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Reaction of AlMe3 with NH2(C5H9) caused the evolution of methane and produced the dimeric species bis(μ-cyclo­pentyl­amino-N:N)bis[dimethylaluminium(III)], [Al(CH3)2-(C5H10N)]2, which was found to adopt a cis configuration of cyclopentyl groups about a bent AlNAlN ring (which has twofold crystallographic symmetry) instead of the more common trans arrangement.

Supporting information


Crystallographic Information File (CIF)
Contains datablocks global, I


Structure factor file (CIF format)
Contains datablock I

CCDC reference: 140928

Comment top

Diorganoaluminium amides [R2AlN(H)R'], where the amide function derives from a primary source R'NH2, have proved useful synthetically in providing access to a range of more exotic organoaluminium compounds and structures. This chemistry centres on the reactivity of the remaining N—H bond, and the products obtained are markedly dependent on the nature of the R' substituent (Waggoner & Power, 1991). The structures of these primary amides have also attracted considerable attention in their own right. It has been established that in amide-bridged dimeric systems larger organic R ligands bound to Al favour a conformation with mutually cis, rather than mutually trans, R' groups (Schaur et al., 1992). Thus when R is methyl a trans arrangement is favoured and indeed only three cis examples have been documented. A mixture of both conformations cocrystallizing in a 2:1 trans:cis ratio was found for R' = iso-propyl (Amirkhalili et al., 1981) and the cis isomer is also known from two cases where R' is chiral, –CHMePh (Robinson et al., 1988) or –CHMe(naphthyl) (Pennington et al., 1990). It has been suggested that in the latter cases the cis conformation is adopted as the 2/m geometry shown by the trans isomer is not accessible for optically active compounds whilst the cis conformation still allows the largest substituents on R' to be mutually trans. It was reported that no interconversion of the isomers was found in solution. It is hence of interest here that the crystal structure of the cycloalkylamide [Me2Al{µ-N(H)R'}2AlMe2] where R' is a simple cyclopentyl group shows it to adopt only the cis conformation.

The two halves of dimeric (I) are related by a twofold rotation axis. The AlNAlN ring is bent about the Al···Al vector (Al1—Cp—Al1* 171.5° where Cp is the ring centroid) as are the three other known cis isomers (range 170.6 to 172.7°). The cyclopentyl groups lie endo with respect to this fold and adopt an envelope conformation with N1 as an equatorial substituent. In contrast the known trans isomers have planar AlNAlN rings with two exceptions where R' is excessively large [R' = biphenyl (Byers et al., 1992); R' = 2,6-diisopropylphenyl (Waggoner & Power, 1991)]. The aluminium centre is pseudo-tetrahedral with the largest deviation from ideal geometry being the closure of the internal ring angle N1—Al1—N1* to 86.8 (1)°. This is compensated for by separating the methyl groups and thus C1—Al1—C2 expands to 120.6 (2)°. N1 is also pseudo-tetrahedral (as opposed to the flat CNAl2 fragment found for R' = 2,6-diisopropylphenyl above) and subtends an endocyclic ring angle of 92.0 (1)°. There are no intermolecular contacts significantly shorter than the sum of van der Waals radii.

Related literature top

For related literature, see: Amirkhalili et al. (1981); Byers et al. (1992); Pennington et al. (1990); Robinson et al. (1988); Schaur et al. (1992); Waggoner & Power (1991).

Experimental top

Synthesis was carried out by adaption of the deprotonation/alkane elimination method of Waggoner & Power (1991). A suitable crystal was obtained from toluene solution and mounted in a glass capilliary.

Refinement top

The amide-H atom was refined isotropically but all other hydrogen atoms were placed in idealized positions. Reflections and their Friedel mates were collected but no reliable conclusion could be reached as to the absolute configuration.

Computing details top

Cell refinement: MSC/AFC Diffractometer Control Software (Molecular Structure Corporation, 1985); data reduction: TEXSAN (Molecular Structure Corporation, 1993); program(s) used to solve structure: SIR92 (Altomare et al., 1994); program(s) used to refine structure: TEXSAN; molecular graphics: ORTEPII (Johnson, 1976); software used to prepare material for publication: TEXSAN.

Figures top
[Figure 1] Fig. 1. An ORTEP view of (I) with ellipsoids at the 40% probability level and H atoms shown as small spheres of arbitrary size. Symmetry code: * = 1 - y, 1 - x, 0.5 - z.
(I) top
Crystal data top
2[Al(CH3)2(C5H10N)]Dx = 1.018 Mg m3
Mr = 282.38Mo Kα radiation, λ = 0.71069 Å
Tetragonal, P41212Cell parameters from 16 reflections
a = 12.380 (2) Åθ = 10.6–13.7°
c = 12.018 (3) ŵ = 0.15 mm1
V = 1841.9 (7) Å3T = 295 K
Z = 4Block, colourless
F(000) = 624.000.42 × 0.40 × 0.35 mm
Data collection top
Rigaku AFC7S
Rint = 0.027
Radiation source: X-ray tubeθmax = 27.5°, θmin = 2.5°
Graphite monochromatorh = 1616
ω/2θ scansk = 1011
2580 measured reflectionsl = 1515
2133 independent reflections3 standard reflections every 150 reflections
1225 reflections with I > 2σ(I) intensity decay: 1.1%
Refinement top
Refinement on F0 constraints
Least-squares matrix: fullH atoms treated by a mixture of independent and constrained refinement
R[F2 > 2σ(F2)] = 0.0461/σ2(F)
wR(F2) = 0.055(Δ/σ)max = 0.0001
1225 reflectionsΔρmax = 0.23 e Å3
86 parametersΔρmin = 0.16 e Å3
0 restraints
Crystal data top
2[Al(CH3)2(C5H10N)]Z = 4
Mr = 282.38Mo Kα radiation
Tetragonal, P41212µ = 0.15 mm1
a = 12.380 (2) ÅT = 295 K
c = 12.018 (3) Å0.42 × 0.40 × 0.35 mm
V = 1841.9 (7) Å3
Data collection top
Rigaku AFC7S
Rint = 0.027
2580 measured reflections3 standard reflections every 150 reflections
2133 independent reflections intensity decay: 1.1%
1225 reflections with I > 2σ(I)
Refinement top
R[F2 > 2σ(F2)] = 0.0460 restraints
wR(F2) = 0.055H atoms treated by a mixture of independent and constrained refinement
1225 reflectionsΔρmax = 0.23 e Å3
86 parametersΔρmin = 0.16 e Å3
Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å2) top
Al10.90291 (8)0.24031 (7)0.30234 (7)0.0505
N10.7862 (2)0.1461 (2)0.3499 (2)0.0506
C10.8784 (3)0.3898 (3)0.3488 (3)0.0768
C21.0423 (3)0.1702 (3)0.3294 (3)0.0698
C30.8009 (3)0.0683 (3)0.4416 (3)0.0599
C40.7056 (3)0.0026 (3)0.4656 (3)0.0880
C50.7203 (5)0.0409 (4)0.5825 (4)0.1162
C60.7898 (4)0.0403 (5)0.6394 (4)0.1065
C70.8233 (3)0.1207 (3)0.5544 (3)0.0868
H10.733 (2)0.180 (2)0.364 (2)0.041 (9)
Atomic displacement parameters (Å2) top
Al10.0565 (6)0.0522 (6)0.0428 (4)0.0047 (5)0.0015 (4)0.0039 (5)
N10.051 (2)0.059 (2)0.043 (1)0.004 (1)0.001 (1)0.000 (1)
C10.096 (3)0.066 (2)0.069 (2)0.005 (2)0.001 (2)0.013 (2)
C20.055 (2)0.090 (3)0.065 (2)0.006 (2)0.000 (2)0.008 (2)
C30.063 (2)0.070 (2)0.046 (2)0.002 (2)0.000 (2)0.013 (2)
C40.102 (3)0.092 (3)0.070 (2)0.030 (2)0.002 (2)0.027 (2)
C50.138 (5)0.128 (4)0.083 (3)0.024 (4)0.024 (3)0.037 (3)
C60.115 (4)0.144 (4)0.061 (3)0.003 (3)0.001 (3)0.026 (3)
C70.108 (3)0.107 (3)0.046 (2)0.012 (3)0.014 (2)0.010 (2)
Geometric parameters (Å, º) top
Al1—Al1i2.805 (2)C3—C41.499 (5)
Al1—N11.943 (3)C3—C71.528 (5)
Al1—N1i1.956 (3)C4—C51.494 (6)
Al1—C11.957 (4)C5—C61.490 (6)
Al1—C21.959 (4)C6—C71.486 (6)
N1—C31.474 (4)
N1—Al1—N1i86.8 (1)Al1i—N1—C3121.1 (2)
N1—Al1—C1111.6 (2)N1—C3—C4115.4 (3)
N1—Al1—C2109.9 (2)N1—C3—C7114.1 (3)
N1i—Al1—C1112.2 (1)C4—C3—C7102.8 (3)
N1i—Al1—C2110.7 (1)C3—C4—C5105.7 (3)
C1—Al1—C2120.6 (2)C4—C5—C6106.7 (4)
Al1—N1—Al1i92.0 (1)C5—C6—C7107.3 (3)
Al1—N1—C3121.3 (2)C3—C7—C6106.0 (3)
Symmetry code: (i) y+1, x+1, z+1/2.

Experimental details

Crystal data
Chemical formula2[Al(CH3)2(C5H10N)]
Crystal system, space groupTetragonal, P41212
Temperature (K)295
a, c (Å)12.380 (2), 12.018 (3)
V3)1841.9 (7)
Radiation typeMo Kα
µ (mm1)0.15
Crystal size (mm)0.42 × 0.40 × 0.35
Data collection
DiffractometerRigaku AFC7S
Absorption correction
No. of measured, independent and
observed [I > 2σ(I)] reflections
2580, 2133, 1225
(sin θ/λ)max1)0.650
R[F2 > 2σ(F2)], wR(F2), S 0.046, 0.055, ?
No. of reflections1225
No. of parameters86
H-atom treatmentH atoms treated by a mixture of independent and constrained refinement
Δρmax, Δρmin (e Å3)0.23, 0.16

Computer programs: MSC/AFC Diffractometer Control Software (Molecular Structure Corporation, 1985), TEXSAN (Molecular Structure Corporation, 1993), SIR92 (Altomare et al., 1994), TEXSAN, ORTEPII (Johnson, 1976).

Selected geometric parameters (Å, º) top
Al1—N11.943 (3)Al1—C11.957 (4)
Al1—N1i1.956 (3)Al1—C21.959 (4)
N1—Al1—N1i86.8 (1)C1—Al1—C2120.6 (2)
N1—Al1—C1111.6 (2)Al1—N1—Al1i92.0 (1)
N1—Al1—C2109.9 (2)Al1—N1—C3121.3 (2)
N1i—Al1—C1112.2 (1)Al1i—N1—C3121.1 (2)
N1i—Al1—C2110.7 (1)
Symmetry code: (i) y+1, x+1, z+1/2.

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