Dibromido[(tert-butyl­amino)dimeth­yl(piperidin-1-ylmeth­yl)silane-κ2N,N′]zinc(II)

Colquhoun, V.P.; Strohmann, C.

doi:10.1107/S1600536809018364

metal-organic compounds

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ISSN: 2056-9890

Volume 65| Part 6| June 2009| Page m680

doi:10.1107/S1600536809018364

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Dibromido[(tert-butylamino)dimethyl(piperidin-1-ylmethyl)silane-κ²N,N′]zinc(II)

Victoria P. Colquhoun ^a and Carsten Strohmann ^a ^*

^aAnorganische Chemie, Technische Universität Dortmund, Otto-Hahn-Strasse 6, 44227 Dortmund, Germany
^*Correspondence e-mail: mail@carsten-strohmann.de

(Received 5 May 2009; accepted 14 May 2009; online 23 May 2009)

The title compound, [ZnBr₂(C₁₂H₂₈N₂Si)], is an example of a neutral coordination compound of a bidentate ligand to a metal centre with the Zn atom being coordinated by two Br and two N atoms, yielding a slightly distorted tetrahedral coordination environment.

Related literature

For the synthesis and structure of cis-(2-amino-1,1-dimethylethylamine)dichloropalladium(II) ethanol hemisolvate, see: Farrugia et al. (2001 ). For niobium and tantalum complexes of silylamides, see: Herrmann et al. (1992 ). For the synthesis and structure of ^tBu₂Si=N-SiCl^tBu₂, see: Lerner et al. (2005 ); for syntheses, structures and properties of chiral zinc halide catalysts, see: Mimoun et al. (1999 ). For the structure and reactivity of lithiated benzylsilanes, see: Ott et al. (2008 ). For syntheses and structures of bis{[diphenyl(piperidinomethyl)silyl]methyl}cadmium and -magnesium, see: Strohmann & Schildbach (2002 ). For a highly diastereomerically enriched, silyl-substituted alkyl lithium, see: Strohmann et al. (2005 ). For the synthesis and structure of a monolithiated allylsilane and its related 1,3-dilithiated allylsilane, see: Strohmann et al. (2006 ). For the synthesis and structure of a lithiated [(benzylsilyl)methyl]amine, see: Strohmann et al. (2002 ).

Experimental

Crystal data

[ZnBr₂(C₁₂H₂₈N₂Si)]
M_r = 453.64
Monoclinic, P 2₁ /c
a = 12.0284 (4) Å
b = 10.6505 (3) Å
c = 14.5633 (5) Å
β = 109.752 (4)°
V = 1755.91 (10) Å³
Z = 4
Mo Kα radiation
μ = 6.01 mm⁻¹
T = 123 K
0.40 × 0.20 × 0.20 mm

Data collection

Oxford Diffraction Xcalibur S diffractometer
Absorption correction: multi-scan (CrysAlis RED; Oxford Diffraction, 2006 $[Oxford Diffraction (2006). CrysAlis CCD and CrysAlis RED. Oxford Diffraction Ltd, Abingdon, England.]$ ) T_min = 0.698, T_max = 1.000 (expected range = 0.210–0.301)
17826 measured reflections
3440 independent reflections
2673 reflections with I > 2σ(I)
R_int = 0.034

Refinement

R[F² > 2σ(F²)] = 0.020
wR(F²) = 0.035
S = 1.04
3440 reflections
172 parameters
H atoms treated by a mixture of independent and constrained refinement
Δρ_max = 0.56 e Å⁻³
Δρ_min = −0.43 e Å⁻³

Data collection: CrysAlis CCD (Oxford Diffraction, 2006 $[Oxford Diffraction (2006). CrysAlis CCD and CrysAlis RED. Oxford Diffraction Ltd, Abingdon, England.]$ ); cell refinement: CrysAlis RED (Oxford Diffraction, 2006 $[Oxford Diffraction (2006). CrysAlis CCD and CrysAlis RED. Oxford Diffraction Ltd, Abingdon, England.]$ ); data reduction: CrysAlis RED; program(s) used to solve structure: SHELXS97 (Sheldrick, 2008 ); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: ORTEP-3 (Farrugia, 1997 ); software used to prepare material for publication: SHELXL97.

Supporting information

Crystal structure: contains datablocks global, I. DOI: 10.1107/S1600536809018364/fi2078sup1.cif

Structure factors: contains datablock I. DOI: 10.1107/S1600536809018364/fi2078Isup2.hkl

checkCIF report

Comment top

The title compound, the adduct of the silazane ligand and zinc bromide crystallized from acetonitrile in the monoclinic crystal system, space group P2₁/c. The H atom H1n was refined freely. It is connected to N1 with a bond length of 0.853 (21) Å which is in the expected range for N—H bonds. Additionally, H1N is forming a weak intermolecular hydrogen bond to Br1ⁱ (i: –x, –y + 1, –z + 1). The H1···Br1ⁱ distance (2.828 (22) Å) and the N1—H1N—Br1ⁱ angle (166.1 (20) Å) are in the typical ranges of such hydrogen bonds (Farrugia et al., 2001). With a value of 1.791 (2) Å, the Si—N bond length is in the upper range of other known systems and is very close to the sum of the covalent radii of silicon and nitrogen (1.86 Å) (Lerner et al., 2005; Herrmann et al., 1992). The bond lengths of 2.128 (2) Å for N1—Zn and 2.110 (2) Å for N2—Zn are similar to other reported dative zinc-nitrogen bonds (Mimoun et al., 1999). The structure of the title compound is a neutral coordination compound of a bidentate ligand and zinc(II) bromide forming a five-membered ring with a typical envelope conformation similar to other known metalla heterocycles (Strohmann et al. 2002, 2005, 2006; Strohmann & Schildbach 2002; Ott et al. 2008). The tip of the envelope is formed by the Si atom with a distance of 0.8312 (7) Å to a least-squares plane through Zn, N1, N2, C3 and Si. The title compound may be regarded as a comparative model structure for a deprotonation transition state as the silazane ligand can also be deprotonated by more reactive organozinc reagents. Thereby new metal silazane compounds are formed which themselves are interesting as deprotonation or alkylation reagents in organic synthesis.

Related literature top

For the synthesis and structure of cis-(2-amino-1,1-dimethylethylamine)dichloropalladium(II) ethanol hemisolvate, see: Farrugia et al. (2001); for niobium and tantalum complexes of silylamides, see Herrmann et al. (1992); for the synthesis and structure of ^tBu₂Si═N-SiCl^tBu_2,see Lerner et al. (2005); for syntheses, structures and properties of chiral zinc halide catalysts, see Mimoun et al. (1999); for the structure and reactivity of lithiated benzylsilanes, see Ott et al. (2008); for syntheses and structures of bis{[diphenyl(piperidinomethyl)silyl]methyl}cadmium and -magnesium, see Strohmann & Schildbach (2002). For a highly diastereomerically enriched, silyl-substituted alkyl lithium, see Strohmann et al. (2005). For the synthesis and structure of a monolithiated allylsilane and its related 1,3-dilithiated allylsilane, see Strohmann et al. (2006); for the synthesis and structure of a lithiated [(benzylsilyl)methyl]amine, see Strohmann et al. (2002).

Experimental top

To 0.38 g (1.7 mmol) dry zinc(II) bromide dissolved in 10 ml dry acetonitrile, 0.38 g (1.7 mmol) N-tert-butyl-1,1-dimethyl-1-(piperidin-1-ylmethyl)silanamine were added and stored at room temperature. After 24 h a colourless crystalline solid of the title compound suitable for single-crystal x-ray studies had formed.

Computing details top

Data collection: CrysAlis CCD (Oxford Diffraction, 2006); cell refinement: CrysAlis RED (Oxford Diffraction, 2006); data reduction: CrysAlis RED (Oxford Diffraction, 2006); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: ORTEP-3 (Farrugia, 1997); software used to prepare material for publication: SHELXL97 (Sheldrick, 2008).

Figures top

Fig. 1. Plot of the asymmetric unit of the title compound with displacement ellipsoids drawn at the 50% probability level.

Dibromido[(tert-butylamino)dimethyl(piperidin-1-ylmethyl)silane-κ²N,N']zinc(II) top

Crystal data top

[ZnBr₂(C₁₂H₂₈N₂Si)]	F(000) = 912
M_r = 453.64	D_x = 1.716 Mg m⁻³
Monoclinic, P2₁/c	Mo Kα radiation, λ = 0.71073 Å
Hall symbol: -P 2ybc	Cell parameters from 9282 reflections
a = 12.0284 (4) Å	θ = 2.4–29.1°
b = 10.6505 (3) Å	µ = 6.01 mm⁻¹
c = 14.5633 (5) Å	T = 123 K
β = 109.752 (4)°	Block, colourless
V = 1755.91 (10) Å³	0.40 × 0.20 × 0.20 mm
Z = 4

Data collection top

Oxford Diffraction Xcalibur S diffractometer	2673 reflections with I > 2σ(I)
Radiation source: Enhance (Mo) X-ray Source	R_int = 0.034
Graphite monochromator	θ_max = 26.0°, θ_min = 2.4°
ω scans	h = −14→14
Absorption correction: multi-scan (CrysAlis RED; Oxford Diffraction, 2006)	k = −13→13
T_min = 0.698, T_max = 1.000	l = −17→17
17826 measured reflections	1 standard reflections every 50 reflections
3440 independent reflections	intensity decay: none

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)] = 0.020	Hydrogen site location: inferred from neighbouring sites
wR(F²) = 0.035	H atoms treated by a mixture of independent and constrained refinement
S = 1.04	w = 1/[σ²(F_o²) + (0.012P)²] where P = (F_o² + 2F_c²)/3
3440 reflections	(Δ/σ)_max = 0.002
172 parameters	Δρ_max = 0.56 e Å⁻³
0 restraints	Δρ_min = −0.43 e Å⁻³

Crystal data top

[ZnBr₂(C₁₂H₂₈N₂Si)]	V = 1755.91 (10) Å³
M_r = 453.64	Z = 4
Monoclinic, P2₁/c	Mo Kα radiation
a = 12.0284 (4) Å	µ = 6.01 mm⁻¹
b = 10.6505 (3) Å	T = 123 K
c = 14.5633 (5) Å	0.40 × 0.20 × 0.20 mm
β = 109.752 (4)°

Data collection top

Oxford Diffraction Xcalibur S diffractometer	2673 reflections with I > 2σ(I)
Absorption correction: multi-scan (CrysAlis RED; Oxford Diffraction, 2006)	R_int = 0.034
T_min = 0.698, T_max = 1.000	1 standard reflections every 50 reflections
17826 measured reflections	intensity decay: none
3440 independent reflections

Refinement top

R[F² > 2σ(F²)] = 0.020	0 restraints
wR(F²) = 0.035	H atoms treated by a mixture of independent and constrained refinement
S = 1.04	Δρ_max = 0.56 e Å⁻³
3440 reflections	Δρ_min = −0.43 e Å⁻³
172 parameters

Special details top

Experimental. CrysAlis RED, Oxford Diffraction Ltd. Empirical absorption correction using spherical harmonics, implemented in SCALE3 ABSPACK scaling algorithm.

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
Br1	0.034333 (19)	0.34304 (2)	0.425367 (16)	0.02008 (7)
Br2	0.36966 (2)	0.21717 (2)	0.546307 (18)	0.02735 (7)
C1	0.43775 (18)	0.4264 (2)	0.80678 (16)	0.0251 (6)
H1A	0.4537	0.3636	0.7637	0.038*
H1B	0.4397	0.3863	0.8679	0.038*
H1C	0.4980	0.4924	0.8209	0.038*
C2	0.2739 (2)	0.6418 (2)	0.80978 (17)	0.0296 (6)
H2A	0.3418	0.6969	0.8175	0.044*
H2B	0.2703	0.6207	0.8742	0.044*
H2C	0.2011	0.6850	0.7714	0.044*
C3	0.16458 (18)	0.3884 (2)	0.74214 (15)	0.0168 (5)
H3A	0.1720	0.3654	0.8098	0.020*
H3B	0.0894	0.4349	0.7138	0.020*
C4	0.03415 (18)	0.2212 (2)	0.65665 (15)	0.0178 (5)
H4A	−0.0202	0.2816	0.6117	0.021*
H4B	0.0116	0.2148	0.7159	0.021*
C5	0.0203 (2)	0.0941 (2)	0.60787 (16)	0.0234 (6)
H5A	0.0380	0.1013	0.5465	0.028*
H5B	−0.0625	0.0656	0.5912	0.028*
C6	0.10247 (19)	−0.0026 (2)	0.67401 (17)	0.0246 (6)
H6A	0.0809	−0.0159	0.7331	0.029*
H6B	0.0954	−0.0837	0.6394	0.029*
C7	0.22848 (19)	0.0459 (2)	0.70248 (17)	0.0215 (6)
H7A	0.2824	−0.0132	0.7490	0.026*
H7B	0.2522	0.0504	0.6437	0.026*
C8	0.23979 (19)	0.1747 (2)	0.74873 (15)	0.0176 (5)
H8A	0.2232	0.1680	0.8107	0.021*
H8B	0.3222	0.2043	0.7646	0.021*
C9	0.32287 (19)	0.5977 (2)	0.56932 (16)	0.0198 (5)
C10	0.2842 (2)	0.5668 (2)	0.46137 (16)	0.0271 (6)
H10A	0.3038	0.4793	0.4529	0.041*
H10B	0.3250	0.6223	0.4295	0.041*
H10C	0.1987	0.5790	0.4320	0.041*
C11	0.2945 (2)	0.7356 (2)	0.58157 (17)	0.0275 (6)
H11A	0.2090	0.7489	0.5533	0.041*
H11B	0.3349	0.7893	0.5481	0.041*
H11C	0.3214	0.7569	0.6511	0.041*
C12	0.45464 (18)	0.5736 (2)	0.61593 (17)	0.0283 (6)
H12A	0.4815	0.6038	0.6835	0.042*
H12B	0.4973	0.6182	0.5792	0.042*
H12C	0.4701	0.4833	0.6152	0.042*
H1N	0.1857 (18)	0.544 (2)	0.5961 (15)	0.024 (7)*
N1	0.25541 (17)	0.51356 (18)	0.61717 (13)	0.0169 (5)
N2	0.15788 (14)	0.26976 (16)	0.68447 (12)	0.0126 (4)
Si	0.29025 (5)	0.49627 (6)	0.74618 (5)	0.01692 (15)
Zn	0.20862 (2)	0.32732 (2)	0.565755 (18)	0.01447 (7)

Atomic displacement parameters (Å²) top

	U¹¹	U²²	U³³	U¹²	U¹³	U²³
Br1	0.01765 (13)	0.02519 (15)	0.01490 (13)	−0.00001 (11)	0.00222 (10)	0.00006 (11)
Br2	0.02695 (14)	0.02831 (15)	0.03360 (15)	0.01126 (12)	0.01917 (12)	0.00731 (13)
C1	0.0218 (14)	0.0238 (15)	0.0254 (15)	−0.0039 (11)	0.0025 (12)	0.0022 (12)
C2	0.0291 (15)	0.0299 (16)	0.0306 (16)	−0.0056 (12)	0.0112 (13)	−0.0105 (12)
C3	0.0175 (13)	0.0198 (14)	0.0152 (13)	0.0025 (11)	0.0081 (11)	−0.0013 (11)
C4	0.0144 (12)	0.0245 (14)	0.0156 (13)	−0.0032 (11)	0.0062 (11)	0.0008 (11)
C5	0.0199 (14)	0.0276 (16)	0.0214 (14)	−0.0114 (12)	0.0052 (12)	−0.0033 (12)
C6	0.0311 (15)	0.0174 (14)	0.0265 (15)	−0.0076 (12)	0.0115 (13)	−0.0007 (11)
C7	0.0254 (14)	0.0150 (14)	0.0252 (14)	0.0025 (11)	0.0099 (12)	0.0047 (11)
C8	0.0152 (12)	0.0183 (14)	0.0175 (13)	0.0015 (11)	0.0030 (10)	0.0054 (11)
C9	0.0178 (13)	0.0194 (14)	0.0220 (14)	−0.0037 (11)	0.0065 (11)	0.0027 (11)
C10	0.0347 (16)	0.0228 (15)	0.0268 (15)	−0.0032 (12)	0.0144 (13)	0.0059 (12)
C11	0.0279 (15)	0.0201 (15)	0.0353 (16)	−0.0060 (12)	0.0118 (13)	−0.0006 (12)
C12	0.0176 (14)	0.0345 (17)	0.0342 (16)	−0.0016 (12)	0.0106 (13)	0.0053 (12)
N1	0.0135 (11)	0.0187 (12)	0.0190 (11)	−0.0038 (9)	0.0064 (10)	−0.0013 (9)
N2	0.0101 (10)	0.0145 (11)	0.0121 (10)	−0.0007 (8)	0.0023 (8)	−0.0006 (8)
Si	0.0168 (4)	0.0177 (4)	0.0158 (4)	−0.0018 (3)	0.0049 (3)	−0.0033 (3)
Zn	0.01415 (14)	0.01651 (15)	0.01335 (15)	0.00006 (12)	0.00541 (12)	−0.00062 (12)

Geometric parameters (Å, º) top

Br1—Zn	2.3887 (4)	C7—C8	1.513 (3)
Br2—Zn	2.3622 (3)	C7—H7A	0.9900
C1—Si	1.850 (2)	C7—H7B	0.9900
C1—H1A	0.9800	C8—N2	1.500 (2)
C1—H1B	0.9800	C8—H8A	0.9900
C1—H1C	0.9800	C8—H8B	0.9900
C2—Si	1.850 (2)	C9—C10	1.517 (3)
C2—H2A	0.9800	C9—C12	1.520 (3)
C2—H2B	0.9800	C9—N1	1.526 (3)
C2—H2C	0.9800	C9—C11	1.532 (3)
C3—N2	1.504 (3)	C10—H10A	0.9800
C3—Si	1.884 (2)	C10—H10B	0.9800
C3—H3A	0.9900	C10—H10C	0.9800
C3—H3B	0.9900	C11—H11A	0.9800
C4—N2	1.496 (2)	C11—H11B	0.9800
C4—C5	1.512 (3)	C11—H11C	0.9800
C4—H4A	0.9900	C12—H12A	0.9800
C4—H4B	0.9900	C12—H12B	0.9800
C5—C6	1.524 (3)	C12—H12C	0.9800
C5—H5A	0.9900	N1—Si	1.7909 (19)
C5—H5B	0.9900	N1—Zn	2.1276 (19)
C6—C7	1.520 (3)	N1—H1N	0.85 (2)
C6—H6A	0.9900	N2—Zn	2.1096 (16)
C6—H6B	0.9900

Si—C1—H1A	109.5	C10—C9—C12	109.55 (19)
Si—C1—H1B	109.5	C10—C9—N1	108.78 (18)
H1A—C1—H1B	109.5	C12—C9—N1	109.40 (18)
Si—C1—H1C	109.5	C10—C9—C11	109.01 (19)
H1A—C1—H1C	109.5	C12—C9—C11	110.46 (19)
H1B—C1—H1C	109.5	N1—C9—C11	109.62 (17)
Si—C2—H2A	109.5	C9—C10—H10A	109.5
Si—C2—H2B	109.5	C9—C10—H10B	109.5
H2A—C2—H2B	109.5	H10A—C10—H10B	109.5
Si—C2—H2C	109.5	C9—C10—H10C	109.5
H2A—C2—H2C	109.5	H10A—C10—H10C	109.5
H2B—C2—H2C	109.5	H10B—C10—H10C	109.5
N2—C3—Si	114.88 (13)	C9—C11—H11A	109.5
N2—C3—H3A	108.5	C9—C11—H11B	109.5
Si—C3—H3A	108.5	H11A—C11—H11B	109.5
N2—C3—H3B	108.5	C9—C11—H11C	109.5
Si—C3—H3B	108.5	H11A—C11—H11C	109.5
H3A—C3—H3B	107.5	H11B—C11—H11C	109.5
N2—C4—C5	112.22 (17)	C9—C12—H12A	109.5
N2—C4—H4A	109.2	C9—C12—H12B	109.5
C5—C4—H4A	109.2	H12A—C12—H12B	109.5
N2—C4—H4B	109.2	C9—C12—H12C	109.5
C5—C4—H4B	109.2	H12A—C12—H12C	109.5
H4A—C4—H4B	107.9	H12B—C12—H12C	109.5
C4—C5—C6	111.29 (19)	C9—N1—Si	124.57 (15)
C4—C5—H5A	109.4	C9—N1—Zn	120.32 (13)
C6—C5—H5A	109.4	Si—N1—Zn	102.34 (9)
C4—C5—H5B	109.4	C9—N1—H1N	102.9 (15)
C6—C5—H5B	109.4	Si—N1—H1N	105.6 (14)
H5A—C5—H5B	108.0	Zn—N1—H1N	96.6 (16)
C7—C6—C5	108.47 (18)	C4—N2—C8	108.62 (16)
C7—C6—H6A	110.0	C4—N2—C3	107.58 (15)
C5—C6—H6A	110.0	C8—N2—C3	108.60 (16)
C7—C6—H6B	110.0	C4—N2—Zn	114.54 (13)
C5—C6—H6B	110.0	C8—N2—Zn	113.37 (12)
H6A—C6—H6B	108.4	C3—N2—Zn	103.75 (12)
C8—C7—C6	111.13 (18)	N1—Si—C1	112.86 (10)
C8—C7—H7A	109.4	N1—Si—C2	114.35 (10)
C6—C7—H7A	109.4	C1—Si—C2	110.18 (11)
C8—C7—H7B	109.4	N1—Si—C3	97.42 (9)
C6—C7—H7B	109.4	C1—Si—C3	113.57 (10)
H7A—C7—H7B	108.0	C2—Si—C3	107.88 (10)
N2—C8—C7	113.13 (18)	N2—Zn—N1	95.62 (7)
N2—C8—H8A	109.0	N2—Zn—Br2	115.47 (5)
C7—C8—H8A	109.0	N1—Zn—Br2	112.03 (5)
N2—C8—H8B	109.0	N2—Zn—Br1	107.97 (5)
C7—C8—H8B	109.0	N1—Zn—Br1	106.69 (5)
H8A—C8—H8B	107.8	Br2—Zn—Br1	116.759 (13)

Experimental details

Crystal data
Chemical formula	[ZnBr₂(C₁₂H₂₈N₂Si)]
M_r	453.64
Crystal system, space group	Monoclinic, P2₁/c
Temperature (K)	123
a, b, c (Å)	12.0284 (4), 10.6505 (3), 14.5633 (5)
β (°)	109.752 (4)
V (Å³)	1755.91 (10)
Z	4
Radiation type	Mo Kα
µ (mm⁻¹)	6.01
Crystal size (mm)	0.40 × 0.20 × 0.20

Data collection
Diffractometer	Oxford Diffraction Xcalibur S diffractometer
Absorption correction	Multi-scan (CrysAlis RED; Oxford Diffraction, 2006)
T_min, T_max	0.698, 1.000
No. of measured, independent and observed [I > 2σ(I)] reflections	17826, 3440, 2673
R_int	0.034
(sin θ/λ)_max (Å⁻¹)	0.617

Refinement
R[F² > 2σ(F²)], wR(F²), S	0.020, 0.035, 1.04
No. of reflections	3440
No. of parameters	172
H-atom treatment	H atoms treated by a mixture of independent and constrained refinement
Δρ_max, Δρ_min (e Å⁻³)	0.56, −0.43

Computer programs: CrysAlis CCD (Oxford Diffraction, 2006), CrysAlis RED (Oxford Diffraction, 2006), SHELXS97 (Sheldrick, 2008), SHELXL97 (Sheldrick, 2008), ORTEP-3 (Farrugia, 1997).

Acknowledgements

This work was supported by the Deutsche Forschungsgemeinschaft. The authors also acknowledge Wacker Chemie AG and Chemetall for providing special chemicals.

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