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Tripivaloylmethane [systematic name: 4-(2,2-dimethylpropanoyl)-2,2,6,6-tetramethylheptane-3,5-dione], C16H28O3, is a 1,3,3′-triketone with C3 molecular symmetry, prepared by α-acylation of 2,2,6,6-tetramethylheptane-3,5-dione with 2,2-dimethylpropanoyl anhydride in the presence of barium metal. The molecules are conformationally chiral and pack so that each molecular site is occupied with equal probability by the two enantiomers. The carbonyl groups of the two superimposed enantiomeric molecules are at an angle of 75.4 (16)°.
Supporting information
CCDC reference: 652517
Compound (I) was prepared by a method similar to that described by Lim et
al. (2001). 2,2,6,6-Tetramethylheptane-3,5-dione (1.0 mmol) was dissolved
in cyclohexane (30 ml); powdered barium metal (0.5 mmol) was added, and the
mixture was heated under reflux for 45 min. 2,2-Dimethylpropanoyl anhydride
(2.0 mmol) was added to the resulting solution, which was then heated under
reflux for a further for 6 h. The resulting precipitate of barium pivaloate
was removed by filtration, and the solution was then left to cool to ambient
temperature, at which point white needles of (I) (0.3 mmol) crystallized from
the mother liquor. NMR (CDCl3): δ(H) 5.92 (s, 1H, –CH), 1.18
(s, 27H, –CH3); δ(C) 27.5 (C4, C5, C6), 45.2 (C3), 64.6 (C1), 207.1
(C2). The compound was crystallized as elongated colourless prisms by slow
isothermal evaporation of a solution in dimethyl sulfoxide.
Crystals of compound (I) are trigonal. Initially, space group R3 was
selected, but during the refinement it was found that the symmetry is higher
as a result of the disorder and the space group was assigned as
R3m, which was confirmed by the successful structure analysis.
Since the space group is achiral, the Friedel equivalents were averaged.
Methyl H atoms were placed in calculated positions and treated as riding, with
C–H = 0.96 Å and Uiso(H) = 1.5Ueq(C). The methine H atom
was located in a difference map and refined isotropically with x and
y coordinates restrained to 0.
Data collection: CrysAlis CCD (Oxford Diffraction, 2003); cell refinement: CrysAlis RED (Oxford Diffraction, 2003); data reduction: CrysAlis RED; program(s) used to solve structure: SHELXS97 (Sheldrick, 1997); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: ORTEP-3 (Farrugia, 1997); software used to prepare material for publication: WinGX (Farrugia, 1999) and PARST97 (Nardelli, 1995).
4-(2,2-dimethylpropanoyl)-2,2,6,6-tetramethylheptane-3,5-dione
top
Crystal data top
C16H28O3 | Dx = 1.08 Mg m−3 |
Mr = 268.38 | Mo Kα radiation, λ = 0.71073 Å |
Trigonal, R3m | Cell parameters from 1072 reflections |
Hall symbol: R 3 -2" | θ = 4.6–32.0° |
a = 15.711 (7) Å | µ = 0.07 mm−1 |
c = 5.792 (2) Å | T = 298 K |
V = 1238.1 (9) Å3 | Prism, colourless |
Z = 3 | 0.65 × 0.29 × 0.22 mm |
F(000) = 444 | |
Data collection top
Oxford Diffraction Xcalibur CCD diffractometer | 433 reflections with I > 2σ(I) |
Radiation source: fine-focus sealed tube | Rint = 0.035 |
Graphite monochromator | θmax = 31.9°, θmin = 4.5° |
ω scan | h = −23→22 |
3386 measured reflections | k = −21→23 |
518 independent reflections | l = −8→8 |
Refinement top
Refinement on F2 | 2 restraints |
Least-squares matrix: full | H atoms treated by a mixture of independent and constrained refinement |
R[F2 > 2σ(F2)] = 0.075 | w = 1/[σ2(Fo2) + (0.1632P)2 + 0.058P] where P = (Fo2 + 2Fc2)/3 |
wR(F2) = 0.234 | (Δ/σ)max < 0.001 |
S = 1.07 | Δρmax = 0.12 e Å−3 |
518 reflections | Δρmin = −0.13 e Å−3 |
50 parameters | |
Crystal data top
C16H28O3 | Z = 3 |
Mr = 268.38 | Mo Kα radiation |
Trigonal, R3m | µ = 0.07 mm−1 |
a = 15.711 (7) Å | T = 298 K |
c = 5.792 (2) Å | 0.65 × 0.29 × 0.22 mm |
V = 1238.1 (9) Å3 | |
Data collection top
Oxford Diffraction Xcalibur CCD diffractometer | 433 reflections with I > 2σ(I) |
3386 measured reflections | Rint = 0.035 |
518 independent reflections | |
Refinement top
R[F2 > 2σ(F2)] = 0.075 | 2 restraints |
wR(F2) = 0.234 | H atoms treated by a mixture of independent and constrained refinement |
S = 1.07 | Δρmax = 0.12 e Å−3 |
518 reflections | Δρmin = −0.13 e Å−3 |
50 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 | Uiso*/Ueq | Occ. (<1) |
C5 | 0.2751 (5) | 0.154 (3) | 0.8404 (13) | 0.142 (14) | 0.5 |
H5A | 0.264 | 0.202 | 0.7673 | 0.213* | 0.5 |
H5B | 0.2737 | 0.1086 | 0.7263 | 0.213* | 0.5 |
H5C | 0.3381 | 0.1856 | 0.915 | 0.213* | 0.5 |
C4 | 0.2015 (5) | 0.1767 (4) | 1.1820 (14) | 0.137 (2) | |
H6A | 0.1385 | 0.1544 | 1.2526 | 0.205* | |
H6B | 0.2202 | 0.2359 | 1.0968 | 0.205* | |
H6C | 0.2495 | 0.1895 | 1.2996 | 0.205* | |
C1 | 0 | 0 | 0.9920 (7) | 0.0443 (9) | |
C3 | 0.1954 (2) | 0.09771 (11) | 1.0186 (7) | 0.0651 (9) | |
C2 | 0.1002 (3) | 0.0802 (3) | 0.9009 (6) | 0.0507 (9) | 0.5 |
O1 | 0.1007 (3) | 0.1278 (4) | 0.7338 (7) | 0.0811 (14) | 0.5 |
H1 | 0 | 0 | 1.160 (4) | 0.066 (19)* | |
Atomic displacement parameters (Å2) top | U11 | U22 | U33 | U12 | U13 | U23 |
C5 | 0.058 (3) | 0.18 (2) | 0.096 (4) | −0.007 (10) | 0.015 (3) | 0.001 (9) |
C4 | 0.162 (6) | 0.112 (4) | 0.135 (4) | 0.068 (4) | −0.012 (4) | −0.032 (3) |
C1 | 0.0465 (12) | 0.0465 (12) | 0.0401 (16) | 0.0232 (6) | 0 | 0 |
C3 | 0.0483 (15) | 0.0738 (16) | 0.0647 (16) | 0.0241 (8) | −0.0025 (13) | −0.0013 (6) |
C2 | 0.0490 (18) | 0.0504 (16) | 0.0494 (18) | 0.0224 (14) | 0.0041 (14) | 0.0019 (13) |
O1 | 0.071 (2) | 0.086 (3) | 0.076 (2) | 0.032 (2) | 0.0107 (17) | 0.0382 (19) |
Geometric parameters (Å, º) top
C5—C3 | 1.518 (11) | C4—H6C | 0.96 |
C5—H5A | 0.96 | C1—C2 | 1.537 (4) |
C5—H5B | 0.96 | C1—H1 | 0.97 (2) |
C5—H5C | 0.96 | C3—C4i | 1.525 (7) |
C4—C3 | 1.526 (7) | C3—C5i | 1.518 (11) |
C4—H6A | 0.96 | C3—C2 | 1.538 (5) |
C4—H6B | 0.96 | C2—O1 | 1.221 (6) |
| | | |
C3—C5—H5A | 109.5 | C4i—C3—C5i | 104.7 (18) |
C3—C5—H5B | 109.5 | C4—C3—C2 | 94.6 (3) |
H5A—C5—H5B | 109.5 | C4i—C3—C2 | 124.1 (3) |
C3—C5—H5C | 109.5 | C5—C3—C2 | 104.4 (9) |
H5A—C5—H5C | 109.5 | C5i—C3—C2 | 110.6 (6) |
H5B—C5—H5C | 109.5 | C4—C3—C2i | 124.1 (3) |
C3—C4—H6A | 109.5 | C4i—C3—C2i | 94.6 (3) |
C3—C4—H6B | 109.5 | C5—C3—C2i | 110.6 (6) |
H6A—C4—H6B | 109.5 | C5i—C3—C2i | 104.4 (9) |
C3—C4—H6C | 109.5 | C2i—C2—O1 | 127.6 (3) |
H6A—C4—H6C | 109.5 | C2i—C2—C1 | 72.08 (16) |
H6B—C4—H6C | 109.5 | O1—C2—C1 | 117.6 (4) |
C2ii—C1—C2 | 108.87 (19) | C2i—C2—C3 | 72.10 (16) |
C2ii—C1—H1 | 110.07 (19) | O1—C2—C3 | 122.3 (4) |
C2iii—C1—H1 | 110.07 (19) | C1—C2—C3 | 120.0 (3) |
C2i—C1—H1 | 110.07 (18) | C2i—C2—C2iv | 120.000 (3) |
C2—C1—H1 | 110.07 (19) | O1—C2—C2iv | 72.5 (3) |
C2iv—C1—H1 | 110.07 (18) | C3—C2—C2iv | 152.00 (19) |
C2v—C1—H1 | 110.07 (18) | C2i—C2—O1iv | 133.6 (2) |
C4—C3—C4i | 103.0 (6) | C1—C2—O1iv | 85.7 (2) |
C4—C3—C5 | 104.7 (18) | C3—C2—O1iv | 150.8 (3) |
C4i—C3—C5 | 120.9 (17) | O1iv—O1—C2 | 107.5 (3) |
C4—C3—C5i | 120.9 (17) | C2—O1—C2iv | 70.1 (3) |
Symmetry codes: (i) x, x−y, z; (ii) −x+y, −x, z; (iii) −y, −x, z; (iv) −x+y, y, z; (v) −y, x−y, z. |
Experimental details
Crystal data |
Chemical formula | C16H28O3 |
Mr | 268.38 |
Crystal system, space group | Trigonal, R3m |
Temperature (K) | 298 |
a, c (Å) | 15.711 (7), 5.792 (2) |
V (Å3) | 1238.1 (9) |
Z | 3 |
Radiation type | Mo Kα |
µ (mm−1) | 0.07 |
Crystal size (mm) | 0.65 × 0.29 × 0.22 |
|
Data collection |
Diffractometer | Oxford Diffraction Xcalibur CCD diffractometer |
Absorption correction | – |
No. of measured, independent and observed [I > 2σ(I)] reflections | 3386, 518, 433 |
Rint | 0.035 |
(sin θ/λ)max (Å−1) | 0.744 |
|
Refinement |
R[F2 > 2σ(F2)], wR(F2), S | 0.075, 0.234, 1.07 |
No. of reflections | 518 |
No. of parameters | 50 |
No. of restraints | 2 |
H-atom treatment | H atoms treated by a mixture of independent and constrained refinement |
Δρmax, Δρmin (e Å−3) | 0.12, −0.13 |
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1,3,3'-Triketones can be obtained by acylation, using acyl halides or acid anhydrides, of β-diketones (Lim et al., 2001), their salts (Rogers & Smith, 1955) or their transition metal complexes (Murdoch & Nonhebel, 1962; Collman et al., 1963 or???1962) with acyl halogenides and acid anhydrides. Alkylation and acylation in the α-position of β-diketones, especially with bulkier groups, affects the keto–enol equilibrium in favour of the keto form. Cyclic 1,3,3'-triketones have attracted some interest because of their application as herbicides, since it has been shown that their derivatives inhibit p-hydroxyphenylpyruvate dioxygenase (Lee et al., 1998, and references therein). 1,3,3'-Triketones have also been studied as chelating ligands with group 2 and lanthanide cations (Ismail et al., 1969 or???1968). Although the crystal structures of many α-substituted β-diketones are known, only one crystal structure of an acyclic 1,3,3'-triketone [Cambridge Structural Database (CSD; Allen, 2002) refcode OCIQOG (Lim et al., 2001)] and one transition metal complex with an acyclical 1,3,3'-triketonate ligand (CSD refcode IGAGUS; Carano et al., 2002) have been reported to date.
The title compound, (I) (Fig. 1), is a potential tridentate monoanionic and neutral ligand for coordination to transition metal ions. Compound (I) crystallizes in the trigonal system, space group R3m, with Z = 3. The molecules of (I) are in the 3(a) special position of the space group, with the methine C–H bond along the threefold axis. The molecule is a triketo tautomer with a C2=O1 distance of 1.221 (6) Å, and a C1—C2═O1 angle of 117.6 (4)°. The molecule has C3 molecular symmetry, and is comformationaly chiral. The space group accommodates equal numbers of M and P enantiomers, so that each molecular site is occupied with equal probability by the two enantiomers. Atoms C1, C3 and C5 and the corresponding H atoms were assigned common sites in both enantiomers. The angle between the C1/C2/O1/C3 planes of the two enantiomers is 75.4 (16)°.
The nature of the disorder raises the question of whether the structure might actually be ordered in space group R3. Refinement of such a model, both with the same unit-cell parameters and with a doubled z, however, led to R values above 1/4, with large and extremely anisotropic Uij ellipsoids. The shapes of the ellipsoids of atoms C2 and O1, as well as the difference map, indicated that these atoms should be split in two. After splitting the atoms and further refinement, the refinements either became unstable or led to a structure that was disordered, where the carbonyl groups were disordered over two positions with occupancies of 0.5. This model was almost identical to the R3m model, but had a much higher R value (0.13). For these reasons, both the ordered and the disordered R3 model were rejected in favour of the disordered R3m model. The question also arose whether the separate pivaloyl groups rather than the entire molecule are disordered. This was easily shown not to be the case, since the inversion of only one pivaloyl group (reducing the symmetry of the molecule to C1) would create a conformer with an unreasonably short non-bonded contact of 1.156 Å between two carbonyl O atoms.
Equal occupancy by the two enantiomers of the average molecular site may be caused by either spatial or temporal disorder, as well as a combination of both; however, from the available data, it is not possible to distinguish between the two. The disorder may be a result of a random displacement of the two enantiomers, since it is unlikely that, in a crystal that consists of domains containing only one enantiomer, the occupancies of both enantiomers would be identical. The placement of enantiomers may be random in all directions, or it could be ordered in some. There are no significant intermolecular interactions in the [100] and [010] directions. The shortest intermolecular distance is a C–H···Oi contact of 3.478 (9) Å [symmetry code: (i) x, y, 1 + z], involving a methyl C—H bond. Such contacts are of identical length and arrangement for all combinations of enantiomers. These observations support the interpretation that there is no spacial correlation of the site occupancies by the two enantiomers.