A pyridyl-substituted cyclo­disilazane [(Apy)₂(μ-SiMe)₂] (ApyH₂ = 2-amino­pyridine)

The title compound, C₁₄H₂₀N₄Si₂ or [(Apy)₂(μ-SiMe)₂], systematic name 2-[2,2,4,4-tetra­methyl-3-(pyridin-2-yl)-1,3,2,4-di­aza­disiletidin-1-yl]pyridine, was obtained as a side product from the reaction of 2-amino-pyridine with LiBuⁿ followed by the addition of Me₂NMe₂SiCl in hexane. The compound was characterized by single-crystal X-ray diffraction analysis and NMR spectroscopy. The title compound lies about an inversion center at the centroid of the cyclo­disilazane ring. The four-membered Si₂N₂ core is strictly planar with the two pyridyl rings placed centrosymmetrically on either side of the Si₂N₂ plane and are almost coplanar with the central four-membered ring.

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Chemical scheme

Structure description

Small inorganic rings represent a well studied structural class due to the novel bonding modes and reactivity these units possess and the ubiquitous role of cyclic inter­mediates in a wide variety of chemical transformations (He et al., 2014). Structural features of N-aromatic cyclo­disilaza­nes have also attracted considerable inter­est (Schneider et al., 2001).

The title compound, [(Apy)₂(μ-SiMe)₂], lies on an inversion center situated at the centroid of the N2/Si1/N2A/Si1A ring (Fig. 1), where the four-membered Si₂N₂ core is strictly planar. The Si—N—Si and N—Si—N bond angles are 95.92 (5) and 84.08 (5)°, respectively. The two pyridyl rings, which are close to planar [r.m.s. deviations = 0.0066 Å] are located centrosymmetrically on either side of the Si₂N₂ plane. They are also close to coplanar with the Si₂N₂ ring, with inter­planar angles of 6.97 (9)°. This coplanarity of the main backbone is also observed in the previously reported aryl substituted cyclo­disilaza­nes with only H or halogen atoms in the ortho positions of the aromatic ring (Szöllösy et al., 1983). In these structures, the corresponding dihedral angles between the planar Si₂N₂ core and the aromatic rings lie in in the range 3 to 8°. However, when the ortho substituents are methyl or isopropyl groups, these angles increase to almost 90° due to steric inter­actions between the ring systems (Schneider et al., 2001; Shah et al., 1996). The Si—C6—C7 or SiA—C6A—C7A planes in the mol­ecule are almost perpendicular to the central Si₂N₂ core with dihedral angles of 89.73 (6)°. The Si—N bond distances, 1.7489 (10) and 1.7524 (11) Å, are similar to those observed in the related 6-Me-pyridyl-substituted cyclo­disilazane [(6-Me-Apy)₂(μ-SiMe)₂] (Junk & Leary, 2004).

Figure 1 The mol­ecular structure of the title compound with displacement ellipsoids drawn at the 30% probability level. Atoms labelled with the suffix A character are related by the symmetry operation −x + 1, −y, −z + 2.

Synthesis and crystallization

The title compound was prepared from 2-amino-pyridine with LiBuⁿ followed by Me₂NMe₂SiCl in hexane as follows. To a stirred solution of 2-amino-pyridine (0.207 g, 2.20 mmol) in hexane (25 ml) at 0°C, LiBuⁿ (1.00 ml, 2.2 M, 2.20 mmol) was added dropwise to form a yellow suspension. The mixture was slowly warmed to room temperature and kept stirring for 12 h. Me₂NSiMe₂Cl (0.30 ml, 2.20 mmol) was added to this solution at 0°C and stirred for 12 h at room temperature, and then filtered to remove LiCl. The filtrate was concentrated in vacuo to ca 5–10 ml. There was a small amount of white solid precipitated at this point. This material was filtered off and the solution was concentrated to obtain the main product ApyHSiMe₂NMe₂ as yellow oil (Duan et al., 2012). The additional white residue was recrystallized from hexane to give colorless block-like crystals of the title compound (< 0.066 g, < 10% yield). The formation of the reported cyclo­disilazane is presumed to occur via the elimination of Me₂NCl.

¹H NMR (600 MHz, CDCl₃): δ 0.64–0.66 (m, 12H, Si—CH₃), 6.37–6.40 (m, 2H, pyrid­yl), 6.64–6.67 (m, 2H, pyrid­yl), 7.41–7.44 (m, 2H, pyrid­yl), 8,12–8.13 (m, 2H, pyrid­yl); ¹³C NMR (150 MHz, CDCl₃): δ 0.81 (SiCH₃), 158.73 (C1), 110.80 (C2), 137.42 (C3), 113.68 (C4), 148.88 (C5).

Refinement

Crystal data, data collection and refinement details are summarized in Table 1.

Table 1
Experimental details

Crystal data
Chemical formula	C14H20N4Si2
Mr	300.52
Crystal system, space group	Monoclinic, P21/n
Temperature (K)	200
a, b, c (Å)	9.8504 (4), 8.5234 (4), 10.3120 (4)
β (°)	109.673 (1)
V (Å^3)	815.25 (6)
Z	2
Radiation type	Mo Kα
μ (mm^−1)	0.21
Crystal size (mm)	0.30 × 0.30 × 0.20
Data collection
Diffractometer	Bruker SMART APEX CCD area detector
Absorption correction	Multi-scan (SADABS; Bruker, 2012)
Tmin, Tmax	0.939, 0.959
No. of measured, independent and observed [I > 2σ(I)] reflections	7684, 1999, 1850
Rint	0.021
(sin θ/λ)max (Å^−1)	0.667
Refinement
R[F^2 > 2σ(F^2)], wR(F^2), S	0.032, 0.089, 0.99
No. of reflections	1999
No. of parameters	93
H-atom treatment	H-atom parameters constrained
Δρmax, Δρmin (e Å^−3)	0.29, −0.23
Computer programs: APEX2 and SAINT (Bruker, 2012), SHELXT (Sheldrick, 2015a), SHELXL2014/7 (Sheldrick, 2015b) and SHELXTL (Sheldrick, 2008).

Structural data

Computing details

Data collection: APEX2 (Bruker, 2012); cell refinement: SAINT (Bruker, 2012); data reduction: SAINT (Bruker, 2012); program(s) used to solve structure: SHELXT (Sheldrick, 2015a); program(s) used to refine structure: SHELXL2014/7 (Sheldrick, 2015b); molecular graphics: SHELXTL (Sheldrick, 2008); software used to prepare material for publication: SHELXTL (Sheldrick, 2008).

2-[2,2,4,4-Tetramethyl-3-(pyridin-2-yl)-1,3,2,4-diazadisiletidin-1-yl]pyridine

Crystal data

C14H20N4Si2	F(000) = 320
Mr = 300.52	Dx = 1.224 Mg m^−3
Monoclinic, P21/n	Mo Kα radiation, λ = 0.71073 Å
a = 9.8504 (4) Å	Cell parameters from 5990 reflections
b = 8.5234 (4) Å	θ = 3.3–28.3°
c = 10.3120 (4) Å	µ = 0.21 mm^−1
β = 109.673 (1)°	T = 200 K
V = 815.25 (6) Å^3	Block, colorless
Z = 2	0.30 × 0.30 × 0.20 mm

Data collection

Bruker SMART APEX CCD area detector diffractometer	1850 reflections with I > 2σ(I)
φ and ω scans	Rint = 0.021
Absorption correction: multi-scan (SADABS; Bruker, 2012)	θmax = 28.3°, θmin = 4.3°
Tmin = 0.939, Tmax = 0.959	h = −12→13
7684 measured reflections	k = −11→11
1999 independent reflections	l = −13→10

Refinement

Refinement on F^2	0 restraints
Least-squares matrix: full	Hydrogen site location: inferred from neighbouring sites
R[F^2 > 2σ(F^2)] = 0.032	H-atom parameters constrained
wR(F^2) = 0.089	w = 1/[σ^2(Fo^2) + (0.0448P)^2 + 0.3604P] where P = (Fo^2 + 2Fc^2)/3
S = 0.99	(Δ/σ)max = 0.001
1999 reflections	Δρmax = 0.29 e Å^−3
93 parameters	Δρmin = −0.23 e Å^−3

Special details

Geometry. All esds (except the esd in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell esds are taken into account individually in the estimation of esds in distances, angles and torsion angles; correlations between esds in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell esds is used for estimating esds involving l.s. planes.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Ų)

	x	y	z	Uiso*/Ueq
Si1	0.39680 (3)	0.09851 (4)	0.94129 (3)	0.02539 (12)
N2	0.58067 (11)	0.07682 (12)	0.96573 (11)	0.0282 (2)
N1	0.81985 (12)	0.11173 (13)	0.99110 (12)	0.0325 (2)
C1	0.68425 (12)	0.16506 (13)	0.93708 (12)	0.0252 (2)
C7	0.27830 (17)	0.08941 (19)	0.75936 (15)	0.0439 (3)
H7A	0.3053	−0.0009	0.7145	0.066*
H7B	0.2889	0.1860	0.7121	0.066*
H7C	0.1779	0.0783	0.7550	0.066*
C2	0.65038 (15)	0.30168 (16)	0.85671 (14)	0.0340 (3)
H2	0.5532	0.3355	0.8174	0.041*
C5	0.92480 (15)	0.19644 (18)	0.96812 (16)	0.0409 (3)
H5	1.0211	0.1594	1.0060	0.049*
C6	0.35809 (16)	0.27296 (16)	1.02919 (15)	0.0372 (3)
H6A	0.2557	0.2739	1.0198	0.056*
H6B	0.3812	0.3681	0.9874	0.056*
H6C	0.4168	0.2695	1.1270	0.056*
C4	0.90132 (17)	0.33314 (19)	0.89331 (17)	0.0445 (4)
H4	0.9793	0.3899	0.8813	0.053*
C3	0.76063 (19)	0.38586 (17)	0.83580 (16)	0.0420 (3)
H3	0.7404	0.4793	0.7824	0.050*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
Si1	0.02209 (18)	0.02372 (18)	0.02890 (19)	0.00267 (10)	0.00666 (13)	0.00351 (11)
N2	0.0237 (5)	0.0254 (5)	0.0358 (5)	0.0021 (4)	0.0106 (4)	0.0066 (4)
N1	0.0263 (5)	0.0327 (6)	0.0386 (6)	−0.0010 (4)	0.0112 (4)	−0.0003 (4)
C1	0.0273 (5)	0.0237 (5)	0.0263 (5)	−0.0015 (4)	0.0113 (4)	−0.0034 (4)
C7	0.0416 (8)	0.0473 (8)	0.0334 (7)	−0.0013 (6)	0.0003 (6)	0.0029 (6)
C2	0.0381 (7)	0.0313 (6)	0.0351 (6)	0.0031 (5)	0.0156 (5)	0.0053 (5)
C5	0.0283 (6)	0.0480 (8)	0.0482 (8)	−0.0069 (6)	0.0153 (6)	−0.0048 (6)
C6	0.0387 (7)	0.0305 (6)	0.0438 (7)	0.0063 (5)	0.0158 (6)	0.0005 (5)
C4	0.0455 (8)	0.0458 (8)	0.0508 (8)	−0.0175 (6)	0.0277 (7)	−0.0073 (7)
C3	0.0586 (9)	0.0325 (7)	0.0425 (7)	−0.0049 (6)	0.0270 (7)	0.0046 (6)

Geometric parameters (Å, º)

Si1—N2^i	1.7489 (10)	C7—H7C	0.9800
Si1—N2	1.7524 (11)	C2—C3	1.378 (2)
Si1—C6	1.8468 (14)	C2—H2	0.9500
Si1—C7	1.8476 (14)	C5—C4	1.373 (2)
Si1—Si1^i	2.6004 (6)	C5—H5	0.9500
N2—C1	1.3773 (15)	C6—H6A	0.9800
N2—Si1^i	1.7489 (10)	C6—H6B	0.9800
N1—C1	1.3416 (15)	C6—H6C	0.9800
N1—C5	1.3458 (17)	C4—C3	1.386 (2)
C1—C2	1.4028 (17)	C4—H4	0.9500
C7—H7A	0.9800	C3—H3	0.9500
C7—H7B	0.9800
N2^i—Si1—N2	84.08 (5)	H7A—C7—H7C	109.5
N2^i—Si1—C6	115.34 (6)	H7B—C7—H7C	109.5
N2—Si1—C6	112.86 (6)	C3—C2—C1	118.78 (13)
N2^i—Si1—C7	116.17 (6)	C3—C2—H2	120.6
N2—Si1—C7	114.25 (7)	C1—C2—H2	120.6
C6—Si1—C7	111.59 (7)	N1—C5—C4	124.06 (14)
N2^i—Si1—Si1^i	42.09 (3)	N1—C5—H5	118.0
N2—Si1—Si1^i	41.99 (3)	C4—C5—H5	118.0
C6—Si1—Si1^i	123.34 (5)	Si1—C6—H6A	109.5
C7—Si1—Si1^i	124.99 (6)	Si1—C6—H6B	109.5
C1—N2—Si1^i	128.16 (8)	H6A—C6—H6B	109.5
C1—N2—Si1	135.72 (8)	Si1—C6—H6C	109.5
Si1^i—N2—Si1	95.92 (5)	H6A—C6—H6C	109.5
C1—N1—C5	117.48 (12)	H6B—C6—H6C	109.5
N1—C1—N2	115.58 (11)	C5—C4—C3	118.06 (13)
N1—C1—C2	122.15 (11)	C5—C4—H4	121.0
N2—C1—C2	122.27 (11)	C3—C4—H4	121.0
Si1—C7—H7A	109.5	C2—C3—C4	119.44 (13)
Si1—C7—H7B	109.5	C2—C3—H3	120.3
H7A—C7—H7B	109.5	C4—C3—H3	120.3
Si1—C7—H7C	109.5
N2^i—Si1—N2—C1	−174.97 (16)	Si1—N2—C1—N1	171.41 (10)
C6—Si1—N2—C1	−59.93 (14)	Si1^i—N2—C1—C2	177.76 (9)
C7—Si1—N2—C1	68.96 (14)	Si1—N2—C1—C2	−8.61 (19)
Si1^i—Si1—N2—C1	−174.97 (16)	N1—C1—C2—C3	−1.76 (19)
N2^i—Si1—N2—Si1^i	0.000 (1)	N2—C1—C2—C3	178.25 (12)
C6—Si1—N2—Si1^i	115.03 (6)	C1—N1—C5—C4	0.0 (2)
C7—Si1—N2—Si1^i	−116.07 (7)	N1—C5—C4—C3	−1.2 (2)
C5—N1—C1—N2	−178.56 (11)	C1—C2—C3—C4	0.6 (2)
C5—N1—C1—C2	1.45 (18)	C5—C4—C3—C2	0.8 (2)
Si1^i—N2—C1—N1	−2.22 (16)

Symmetry code: (i) −x+1, −y, −z+2.