Bis[μ-N-(2,6-dimethyl­phen­yl)acetamidato]bis­(dimethyl­aluminium)

Fawcett, J.; Solan, G.A.

doi:10.1107/S1600536805015941

metal-organic compounds

CRYSTALLOGRAPHIC
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ISSN: 2056-9890

Volume 61| Part 6| June 2005| Pages m1210-m1211

https://doi.org/10.1107/S1600536805015941

Bis[μ-N-(2,6-dimethylphenyl)acetamidato]bis(dimethylaluminium)

John Fawcett ^a and Gregory A. Solan ^a ^*

^aDepartment of Chemistry, University of Leicester, Leicester LE1 7RH, England
^*Correspondence e-mail: jxf@leicester.ac.uk

(Received 16 May 2005; accepted 19 May 2005; online 28 May 2005)

The structure of the title compound, [Al₂(CH₃)₄(C₁₀H₁₂NO)₂] or [Me₂Al{μ-(2,6-Me₂C₆H₃)NCMeO}]₂, consists of a four-coordinate dimeric centrosymmetric eight-membered ring Al-containing species.

Comment

The synthesis and structural characterization of alkylaluminium complexes containing N,O-amidate ligands, [R^INCR(=O)]⁻ (R = alkyl or aryl), has recently received attention due, in part, to the rich variety of bonding modes that are accessible. For example, the ligand can bridge, chelate or act as a monodentate ligand to a single metal centre, the precise bonding mode being dependent on the acidity and the steric bulk of the amide precursor employed (Huang et al., 2002 ). Furthermore, the reactions of amides with R₃Al have allowed access to aluminium diketimates, some of which are not obtainable by more conventional synthetic routes (Huang et al., 2001 ).

We report here the synthesis and the crystal structure of [Me₂Al{μ-(2,6-Me₂C₆H₃)NCMeO}]₂, (I). The ¹H NMR spectrum gives methyl resonances in a ratio of 12:6:12, corresponding to the aromatic (δ 2.40), acetamide (δ 1.70) and aluminium methyls (δ −0.15), respectively. The X-ray analysis of (I) reveals a dimeric structure based on a centrosymmetric eight-membered ring. The bridging amidate ligand coordinates to the two Al atoms through both the N and the O atoms. The geometry at each Al atom can be best described as distorted tetrahedral, with two methyl C atoms, an N atom and an O atom occupying the coordination sites. The C3—O1 [1.296 (4) Å] and C3—N1A [1.298 (4) Å] bond lengths suggest some delocalization within the OCN moiety. The Al1—O1 [1.800 (3) Å], Al1—N1 [1.961 (3) Å], Al1—C1 [1.968 (5) Å] and Al1—C2 [1.961 (4) Å] bond distances in (I) are comparable with the corresponding distances observed in the related structures [Me₂Al{μ-(C₆H₅)NCPhO}]₂ (Kai et al., 1971 ) and [Me₂Al{μ-(2,6-Pr₂ⁱC₆H₃)NCPhO}]₂ (Huang et al., 2002). The benzene rings are arranged orthogonal to the puckered eight-membered ring. There are no intermolecular packing interactions of note.

Figure 1
Molecular structure of (I)

, showing the atom-numbering scheme and 50% probability displacement ellipsoids. The molecule is located on a centre of symmetry [primed atoms are generated by (1 − x, 2 − y, 2 − z)]. H atoms have been omitted for clarity.

Experimental

Under an atmosphere of nitrogen, trimethylaluminium (3.07 ml, 6.13 mmol, 2M solution in toluene) was added to a solution of N-(2,6-dimethylphenyl)acetamide (0.50 g, 3.06 mmol) in toluene (30 ml), and the reaction mixture was heated to reflux for 12 h. On cooling to room temperature, the volatiles were removed under reduced pressure and the residue dried overnight. Slow cooling of a hot acetonitrile (40 ml) solution containing the complex gave pale-yellow crystals of the title compound suitable for single-crystal X-ray diffraction analysis (yield 0.50 g, 75%). Analysis found: C 65.89, H 8.31, N 6.57%; calculated for C₂₄H₃₆Al₂N₂O₂: C 65.75, H 8.22, N 6.39%. ¹H NMR (C₆D₆): δ 7.20–7.05 (m, 6H, Ar—H), 2.40 (s, 12H, Ar—Me), 1.70 [s, 6H, MeC(O)] and −0.15 (s, 12H, Al—CH₃).

Crystal data

[Al₂(CH₃)₄(C₁₀H₁₂NO)₂]
M_r = 438.51
Monoclinic, P 2₁ /n
a = 11.028 (2) Å
b = 10.4955 (9) Å
c = 11.116 (5) Å
β = 90.37 (3)°
V = 1286.6 (6) Å³
Z = 2
D_x = 1.132 Mg m⁻³
Mo Kα radiation
Cell parameters from 27 reflections
θ = 4.7–12.5°
μ = 0.13 mm⁻¹
T = 200 (2) K
Block, pale yellow
0.53 × 0.41 × 0.41 mm

Data collection

Bruker P4 diffractometer
ω scans
Absorption correction: none
2650 measured reflections
2257 independent reflections
1598 reflections with I > 2s(I)
R_int = 0.029
θ_max = 25.0°
h = 0 → 13
k = −1 → 12
l = −13 → 13
2 standard reflections every 1000 reflections intensity decay: <1%

Refinement

Refinement on F²
R[F² > 2σ(F²)] = 0.064
wR(F²) = 0.190
S = 1.07
2257 reflections
137 parameters
H-atom parameters constrained
w = 1/[σ²(F_o²) + (0.065P)² + 3.0349P] where P = (F_o² + 2F_c²)/3
(Δ/σ)_max < 0.001
Δρ_max = 0.54 e Å⁻³
Δρ_min = −0.54 e Å⁻³
Extinction correction: SHELXL97
Extinction coefficient: 0.023 (4)

Table 1
Selected geometric parameters (Å, °)

Al1—O1	1.800 (3)
Al1—N1	1.961 (3)
Al1—C2	1.961 (4)
Al1—C1	1.968 (5)

O1—Al1—N1	103.37 (13)
O1—Al1—C2	107.46 (17)
N1—Al1—C2	105.81 (18)
O1—Al1—C1	109.21 (16)
N1—Al1—C1	110.47 (17)
C2—Al1—C1	119.3 (2)

All H atoms were included in calculated positions and treated as riding on the bonded atom (C—H = 0.93 and 0.96 Å). U_iso(H) was set to 1.5U_eq(C) for methyl H atoms and 1.2U_eq(C) for all other H atoms.

Data collection: XSCANS (Fait, 1991 ); cell refinement: XSCANS; data reduction: SHELXTL (Sheldrick, 2000 ); program(s) used to solve structure: SHELXS97 (Sheldrick, 1990 ); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997 ); molecular graphics: SHELXTL; software used to prepare material for publication: SHELXTL.

Supporting information

Crystal structure: contains datablocks I, global. DOI: https://doi.org/10.1107/S1600536805015941/hg6191sup1.cif

Structure factors: contains datablock I. DOI: https://doi.org/10.1107/S1600536805015941/hg6191Isup2.hkl

Computing details top

Data collection: XSCANS (Fait, 1991); cell refinement: XSCANS; data reduction: SHELXTL (Sheldrick, 2000); program(s) used to solve structure: SHELXS97 (Sheldrick, 1990); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: SHELXTL; software used to prepare material for publication: SHELXTL.

bis[µ-N-(2,6-dimethylphenyl)acetamidato]bis[dimethylaluminium top

Crystal data top

[Al₂(CH₃)₄(C₁₀H₁₂NO)₂]	F(000) = 472
M_r = 438.51	D_x = 1.132 Mg m⁻³
Monoclinic, P2₁/n	Mo Kα radiation, λ = 0.71073 Å
Hall symbol: -P 2yn	Cell parameters from 27 reflections
a = 11.028 (2) Å	θ = 4.7–12.5°
b = 10.4955 (9) Å	µ = 0.13 mm⁻¹
c = 11.116 (5) Å	T = 200 K
β = 90.37 (3)°	Block, pale yellow
V = 1286.6 (6) Å³	0.53 × 0.41 × 0.41 mm
Z = 2

Data collection top

Bruker P4 diffractometer	R_int = 0.029
Radiation source: fine-focus sealed tube	θ_max = 25.0°, θ_min = 2.6°
Graphite monochromator	h = 0→13
ω scans	k = −1→12
2650 measured reflections	l = −13→13
2257 independent reflections	2 standard reflections every 1000 reflections
1598 reflections with I > 2s(I)	intensity decay: <1%

Refinement top

Refinement on F²	Secondary atom site location: difference Fourier map
Least-squares matrix: full	Hydrogen site location: inferred from neighbouring sites
R[F² > 2σ(F²)] = 0.064	H-atom parameters constrained
wR(F²) = 0.190	w = 1/[σ²(F_o²) + (0.065P)² + 3.0349P] where P = (F_o² + 2F_c²)/3
S = 1.07	(Δ/σ)_max < 0.001
2257 reflections	Δρ_max = 0.54 e Å⁻³
137 parameters	Δρ_min = −0.54 e Å⁻³
0 restraints	Extinction correction: SHELXL97, Fc^*=kFc[1+0.001xFc²λ³/sin(2θ)]^-1/4
Primary atom site location: structure-invariant direct methods	Extinction coefficient: 0.023 (4)

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.

Refinement. Refinement of F² against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F², conventional R-factors R are based on F, with F set to zero for negative F². The threshold expression of F² > σ(F²) is used only for calculating R-factors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F² are statistically about twice as large as those based on F, and R- factors based on ALL data will be even larger.

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

	x	y	z	U_iso*/U_eq
Al1	0.56700 (10)	1.01577 (11)	0.83404 (10)	0.0346 (4)
O1	0.6307 (2)	1.0135 (2)	0.9835 (2)	0.0328 (6)
N1	0.4303 (3)	0.8969 (3)	0.8447 (2)	0.0305 (7)
C1	0.5088 (4)	1.1888 (4)	0.7972 (4)	0.0541 (12)
H1A	0.4511	1.2149	0.8567	0.081*
H1B	0.4708	1.1891	0.7193	0.081*
H1C	0.5761	1.2467	0.7974	0.081*
C2	0.6846 (4)	0.9348 (5)	0.7268 (4)	0.0571 (12)
H2A	0.7042	0.8514	0.7566	0.086*
H2B	0.7569	0.9856	0.7237	0.086*
H2C	0.6502	0.9277	0.6475	0.086*
C3	0.6447 (3)	1.0996 (3)	1.0659 (3)	0.0295 (8)
C4	0.7501 (4)	1.1884 (4)	1.0544 (4)	0.0422 (10)
H4A	0.7497	1.2485	1.1195	0.063*
H4B	0.7443	1.2331	0.9793	0.063*
H4C	0.8241	1.1402	1.0568	0.063*
C5	0.4160 (3)	0.8022 (3)	0.7517 (3)	0.0307 (8)
C6	0.4677 (3)	0.6807 (4)	0.7681 (3)	0.0371 (9)
C7	0.4593 (4)	0.5944 (4)	0.6738 (4)	0.0465 (11)
H7A	0.4930	0.5137	0.6825	0.056*
C8	0.4015 (4)	0.6264 (4)	0.5674 (4)	0.0501 (11)
H8A	0.3963	0.5673	0.5053	0.060*
C9	0.3515 (4)	0.7460 (4)	0.5530 (4)	0.0478 (11)
H9A	0.3137	0.7669	0.4806	0.057*
C10	0.3567 (3)	0.8355 (4)	0.6445 (3)	0.0381 (9)
C6A	0.5284 (4)	0.6454 (4)	0.8838 (4)	0.0518 (11)
H6D	0.5565	0.5589	0.8799	0.078*
H6E	0.4724	0.6541	0.9490	0.078*
H6F	0.5962	0.7013	0.8968	0.078*
C10A	0.3007 (5)	0.9660 (4)	0.6288 (4)	0.0565 (12)
H10D	0.2638	0.9720	0.5506	0.085*
H10E	0.3625	1.0300	0.6367	0.085*
H10F	0.2402	0.9789	0.6893	0.085*

Atomic displacement parameters (Å²) top

	U¹¹	U²²	U³³	U¹²	U¹³	U²³
Al1	0.0355 (7)	0.0404 (7)	0.0280 (6)	−0.0045 (5)	0.0018 (4)	−0.0007 (5)
O1	0.0343 (14)	0.0327 (13)	0.0314 (13)	−0.0004 (11)	−0.0006 (10)	−0.0060 (11)
N1	0.0320 (16)	0.0324 (16)	0.0270 (14)	−0.0010 (13)	−0.0022 (12)	−0.0049 (12)
C1	0.063 (3)	0.048 (3)	0.051 (3)	−0.008 (2)	−0.011 (2)	0.011 (2)
C2	0.049 (3)	0.078 (3)	0.045 (2)	−0.003 (2)	0.014 (2)	−0.009 (2)
C3	0.0275 (18)	0.0294 (18)	0.0316 (18)	0.0031 (15)	−0.0027 (14)	0.0008 (15)
C4	0.038 (2)	0.039 (2)	0.049 (2)	−0.0064 (18)	0.0086 (18)	−0.0060 (18)
C5	0.0284 (19)	0.0312 (18)	0.0325 (18)	−0.0006 (15)	0.0005 (14)	−0.0055 (15)
C6	0.033 (2)	0.038 (2)	0.040 (2)	−0.0002 (16)	0.0039 (16)	−0.0028 (17)
C7	0.043 (2)	0.037 (2)	0.060 (3)	0.0024 (18)	0.010 (2)	−0.011 (2)
C8	0.049 (3)	0.054 (3)	0.047 (2)	0.000 (2)	0.006 (2)	−0.023 (2)
C9	0.043 (2)	0.061 (3)	0.039 (2)	−0.001 (2)	−0.0021 (18)	−0.014 (2)
C10	0.036 (2)	0.041 (2)	0.037 (2)	0.0018 (17)	−0.0050 (16)	−0.0058 (17)
C6A	0.057 (3)	0.047 (2)	0.051 (2)	0.015 (2)	−0.003 (2)	0.000 (2)
C10A	0.069 (3)	0.058 (3)	0.042 (2)	0.018 (2)	−0.018 (2)	−0.007 (2)

Geometric parameters (Å, º) top

Al1—O1	1.800 (3)	C5—C10	1.400 (5)
Al1—N1	1.961 (3)	C5—C6	1.408 (5)
Al1—C2	1.961 (4)	C6—C7	1.387 (5)
Al1—C1	1.968 (5)	C6—C6A	1.494 (6)
O1—C3	1.296 (4)	C7—C8	1.382 (6)
N1—C3ⁱ	1.298 (4)	C7—H7A	0.9300
N1—C5	1.443 (4)	C8—C9	1.379 (6)
C1—H1A	0.9600	C8—H8A	0.9300
C1—H1B	0.9600	C9—C10	1.386 (5)
C1—H1C	0.9600	C9—H9A	0.9300
C2—H2A	0.9600	C10—C10A	1.512 (6)
C2—H2B	0.9600	C6A—H6D	0.9600
C2—H2C	0.9600	C6A—H6E	0.9600
C3—N1ⁱ	1.298 (4)	C6A—H6F	0.9600
C3—C4	1.496 (5)	C10A—H10D	0.9600
C4—H4A	0.9600	C10A—H10E	0.9600
C4—H4B	0.9600	C10A—H10F	0.9600
C4—H4C	0.9600

O1—Al1—N1	103.37 (13)	C10—C5—C6	121.6 (3)
O1—Al1—C2	107.46 (17)	C10—C5—N1	119.1 (3)
N1—Al1—C2	105.81 (18)	C6—C5—N1	119.3 (3)
O1—Al1—C1	109.21 (16)	C7—C6—C5	117.9 (4)
N1—Al1—C1	110.47 (17)	C7—C6—C6A	121.1 (4)
C2—Al1—C1	119.3 (2)	C5—C6—C6A	121.0 (3)
C3—O1—Al1	133.4 (2)	C8—C7—C6	121.1 (4)
C3ⁱ—N1—C5	120.0 (3)	C8—C7—H7A	119.5
C3ⁱ—N1—Al1	121.5 (2)	C6—C7—H7A	119.5
C5—N1—Al1	118.4 (2)	C9—C8—C7	120.2 (4)
Al1—C1—H1A	109.7	C9—C8—H8A	119.9
Al1—C1—H1B	109.3	C7—C8—H8A	119.9
H1A—C1—H1B	109.5	C8—C9—C10	121.1 (4)
Al1—C1—H1C	109.4	C8—C9—H9A	119.4
H1A—C1—H1C	109.5	C10—C9—H9A	119.4
H1B—C1—H1C	109.5	C9—C10—C5	118.2 (4)
Al1—C2—H2A	109.5	C9—C10—C10A	121.0 (4)
Al1—C2—H2B	109.5	C5—C10—C10A	120.9 (3)
H2A—C2—H2B	109.5	C6—C6A—H6D	109.8
Al1—C2—H2C	109.5	C6—C6A—H6E	109.8
H2A—C2—H2C	109.5	H6D—C6A—H6E	109.5
H2B—C2—H2C	109.5	C6—C6A—H6F	108.8
O1—C3—N1ⁱ	119.1 (3)	H6D—C6A—H6F	109.5
O1—C3—C4	117.6 (3)	H6E—C6A—H6F	109.5
N1ⁱ—C3—C4	123.2 (3)	C10—C10A—H10D	109.5
C3—C4—H4A	109.7	C10—C10A—H10E	109.5
C3—C4—H4B	109.4	H10D—C10A—H10E	109.5
H4A—C4—H4B	109.5	C10—C10A—H10F	109.4
C3—C4—H4C	109.3	H10D—C10A—H10F	109.5
H4A—C4—H4C	109.5	H10E—C10A—H10F	109.5
H4B—C4—H4C	109.5

N1—Al1—O1—C3	−117.9 (3)	C10—C5—C6—C7	0.6 (5)
C2—Al1—O1—C3	130.5 (3)	N1—C5—C6—C7	−175.8 (3)
C1—Al1—O1—C3	−0.3 (4)	C10—C5—C6—C6A	−178.7 (4)
O1—Al1—N1—C3ⁱ	45.6 (3)	N1—C5—C6—C6A	4.9 (5)
C2—Al1—N1—C3ⁱ	158.4 (3)	C5—C6—C7—C8	−0.3 (6)
C1—Al1—N1—C3ⁱ	−71.1 (3)	C6A—C6—C7—C8	179.1 (4)
O1—Al1—N1—C5	−132.9 (2)	C6—C7—C8—C9	0.3 (6)
C2—Al1—N1—C5	−20.1 (3)	C7—C8—C9—C10	−0.7 (7)
C1—Al1—N1—C5	110.3 (3)	C8—C9—C10—C5	1.1 (6)
Al1—O1—C3—N1ⁱ	101.3 (4)	C8—C9—C10—C10A	−179.4 (4)
Al1—O1—C3—C4	−80.4 (4)	C6—C5—C10—C9	−1.0 (6)
C3ⁱ—N1—C5—C10	97.9 (4)	N1—C5—C10—C9	175.4 (3)
Al1—N1—C5—C10	−83.5 (4)	C6—C5—C10—C10A	179.4 (4)
C3ⁱ—N1—C5—C6	−85.5 (4)	N1—C5—C10—C10A	−4.1 (6)
Al1—N1—C5—C6	93.0 (4)

Symmetry code: (i) −x+1, −y+2, −z+2.

Acknowledgements

We thank the University of Leicester for financial support.

References

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