2,4,6-Trimethylphenyl isocyanide

The title compound, C₁₀H₁₁N, displays a crystallographic mirror plane that incorporates all the non-H atoms, as well as the H atoms attached to the aromatic ring. The iso­cyano group is almost linear and shows an N[triple bond]C bond distance of 1.158 (3) Å.

S1. Comment

We are currently interested in the reactions of α-H-free isocyanides with trimethylsilyl-substituted lithium amides, -alkyls and -silyls that have previously led to a wide variety of products. A neutral isocyanide adduct (Caro et al., 1998), a lithium-1-azabuta-1,3-dienylamide (Hitchcock et al., 2001), a silacyclobutene derivative (Hitchcock et al., 1999), and a series of lithium-1-azaallyls (Hitchcock et al., 2001) and lithium-β-diketiminates (Hitchcock et al., 2001) have so far been isolated and crystallographically characterized. The isolated products are believed to depend on, amongst other factors, the lithium starting material, the solvent, and the steric and electronic properties of the isocyanide. As a recent search of the Cambridge Structural Database (CSD, Release?; Allen & Kennard, 1993) has revealed that only a comparatively small number of simple aryl isocyanides have so far been structurally characterized, the majority of which carry electron-withdrawing substituents, we decided to determine the solid-state structure of 2,4,6-trimethylphenyl isocyanide, (I), by X-ray diffraction. \sch

Compound (I) crystallizes in the orthorhombic space group Pnma, with all the atoms lying on a mirror plane. Its structure is isomorphous with that of the previously described 2,4,6-trimethylphenyl nitrile (Britton, 1979; CSD Refcode MESITN; space group Pnma, cell parameters 15.637, 6.998 and 8.256 Å). The molecule (Fig. 1) is located on a crystallographic mirror plane that includes all non-H atoms and the H atoms attached to the aromatic ring (atoms H3 and H5). The H atoms bound to the three methyl groups are staggered relative to the phenyl group, resulting in them being disordered in two positions, which are related by symmetry, above and below the mirror plane.

The N≡C bond distance of 1.158 (3) Å (Table 1) lies well within the range (1.153–1.163 Å; References?) found in aromatic isocyanides, but is slightly longer than those found in aliphatic isocyanides (e.g. Lane et al., 1994). This has been attributed to the possibility of delocalization of π-electron density from the isocyanide moiety into the aromatic ring, which partially reduces the N≡C bond order in aromatic isocyanides (Colapietro et al., 1984). This notion is supported by a comparatively short N1≡C1 distance [1.407 (3) Å].

The endocyclic bond angles within the aromatic ring deviate periodically by up to 3° (Table 1) from the expected value of 120° for an ideal hexagon. This has been attributed (Domenicano & Murray-Rust, 1979) to the electronic properties of the methyl- (σ-donating) and isocyano-substituents (σ-withdrawing, π-donating).

The supramolecular structure of (I) shows parallel layers of isocyanide molecules, which are stacked in an ABA pattern along the b axis (Fig. 2). Molecules in adjacent layers are arranged in such a fashion that the isocyano groups of two closest molecules point in opposite directions and one of the o-methyl groups (C8) is located above or below the aromatic ring of the adjacent isocyanide, with non-bonding intermolecular distances ranging from 3.583 (1) Å (C8···C1) to 3.843 (1) Å (C8···C4). This arrangement differs from that found in halogenated aryl isocyanides. In 2,4,6-trichlorophenyl isocyanide (Pink et al., 2000) and pentafluorophenyl isocyanide (Lentz & Preugschat, 1993), the isocyano groups of neighbouring molecules point in the same direction and the isocyano and 4-halogeno groups are located in the centre of the aromatic ring of adjacent molecules. A similar arrangement is found for 1,4-diisocyanobenzene (Colapietro et al., 1984). In 4-bromophenyl isocyanide (Britton et al., 1978), 4-iodophenyl isocyanide (Britton et al., 1978) and 2,4,6-tribromophenyl isocyanide (Carter et al., 1977), the isocyano groups of molecules in different layers point in opposite directions, and there are close contacts between the isocyano group of one molecule and the halogen substituent in the 4-position of the adjacent molecule.

S2. Experimental

Compound (I) was prepared from 2,4,6-trimethylphenyl amine and formic acid, as described by Ugi et al. (1965). Crystals of (I) suitable for an X-ray diffraction study were obtained from a solution of the isocyanide in hexane at 213 K.

S3. Refinement

H atoms were treated as riding atoms with C—H = 0.95–0.98 Å.

Computing details

Data collection: SMART (Bruker, 1999); cell refinement: SAINT+ (Bruker, 1999); data reduction: SAINT+; program(s) used to solve structure: SHELXTL (Bruker, 1999); program(s) used to refine structure: SHELXTL; molecular graphics: PLATON (Spek, 1990) and ORTEP-3 for Windows (Farrugia, 1997); software used to prepare material for publication: SHELXTL.

Figures

	Fig. 1. A view of the molecule of (I) showing the atom-numbering scheme. Displacement ellipsoids are drawn at the 50% probability level and H atoms are shown as small spheres of arbitrary radii.
	Fig. 2. The packing of (I) viewed along the b axis. H atoms have been omitted for clarity [symmetry codes: (i) 1/2 - x, -y, z + 1/2; (ii) x + 1/2, 1/2 - y, 1/2 - z].

2,4,6-Trimethylphenyl isocyanide

Crystal data

C10H11N	F(000) = 312
Mr = 145.20	Dx = 1.086 Mg m^−3
Orthorhombic, Pnma	Mo Kα radiation, λ = 0.71073 Å
Hall symbol: -P 2ac 2n	Cell parameters from 932 reflections
a = 15.7210 (19) Å	θ = 2.6–24.5°
b = 6.8582 (8) Å	µ = 0.06 mm^−1
c = 8.2338 (10) Å	T = 173 K
V = 887.75 (18) Å^3	Plate, colourless
Z = 4	0.36 × 0.22 × 0.10 mm

Data collection

Bruker SMART 1K CCD area-detector diffractometer	1189 independent reflections
Radiation source: fine-focus sealed tube	590 reflections with I > 2σ(I)
Graphite monochromator	Rint = 0.087
ω scans	θmax = 28.3°, θmin = 2.6°
Absorption correction: multi-scan (SADABS; Sheldrick, 1996)	h = −20→20
Tmin = 0.977, Tmax = 0.994	k = −9→4
5953 measured reflections	l = −10→10

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)] = 0.046	Hydrogen site location: inferred from neighbouring sites
wR(F^2) = 0.115	H-atom parameters constrained
S = 0.91	w = 1/[σ^2(Fo^2) + (0.0547P)^2] where P = (Fo^2 + 2Fc^2)/3
1189 reflections	(Δ/σ)max < 0.001
70 parameters	Δρmax = 0.15 e Å^−3
0 restraints	Δρmin = −0.26 e Å^−3

Special details

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	Occ. (<1)
N1	−0.02540 (12)	0.2500	0.7232 (2)	0.0465 (6)
C1	0.03802 (13)	0.2500	0.8437 (2)	0.0324 (5)
C2	0.01361 (13)	0.2500	1.0064 (3)	0.0325 (6)
C3	0.07817 (14)	0.2500	1.1210 (2)	0.0338 (6)
H3	0.0635	0.2500	1.2329	0.041*
C4	0.16342 (13)	0.2500	1.0779 (2)	0.0299 (5)
C5	0.18442 (12)	0.2500	0.9139 (2)	0.0291 (5)
H1	0.2427	0.2500	0.8836	0.035*
C6	0.12322 (13)	0.2500	0.7936 (2)	0.0296 (5)
C7	−0.07669 (18)	0.2500	0.6223 (4)	0.0736 (9)
C8	−0.07834 (13)	0.2500	1.0562 (3)	0.0486 (7)
H8A	−0.1025	0.1200	1.0386	0.073*	0.50
H8B	−0.1096	0.3456	0.9909	0.073*	0.50
H8C	−0.0829	0.2844	1.1714	0.073*	0.50
C9	0.23236 (15)	0.2500	1.2053 (3)	0.0481 (7)
H9A	0.2869	0.2163	1.1549	0.072*	0.50
H9B	0.2186	0.1539	1.2894	0.072*	0.50
H9C	0.2364	0.3798	1.2545	0.072*	0.50
C10	0.14662 (15)	0.2500	0.6159 (2)	0.0466 (7)
H10A	0.1295	0.3741	0.5668	0.070*	0.50
H10B	0.1173	0.1425	0.5609	0.070*	0.50
H10C	0.2083	0.2334	0.6046	0.070*	0.50

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
N1	0.0354 (12)	0.0413 (13)	0.0627 (14)	0.000	−0.0165 (11)	0.000
C1	0.0250 (12)	0.0272 (12)	0.0451 (14)	0.000	−0.0097 (11)	0.000
C2	0.0268 (13)	0.0222 (13)	0.0485 (14)	0.000	0.0101 (11)	0.000
C3	0.0379 (14)	0.0297 (12)	0.0338 (13)	0.000	0.0099 (11)	0.000
C4	0.0319 (13)	0.0266 (13)	0.0311 (12)	0.000	0.0006 (11)	0.000
C5	0.0230 (12)	0.0306 (12)	0.0338 (12)	0.000	0.0023 (10)	0.000
C6	0.0297 (13)	0.0279 (13)	0.0312 (13)	0.000	0.0000 (10)	0.000
C7	0.0538 (17)	0.073 (2)	0.094 (2)	0.000	−0.0323 (18)	0.000
C8	0.0293 (13)	0.0336 (14)	0.083 (2)	0.000	0.0164 (13)	0.000
C9	0.0477 (16)	0.0575 (17)	0.0391 (14)	0.000	−0.0100 (12)	0.000
C10	0.0518 (16)	0.0580 (18)	0.0301 (14)	0.000	0.0002 (11)	0.000

Geometric parameters (Å, º)

N1—C7	1.158 (3)	C5—H1	0.9500
N1—C1	1.407 (3)	C6—C10	1.508 (3)
C1—C2	1.394 (3)	C8—H8A	0.9800
C1—C6	1.402 (3)	C8—H8B	0.9800
C2—C3	1.386 (3)	C8—H8C	0.9800
C2—C8	1.502 (3)	C9—H9A	0.9800
C3—C4	1.386 (3)	C9—H9B	0.9800
C3—H3	0.9500	C9—H9C	0.9800
C4—C5	1.390 (3)	C10—H10A	0.9800
C4—C9	1.509 (3)	C10—H10B	0.9800
C5—C6	1.381 (3)	C10—H10C	0.9800
C7—N1—C1	179.0 (3)	C2—C8—H8A	109.5
C2—C1—C6	123.10 (18)	C2—C8—H8B	109.5
C2—C1—N1	118.9 (2)	H8A—C8—H8B	109.5
C6—C1—N1	118.01 (19)	C2—C8—H8C	109.5
C3—C2—C1	116.92 (19)	H8A—C8—H8C	109.5
C3—C2—C8	121.3 (2)	H8B—C8—H8C	109.5
C1—C2—C8	121.8 (2)	C4—C9—H9A	109.5
C2—C3—C4	122.26 (19)	C4—C9—H9B	109.5
C2—C3—H3	118.9	H9A—C9—H9B	109.5
C4—C3—H3	118.9	C4—C9—H9C	109.5
C3—C4—C5	118.57 (19)	H9A—C9—H9C	109.5
C3—C4—C9	121.09 (19)	H9B—C9—H9C	109.5
C5—C4—C9	120.34 (19)	C6—C10—H10A	109.5
C6—C5—C4	122.10 (19)	C6—C10—H10B	109.5
C6—C5—H1	118.9	H10A—C10—H10B	109.5
C4—C5—H1	118.9	C6—C10—H10C	109.5
C5—C6—C1	117.04 (18)	H10A—C10—H10C	109.5
C5—C6—C10	121.72 (19)	H10B—C10—H10C	109.5
C1—C6—C10	121.24 (19)
C6—C1—C2—C3	0.0	C3—C4—C5—C6	0.0
N1—C1—C2—C3	180.0	C9—C4—C5—C6	180.0
C6—C1—C2—C8	180.0	C4—C5—C6—C1	0.0
N1—C1—C2—C8	0.0	C4—C5—C6—C10	180.0
C1—C2—C3—C4	0.0	C2—C1—C6—C5	0.0
C8—C2—C3—C4	180.0	N1—C1—C6—C5	180.0
C2—C3—C4—C5	0.0	C2—C1—C6—C10	180.0
C2—C3—C4—C9	180.0	N1—C1—C6—C10	0.0