(R,R)-N,N′-Bis(ferrocenylmethyl)cyclohexane-1,2-diamine

In the structure of the title compound, [Fe2(C5H5)2(C18H24N2)], the cyclohexane ring has a chair configuration and the two ferrocenemethylamino groups are bonded to it equatorially, as expected. The configuration of the two ferrocence nuclei may be due to intramolecular N—H⋯N hydrogen bonding involving the two NH groups.


S1. Comment
The chemistry of ferrocene has received much attention as both ferrocene and its derivatives have applications in many fields. For example, ferrocene has been employed as a marker for the electrochemical detection of amino acids in selective anion sensors (Beer et al., 1998). It also has applications in catalysis (Yang et al., 2002), non-linear optical (NLO) materials (Roberto et al., 2000) and medicinal materials. As part of our continuing studies on new ferrocene compounds, we report herein on the crystal structure of the title compound, R,R)-N 1 ,N 2 -Cyclohexane-1,2-bis((ferrocenylmethylene)amine, (I).
The molecular structure of the title compound is illustrated in Fig. 1. It consists of (1R,2R)-cyclohexane-1,2-diamine units, in which the hydrogen atoms of the two amine groups have been substituted by ferrocenylmethyl units. The cyclohexane ring has a chair conformation and the two ferrocenemethylamino groups are equatorially bonded to it, with torsion angles C1-C11-N1-C12 and C19-C18-N2-C17 being 178.4 (3) and 168.3 (3)°, respectively. The bond lengths and angles and the conformation of the ferrocenyl group, are similar to those observed in other ferrocenemethylamino derivatives (Hess et al., 1999;Base et al., 2002). The Cp ring planes (C6-C10 and C19-C23), are inclined to one another by 48.84 (15)°. The intramolecular Fe-Fe distance is 7.6054 (11) Å, while the nearest intermolecular Fe-Fe separation is 5.9384 (7) Å. The orientation of the two ferrocence nuclei is probably due to the presence of the intramolecular N1-H1···N22 hydrogen bond (Table 1).
The crystal packing of the title compound is illustrated in Fig. 2.

S2. Experimental
The title compound was synthesized by reducing the corresponding Schiff base (R,R)-N1,N2-Cyclohexane-1,2-bis-((ferrocenylmethylene)) (5 mmol) (Cho et al., 1999), with sodium borohydride (40 mmol) in methanol, in an ice bath. 40 ml NaOH solution (1 mol.L -1 ) was added and the mixture was stirred at rt for an 1 h (Sutcliffe et al., 2002)). The mixture was extracted with CHCl 3 and the solvent removed under vacumn. The crude product was purified by recrystalization from acetone. Red crystals, suitable for X-ray diffraction analysis, were obtained by slow evaporation of a methanol solution after 3 days.

S3. Refinement
The H-atoms were included in calculated positions and treated as riding atoms: N-H = 0.86 Å, C-H = 0.93 -0.97 Å, with U iso (H) = 1.2U eq (parent N-or C-atom).    where P = (F o 2 + 2F c 2 )/3 (Δ/σ) max = 0.005 Δρ max = 0.27 e Å −3 Δρ min = −0.45 e Å −3 Extinction correction: SHELXL97 (Sheldrick, 2008), Fc * =kFc[1+0.001xFc 2 λ 3 /sin(2θ)] -1/4 Extinction coefficient: 0.0039 (6) Absolute structure: Flack (1983), 2567 Friedel pairs Absolute structure parameter: 0.035 (19) Special details Geometry. Bond distances, angles etc. have been calculated using the rounded fractional coordinates. All su's are estimated from the variances of the (full) variance-covariance matrix. The cell esds are taken into account in the estimation of distances, angles and torsion angles 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 R-factors(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.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å 2 )
x y z U iso */U eq