Crystal structure of tris­(1,3-dimesityl-4,5-di­hydro-1H-imidazol-3-ium) tetra­bromido­cobaltate(II) bromide chloro­form hexa­solvate

Eduard Rais; Ulrich Flörke; René Wilhelm

doi:10.1107/S2056989015016254

. 2015 Sep 12;71(Pt 10):m177–m178. doi: 10.1107/S2056989015016254

Crystal structure of tris(1,3-dimesityl-4,5-dihydro-1H-imidazol-3-ium) tetrabromidocobaltate(II) bromide chloroform hexasolvate

Eduard Rais ^a, Ulrich Flörke ^a,^*, René Wilhelm ^a,^*

PMCID: PMC4647430 PMID: 26594424

Abstract

In the unit cell of the title compound, (C₂₁H₂₇N₂)₃[CoBr₄]Br·6CHCl₃, the tetrabromidocobaltate(II) anion and the bromide anion are located on a crystallographic threefold rotation axis. For the [CoBr₄]²⁻ group, the axis runs through one of the Br ligands and the Co^II atom. All other structure moieties lie on general sites. Various tris(1,3-dimesityl-4,5-dihydro-1H-imidazol-3-ium) structures with different counter-ions have been reported. In the title compound, the N—C—N angle is 113.7 (5)°, with short C—N bond lengths of 1.297 (7) and 1.307 (7) Å. The two mesityl planes make a dihedral angle of 34.6 (1)° and the dihedral angles between the mesityl and N–C–N planes are 82.0 (1) and 88.5 (1)°, respectively. The imidazoline ring is almost planar, with atom deviations in the range 0.003 (5)–0.017 (5) Å from the best plane; the mean deviation is 0.012 (5) Å. In the crystal, non-covalent interactions of the C—H⋯Br type occur between the Br⁻ anion and the cation, as well as between the [CoBr₄]²⁻ anion and both the chloroform solvent molecules. These H⋯A distances are slightly shorter than the sum of van der Waals radii.

Keywords: crystal structure, imidazolium salt, absolute structure, C—H⋯Br interactions

Related literature

For similar tris(1,3-dimesityl-4,5-dihydro-1H-imidazol-3-ium) structures, see: Arduengo et al. (1995 ▸); Hagos et al. (2008 ▸); Santoro et al. (2013 ▸); Buchalski et al. (2015 ▸). For synthesis of 2-bromo-1,3-dimesityl-4,5-dihydro-1H-imidazol-3-ium bromide, see: Wiggins et al. (2012 ▸). For the application of 1,3-dimesityl-4,5-dihydro-1H-imidazol-3-ium cation as a carbene precursor, see: Díez-González et al. (2009 ▸). For catalytic application of imidazolium based [CoCl₄]²⁻ salts, see: Bica & Gärtner (2008 ▸); Wang et al. (2015 ▸). graphic file with name e-71-0m177-scheme1.jpg

Experimental

Crystal data

(C₂₁H₂₇N₂)₃[CoBr₄]Br·6CHCl₃
M _r = 2097.02
Trigonal,
a = 16.0535 (14) Å
c = 61.790 (12) Å
V = 13791 (4) Å³
Z = 6
Mo Kα radiation
μ = 2.92 mm⁻¹
T = 130 K
0.22 × 0.21 × 0.20 mm

Data collection

Bruker SMART APEX diffractometer
Absorption correction: multi-scan (SADABS; Sheldrick, 2004 ▸) T _min = 0.279, T _max = 1.0
41734 measured reflections
7309 independent reflections
4427 reflections with I > 2σ(I)
R _int = 0.077

Refinement

R[F ² > 2σ(F ²)] = 0.040
wR(F ²) = 0.078
S = 0.79
7309 reflections
306 parameters
1 restraint
H-atom parameters constrained
Δρ_max = 0.65 e Å⁻³
Δρ_min = −0.65 e Å⁻³
Absolute structure: Flack (1983 ▸), 1821 Friedel pairs
Absolute structure parameter: 0.020 (11)

Data collection: SMART (Bruker, 2002 ▸); cell refinement: SAINT (Bruker, 2002 ▸); data reduction: SAINT; program(s) used to solve structure: SHELXTL (Sheldrick, 2008 ▸); program(s) used to refine structure: SHELXL2013 (Sheldrick, 2015 ▸); molecular graphics: SHELXTL; software used to prepare material for publication: SHELXTL and local programs.

Supplementary Material

Crystal structure: contains datablock(s) I, global. DOI: 10.1107/S2056989015016254/nr2061sup1.cif

e-71-0m177-sup1.cif^{(1.5MB, cif)}

Structure factors: contains datablock(s) I. DOI: 10.1107/S2056989015016254/nr2061Isup2.hkl

e-71-0m177-Isup2.hkl^{(358KB, hkl)}

Click here for additional data file.^{(190.4KB, tif)}

. DOI: 10.1107/S2056989015016254/nr2061fig1.tif

Molecular structure of the title compound with anisotropic displacement ellipsoids drawn at the 50% probability level. Non-stoichiometric representation.

Click here for additional data file.^{(175.3KB, tif)}

a . DOI: 10.1107/S2056989015016254/nr2061fig2.tif

Crystal packing approximately viewed along a axis with intermolecular hydrogen bonding pattern drawn as dotted lines. H-atoms not involved are omitted.

CCDC reference: 1421420

Additional supporting information: crystallographic information; 3D view; checkCIF report

Table 1. Hydrogen-bond geometry (, ).

DHA	DH	HA	D A	DHA
C1H1ABr3ⁱⁱ	0.95	2.58	3.373(4)	141
C100H10Br1ⁱ	1.00	2.71	3.668(5)	161
C200H20Br2ⁱⁱⁱ	1.00	2.54	3.454(6)	152

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Symmetry codes: (i) Inline graphic ; (ii) ; (iii) .

supplementary crystallographic information

S1. Synthesis and crystallization

All manipulations were carried out under nitrogen atmosphere using standard Schlenk techniques. MeCN was dried with an MBRAUN MB SPS-800 solvent purification system under nitrogen. CHCl₃ was dried over activated molecular sieve with 3 Å pore diameter. 2-Bromo-1,3-dimesityl-4,5-dihydro-1H-imidazol-3-ium bromide (0.080 g, 0.172 mmol, 1 eq) and Cobalt powder (0.227 g, 3.852 mmol, 22 eq, grain size < 150 µm) were filled into a sealed schlenk tube equipped with a stirring bar. MeCN (3 mL) was added and the mixture was stirred and heated at 100 °C for 40 h under inert gas. The cooled down mixture was filtrated and the solvent was then removed under vacuum. The residual brown oil was separated by decantation and was dissolved in CHCl₃ (0.7 mL). Crystal growth could be observed after one day. The NMR spectra are not suitable because of the paramagnetic properties of the [CoBr₄]^2- anion.

S2. Refinement

Hydrogen atom positions were clearly derived from difference Fourier maps and then refined at idealized positions riding on the carbon atoms with isotropic displacement parameters U_iso(H) = 1.2U(C_eq) or 1.5U(-CH₃) and C–H 0.95-1.00 Å. All CH₃ hydrogen atoms were allowed to rotate but not to tip. It was not possible to refine a satisfactory split model for the C100–chloroform.

S3. Chemical Context

The cation is a common precursor for the synthesis of 1,3-dimesityl-4,5-dihydroimidazol-2-ylidene, which is used as a ligand in various catalytic applications (Díez-González et al., 2009). Alkyl-substituted imidazolium cations with [CoX₄]^2- anions (X = Cl, Br) are used as metal-containing ionic liquids (Bica & Gaertner, 2008; Wang et al., 2015).