Penta­fluoro­phenyl­boronic acid

Horton, P.N.; Hursthouse, M.B.; Beckett, M.A.; Rugen-Hankey, M.P.

doi:10.1107/S1600536804022408

organic compounds

CRYSTALLOGRAPHIC
COMMUNICATIONS

ISSN: 2056-9890

Volume 60| Part 12| December 2004| Pages o2204-o2206

https://doi.org/10.1107/S1600536804022408

Pentafluorophenylboronic acid

Peter N. Horton,^a ^* Michael B. Hursthouse,^a Michael A. Beckett ^b and Martin P. Rugen-Hankey ^b

^aSchool of Chemistry, University of Southampton, Highfield, Southampton, SO17 1BJ, England, and ^bChemistry Department, University of Wales, Bangor, LL57 2UW, Wales
^*Correspondence e-mail: pnh@soton.ac.uk

(Received 5 August 2004; accepted 9 September 2004; online 6 November 2004)

Crystals of the title compound, C₆F₅B(OH)₂, were obtained from an attempted recrystallization of (C₆F₅)₃B₃O₃·Et₃PO from THF/hexane solution. The central B atom of the boronic acid has a trigonal planar configuration with two hydroxyl groups and one pentafluorphenyl substituent.

Comment

There has been much recent interest in the chemistry of perfluoroarylboron compounds owing to their use as Lewis acid catalysts in organic transformations (Piers & Chivers, 1997 ; Ishihara & Yamamoto, 1999 ). We have recently explored the chemistry of phosphoryl donors towards B(C₆F₅)₃ (Beckett et al., 2000 , 2001 ) and are now examining the related boroxine, (C₆F₅)₃B₃O₃. The adduct (C₆F₅)₃B₃O₃·Et₃PO, (1), is readily obtained from the stoichiometric reaction of Et₃PO with (C₆F₅)₃B₃O₃ in THF solution. Compound (1), a colourless solid which gave satisfactory elemental analysis data, was characterized by IR and NMR spectroscopy. The strongly Lewis acidic nature of (C₆F₅)₃B₃O₃ is reflected in the ³¹P chemical shift of (1), which is considerably downfield of that of free Et₃PO (Mayer et al., 1975 ). An attempted recrystallization of (1), by slow diffusion of hexane into a THF solution of the compound, afforded crystals of the title compound (C₆F₅)B(OH)₂, (2). Presumably, (2) arose as a consequence of hydrolysis of (1), caused by H₂O in our recrystallization solvents. Compound (2) is well documented in the literature (Chambers & Chivers, 1965 ; Frohn et al., 2002 ), but its crystal and molecular structure has not been previously reported.

Crystallographic studies on compounds which contain a similar (C₆F₅)BO₂ motif are limited to the cyclic pentafluorophenylboronic acid ester of 2,3-dihydroxynaphthalene, (C₆F₅)BO₂C₁₀H₆ (Vagedes et al., 1999 ) and the metallocycle [ZrCp₂{μ-O₂B(C₆F₅)}]₂ (Balkwill et al., 2002 ). The motif also appears in the borate anion of the salt [CpNi(C₆H₆)NiCp][B₃O₃(C₆F₅)₅] (Priego et al., 2000 ), in which there are B atoms with both trigonal and tetrahedral geometry. The cyclic trimeric borinic acid derivative [{(C₆F₅)₂B(OH)}₃] contains the C₆F₅BO₂ motif with tetrahedral boron (Beringhelli et al., 2003 ).

B and C atoms are essentially trigonal planar and most of the B—O, B—C, and C—F bond lengths are unremarkable, with structural data for the C₆F₅BO₂ motif similar to those previously reported. Bond angles at B and C are consistent with sp² hybridization but with significant deviations from the expected 120° angles occurring in close proximity to the B(OH)₂ substituent on C1. Thus the angles C6—C1—C2 [115.31 (16)°], F1—C2—C3 [116.81 (17)°] and F5—C6—C5 [117.20 (16)°] are significantly smaller than the other C—C—C and C—C—F angles respectively. The B(OH)₂ group is twisted by 38.14 (15)° relative to the C₆F₅ group. The B—O distances are equivalent and average 1.359 Å, consistent with relatively strong π-interactions and a bond order >1 (Beckett et al., 1996 ). Conversely, the C1—B1 bond length [1.579 (3) Å] is slightly greater than that typically found in boroxines e.g. (4-MeC₆H₄)₃B₃O₃, 1.543 (4) Å (Beckett et al., 1996), indicating a weakening of this bond by the electron-withdrawing C₆F₅ group. The H atoms were located and H—O—B angles and H—O distances average 113.3° and 0.855 Å, respectively. Both H atoms are involved in hydrogen bonds, H2O in a hydrogen-bond dimer (equivalent to the carboxylic acid dimer) and H1O in an extended tape (see Fig. 2), which combine, giving a two-dimensional extended structure.

Figure 1
View of the structure of (C₆F₅)B(OH)₂, showing the numbering scheme. Displacement ellipsoids are drawn at the 50% probability level.

Figure 2
View showing hydrogen bonding (dashed lines).

Experimental

To a stirred solution of (C₆F₅)₃B₃O₃ (0.50 g, 0.86 mmol) in THF (25 cm³) was added Et₃PO (0.12 g; 0.89 mmol). The reaction mixture was stirred at room temperature for 1 h. Removal of volatiles in vacuo afforded the adduct (C₆F₅)₃B₃O₃·Et₃PO, (1), a colourless solid (0.58 g; 94%). NMR (δ/p.p.m.; C₆D₆/RT): ¹H (500.1 MHz): 1.4 (q, 6H, ³J 6.6 Hz), 0.7 (t, 9H, ³J 6.6 Hz); ³¹P (202.4 MHz): +80.0; {Δδ = 39.0 p.p.m., AN (acceptor number) = 86 (Mayer et al., 1975)}. IR (KBr disc, η_max cm⁻¹): 3385 (m), 2984 (m), 1649 (s), 1486 (s), 1340 (s), 1244 (s), 1100 (s), 976 (s), 935 (m), 781 (m). Elemental analysis (%) required for C₂₄H₁₅B₃F₁₅PO₄: C 40.3, H 2.1; Found: C, 40.2, H 2.0%. A few crystals of C₆F₅B(OH)₂, (2), suitable for X-ray diffraction, were grown by slow (14 days) diffusion of hexane into a THF solution of (1).

Crystal data

C₆H₂BF₅O₂
M_r = 211.89
Monoclinic, P2₁/c
a = 12.6214 (6) Å
b = 6.2949 (2) Å
c = 9.3973 (4) Å
β = 98.254 (2)°
V = 738.89 (5) Å³
Z = 4
D_x = 1.905 Mg m⁻³
Mo Kα radiation
Cell parameters from 1621 reflections
θ = 2.9–27.5°
μ = 0.22 mm⁻¹
T = 120 (2) K
Plate, colourless
0.15 × 0.08 × 0.02 mm

Data collection

Nonius Kappa CCD area-detector diffractometer
φ and ω scans
Absorption correction: multi-scan (SORTAV; Blessing, 1997 ) T_min = 0.968, T_max = 0.996
5560 measured reflections
1692 independent reflections
1186 reflections with >2σ(I)
R_int = 0.070
θ_max = 27.5°
h = −16 → 14
k = −8 → 6
l = −10 → 12

Refinement

Refinement on F²
R[F² > 2σ(F²)] = 0.044
wR(F²) = 0.116
S = 1.03
1692 reflections
135 parameters
All H-atom parameters refined
w = 1/[σ²(F_o²) + (0.0634P)²] where P = (F_o² + 2F_c²)/3
(Δ/σ)_max < 0.001
Δρ_max = 0.27 e Å⁻³
Δρ_min = −0.31 e Å⁻³

Table 1
Hydrogen-bonding geometry (Å, °)

D—H⋯A	D—H	H⋯A	D⋯A	D—H⋯A
O2—H2O⋯O1ⁱ	0.92 (3)	1.81 (3)	2.7326 (18)	176 (2)
O1—H1O⋯O2ⁱⁱ	0.82 (3)	1.99 (3)	2.7653 (19)	160 (2)
Symmetry codes: (i) -x,-1-y,-z; (ii) $[x,-{\script{1\over 2}}-y,z-{\script{1\over 2}}]$ .

Data collection: COLLECT (Hooft, 1998 ) and DENZO (Otwinowski & Minor, 1997 ); cell refinement: DENZO and COLLECT; data reduction: DENZO and COLLECT; program(s) used to solve structure: SHELXS97 (Sheldrick, 1997 ); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: ORTEP3 for Windows (Farrugia, 1997 ); software used to prepare material for publication: WinGX (Farrugia, 1999).

Supporting information

Crystal structure: contains datablocks 2, global. DOI: https://doi.org/10.1107/S1600536804022408/wk6027sup1.cif

Structure factors: contains datablock 2. DOI: https://doi.org/10.1107/S1600536804022408/wk60272sup2.hkl

Computing details top

Data collection: DENZO (Otwinowski and Minor, 1997); cell refinement: DENZO (Otwinowski & Minor, 1997) and COLLECT (Hooft, 1998); data reduction: DENZO (Otwinowski & Minor, 1997) and COLLECT (Hooft, 1998); program(s) used to solve structure: SHELXS97 (Sheldrick, 1997); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: ORTEP-3 for Windows (Farrugia, 1997).

Pentafluoroboronic acid top

Crystal data top

C₆H₂BF₅O₂	F(000) = 416
M_r = 211.89	D_x = 1.905 Mg m⁻³
Monoclinic, P2₁/c	Mo Kα radiation, λ = 0.71073 Å
a = 12.6214 (6) Å	Cell parameters from 1621 reflections
b = 6.2949 (2) Å	θ = 2.9–27.5°
c = 9.3973 (4) Å	µ = 0.22 mm⁻¹
β = 98.254 (2)°	T = 120 K
V = 738.89 (5) Å³	Plate, colourless
Z = 4	0.15 × 0.08 × 0.02 mm

Data collection top

Nonius KappaCCD Area Detector diffractometer	1692 independent reflections
Radiation source: Nonius FR591 rotating anode	1186 reflections with I > 2σ(I)
Graphite monochromator	R_int = 0.070
Detector resolution: 9.091 pixels mm^-1	θ_max = 27.5°, θ_min = 3.3°
φ and ω scans to fill Ewald Sphere	h = −16→14
Absorption correction: multi-scan (SORTAV; Blessing 1997)	k = −8→6
T_min = 0.968, T_max = 0.996	l = −10→12
5560 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)] = 0.044	Hydrogen site location: difference Fourier map
wR(F²) = 0.116	All H-atom parameters refined
S = 1.03	w = 1/[σ²(F_o²) + (0.0634P)²] where P = (F_o² + 2F_c²)/3
1692 reflections	(Δ/σ)_max < 0.001
135 parameters	Δρ_max = 0.27 e Å⁻³
0 restraints	Δρ_min = −0.31 e Å⁻³

Special details top

Experimental. PLEASE NOTE cell_measurement_ fields are not relevant to area detector data, the entire data set is used to refine the cell, which is indexed from all observed reflections in a 10 degree phi range.

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 (Å²) top

	x	y	z	U_iso*/U_eq
C1	0.20469 (15)	−0.1065 (3)	−0.0334 (2)	0.0205 (4)
C2	0.28746 (15)	−0.1513 (3)	−0.1108 (2)	0.0215 (4)
C3	0.37112 (14)	−0.0124 (3)	−0.12031 (19)	0.0233 (4)
C4	0.37121 (15)	0.1827 (3)	−0.0553 (2)	0.0244 (5)
C5	0.28903 (15)	0.2369 (3)	0.0197 (2)	0.0232 (4)
C6	0.20904 (15)	0.0925 (3)	0.03115 (19)	0.0212 (4)
B1	0.11484 (17)	−0.2747 (3)	−0.0150 (2)	0.0208 (5)
O1	0.07353 (11)	−0.4073 (2)	−0.12348 (16)	0.0236 (3)
O2	0.07956 (11)	−0.2880 (2)	0.11424 (13)	0.0248 (3)
F1	0.29011 (9)	−0.33900 (16)	−0.17951 (12)	0.0257 (3)
F2	0.45090 (9)	−0.06577 (18)	−0.19359 (13)	0.0314 (3)
F3	0.45065 (10)	0.31949 (18)	−0.06461 (13)	0.0352 (3)
F4	0.28823 (10)	0.42794 (16)	0.08323 (12)	0.0308 (3)
F5	0.13194 (9)	0.15083 (17)	0.10926 (12)	0.0276 (3)
H1O	0.086 (2)	−0.374 (4)	−0.204 (3)	0.041 (7)*
H2O	0.029 (2)	−0.394 (4)	0.115 (3)	0.044 (7)*

Atomic displacement parameters (Å²) top

	U¹¹	U²²	U³³	U¹²	U¹³	U²³
C1	0.0227 (10)	0.0246 (9)	0.0144 (9)	0.0001 (7)	0.0036 (8)	0.0033 (7)
C2	0.0292 (11)	0.0193 (9)	0.0160 (9)	0.0005 (7)	0.0036 (8)	0.0003 (7)
C3	0.0185 (10)	0.0335 (10)	0.0185 (10)	0.0014 (7)	0.0043 (8)	0.0041 (8)
C4	0.0245 (11)	0.0272 (10)	0.0208 (10)	−0.0083 (8)	0.0010 (8)	0.0045 (8)
C5	0.0307 (11)	0.0208 (9)	0.0175 (9)	−0.0017 (7)	0.0009 (8)	0.0000 (7)
C6	0.0248 (10)	0.0255 (9)	0.0141 (10)	0.0035 (7)	0.0059 (8)	0.0001 (7)
B1	0.0243 (12)	0.0214 (10)	0.0172 (11)	0.0021 (8)	0.0046 (9)	−0.0007 (8)
O1	0.0282 (8)	0.0288 (7)	0.0150 (8)	−0.0054 (5)	0.0071 (6)	−0.0002 (6)
O2	0.0281 (8)	0.0303 (8)	0.0170 (7)	−0.0084 (6)	0.0071 (6)	−0.0024 (5)
F1	0.0301 (7)	0.0247 (6)	0.0236 (6)	0.0011 (4)	0.0087 (5)	−0.0038 (4)
F2	0.0232 (6)	0.0430 (7)	0.0304 (7)	0.0010 (5)	0.0119 (5)	0.0006 (5)
F3	0.0327 (7)	0.0363 (7)	0.0370 (7)	−0.0142 (5)	0.0063 (5)	0.0037 (5)
F4	0.0447 (7)	0.0217 (6)	0.0257 (7)	−0.0057 (5)	0.0041 (6)	−0.0034 (4)
F5	0.0328 (7)	0.0261 (6)	0.0263 (7)	0.0005 (5)	0.0123 (5)	−0.0040 (4)

Geometric parameters (Å, º) top

C1—C2	1.385 (3)	C4—C5	1.378 (3)
C1—C6	1.389 (3)	C5—F4	1.343 (2)
C1—B1	1.579 (3)	C5—C6	1.374 (3)
C2—F1	1.349 (2)	C6—F5	1.351 (2)
C2—C3	1.384 (3)	B1—O2	1.355 (3)
C3—F2	1.342 (2)	B1—O1	1.362 (2)
C3—C4	1.372 (3)	O1—H1O	0.82 (3)
C4—F3	1.334 (2)	O2—H2O	0.92 (3)

C2—C1—C6	115.31 (16)	F4—C5—C6	120.34 (17)
C2—C1—B1	121.92 (16)	F4—C5—C4	120.20 (16)
C6—C1—B1	122.73 (17)	C6—C5—C4	119.45 (17)
F1—C2—C3	116.81 (17)	F5—C6—C5	117.20 (16)
F1—C2—C1	120.14 (16)	F5—C6—C1	119.74 (16)
C3—C2—C1	123.04 (17)	C5—C6—C1	123.07 (17)
F2—C3—C4	120.00 (17)	O2—B1—O1	119.55 (18)
F2—C3—C2	120.72 (17)	O2—B1—C1	118.24 (17)
C4—C3—C2	119.28 (17)	O1—B1—C1	122.20 (18)
F3—C4—C3	120.10 (17)	B1—O1—H1O	115.6 (18)
F3—C4—C5	120.11 (16)	B1—O2—H2O	111.4 (16)
C3—C4—C5	119.79 (16)

Hydrogen-bond geometry (Å, º) top

D—H···A	D—H	H···A	D···A	D—H···A
O2—H2O···O1ⁱ	0.92 (3)	1.81 (3)	2.7326 (18)	176 (2)
O1—H1O···O2ⁱⁱ	0.82 (3)	1.99 (3)	2.7653 (19)	160 (2)

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

Acknowledgements

The authors thank the EPSRC for funding the crystallographic facilities.

References

Balkwill, J. E., Cole, S. C., Coles, M. P. & Hitchcock, P. B. (2002) Inorg. Chem. 41, 3548–3552. Web of Science CSD CrossRef PubMed CAS Google Scholar
Beckett, M. A., Brassington, D. S., Coles, S. J. & Hursthouse, M. B. (2000) Inorg. Chem. Commun. 3, 530–533. Web of Science CSD CrossRef CAS Google Scholar
Beckett, M. A., Brassington., D. S., Light, M. E. & Hursthouse, M. B. (2001). J. Chem. Soc. Dalton Trans. pp. 1768–1772. Web of Science CSD CrossRef Google Scholar
Beckett, M. A., Strickland, G. C., Varma, K. S., Hibbs, D. E., Hursthouse, M. B. & Malik, K. M. A (1996). J. Organomet. Chem. 535, 33–41. CSD CrossRef Web of Science Google Scholar
Beringhelli, T., D'Alfonso, G., Donghi, D., Maggioni, D., Mercandelli, P. & Sironi, A. (2003) Organometallics, 22, 1588–1590. Web of Science CSD CrossRef CAS Google Scholar
Blessing, R. H. (1997). J. Appl. Cryst. 30, 421–426. CrossRef CAS Web of Science IUCr Journals Google Scholar
Chambers, R. N. & Chivers, T. (1965). J. Chem. Soc. pp. 3933–3939. CrossRef Web of Science Google Scholar
Farrugia, L. J. (1997). J. Appl. Cryst. 30, 565. CrossRef IUCr Journals Google Scholar
Farrugia, L. J. (1999). J. Appl. Cryst. 32, 837–838. CrossRef CAS IUCr Journals Google Scholar
Frohn, H.-J., Adonin, N. Y., Bardin, V. V. & Starichenko, V. F. (2002). Z. Anorg. Allg. Chem. 628, 2827–2833. CrossRef CAS Google Scholar
Hooft, R. (1998). COLLECT. Nonius BV, The Netherlands. Google Scholar
Ishihara, K. & Yamamoto, H. (1999). Eur. J. Org. Chem. pp. 527–538. CrossRef Google Scholar
Mayer, U., Gutmann, V. & Gerger, W. (1975). Monatash. Chem. 106, 1275–1257. Google Scholar
Otwinowski, Z. & Minor, W. (1997). Methods in Enzymology, Vol. 276, Macromolecular Crystallography, Part A, edited by C. W. Carter Jr and R. M. Sweet, pp. 307–326. New York: Academic Press. Google Scholar
Piers, W. E. & Chivers, T. (1997). Chem. Soc. Rev. 26, 345–354. CrossRef CAS Web of Science Google Scholar
Priego, J. L., Doerrer, L. H., Rees, L. H. & Green, M. L. H. (2000) Chem. Commun. pp. 779–780. Web of Science CSD CrossRef Google Scholar
Sheldrick, G. M. (1997). SHELXS97 and SHELXL97. University of Göttingen, Germany. Google Scholar
Vagedes, D., Frohlich, R. & Erker, G. (1999). Angew. Chem. Int. Ed. Engl. 38, 3362–3365. Web of Science CrossRef PubMed CAS Google Scholar

© International Union of Crystallography. Prior permission is not required to reproduce short quotations, tables and figures from this article, provided the original authors and source are cited. For more information, click here.