Crystal structure of 1,1-diacetylferrocene dihydrazone

The title compound, [Fe(C7H9N2)2], crystallizes with two crystallographically independent molecules in the unit cell. These represent the chiral atropoisomers distinguished by the mutual arrangement of the two acetyl–hydrazone groups with a cis conformation of the C=N bonds. The two cyclopentadienyl (Cp) rings are planar and nearly parallel, the tilt between the two rings being 3.16 (16)° [4.40 (18)° for the second independent molecule]. The conformation of the Cp rings is close to eclipsed, the twist angle being 0.1 (2)° [3.3 (2)°]. The two acetyl–hydrazone substituents are also planar and are inclined at 13.99 (15)/9.17 (16)° [6.83 (17)/14.59 (15)°] relative to the Cp rings. The Fe—C bond lengths range from 2.035 (3) to 2.065 (2) Å, with an average of 2.050 (3) Å [2.036 (3) to 2.069 (2), average 2.046 (3) Å], which agrees well with those reported for most ferrocene derivatives. In the crystal, the molecules form dimers via two strong N—H⋯N hydrogen bonds. The dimers are linked into a three-dimensional framework by weak N—H⋯N hydrogen bonds.

The title compound, [Fe(C 7 H 9 N 2 ) 2 ], crystallizes with two crystallographically independent molecules in the unit cell. These represent the chiral atropoisomers distinguished by the mutual arrangement of the two acetyl-hydrazone groups with a cis conformation of the C N bonds. The two cyclopentadienyl (Cp) rings are planar and nearly parallel, the tilt between the two rings being 3. 16 (16) [4.40 (18) for the second independent molecule]. The conformation of the Cp rings is close to eclipsed, the twist angle being 0.1 (2) [3.3 (2) ]. The two acetyl-hydrazone substituents are also planar and are inclined at 13.99 (15)/9.17 (16) [6.83 (17)/ 14.59 (15) ] relative to the Cp rings. The Fe-C bond lengths range from 2.035 (3) to 2.065 (2) Å , with an average of 2.050 (3) Å [2.036 (3) to 2.069 (2), average 2.046 (3) Å ], which agrees well with those reported for most ferrocene derivatives. In the crystal, the molecules form dimers via two strong N-HÁ Á ÁN hydrogen bonds. The dimers are linked into a threedimensional framework by weak N-HÁ Á ÁN hydrogen bonds.
We thank Professor Abel M. Maharramov for fruitful discussions and help with this work.

Comment
The Nenajdenko-Shastin catalytic olefination reaction discovered by us recently is a facile approach to functionally substituted halogen-alkenes (Korotchenko et al., 2001;Nenajdenko et al., 2004) (Fig. 1). To study the further synthetic potential of this reaction, we have investigated the olefination of 1,1-diacetylferrocene as a representative of metallocenes. The structure of the reaction product, C 14 H 18 FeN 4 , I, has been unambiguously established by X-ray diffraction analysis. It has been revealed that the olefination of 1,1-diacetylferrocene allows the developing of a simple and convenient way to obtain the halogen-substituted ferrocene-alkenes II-V (Fig. 2).
The I crystallizes in the non-centrosymmetric orthorhombic space group Pna2 1 with two crystallographically independent molecules in the unit cell. The two crystallographically independent molecules of I represent the chiral atropoisomers (Fig. 3). The atropoisomers are distinguished by the mutual arrangement of the two acetyl-hydrazone groups having the cis-configuration of the C═N bonds (the disposition of the hydrazone groups is right/left and left/right, respectively). The two Cp rings are planar (r.m.s. deviations are 0.001, 0.003 and 0.003, 0.002 for the two crystallographically independent molecules, respectively) and nearly parallel, the ring-tilt between the two rings being 3.16 (16)° and 4.40 (18)° for the two crystallographically independent molecules, respectively. The conformation of the Cp rings is close to eclipsed, which is common for ferrocene derivatives. The twist angle of the Cp rings is defined as the torsion angle between a ring C atom, the two ring centers and the corresponding C atom on the opposite ring. The value of the twist angle in I is 0.1 (2)° and 3.3 (2)° for the two crystallographically independent molecules, respectively. The two acetyl-hydrazone substituents are also planar (r.m.s. deviations are 0.012, 0.026 and 0.018, 0.027 for the two crystallographically independent molecules, respectively) and are inclined relative to the Cp rings at 13.99 (15)°, 9.17 (16)° and 6.83 (17)°, 14.59 (15)° for the two crystallographically independent molecules, respectively. The Fe-C distances are as expected for a ferrocene derivative, ranging from 2.035 (3)Å to 2.065 (2)Å, with an average of 2.050 (3)Å and 2.046 (3)Å (for the two crystallographically independent molecules, respectively), which agree well with those reported for most of ferrocene derivatives (Xiao et al., 1999;Fang et al., 2001;Lopez et al., 2003;Zhang et al., 2006;Zhou et al., 2007;Qiao et al., 2009).
In the crystal, the molecules of I form a dimers via the two strong intermolecular N-H···N hydrogen bonds (Fig. 4, Table 1). Further, the dimers are linked into three-dimensional framework by the additional weak intermolecular N-H···N hydrogen bonds (Fig. 5, Table 1).

Experimental
The product I was prepared by use of the methodics described in Abd-Elzaher et al., 2005

Refinement
The value of Flack parameter 0.475 (16) (3181 Friedel pairs measured, 99%) indicates that, in this case, the absolute structure cannot be objectively determined due to the specifical (pseudo-centrosymmetrical) arrangement of heavy Fe atoms.
The hydrogen atoms of the amino-groups were localized in the difference Fourier maps and refined isotropically with fixed displacement parameters (U iso (H) = 1.2U eq (N)). The other hydrogen atoms were placed in calculated positions with with C-H = 0.96Å (Cp H) and 0.98Å (methyl H) and refined within the riding model with fixed isotropic displacement parameters (U iso (H) = 1.2U eq (C)).

Figure 1
The Nenajdenko-Shastin catalytic olefination reaction as a general method for the preparation of alkenes.
where P = (F o 2 + 2F c 2 )/3 (Δ/σ) max = 0.002 Δρ max = 0.43 e Å −3 Δρ min = −0.25 e Å −3 Absolute structure: Flack (1983), 3181 Friedel pairs Absolute structure parameter: 0.475 (16) Special details Geometry. All s.u.'s (except the s.u. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell s.u.'s are taken into account individually in the estimation of s.u.'s in distances, angles and torsion angles; correlations between s.u.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell s.u.'s is used for estimating s.u.'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 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.