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The title compound, [{Al(CH3)2}2(C12H18O)2], formed by the Me3Al-mediated alkyl­ation of mesityl­aldehyde, is dimeric in the solid state, with a central Al2O2 planar ring core residing on an inversion centre.

Supporting information

cif

Crystallographic Information File (CIF) https://doi.org/10.1107/S1600536801013095/bt6073sup1.cif
Contains datablocks global, I

hkl

Structure factor file (CIF format) https://doi.org/10.1107/S1600536801013095/bt6073Isup2.hkl
Contains datablock I

CCDC reference: 172188

Key indicators

  • Single-crystal X-ray study
  • T = 160 K
  • Mean [sigma](C-C) = 0.005 Å
  • R factor = 0.076
  • wR factor = 0.216
  • Data-to-parameter ratio = 15.4

checkCIF results

No syntax errors found

ADDSYM reports no extra symmetry


Yellow Alert Alert Level C:
RADNW_01 Alert C The radiation wavelength lies outside the expected range for the supplied radiation type. Expected range 1.54175-1.54180 Wavelength given = 1.54184 REFLT_03 From the CIF: _diffrn_reflns_theta_max 67.50 From the CIF: _reflns_number_total 2201 TEST2: Reflns within _diffrn_reflns_theta_max Count of symmetry unique reflns 2380 Completeness (_total/calc) 92.48% Alert C: < 95% complete PLAT_743 Alert C Torsion Calc 0.00(11), Rep 0.00 .... Missing s.u. O -AL -O -AL 3.665 1.555 1.555 3.665
0 Alert Level A = Potentially serious problem
0 Alert Level B = Potential problem
3 Alert Level C = Please check

Comment top

For many years, aluminium alkoxides and aryloxides have been utilized as reagents in organic synthesis (Zietz et al., 1983). However, the development of heterobimetallic reagents for use in asymmetric transformations has led to an increased awareness of the importance of aluminium in synthesis (Yamamoto & Maruoka, 1988; Saito & Yamamoto, 1997; Saito et al., 1998; Saito et al., 1999; Cogan & Ellman, 1999). In this regard, we have recently reported the syntheses and solid-state structures of dimethylaluminium enolates and aryloxides, produced from the reactions of trimethylaluminium and aromatic methyl ketones (Allan et al., 2000). The unexpected formation of enolate species was found to be a consequence of steric crowding in the ketones, when both the 2- and 6-positions of the aromatic rings carried methyl groups. We report here the structure of the title compound, (I), which is produced from the addition reaction between trimethylaluminium and 2,4,6-trimethylbenzaldehyde (mesitylaldehyde).

As can be seen from Fig. 1, complex (I) adopts a dimeric structure with a planar central Al2O2 ring core. The molecule is crystallographically centrosymmetric. Each Al atom is tetracoordinate by bonding to two methyl groups and two bridging O atoms. Although the average of the angles around each metal is 108.4°, these vary from 80.20 (9)° for O—Al—Oi to 119.49 (16)° for C1—Al—C2, giving a highly distorted pseudo-tetrahedral geometry at aluminium [symmetry code: (i) 1 - x, 1 - y, -z]. The internal Al2O2 ring angles at the metal atoms are smaller than at the oxygen atoms [80.20 (9) and 99.80 (9)°, respectively], which is consistent with sp2 hybridization for the bridging O atoms (van der Steen et al., 1991). The two independent Al—O distances are essentially the same at 1.844 (2) and 1.848 (2) Å for Al—O and Al—Oi respectively. Similarly, the remaining bond lengths and angles within (I) are in accord with those found in related systems (Schumann et al., 1996; Hitchcock et al., 1990; Sierra et al., 1989).

It is notable that the α-carbon atom C3 lies 0.434 Å out of the Al2O2 ring plane, and that the groups attached to this atom are staggered with respect to the ring, with torsion angles of -30.5 (4), 86.3 and -157.3 (2)° for Al—O—C3—C4, Al—O—C3—H3, Al—O—C3—C5, respectively. These differ markedly from those found in the closely related enolate analogue [Me2AlOC(2,4,6-Me3C6H2)=CH2], (II), where the olefin bond lies close the Al2O2 ring plane (Allan et al., 2000). This difference is most likely a consequence of the sp3 versus sp2 hybridization of the α-carbons in (I) and (II), respectively, which alters the minimum energy orientation of the attached groups.

Experimental top

Under an inert atmosphere of argon gas, mesitylaldehyde (0.35 g, 2.36 mmol) was added dropwise to a 195 K cooled solution of Me3Al (2.4 mmol of a 2M solution in toluene) in 3 ml of toluene, producing a yellow solution. The reaction mixture was allowed to warm slowly to ambient temperature with constant stirring and stirred for a further 20 h. All toluene was removed in vacuo, the residue was dissolved in 5 ml of hexane and a crystalline product was obtained on cooling the mixture to 245 K for 24 h. Yield: 0.153 g, 29.5%; m.p. 417–419 K. 1H NMR (C6D6, 400 MHz): δ 6.66 (broad s, 2H, m-H, Ph), 5.58 (q, J = 6.8 Hz, 1H, HCO), 2.54 (broad s, 3H, o-Me, Ph), 2.14 (broad s, 3H, o-Me, Ph), 2.01 (m, 3H, p-Me, Ph), 1.36 (m, 3H, Me), -0.44, -0.53, -0.62 (s, 6H, Me—Al). The presence of three signals for the methyl groups attached to the metal and the broad resonances obtained for some of the ligand H atoms indicates that a dynamic process is in operation in solution.

Refinement top

The high-angle data (θ = 60–67.5°) are incomplete because of restrictions imposed by the low-temperature device; data up to θ = 60° are 98% complete. H atoms were placed geometrically and refined with a riding model (including free rotation about C—C bonds), and with Uiso constrained to be 1.2 (1.5 for methyl groups) times Ueq of the carrier atom.

Computing details top

Data collection: DIF4 (Stoe & Cie, 1988); cell refinement: DIF4; data reduction: local programs; program(s) used to solve structure: SHELXTL (Sheldrick, 1997); program(s) used to refine structure: SHELXTL; molecular graphics: SHELXTL; software used to prepare material for publication: SHELXTL and local programs.

Figures top
[Figure 1] Fig. 1. The molecular structure of (I) with unique atom labels and 50% probability ellipsoids for non-H atoms.
Bis[µ-1-(2,4,6-trimethylphenyl)ethanolato-O:O]bis(dimethylaluminium) top
Crystal data top
[Al(CH3)2(C12H18O)2]F(000) = 480
Mr = 440.56Dx = 1.110 Mg m3
Monoclinic, P21/cCu Kα radiation, λ = 1.54184 Å
a = 7.224 (3) ÅCell parameters from 32 reflections
b = 15.380 (6) Åθ = 19.0–28.0°
c = 12.204 (5) ŵ = 1.12 mm1
β = 103.48 (4)°T = 160 K
V = 1318.6 (9) Å3Block, colourless
Z = 20.7 × 0.7 × 0.6 mm
Data collection top
Stoe-Siemens
diffractometer
Rint = 0.000
Radiation source: fine-focus sealed tubeθmax = 67.5°, θmin = 4.7°
Graphite monochromatorh = 78
ω/θ scansk = 1418
2201 measured reflectionsl = 1014
2201 independent reflections5 standard reflections every 60 min
1912 reflections with I > 2σ(I) intensity decay: none
Refinement top
Refinement on F2Secondary atom site location: difference Fourier map
Least-squares matrix: fullHydrogen site location: inferred from neighbouring sites
R[F2 > 2σ(F2)] = 0.077H-atom parameters constrained
wR(F2) = 0.217 w = 1/[σ2(Fo2) + (0.1463P)2 + 0.8656P]
where P = (Fo2 + 2Fc2)/3
S = 1.05(Δ/σ)max = 0.003
2201 reflectionsΔρmax = 0.54 e Å3
143 parametersΔρmin = 0.84 e Å3
0 restraintsExtinction correction: SHELXTL, Fc*=kFc[1+0.001xFc2λ3/sin(2θ)]-1/4
Primary atom site location: structure-invariant direct methodsExtinction coefficient: 0.011 (2)
Crystal data top
[Al(CH3)2(C12H18O)2]V = 1318.6 (9) Å3
Mr = 440.56Z = 2
Monoclinic, P21/cCu Kα radiation
a = 7.224 (3) ŵ = 1.12 mm1
b = 15.380 (6) ÅT = 160 K
c = 12.204 (5) Å0.7 × 0.7 × 0.6 mm
β = 103.48 (4)°
Data collection top
Stoe-Siemens
diffractometer
Rint = 0.000
2201 measured reflections5 standard reflections every 60 min
2201 independent reflections intensity decay: none
1912 reflections with I > 2σ(I)
Refinement top
R[F2 > 2σ(F2)] = 0.0770 restraints
wR(F2) = 0.217H-atom parameters constrained
S = 1.05Δρmax = 0.54 e Å3
2201 reflectionsΔρmin = 0.84 e Å3
143 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
xyzUiso*/Ueq
Al0.44345 (12)0.55944 (5)0.07415 (7)0.0324 (4)
O0.4687 (3)0.44128 (12)0.05642 (16)0.0322 (5)
C10.6373 (5)0.6039 (2)0.2005 (3)0.0477 (9)
H1A0.62040.66670.20750.072*
H1B0.76390.59230.18750.072*
H1C0.62520.57500.27010.072*
C20.1802 (5)0.5975 (2)0.0545 (3)0.0480 (8)
H2A0.13530.58310.12210.072*
H2B0.10030.56800.01090.072*
H2C0.17270.66050.04230.072*
C30.3788 (4)0.36716 (19)0.0958 (3)0.0352 (7)
H30.25660.35600.03930.042*
C40.3290 (5)0.3876 (2)0.2072 (3)0.0497 (9)
H4A0.44580.40000.26440.075*
H4B0.26430.33750.23110.075*
H4C0.24480.43830.19810.075*
C50.5027 (4)0.28651 (18)0.0991 (2)0.0334 (7)
C60.6914 (4)0.28329 (19)0.1616 (2)0.0364 (7)
C70.8002 (4)0.2092 (2)0.1550 (3)0.0386 (7)
H70.92830.20720.19740.046*
C80.7267 (5)0.13858 (19)0.0884 (3)0.0381 (7)
C90.5395 (5)0.14193 (19)0.0308 (3)0.0384 (7)
H90.48630.09330.01350.046*
C100.4243 (4)0.21397 (19)0.0350 (2)0.0356 (7)
C110.7867 (5)0.3558 (2)0.2392 (3)0.0491 (9)
H11A0.75760.34900.31330.074*
H11B0.73900.41210.20700.074*
H11C0.92470.35300.24740.074*
C120.8498 (6)0.0601 (2)0.0815 (3)0.0514 (9)
H12A0.98020.07920.08400.077*
H12B0.79890.02910.01070.077*
H12C0.85000.02130.14520.077*
C130.2174 (5)0.2098 (2)0.0277 (3)0.0444 (8)
H13A0.13610.21980.02510.067*
H13B0.18990.15230.06240.067*
H13C0.19210.25450.08650.067*
Atomic displacement parameters (Å2) top
U11U22U33U12U13U23
Al0.0411 (7)0.0270 (5)0.0326 (6)0.0017 (3)0.0156 (4)0.0041 (3)
O0.0418 (12)0.0272 (10)0.0307 (10)0.0014 (8)0.0145 (9)0.0001 (7)
C10.060 (2)0.0455 (19)0.0394 (17)0.0086 (15)0.0158 (15)0.0112 (14)
C20.054 (2)0.0391 (17)0.057 (2)0.0090 (15)0.0259 (16)0.0015 (15)
C30.0392 (17)0.0300 (14)0.0407 (16)0.0009 (12)0.0178 (13)0.0018 (11)
C40.065 (2)0.0439 (19)0.0506 (19)0.0099 (16)0.0354 (17)0.0080 (15)
C50.0413 (17)0.0258 (14)0.0359 (14)0.0030 (12)0.0144 (12)0.0048 (11)
C60.0440 (18)0.0336 (15)0.0338 (14)0.0013 (13)0.0137 (12)0.0035 (11)
C70.0403 (17)0.0358 (16)0.0401 (15)0.0049 (13)0.0098 (13)0.0058 (12)
C80.0494 (19)0.0299 (15)0.0392 (16)0.0060 (13)0.0183 (13)0.0074 (12)
C90.0492 (19)0.0291 (15)0.0406 (16)0.0009 (12)0.0182 (14)0.0010 (12)
C100.0420 (18)0.0322 (15)0.0353 (15)0.0012 (12)0.0142 (12)0.0025 (12)
C110.051 (2)0.0446 (19)0.0481 (19)0.0016 (15)0.0040 (15)0.0079 (14)
C120.058 (2)0.0350 (17)0.065 (2)0.0098 (14)0.0218 (18)0.0042 (15)
C130.0428 (19)0.0386 (17)0.0508 (19)0.0020 (14)0.0087 (15)0.0006 (14)
Geometric parameters (Å, º) top
Al—O1.844 (2)C5—C101.404 (4)
Al—Oi1.848 (2)C6—C71.397 (4)
Al—C11.950 (3)C6—C111.520 (4)
Al—C21.950 (4)C7—C81.386 (4)
O—C31.448 (3)C7—H70.950
O—Ali1.848 (2)C8—C91.372 (5)
C1—H1A0.980C8—C121.512 (4)
C1—H1B0.980C9—C101.394 (4)
C1—H1C0.980C9—H90.950
C2—H2A0.980C10—C131.514 (4)
C2—H2B0.980C11—H11A0.980
C2—H2C0.980C11—H11B0.980
C3—C41.518 (4)C11—H11C0.980
C3—C51.525 (4)C12—H12A0.980
C3—H31.000C12—H12B0.980
C4—H4A0.980C12—H12C0.980
C4—H4B0.980C13—H13A0.980
C4—H4C0.980C13—H13B0.980
C5—C61.399 (4)C13—H13C0.980
O—Al—Oi80.20 (9)C10—C5—C3118.3 (3)
O—Al—C1111.46 (13)C7—C6—C5119.2 (3)
Oi—Al—C1110.88 (13)C7—C6—C11117.1 (3)
O—Al—C2113.67 (13)C5—C6—C11123.8 (3)
Oi—Al—C2114.63 (13)C8—C7—C6122.0 (3)
C1—Al—C2119.49 (16)C8—C7—H7119.0
C3—O—Al132.26 (17)C6—C7—H7119.0
C3—O—Ali123.53 (16)C9—C8—C7117.9 (3)
Al—O—Ali99.80 (9)C9—C8—C12121.6 (3)
Al—C1—H1A109.5C7—C8—C12120.6 (3)
Al—C1—H1B109.5C8—C9—C10122.5 (3)
H1A—C1—H1B109.5C8—C9—H9118.8
Al—C1—H1C109.5C10—C9—H9118.8
H1A—C1—H1C109.5C9—C10—C5119.0 (3)
H1B—C1—H1C109.5C9—C10—C13118.4 (3)
Al—C2—H2A109.5C5—C10—C13122.6 (3)
Al—C2—H2B109.5C6—C11—H11A109.5
H2A—C2—H2B109.5C6—C11—H11B109.5
Al—C2—H2C109.5H11A—C11—H11B109.5
H2A—C2—H2C109.5C6—C11—H11C109.5
H2B—C2—H2C109.5H11A—C11—H11C109.5
O—C3—C4110.7 (2)H11B—C11—H11C109.5
O—C3—C5110.1 (2)C8—C12—H12A109.5
C4—C3—C5113.9 (2)C8—C12—H12B109.5
O—C3—H3107.3H12A—C12—H12B109.5
C4—C3—H3107.3C8—C12—H12C109.5
C5—C3—H3107.3H12A—C12—H12C109.5
C3—C4—H4A109.5H12B—C12—H12C109.5
C3—C4—H4B109.5C10—C13—H13A109.5
H4A—C4—H4B109.5C10—C13—H13B109.5
C3—C4—H4C109.5H13A—C13—H13B109.5
H4A—C4—H4C109.5C10—C13—H13C109.5
H4B—C4—H4C109.5H13A—C13—H13C109.5
C6—C5—C10119.4 (3)H13B—C13—H13C109.5
C6—C5—C3122.3 (3)
Oi—Al—O—C3156.1 (3)C3—C5—C6—C7176.0 (3)
C1—Al—O—C395.2 (3)C10—C5—C6—C11176.2 (3)
C2—Al—O—C343.4 (3)C3—C5—C6—C115.1 (4)
Oi—Al—O—Ali0.0C5—C6—C7—C80.1 (4)
C1—Al—O—Ali108.71 (14)C11—C6—C7—C8178.9 (3)
C2—Al—O—Ali112.71 (15)C6—C7—C8—C92.1 (4)
Al—O—C3—C430.5 (4)C6—C7—C8—C12178.8 (3)
Ali—O—C3—C4178.1 (2)C7—C8—C9—C101.7 (4)
Al—O—C3—C5157.29 (19)C12—C8—C9—C10179.2 (3)
Ali—O—C3—C551.3 (3)C8—C9—C10—C50.9 (4)
O—C3—C5—C657.3 (3)C8—C9—C10—C13177.5 (3)
C4—C3—C5—C667.7 (4)C6—C5—C10—C93.1 (4)
O—C3—C5—C10121.4 (3)C3—C5—C10—C9175.6 (2)
C4—C3—C5—C10113.6 (3)C6—C5—C10—C13175.3 (3)
C10—C5—C6—C72.7 (4)C3—C5—C10—C136.0 (4)
Symmetry code: (i) x+1, y+1, z.

Experimental details

Crystal data
Chemical formula[Al(CH3)2(C12H18O)2]
Mr440.56
Crystal system, space groupMonoclinic, P21/c
Temperature (K)160
a, b, c (Å)7.224 (3), 15.380 (6), 12.204 (5)
β (°) 103.48 (4)
V3)1318.6 (9)
Z2
Radiation typeCu Kα
µ (mm1)1.12
Crystal size (mm)0.7 × 0.7 × 0.6
Data collection
DiffractometerStoe-Siemens
diffractometer
Absorption correction
No. of measured, independent and
observed [I > 2σ(I)] reflections
2201, 2201, 1912
Rint0.000
(sin θ/λ)max1)0.599
Refinement
R[F2 > 2σ(F2)], wR(F2), S 0.077, 0.217, 1.05
No. of reflections2201
No. of parameters143
H-atom treatmentH-atom parameters constrained
Δρmax, Δρmin (e Å3)0.54, 0.84

Computer programs: DIF4 (Stoe & Cie, 1988), DIF4, SHELXTL (Sheldrick, 1997), SHELXTL and local programs.

Selected geometric parameters (Å, º) top
Al—O1.844 (2)Al—C21.950 (4)
Al—Oi1.848 (2)O—C31.448 (3)
Al—C11.950 (3)
O—Al—Oi80.20 (9)C1—Al—C2119.49 (16)
O—Al—C1111.46 (13)C3—O—Al132.26 (17)
Oi—Al—C1110.88 (13)C3—O—Ali123.53 (16)
O—Al—C2113.67 (13)Al—O—Ali99.80 (9)
Oi—Al—C2114.63 (13)
Symmetry code: (i) x+1, y+1, z.
 

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