Crystal structure of 4-(meth­oxy­carbon­yl)phenyl­boronic acid

Flanagan, K.J.; Senge, M.O.

doi:10.1107/S2056989015015923

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ISSN: 2056-9890

Volume 71| Part 10| October 2015| Pages 1151-1154

doi:10.1107/S2056989015015923

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Crystal structure of 4-(methoxycarbonyl)phenylboronic acid

Keith J. Flanagan ^a ^* and Mathias O. Senge ^a

^aSchool of Chemistry, SFI Tetrapyrrole Laboratory, Trinity Biomedical Sciences Institute, 152-160 Pearse Street, Trinity College Dublin, The University of Dublin, Dublin 2, Ireland
^*Correspondence e-mail: kflanaga@tcd.ie

Edited by H. Stoeckli-Evans, University of Neuchâtel, Switzerland (Received 6 August 2015; accepted 25 August 2015; online 12 September 2015)

In the title compound, C₈H₉BO₄, the methoxycarbonyl group is rotated out of the plane of the benzene ring by 7.70 (6)°. In the crystal, molecules are linked via pairs of O—H⋯O hydrogen bonds, involving the boronic acid OH groups, forming inversion dimers. The dimers are linked via O—H⋯O hydrogen bonds, involving a boronic acid OH group and the carbonyl O atom, forming undulating sheets parallel to (10-2). Within the sheets there are also C—H⋯O hydrogen bonds present, also involving the carbonyl O atom. The sheets are linked via C—H⋯π and offset face-to-face π-interactions between inversion-related molecules [inter-centroid distance = 3.7843 (16) Å, interplanar distance = 3.3427 (4) Å and offset = 1.744 Å], forming a three-dimensional structure.

Keywords: crystal structure; boronic acid; methoxycarbonyl; ester; protecting groups; Suzuki coupling; hydrogen bonding; inversion dimers; π–π interactions..

CCDC reference: 1416885

1. Chemical context

Boronic acids have been widely studied, mainly due to their roles in coupling reactions such as Suzuki (Suzuki, 2011 ), Chan–Lam (Lam et al., 2000 ) and Liebeskind–Srogl (Liebeskind & Srogl, 2000 ). Complexes of boronic acids are well known, and many examples have been structurally characterized (e.g., Roşca et al., 2012 ; Filthaus et al., 2008 ; Cyrański et al., 2008 ; Rettig & Trotter, 1977 ). Many examples exist of similar compounds such as 2-methylimidazolium (4-carboxybenzene)(2-methylimidazolyl)boronate monohydrate (Aakeröy et al., 2005 ) and 4-carboxyphenylboronic acid (SeethaLekshmi & Pedireddi, 2007 ). However, no examples of methoxy-protected derivatives have been published to date. We report herein on the crystal structure of the title compound, the 4-(methoxycarbonyl) derivative of phenylboronic acid.

2. Structural commentary

The title molecule, Fig. 1, is almost completely planar with the methoxycarbonyl group inclined to the benzene ring by 7.70 (6)°. The angle around atom B1, O1—B1—O2 is 118.16 (9)°, very close to the ideal value of 120°. The bond lengths and angles are similar to those reported for 4-carboxyphenylboronic acid derivatives (SeethaLekshmi & Pedireddi, 2007) in which the carboxylic group is rotated from the plane of the benzene ring by ca 13.83–26.44°, and the O—B—O bond angles are in the range of ca 118.1–122.5°. Aakeröy et al. (2005) reported the structures of 4-acetylpyridine oxime 4-carboxybenzeneboronate dihydrate and 4-acetylpyridine oxime 4-carboxybenzeneboronate dihydrate in which the 4-carboxy groups are inclined to the benzene ring by ca 10.45–14.08°, close to the value observed for the methoxycarbonyl group in the title compound.

Figure 1
The molecular structure of the title compound, showing the atom labelling. Displacement ellipsoids are drawn at the 50% probability level.

3. Supramolecular features

In the crystal of the title compound, there are hydrogen bonds between the carbonyl atom O4 and the hydroxy group O2–H2A of the boronic acid and atom O2 of the boronic acid with a D⋯A distance of 2.753 (1) Å (Fig. 2 and Table 1). The hydroxy group O1–-H1A of the boronic acid is in an inversion-related hydrogen-bonded network with the oxygen O2 of the boronic acid at a distance of 2.762 (1) Å (Fig. 2 and Table 1).

Table 1
Hydrogen-bond geometry (Å, °)

Cg is the centroid of ring C1–C6.

D—H⋯A	D—H	H⋯A	D⋯A	D—H⋯A
O1—H1A⋯O2ⁱ	0.86 (2)	1.90 (2)	2.762 (1)	178.4 (18)
O2—H2A⋯O4ⁱⁱ	0.84 (2)	1.94 (2)	2.753 (1)	162.2 (16)
C2—H2⋯O4ⁱⁱ	0.95	2.59	3.500 (1)	160
C5—H5⋯Cgⁱⁱⁱ	0.95	2.75	3.534 (1)	141
Symmetry codes: (i) -x+2, -y+1, -z+2; (ii) $[-x+1, y-{\script{1\over 2}}, -z+{\script{3\over 2}}]$ ; (iii) $[x, -y+{\script{3\over 2}}, z-{\script{1\over 2}}]$ .

Figure 2
Hydrogen bonding (dashed lines) in the crystal of the title compound [see Table 1

for details; symmetry codes: (A) −x + 2, −y + 1, −z + 2; (B) −x + 1, y − $[{1\over 2}]$ , −z + $[{3\over 2}]$ ]. Displacement ellipsoids are drawn at the 50% probability level.

The presence of the methoxy group on the carbonyl removes hydrogen-bond donation of the carboxylic acid seen in related structures. Atom C8 creates a shield around atom O3, removing its ability to participate in hydrogen bonding due to steric effects. It is noteworthy that the methoxy protecting group is small compared to other protecting groups and therefore exhibits no steric effects on the hydrogen-bonding capabilities to atom O4 in this structure, as seen in other examples. As exemplified by the work of Lemmerer (2012 ), most literature examples exhibit an almost exclusive head-to-tail hydrogen-bonding network between the boronic and carboxylic acids whereas the title compound exhibits exclusively head-to-head hydrogen-bonding interactions with the boronic acid subunit. This is due to the steric effects and removal of hydrogen-donating abilities in the methoxycarbonyl subunit (Fig. 2). The group can still act as a hydrogen acceptor, as shown in the packing diagram (Fig. 2). Atom O4 can accept H atoms from the hydroxy group O2—H2A to create an offset face-to-face overlap in the packing unit. Yang et al. (2005 ) published a structure of the boronic ester derivative of the title compound. This structure showed similar effects, however no hydrogen bonds were visible in the reported structure.

Hydrogen bonding and π-stacking within the unit cell forms a strong set of dimeric pairs. This can be easily observed in Fig. 3. These dimeric pairs line up to form a zigzag stacking pattern with a consistent spacing throughout the unit cell. This is aided by the hydrogen bond between O4 and O2—H2A [2.753 (1) Å] and a close contact between atom O4 and the hydrogen on atom C2 at a distance of 2.59 Å. The unit cell consists of four molecular units which form π-aggregated pairs in a head-to-tail fashion and are stabilized through offset face-to-face π-interactions [inter-centroid distance = 3.7843 (16) Å; inter-planar distance = 3.3427 (4) Å, offset = 1.744 Å]; see Fig. 4. The hydroxy group O1—H1A of the boronic acid is in an inversion-related hydrogen-bonded network with the oxygen O2 of the boronic acid at a distance of 2.762 (1) Å, forming a head-to-head hydrogen-bonded network with adjacent molecules (Fig. 5). There are also C—H⋯π interactions (Table 1) present between the undulating sheets parallel to (10 $[\overline{2}]$ ). The sum of all of these intermolecular interactions leads to the formation of a three-dimensional structure.

Figure 3
View of the π-aggregated structure as viewed approximately along the a axis.

Figure 4
A view approximately along the b axis, showing the offset face-to-face π-interactions involving inversion-related molecules.

Figure 5
Crystal packing diagram of the title compound viewed along the c axis, showing the offset face-to-face π-interactions involving inversion-related molecules (dashed lines; see Table 1

for details).

4. Database survey

A search of the Cambridge Structural Database (Version 5.36, update Nov. 2014; Groom & Allen, 2014 ) gave fourteen hits for free carboxylic acid derivatives of the title compound and one for the boronic ester. Soundararajan et al. (1993 ) published a structure of 4-carboxy-2-nitrobenzeneboronic acid. The carboxylic group deviated from the mean plane with an angle of ca 5.84° and the O—B—O bond angle was ca 119.88°. Aakeröy et al. (2004 ) reported the structure of a 4-carboxybenzeneboronic acid 4,4′-bipyridine derivative with the carboxylic group being rotated from the plane by ca 4.20° and an O—B—O bond angle of ca 118.09°. They also reported the structures of 2-methylimidazolium(4-carboxybenzene)(2-methylimidazolyl)boronate monohydrate, tris(4-(dimethylamino)pyridinium) bis(4-(dimethylamino)pyridine) tris(4-carboxybenzeneboronate) trihydrate and 4-acetylpyridine oxime 4-carboxybenzeneboronate dihydrate which presented out-of-plane tilt angles of ca 10.45–27.74° and O—B—O bond angles of ca 114.23–124.94° (Aakeröy et al., 2005).

SeethaLekshmi & Pedireddi (2006 ) reported on a selection of carboxylatophenylboronic acid derivatives, hexaaqua-M(II) bis(4-carboxylatophenylboronic acid) tetrahydrate, where M is nickel, manganese or cobalt. These structures where similar to the title compound and exhibited similar characteristics for the O—B—O bond angle and the out-of-plane tilt of the carboxyl acid group compared to the title compound. The carboxylic group deviated from the plane with an angle of ca 3.40–4.53° and the O—B—O bond angles were in the range of ca 121.43–122.18° (SeethaLekshmi & Pedireddi, 2006). They also published a selection of 4-carboxyphenylboronic acids including the monohydrate and the hydrate derivatives of this compound. The carboxylic group deviated from the mean plane with an angle of ca 13.83–26.44° and the O—B—O bond angles were in the range of ca 118.08–122.50° (SeethaLekshmi & Pedireddi, 2007).

The structure of bis(8-chloro-1-methyl-6-phenyl-4H-[1,2,4]triazolo[4,3-a][1,4]benzodiazepine) 4-(dihydroxyboryl)benzoic acid monohydrate exhibited a tilt angle of ca 2.14° for the carboxylic group and an O—B—O bond angle of ca 126.53° (Varughese et al., 2011 ). Likewise, the relevant values in the structure of a cyclopentanaminium 4-(dihydroxyboryl)benzoate trihydrate were ca 29.67 and 126.53°, respectively (Lemmerer, 2012). Finally, methyl 4-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)benzoate showed similar features to the title compound with a methoxycarbonyl deviation from the ring plane of ca 4.97° (Yang et al., 2005).

5. Synthesis and crystallization

The compound was purchased from Alfa Aesar and was purified with silica gel column chromatography using CH₂Cl₂:MeOH (19:1). The compound was then crystallized from a solution of 1% MeOH in CH₂Cl₂ layered with hexane to give a single crystal suitable for X-ray diffraction.

6. Refinement

Crystal data, data collection and structure refinement details are summarized in Table 2. The donor OH H atoms were located in a difference Fourier map and freely refined. The C-bound H atoms were placed in their expected calculated positions and refined as riding: C—H = 0.95–0.98 Å with U_iso(H) = 1.5U_eq(C) for methyl H atoms and 1.2U_iso(C) for other H atoms.

Table 2
Experimental details

Crystal data
Chemical formula	C₈H₉BO₄
M_r	179.96
Crystal system, space group	Monoclinic, P2₁/c
Temperature (K)	100
a, b, c (Å)	11.2449 (6), 12.0672 (6), 6.8598 (3)
β (°)	105.121 (1)
V (Å³)	898.61 (8)
Z	4
Radiation type	Mo Kα
μ (mm⁻¹)	0.10
Crystal size (mm)	0.35 × 0.10 × 0.10

Data collection
Diffractometer	Bruker SMART APEXII area detector
Absorption correction	Multi-scan (SADABS; Bruker, 2014 )
T_min, T_max	0.706, 0.746
No. of measured, independent and observed [I > 2σ(I)] reflections	31992, 2056, 1872
R_int	0.021
(sin θ/λ)_max (Å⁻¹)	0.649

Refinement
R[F² > 2σ(F²)], wR(F²), S	0.032, 0.094, 1.10
No. of reflections	2056
No. of parameters	126
H-atom treatment	H atoms treated by a mixture of independent and constrained refinement
Δρ_max, Δρ_min (e Å⁻³)	0.39, −0.22
Computer programs: APEX2 and SAINT-Plus (Bruker, 2014), SHELXT (Sheldrick, 2015a ), XP in SHELXTL (Sheldrick, 2008 ), SHELXL2014 (Sheldrick, 2015b ) and publCIF (Westrip, 2010 ).

Supporting information

CCDC reference: 1416885

Crystal structure: contains datablocks I, publication_text. DOI: 10.1107/S2056989015015923/su5188sup1.cif

Structure factors: contains datablock I. DOI: 10.1107/S2056989015015923/su5188Isup2.hkl

Supporting information file. DOI: 10.1107/S2056989015015923/su5188Isup3.cml

checkCIF report

Chemical context top

Boronic acids have been widely studied, mainly due to their roles in coupling reactions such as Suzuki (Suzuki, 2011), Chan–Lam (Lam et al., 2000) and Liebeskind–Srogl (Liebeskind & Srogl, 2000). Complexes of boronic acids are well known, and many examples have been structurally characterized (e.g., Roşca et al., 2012; Filthaus et al., 2008; Cyrański et al., 2008; Rettig & Trotter, 1977). Many examples exist of similar compounds such as 2-methylimidazolium (4-carboxybenzene)(2-methylimidazolyl)boronate monohydrate (Aakeröy et al., 2005) and 4-carboxyphenylboronic acid (SeethaLekshmi & Pedireddi, 2007). However, no examples of methoxy-protected derivatives have been published to date. We report herein on the crystal structure of the title compound, the 4-(methoxycarbonyl) derivative of phenylboronic acid.

Structural commentary top

Supramolecular features top

In the crystal of the title compound, there are hydrogen bonds between the carbonyl atom O4 and the hydroxy group O2–H2A of the boronic acid and atom O2 of the boronic acid with a D···A distance of 2.753 (1) Å (Fig. 2 and Table 1). The hydroxy group O1–-H1A of the boronic acid is in an inversion-related hydrogen-bonded network with the oxygen O2 of the boronic acid at a distance of 2.762 (1) Å (Fig. 2 and Table 1).

The presence of the methoxy group on the carbonyl removes hydrogen-bond donation of the carboxylic acid seen in related structures. Atom C8 creates a shield around atom O3, removing its ability to participate in hydrogen bonding due to steric effects. It is noteworthy that the methoxy protecting group is small compared to other protecting groups and therefore exhibits no steric effects on the hydrogen-bonding capabilities to atom O4 in this structure, as seen in other examples. As exemplified by the work of Lemmerer (2012), most literature examples exhibit an almost exclusive head-to-tail hydrogen-bonding network between the boronic and carboxylic acids whereas the title compound exhibits exclusively head-to-head hydrogen-bonding interactions with the boronic acid subunit. This is due to the steric effects and removal of hydrogen-donating abilities in the methoxycarbonyl subunit (Fig. 2). The group can still act as a hydrogen acceptor, as shown in the packing diagram (Fig. 2). Atom O4 can accept H atoms from the hydroxy group O2—H2A to create an off-set face-to-face overlap in the packing unit. Yang et al. (2005) published a structure of the boronic ester derivative of the title compound. This structure showed similar effects, however no hydrogen bonds were visible in the reported structure.

Hydrogen bonding and π-stacking within the unit cell forms a strong set of dimeric pairs. This can be easily observed in Fig. 3. These dimeric pairs line up to for a zigzag stacking pattern with a consistent spacing throughout the unit cell. This is aided by the hydrogen bond between O4 and O2—H2A [2.753 (1) Å] and a close contact between atom O4 and the hydrogen on atom C2 at a distance of 2.59 Å. The unit cell consists of four molecular units which form π-aggregated pairs in a head-to-tail fashion and are stabilized through off-set face-to-face π-interactions [inter-centroid distance = 3.7843 (16) Å; inter-planar distance = 3.3427 (4) Å, offset = 1.744 Å]; see Fig. 4. The hydroxy group O1—H1A of the boronic acid is in an inversion-related hydrogen-bonded network with the oxygen O2 of the boronic acid at a distance of 2.762 (1) Å, forming a head-to-head hydrogen-bonded network with adjacent molecules (Fig. 5). There are also C—H···π interactions (Table 1) present between the undulating sheets parallel to (102). The sum of all of these intermolecular interactions leads to the formation of a three-dimensional structure.

Database survey top

A search of the Cambridge Structural Database (Version 5.36, update Nov. 2014; Groom & Allen, 2014) gave fourteen hits for free carboxylic acid derivatives of the title compound and one for the boronic ester. Soundararajan et al. (1993) published a structure of 4-carboxy-2-nitrobenzeneboronic acid. The carboxylic group deviated from the mean plane with an angle of ca 5.84° and the O—B—O bond angle was ca 119.88°. Aakeröy et al. (2004) reported the structure of a 4-carboxybenzeneboronic acid 4,4'-bipyridine derivative with the carboxylic group being rotated from the plane by ca 4.20° and an O—B—O bond angle of ca 118.09°. They also reported the structures of 2-methylimidazolium(4-carboxybenzene)(2-methylimidazolyl)boronate monohydrate, tris(4-(dimethylamino)pyridinium) bis(4-(dimethylamino)pyridine) tris(4-carboxybenzeneboronate) trihydrate and 4-acetylpyridine oxime 4-carboxybenzeneboronate dihydrate which presented out-of-plane tilt angles of ca 10.45–27.74° and O—B—O bond angles of ca 114.23–124.94° (Aakeröy et al., 2005).

SeethaLekshmi & Pedireddi (2006) reported on a selection of carboxylatophenylboronic acid derivatives, hexaaqua-M(II) bis(4-carboxylatophenylboronic acid) tetrahydrate, where M is nickel, manganese or cobalt. These structures where similar to the title compound and exhibited similar characteristics for the O—B—O bond angle and the out-of-plane tilt of the carboxyl acid group compared to the title compound. The carboxylic group deviated from the plane with an angle of ca 3.40–4.53° and the O—B—O bond angles were in the range of ca 121.43–122.18° (SeethaLekshmi & Pedireddi, 2006). They also published a selection of 4-carboxyphenylboronic acids including the monohydrate and the hydrate derivatives of this compound. The carboxylic group deviated from the mean plane with an angle of ca 13.83–26.44° and the O—B—O bond angles were in the range of ca 118.08–122.50° (SeethaLekshmi & Pedireddi, 2007).

The structure of bis(8-chloro-1-methyl-6-phenyl-4H-[1,2,4]triazolo[4,3-a][1,4]benzodiazepine) 4-(dihydroxyboryl)benzoic acid monohydrate exhibited a tilt angle of ca 2.14° for the carboxylic group and an O—B—O bond angle of ca 126.53° (Varughese et al., 2011). Likewise, the relevant values in the structure of a cyclopentanaminium 4-(dihydroxyboryl)benzoate trihydrate were ca 29.67 and 126.53°, respectively (Lemmerer, 2012). Finally, methyl 4-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)benzoate showed similar features to the title compound with a methoxycarbonyl deviation from the ring plane of ca 4.97° (Yang et al., 2005).

Synthesis and crystallization top

Refinement top

Related literature top

For related literature, see: Aakeröy et al. (2004, 2005); Cyrański et al. (2008); Filthaus et al. (2008); Groom & Allen (2014); Lam et al. (2000); Lemmerer (2012); Liebeskind & Srogl (2000); Rettig & Trotter (1977); Roşca et al. (2012); SeethaLekshmi & Pedireddi (2006, 2007); Soundararajan et al. (1993); Suzuki (2011); Varughese et al. (2011); Yang et al. (2005).

Computing details top

Data collection: APEX2 (Bruker, 2014); cell refinement: SAINT-Plus (Bruker, 2014); data reduction: SAINT-Plus (Bruker, 2014); program(s) used to solve structure: SHELXT (Sheldrick, 2015a); program(s) used to refine structure: SHELXL2014 (Sheldrick, 2015b); molecular graphics: XP in SHELXTL (Sheldrick, 2008); software used to prepare material for publication: SHELXL2014 (Sheldrick, 2015b) and publCIF (Westrip, 2010).

Figures top

	Fig. 1. The molecular structure of the title compound, showing the atom labelling. Displacement ellipsoids are drawn at the 50% probability level.
	Fig. 2. Hydrogen bonding (dashed lines) in the crystal of the title compound [see Table 1 for details; symmetry codes: (A) -x + 2, -y + 1, -z + 2; (B) -x + 1, y - 1/2, -z + 3/2]. Displacement ellipsoids are drawn at the 50% probability level.
	Fig. 3. View of the π-aggregated structure as viewed approximately along the a axis.
	Fig. 4. A view approximately along the b axis, showing the off-set face-to-face π-interactions involving inversion-related molecules.
	Fig. 5. Crystal packing diagram of the title compound viewed along the c axis, showing the off-set face-to-face π-interactions involving inversion-related molecules (dashed lines; see Table 1 for details).

4-(Methoxycarbonyl)benzeneboronic acid top

Crystal data top

C₈H₉BO₄	F(000) = 376
M_r = 179.96	D_x = 1.330 Mg m⁻³
Monoclinic, P2₁/c	Mo Kα radiation, λ = 0.71073 Å
a = 11.2449 (6) Å	Cell parameters from 9864 reflections
b = 12.0672 (6) Å	θ = 2.5–31.1°
c = 6.8598 (3) Å	µ = 0.10 mm⁻¹
β = 105.121 (1)°	T = 100 K
V = 898.61 (8) Å³	Block, white
Z = 4	0.35 × 0.10 × 0.10 mm

Data collection top

Bruker SMART APEXII area-detector diffractometer	2056 independent reflections
Radiation source: sealed tube	1872 reflections with I > 2σ(I)
Detector resolution: 8.258 pixels mm^-1	R_int = 0.021
φ and ω scans	θ_max = 27.5°, θ_min = 1.9°
Absorption correction: multi-scan (SADABS; Bruker, 2014)	h = −14→14
T_min = 0.706, T_max = 0.746	k = −15→15
31992 measured reflections	l = −8→8

Refinement top

Refinement on F²	0 restraints
Least-squares matrix: full	Hydrogen site location: mixed
R[F² > 2σ(F²)] = 0.032	H atoms treated by a mixture of independent and constrained refinement
wR(F²) = 0.094	w = 1/[σ²(F_o²) + (0.0494P)² + 0.2551P] where P = (F_o² + 2F_c²)/3
S = 1.10	(Δ/σ)_max < 0.001
2056 reflections	Δρ_max = 0.39 e Å⁻³
126 parameters	Δρ_min = −0.22 e Å⁻³

Crystal data top

C₈H₉BO₄	V = 898.61 (8) Å³
M_r = 179.96	Z = 4
Monoclinic, P2₁/c	Mo Kα radiation
a = 11.2449 (6) Å	µ = 0.10 mm⁻¹
b = 12.0672 (6) Å	T = 100 K
c = 6.8598 (3) Å	0.35 × 0.10 × 0.10 mm
β = 105.121 (1)°

Data collection top

Bruker SMART APEXII area-detector diffractometer	2056 independent reflections
Absorption correction: multi-scan (SADABS; Bruker, 2014)	1872 reflections with I > 2σ(I)
T_min = 0.706, T_max = 0.746	R_int = 0.021
31992 measured reflections

Refinement top

R[F² > 2σ(F²)] = 0.032	0 restraints
wR(F²) = 0.094	H atoms treated by a mixture of independent and constrained refinement
S = 1.10	Δρ_max = 0.39 e Å⁻³
2056 reflections	Δρ_min = −0.22 e Å⁻³
126 parameters

Special details top

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.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å²) top

	x	y	z	U_iso*/U_eq
O1	0.90580 (7)	0.61792 (6)	0.84477 (13)	0.0258 (2)
H1A	0.9797 (19)	0.5946 (15)	0.897 (3)	0.054 (5)*
C1	0.67921 (8)	0.57954 (8)	0.78322 (14)	0.0163 (2)
B1	0.81840 (10)	0.54762 (9)	0.87529 (16)	0.0185 (2)
O2	0.85621 (7)	0.45309 (6)	0.98510 (12)	0.02287 (19)
H2A	0.8020 (17)	0.4076 (14)	0.997 (3)	0.046 (4)*
C2	0.58139 (9)	0.51156 (8)	0.80135 (14)	0.0166 (2)
H2	0.5989	0.4434	0.8724	0.020*
O3	0.21983 (6)	0.60624 (6)	0.54273 (12)	0.02136 (18)
C3	0.45926 (9)	0.54182 (8)	0.71743 (14)	0.0161 (2)
H3	0.3942	0.4945	0.7303	0.019*
O4	0.27900 (6)	0.77238 (6)	0.45341 (11)	0.02041 (18)
C4	0.43313 (8)	0.64218 (8)	0.61442 (13)	0.0153 (2)
C5	0.52908 (9)	0.71113 (8)	0.59350 (14)	0.0169 (2)
H5	0.5112	0.7793	0.5227	0.020*
C6	0.65052 (9)	0.67947 (8)	0.67660 (15)	0.0177 (2)
H6	0.7153	0.7263	0.6610	0.021*
C7	0.30450 (8)	0.68109 (8)	0.52886 (14)	0.0163 (2)
C8	0.09288 (9)	0.64329 (9)	0.47857 (19)	0.0271 (2)
H8A	0.0381	0.5827	0.4945	0.041*
H8B	0.0813	0.7065	0.5614	0.041*
H8C	0.0735	0.6657	0.3364	0.041*

Atomic displacement parameters (Å²) top

	U¹¹	U²²	U³³	U¹²	U¹³	U²³
O1	0.0150 (4)	0.0242 (4)	0.0365 (4)	−0.0005 (3)	0.0034 (3)	0.0100 (3)
C1	0.0156 (4)	0.0176 (5)	0.0155 (4)	0.0006 (3)	0.0036 (3)	−0.0014 (4)
B1	0.0160 (5)	0.0190 (5)	0.0199 (5)	0.0002 (4)	0.0035 (4)	0.0001 (4)
O2	0.0144 (3)	0.0211 (4)	0.0314 (4)	−0.0013 (3)	0.0029 (3)	0.0073 (3)
C2	0.0180 (5)	0.0156 (4)	0.0162 (4)	0.0017 (3)	0.0045 (3)	0.0007 (3)
O3	0.0147 (3)	0.0180 (4)	0.0306 (4)	0.0001 (3)	0.0046 (3)	0.0004 (3)
C3	0.0162 (4)	0.0160 (4)	0.0165 (4)	−0.0010 (3)	0.0051 (3)	−0.0017 (3)
O4	0.0190 (3)	0.0188 (4)	0.0232 (4)	0.0034 (3)	0.0051 (3)	0.0029 (3)
C4	0.0159 (4)	0.0162 (4)	0.0136 (4)	0.0014 (3)	0.0036 (3)	−0.0025 (3)
C5	0.0195 (5)	0.0156 (4)	0.0158 (4)	0.0011 (3)	0.0050 (3)	0.0010 (3)
C6	0.0166 (4)	0.0182 (5)	0.0188 (4)	−0.0015 (3)	0.0054 (3)	0.0007 (3)
C7	0.0172 (4)	0.0170 (4)	0.0148 (4)	0.0004 (3)	0.0045 (3)	−0.0031 (3)
C8	0.0147 (5)	0.0260 (5)	0.0396 (6)	0.0013 (4)	0.0053 (4)	0.0015 (5)

Geometric parameters (Å, º) top

O1—B1	1.3552 (13)	C3—C4	1.3942 (13)
O1—H1A	0.86 (2)	C3—H3	0.9500
C1—C2	1.4034 (13)	O4—C7	1.2191 (12)
C1—C6	1.4035 (13)	C4—C5	1.3992 (13)
C1—B1	1.5752 (14)	C4—C7	1.4880 (13)
B1—O2	1.3720 (13)	C5—C6	1.3891 (13)
O2—H2A	0.841 (18)	C5—H5	0.9500
C2—C3	1.3923 (13)	C6—H6	0.9500
C2—H2	0.9500	C8—H8A	0.9800
O3—C7	1.3336 (12)	C8—H8B	0.9800
O3—C8	1.4503 (12)	C8—H8C	0.9800

B1—O1—H1A	113.1 (12)	C5—C4—C7	117.91 (8)
C2—C1—C6	118.00 (8)	C6—C5—C4	119.75 (9)
C2—C1—B1	122.77 (8)	C6—C5—H5	120.1
C6—C1—B1	119.23 (8)	C4—C5—H5	120.1
O1—B1—O2	118.16 (9)	C5—C6—C1	121.19 (9)
O1—B1—C1	118.02 (9)	C5—C6—H6	119.4
O2—B1—C1	123.82 (9)	C1—C6—H6	119.4
B1—O2—H2A	118.0 (12)	O4—C7—O3	123.30 (9)
C3—C2—C1	121.43 (9)	O4—C7—C4	123.32 (9)
C3—C2—H2	119.3	O3—C7—C4	113.37 (8)
C1—C2—H2	119.3	O3—C8—H8A	109.5
C7—O3—C8	115.73 (8)	O3—C8—H8B	109.5
C2—C3—C4	119.48 (9)	H8A—C8—H8B	109.5
C2—C3—H3	120.3	O3—C8—H8C	109.5
C4—C3—H3	120.3	H8A—C8—H8C	109.5
C3—C4—C5	120.15 (9)	H8B—C8—H8C	109.5
C3—C4—C7	121.91 (8)

C2—C1—B1—O1	178.38 (9)	C7—C4—C5—C6	178.03 (8)
C6—C1—B1—O1	−1.02 (14)	C4—C5—C6—C1	−0.52 (14)
C2—C1—B1—O2	−1.88 (15)	C2—C1—C6—C5	0.81 (14)
C6—C1—B1—O2	178.73 (9)	B1—C1—C6—C5	−179.77 (9)
C6—C1—C2—C3	−0.29 (14)	C8—O3—C7—O4	−5.45 (14)
B1—C1—C2—C3	−179.69 (9)	C8—O3—C7—C4	174.59 (8)
C1—C2—C3—C4	−0.52 (14)	C3—C4—C7—O4	173.53 (9)
C2—C3—C4—C5	0.82 (14)	C5—C4—C7—O4	−4.78 (14)
C2—C3—C4—C7	−177.45 (8)	C3—C4—C7—O3	−6.51 (13)
C3—C4—C5—C6	−0.31 (14)	C5—C4—C7—O3	175.18 (8)

Hydrogen-bond geometry (Å, º) top

Cg is the centroid of ring C1–C6.

D—H···A	D—H	H···A	D···A	D—H···A
O1—H1A···O2ⁱ	0.86 (2)	1.90 (2)	2.762 (1)	178.4 (18)
O2—H2A···O4ⁱⁱ	0.84 (2)	1.94 (2)	2.753 (1)	162.2 (16)
C2—H2···O4ⁱⁱ	0.95	2.59	3.500 (1)	160
C5—H5···Cgⁱⁱⁱ	0.95	2.75	3.534 (1)	141

Symmetry codes: (i) −x+2, −y+1, −z+2; (ii) −x+1, y−1/2, −z+3/2; (iii) x, −y+3/2, z−1/2.

Hydrogen-bond geometry (Å, º) top

Cg is the centroid of ring C1–C6.

D—H···A	D—H	H···A	D···A	D—H···A
O1—H1A···O2ⁱ	0.86 (2)	1.90 (2)	2.762 (1)	178.4 (18)
O2—H2A···O4ⁱⁱ	0.84 (2)	1.94 (2)	2.753 (1)	162.2 (16)
C2—H2···O4ⁱⁱ	0.95	2.59	3.500 (1)	160
C5—H5···Cgⁱⁱⁱ	0.95	2.75	3.534 (1)	141

Symmetry codes: (i) −x+2, −y+1, −z+2; (ii) −x+1, y−1/2, −z+3/2; (iii) x, −y+3/2, z−1/2.

Experimental details

Crystal data
Chemical formula	C₈H₉BO₄
M_r	179.96
Crystal system, space group	Monoclinic, P2₁/c
Temperature (K)	100
a, b, c (Å)	11.2449 (6), 12.0672 (6), 6.8598 (3)
β (°)	105.121 (1)
V (Å³)	898.61 (8)
Z	4
Radiation type	Mo Kα
µ (mm⁻¹)	0.10
Crystal size (mm)	0.35 × 0.10 × 0.10

Data collection
Diffractometer	Bruker SMART APEXII area-detector diffractometer
Absorption correction	Multi-scan (SADABS; Bruker, 2014)
T_min, T_max	0.706, 0.746
No. of measured, independent and observed [I > 2σ(I)] reflections	31992, 2056, 1872
R_int	0.021
(sin θ/λ)_max (Å⁻¹)	0.649

Refinement
R[F² > 2σ(F²)], wR(F²), S	0.032, 0.094, 1.10
No. of reflections	2056
No. of parameters	126
H-atom treatment	H atoms treated by a mixture of independent and constrained refinement
Δρ_max, Δρ_min (e Å⁻³)	0.39, −0.22

Computer programs: APEX2 (Bruker, 2014), SAINT-Plus (Bruker, 2014), SHELXT (Sheldrick, 2015a), XP in SHELXTL (Sheldrick, 2008), SHELXL2014 (Sheldrick, 2015b) and publCIF (Westrip, 2010).

Acknowledgements

This work was supported by a grant from the Science Foundation Ireland (SFI IvP 13/IA/1894).

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Volume 71| Part 10| October 2015| Pages 1151-1154

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