Bis[μ-N-(tert-butyl­dimethyl­silyl)-N-(pyridin-2-ylmeth­yl)amido]­bis­[methyl­cobalt(II)]

Astrid Malassa; Christine Agthe; Helmar Görls; Matthias Westerhausen

doi:10.1107/S1600536812032321

. 2012 Aug 11;68(Pt 9):m1167–m1168. doi: 10.1107/S1600536812032321

Bis[μ-N-(tert-butyldimethylsilyl)-N-(pyridin-2-ylmethyl)amido]bis[methylcobalt(II)]

Astrid Malassa ^a, Christine Agthe ^a, Helmar Görls ^a, Matthias Westerhausen ^a,^*

PMCID: PMC3435591 PMID: 22969464

Abstract

The green title complex, [Co₂(CH₃)₂(C₁₂H₂₁N₂Si)₂], was obtained from bis{[μ-N-tert-butyldimethylsilyl-N-(pyridin-2-ylmethyl)amido]chloridocobalt(II)} and methyllithium in diethyl ether at 195 K via a metathesis reaction. The dimeric cobalt(II) complex exhibits a crystallographic center of inversion in the middle of the Co₂N₂ ring (average Co—N = 2.050 Å). The Co^II atom shows a distorted tetrahedral coordination sphere. The exocyclic Co—N bond length to the pyridyl group shows a similar value of 2.045 (4) Å. The exocyclic methyl group has a rather long Co—C bond length of 2.019 (5) Å.

Related literature

The metathetical conversion of a cobalt chloride functionality into a methyl cobalt fragment via the reaction with methyllithium was reported earlier for tetra-coordinate cobalt(II) complexes bound to three additional aza-bases, see: Au-Yeung et al. (2007 ▶); Bowman et al. (2010 ▶); Humphries et al. (2005 ▶); Kleigrewe et al. (2005 ▶), Wallenhorst et al. (2008 ▶). The synthesis of dialkyl cobalt complexes succeeds starting from hexa-coordinate [(L)₄CoCl₂] with L being a pyridyl base, see: Milani et al. (2003 ▶); Zhu et al. (2010 ▶). The coordination number of the final cobalt(II) complexes depends on intramolecular steric strain yielding hexa-coordinate [(bpy)₂CoMe₂] (bpy = 2,2′-bipyridine) and tetra-coordinate [(py)₂CoR ₂] (R = CH₂C(Me₂)Ph). The formation of para-tolylcobalt complexes was reported by Zhu & Budzelaar (2010 ▶) who proposed a radical mechanism.

Experimental

Crystal data

[Co₂(CH₃)₂(C₁₂H₂₁N₂Si)₂]
M _r = 590.72
Triclinic,
a = 8.4751 (8) Å
b = 9.8055 (12) Å
c = 10.6130 (6) Å
α = 72.837 (6)°
β = 83.450 (6)°
γ = 69.216 (6)°
V = 787.81 (13) Å³
Z = 1
Mo Kα radiation
μ = 1.15 mm⁻¹
T = 183 K
0.06 × 0.06 × 0.04 mm

Data collection

Nonius KappaCCD diffractometer
5417 measured reflections
3551 independent reflections
1685 reflections with I > 2σ(I)
R _int = 0.074

Refinement

R[F ² > 2σ(F ²)] = 0.061
wR(F ²) = 0.129
S = 0.92
3551 reflections
160 parameters
H-atom parameters constrained
Δρ_max = 0.39 e Å⁻³
Δρ_min = −0.39 e Å⁻³

Data collection: COLLECT (Nonius, 1998 ▶); cell refinement: DENZO (Otwinowski & Minor, 1997 ▶); data reduction: DENZO; program(s) used to solve structure: SHELXS97 (Sheldrick, 2008 ▶); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008 ▶); molecular graphics: SHELXTL/PC (Sheldrick, 2008 ▶); software used to prepare material for publication: SHELXL97.

Supplementary Material

Crystal structure: contains datablock(s) I, global. DOI: 10.1107/S1600536812032321/im2393sup1.cif

e-68-m1167-sup1.cif^{(23.4KB, cif)}

Structure factors: contains datablock(s) I. DOI: 10.1107/S1600536812032321/im2393Isup2.hkl

e-68-m1167-Isup2.hkl^{(174.1KB, hkl)}

Additional supplementary materials: crystallographic information; 3D view; checkCIF report

Acknowledgments

We thank the Deutsche Forschungsgemeinschaft (DFG, Bonn–Bad Godesberg, Germany) for generous financial support. We also acknowledge funding from the Fonds der Chemischen Industrie (Frankfurt/Main, Germany).

supplementary crystallographic information

Comment

Au-Yeung et al. (2007) performed a metathetical ligand substitution reaction at (tmeda)cobalt(II) 2,6-dimethylphenyl-N-trimethylsilylamide chloride (tmeda = tetramethylethylenediamine) with methyllithium in toluene. Whereas in this complex the cobalt(II) adopts a distorted tetrahedral coordination sphere, severe distortions were observed using tridentate aza-Lewis bases (Bowman et al., 2010; Humphries et al., 2005; Kleigrewe et al., 2005; Wallenhorst et al., 2008). Treatment of tetrakis(pyridine)cobalt(II) dichloride with trimethylsilylmethyllithium or 2-methyl-2-phenylpropyllithium in n-pentane yielded [(py)₂CoR₂] (R = CH₂SiMe₃)₂, CH₂C(Me₂)Ph), respectively, with tetra-coordinate cobalt centers (Zhu et al., 2010). Less bulky methyl groups allowed the formation of [(bpy)₂CoMe₂] with a hexa-coordinate cobalt atom in a slightly distorted octahedral environment (Milani et al., 2003). Contrary to these procedures, a radical mechanism was discussed by Zhu & Budzelaar (2010) for the formation of para-tolyl-cobalt complexes. Whereas all of these cobalt(II) complexes represent mononuclear derivatives, the reaction of bis[N-(pyidin-2-ylmethyl)-N-(tert-butyldimethylsilyl)amido cobalt(II) chloride] with methyllithium in tetrahydrofuran (THF) yielded the centrosymmetric dinuclear title compound 1 with a central planar Co₂N₂ ring.

Experimental

Bis{chlorido-[N-(pyidin-2-ylmethyl)-N-(tert-butyldimethylsilyl)amido]cobalt(II)} (0.84 g, 1.32 mmol) was dissolved in 15 ml of THF and this solution cooled to -78 °C. Then 1.7 ml (2,72 mmol) of a 1,6M methyllithium solution in diethyl ether was added dropwise. A brown reaction solution formed which was warmed to ambient temperature and stirred for an additional hour. Thereafter all volatile materials were removed and the residue dried in vacuo. This residue was extracted with 15 ml of n-hexane. The volume of this solution was reduced to third of the original volume and cooled to -20 °C. Within several hours green rod-like crystals of 1 precipitated. Yield: 0.21 g (0.36 mmol, 27%).