2,3-Difluoro-4-formyl­phenyl­boronic acid

The mol­ecule of the title compound, 2,3-F₂-4-(CHO)C₆H₂B(OH)₂ or C₇H₅BF₂O₃, contains a formyl group coplanar with the benzene ring. The boronic acid group is twisted with respect to the benzene ring plane. The mol­ecules are organized into infinite chains via inter­molecular O—H...O hydrogen bonds. These chains are additionally connected via strong O—H...O hydrogen bonds, producing a folded layer structure perpendicular to the a axis. These layers are paired due to B...F inter­actions.

S1. Comment

Arylboronic acids containing a carbonyl group are valuable starting materials in organic synthesis. The high reactivity of this group enables modification of the structure of boronic acids to obtain a wide range of compounds possessing interesting properties. Recently, the synthesis of (N-alkyl)aminomethylphenylboronic acids via reductive amination of formylphenylboronic acids was published (Gravel et al., 2002). The formation of arylboronic acids containing a chalcone moiety in an aldol-type reaction between 4-acetylphenylboronic acids and aldehydes is also known (DiCesare & Lakowicz, 2002). The products obtained have found applications as potential saccharide (Wang et al., 2002) and hormone receptors (Secor & Glass, 2004) or as reagents in Suzuki coupling (Miyaura & Suzuki, 1995). The determination of the crystal structures of boronic acids can be helpful in the elucidation of the influence of hydrogen-bond formation on the activity of these compounds as potential pharmaceutical agents (Yang et al., 2003). Against this background, we present here the crystal structure of the title compound, (I).

The molecular structure of (I) is presented in Fig. 1, with selected geometry details in Table 1. The formyl group is essentially coplanar with the benzene ring [torsion angle C5—C4—C7—O3 - 0.7 (2)°] and the boronic acid group is twisted around the C—B bond [torsion angle C2—C1—B2—O2 18.2 (2)°], thus producing a non-planar six-membered ring. The boronic acid group has an exo–endo conformation. The endo-oriented OH group is engaged in a relatively weak intramolecular O—H···F interaction with atom F1,

The supramolecular assembly in (I) (Fig. 2) is primarily achieved due to O—H···O intermolecular hydrogen-bonding interactions (Table 2), of which there are two types. The exo-oriented OH group is the H-atom donor engaged in the nearly linear hydrogen bond with the O atom from the formyl group of an adjacent molecule. As a result, the molecules are connected in a `head-to-tail' fashion to form an infinite chain aligned along the crystallographic b axis. The exo –H group acts simultaneously as the H-atom acceptor for the endo OH group of another molecule; this hydrogen bond is weaker, but it seems to be responsible for the twisting of the boronic acid group. Thus,the hydrogen-bonded network in (I) can be described as a folded layer. It should be noted that a similar structure was reported for the related 4-formylphenylboronic acid (Fronczek et al., 2001), whereas molecules of the isomeric 3-formyl- (Zarychta et al., 2004) and 2-formylphenylboronic acids (Scouten et al., 1994) form centrosymmetric dimers via intermolecular hydrogen bonds between boronic acid groups.

Examination of the crystal packing in (I) reveals that layers are paired due to weak interactions of their `fluorinated' sides. These interactions are represented by relatively short B2···F2ⁱⁱⁱ distances of 3.301 (2) Å, [symmetry code: -x, 1 - y, 2 - z], presumably the result of electrostatic attractive forces between B and F atoms, producing centrosymmetric dimeric motifs. According to Batsanov (2000), the sum of the van der Waals radii for B and F is 3.51 Å.

In conclusion, the supramolecular structure of (I) is achieved via two types of intermolecular hydrogen bonds to form a folded layer structure. In addition, the layers are paired due to B···F interactions.

Related literature

For related literature, see: Batsanov (2000); DiCesare & Lakowicz (2002); Fronczek et al. (2001); Gravel et al. (2002); Miyaura & Suzuki (1995); Scouten et al. (1994); Secor & Glass (2004); Wang et al. (2002); Yang et al. (2003); Zarychta et al. (2004).

S2. Experimental

2,3-Difluoro-4-formylphenylboronic acid was received from Aldrich, crystallized from tetrahydrofuran and dried in air.

S3. Refinement

All H atoms were located geometrically and their positions were refined, while their displacement parameters were not. The refined C—H distances are in the range 0.949–1.061 (16) Å. U_iso(H) values were fixed at 0.040 (aromatic C—H) and 0.057 Ų (hydroxy O—H).

Computing details

Data collection: CrysAlis CCD (Oxford Diffraction, 2005); cell refinement: CrysAlis RED (Oxford Diffraction, 2005); data reduction: CrysAlis RED; program(s) used to solve structure: SHELXS97 (Sheldrick, 1997); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: DIAMOND (Brandenburg, 1999); software used to prepare material for publication: SHELXTL (Sheldrick, 1990).

Figures

	Fig. 1. The molecular structure of (I), showing the atom-labelling scheme. Displacement ellipsoids are drawn at the 50% probability level and H atoms are shown as small spheres of arbitrary radii.
	Fig. 2. The hydrogen-bonding pattern for (I). Hydrogen bonds are shown as dashed lines.
	Fig. 3. The crystal packing for (I), showing the B···F interactions as dotted lines.

2,3-Difluoro-4-formylphenylboronic acid

Crystal data

C7H5BF2O3	Z = 4
Mr = 185.92	F(000) = 376
Monoclinic, P21/c	Dx = 1.618 Mg m^−3
a = 7.9154 (12) Å	Mo Kα radiation, λ = 0.71073 Å
b = 9.8527 (15) Å	µ = 0.15 mm^−1
c = 9.8141 (13) Å	T = 293 K
β = 94.198 (12)°	Prismatic, colourless
V = 763.33 (19) Å^3	0.74 × 0.21 × 0.17 mm

Data collection

Kuma KM-4 CCD area-detector diffractometer	1827 independent reflections
Radiation source: fine-focus sealed tube	1135 reflections with I > 2σ(I)
Graphite monochromator	Rint = 0.014
Detector resolution: 8.6479 pixels mm^-1	θmax = 28.6°, θmin = 2.9°
ω scans	h = −9→10
Absorption correction: multi-scan (CrysAlis RED; Oxford Diffraction, 2005)	k = −13→13
Tmin = 0.92, Tmax = 0.97	l = −12→13
7011 measured reflections

Refinement

Refinement on F^2	Primary atom site location: structure-invariant direct methods
Least-squares matrix: full	Secondary atom site location: difference Fourier map
R[F^2 > 2σ(F^2)] = 0.039	Hydrogen site location: inferred from neighbouring sites
wR(F^2) = 0.109	Only H-atom coordinates refined
S = 0.90	w = 1/[σ^2(Fo^2) + (0.0733P)^2] where P = (Fo^2 + 2Fc^2)/3
1827 reflections	(Δ/σ)max < 0.001
133 parameters	Δρmax = 0.25 e Å^−3
0 restraints	Δρmin = −0.26 e Å^−3

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 (Ų)

	x	y	z	Uiso*/Ueq
F1	0.08133 (11)	0.44514 (8)	0.81222 (8)	0.0451 (3)
F2	0.08435 (11)	0.71320 (8)	0.81950 (9)	0.0506 (3)
O1	0.31103 (16)	0.20733 (10)	1.13513 (10)	0.0479 (3)
O2	0.22559 (18)	0.18922 (11)	0.90638 (12)	0.0668 (4)
O3	0.33564 (16)	0.92918 (9)	1.11936 (12)	0.0549 (3)
C1	0.25962 (17)	0.42850 (12)	1.01712 (14)	0.0300 (3)
C2	0.17349 (16)	0.50549 (13)	0.91650 (12)	0.0310 (3)
C3	0.17390 (16)	0.64581 (13)	0.91945 (13)	0.0329 (3)
C4	0.26279 (17)	0.71563 (13)	1.02367 (14)	0.0335 (3)
C5	0.35048 (18)	0.64050 (13)	1.12635 (14)	0.0348 (3)
C6	0.34761 (17)	0.50024 (13)	1.12289 (14)	0.0334 (3)
C7	0.2625 (2)	0.86563 (15)	1.02785 (17)	0.0443 (4)
B2	0.2637 (2)	0.26766 (15)	1.01568 (15)	0.0335 (4)
H5	0.4161 (18)	0.6860 (15)	1.1971 (15)	0.040*
H6	0.4079 (18)	0.4511 (15)	1.1891 (16)	0.040*
H7	0.1997 (18)	0.9145 (14)	0.9421 (16)	0.040*
H1	0.311 (2)	0.1237 (19)	1.1298 (17)	0.057*
H2	0.215 (2)	0.2272 (17)	0.8339 (18)	0.057*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
F1	0.0570 (6)	0.0356 (5)	0.0403 (5)	−0.0017 (4)	−0.0131 (4)	−0.0057 (3)
F2	0.0645 (6)	0.0352 (5)	0.0494 (5)	0.0096 (4)	−0.0154 (4)	0.0079 (4)
O1	0.0870 (8)	0.0191 (5)	0.0360 (6)	−0.0005 (5)	−0.0066 (5)	0.0002 (4)
O2	0.1323 (12)	0.0271 (6)	0.0373 (7)	0.0051 (6)	−0.0199 (7)	−0.0028 (5)
O3	0.0816 (9)	0.0250 (5)	0.0562 (7)	−0.0026 (5)	−0.0075 (6)	−0.0034 (5)
C1	0.0366 (7)	0.0232 (6)	0.0306 (7)	0.0000 (5)	0.0048 (6)	0.0004 (5)
C2	0.0355 (8)	0.0281 (7)	0.0291 (7)	−0.0009 (5)	0.0003 (6)	−0.0024 (5)
C3	0.0388 (8)	0.0271 (7)	0.0323 (7)	0.0049 (6)	−0.0014 (6)	0.0048 (6)
C4	0.0420 (8)	0.0231 (7)	0.0357 (7)	0.0009 (5)	0.0049 (6)	0.0001 (6)
C5	0.0435 (8)	0.0261 (7)	0.0340 (8)	−0.0025 (6)	−0.0021 (6)	−0.0032 (6)
C6	0.0430 (8)	0.0259 (7)	0.0304 (7)	0.0018 (6)	−0.0025 (6)	0.0017 (5)
C7	0.0610 (10)	0.0254 (7)	0.0459 (9)	0.0013 (7)	0.0000 (8)	0.0016 (7)
B2	0.0428 (9)	0.0241 (7)	0.0333 (8)	−0.0007 (6)	0.0017 (6)	−0.0011 (6)

Geometric parameters (Å, º)

F1—C2	1.3505 (14)	C1—B2	1.5851 (19)
F2—C3	1.3431 (15)	C2—C3	1.3828 (19)
O1—B2	1.3430 (18)	C3—C4	1.3817 (19)
O1—H1	0.826 (19)	C4—C5	1.3939 (19)
O2—B2	1.3385 (18)	C4—C7	1.4785 (19)
O2—H2	0.803 (18)	C5—C6	1.3825 (19)
O3—C7	1.2073 (19)	C5—H5	0.949 (16)
C1—C2	1.3845 (18)	C6—H6	0.916 (16)
C1—C6	1.3987 (19)	C7—H7	1.061 (16)
B2—O1—H1	112.8 (12)	C5—C4—C7	120.83 (13)
B2—O2—H2	116.4 (12)	C6—C5—C4	120.44 (13)
C2—C1—C6	116.42 (12)	C6—C5—H5	119.8 (9)
C2—C1—B2	123.41 (12)	C4—C5—H5	119.7 (9)
C6—C1—B2	120.17 (12)	C5—C6—C1	121.99 (13)
F1—C2—C3	117.15 (11)	C5—C6—H6	120.3 (9)
F1—C2—C1	120.65 (12)	C1—C6—H6	117.7 (9)
C3—C2—C1	122.18 (12)	O3—C7—C4	122.51 (14)
F2—C3—C4	120.49 (12)	O3—C7—H7	121.7 (8)
F2—C3—C2	118.60 (11)	C4—C7—H7	115.7 (8)
C4—C3—C2	120.90 (12)	O2—B2—O1	118.43 (13)
C3—C4—C5	118.06 (12)	O1—B2—C1	116.06 (12)
C3—C4—C7	121.10 (13)	O2—B2—C1	125.51 (13)
C6—C1—C2—F1	−178.26 (11)	C3—C4—C5—C6	−0.01 (19)
B2—C1—C2—F1	2.50 (19)	C7—C4—C5—C6	178.86 (12)
C6—C1—C2—C3	0.09 (19)	C4—C5—C6—C1	0.7 (2)
B2—C1—C2—C3	−179.15 (12)	C2—C1—C6—C5	−0.76 (19)
F1—C2—C3—F2	−0.25 (17)	B2—C1—C6—C5	178.51 (12)
C1—C2—C3—F2	−178.64 (11)	C3—C4—C7—O3	178.17 (14)
F1—C2—C3—C4	179.02 (12)	C5—C4—C7—O3	−0.7 (2)
C1—C2—C3—C4	0.62 (19)	C2—C1—B2—O2	18.2 (2)
F2—C3—C4—C5	178.60 (11)	C6—C1—B2—O2	−160.99 (14)
C2—C3—C4—C5	−0.65 (19)	C2—C1—B2—O1	−162.35 (13)
F2—C3—C4—C7	−0.3 (2)	C6—C1—B2—O1	18.4 (2)
C2—C3—C4—C7	−179.52 (12)

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
O1—H1···O3^i	0.826 (19)	1.929 (19)	2.7526 (14)	174.3 (16)
O2—H2···O1^ii	0.803 (18)	2.242 (17)	2.9744 (17)	152.0 (16)
O2—H2···F1	0.803 (18)	2.395 (17)	2.8917 (14)	121.1 (14)

Symmetry codes: (i) x, y−1, z; (ii) x, −y+1/2, z−1/2.