(1R,2R)-N,N′-Diisobutyl-N,N′-dimethylcyclohexane-1,2-diamine

The title compound, C16H34N2, is a chiral diamine with fixed R configuration at both stereogenic carbon centres of the cyclohexane backbone. Due to their different substituents, the two N atoms also become stereogenic. In the crystal structure, the configuration at one of the two nitrogen centres is fixed, with the free electron pair pointing inward and the isobutyl group in a trans position towards the cyclohexane backbone resulting in an R configuration. The isobutyl group at the second N atom, however, is disordered with 75% S configuration and 25% R configuration. In both cases, the isobutyl group is arranged in a trans position towards the cyclohexane backbone.

The title compound, C 16 H 34 N 2 , is a chiral diamine with fixed R configuration at both stereogenic carbon centres of the cyclohexane backbone. Due to their different substituents, the two N atoms also become stereogenic. In the crystal structure, the configuration at one of the two nitrogen centres is fixed, with the free electron pair pointing inward and the isobutyl group in a trans position towards the cyclohexane backbone resulting in an R configuration. The isobutyl group at the second N atom, however, is disordered with 75% S configuration and 25% R configuration. In both cases, the isobutyl group is arranged in a trans position towards the cyclohexane backbone.

Related literature
The synthesis of the title compound is described by Kizirian et al. (2003). For the crystal structure of the related molecule (1R,2R)-N,N 0 -dimethylcyclohexane-1,2-diamine, see Strohmann et al. (2008b). Crystal structures of (1R,2R)-N,N 0 -tetramethylcyclohexane-1,2-diamine coordinated to lithium organyls are described by Strohmann & Gessner (2007a) and Strohmann & Gessner (2008). Other related diamines coordinated to lithium organyls are specified by Strohmann &Gessner (2007b) andStrohmann et al. (2008a). The use of chiral nitrogen ligands to enhance the stereoselectivity of deprotonation or addition reactions is discussed by Kizirian (2008)   TMCDA] and its derivatives are often used to enhance the stereoselectivity of deprotonation or addition reactions by coordinating to organolithium reagents (Kizirian, 2008). In the case of the cyclohexanediamine ligands, derivatives with three different substituents at the nitrogen centres revealed to be more efficient than their symmetric analogues (Kizirian et al., 2003;Stead et al., 2008).
The title compound represents the crystal structure of such an uncoordinated (R,R)-TMCDA derivative (for related crystal structures, see: Strohmann & Gessner, 2007a,b;Strohmann & Gessner, 2008;Strohmann et al. et al., 2008b;Strohmann et al., 2008a). Fig. 1), crystallizes at -78 °C in the orthorhombic crystal system, space group P2 1 2 1 2 1 . The asymmetric unit contains one molecule of the chiral diamine. The configuration at one of the two nitrogen centres is fixed with the free electron pair pointing inward and the isobutyl group arranged in a trans-position towards the cyclohexane backbone. The second nitrogen centre, however, can be described by a model that has the free electron pair pointing outwards in 75% of all molecules and inwards in the others.

Experimental
The title compound (100 mg, 0.39 mmol) was diluted in n-pentane (2 ml). After cooling to -78 °C, clear crystals suitable for single-crystal x-ray studies were obtained. For synthesis of the title compound, see Kizirian et al. (2003).

Refinement
H atoms were refined using a riding model in their ideal geometric positions with U iso (H) = 1.5U eq (C) for methyl H atoms and U iso (H) = 1.2U eq (C) for all other H atoms. H14 was located from the Fourier map and refined and its coordinates were refined freely yielding a C-H distance of 1.03 (3) Å. The Friedel pairs were not merged and the Flack parameter (Flack, 1983) yielded an indeterminate value with large uncertainty (1(4)). The following distances were restrained using DFIX: C13b-N2 and N2-C13a at 1.43 Å, C14-C16b, C14-16a, C14-C15a and C14-C15b at 1.52 Å. For the description of the disorder, a splitting model was used which had the free electron pair at the nitrogen centre pointing outwards in 75% of all molecules and inwards in the others. Absolute structure: not determined in the present model. Absolute configuration: known from starting material.
supplementary materials sup-2 Figures Fig. 1. The molecular structure of the title compound with thermal ellipsoids drawn at the 50% probability level.

Special details
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 F 2 against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F 2 , conventional R-factors R are based on F, with F set to zero for negative F 2 . The threshold expression of F 2 > σ(F 2 ) is used only for calculating Rfactors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F 2 are statistically about twice as large as those based on F, and R-factors based on ALL data will be even larger.