organic compounds
Bis(2,6-dimethylpyridyl)iodonium dibromoiodate
aDepartment of Chemistry, University of Durham, South Road, Durham DH1 3LE, England, and bGlaxoSmithKline Pharmaceuticals, New Frontiers Science Park, Third Avenue, Harlow, Essex, CM19 5AW, England
*Correspondence e-mail: andy.whiting@durham.ac.uk
The 14H18IN2+·Br2I−, isostructural with the Cl2I analogue, comprises discrete centrosymmetric cations and anions, both with linear coordination of the I atoms.
of the title compound, CComment
Electropositive sources of iodine are useful reagents for the iododeboronation of alkenylboronate derivatives (Brown et al., 1973). Iodine monochloride is an important representative of such reagents (Stewart & Whiting, 1995; Lightfoot et al., 2004), but its shortcomings concerning reactivity, stereocontrol and necessitated the development of adjusted reagents involving amine–ICl complexes (Batsanov et al., 2005). In the course of the latter work, we obtained bis(2,6-dimethylpyridyl)iodonium dichloroiodate (I), the of which unexpectedly comprised discrete I(NC7H9)2+ and ICl2− ions rather than neutral Cl—I—NC7H9 molecules (Batsanov et al., 2005), but which also proved to be active in iododeboronation. Continuing these studies, we have prepared the bromide analogue of compound (I), viz. I(NC7H9)2+·IBr2− (II), which proved not to be superior to (I) as an iododeboronation agent.
The crystals of (II) are isomorphous with those of (I), with an increase of the volume per molecule by 14 Å3, or ca 3%. The structure comprises discrete bis(2,6-dimethylpyridyl)iodonium cations and IBr2− anions (Fig. 1). In both ions, the central I atoms occupy special positions at inversion centres, hence the N—I1—N′ and Br—I2—Br′ angles exactly equal 180°.
Atom I1 is tilted out of the pyridine ring plane by 0.190 (5) Å, whereas atoms C1 and C7 deviate on the opposite side of the plane by 0.026 (6) and 0.080 (6) Å, respectively. Thus, the two rings of the cation are parallel but not coplanar, with an interplanar separation of 0.38 Å, cf. 0.60 Å in (I). The I1—N bond distance of 2.294 (3) Å agrees with 2.300 (1) Å in (I), 2.259 (3) Å in bis(pyridine)iodonium (Álvarez-Rúa et al., 2002) and 2.29 (1) Å in bis(2,4,6-collidine)iodonium (Brayer & James, 1982). All these distances are much longer than the single Nsp2—I bonds in N-iodosuccinimide [2.059 (4) Å; Padmanabhan et al., 1990] or diiodoformamide [mean 2.07 (3) Å; Pritzkow, 1974] and can be regarded as hypervalent bonds. Likewise, the I2—Br bond length of 2.6962 (4) Å is normal for IBr2− anions in the solid state, cf. 2.710 (1) Å in [Me3S][IBr2] (Svensson & Kloo, 2000), 2.709 (2) Å in [H2(pc)][IBr2] or 2.6986 (4) Å in [H2(pc)]2[IBr2]Br (pc is phthalocyanine; Gardberg et al., 2002). However, these bonds also are much weaker than a single bond, as observed in the IBr molecule in the gas phase (2.469 Å; Huber & Herzberg, 1979).
Experimental
A 1.0 M solution of IBr in dichloromethane (DCM; 30 mmol, 30 ml) was cooled to 273 K with stirring under argon prior to the dropwise addition of 2,6-lutidine (30 mmol, 3.50 ml). After 30 min, the reaction was allowed to warm to room temperature before the addition of hexane (40 ml) to induce precipitation of the product. Filtration, drying (MgSO4) and evaporation gave the product as an orange solid (7.37 g, 78%). IR νmax, cm−1: 2978, 1601, 1466, 1377, 1161 and 792. 1H NMR (400 MHz, CDCl3, δ, p.p.m.): 2.78 (6H, s, 2 × Me), 7.13 (2H, d, J = 7.6 Hz, Ar—H) and 7.62 (1H, t, J = 7.6 Hz, Ar—H). 13C NMR (100 MHz, CDCl3, δ, p.p.m.): 28.1 (Me), 123.0 (Ar), 139.2 (Ar) and 157.6 (Ar). (C7H9NIBr)2 requires: C 26.76, H 2.89, N 4.46%; found: C 26.22, H 2.88, N 4.28%. Single crystals of X-ray quality were obtained by slow evaporation of a solution in DCM–hexane (1:1). To test the deboronation properties of (II), it has been reacted with 4,4,5,5-tetramethyl-2-non-1-enyl-1,3,2-dioxaborolane and 4,4,6-trimethyl-2-non-1-enyl-1,3,2-dioxaborinane in DCM, yielding BrCH=CHC7H15 as the sole product and with complete selectivity for the Z-alkene in both cases. However, the maximum conversions achieved (47 and 52%, respectively) were low.
Crystal data
|
Methyl groups were treated as rigid bodies (C—H = 0.98 Å) rotating around the C—C bonds, with a common refined Uiso value for three H atoms. Aromatic H atoms were treated as riding on the C atoms [C—H = 0.95 Å and Uiso(H) = 1.2Ueq(C)]. The five strongest maxima and minima of the final difference map are located at distances of 0.8–0.9 Å from atoms I1 and I2.
Data collection: SMART (Bruker, 2001); cell SAINT (Bruker, 2001); data reduction: SAINT; program(s) used to solve structure: SHELXTL (Bruker, 2001); program(s) used to refine structure: SHELXTL; molecular graphics: SHELXTL; software used to prepare material for publication: SHELXTL.
Supporting information
https://doi.org/10.1107/S1600536806003680/bt6812sup1.cif
contains datablocks global, II. DOI:Structure factors: contains datablock II. DOI: https://doi.org/10.1107/S1600536806003680/bt6812IIsup2.hkl
Data collection: SMART (Bruker, 2001); cell
SMART; data reduction: SAINT (Bruker, 2001); program(s) used to solve structure: SHELXTL (Bruker, 2001); program(s) used to refine structure: SHELXTL; molecular graphics: SHELXTL; software used to prepare material for publication: SHELXTL.C14H18IN2+·Br2I− | F(000) = 292 |
Mr = 627.92 | Dx = 2.254 Mg m−3 |
Triclinic, P1 | Melting point: 383(1) K |
a = 7.5777 (7) Å | Mo Kα radiation, λ = 0.71073 Å |
b = 8.2610 (7) Å | Cell parameters from 3235 reflections |
c = 8.5800 (7) Å | θ = 2.5–30.0° |
α = 99.09 (1)° | µ = 7.71 mm−1 |
β = 101.45 (1)° | T = 120 K |
γ = 114.20 (1)° | Block, orange |
V = 462.6 (1) Å3 | 0.10 × 0.08 × 0.02 mm |
Z = 1 |
Bruker SMART 6K CCD area-detector diffractometer | 2693 independent reflections |
Radiation source: fine-focus sealed tube | 2309 reflections with I > 2σ(I) |
Graphite monochromator | Rint = 0.037 |
Detector resolution: 5.6 pixels mm-1 | θmax = 30.0°, θmin = 2.5° |
ω scans | h = −10→10 |
Absorption correction: multi-scan (SADABS; Bruker, 2003) | k = −11→11 |
Tmin = 0.637, Tmax = 0.861 | l = −12→12 |
6548 measured reflections |
Refinement on F2 | Primary atom site location: structure-invariant direct methods |
Least-squares matrix: full | Secondary atom site location: difference Fourier map |
R[F2 > 2σ(F2)] = 0.031 | Hydrogen site location: inferred from neighbouring sites |
wR(F2) = 0.076 | H-atom parameters constrained |
S = 0.99 | w = 1/[σ2(Fo2) + (0.0387P)2] where P = (Fo2 + 2Fc2)/3 |
2693 reflections | (Δ/σ)max < 0.001 |
98 parameters | Δρmax = 2.54 e Å−3 |
0 restraints | Δρmin = −1.41 e Å−3 |
Experimental. The data collection nominally covered full sphere of reciprocal space, by a combination of 3 sets of ω scans; each set at different φ angles and each scan (20 s exposure) covering 0.3° in ω. Crystal to detector distance 4.85 cm. |
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. |
x | y | z | Uiso*/Ueq | ||
I1 | 0.5000 | 0.5000 | 0.5000 | 0.01576 (9) | |
I2 | 0.0000 | 0.0000 | 0.5000 | 0.01764 (9) | |
Br | −0.12080 (6) | 0.18586 (6) | 0.30774 (5) | 0.02574 (10) | |
N | 0.3548 (4) | 0.4793 (4) | 0.2315 (3) | 0.0157 (5) | |
C1 | 0.3316 (6) | 0.1696 (5) | 0.1580 (5) | 0.0237 (8) | |
H11 | 0.4749 | 0.2085 | 0.2109 | 0.028 (7)* | |
H12 | 0.2822 | 0.0684 | 0.0584 | 0.028 (7)* | |
H13 | 0.2535 | 0.1279 | 0.2347 | 0.028 (7)* | |
C2 | 0.3060 (5) | 0.3288 (5) | 0.1115 (4) | 0.0186 (7) | |
C3 | 0.2344 (5) | 0.3203 (5) | −0.0527 (4) | 0.0225 (7) | |
H3 | 0.2021 | 0.2140 | −0.1366 | 0.027* | |
C4 | 0.2092 (6) | 0.4668 (6) | −0.0944 (4) | 0.0230 (7) | |
H4 | 0.1604 | 0.4626 | −0.2066 | 0.028* | |
C5 | 0.2572 (5) | 0.6189 (5) | 0.0308 (4) | 0.0210 (7) | |
H5 | 0.2416 | 0.7207 | 0.0046 | 0.025* | |
C6 | 0.3291 (5) | 0.6239 (5) | 0.1946 (4) | 0.0173 (6) | |
C7 | 0.3721 (6) | 0.7836 (6) | 0.3326 (5) | 0.0256 (8) | |
H71 | 0.2964 | 0.7385 | 0.4099 | 0.033 (7)* | |
H72 | 0.3305 | 0.8685 | 0.2873 | 0.033 (7)* | |
H73 | 0.5173 | 0.8483 | 0.3908 | 0.033 (7)* |
U11 | U22 | U33 | U12 | U13 | U23 | |
I1 | 0.01858 (15) | 0.01675 (16) | 0.01325 (15) | 0.00838 (12) | 0.00566 (11) | 0.00521 (11) |
I2 | 0.01924 (16) | 0.02170 (17) | 0.01317 (15) | 0.01004 (13) | 0.00530 (11) | 0.00509 (12) |
Br | 0.0292 (2) | 0.0335 (2) | 0.02382 (19) | 0.01926 (17) | 0.01002 (15) | 0.01507 (16) |
N | 0.0171 (13) | 0.0173 (14) | 0.0139 (13) | 0.0083 (11) | 0.0056 (10) | 0.0051 (11) |
C1 | 0.036 (2) | 0.0186 (18) | 0.0163 (17) | 0.0139 (16) | 0.0061 (15) | 0.0035 (14) |
C2 | 0.0186 (16) | 0.0225 (18) | 0.0160 (16) | 0.0097 (14) | 0.0073 (13) | 0.0051 (13) |
C3 | 0.0237 (18) | 0.026 (2) | 0.0155 (16) | 0.0114 (15) | 0.0044 (13) | 0.0023 (14) |
C4 | 0.0255 (18) | 0.031 (2) | 0.0155 (16) | 0.0143 (16) | 0.0065 (14) | 0.0100 (15) |
C5 | 0.0235 (17) | 0.0264 (19) | 0.0196 (17) | 0.0141 (15) | 0.0087 (14) | 0.0123 (15) |
C6 | 0.0201 (16) | 0.0201 (17) | 0.0163 (16) | 0.0107 (14) | 0.0101 (13) | 0.0065 (13) |
C7 | 0.033 (2) | 0.028 (2) | 0.0201 (18) | 0.0191 (17) | 0.0072 (15) | 0.0059 (15) |
I1—Ni | 2.294 (3) | C3—C4 | 1.389 (5) |
I1—N | 2.294 (3) | C3—H3 | 0.9500 |
I2—Br | 2.6962 (4) | C4—C5 | 1.382 (5) |
I2—Brii | 2.6962 (4) | C4—H4 | 0.9500 |
N—C2 | 1.345 (5) | C5—C6 | 1.390 (5) |
N—C6 | 1.361 (4) | C5—H5 | 0.9500 |
C1—C2 | 1.507 (5) | C6—C7 | 1.500 (5) |
C1—H11 | 0.9801 | C7—H71 | 0.9800 |
C1—H12 | 0.9800 | C7—H72 | 0.9800 |
C1—H13 | 0.9800 | C7—H73 | 0.9801 |
C2—C3 | 1.385 (5) | ||
Ni—I1—N | 180.0 | C4—C3—H3 | 120.1 |
Br—I2—Brii | 179.999 (12) | C5—C4—C3 | 118.6 (3) |
C2—N—C6 | 120.8 (3) | C5—C4—H4 | 120.8 |
C2—N—I1 | 119.8 (2) | C3—C4—H4 | 120.7 |
C6—N—I1 | 119.4 (2) | C4—C5—C6 | 120.3 (3) |
C2—C1—H11 | 109.7 | C4—C5—H5 | 119.7 |
C2—C1—H12 | 109.3 | C6—C5—H5 | 120.0 |
H11—C1—H12 | 109.5 | N—C6—C5 | 119.8 (3) |
C2—C1—H13 | 109.4 | N—C6—C7 | 119.1 (3) |
H11—C1—H13 | 109.5 | C5—C6—C7 | 121.1 (3) |
H12—C1—H13 | 109.5 | C6—C7—H71 | 109.5 |
N—C2—C3 | 120.7 (3) | C6—C7—H72 | 109.4 |
N—C2—C1 | 119.0 (3) | H71—C7—H72 | 109.5 |
C3—C2—C1 | 120.3 (3) | C6—C7—H73 | 109.6 |
C2—C3—C4 | 119.9 (3) | H71—C7—H73 | 109.5 |
C2—C3—H3 | 120.0 | H72—C7—H73 | 109.5 |
Symmetry codes: (i) −x+1, −y+1, −z+1; (ii) −x, −y, −z+1. |
Acknowledgements
The authors are grateful to the EPSRC for a DTA award to SJRT and to GlaxoSmithKline Pharmaceuticals for a CASE studentship.
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