3-(4,4,5,5-Tetra­methyl-1,3,2-dioxaborolan-2-yl)aniline

Batsanov, A.S.; Giles, R.F.; Probert, M.R.; Smith, G.E.; Whiting, A.

doi:10.1107/S1600536805043151

organic compounds

CRYSTALLOGRAPHIC
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ISSN: 2056-9890

Volume 62| Part 2| February 2006| Pages o466-o468

https://doi.org/10.1107/S1600536805043151

3-(4,4,5,5-Tetramethyl-1,3,2-dioxaborolan-2-yl)aniline

Andrei S. Batsanov,^a ^* Richard F. Giles,^b Michael R. Probert,^a Gillian E. Smith ^c and Andrew Whiting ^a

^aDepartment of Chemistry, University of Durham, South Road, Durham DH1 3LE, England, ^bINRS–Énergie, Matériaux et Télécommunications, Université du Québec, Varennes, Québec, Canada J3X 1S2, and ^cGlaxoSmithKline Research and Development Ltd, Old Powder Mills, Leigh, Nr Tonbridge, Kent TN11 9AN, England
^*Correspondence e-mail: a.s.batsanov@durham.ac.uk

(Received 21 December 2005; accepted 23 December 2005; online 7 January 2006)

In the title compound, C₁₂H₁₈BNO₂, the amino group is less pyramidal than in aniline, only one of its H atoms forming a strong hydrogen bond.

Comment

In the course of our studies (Giles et al., 2003 ; Coghlan et al., 2005 ) into the potential catalytic utility of bifunctional compounds (Rowlands, 2001 ) containing both a nitrogen-based Lewis base and a boron-based Lewis acid, we turned to the title compound, (I), as a protected precursor for the synthesis of phenylguanidine-2-boronic acid derivatives, which we were interested in as bifunctional catalysts. Unfortunately, synthesis of such compounds proved unsuccessful, producing a complex mixture of products.

Compound (I) was prepared by a modified version of the procedure reported by Vogels et al. (1999 ), who synthesized it en route to various platinum complexes and imines (Vogels et al., 2001 ; King et al., 2002 ).

The asymmetric unit contains one molecule. The B atom has planar-trigonal coordination; the coordination plane is inclined by 10.4 (2)° to the benzene ring plane. The borolane ring adopts a twist conformation, the C7 and C8 atoms deviating from the BO₂ plane by 0.20 (2) and 0.27 (2) Å in opposite directions, with two equatorial (C9 and C11) and two axial (C10 and C12) methyl substituents. The amino group forms one strong intermolecular hydrogen bond (Table 2). The remaining amino hydrogen atom, H2N, points towards the pπ orbital of the benzene C4 atom of another molecule. The H2N⋯C4ⁱⁱ distance [2.61 (2) Å, corrected for the idealized N—H bond length of 1.01 Å; symmetry code: (ii) 1 − x, $[{1\over 2}]$ + y, $[{1\over 2}]$ − z], which is considerably shorter than the sum of van der Waals radii of 2.88 Å (Rowland & Taylor, 1996 ) and the N—H⋯C angle of 167 (2)° suggest that this contact is a weak hydrogen bond.

The N atom in (I) has a less pyramidal geometry than in unsubstituted aniline. The dihedral angle between the benzene ring and the NH₂ group (so-called `inversion angle'), which equals 37–38° in both solid (Fukuyo et al., 1982 ) and gaseous (Lister et al., 1974 ) aniline, is reduced to 16 (2)° in (I). The C1—N bond in (I) [1.3790 (18) Å] is shorter than in aniline [solid: 1.392 (6) Å; gas: 1.402 (2) Å]. Both differences indicate that the boryl substituent enhances the interaction of the electron lone pair of N with the aromatic ring and hence sp² hybridization of the N atom. It is noteworthy that, in the two complexes of Pd and Pt where molecule (I) acts as an N-ligand (Vogels et al., 1999), the C—N bond is lengthened to 1.438 (4) and 1.45 (1) Å, respectively, as the π-conjugation is disrupted, the lone pair being donated to the metal atom instead.

In (I), the N atom deviates by 0.081 (2) Å from the benzene ring plane, but its H atoms are situated on the other side of this plane, 0.04 (2) Å from it. A similar, but stronger, distortion is shown by the aniline molecule in its crystal structure, where the amino group both donates and accepts a hydrogen bond.

Figure 1
Molecular structure of (I)

. Atomic displacement ellipsoids are drawn at the 50% probability level.

Experimental

3-Aminophenylboronic acid (1.00 g, 6.45 mmol) and pinacol (0.763 g, 6.45 mmol) were added to ethyl acetate (150 ml). After stirring for 20 h, the solution was dried (MgSO₄), filtered and evaporated to yield a brown solid, which was dissolved in a minimal amount of ethyl acetate and absorbed on to silica gel. Purification was by silica gel chromatography (hexane/ethyl acetate, 1:1 as eluant), which gave an orange oil which crystallized on standing for 48 h to give large orange crystals of (I) [yield 1.31 g, 93%; m.p. 363 K, cf. 366 K according to Vogels et al. (1999)]. UV ∊, mol dm⁻³ cm⁻¹ (MeCN) 215 (∊ 27410), 246 (∊ 7100), 311 (∊ 2560); MS (ES+) 220.1 (M⁺ + H). Found: C 65.77, H 8.31, N 6.31%; C₁₂H₁₉BNO₂ requires: C 65.70, H 8.28, N 6.39%. All other spectroscopic and analytical details were identical to those reported by Vogels et al. (1999).

Crystal data

C₁₂H₁₈BNO₂
M_r = 219.08
Monoclinic, P 2₁ /c
a = 9.823 (1) Å
b = 10.658 (1) Å
c = 12.547 (1) Å
β = 109.10 (1)°
V = 1241.3 (2) Å³
Z = 4
D_x = 1.172 Mg m⁻³
Mo Kα radiation
Cell parameters from 2346 reflections
θ = 2.6–27.0°
μ = 0.08 mm⁻¹
T = 120 (2) K
Block, orange
0.3 × 0.3 × 0.2 mm

Data collection

Bruker SMART 6K CCD area-detector diffractometer
ω scans
Absorption correction: none
7402 measured reflections
2697 independent reflections
1905 reflections with I > 2σ(I)
R_int = 0.029
θ_max = 27.0°
h = −12 → 12
k = −13 → 11
l = −16 → 13

Refinement

Refinement on F²
R[F² > 2σ(F²)] = 0.043
wR(F²) = 0.122
S = 1.04
2697 reflections
161 parameters
H atoms treated by a mixture of independent and constrained refinement
w = 1/[σ²(F_o²) + (0.0669P)²] where P = (F_o² + 2F_c²)/3
(Δ/σ)_max < 0.001
Δρ_max = 0.25 e Å⁻³
Δρ_min = −0.20 e Å⁻³

Table 1
Selected geometric parameters (Å, °)

O1—B	1.3657 (18)
O1—C7	1.4714 (16)
O2—B	1.3712 (18)
O2—C8	1.4703 (16)
N—C1	1.3790 (18)
C3—B	1.550 (2)

C2—C1—C6	118.32 (13)
C2—C3—C4	118.19 (13)
O1—B—O2	113.35 (13)
O1—B—C3	124.76 (13)
O2—B—C3	121.89 (13)

B—O1—C7—C8	−22.51 (14)
B—O2—C8—C7	−23.98 (14)
O1—C7—C8—O2	27.80 (13)
C7—O1—B—O2	8.34 (16)
C8—O2—B—O1	11.01 (16)
C2—C3—B—O1	9.9 (2)
C4—C3—B—O2	8.3 (2)

Table 2
Hydrogen-bond geometry (Å, °)

D—H⋯A	D—H	H⋯A	D⋯A	D—H⋯A
N—H1N⋯O2ⁱ	0.92 (2)	2.20 (2)	3.0743 (17)	158.4 (16)
Symmetry code: (i) $[x, -y+{\script{1\over 2}}, z-{\script{1\over 2}}]$ .

Amino H atoms were refined in an isotropic approximation, giving N—H distances of 0.92 (2) and 0.85 (2) Å. Phenyl H atoms were treated as riding in idealized positions with C—H bond lengths of 0.95 Å and U_iso(H) = 1.2U_eq(C). Methyl groups were refined as rigid bodies rotating around the C—C bonds, with C—H bond lengths of 0.98 Å and a common refined U_iso(H) for all three H atoms of each methyl group.

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, I. DOI: https://doi.org/10.1107/S1600536805043151/rz2002sup1.cif

Structure factors: contains datablock 02srv156. DOI: https://doi.org/10.1107/S1600536805043151/rz2002Isup2.hkl

Computing details top

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.

3-(4,4,5,5-Tetramethyl-1,3,2-dioxaborolan-2-yl)aniline top

Crystal data top

C₁₂H₁₈BNO₂	F(000) = 472
M_r = 219.08	D_x = 1.172 Mg m⁻³
Monoclinic, P2₁/c	Melting point: 363 K
Hall symbol: -P 2ybc	Mo Kα radiation, λ = 0.71073 Å
a = 9.823 (1) Å	Cell parameters from 2346 reflections
b = 10.658 (1) Å	θ = 2.6–27.0°
c = 12.547 (1) Å	µ = 0.08 mm⁻¹
β = 109.10 (1)°	T = 120 K
V = 1241.3 (2) Å³	Block, orange
Z = 4	0.3 × 0.3 × 0.2 mm

Data collection top

Bruker SMART 6K CCD area-detector diffractometer	1905 reflections with I > 2σ(I)
Radiation source: fine-focus sealed tube	R_int = 0.029
Graphite monochromator	θ_max = 27.0°, θ_min = 2.2°
Detector resolution: 8 pixels mm^-1	h = −12→12
ω scans	k = −13→11
7402 measured reflections	l = −16→13
2697 independent 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)] = 0.043	Hydrogen site location: inferred from neighbouring sites
wR(F²) = 0.122	H atoms treated by a mixture of independent and constrained refinement
S = 1.04	w = 1/[σ²(F_o²) + (0.0669P)²] where P = (F_o² + 2F_c²)/3
2697 reflections	(Δ/σ)_max < 0.001
161 parameters	Δρ_max = 0.25 e Å⁻³
0 restraints	Δρ_min = −0.20 e Å⁻³

Special details top

Experimental. The data collection nominally covered over a hemisphere of reciprocal Space, by a combination of 3 sets of ω scans each set at different φ and/or 2θ angles and each scan (10 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
O1	0.15436 (10)	0.04664 (8)	0.16868 (7)	0.0263 (3)
O2	0.22355 (11)	0.03227 (9)	0.36090 (8)	0.0316 (3)
N	0.36360 (17)	0.49698 (14)	0.11742 (11)	0.0404 (4)
H1N	0.315 (2)	0.4675 (17)	0.0457 (17)	0.059 (6)*
H2N	0.420 (2)	0.5598 (18)	0.1268 (14)	0.053 (6)*
C1	0.38192 (15)	0.41584 (13)	0.20664 (11)	0.0273 (3)
C2	0.31038 (15)	0.30068 (13)	0.19234 (11)	0.0251 (3)
H2	0.2532	0.2755	0.1186	0.030*
C3	0.32043 (15)	0.22174 (13)	0.28355 (11)	0.0245 (3)
C4	0.40955 (15)	0.25901 (13)	0.39138 (11)	0.0275 (3)
H4	0.4179	0.2071	0.4548	0.033*
C5	0.48483 (16)	0.37062 (13)	0.40580 (12)	0.0297 (3)
H5	0.5474	0.3934	0.4785	0.036*
C6	0.47049 (16)	0.44930 (13)	0.31530 (12)	0.0287 (3)
H6	0.5207	0.5270	0.3268	0.034*
C7	0.06845 (15)	−0.05605 (13)	0.19253 (11)	0.0256 (3)
C8	0.15477 (16)	−0.08840 (13)	0.31807 (12)	0.0294 (3)
C9	0.06005 (18)	−0.16155 (14)	0.11008 (13)	0.0367 (4)
H91	0.0021	−0.1346	0.0341	0.047 (3)*
H92	0.0152	−0.2350	0.1317	0.047 (3)*
H93	0.1573	−0.1833	0.1109	0.047 (3)*
C10	−0.08028 (16)	−0.00340 (14)	0.17633 (13)	0.0350 (4)
H101	−0.1204	0.0320	0.1002	0.049 (3)*
H102	−0.0735	0.0627	0.2322	0.049 (3)*
H103	−0.1436	−0.0705	0.1861	0.049 (3)*
C11	0.06293 (18)	−0.12685 (15)	0.38863 (12)	0.0396 (4)
H111	0.1246	−0.1416	0.4666	0.054 (3)*
H112	0.0103	−0.2039	0.3579	0.054 (3)*
H113	−0.0058	−0.0596	0.3871	0.054 (3)*
C12	0.27576 (17)	−0.18112 (15)	0.33107 (14)	0.0414 (4)
H121	0.3375	−0.1841	0.4103	0.051 (3)*
H122	0.3332	−0.1550	0.2840	0.051 (3)*
H123	0.2353	−0.2647	0.3074	0.051 (3)*
B	0.23205 (17)	0.09875 (15)	0.26972 (13)	0.0249 (3)

Atomic displacement parameters (Å²) top

	U¹¹	U²²	U³³	U¹²	U¹³	U²³
O1	0.0288 (6)	0.0239 (5)	0.0248 (5)	−0.0048 (4)	0.0070 (4)	0.0017 (4)
O2	0.0373 (6)	0.0275 (6)	0.0252 (5)	−0.0099 (5)	0.0036 (4)	0.0013 (4)
N	0.0512 (9)	0.0350 (8)	0.0296 (7)	−0.0166 (7)	0.0057 (6)	0.0049 (6)
C1	0.0271 (8)	0.0276 (8)	0.0280 (7)	−0.0006 (6)	0.0101 (6)	0.0010 (6)
C2	0.0231 (7)	0.0265 (8)	0.0245 (7)	−0.0001 (6)	0.0062 (6)	−0.0015 (5)
C3	0.0232 (7)	0.0225 (7)	0.0277 (7)	0.0007 (6)	0.0081 (6)	−0.0012 (5)
C4	0.0294 (8)	0.0240 (8)	0.0264 (7)	0.0015 (6)	0.0055 (6)	0.0025 (6)
C5	0.0296 (8)	0.0288 (8)	0.0266 (7)	−0.0013 (6)	0.0035 (6)	−0.0034 (6)
C6	0.0290 (8)	0.0241 (8)	0.0320 (8)	−0.0057 (6)	0.0087 (6)	−0.0021 (6)
C7	0.0285 (8)	0.0219 (7)	0.0247 (7)	−0.0038 (6)	0.0067 (6)	0.0027 (5)
C8	0.0301 (8)	0.0247 (8)	0.0280 (7)	−0.0066 (6)	0.0022 (6)	0.0025 (6)
C9	0.0457 (10)	0.0310 (9)	0.0311 (8)	−0.0061 (7)	0.0092 (7)	−0.0033 (6)
C10	0.0284 (8)	0.0330 (9)	0.0400 (9)	−0.0021 (7)	0.0064 (7)	0.0070 (7)
C11	0.0448 (10)	0.0404 (10)	0.0300 (8)	−0.0143 (8)	0.0073 (7)	0.0049 (7)
C12	0.0324 (9)	0.0281 (9)	0.0522 (10)	−0.0025 (7)	−0.0018 (7)	0.0095 (7)
B	0.0244 (8)	0.0221 (8)	0.0268 (8)	0.0022 (7)	0.0066 (7)	0.0024 (6)

Geometric parameters (Å, º) top

O1—B	1.3657 (18)	C7—C9	1.5118 (19)
O1—C7	1.4714 (16)	C7—C10	1.515 (2)
O2—B	1.3712 (18)	C7—C8	1.5636 (18)
O2—C8	1.4703 (16)	C8—C12	1.513 (2)
N—C1	1.3790 (18)	C8—C11	1.513 (2)
N—H1N	0.92 (2)	C9—H91	0.9800
N—H2N	0.85 (2)	C9—H92	0.9800
C1—C2	1.3964 (19)	C9—H93	0.9800
C1—C6	1.4024 (19)	C10—H101	0.9811
C2—C3	1.3976 (19)	C10—H102	0.9811
C2—H2	0.9500	C10—H103	0.9810
C3—C4	1.4070 (19)	C11—H111	0.9800
C3—B	1.550 (2)	C11—H112	0.9800
C4—C5	1.3810 (19)	C11—H113	0.9800
C4—H4	0.9500	C12—H121	0.9809
C5—C6	1.3812 (19)	C12—H122	0.9809
C5—H5	0.9501	C12—H123	0.9808
C6—H6	0.9500

B—O1—C7	107.29 (10)	C12—C8—C11	110.97 (12)
B—O2—C8	107.05 (11)	O2—C8—C7	102.01 (10)
C1—N—H1N	117.7 (12)	C12—C8—C7	113.62 (12)
C1—N—H2N	118.3 (12)	C11—C8—C7	114.74 (12)
H1N—N—H2N	120.4 (17)	C7—C9—H91	109.4
N—C1—C2	121.36 (13)	C7—C9—H92	109.5
N—C1—C6	120.29 (14)	H91—C9—H92	109.5
C2—C1—C6	118.32 (13)	C7—C9—H93	109.5
C1—C2—C3	121.75 (13)	H91—C9—H93	109.5
C1—C2—H2	119.0	H92—C9—H93	109.5
C3—C2—H2	119.2	C7—C10—H101	109.6
C2—C3—C4	118.19 (13)	C7—C10—H102	109.5
C2—C3—B	122.04 (12)	H101—C10—H102	109.4
C4—C3—B	119.72 (12)	C7—C10—H103	109.6
C5—C4—C3	120.48 (13)	H101—C10—H103	109.4
C5—C4—H4	119.7	H102—C10—H103	109.4
C3—C4—H4	119.8	C8—C11—H111	109.6
C4—C5—C6	120.60 (13)	C8—C11—H112	109.6
C4—C5—H5	119.8	H111—C11—H112	109.5
C6—C5—H5	119.6	C8—C11—H113	109.3
C5—C6—C1	120.58 (13)	H111—C11—H113	109.5
C5—C6—H6	119.7	H112—C11—H113	109.5
C1—C6—H6	119.7	C8—C12—H121	109.5
O1—C7—C9	108.69 (11)	C8—C12—H122	109.6
O1—C7—C10	106.81 (11)	H121—C12—H122	109.4
C9—C7—C10	110.44 (13)	C8—C12—H123	109.5
O1—C7—C8	102.17 (10)	H121—C12—H123	109.4
C9—C7—C8	114.55 (12)	H122—C12—H123	109.4
C10—C7—C8	113.46 (12)	O1—B—O2	113.35 (13)
O2—C8—C12	106.33 (11)	O1—B—C3	124.76 (13)
O2—C8—C11	108.28 (12)	O2—B—C3	121.89 (13)

N—C1—C2—C3	−175.49 (14)	C9—C7—C8—O2	145.12 (12)
C6—C1—C2—C3	2.7 (2)	C10—C7—C8—O2	−86.79 (13)
C1—C2—C3—C4	−2.2 (2)	O1—C7—C8—C12	−86.21 (13)
C1—C2—C3—B	175.13 (13)	C9—C7—C8—C12	31.12 (17)
C2—C3—C4—C5	−0.1 (2)	C10—C7—C8—C12	159.20 (12)
B—C3—C4—C5	−177.57 (13)	O1—C7—C8—C11	144.62 (12)
C3—C4—C5—C6	2.0 (2)	C9—C7—C8—C11	−98.05 (16)
C4—C5—C6—C1	−1.6 (2)	C10—C7—C8—C11	30.03 (18)
N—C1—C6—C5	177.44 (15)	C7—O1—B—O2	8.34 (16)
C2—C1—C6—C5	−0.8 (2)	C7—O1—B—C3	−170.73 (13)
B—O1—C7—C9	−143.96 (13)	C8—O2—B—O1	11.01 (16)
B—O1—C7—C10	96.87 (13)	C8—O2—B—C3	−169.88 (13)
B—O1—C7—C8	−22.51 (14)	C2—C3—B—O1	9.9 (2)
B—O2—C8—C12	95.31 (13)	C4—C3—B—O1	−172.73 (13)
B—O2—C8—C11	−145.38 (13)	C2—C3—B—O2	−169.06 (13)
B—O2—C8—C7	−23.98 (14)	C4—C3—B—O2	8.3 (2)
O1—C7—C8—O2	27.80 (13)

Hydrogen-bond geometry (Å, º) top

D—H···A	D—H	H···A	D···A	D—H···A
N—H1N···O2ⁱ	0.92 (2)	2.20 (2)	3.0743 (17)	158.4 (16)

Symmetry code: (i) x, −y+1/2, z−1/2.

Acknowledgements

We thank the EPSRC for a DTA studentship (for RG), GlaxoSmithKline for CASE funding (RG) and the EPSRC National Mass Spectroscopy Service Centre at Swansea.

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