2,4,6-Tris­(4-fluoro­phen­yl)-2-(1-pyrid­yl)-boroxine

Wayne H Pearson; Shirley Lin; Peter M Iovine

doi:10.1107/S1600536807064367

. 2007 Dec 12;64(Pt 1):o235. doi: 10.1107/S1600536807064367

2,4,6-Tris(4-fluorophenyl)-2-(1-pyridyl)-boroxine

Wayne H Pearson ^a,^*, Shirley Lin ^a, Peter M Iovine ^b

PMCID: PMC2915295 PMID: 21200802

Abstract

Crystals of the title compound, C₂₃H₁₇B₃F₃NO₃, were obtained unintentionally by slow evaporation of a chloroform solution of the preformed boroxine–pyridine adduct. The molecule contains three fluoro-substituted benzene rings, each bonded to one of the three B atoms of a six-membered boroxine ring. A pyridyl ring is also bound to one of the B atoms through a Lewis acid–base interaction. The binding of the pyridyl substituent causes the otherwise planar boroxine ring to twist, resulting in a maximum torsion angle within the ring of 17.6 (2)°.

Related literature

For related literature, see: Beckett et al. (1997 ▶, 1998 ▶); Beckmann et al. (2001 ▶); Frost et al. (2006 ▶); Hall (2005 ▶); Iovine et al. (2006 ▶); Kua et al. (2006 ▶); Perttu et al. (2005 ▶); Sánchez et al. (2004 ▶); Wu et al. (1999 ▶).

Experimental

Crystal data

C₂₃H₁₇B₃F₃NO₃
M _r = 444.81
Monoclinic,
a = 11.6333 (5) Å
b = 14.0230 (7) Å
c = 14.1181 (7) Å
β = 109.337 (3)°
V = 2173.21 (18) Å³
Z = 4
Cu Kα radiation
μ = 0.88 mm⁻¹
T = 173 (1) K
0.21 × 0.17 × 0.09 mm

Data collection

Bruker Kappa APEXII diffractometer
Absorption correction: multi-scan (SADABS; Bruker, 2007 ▶) T _min = 0.627, T _max = 0.925
14062 measured reflections
3644 independent reflections
2938 reflections with I > 2σ(I)
R _int = 0.034

Refinement

R[F ² > 2σ(F ²)] = 0.038
wR(F ²) = 0.103
S = 1.05
3644 reflections
298 parameters
H-atom parameters constrained
Δρ_max = 0.21 e Å⁻³
Δρ_min = −0.18 e Å⁻³

Data collection: APEX2 (Bruker, 2007 ▶); cell refinement: APEX2; data reduction: APEX2; program(s) used to solve structure: SHELXTL (Bruker, 1997 ▶); program(s) used to refine structure: SHELXTL; molecular graphics: SHELXTL; software used to prepare material for publication: SHELXTL.

Supplementary Material

Crystal structure: contains datablocks I, global. DOI: 10.1107/S1600536807064367/ln2002sup1.cif

e-64-0o235-sup1.cif^{(21.6KB, cif)}

Structure factors: contains datablocks I. DOI: 10.1107/S1600536807064367/ln2002Isup2.hkl

e-64-0o235-Isup2.hkl^{(178.7KB, hkl)}

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

Table 1. Selected torsion angles (°).

B3—O3—B1—O1	6.2 (2)
B3—O3—B1—C1	−172.23 (14)
B2—O1—B1—O3	4.7 (2)
B3—O2—B2—O1	−8.1 (2)
B1—O1—B2—O2	−3.7 (2)
B1—O3—B3—O2	−16.6 (2)
B2—O2—B3—O3	17.6 (2)

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Acknowledgments

This research was supported by Cottrell College Science Awards from Research Corporation (to SL and PMI).

supplementary crystallographic information

Comment

Boroxines are cyclic trimers of organoboronic acids produced by dehydration of the acids (Hall, 2005). Arylboroxines have recently found applications in the areas of covalent organic frameworks, nanoscale molecular scaffolds, and noncovalent polymer functionalization (Iovine et al., 2006). The Lewis acidic boroxines are known to form 1:1 adducts with a variety of nitrogenous Lewis bases such as amines, pyridines, azaindoles, and salen-type ligands (Kua et al., 2006).

The structure of the title molecule (Fig. 1) contains features that are consistent with similar boroxine compounds (Beckett et al., 1997, 1998; Beckmann et al., 2001; Frost et al., 2006; Sánchez et al., 2004; Wu et al., 1999). Two of the boron atoms, B1 and B2, are centered in a trigonal planar geometry, while B3 is part of a tetrahedral geometry. The boron-oxygen bonds involving B3 are elongated, by just over 0.10 Å, compared to the other boron-oxygen bonds. As expected, the boron-carbon bonds involving the sp² hybridized B1 and B2 are shorter than the B3—C13 bond involving the sp³ hybridized boron atom. The four-coordinate bonding of B3 causes considerable distortion in the boroxine ring. Torsion angles involving B3 average 12.1 (2)° while the torsion angles that do not contain B3 average 4.2 (2)°. The approximate Td symmetry of the molecule results in a rather open packing arrangement, as seen by viewing down the unit cell a axis (Fig. 2).

Experimental

The title compound was synthesized by stirring 4-fluorophenylboronic acid with pyridine in CH₂Cl₂ in the presence of activated 4 Å molecular sieves. After decanting the reaction solution away from the sieves, the solvent was removed in vacuo and the resulting solid was dried at 323 K at atmospheric pressure (Perttu et al., 2005). Crystals of the title compound were obtained unintentionally by slow evaporation of a chloroform solution of the pre-formed boroxine:pyridine adduct (m.p. 513 decomp.).