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
CCDC reference: 140928
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.
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.
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.
Crystal data top
2[Al(CH3)2(C5H10N)] | Dx = 1.018 Mg m−3 |
Mr = 282.38 | Mo Kα radiation, λ = 0.71069 Å |
Tetragonal, P41212 | Cell parameters from 16 reflections |
a = 12.380 (2) Å | θ = 10.6–13.7° |
c = 12.018 (3) Å | µ = 0.15 mm−1 |
V = 1841.9 (7) Å3 | T = 295 K |
Z = 4 | Block, colourless |
F(000) = 624.00 | 0.42 × 0.40 × 0.35 mm |
Data collection top
Rigaku AFC7S diffractometer | Rint = 0.027 |
Radiation source: X-ray tube | θmax = 27.5°, θmin = 2.5° |
Graphite monochromator | h = −16→16 |
ω/2θ scans | k = −10→11 |
2580 measured reflections | l = −15→15 |
2133 independent reflections | 3 standard reflections every 150 reflections |
1225 reflections with I > 2σ(I) | intensity decay: 1.1% |
Refinement top
Refinement on F | 0 constraints |
Least-squares matrix: full | H atoms treated by a mixture of independent and constrained refinement |
R[F2 > 2σ(F2)] = 0.046 | 1/σ2(F) |
wR(F2) = 0.055 | (Δ/σ)max = 0.0001 |
1225 reflections | Δρmax = 0.23 e Å−3 |
86 parameters | Δρmin = −0.16 e Å−3 |
0 restraints | |
Crystal data top
2[Al(CH3)2(C5H10N)] | Z = 4 |
Mr = 282.38 | Mo Kα radiation |
Tetragonal, P41212 | µ = 0.15 mm−1 |
a = 12.380 (2) Å | T = 295 K |
c = 12.018 (3) Å | 0.42 × 0.40 × 0.35 mm |
V = 1841.9 (7) Å3 | |
Data collection top
Rigaku AFC7S diffractometer | Rint = 0.027 |
2580 measured reflections | 3 standard reflections every 150 reflections |
2133 independent reflections | intensity decay: 1.1% |
1225 reflections with I > 2σ(I) | |
Refinement top
R[F2 > 2σ(F2)] = 0.046 | 0 restraints |
wR(F2) = 0.055 | H atoms treated by a mixture of independent and constrained refinement |
1225 reflections | Δρmax = 0.23 e Å−3 |
86 parameters | Δρmin = −0.16 e Å−3 |
Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å2) top | x | y | z | Uiso*/Ueq | |
Al1 | 0.90291 (8) | 0.24031 (7) | 0.30234 (7) | 0.0505 | |
N1 | 0.7862 (2) | 0.1461 (2) | 0.3499 (2) | 0.0506 | |
C1 | 0.8784 (3) | 0.3898 (3) | 0.3488 (3) | 0.0768 | |
C2 | 1.0423 (3) | 0.1702 (3) | 0.3294 (3) | 0.0698 | |
C3 | 0.8009 (3) | 0.0683 (3) | 0.4416 (3) | 0.0599 | |
C4 | 0.7056 (3) | −0.0026 (3) | 0.4656 (3) | 0.0880 | |
C5 | 0.7203 (5) | −0.0409 (4) | 0.5825 (4) | 0.1162 | |
C6 | 0.7898 (4) | 0.0403 (5) | 0.6394 (4) | 0.1065 | |
C7 | 0.8233 (3) | 0.1207 (3) | 0.5544 (3) | 0.0868 | |
H1 | 0.733 (2) | 0.180 (2) | 0.364 (2) | 0.041 (9) | |
H2 | 1.0957 | 0.2001 | 0.2804 | 0.0838 | |
H3 | 1.0637 | 0.1819 | 0.4052 | 0.0838 | |
H4 | 1.0358 | 0.0940 | 0.3158 | 0.0838 | |
H5 | 0.9323 | 0.4355 | 0.3161 | 0.0922 | |
H6 | 0.8828 | 0.3945 | 0.4284 | 0.0922 | |
H7 | 0.8081 | 0.4126 | 0.3248 | 0.0922 | |
H8 | 0.8611 | 0.0227 | 0.4234 | 0.0719 | |
H9 | 0.6397 | 0.0376 | 0.4587 | 0.1056 | |
H10 | 0.7041 | −0.0628 | 0.4152 | 0.1056 | |
H11 | 0.6516 | −0.0460 | 0.6191 | 0.1394 | |
H12 | 0.7548 | −0.1104 | 0.5830 | 0.1394 | |
H13 | 0.7499 | 0.0753 | 0.6976 | 0.1279 | |
H14 | 0.8523 | 0.0056 | 0.6705 | 0.1279 | |
H15 | 0.8988 | 0.1369 | 0.5618 | 0.1042 | |
H16 | 0.7820 | 0.1860 | 0.5622 | 0.1042 | |
Atomic displacement parameters (Å2) top | U11 | U22 | U33 | U12 | U13 | U23 |
Al1 | 0.0565 (6) | 0.0522 (6) | 0.0428 (4) | −0.0047 (5) | −0.0015 (4) | −0.0039 (5) |
N1 | 0.051 (2) | 0.059 (2) | 0.043 (1) | 0.004 (1) | 0.001 (1) | 0.000 (1) |
C1 | 0.096 (3) | 0.066 (2) | 0.069 (2) | −0.005 (2) | 0.001 (2) | −0.013 (2) |
C2 | 0.055 (2) | 0.090 (3) | 0.065 (2) | −0.006 (2) | 0.000 (2) | −0.008 (2) |
C3 | 0.063 (2) | 0.070 (2) | 0.046 (2) | 0.002 (2) | 0.000 (2) | 0.013 (2) |
C4 | 0.102 (3) | 0.092 (3) | 0.070 (2) | −0.030 (2) | 0.002 (2) | 0.027 (2) |
C5 | 0.138 (5) | 0.128 (4) | 0.083 (3) | −0.024 (4) | 0.024 (3) | 0.037 (3) |
C6 | 0.115 (4) | 0.144 (4) | 0.061 (3) | 0.003 (3) | −0.001 (3) | 0.026 (3) |
C7 | 0.108 (3) | 0.107 (3) | 0.046 (2) | −0.012 (3) | −0.014 (2) | 0.010 (2) |
Geometric parameters (Å, º) top
Al1—Al1i | 2.805 (2) | C3—C4 | 1.499 (5) |
Al1—N1 | 1.943 (3) | C3—C7 | 1.528 (5) |
Al1—N1i | 1.956 (3) | C4—C5 | 1.494 (6) |
Al1—C1 | 1.957 (4) | C5—C6 | 1.490 (6) |
Al1—C2 | 1.959 (4) | C6—C7 | 1.486 (6) |
N1—C3 | 1.474 (4) | | |
| | | |
N1—Al1—N1i | 86.8 (1) | Al1i—N1—C3 | 121.1 (2) |
N1—Al1—C1 | 111.6 (2) | N1—C3—C4 | 115.4 (3) |
N1—Al1—C2 | 109.9 (2) | N1—C3—C7 | 114.1 (3) |
N1i—Al1—C1 | 112.2 (1) | C4—C3—C7 | 102.8 (3) |
N1i—Al1—C2 | 110.7 (1) | C3—C4—C5 | 105.7 (3) |
C1—Al1—C2 | 120.6 (2) | C4—C5—C6 | 106.7 (4) |
Al1—N1—Al1i | 92.0 (1) | C5—C6—C7 | 107.3 (3) |
Al1—N1—C3 | 121.3 (2) | C3—C7—C6 | 106.0 (3) |
Symmetry code: (i) −y+1, −x+1, −z+1/2. |
Experimental details
Crystal data |
Chemical formula | 2[Al(CH3)2(C5H10N)] |
Mr | 282.38 |
Crystal system, space group | Tetragonal, P41212 |
Temperature (K) | 295 |
a, c (Å) | 12.380 (2), 12.018 (3) |
V (Å3) | 1841.9 (7) |
Z | 4 |
Radiation type | Mo Kα |
µ (mm−1) | 0.15 |
Crystal size (mm) | 0.42 × 0.40 × 0.35 |
|
Data collection |
Diffractometer | Rigaku AFC7S diffractometer |
Absorption correction | – |
No. of measured, independent and observed [I > 2σ(I)] reflections | 2580, 2133, 1225 |
Rint | 0.027 |
(sin θ/λ)max (Å−1) | 0.650 |
|
Refinement |
R[F2 > 2σ(F2)], wR(F2), S | 0.046, 0.055, ? |
No. of reflections | 1225 |
No. of parameters | 86 |
H-atom treatment | H atoms treated by a mixture of independent and constrained refinement |
Δρmax, Δρmin (e Å−3) | 0.23, −0.16 |
Selected geometric parameters (Å, º) topAl1—N1 | 1.943 (3) | Al1—C1 | 1.957 (4) |
Al1—N1i | 1.956 (3) | Al1—C2 | 1.959 (4) |
| | | |
N1—Al1—N1i | 86.8 (1) | C1—Al1—C2 | 120.6 (2) |
N1—Al1—C1 | 111.6 (2) | Al1—N1—Al1i | 92.0 (1) |
N1—Al1—C2 | 109.9 (2) | Al1—N1—C3 | 121.3 (2) |
N1i—Al1—C1 | 112.2 (1) | Al1i—N1—C3 | 121.1 (2) |
N1i—Al1—C2 | 110.7 (1) | | |
Symmetry code: (i) −y+1, −x+1, −z+1/2. |
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.