Crystal structure of (1E,1′E)-1,1′-(pyridine-2,6-diyl)bis[N-(2,3,4,5,6-pentafluorophenyl)ethan-1-imine]

The synthesis and crystal structure of a potentially redox non-innocent pentafluorophenyl-substituted pyridine diimine ligand system are reported.


Chemical context
The utilization of non-innocent ligand systems in organometallic chemistry can produce secondary reactivity and can result in unique mechanistic and redox properties (Babbini & Iluc, 2015;Praneeth et al., 2012). Redox non-innocence is generally observed with chelate ligands which possess lowlying -systems that can allow electron transfer (Lyaskovskyy & de Bruin, 2012). These ligand systems allow multiple-electron redox events to take place on metal centers, which are usually relegated to single-electron events (Haneline & Heyduk, 2006). This is useful for the utilization of benign and economically viable first-row transition metals instead of traditional noble-metal catalysts (Chirik & Wieghardt, 2010). The development of new and varied ligands systems is essential for the understanding of the structure-property relationships, which give rise to redox non-innocence. Given the significance and current interest in redox-active ligand systems, herein we report on the synthesis and crystal structure of a potential redox-active pyridine diimine system containing electron-withdrawing substituents.

Structural commentary
The title compound, Fig. 1, crystallizes in the monoclinic space group P2 1 /m with the mirror plane, at (x, 0.25, z), bisecting the ISSN 2056-9890 pyridine N atom, N1, and C atom, C1. Thus, only half of the molecule is present in the asymmetric unit (Fig. 1). The pentafluorophenyl groups are oriented in a synclinal fashion with respect to the pyridine ring, with the two rings being inclined to one another by 73.67 (6) . The imine nitrogen atom, N2, is oriented in an anti-conformation with respect to the pyridine nitrogen, N1. This orientation is in contrast with the molecule acting as a tridentate ligand coordinating to the chromium ion in complex trichloro(2,6-bis(1-(pentafluorophenylimino)ethyl)pyridine-N,N 0 ,N 00 )chromium(III) acetonitrile monosolvate (Nakayama et al., 2005). Here, the imine N atoms adopt a syn-conformation upon coordination to the chromium ion.

Supramolecular features
In the crystal, the molecules stack along the a axis (Fig. 2). Despite the presence of multiple aromatic rings within the molecule, there are no obvious -stacking interactions; the phenyl rings are clearly offset. Thus the only intermolecular interactions present are typical van der Waals interactions.

Synthesis and crystallization
The reagent 2,6-diacetylpyridine was synthesized by a previously reported method (Su & Feng, 2010), and the ligand was prepared by a modification of a previously reported Schiff-base condensation method (Small & Brookhart, 1999).

Special details
Experimental. All other reagents and solvents were purchased commercially and used without further purification. 1 H NMR was collected on a Varian 60 MHz NMR. Mass spectra were collected using direct injection on a ThermoScientific TSQ-ESI Mass spectrometer. Geometry. All esds (except the esd in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell esds are taken into account individually in the estimation of esds in distances, angles and torsion angles; correlations between esds in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell esds is used for estimating esds involving l.s. planes.