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

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.

Key indicators

• Single-crystal X-ray study
• T = 183 K
• Mean [sigma](C-C) = 0.008 Å
• R factor = 0.061
• wR factor = 0.129
• Data-to-parameter ratio = 22.2

checkCIF/PLATON results

No syntax errors found



Alert level C
PLAT026_ALERT_3_C Ratio Observed / Unique Reflections too Low ....         47 Perc.
PLAT029_ALERT_3_C _diffrn_measured_fraction_theta_full Low .......      0.979
PLAT341_ALERT_3_C Low Bond Precision on  C-C Bonds ...............     0.0078 Ang
PLAT601_ALERT_2_C Structure Contains Solvent Accessible VOIDS of .         40 A   3 
PLAT906_ALERT_3_C Large K value in the Analysis of Variance ......      4.344
PLAT910_ALERT_3_C Missing # of FCF Reflections Below Th(Min) .....          6
PLAT911_ALERT_3_C Missing # FCF Refl Between THmin & STh/L=  0.600          5
PLAT913_ALERT_3_C Missing # of Very Strong Reflections in FCF ....          2

Alert level G
PLAT005_ALERT_5_G No _iucr_refine_instructions_details in CIF ....          ?
PLAT154_ALERT_1_G The su's on the Cell Angles are Equal ..........    0.00600 Deg.
PLAT912_ALERT_4_G Missing # of FCF Reflections Above STh/L=  0.600         64

   0 ALERT level A = Most likely a serious problem - resolve or explain
   0 ALERT level B = A potentially serious problem, consider carefully
   8 ALERT level C = Check. Ensure it is not caused by an omission or oversight
   3 ALERT level G = General information/check it is not something unexpected

   1 ALERT type 1 CIF construction/syntax error, inconsistent or missing data
   1 ALERT type 2 Indicator that the structure model may be wrong or deficient
   7 ALERT type 3 Indicator that the structure quality may be low
   1 ALERT type 4 Improvement, methodology, query or suggestion
   1 ALERT type 5 Informative message, check

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S1. 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.

Related literature

The metathetical conversion of a cobalt chloride functionality into a methyl cobalt fragment via the reaction with LiR 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)₂CoR₂] (R = CH₂C(Me₂)Ph). The formation of para-tolylcobalt complexes was reported by Zhu & Budzelaar (2010) who proposed a radical mechanism.

S2. 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%).

S3. Refinement

All hydrogen atoms were calculated to idealized positions with C–H distances of 0.98 (methyl), 0.99 (methylene) and 0.95 (phenyl) Å, and were refined with 1.2 times (1.5 for all methyl groups) the isotropic displacement parameter of the corresponding carbon atom. All methyl groups were allowed to rotate but not to tip.

Computing details

Data collection: COLLECT (Nonius, 1998); cell refinement: DENZO (Otwinowski & Minor, 1997); data reduction: DENZO (Otwinowski & Minor, 1997); 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 (Sheldrick, 2008).

Figures

	Fig. 1. Molecular structure and numbering scheme of the title compound 1; Displacement ellipsoids are at the 40% probability level. H atoms are neglected for clarity reasons. Symmetry-related atoms are marked with the letter i [symmetry code: (i) -x + 1, -y + 1, -z + 1].
	Fig. 2. Packing of the molecules by short ring-interactions (distance between the centroids of the aromatic rings 3.689 (3) Å).

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

Crystal data

[Co2(CH3)2(C12H21N2Si)2]	Z = 1
Mr = 590.72	F(000) = 314
Triclinic, P1	Dx = 1.245 Mg m^−3
Hall symbol: -P 1	Mo Kα radiation, λ = 0.71073 Å
a = 8.4751 (8) Å	Cell parameters from 5417 reflections
b = 9.8055 (12) Å	θ = 3.3–27.5°
c = 10.6130 (6) Å	µ = 1.15 mm^−1
α = 72.837 (6)°	T = 183 K
β = 83.450 (6)°	Prism, green
γ = 69.216 (6)°	0.06 × 0.06 × 0.04 mm
V = 787.81 (13) Å^3

Data collection

Nonius KappaCCD diffractometer	1685 reflections with I > 2σ(I)
Radiation source: fine-focus sealed tube	Rint = 0.074
Graphite monochromator	θmax = 27.5°, θmin = 3.3°
phi– + ω–scan	h = −10→9
5417 measured reflections	k = −10→12
3551 independent reflections	l = −13→13

Refinement

Refinement on F^2	Primary atom site location: structure-invariant direct methods
Least-squares matrix: full	Secondary atom site location: difference Fourier map
R[F^2 > 2σ(F^2)] = 0.061	Hydrogen site location: inferred from neighbouring sites
wR(F^2) = 0.129	H-atom parameters constrained
S = 0.92	w = 1/[σ^2(Fo^2) + (0.0369P)^2] where P = (Fo^2 + 2Fc^2)/3
3551 reflections	(Δ/σ)max < 0.001
160 parameters	Δρmax = 0.39 e Å^−3
0 restraints	Δρmin = −0.39 e Å^−3

Special details

Experimental. IR (in Nujol between KBr windows, cm^-1): = 1715 w, 1583 m, 1273 m, 1244 s, 1146 m, 1080 m, 1036 m, 1008 m, 889 m, 828 s, 770 m, 736 m. MS (DEI, rel. intensity in brackets): m/z = 501 ([M - CoMe₂]⁺, 11%), 165 ([Pyr-CH₂-NHSiMe₂]⁺, 100%). Elemental analysis (C₂₆H₄₈Co₂N₄Si₂, 590,72): calcd.: C 52.86, H 8.19, N 9.48; found: C 49.47, H 7.70, N 9.03 (the rather large deviations are caused by extreme sensitivity of the complex towards moisture and air; the low carbon value is a consequence of carbide and carbonate formation despite the fact that V₂O₅ was added prior to combustion).

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 (Ų)

	x	y	z	Uiso*/Ueq
Co1	0.50875 (8)	0.62393 (8)	0.52394 (5)	0.0360 (2)
Si1	0.36965 (16)	0.43232 (17)	0.77488 (11)	0.0373 (4)
N1	0.2891 (5)	0.7874 (4)	0.4452 (3)	0.0342 (10)
N2	0.3562 (4)	0.4948 (4)	0.6037 (3)	0.0306 (9)
C1	0.2668 (7)	0.9328 (6)	0.3756 (4)	0.0466 (14)
H1A	0.3599	0.9681	0.3636	0.056*
C2	0.1139 (7)	1.0311 (6)	0.3217 (4)	0.0524 (15)
H2A	0.1017	1.1325	0.2732	0.063*
C3	−0.0218 (7)	0.9803 (7)	0.3391 (5)	0.0570 (16)
H3A	−0.1275	1.0452	0.3003	0.068*
C4	−0.0012 (6)	0.8329 (6)	0.4142 (4)	0.0429 (13)
H4A	−0.0938	0.7967	0.4294	0.052*
C5	0.1560 (6)	0.7389 (6)	0.4668 (4)	0.0349 (12)
C6	0.1808 (5)	0.5827 (6)	0.5525 (4)	0.0387 (12)
H6A	0.1501	0.5256	0.5020	0.046*
H6B	0.1020	0.5892	0.6286	0.046*
C7	0.2682 (6)	0.5989 (6)	0.8446 (4)	0.0529 (15)
H7A	0.3243	0.6742	0.8080	0.079*
H7B	0.2788	0.5648	0.9408	0.079*
H7C	0.1485	0.6445	0.8213	0.079*
C8	0.5975 (6)	0.3468 (6)	0.8222 (4)	0.0504 (15)
H8A	0.6571	0.4165	0.7746	0.076*
H8B	0.6479	0.2504	0.7993	0.076*
H8C	0.6067	0.3288	0.9174	0.076*
C9	0.2621 (6)	0.2877 (6)	0.8564 (4)	0.0430 (13)
C10	0.0704 (6)	0.3488 (6)	0.8314 (5)	0.0594 (16)
H10A	0.0208	0.2719	0.8808	0.089*
H10B	0.0505	0.3722	0.7370	0.089*
H10C	0.0180	0.4411	0.8606	0.089*
C11	0.3389 (6)	0.1452 (6)	0.8085 (4)	0.0502 (14)
H11A	0.2790	0.0739	0.8499	0.075*
H11B	0.4584	0.0976	0.8324	0.075*
H11C	0.3288	0.1728	0.7125	0.075*
C12	0.2873 (7)	0.2393 (7)	1.0077 (4)	0.0700 (19)
H12A	0.2415	0.1575	1.0491	0.105*
H12B	0.2284	0.3263	1.0430	0.105*
H12C	0.4080	0.2034	1.0267	0.105*
C13	0.6200 (6)	0.7259 (7)	0.6082 (4)	0.0580 (16)
H13A	0.6269	0.8189	0.5442	0.087*
H13B	0.7339	0.6571	0.6363	0.087*
H13C	0.5532	0.7510	0.6850	0.087*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
Co1	0.0333 (4)	0.0450 (5)	0.0363 (4)	−0.0195 (3)	0.0038 (3)	−0.0147 (3)
Si1	0.0355 (8)	0.0459 (10)	0.0285 (7)	−0.0122 (8)	0.0012 (5)	−0.0098 (6)
N1	0.039 (2)	0.033 (3)	0.033 (2)	−0.015 (2)	0.0103 (16)	−0.0130 (19)
N2	0.026 (2)	0.036 (3)	0.0285 (17)	−0.009 (2)	−0.0019 (15)	−0.0068 (16)
C1	0.051 (4)	0.038 (4)	0.050 (3)	−0.017 (3)	0.020 (3)	−0.015 (3)
C2	0.059 (4)	0.037 (4)	0.048 (3)	−0.010 (3)	0.011 (3)	−0.004 (3)
C3	0.051 (4)	0.050 (4)	0.054 (3)	0.000 (3)	−0.005 (3)	−0.010 (3)
C4	0.032 (3)	0.045 (4)	0.046 (3)	−0.009 (3)	0.001 (2)	−0.010 (3)
C5	0.037 (3)	0.041 (3)	0.024 (2)	−0.012 (3)	0.0019 (19)	−0.008 (2)
C6	0.038 (3)	0.044 (4)	0.037 (2)	−0.022 (3)	0.003 (2)	−0.007 (2)
C7	0.061 (4)	0.057 (4)	0.045 (3)	−0.018 (3)	0.003 (2)	−0.024 (3)
C8	0.045 (3)	0.070 (4)	0.038 (3)	−0.014 (3)	−0.007 (2)	−0.020 (3)
C9	0.044 (3)	0.042 (4)	0.029 (2)	−0.005 (3)	0.005 (2)	−0.003 (2)
C10	0.050 (4)	0.054 (4)	0.068 (3)	−0.022 (3)	0.016 (3)	−0.009 (3)
C11	0.048 (3)	0.042 (4)	0.056 (3)	−0.018 (3)	0.010 (2)	−0.007 (3)
C12	0.084 (4)	0.064 (5)	0.040 (3)	−0.019 (4)	0.001 (3)	0.009 (3)
C13	0.055 (4)	0.089 (5)	0.055 (3)	−0.047 (4)	0.013 (3)	−0.034 (3)

Geometric parameters (Å, º)

Co1—C13	2.019 (5)	C6—H6B	0.9900
Co1—N2^i	2.032 (3)	C7—H7A	0.9800
Co1—N1	2.045 (4)	C7—H7B	0.9800
Co1—N2	2.067 (4)	C7—H7C	0.9800
Co1—Co1^i	2.6812 (14)	C8—H8A	0.9800
Si1—N2	1.741 (3)	C8—H8B	0.9800
Si1—C8	1.873 (4)	C8—H8C	0.9800
Si1—C7	1.877 (5)	C9—C11	1.528 (7)
Si1—C9	1.898 (5)	C9—C10	1.544 (6)
N1—C5	1.345 (5)	C9—C12	1.551 (6)
N1—C1	1.354 (6)	C10—H10A	0.9800
N2—C6	1.499 (5)	C10—H10B	0.9800
N2—Co1^i	2.032 (3)	C10—H10C	0.9800
C1—C2	1.376 (6)	C11—H11A	0.9800
C1—H1A	0.9500	C11—H11B	0.9800
C2—C3	1.381 (7)	C11—H11C	0.9800
C2—H2A	0.9500	C12—H12A	0.9800
C3—C4	1.388 (7)	C12—H12B	0.9800
C3—H3A	0.9500	C12—H12C	0.9800
C4—C5	1.390 (6)	C13—H13A	0.9800
C4—H4A	0.9500	C13—H13B	0.9800
C5—C6	1.487 (6)	C13—H13C	0.9800
C6—H6A	0.9900
C13—Co1—N2^i	119.40 (17)	N2—C6—H6B	108.5
C13—Co1—N1	105.8 (2)	H6A—C6—H6B	107.5
N2^i—Co1—N1	112.97 (13)	Si1—C7—H7A	109.5
C13—Co1—N2	130.97 (16)	Si1—C7—H7B	109.5
N2^i—Co1—N2	98.30 (12)	H7A—C7—H7B	109.5
N1—Co1—N2	84.19 (15)	Si1—C7—H7C	109.5
C13—Co1—Co1^i	151.34 (17)	H7A—C7—H7C	109.5
N2^i—Co1—Co1^i	49.71 (10)	H7B—C7—H7C	109.5
N1—Co1—Co1^i	102.57 (11)	Si1—C8—H8A	109.5
N2—Co1—Co1^i	48.59 (10)	Si1—C8—H8B	109.5
N2—Si1—C8	108.95 (18)	H8A—C8—H8B	109.5
N2—Si1—C7	109.2 (2)	Si1—C8—H8C	109.5
C8—Si1—C7	108.4 (2)	H8A—C8—H8C	109.5
N2—Si1—C9	114.74 (19)	H8B—C8—H8C	109.5
C8—Si1—C9	108.4 (2)	C11—C9—C10	107.8 (4)
C7—Si1—C9	107.0 (2)	C11—C9—C12	107.5 (4)
C5—N1—C1	119.0 (4)	C10—C9—C12	107.5 (4)
C5—N1—Co1	113.7 (3)	C11—C9—Si1	111.1 (3)
C1—N1—Co1	127.3 (3)	C10—C9—Si1	113.3 (3)
C6—N2—Si1	114.5 (2)	C12—C9—Si1	109.4 (3)
C6—N2—Co1^i	109.3 (2)	C9—C10—H10A	109.5
Si1—N2—Co1^i	125.9 (2)	C9—C10—H10B	109.5
C6—N2—Co1	108.8 (3)	H10A—C10—H10B	109.5
Si1—N2—Co1	111.27 (17)	C9—C10—H10C	109.5
Co1^i—N2—Co1	81.70 (12)	H10A—C10—H10C	109.5
N1—C1—C2	122.1 (5)	H10B—C10—H10C	109.5
N1—C1—H1A	118.9	C9—C11—H11A	109.5
C2—C1—H1A	118.9	C9—C11—H11B	109.5
C1—C2—C3	119.1 (5)	H11A—C11—H11B	109.5
C1—C2—H2A	120.4	C9—C11—H11C	109.5
C3—C2—H2A	120.4	H11A—C11—H11C	109.5
C2—C3—C4	119.0 (5)	H11B—C11—H11C	109.5
C2—C3—H3A	120.5	C9—C12—H12A	109.5
C4—C3—H3A	120.5	C9—C12—H12B	109.5
C3—C4—C5	119.4 (5)	H12A—C12—H12B	109.5
C3—C4—H4A	120.3	C9—C12—H12C	109.5
C5—C4—H4A	120.3	H12A—C12—H12C	109.5
N1—C5—C4	121.3 (4)	H12B—C12—H12C	109.5
N1—C5—C6	117.8 (4)	Co1—C13—H13A	109.5
C4—C5—C6	120.8 (4)	Co1—C13—H13B	109.5
C5—C6—N2	115.1 (4)	H13A—C13—H13B	109.5
C5—C6—H6A	108.5	Co1—C13—H13C	109.5
N2—C6—H6A	108.5	H13A—C13—H13C	109.5
C5—C6—H6B	108.5	H13B—C13—H13C	109.5

Symmetry code: (i) −x+1, −y+1, −z+1.