 (10)	0.0264 (10)	0.0006 (9)	0.0074 (9)	0.0003 (8)
C111	0.0422 (12)	0.0309 (11)	0.0295 (11)	0.0062 (9)	−0.0052 (9)	−0.0010 (8)
C121	0.0299 (10)	0.0267 (10)	0.0335 (11)	0.0039 (8)	0.0000 (8)	−0.0023 (8)
C12	0.0332 (10)	0.0194 (9)	0.0267 (9)	−0.0025 (8)	0.0051 (8)	−0.0018 (7)
C22	0.0390 (12)	0.0257 (10)	0.0309 (10)	−0.0029 (9)	0.0045 (9)	0.0001 (8)
C32	0.0524 (14)	0.0356 (12)	0.0278 (10)	−0.0059 (10)	0.0092 (10)	−0.0010 (9)
C42	0.0449 (14)	0.0489 (13)	0.0361 (12)	−0.0058 (11)	0.0183 (10)	−0.0042 (10)
C52	0.0325 (12)	0.0449 (13)	0.0390 (12)	−0.0043 (9)	0.0087 (9)	−0.0041 (10)
C62	0.0349 (11)	0.0239 (10)	0.0304 (10)	−0.0051 (8)	0.0064 (8)	−0.0041 (8)
C72	0.0239 (10)	0.0297 (10)	0.0360 (10)	−0.0065 (8)	0.0053 (8)	−0.0033 (8)
C82	0.0298 (11)	0.0332 (11)	0.0354 (11)	−0.0032 (9)	0.0027 (8)	−0.0048 (9)
C92	0.0349 (12)	0.0465 (13)	0.0361 (11)	−0.0050 (10)	0.0043 (9)	−0.0096 (10)
C102	0.0331 (12)	0.0549 (14)	0.0318 (11)	−0.0042 (10)	0.0011 (9)	0.0018 (10)
C112	0.0297 (11)	0.0446 (13)	0.0432 (12)	0.0014 (9)	0.0020 (9)	0.0052 (10)
C122	0.0282 (11)	0.0372 (11)	0.0386 (11)	−0.0029 (9)	0.0065 (9)	−0.0047 (9)

Geometric parameters (Å, º) top

Si1—O1	1.6287 (12)	C91—C101	1.382 (3)
Si1—O2	1.6290 (13)	C91—H91	0.9500
Si1—C12	1.8684 (19)	C101—C111	1.386 (3)
Si1—C11	1.8746 (17)	C101—H101	0.9500
Si2—O2ⁱ	1.6342 (13)	C111—C121	1.387 (3)
Si2—O1	1.6347 (12)	C111—H111	0.9500
Si2—C2	1.8452 (19)	C121—H121	0.9500
Si2—C1	1.8494 (19)	C12—C22	1.407 (3)
O2—Si2ⁱ	1.6342 (13)	C12—C62	1.415 (3)
C1—H1A	0.9800	C22—C32	1.388 (3)
C1—H1B	0.9800	C22—H22	0.9500
C1—H1C	0.9800	C32—C42	1.380 (3)
C2—H2A	0.9800	C32—H32	0.9500
C2—H2B	0.9800	C42—C52	1.383 (3)
C2—H2C	0.9800	C42—H42	0.9500
C11—C21	1.401 (2)	C52—C62	1.399 (3)
C11—C61	1.411 (2)	C52—H52	0.9500
C21—C31	1.384 (3)	C62—C72	1.493 (3)
C21—H21	0.9500	C72—C122	1.395 (3)
C31—C41	1.381 (3)	C72—C82	1.396 (3)
C31—H31	0.9500	C82—C92	1.388 (3)
C41—C51	1.382 (3)	C82—H82	0.9500
C41—H41	0.9500	C92—C102	1.387 (3)
C51—C61	1.392 (2)	C92—H92	0.9500
C51—H51	0.9500	C102—C112	1.378 (3)
C61—C71	1.501 (2)	C102—H102	0.9500
C71—C121	1.393 (3)	C112—C122	1.385 (3)
C71—C81	1.393 (3)	C112—H112	0.9500
C81—C91	1.382 (3)	C122—H122	0.9500
C81—H81	0.9500

O1—Si1—O2	109.98 (7)	C71—C81—H81	119.5
O1—Si1—C12	110.05 (7)	C101—C91—C81	120.13 (19)
O2—Si1—C12	105.00 (8)	C101—C91—H91	119.9
O1—Si1—C11	105.97 (7)	C81—C91—H91	119.9
O2—Si1—C11	107.49 (7)	C91—C101—C111	119.62 (18)
C12—Si1—C11	118.22 (8)	C91—C101—H101	120.2
O2ⁱ—Si2—O1	107.88 (7)	C111—C101—H101	120.2
O2ⁱ—Si2—C2	107.71 (8)	C101—C111—C121	120.29 (18)
O1—Si2—C2	107.68 (8)	C101—C111—H111	119.9
O2ⁱ—Si2—C1	109.78 (8)	C121—C111—H111	119.9
O1—Si2—C1	109.94 (8)	C111—C121—C71	120.53 (18)
C2—Si2—C1	113.66 (10)	C111—C121—H121	119.7
Si1—O1—Si2	141.85 (8)	C71—C121—H121	119.7
Si1—O2—Si2ⁱ	142.12 (8)	C22—C12—C62	117.63 (17)
Si2—C1—H1A	109.5	C22—C12—Si1	116.64 (14)
Si2—C1—H1B	109.5	C62—C12—Si1	125.51 (14)
H1A—C1—H1B	109.5	C32—C22—C12	121.96 (19)
Si2—C1—H1C	109.5	C32—C22—H22	119.0
H1A—C1—H1C	109.5	C12—C22—H22	119.0
H1B—C1—H1C	109.5	C42—C32—C22	119.55 (19)
Si2—C2—H2A	109.5	C42—C32—H32	120.2
Si2—C2—H2B	109.5	C22—C32—H32	120.2
H2A—C2—H2B	109.5	C32—C42—C52	120.13 (19)
Si2—C2—H2C	109.5	C32—C42—H42	119.9
H2A—C2—H2C	109.5	C52—C42—H42	119.9
H2B—C2—H2C	109.5	C42—C52—C62	121.1 (2)
C21—C11—C61	117.57 (16)	C42—C52—H52	119.4
C21—C11—Si1	119.05 (13)	C62—C52—H52	119.4
C61—C11—Si1	123.23 (13)	C52—C62—C12	119.58 (18)
C31—C21—C11	122.07 (17)	C52—C62—C72	117.58 (18)
C31—C21—H21	119.0	C12—C62—C72	122.79 (16)
C11—C21—H21	119.0	C122—C72—C82	117.48 (18)
C41—C31—C21	119.56 (17)	C122—C72—C62	119.97 (17)
C41—C31—H31	120.2	C82—C72—C62	122.54 (17)
C21—C31—H31	120.2	C92—C82—C72	121.05 (19)
C31—C41—C51	119.77 (17)	C92—C82—H82	119.5
C31—C41—H41	120.1	C72—C82—H82	119.5
C51—C41—H41	120.1	C102—C92—C82	120.29 (19)
C41—C51—C61	121.25 (17)	C102—C92—H92	119.9
C41—C51—H51	119.4	C82—C92—H92	119.9
C61—C51—H51	119.4	C112—C102—C92	119.40 (19)
C51—C61—C11	119.77 (16)	C112—C102—H102	120.3
C51—C61—C71	118.35 (16)	C92—C102—H102	120.3
C11—C61—C71	121.87 (15)	C102—C112—C122	120.3 (2)
C121—C71—C81	118.42 (17)	C102—C112—H112	119.9
C121—C71—C61	121.58 (16)	C122—C112—H112	119.9
C81—C71—C61	119.90 (16)	C112—C122—C72	121.49 (19)
C91—C81—C71	121.01 (18)	C112—C122—H122	119.3
C91—C81—H81	119.5	C72—C122—H122	119.3

O1—Si2—O2ⁱ—Si1ⁱ	−74.36 (14)	C81—C91—C101—C111	0.1 (3)
O2—Si1—O1—Si2	−52.51 (15)	C91—C101—C111—C121	−0.6 (3)
C12—Si1—O1—Si2	62.69 (15)	C101—C111—C121—C71	0.5 (3)
C11—Si1—O1—Si2	−168.40 (12)	C81—C71—C121—C111	0.1 (3)
O2ⁱ—Si2—O1—Si1	84.84 (14)	C61—C71—C121—C111	−176.07 (16)
C2—Si2—O1—Si1	−159.17 (13)	O1—Si1—C12—C22	−127.17 (14)
C1—Si2—O1—Si1	−34.85 (16)	O2—Si1—C12—C22	−8.85 (15)
O1—Si1—O2—Si2ⁱ	−37.42 (15)	C11—Si1—C12—C22	110.94 (14)
C12—Si1—O2—Si2ⁱ	−155.78 (13)	O1—Si1—C12—C62	47.32 (17)
C11—Si1—O2—Si2ⁱ	77.52 (14)	O2—Si1—C12—C62	165.63 (15)
O1—Si1—C11—C21	7.60 (16)	C11—Si1—C12—C62	−74.57 (17)
O2—Si1—C11—C21	−109.97 (15)	C62—C12—C22—C32	0.6 (3)
C12—Si1—C11—C21	131.54 (15)	Si1—C12—C22—C32	175.55 (14)
O1—Si1—C11—C61	−176.83 (14)	C12—C22—C32—C42	0.3 (3)
O2—Si1—C11—C61	65.60 (16)	C22—C32—C42—C52	−0.8 (3)
C12—Si1—C11—C61	−52.89 (18)	C32—C42—C52—C62	0.3 (3)
C61—C11—C21—C31	−0.1 (3)	C42—C52—C62—C12	0.7 (3)
Si1—C11—C21—C31	175.77 (15)	C42—C52—C62—C72	−176.95 (19)
C11—C21—C31—C41	−0.7 (3)	C22—C12—C62—C52	−1.1 (3)
C21—C31—C41—C51	0.3 (3)	Si1—C12—C62—C52	−175.54 (14)
C31—C41—C51—C61	0.8 (3)	C22—C12—C62—C72	176.41 (17)
C41—C51—C61—C11	−1.6 (3)	Si1—C12—C62—C72	2.0 (3)
C41—C51—C61—C71	177.46 (18)	C52—C62—C72—C122	52.9 (2)
C21—C11—C61—C51	1.1 (3)	C12—C62—C72—C122	−124.6 (2)
Si1—C11—C61—C51	−174.49 (14)	C52—C62—C72—C82	−126.4 (2)
C21—C11—C61—C71	−177.85 (16)	C12—C62—C72—C82	56.1 (3)
Si1—C11—C61—C71	6.5 (2)	C122—C72—C82—C92	1.5 (3)
C51—C61—C71—C121	78.6 (2)	C62—C72—C82—C92	−179.20 (18)
C11—C61—C71—C121	−102.4 (2)	C72—C82—C92—C102	−0.5 (3)
C51—C61—C71—C81	−97.5 (2)	C82—C92—C102—C112	−0.4 (3)
C11—C61—C71—C81	81.5 (2)	C92—C102—C112—C122	0.3 (3)
C121—C71—C81—C91	−0.7 (3)	C102—C112—C122—C72	0.8 (3)
C61—C71—C81—C91	175.58 (17)	C82—C72—C122—C112	−1.7 (3)
C71—C81—C91—C101	0.6 (3)	C62—C72—C122—C112	179.02 (17)

Symmetry code: (i) −x+1, −y+1, −z+1.

Experimental details

Crystal data
Chemical formula	C₅₂H₄₈O₄Si₄
M_r	849.26
Crystal system, space group	Orthorhombic, Pbca
Temperature (K)	110
a, b, c (Å)	17.3418 (2), 14.6488 (2), 17.9584 (2)
V (Å³)	4562.09 (10)
Z	4
Radiation type	Mo Kα
µ (mm⁻¹)	0.18
Crystal size (mm)	0.30 × 0.12 × 0.03

Data collection
Diffractometer	Nonius KappaCCD diffractometer
Absorption correction	–
No. of measured, independent and observed [I > 2σ(I)] reflections	68467, 4317, 3247
R_int	0.081
(sin θ/λ)_max (Å⁻¹)	0.610

Refinement
R[F² > 2σ(F²)], wR(F²), S	0.036, 0.097, 1.07
No. of reflections	4317
No. of parameters	273
H-atom treatment	H-atom parameters constrained
Δρ_max, Δρ_min (e Å⁻³)	0.26, −0.33

Computer programs: COLLECT (Nonius, 1999), HKL-2000 (Otwinowski & Minor, 1997) and SORTAV (Blessing, 1997), SIR97 (Altomare et al., 1999), SHELXL97 (Sheldrick, 2008), PLATON (Spek, 2009), manual editing of SHELXL output.

Selected geometric parameters (Å, º) top

Si1—O1	1.6287 (12)	Si2—O2ⁱ	1.6342 (13)
Si1—O2	1.6290 (13)	Si2—O1	1.6347 (12)
Si1—C12	1.8684 (19)	Si2—C2	1.8452 (19)
Si1—C11	1.8746 (17)	Si2—C1	1.8494 (19)

O1—Si1—O2	109.98 (7)	Si1—O1—Si2	141.85 (8)
O2ⁱ—Si2—O1	107.88 (7)	Si1—O2—Si2ⁱ	142.12 (8)

O1—Si2—O2ⁱ—Si1ⁱ	−74.36 (14)	O1—Si1—O2—Si2ⁱ	−37.42 (15)
O2—Si1—O1—Si2	−52.51 (15)	C11—C61—C71—C81	81.5 (2)
O2ⁱ—Si2—O1—Si1	84.84 (14)	C12—C62—C72—C82	56.1 (3)

Symmetry code: (i) −x+1, −y+1, −z+1.

Acknowledgements

Financial assistance for this project was provided by the Dutch Organization for Scientific Research, Chemical Sciences (NWO-CW).

References

Altomare, A., Burla, M. C., Camalli, M., Cascarano, G. L., Giacovazzo, C., Guagliardi, A., Moliterni, A. G. G., Polidori, G. & Spagna, R. (1999). J. Appl. Cryst. 32, 115–119. Web of Science CrossRef CAS IUCr Journals Google Scholar
Blessing, R. H. (1997). J. Appl. Cryst. 30, 421–426. CrossRef CAS Web of Science IUCr Journals Google Scholar
Couzijn, E. P. A., Ehlers, A. W., Schakel, M. & Lammertsma, K. (2006). J. Am. Chem. Soc. 128, 13634–13639. Web of Science CrossRef PubMed CAS Google Scholar
Couzijn, E. P. A., Schakel, M., de Kanter, F. J. J., Ehlers, A. W., Lutz, M., Spek, A. L. & Lammertsma, K. (2004). Angew. Chem. Int. Ed. 43, 3440–3442. Web of Science CSD CrossRef CAS Google Scholar
Couzijn, E. P. A., Slootweg, J. C., Ehlers, A. W. & Lammertsma, K. (2009). J. Am. Chem. Soc. 131, 3741–3751. Web of Science CrossRef PubMed CAS Google Scholar
Deerenberg, S., Schakel, M., de Keijzer, A. H. J. F., Kranenburg, M., Lutz, M., Spek, A. L. & Lammertsma, K. (2002). Chem. Commun. pp. 348–349. Web of Science CSD CrossRef Google Scholar
Evans, D. G. & Boeyens, J. C. A. (1989). Acta Cryst. B45, 581–590. CrossRef CAS Web of Science IUCr Journals Google Scholar
Gilman, H. & Gorsich, R. D. (1958). J. Am. Chem. Soc. 80, 1883–1884. CrossRef CAS Web of Science Google Scholar
Hensen, K., Gebhardt, F., Kettner, M., Pickel, P. & Bolte, M. (1997). Acta Cryst. C53, 1867–1869. Web of Science CSD CrossRef CAS IUCr Journals Google Scholar
Keijzer, A. H. J. F. de, de Kanter, F. J. J., Schakel, M., Osinga, V. P. & Klumpp, G. W. (1997). J. Organomet. Chem. 548, 29–32. Google Scholar
Malinovskii, S. T., Tesuro Vallina, A. & Stoeckli-Evans, H. (2007). J. Struct. Chem. 48, 128–136. Web of Science CrossRef CAS Google Scholar
Nonius (1999). COLLECT. Nonius BV, Delft, The Netherlands. Google Scholar
Otwinowski, Z. & Minor, W. (1997). Methods in Enzymology, Vol. 276, Macromolecular Crystallography, Part A, edited by C. W. Carter Jr & R. M. Sweet, pp. 307–326. New York: Academic Press. Google Scholar
Sheldrick, G. M. (2008). Acta Cryst. A64, 112–122. Web of Science CrossRef CAS IUCr Journals Google Scholar
Spek, A. L. (2009). Acta Cryst. D65, 148–155. Web of Science CrossRef CAS IUCr Journals Google Scholar
Steinfink, H., Post, B. & Fankuchen, I. (1955). Acta Cryst. 8, 420–424. CSD CrossRef CAS IUCr Journals Web of Science Google Scholar