Tetra­kis(di­meth­oxy­bor­yl)methane

Liu, S.; Girolami, G.S.

doi:10.1107/S2414314616012645

organic compounds

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ISSN: 2414-3146

Volume 1| Part 8| August 2016| x161264

doi:10.1107/S2414314616012645

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Tetrakis(dimethoxyboryl)methane

Sumeng Liu ^a and Gregory S. Girolami ^a ^*

^aSchool of Chemical Sciences, University of Illinois at Urbana-Champaign, 600, South Mathews Avenue, Urbana, IL 61801, USA
^*Correspondence e-mail: girolami@scs.illinois.edu

Edited by C. Rizzoli, Universita degli Studi di Parma, Italy (Received 9 July 2016; accepted 4 August 2016; online 12 August 2016)

The title compound, tetrakis(dimethoxyboryl)methane (systematic name: octamethyl methanetetrayltetraboronate), C₉H₂₄B₄O₈ or C[B(OMe)₂]₄, is a useful synthetic intermediate. Crystals of this compound at 102 K conform to the orthorhombic space group Pbcn. The molecules, which reside on sites of crystallographic twofold symmetry, have idealized -4 point symmetry like most other CX₄ molecules in which each X group bears two non-H substituents at the 1-position. The central C atom has a slightly distorted tetrahedral coordination geometry, with C—B bond lengths of 1.5876 (16) and 1.5905 (16) Å. One of the methoxy groups is disordered over two sets of sites; the major component has an occupancy factor of 0.676 (8).

Keywords: crystal structure; tetrakis(dimethoxyboryl)methane; methane derivative.

CCDC reference: 1497734

Structure description

Tetrakis(dimethoxyboryl)methane (systematic name: octamethyl methanetetrayltetraboronate), which was first reported in 1969 (Castle et al., 1969 ), is a useful synthetic intermediate (Matteson, 1975 ; Scherbaum et al., 1988 ). For example, treatment with ethanol-free lithium ethoxide generates the tris(dimethoxyboryl)methide anion, {C[B(OMe)₂]₃}⁻, whereas treatment with mercuric salts generates C(HgX)₄ derivatives (Matteson, 1975). Several crystal structures of tetrasubstituted methanes are known in which the central C atom forms four C—N bonds; these include tetrakis(pyrazolyl)methane, C(N₂C₃H₃)₄ (Claramunt et al., 1989 ), tetrakis(4,5,6,7,8,9-hexahydro-1H-cycloocta[d][1,2,3]triazol-1-yl)methane, C(N₃C₈H₁₂)₄ (Banert et al., 2007 ), tetrakis(pyrrolyl)methane, C(NC₄H₄)₄ (Müller et al., 2001 ), and tetrakis(3,5-dimethyl-1H-pyrazol-1-yl)methane, C(N₂C₃HMe₂)₄ (Benisvy et al., 2009 ). All of these molecules adopt idealized $[\overline{4}]$ geometries and each substituent is planar, as we see for C[B(OMe)₂]₄. In all of these CX₄ molecules, each planar X group bears two non-H substituents at the 1-position. Secondary interactions between the substituents (such as between a C—H bond and an aromatic ring) may be relevant to the formation of this geometry (Banert et al., 2007). In fact, as mentioned above, the present molecule features 2.5 Å B⋯H—C interactions between each B atom and a methyl H atom on another B(OMe)₂ substituent. Some other CX₄ compounds adopt idealized $[\overline{4}]$ 2m geometries (Columbus & Biali, 1994 ; Heard et al., 2000 ; Kozhushkov et al., 2001 ; Narasimhamurthy et al., 1990 ). This point group is seen, for example, when X is an alkoxy, thiolate, or a primary or secondary alkyl group. In these CX₄ molecules, there are no weak inter-ligand bonding interactions, and typically (although not invariably) the X group bears one non-H substituent at the 1-position. For borates with boron attached to a Csp³ atom, the C—B bond length is typically 1.575 Å (Wadepohl et al., 2000 ; Al-Masri et al., 2005 ; Harlow et al., 2013 ), but is slightly longer, 1.603 (2) Å, in the sterically crowded molecule (E)-2-(1,1-dicyclohexyl-3-phenyl-3-allyl)-5,5-dimethyl-1,3,2-dioxaborinane (El-Hiti et al., 2013 ). The C—B bond length in C[B(OMe)₂]₄ lies within this range.

The structure of the title compound (Fig. 1) is the first of a nonpolyhedral compound in which a single C atom is connected to four B atoms. Molecules of C[B(OMe)₂]₄ reside on crystallographic twofold axes, but adopt idealized $[\overline{4}]$ geometries. The central C atom has a slightly distorted tetrahedral coordination geometry, with C—B bond distances of 1.5876 (16) and 1.5905 (16) Å. The B atoms have trigonal planar geometries owing to π donation from the methoxy groups. Each B atom also forms a long intramolecular contact of 2.5 Å to a methyl H atom on another B(OMe)₂ substituent, consistent with the presence of a weak B⋯H—C interaction. One of the methyl groups is disordered over two sites.

Figure 1
The molecular structure of the title compound, shown with 35% probability displacement ellipsoids. The H atoms are depicted with arbitrary radii. [Symmetry code: (i) −x, y, $[{3\over 2}]$ − z.]

Synthesis and crystallization

The title compound was synthesized according to a literature procedure (Castle et al., 1969), but on a reduced scale. The product was sublimed at 348 K (10 mTorr) to give colorless crystals [m.p. 350–351 K; literature 349–351 K (Castle et al., 1969)]. ¹H NMR (400 MHz, CCl₄): δ 3.62 (s); literature: δ 3.45 (Castle et al., 1969). ¹¹B NMR (400 MHz, CCl₄): δ 30.6 (s), referenced to BF₃·Et₂O. The crystal used for the X-ray analysis was grown by slow sublimation in a vacuum.

Refinement

Crystal data, data collection, and structure refinement details are summarized in Table 1. One of the methoxy groups is disordered over two sets of sites; the major component has an occupancy factor of 0.676 (8). The disordered O—C bond lengths were restrained to be 1.43 (1) Å, and the anisotropic displacement parameters of the disordered partial C atoms were restrained to be equal. H atoms were placed in idealized positions, with C—H = 0.98 Å; the methyl groups were allowed to rotate about the C—O axis to find the best least-squares positions. The displacement parameters for the methyl H atoms were set at 1.5 times U_eq(C). An isotropic extinction parameter was refined to a final value of x = 2.708 × 10⁻⁶, where F_c is multiplied by the factor k [1 + F_c² × λ³/sin (2θ)]^−1/4, with k being the overall scale factor.

Table 1
Experimental details

Crystal data
Chemical formula	C₉H₂₄B₄O₈
M_r	303.52
Crystal system, space group	Orthorhombic, Pbcn
Temperature (K)	102
a, b, c (Å)	7.5362 (2), 15.1084 (4), 14.5384 (4)
V (Å³)	1655.34 (8)
Z	4
Radiation type	Cu Kα
μ (mm⁻¹)	0.83
Crystal size (mm)	0.41 × 0.31 × 0.15

Data collection
Diffractometer	Bruker APEXII CCD
Absorption correction	Integration (SADABS; Bruker, 2005 )
T_min, T_max	0.800, 0.921
No. of measured, independent and observed [I > 2σ(I)] reflections	18589, 1515, 1407
R_int	0.113
(sin θ/λ)_max (Å⁻¹)	0.602

Refinement
R[F² > 2σ(F²)], wR(F²), S	0.037, 0.100, 1.07
No. of reflections	1515
No. of parameters	106
No. of restraints	2
H-atom treatment	H-atom parameters constrained
Δρ_max, Δρ_min (e Å⁻³)	0.30, −0.19
Computer programs: APEX2 and SAINT (Bruker, 2008 ), SHELXS97 and SHELXTL (Sheldrick, 2008 ), SHELXL2014 (Sheldrick, 2015 ) and publCIF (Westrip, 2010 ).

Structural data

CCDC reference: 1497734

Crystal structure: contains datablock I. DOI: 10.1107/S2414314616012645/rz4004sup1.cif

Structure factors: contains datablock I. DOI: 10.1107/S2414314616012645/rz4004Isup2.hkl

Supporting information file. DOI: 10.1107/S2414314616012645/rz4004Isup3.cdx

Supporting information file. DOI: 10.1107/S2414314616012645/rz4004Isup4.cml

checkCIF report

Computing details top

Data collection: APEX2 (Bruker, 2008); cell refinement: SAINT (Bruker, 2008); data reduction: SAINT (Bruker, 2008); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL2014 (Sheldrick, 2015); molecular graphics: SHELXTL (Sheldrick, 2008); software used to prepare material for publication: publCIF (Westrip, 2010).

Octamethyl methanetetrayltetraboronate top

Crystal data top

C₉H₂₄B₄O₈	D_x = 1.218 Mg m⁻³
M_r = 303.52	Melting point: 350 K
Orthorhombic, Pbcn	Cu Kα radiation, λ = 1.54178 Å
a = 7.5362 (2) Å	Cell parameters from 9956 reflections
b = 15.1084 (4) Å	θ = 5.9–68.2°
c = 14.5384 (4) Å	µ = 0.83 mm⁻¹
V = 1655.34 (8) Å³	T = 102 K
Z = 4	Prism, colourless
F(000) = 648	0.41 × 0.31 × 0.15 mm

Data collection top

Bruker APEXII CCD diffractometer	1407 reflections with I > 2σ(I)
φ and ω scans	R_int = 0.113
Absorption correction: integration (SADABS; Bruker, 2005)	θ_max = 68.2°, θ_min = 5.9°
T_min = 0.800, T_max = 0.921	h = −9→9
18589 measured reflections	k = −18→16
1515 independent reflections	l = −15→17

Refinement top

Refinement on F²	Hydrogen site location: inferred from neighbouring sites
Least-squares matrix: full	H-atom parameters constrained
R[F² > 2σ(F²)] = 0.037	w = 1/[σ²(F_o²) + (0.0429P)² + 0.7225P] where P = (F_o² + 2F_c²)/3
wR(F²) = 0.100	(Δ/σ)_max = 0.001
S = 1.07	Δρ_max = 0.30 e Å⁻³
1515 reflections	Δρ_min = −0.19 e Å⁻³
106 parameters	Extinction correction: SHELXL2014 (Sheldrick, 2015), Fc^*=kFc[1+0.001xFc²λ³/sin(2θ)]^-1/4
2 restraints	Extinction coefficient: 0.0027 (5)

Special details top

Experimental. One distinct cell was identified using APEX2 (Bruker, 2010). Frame series were integrated and filtered for statistical outliers using SAINT (Bruker, 2005) then corrected for absorption by integration using SHELXTL/XPREP V2005/2 (Bruker, 2005) before using SADABS (Bruker, 2005) to sort, merge, and scale the combined data. No decay correction was applied.

Geometry. All esds (except the esd in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell esds are taken into account individually in the estimation of esds in distances, angles and torsion angles; correlations between esds in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell esds is used for estimating esds involving l.s. planes.

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

	x	y	z	U_iso*/U_eq	Occ. (<1)
C1	0.0000	0.90014 (10)	0.7500	0.0155 (4)
B1	0.12770 (19)	0.95880 (9)	0.81186 (9)	0.0169 (3)
O11	0.08349 (11)	1.03111 (5)	0.86281 (6)	0.0192 (3)
C11	−0.09245 (17)	1.06218 (9)	0.87896 (9)	0.0227 (3)
H11A	−0.1752	1.0308	0.8384	0.034*
H11B	−0.0982	1.1258	0.8663	0.034*
H11C	−0.1249	1.0512	0.9432	0.034*
O12	0.30328 (12)	0.93573 (6)	0.81320 (7)	0.0254 (3)
C12	0.42669 (19)	0.98075 (12)	0.87109 (11)	0.0369 (4)
H12A	0.3794	0.9837	0.9338	0.055*
H12B	0.4459	1.0408	0.8477	0.055*
H12C	0.5396	0.9486	0.8715	0.055*
B2	−0.11652 (19)	0.84032 (9)	0.81675 (9)	0.0193 (3)
O21	−0.11510 (12)	0.86140 (6)	0.90809 (6)	0.0208 (3)
C21	−0.2149 (2)	0.81036 (9)	0.97275 (9)	0.0286 (4)
H21A	−0.1618	0.7514	0.9787	0.043*
H21B	−0.3375	0.8047	0.9512	0.043*
H21C	−0.2136	0.8400	1.0327	0.043*
O22	−0.21478 (16)	0.76806 (6)	0.79387 (6)	0.0334 (3)
C22A	−0.2612 (10)	0.7418 (4)	0.7017 (3)	0.0324 (11)	0.677 (14)
H22A	−0.2640	0.6771	0.6978	0.049*	0.677 (14)
H22B	−0.1728	0.7649	0.6584	0.049*	0.677 (14)
H22C	−0.3784	0.7657	0.6860	0.049*	0.677 (14)
C22B	−0.2050 (18)	0.7274 (8)	0.7041 (6)	0.0324 (11)	0.323 (14)
H22D	−0.2996	0.6833	0.6980	0.049*	0.323 (14)
H22E	−0.0895	0.6985	0.6967	0.049*	0.323 (14)
H22F	−0.2193	0.7729	0.6566	0.049*	0.323 (14)

Atomic displacement parameters (Å²) top

	U¹¹	U²²	U³³	U¹²	U¹³	U²³
C1	0.0213 (8)	0.0111 (7)	0.0141 (8)	0.000	0.0014 (6)	0.000
B1	0.0188 (7)	0.0150 (6)	0.0168 (6)	−0.0001 (5)	0.0010 (5)	0.0023 (5)
O11	0.0176 (5)	0.0168 (5)	0.0233 (5)	−0.0019 (3)	0.0011 (3)	−0.0041 (3)
C11	0.0220 (7)	0.0186 (6)	0.0277 (7)	0.0026 (5)	0.0022 (5)	−0.0058 (5)
O12	0.0186 (5)	0.0303 (5)	0.0273 (5)	0.0039 (4)	−0.0027 (4)	−0.0042 (4)
C12	0.0192 (7)	0.0502 (10)	0.0413 (9)	0.0013 (6)	−0.0075 (6)	−0.0095 (7)
B2	0.0273 (7)	0.0132 (6)	0.0172 (7)	−0.0029 (5)	−0.0005 (6)	0.0003 (5)
O21	0.0288 (5)	0.0187 (5)	0.0149 (5)	−0.0073 (4)	0.0024 (4)	−0.0001 (3)
C21	0.0404 (8)	0.0275 (7)	0.0178 (7)	−0.0126 (6)	0.0055 (6)	0.0019 (5)
O22	0.0583 (7)	0.0247 (5)	0.0173 (5)	−0.0221 (5)	0.0004 (4)	−0.0021 (4)
C22A	0.052 (3)	0.025 (2)	0.0204 (8)	−0.0169 (19)	−0.0027 (15)	−0.0053 (10)
C22B	0.052 (3)	0.025 (2)	0.0204 (8)	−0.0169 (19)	−0.0027 (15)	−0.0053 (10)

Geometric parameters (Å, º) top

C1—B1ⁱ	1.5876 (16)	B2—O22	1.3604 (17)
C1—B1	1.5876 (16)	B2—O21	1.3656 (16)
C1—B2ⁱ	1.5905 (16)	O21—C21	1.4295 (15)
C1—B2	1.5905 (16)	C21—H21A	0.9800
B1—O11	1.3613 (16)	C21—H21B	0.9800
B1—O12	1.3685 (17)	C21—H21C	0.9800
O11—C11	1.4260 (15)	O22—C22A	1.441 (4)
C11—H11A	0.9800	O22—C22B	1.444 (8)
C11—H11B	0.9800	C22A—H22A	0.9800
C11—H11C	0.9800	C22A—H22B	0.9800
O12—C12	1.4268 (18)	C22A—H22C	0.9800
C12—H12A	0.9800	C22B—H22D	0.9800
C12—H12B	0.9800	C22B—H22E	0.9800
C12—H12C	0.9800	C22B—H22F	0.9800

B1ⁱ—C1—B1	112.12 (13)	O22—B2—C1	127.39 (11)
B1ⁱ—C1—B2ⁱ	107.83 (7)	O21—B2—C1	117.16 (10)
B1—C1—B2ⁱ	109.16 (7)	B2—O21—C21	120.63 (10)
B1ⁱ—C1—B2	109.16 (7)	O21—C21—H21A	109.5
B1—C1—B2	107.83 (7)	O21—C21—H21B	109.5
B2ⁱ—C1—B2	110.74 (14)	H21A—C21—H21B	109.5
O11—B1—O12	115.68 (11)	O21—C21—H21C	109.5
O11—B1—C1	127.44 (11)	H21A—C21—H21C	109.5
O12—B1—C1	116.87 (10)	H21B—C21—H21C	109.5
B1—O11—C11	125.54 (10)	B2—O22—C22A	125.5 (2)
O11—C11—H11A	109.5	B2—O22—C22B	122.3 (5)
O11—C11—H11B	109.5	O22—C22A—H22A	109.5
H11A—C11—H11B	109.5	O22—C22A—H22B	109.5
O11—C11—H11C	109.5	H22A—C22A—H22B	109.5
H11A—C11—H11C	109.5	O22—C22A—H22C	109.5
H11B—C11—H11C	109.5	H22A—C22A—H22C	109.5
B1—O12—C12	121.15 (11)	H22B—C22A—H22C	109.5
O12—C12—H12A	109.5	O22—C22B—H22D	109.5
O12—C12—H12B	109.5	O22—C22B—H22E	109.5
H12A—C12—H12B	109.5	H22D—C22B—H22E	109.5
O12—C12—H12C	109.5	O22—C22B—H22F	109.5
H12A—C12—H12C	109.5	H22D—C22B—H22F	109.5
H12B—C12—H12C	109.5	H22E—C22B—H22F	109.5
O22—B2—O21	115.42 (11)

Symmetry code: (i) −x, y, −z+3/2.

Acknowledgements

This work was supported financially by the National Science Foundation (CHE-13–62931). X-ray data were collected in the George L. Clark X-Ray Facility at the University of Illinois.

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