Bis(2,6-dimethyl­pyrid­yl)iodonium dibromo­iodate

Batsanov, A.S.; Lightfoot, A.P.; Twiddle, S.J.R.; Whiting, A.

doi:10.1107/S1600536806003680

organic compounds

CRYSTALLOGRAPHIC
COMMUNICATIONS

ISSN: 2056-9890

Volume 62| Part 3| March 2006| Pages o901-o902

https://doi.org/10.1107/S1600536806003680

Bis(2,6-dimethylpyridyl)iodonium dibromoiodate

Andrei S. Batsanov,^a Andrew P. Lightfoot,^b Steven J. R. Twiddle ^a and Andrew Whiting ^a ^*

^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

(Received 27 January 2006; accepted 30 January 2006; online 3 February 2006)

The crystal structure of the title compound, C₁₄H₁₈IN₂⁺·Br₂I⁻, isostructural with the Cl₂I analogue, comprises discrete centrosymmetric cations and anions, both with linear coordination of the I atoms.

Comment

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 chemoselectivity 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 crystal structure 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 ).

Figure 1
The cation and anion in (II)

. Atomic displacement ellipsoids are drawn at the 50% probability level. Br′ is generated by the symmetry operator (−x, −y, 1 − z), and the other primed atoms are generated by the symmetry operator (1 − x, 1 − y, 1 − z).

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 ν_max, 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

C₁₄H₁₈IN₂⁺·Br₂I⁻
M_r = 627.92
Triclinic, $[P \overline 1]$
a = 7.5777 (7) Å
b = 8.2610 (7) Å
c = 8.5800 (7) Å
α = 99.09 (1)°
β = 101.45 (1)°
γ = 114.20 (1)°
V = 462.6 (1) Å³
Z = 1
D_x = 2.254 Mg m⁻³
Mo Kα radiation
Cell parameters from 3235 reflections
θ = 2.5–30.0°
μ = 7.71 mm⁻¹
T = 120 (2) K
Block, orange
0.10 × 0.08 × 0.02 mm

Data collection

Bruker SMART 6K CCD area-detector diffractometer
ω scans
Absorption correction: multi-scan(SADABS; Bruker, 2003 )T_min = 0.637, T_max = 0.861
6548 measured reflections
2693 independent reflections
2309 reflections with I > 2σ(I)
R_int = 0.037
θ_max = 30.0°
h = −10 → 10
k = −11 → 11
l = −12 → 12

Refinement

Refinement on F²
R[F² > 2σ(F²)] = 0.031
wR(F²) = 0.076
S = 0.99
2693 reflections
98 parameters
H-atom parameters constrained
w = 1/[σ²(F_o²) + (0.0387P)²] where P = (F_o² + 2F_c²)/3
(Δ/σ)_max < 0.001
Δρ_max = 2.54 e Å⁻³
Δρ_min = −1.41 e Å⁻³

Methyl groups were treated as rigid bodies (C—H = 0.98 Å) rotating around the C—C bonds, with a common refined U_iso value for three H atoms. Aromatic H atoms were treated as riding on the C atoms [C—H = 0.95 Å and U_iso(H) = 1.2U_eq(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 refinement: 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

Crystal structure: contains datablocks global, II. DOI: https://doi.org/10.1107/S1600536806003680/bt6812sup1.cif

Structure factors: contains datablock II. DOI: https://doi.org/10.1107/S1600536806003680/bt6812IIsup2.hkl

Computing details top

Data collection: SMART (Bruker, 2001); cell refinement: 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.

Bis(2,6-dimethylpyridyl)iodinium dibromoiodate top

Crystal data top

C₁₄H₁₈IN₂⁺·Br₂I⁻	F(000) = 292
M_r = 627.92	D_x = 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

Data collection top

Bruker SMART 6K CCD area-detector diffractometer	2693 independent reflections
Radiation source: fine-focus sealed tube	2309 reflections with I > 2σ(I)
Graphite monochromator	R_int = 0.037
Detector resolution: 5.6 pixels mm^-1	θ_max = 30.0°, θ_min = 2.5°
ω scans	h = −10→10
Absorption correction: multi-scan (SADABS; Bruker, 2003)	k = −11→11
T_min = 0.637, T_max = 0.861	l = −12→12
6548 measured reflections

Refinement top

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(F_o²) + (0.0387P)²] where P = (F_o² + 2F_c²)/3
2693 reflections	(Δ/σ)_max < 0.001
98 parameters	Δρ_max = 2.54 e Å⁻³
0 restraints	Δρ_min = −1.41 e Å⁻³

Special details top

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.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å²) top

	x	y	z	U_iso*/U_eq
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)*

Atomic displacement parameters (Å²) top

	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)

Geometric parameters (Å, º) top

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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