organic compounds 2,4,6-Trimethylphenyl isocyanide

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1 organic compounds Acta Crystallographica Section C Crystal Structure Communications ISSN Manuel A. Fernandes, Marcus Layh* and Bernard Omondi Molecular Sciences Institute, School of Chemistry, University of the Witwatersrand, PO Wits 2050, South Africa Correspondence marcus@aurum.chem.wits.ac.za Received 17 April 2002 Accepted 8 May 2002 Online 12 June 2002 The title compound, C 10 H 11 N, 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 C bond distance of (3) A Ê. Comment We are currently interested in the reactions of -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-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, Version 5.22; 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. atoms and the H atoms attached to the aromatic ring (atoms H3 and H5). The H atoms of the three methyl groups are staggered relative to the phenyl group, resulting in them being disordered over two symmetry-related positions, above and below the mirror plane. The N C bond distance of (3) A Ê (Table 1) lies well within the range found in aromatic isocyanides (1.153± A Ê ), 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 -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 of (3) A Ê. 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 (-donating) and isocyano substituents (-withdrawing and -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 (1) (C8C1) to (1) A Ê (C8C4). This arrangement differs from that found in halogenated aryl isocyanides. In 2,4,6-trichlorophenyl isocyanide (Pink et al., 2000) and penta uorophenyl 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 Compound (I) crystallizes in the orthorhombic space group Pnma, with all non-h atoms lying in 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 , and A Ê ). The molecule of (I) (Fig. 1) is located on a crystallographic mirror plane that includes all the non-h Figure 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. o384 # 2002 International Union of Crystallography DOI: /S Acta Cryst. (2002). C58, o384±o385

2 organic compounds Table 1 Selected geometric parameters (A Ê, ). N1ÐC (3) N1ÐC (3) C1ÐC (3) C1ÐC (3) C2ÐC (3) C2ÐC (3) C3ÐC (3) C4ÐC (3) C4ÐC (3) C5ÐC (3) C7ÐN1ÐC (3) C2ÐC1ÐC (18) C3ÐC2ÐC (19) C2ÐC3ÐC (19) C3ÐC4ÐC (19) C6ÐC5ÐC (19) C5ÐC6ÐC (18) Figure 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 ; (ii) x + 1 2, 1 2 y, 1 2 z]. 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. Experimental Compound (I) was prepared from 2,4,6-trimethylaniline and formic acid, followed by treatment of the product with phosgene, 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. Crystal data C 10 H 11 N M r = Orthorhombic, Pnma a = (19) A Ê b = (8) A Ê c = (10) A Ê V = (18) A Ê 3 Z =4 D x = Mg m 3 Data collection Bruker SMART 1K CCD areadetector diffractometer! scans Absorption correction: multi-scan (SADABS; Sheldrick, 1996) T min = 0.977, T max = measured re ections Re nement Re nement on F 2 R[F 2 >2(F 2 )] = wr(f 2 ) = S = re ections 70 parameters Mo K radiation Cell parameters from 932 re ections = 2.6±24.5 = 0.06 mm 1 T = 173 (2) K Plate, colourless mm 1189 independent re ections 590 re ections with I > 2(I) R int = max = 28.3 h = 20! 20 k = 9! 4 l = 10! 10 H-atom parameters constrained w = 1/[ 2 (F o 2 ) + (0.0547P) 2 ] where P =(F o 2 +2F c 2 )/3 (/) max < max = 0.15 e A Ê 3 min = 0.26 e A Ê 3 H atoms were treated as riding atoms with CÐH distances in the range 0.95±0.98 A Ê. Data collection: SMART (Bruker, 1999); cell re nement: SAINT- Plus (Bruker, 1999); data reduction: SAINT-Plus; program(s) used to solve structure: SHELXTL (Bruker, 1999); program(s) used to re ne structure: SHELXTL; molecular graphics: PLATON (Spek, 1990) and ORTEP-3 for Windows (Farrugia, 1997); software used to prepare material for publication: SHELXTL. The authors thank the University of the Witwatersrand for nancial support. Supplementary data for this paper are available from the IUCr electronic archives (Reference: GD1206). Services for accessing these data are described at the back of the journal. References Allen, F. H. & Kennard, O. (1993). Chem. Des. Autom. News, 8, 1, 31±37. Britton, D. (1979). Cryst. Struct. Commun. 8, 667±671. Britton, D., Konnert, S. & Lam, S. (1978). Cryst. Struct. Commun. 7, 445±448. Bruker (1999). SMART (Version 5.050) SAINT-Plus (Version 6.02; includes XPREP and SADABS) and SHELXTL (Version 5.10; includes XS, XL, XP and XSHELL). Bruker AXS Inc., Madison, Wisconsin, USA. Caro, C., Hitchcock, P. B., Lappert, M. F. & Layh, M. (1998). Chem. Commun. pp. 1297±1298. Carter, V. B., Britton, D. & Gleason, W. B. (1977). Cryst. Struct. Commun. 6, 543±548. Colapietro, M., Domenicano, A., Portalone, G., Torrini, I., Hargittai, I. & Schultz, G. (1984). J. Mol. Struct. 125, 19±32. Domenicano, A. & Murray-Rust, P. (1979). Tetrahedron Lett. 24, 2283±2286. Farrugia, L. J. (1997). J. Appl. Cryst. 30, 565. Hitchcock, P. B., Lappert, M. F. & Layh, M. (1999). Angew. Chem. Int. Ed. 38, 501±504. Hitchcock, P. B., Lappert, M. F. & Layh, M. (2001). J. Chem. Soc. Dalton Trans. pp. 2409±2416. Lane, T. M., Grubisha, D. S., Cuie, H. & Bennett, D. W. (1994). J. Mol. Struct. 328, 133±144. Lentz, D. & Preugschat, D. (1993). Acta Cryst. C49, 52±54. Pink, M., Britton, D., Noland, W. E. & Pinnow, M. J. (2000). Acta Cryst. C56, 1271±1273. Sheldrick, G. M. (1996). SADABS. University of GoÈttingen, Germany. Spek, A. L. (1990). Acta Cryst. A46, C-34. Ugi, I., Fetzer, U., Eholzer, E., Knupfer, H. & Offermann, K. (1965). Angew. Chem. Int. Ed. Engl. 4, 472±484. Acta Cryst. (2002). C58, o384±o385 Manuel A. Fernandes et al. C 10 H 11 N o385

3 supporting information [doi: /s ] Manuel A. Fernandes, Marcus Layh and Bernard Omondi 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. Crystal data C 10 H 11 N M r = Orthorhombic, Pnma Hall symbol: -P 2ac 2n a = (19) Å b = (8) Å c = (10) Å V = (18) Å 3 Z = 4 Data collection Bruker SMART 1K CCD area-detector diffractometer Radiation source: fine-focus sealed tube Graphite monochromator ω scans Absorption correction: multi-scan (SADABS; Sheldrick, 1996) T min = 0.977, T max = Refinement Refinement on F 2 Least-squares matrix: full R[F 2 > 2σ(F 2 )] = wr(f 2 ) = S = reflections 70 parameters 0 restraints Primary atom site location: structure-invariant direct methods F(000) = 312 D x = Mg m 3 Mo Kα radiation, λ = Å Cell parameters from 932 reflections θ = µ = 0.06 mm 1 T = 173 K Plate, colourless mm 5953 measured reflections 1189 independent reflections 590 reflections with I > 2σ(I) R int = θ max = 28.3, θ min = 2.6 h = k = 9 4 l = Secondary atom site location: difference Fourier map Hydrogen site location: inferred from neighbouring sites H-atom parameters constrained w = 1/[σ 2 (F o2 ) + (0.0547P) 2 ] where P = (F o 2 + 2F c2 )/3 (Δ/σ) max < Δρ max = 0.15 e Å 3 Δρ min = 0.26 e Å 3 sup-1

4 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 F 2 against ALL reflections. The weighted R-factor wr and goodness of fit S are based on F 2, conventional R-factors R are based on F, with F set to zero for negative F 2. The threshold expression of F 2 > σ(f 2 ) is used only for calculating R-factors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F 2 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 (Å 2 ) x y z U iso */U eq Occ. (<1) N (12) (2) (6) C (13) (2) (5) C (13) (3) (6) C (14) (2) (6) H * C (13) (2) (5) C (12) (2) (5) H * C (13) (2) (5) C (18) (4) (9) C (13) (3) (7) H8A * 0.50 H8B * 0.50 H8C * 0.50 C (15) (3) (7) H9A * 0.50 H9B * 0.50 H9C * 0.50 C (15) (2) (7) H10A * 0.50 H10B * 0.50 H10C * 0.50 Atomic displacement parameters (Å 2 ) U 11 U 22 U 33 U 12 U 13 U 23 N (12) (13) (14) (11) C (12) (12) (14) (11) C (13) (13) (14) (11) C (14) (12) (13) (11) C (13) (13) (12) (11) C (12) (12) (12) (10) C (13) (13) (13) (10) C (17) (2) (2) (18) C (13) (14) (2) (13) sup-2

5 C (16) (17) (14) (12) C (16) (18) (14) (11) Geometric parameters (Å, º) N1 C (3) C5 H N1 C (3) C6 C (3) C1 C (3) C8 H8A C1 C (3) C8 H8B C2 C (3) C8 H8C C2 C (3) C9 H9A C3 C (3) C9 H9B C3 H C9 H9C C4 C (3) C10 H10A C4 C (3) C10 H10B C5 C (3) C10 H10C C7 N1 C (3) C2 C8 H8A C2 C1 C (18) C2 C8 H8B C2 C1 N (2) H8A C8 H8B C6 C1 N (19) C2 C8 H8C C3 C2 C (19) H8A C8 H8C C3 C2 C (2) H8B C8 H8C C1 C2 C (2) C4 C9 H9A C2 C3 C (19) C4 C9 H9B C2 C3 H H9A C9 H9B C4 C3 H C4 C9 H9C C3 C4 C (19) H9A C9 H9C C3 C4 C (19) H9B C9 H9C C5 C4 C (19) C6 C10 H10A C6 C5 C (19) C6 C10 H10B C6 C5 H H10A C10 H10B C4 C5 H C6 C10 H10C C5 C6 C (18) H10A C10 H10C C5 C6 C (19) H10B C10 H10C C1 C6 C (19) C6 C1 C2 C3 0.0 C3 C4 C5 C6 0.0 N1 C1 C2 C C9 C4 C5 C C6 C1 C2 C C4 C5 C6 C1 0.0 N1 C1 C2 C8 0.0 C4 C5 C6 C C1 C2 C3 C4 0.0 C2 C1 C6 C5 0.0 C8 C2 C3 C N1 C1 C6 C C2 C3 C4 C5 0.0 C2 C1 C6 C C2 C3 C4 C N1 C1 C6 C sup-3