organic compounds
Tetrakis(dimethoxyboryl)methane
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
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 Pbcn. The molecules, which reside on sites of crystallographic twofold symmetry, have idealized -4 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).
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 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 2m geometries (Columbus & Biali, 1994; Heard et al., 2000; Kozhushkov et al., 2001; Narasimhamurthy et al., 1990). This 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 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.
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 in a vacuum.
Refinement
Crystal data, data collection, and structure . 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 Ueq(C). An isotropic extinction parameter was refined to a final value of x = 2.708 × 10−6, where Fc is multiplied by the factor k [1 + Fc2 × λ3/sin (2θ)]−1/4, with k being the overall scale factor.
details are summarized in Table 1Structural data
CCDC reference: 1497734
10.1107/S2414314616012645/rz4004sup1.cif
contains datablock I. DOI: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
Data collection: APEX2 (Bruker, 2008); cell
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).C9H24B4O8 | Dx = 1.218 Mg m−3 |
Mr = 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 |
Bruker APEXII CCD diffractometer | 1407 reflections with I > 2σ(I) |
φ and ω scans | Rint = 0.113 |
Absorption correction: integration (SADABS; Bruker, 2005) | θmax = 68.2°, θmin = 5.9° |
Tmin = 0.800, Tmax = 0.921 | h = −9→9 |
18589 measured reflections | k = −18→16 |
1515 independent reflections | l = −15→17 |
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(Fo2) + (0.0429P)2 + 0.7225P] where P = (Fo2 + 2Fc2)/3 |
wR(F2) = 0.100 | (Δ/σ)max = 0.001 |
S = 1.07 | Δρmax = 0.30 e Å−3 |
1515 reflections | Δρmin = −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) |
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. |
x | y | z | Uiso*/Ueq | 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) |
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) |
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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