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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

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).

3D view (loading...)
[Scheme 3D1]
Chemical scheme
[Scheme 1]

Structure description

Tetra­kis­(di­meth­oxy­bor­yl)methane (systematic name: octa­methyl methane­tetra­yltetra­boronate), which was first reported in 1969 (Castle et al., 1969[Castle, R. B. & Matteson, D. S. (1969). J. Organomet. Chem. 20, 19-28.]), is a useful synthetic inter­mediate (Matteson, 1975[Matteson, D. S. (1975). Synthesis, 7, 147-158.]; Scherbaum et al., 1988[Scherbaum, F., Grohmann, A., Huber, B., Krüger, C. & Schmidbaur, H. (1988). Angew. Chem. Int. Ed. 27, 1544-1546.]). 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[Matteson, D. S. (1975). Synthesis, 7, 147-158.]). 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[Claramunt, R. M., Elguero, J., Fabre, M. J., Foces-Foces, C., Cano, F. H., Fuentes, I. H., Jaime, C. & López, C. (1989). Tetrahedron, 45, 7805-7816.]), 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[Banert, K., Joo, Y.-H., Rüffer, T., Walfort, B. & Lang, H. (2007). Angew. Chem. Int. Ed. 46, 1168-1171.]), tetra­kis­(pyrrol­yl)methane, C(NC4H4)4 (Müller et al., 2001[Müller, M., Lork, E. & Mews, R. (2001). Angew. Chem. Int. Ed. 40, 1247-1249.]), and tetra­kis­(3,5-dimethyl-1H-pyrazol-1-yl)methane, C(N2C3HMe2)4 (Benisvy et al., 2009[Benisvy, L., Wanke, R., Kuznetsov, M. L., Guedes da Silva, M. F. C. & Pombeiro, A. J. L. (2009). Tetrahedron, 65, 9218-9223.]). 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[Banert, K., Joo, Y.-H., Rüffer, T., Walfort, B. & Lang, H. (2007). Angew. Chem. Int. Ed. 46, 1168-1171.]). 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[Columbus, I. & Biali, S. E. (1994). J. Org. Chem. 59, 8132-8138.]; Heard et al., 2000[Heard, G. L., Gillespie, R. J. & Rankin, D. W. H. (2000). J. Mol. Struct. 520, 237-248.]; Kozhushkov et al., 2001[Kozhushkov, S. I., Kostikov, R. R., Molchanov, A. P., Boese, R., Benet-Buchholz, J., Schreiner, P. R., Rinderspacher, C., Ghiviriga, I. & de Meijere, A. (2001). Angew. Chem. Int. Ed. 40, 180-183.]; Narasimhamurthy et al., 1990[Narasimhamurthy, N., Manohar, H., Samuelson, A. G. & Chandrasekhar, J. (1990). J. Am. Chem. Soc. 112, 2937-2941.]). 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[Wadepohl, H., Arnold, U., Kohl, U., Pritzkow, H. & Wolf, A. (2000). J. Chem. Soc. Dalton Trans. pp. 3554-3565.]; Al-Masri et al., 2005[Al-Masri, H. T., Sieler, J., Junk, P. C., Domasevitch, K. V. & Hey-Hawkins, E. (2005). J. Organomet. Chem. 690, 469-476.]; Harlow et al., 2013[Harlow, G. P., Zakharov, L. N., Wu, G. & Liu, S.-Y. (2013). Organometallics, 32, 6650-6653.]), 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[El-Hiti, G. A., Smith, K., Elliott, M. C., Jones, D. H. & Kariuki, B. M. (2013). Acta Cryst. E69, o1403.]). The C—B bond length in C[B(OMe)2]4 lies within this range.

The structure of the title compound (Fig. 1[link]) 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]
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[Castle, R. B. & Matteson, D. S. (1969). J. Organomet. Chem. 20, 19-28.]), 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[Castle, R. B. & Matteson, D. S. (1969). J. Organomet. Chem. 20, 19-28.])]. 1H NMR (400 MHz, CCl4): δ 3.62 (s); literature: δ 3.45 (Castle et al., 1969[Castle, R. B. & Matteson, D. S. (1969). J. Organomet. Chem. 20, 19-28.]). 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[link]. 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.

Table 1
Experimental details

Crystal data
Chemical formula C9H24B4O8
Mr 303.52
Crystal system, space group Orthorhombic, Pbcn
Temperature (K) 102
a, b, c (Å) 7.5362 (2), 15.1084 (4), 14.5384 (4)
V3) 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[Bruker (2005). SADABS. Bruker AXS Inc. Madison, Wisconsin, USA.])
Tmin, Tmax 0.800, 0.921
No. of measured, independent and observed [I > 2σ(I)] reflections 18589, 1515, 1407
Rint 0.113
(sin θ/λ)max−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
Δρmax, Δρmin (e Å−3) 0.30, −0.19
Computer programs: APEX2 and SAINT (Bruker, 2008[Bruker (2008). APEX2 and SAINT. Bruker AXS Inc., Madison, Wisconsin, USA.]), SHELXS97 and SHELXTL (Sheldrick, 2008[Sheldrick, G. M. (2008). Acta Cryst. A64, 112-122.]), SHELXL2014 (Sheldrick, 2015[Sheldrick, G. M. (2015). Acta Cryst. A71, 3-8.]) and publCIF (Westrip, 2010[Westrip, S. P. (2010). J. Appl. Cryst. 43, 920-925.]).

Structural data


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
C9H24B4O8Dx = 1.218 Mg m3
Mr = 303.52Melting point: 350 K
Orthorhombic, PbcnCu Kα radiation, λ = 1.54178 Å
a = 7.5362 (2) ÅCell parameters from 9956 reflections
b = 15.1084 (4) Åθ = 5.9–68.2°
c = 14.5384 (4) ŵ = 0.83 mm1
V = 1655.34 (8) Å3T = 102 K
Z = 4Prism, colourless
F(000) = 6480.41 × 0.31 × 0.15 mm
Data collection top
Bruker APEXII CCD
diffractometer
1407 reflections with I > 2σ(I)
φ and ω scansRint = 0.113
Absorption correction: integration
(SADABS; Bruker, 2005)
θmax = 68.2°, θmin = 5.9°
Tmin = 0.800, Tmax = 0.921h = 99
18589 measured reflectionsk = 1816
1515 independent reflectionsl = 1517
Refinement top
Refinement on F2Hydrogen site location: inferred from neighbouring sites
Least-squares matrix: fullH-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 = 1.07Δρmax = 0.30 e Å3
1515 reflectionsΔρmin = 0.19 e Å3
106 parametersExtinction correction: SHELXL2014 (Sheldrick, 2015), Fc*=kFc[1+0.001xFc2λ3/sin(2θ)]-1/4
2 restraintsExtinction 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
xyzUiso*/UeqOcc. (<1)
C10.00000.90014 (10)0.75000.0155 (4)
B10.12770 (19)0.95880 (9)0.81186 (9)0.0169 (3)
O110.08349 (11)1.03111 (5)0.86281 (6)0.0192 (3)
C110.09245 (17)1.06218 (9)0.87896 (9)0.0227 (3)
H11A0.17521.03080.83840.034*
H11B0.09821.12580.86630.034*
H11C0.12491.05120.94320.034*
O120.30328 (12)0.93573 (6)0.81320 (7)0.0254 (3)
C120.42669 (19)0.98075 (12)0.87109 (11)0.0369 (4)
H12A0.37940.98370.93380.055*
H12B0.44591.04080.84770.055*
H12C0.53960.94860.87150.055*
B20.11652 (19)0.84032 (9)0.81675 (9)0.0193 (3)
O210.11510 (12)0.86140 (6)0.90809 (6)0.0208 (3)
C210.2149 (2)0.81036 (9)0.97275 (9)0.0286 (4)
H21A0.16180.75140.97870.043*
H21B0.33750.80470.95120.043*
H21C0.21360.84001.03270.043*
O220.21478 (16)0.76806 (6)0.79387 (6)0.0334 (3)
C22A0.2612 (10)0.7418 (4)0.7017 (3)0.0324 (11)0.677 (14)
H22A0.26400.67710.69780.049*0.677 (14)
H22B0.17280.76490.65840.049*0.677 (14)
H22C0.37840.76570.68600.049*0.677 (14)
C22B0.2050 (18)0.7274 (8)0.7041 (6)0.0324 (11)0.323 (14)
H22D0.29960.68330.69800.049*0.323 (14)
H22E0.08950.69850.69670.049*0.323 (14)
H22F0.21930.77290.65660.049*0.323 (14)
Atomic displacement parameters (Å2) top
U11U22U33U12U13U23
C10.0213 (8)0.0111 (7)0.0141 (8)0.0000.0014 (6)0.000
B10.0188 (7)0.0150 (6)0.0168 (6)0.0001 (5)0.0010 (5)0.0023 (5)
O110.0176 (5)0.0168 (5)0.0233 (5)0.0019 (3)0.0011 (3)0.0041 (3)
C110.0220 (7)0.0186 (6)0.0277 (7)0.0026 (5)0.0022 (5)0.0058 (5)
O120.0186 (5)0.0303 (5)0.0273 (5)0.0039 (4)0.0027 (4)0.0042 (4)
C120.0192 (7)0.0502 (10)0.0413 (9)0.0013 (6)0.0075 (6)0.0095 (7)
B20.0273 (7)0.0132 (6)0.0172 (7)0.0029 (5)0.0005 (6)0.0003 (5)
O210.0288 (5)0.0187 (5)0.0149 (5)0.0073 (4)0.0024 (4)0.0001 (3)
C210.0404 (8)0.0275 (7)0.0178 (7)0.0126 (6)0.0055 (6)0.0019 (5)
O220.0583 (7)0.0247 (5)0.0173 (5)0.0221 (5)0.0004 (4)0.0021 (4)
C22A0.052 (3)0.025 (2)0.0204 (8)0.0169 (19)0.0027 (15)0.0053 (10)
C22B0.052 (3)0.025 (2)0.0204 (8)0.0169 (19)0.0027 (15)0.0053 (10)
Geometric parameters (Å, º) top
C1—B1i1.5876 (16)B2—O221.3604 (17)
C1—B11.5876 (16)B2—O211.3656 (16)
C1—B2i1.5905 (16)O21—C211.4295 (15)
C1—B21.5905 (16)C21—H21A0.9800
B1—O111.3613 (16)C21—H21B0.9800
B1—O121.3685 (17)C21—H21C0.9800
O11—C111.4260 (15)O22—C22A1.441 (4)
C11—H11A0.9800O22—C22B1.444 (8)
C11—H11B0.9800C22A—H22A0.9800
C11—H11C0.9800C22A—H22B0.9800
O12—C121.4268 (18)C22A—H22C0.9800
C12—H12A0.9800C22B—H22D0.9800
C12—H12B0.9800C22B—H22E0.9800
C12—H12C0.9800C22B—H22F0.9800
B1i—C1—B1112.12 (13)O22—B2—C1127.39 (11)
B1i—C1—B2i107.83 (7)O21—B2—C1117.16 (10)
B1—C1—B2i109.16 (7)B2—O21—C21120.63 (10)
B1i—C1—B2109.16 (7)O21—C21—H21A109.5
B1—C1—B2107.83 (7)O21—C21—H21B109.5
B2i—C1—B2110.74 (14)H21A—C21—H21B109.5
O11—B1—O12115.68 (11)O21—C21—H21C109.5
O11—B1—C1127.44 (11)H21A—C21—H21C109.5
O12—B1—C1116.87 (10)H21B—C21—H21C109.5
B1—O11—C11125.54 (10)B2—O22—C22A125.5 (2)
O11—C11—H11A109.5B2—O22—C22B122.3 (5)
O11—C11—H11B109.5O22—C22A—H22A109.5
H11A—C11—H11B109.5O22—C22A—H22B109.5
O11—C11—H11C109.5H22A—C22A—H22B109.5
H11A—C11—H11C109.5O22—C22A—H22C109.5
H11B—C11—H11C109.5H22A—C22A—H22C109.5
B1—O12—C12121.15 (11)H22B—C22A—H22C109.5
O12—C12—H12A109.5O22—C22B—H22D109.5
O12—C12—H12B109.5O22—C22B—H22E109.5
H12A—C12—H12B109.5H22D—C22B—H22E109.5
O12—C12—H12C109.5O22—C22B—H22F109.5
H12A—C12—H12C109.5H22D—C22B—H22F109.5
H12B—C12—H12C109.5H22E—C22B—H22F109.5
O22—B2—O21115.42 (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.

References

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