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Acta Crystallogr Sect E Struct Rep Online. 2010 January 1; 66(Pt 1): o40–o41.
Published online 2009 December 4. doi:  10.1107/S1600536809050843
PMCID: PMC2980129

1,4-Bis(4-bromo-2,6-diisopropyl­phen­yl)-1,4-diaza­buta-1,3-diene

Abstract

The molecule of the title compound, C26H34Br2N2, lies on a crystallographic inversion center and hence the two imine groups are s-trans. The dihedral angle between the central 1,4-diaza­buta-1,3-diene unit and the attached substituted phenyl ring is 88.4 (7)°. The structure features a C—H(...)N close contact. The crystal selected for this study proved to be a non-merohedral twin with a minor component of 21.8 (3)%.

Related literature

1,4-diaza-1,3-butadiene (DAB) ligands containing sterically demanding N-substituents have proved to be versatile platforms for stabilizing s- and p-block atoms in unusual oxidation states or coordination geometries, see: Baker et al. (2008 [triangle]); Hill et al. (2009 [triangle]); Liu et al. (2009 [triangle]); Martin et al. (2009 [triangle]); Segawa et al. (2008 [triangle]). The title compound was prepared as part of our continuing studies on the chemistry of N-heterocyclic silylenes and germylenes, see: Hill et al. (2005 [triangle]); Naka et al. (2004 [triangle]); Tomasik et al. (2009 [triangle]). For the use of DAB ligands in olefin polymerization catalysis, see: Ittel et al. (2000 [triangle]); Jung et al. (2007 [triangle]). For related structures, see: (2003); Müller et al. (2003 [triangle]); Schaub et al. (2006 [triangle]); Berger et al. (2001 [triangle]); Laine et al. (1999 [triangle]). For the preparation of 4-bromo-2,6-di-iso-propyl aniline, see: Liu et al. (2005 [triangle]). For a description of the Cambridge Structural Database, see: Allen (2002 [triangle]).

An external file that holds a picture, illustration, etc.
Object name is e-66-00o40-scheme1.jpg

Experimental

Crystal data

  • C26H34Br2N2
  • M r = 534.37
  • Monoclinic, An external file that holds a picture, illustration, etc.
Object name is e-66-00o40-efi1.jpg
  • a = 8.961 (3) Å
  • b = 17.848 (7) Å
  • c = 8.620 (3) Å
  • β = 104.260 (11)°
  • V = 1336.2 (8) Å3
  • Z = 2
  • Mo Kα radiation
  • μ = 3.05 mm−1
  • T = 300 K
  • 0.43 × 0.35 × 0.29 mm

Data collection

  • Bruker SMART X2S diffractometer
  • Absorption correction: multi-scan (TWINABS; Bruker, 2007 [triangle]) T min = 0.103, T max = 0.428
  • 2286 measured reflections
  • 2286 independent reflections
  • 1585 reflections with I > 2σ(I)
  • R int = 0.110

Refinement

  • R[F 2 > 2σ(F 2)] = 0.069
  • wR(F 2) = 0.199
  • S = 1.04
  • 2286 reflections
  • 142 parameters
  • H-atom parameters constrained
  • Δρmax = 0.53 e Å−3
  • Δρmin = −0.60 e Å−3

Data collection: GIS (Bruker, 2009 [triangle]); cell refinement: SAINT (Bruker, 2007 [triangle]); data reduction: SAINT; program(s) used to solve structure: SHELXTL (Sheldrick, 2008 [triangle]); program(s) used to refine structure: SHELXTL and OLEX2 (Dolomanov et al., 2009 [triangle]); mol­ecular graphics: SHELXTL and OLEX2; software used to prepare material for publication: SHELXTL, OLEX2 (Dolomanov et al., 2009 [triangle]), publCIF (Westrip, 2009 [triangle]) and modiCIFer (Guzei, 2007 [triangle]).

Table 1
Hydrogen-bond geometry (Å, °)

Supplementary Material

Crystal structure: contains datablocks global, I. DOI: 10.1107/S1600536809050843/bx2248sup1.cif

Structure factors: contains datablocks I. DOI: 10.1107/S1600536809050843/bx2248Isup2.hkl

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

Acknowledgments

We gratefully acknowledge Bruker AXS sponsorship of this publication.

supplementary crystallographic information

Comment

1,4-diaza-1,3-butadiene (DAB) ligands bearing bulky aryl or alkyl groups on the nitrogen atoms have proven to be versatile platforms for stabilizing s- and p-block atoms in unusual oxidation states or coordination geometries (Baker et al. (2008); Hill et al. (2009); Liu et al. (2009); Martin et al. (2009); Segawa et al. (2008)). The title compound, (I), was prepared as part of our continuing studies upon the chemistry of N-heterocyclic silylenes and germylenes (Hill et al. (2005); Naka et al. (2004); Tomasik et al. (2009)), the silicon(II) and germanium(II) analogues of the well known Arduengo N-heterocyclic carbenes. DAB ligands are ideal in this regard since their stereo-electronic properties are easily tuned by alteration of the N– and C-substituents.

DAB ligands have also been used extensively in d-block coordination chemistry, particularly within the field of olefin polymerization catalysis (Ittel et al. 2000). Jung et al. (2007) recently used the title compound as a precursor to an N-heterocyclic carbene in the synthesis of a catalytically active cationic (η3-allyl)(NHC)palladium complex.

The molecule of (I) resides on a crystallographic inversion center and hence the two imine groups are s-trans. The dihedral angle between the central 1,4-diazabuta-1,3-diene moiety and the attached substituted phenyl ring is 88.4 (7)°. The molecular symmetry approaches C2h, however, the positions of the isopropyl groups break the mirror plane symmetry: both H atoms on the tertiary C atoms of the two symmetry-independent iPr groups point toward atom N1, but reside on the opposite sides of the phenyl ring. This is illustrated with two disparate but "would be equivalent" torsion angles, one for each iPr group: C2—C3—C8—C9 (-96.5 (8)°) and C2—C7—C11—C13 (163.6 (7)°). This geometry differs from that of the unbrominated congener of (I), 1,4-bis(2,6-diisopropyl-phenyl)-1,4-diazabuta-1,3-diene, (II). For related structures, see: Müller et al. (2003), Schaub et al. (2006). Compound (II), structurally characterized at 173 K by Berger et al. (2001) and at 193 K by Laine et al.(1999), crystallizes with the molecule of (II) on an inversion center. The H atoms of the tertiary C atom of the isopropyl groups point toward the N atom and, in contrast to (I), are located on the same side of the phenyl ring. The overall symmetry of (II) is much closer to C2h as the iPr groups are oriented very similarly: in the 193 K structure of (II) two "would be equivalent" Me—C(H)—C—C(N) torsion angles measured 144.6 and 145.4°. The C—Br distance of 1.897 (6) Å is in excellent agreement with the value of 1.899 (11) Å obtained by averaging 2303 C—Br bond lengths from 1736 relevant compounds reported to the Cambridge Structural Database (Allen, 2002).

Experimental

4-Bromo-2,6-di-iso-propyl aniline was prepared according to the literature procedure (Liu et al. 2005). To a stirred solution of 4-bromo-2,6-di-iso-propyl aniline (3.0 g,11.71 mmol) in methanol (40 cm3) containing 4 drops of formic acid was added glyoxal (0.85 g, 5.80 mmol, 40% aqueous soln.) slowly dropwise. The reaction mixture was stirred for 24 h at room temperature, filtered, and the precipitate washed with cold MeOH (2 x 10 mL). This yellow solid was dried in vacuo and recrystallized from EtOH to give a crop of pale yellow needles suitable for X-ray diffraction analysis. Yield 3.53 g, 56%.

1H-NMR (CD2Cl2, 300 MHz): δ 1.19 (d, 3J = 6.9 Hz, 24H, CH3), 2.91 (sept, 3J = 6.8 Hz, 4H, CH), 7.31 (s, 4H, aromatic), 8.07 (s, 2H, CH); 13C{1H}-NMR (CD2Cl2, 75 MHz): δ 22.80, 28.43, 119.42, 126.79, 139.29, 147.52, 163.97.

Refinement

All H-atoms were placed in idealized locations with C—H distances 0.93 - 0.98 Å and refined as riding with appropriate thermal displacement coefficients Uiso(H) = 1.2 or 1.5 times Ueq(bearing atom). The crystal of (I) selected for this study proved to be a non-merohedral twin. The two twin components are related by a 179.9° rotation about the [001] direction in reciprocal space with the minor component contribution of 21.8 (3)%.

Figures

Fig. 1.
Molecular structure of (I). The thermal ellipsoids are shown at 30% probability level. Atoms labeled with the suffixes A and unlabeled are generated by the symmetry operation (-x+1, -y+1, -z+1).

Crystal data

C26H34Br2N2F(000) = 548
Mr = 534.37Dx = 1.328 Mg m3
Monoclinic, P21/cMo Kα radiation, λ = 0.71073 Å
Hall symbol: -P 2ybcCell parameters from 999 reflections
a = 8.961 (3) Åθ = 2.3–24.8°
b = 17.848 (7) ŵ = 3.05 mm1
c = 8.620 (3) ÅT = 300 K
β = 104.260 (11)°Block, yellow
V = 1336.2 (8) Å30.43 × 0.35 × 0.29 mm
Z = 2

Data collection

Bruker SMART X2S diffractometer2286 independent reflections
Radiation source: micro-focus sealed tube1585 reflections with I > 2σ(I)
doubly curved silicon crystalRint = 0.110
ω scansθmax = 24.8°, θmin = 2.3°
Absorption correction: multi-scan (TWINABS; Bruker, 2007)h = 0→10
Tmin = 0.103, Tmax = 0.428k = −21→0
2286 measured reflectionsl = −10→9

Refinement

Refinement on F2Secondary atom site location: difference Fourier map
Least-squares matrix: fullHydrogen site location: inferred from neighbouring sites
R[F2 > 2σ(F2)] = 0.069H-atom parameters constrained
wR(F2) = 0.199w = 1/[σ2(Fo2) + (0.0949P)2 + 1.843P] where P = (Fo2 + 2Fc2)/3
S = 1.04(Δ/σ)max = 0.001
2286 reflectionsΔρmax = 0.53 e Å3
142 parametersΔρmin = −0.60 e Å3
0 restraintsExtinction correction: SHELXTL (Sheldrick, 2008), Fc*=kFc[1+0.001xFc2λ3/sin(2θ)]-1/4
Primary atom site location: structure-invariant direct methodsExtinction coefficient: 0.038 (5)

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 (Å2)

xyzUiso*/Ueq
Br11.14981 (9)0.69711 (6)0.27272 (12)0.0957 (6)
N10.6097 (6)0.5812 (3)0.5079 (7)0.0523 (14)
C10.5657 (8)0.5148 (3)0.4744 (8)0.0513 (17)
H10.61730.48470.41660.062*
C20.7381 (6)0.6090 (3)0.4544 (7)0.0395 (14)
C30.7094 (7)0.6469 (3)0.3074 (7)0.0409 (14)
C40.8336 (7)0.6738 (3)0.2564 (7)0.0456 (15)
H40.81790.69920.15950.055*
C50.9804 (7)0.6630 (4)0.3489 (8)0.0500 (16)
C61.0083 (7)0.6289 (4)0.4968 (8)0.0529 (16)
H61.10860.62450.55910.063*
C70.8860 (8)0.6012 (3)0.5528 (8)0.0485 (16)
C80.5477 (7)0.6575 (4)0.2044 (9)0.0536 (16)
H80.47800.65000.27460.064*
C90.5079 (12)0.5984 (6)0.0770 (14)0.119 (4)
H9C0.56720.6062−0.00040.179*
H9B0.40020.60130.02510.179*
H9A0.53090.54980.12470.179*
C100.5185 (9)0.7356 (5)0.1375 (14)0.088 (3)
H10C0.54960.77140.22240.132*
H10A0.41080.74160.08830.132*
H10B0.57660.74360.05900.132*
C110.9157 (9)0.5652 (4)0.7203 (8)0.0626 (18)
H110.85330.51950.70900.075*
C120.8601 (13)0.6152 (5)0.8316 (10)0.101 (3)
H12B0.85730.58800.92690.151*
H12A0.75860.63270.78080.151*
H12C0.92850.65720.85910.151*
C131.0834 (11)0.5415 (5)0.7895 (10)0.087 (3)
H13A1.11580.50930.71480.131*
H13B1.09150.51520.88840.131*
H13C1.14780.58520.80860.131*

Atomic displacement parameters (Å2)

U11U22U33U12U13U23
Br10.0555 (5)0.1428 (10)0.0961 (8)−0.0228 (5)0.0324 (5)0.0295 (6)
N10.067 (3)0.034 (3)0.065 (4)−0.011 (2)0.036 (3)−0.001 (2)
C10.068 (4)0.035 (3)0.063 (4)−0.014 (3)0.040 (4)−0.007 (3)
C20.053 (3)0.027 (3)0.046 (4)−0.006 (2)0.026 (3)−0.004 (3)
C30.046 (3)0.033 (3)0.046 (4)−0.005 (3)0.015 (3)−0.003 (3)
C40.053 (4)0.046 (3)0.039 (3)−0.006 (3)0.014 (3)0.002 (3)
C50.046 (4)0.059 (4)0.050 (4)−0.011 (3)0.021 (3)0.000 (3)
C60.052 (3)0.057 (4)0.050 (4)−0.006 (3)0.014 (3)0.006 (3)
C70.064 (4)0.042 (3)0.043 (4)−0.006 (3)0.020 (3)0.002 (3)
C80.046 (3)0.052 (4)0.063 (4)−0.005 (3)0.014 (3)0.007 (3)
C90.093 (7)0.119 (8)0.117 (9)−0.024 (6)−0.030 (6)−0.045 (7)
C100.063 (5)0.080 (5)0.115 (8)0.008 (4)0.013 (6)0.039 (6)
C110.083 (5)0.059 (4)0.052 (4)−0.003 (4)0.027 (4)0.014 (4)
C120.161 (10)0.094 (6)0.063 (6)0.043 (6)0.058 (6)0.026 (5)
C130.109 (7)0.081 (6)0.072 (6)0.025 (5)0.025 (5)0.019 (5)

Geometric parameters (Å, °)

Br1—C51.897 (6)C8—H80.9800
N1—C11.260 (7)C9—H9C0.9600
N1—C21.429 (7)C9—H9B0.9600
C1—C1i1.455 (11)C9—H9A0.9600
C1—H10.9300C10—H10C0.9600
C2—C71.393 (9)C10—H10A0.9600
C2—C31.403 (8)C10—H10B0.9600
C3—C41.380 (8)C11—C121.483 (11)
C3—C81.513 (9)C11—C131.533 (12)
C4—C51.374 (9)C11—H110.9800
C4—H40.9300C12—H12B0.9600
C5—C61.379 (9)C12—H12A0.9600
C6—C71.393 (9)C12—H12C0.9600
C6—H60.9300C13—H13A0.9600
C7—C111.542 (9)C13—H13B0.9600
C8—C91.501 (12)C13—H13C0.9600
C8—C101.507 (10)
C1—N1—C2118.9 (5)C8—C9—H9B109.5
N1—C1—C1i120.3 (7)H9C—C9—H9B109.5
N1—C1—H1119.9C8—C9—H9A109.5
C1i—C1—H1119.9H9C—C9—H9A109.5
C7—C2—C3122.3 (5)H9B—C9—H9A109.5
C7—C2—N1119.3 (5)C8—C10—H10C109.5
C3—C2—N1118.4 (5)C8—C10—H10A109.5
C4—C3—C2118.2 (5)H10C—C10—H10A109.5
C4—C3—C8120.0 (5)C8—C10—H10B109.5
C2—C3—C8121.8 (5)H10C—C10—H10B109.5
C5—C4—C3119.9 (6)H10A—C10—H10B109.5
C5—C4—H4120.1C12—C11—C13111.5 (8)
C3—C4—H4120.1C12—C11—C7110.3 (6)
C4—C5—C6121.9 (6)C13—C11—C7114.0 (6)
C4—C5—Br1119.2 (5)C12—C11—H11106.9
C6—C5—Br1118.9 (5)C13—C11—H11106.9
C5—C6—C7119.9 (6)C7—C11—H11106.9
C5—C6—H6120.1C11—C12—H12B109.5
C7—C6—H6120.1C11—C12—H12A109.5
C6—C7—C2117.7 (6)H12B—C12—H12A109.5
C6—C7—C11120.2 (6)C11—C12—H12C109.5
C2—C7—C11122.1 (6)H12B—C12—H12C109.5
C9—C8—C10112.5 (8)H12A—C12—H12C109.5
C9—C8—C3111.2 (6)C11—C13—H13A109.5
C10—C8—C3113.0 (5)C11—C13—H13B109.5
C9—C8—H8106.5H13A—C13—H13B109.5
C10—C8—H8106.5C11—C13—H13C109.5
C3—C8—H8106.5H13A—C13—H13C109.5
C8—C9—H9C109.5H13B—C13—H13C109.5
C2—N1—C1—C1i−179.3 (8)C5—C6—C7—C11−178.1 (6)
C1—N1—C2—C7−90.5 (7)C3—C2—C7—C6−3.5 (9)
C1—N1—C2—C392.9 (7)N1—C2—C7—C6−179.9 (6)
C7—C2—C3—C43.3 (8)C3—C2—C7—C11174.9 (5)
N1—C2—C3—C4179.8 (5)N1—C2—C7—C11−1.6 (8)
C7—C2—C3—C8−177.7 (5)C4—C3—C8—C982.5 (8)
N1—C2—C3—C8−1.2 (8)C2—C3—C8—C9−96.4 (8)
C2—C3—C4—C50.1 (9)C4—C3—C8—C10−45.1 (9)
C8—C3—C4—C5−178.9 (6)C2—C3—C8—C10135.9 (7)
C3—C4—C5—C6−3.3 (10)C6—C7—C11—C12108.2 (9)
C3—C4—C5—Br1177.6 (5)C2—C7—C11—C12−70.1 (9)
C4—C5—C6—C73.1 (10)C6—C7—C11—C13−18.1 (10)
Br1—C5—C6—C7−177.8 (5)C2—C7—C11—C13163.6 (7)
C5—C6—C7—C20.3 (9)

Symmetry codes: (i) −x+1, −y+1, −z+1.

Hydrogen-bond geometry (Å, °)

D—H···AD—HH···AD···AD—H···A
C8—H8···N10.982.402.880 (9)109

Footnotes

Supplementary data and figures for this paper are available from the IUCr electronic archives (Reference: BX2248).

References

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