2,4-Difluoro­phenyl­boronic acid

Patricia Rodríguez-Cuamatzi; Hugo Tlahuext; Herbert Höpfl

doi:10.1107/S1600536808040646

. 2008 Dec 10;65(Pt 1):o44–o45. doi: 10.1107/S1600536808040646

2,4-Difluorophenylboronic acid

Patricia Rodríguez-Cuamatzi ^a, Hugo Tlahuext ^b, Herbert Höpfl ^b,^*

PMCID: PMC2967960 PMID: 21581686

Abstract

The molecular structure of the title compound, C₆H₅BF₂O₂, is essentially planar (mean deviation = 0.019 Å), indicating electronic delocalization between the dihydroxyboryl group and the aromatic ring. In the crystal structure, inversion dimers linked by two O—H⋯O hydrogen bonds arise. An intramolecular O—H⋯F hydrogen bond reinforces the conformation and the same H atom is also involved in an intermolecular O—H⋯F link, leading to molecular sheets in the crystal.

Related literature

For general backround to boronic acids, see: Hall (2005 ▶); Höpfl (2002 ▶); Fujita et al. (2008 ▶); Soloway et al. (1998 ▶). For hydrogen-bond motifs, see: Bernstein et al. (1995 ▶); Desiraju (2002 ▶). For related structures, see: Wu et al. (2006 ▶); Bradley et al. (1996 ▶); Horton et al. (2004 ▶). For crystal engineering, see: Fournier et al. (2003 ▶); Rodríguez-Cuamatzi et al. (2004 ▶, 2005 ▶).

Experimental

Crystal data

C₆H₅BF₂O₂
M _r = 157.91
Monoclinic,
a = 3.7617 (11) Å
b = 12.347 (4) Å
c = 14.620 (4) Å
β = 95.450 (5)°
V = 676.0 (3) Å³
Z = 4
Mo Kα radiation
μ = 0.15 mm⁻¹
T = 293 (2) K
0.37 × 0.35 × 0.22 mm

Data collection

Bruker SMART APEX CCD area-detector diffractometer
Absorption correction: multi-scan (SADABS; Sheldrick, 1996 ▶) T _min = 0.947, T _max = 0.968
3196 measured reflections
1190 independent reflections
1012 reflections with I > 2σ(I)
R _int = 0.028

Refinement

R[F ² > 2σ(F ²)] = 0.056
wR(F ²) = 0.127
S = 1.15
1190 reflections
106 parameters
2 restraints
H atoms treated by a mixture of independent and constrained refinement
Δρ_max = 0.14 e Å⁻³
Δρ_min = −0.18 e Å⁻³

Data collection: SMART (Bruker, 2000 ▶); cell refinement: SAINT-Plus-NT (Bruker, 2001 ▶); data reduction: SAINT-Plus-NT; program(s) used to solve structure: SHELXTL-NT (Sheldrick, 2008 ▶); program(s) used to refine structure: SHELXTL-NT; molecular graphics: CAMERON (Watkin et al., 1996 ▶); software used to prepare material for publication: PLATON (Spek, 2003 ▶) and publCIF (Westrip, 2009 ▶).

Supplementary Material

Crystal structure: contains datablocks I, global. DOI: 10.1107/S1600536808040646/hb2865sup1.cif

e-65-00o44-sup1.cif^{(14.2KB, cif)}

Structure factors: contains datablocks I. DOI: 10.1107/S1600536808040646/hb2865Isup2.hkl

e-65-00o44-Isup2.hkl^{(58.9KB, hkl)}

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

Table 1. Hydrogen-bond geometry (Å, °).

D—H⋯A	D—H	H⋯A	D⋯A	D—H⋯A
O1—H1⋯F1	0.841 (15)	2.16 (3)	2.799 (3)	133 (2)
O1—H1⋯F2ⁱ	0.841 (15)	2.39 (2)	3.086 (3)	140 (3)
O2—H2⋯O1ⁱⁱ	0.841 (19)	1.97 (2)	2.809 (3)	174 (3)

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Symmetry codes: (i) Inline graphic ; (ii) .

Acknowledgments

This work was supported by Consejo Nacional de Ciencia y Tecnología (CIAM-59213 for HH).

supplementary crystallographic information

Comment

Boronic acids, RB(OH)₂ with R = alkyl and aryl, have applications in organic synthesis (Hall, 2005), host–guest chemistry (Höpfl, 2002), the molecular recognition of biochemically active molecules (Fujita et al., 2008) and in medicine as antibiotics, inhibitors and for the treatment of tumors (Soloway et al., 1998). Similar to carboxylic acids they are capable to form hydrogen-bonded dimeric units and, therefore, boronic acids have been used recently as new building blocks in crystal engineering (Fournier et al., 2003; Rodríguez-Cuamatzi et al., 2004; Rodríguez-Cuamatzi et al., 2005). Previously, the structures of 3-fluorophenylboronic acid (Wu et al., 2006), 2,6-difluoroboronic acid (Bradley et al., 1996) and pentafluoroboronic acid (Horton et al., 2004) had been reported. We now present the crystal structure of (I).

The molecular structure is essentially planar, O1—B1—C1—C2 = 4.4 (4)°, indicating that there is a π···π interaction between the dihydroxyboryl group and the aromatic ring, to which it is attached (Fig. 1). This interaction is also evidenced by the B—C bond length of 1.566 (3) Å, which is significantly shorter than that observed in boronates containing tetra-coordinate boron atoms (Höpfl, 2002). The crystal structure is stabilized by strong O2—H2···O1 hydrogen-bonding interactions, forming R₂²(8) motifs (Bernstein et al., 1995), as well as, O1—H1···F1 and O1—H1···F2 bifurcated hydrogen bonds (Fig. 2; Table 1) (Desiraju, 2002). Due to these interactions each boronic acid homodimer is linked to two neighboring homodimeric units, thus creating a two-dimensional hydrogen-bonded network, in which fluorine is therefore an essential structural component.

Experimental

2,4-Difluorophenylboronic acid was purchased from Aldrich and crystallized from water to yield colourless blocks of (I).