Tetrakis(dicyclohexylamido)zirconium(IV)

The crystal structure of Zr(C12H22N)4 is isotypic with its cerium(IV) analogue.

The reaction of ZrCl 4 with three equivalents of LiNCy 2 (Cy is cyclohexyl) resulted in the formation of tris(dicyclohexylamido)zirconium chloride and the title compound, [Zr(C 12 H 22 N) 4 ]. The latter is isotypic with its cerium(IV) analogue and crystallizes with three independent molecules in the asymmetric unit. One molecule is located about a twofold rotation axis, and the other two on fourfold inversion axes. In each molecule, the Zr IV atom has a distorted tetrahedral coordination environment. The crystal under investigation was twinned by inversion in a 1:1 ratio.

Structure description
Amido complexes of group 4 metals play an important role in synthetic chemistry. They are widely used as catalysts in hydroaminoalkylation reactions (Roesky et al., 2009) or in the catalysis of olefin polymerization reactions (Shafir & Arnold, 2001;Motolko et al., 2017). Tetrakis(dialkylamido)zirconium(IV) compounds are commonly known as precursors of a variety of more complex zirconium-containing compounds (Diamond et al., 1995(Diamond et al., , 1996. Amido ligands are known for their ability to stabilize electron-deficient transition-metal complexes by N(p )-M(d ) interactions (Yu et al., 2004). Combined with the possibility of double substitution at the nitrogen atom, which allows a broad variety in ligand design (Kasani et al., 1997), amido ligands appear to be an interesting alternative to Cp-based ligands (Kempe, 2000;Gué rin et al., 2000). In particular, dicyclohexylamine seems to be useful due to its steric demand that is similar to cyclopentadienyl ligands (Duan et al., 1997). Additionally, dicyclohexylamido complexes of group 4 metals show close contacts between the central metal cation and the carbon atom of the CH group of one dicyclohexylamido ligand, which is an indicator for attractive agostic interactions (Duan et al., 1997;Adler et al., 2014b). The understanding of these interactions is very important (Scherer et al., 2010) because they are considered to be intermediates in C-H bond-activation processes.
No significant supramolecular features are observed in the crystal structure of 1. The molecular packing (Fig. 2) appears to be dominated by van der Waals interactions only.

Synthesis and crystallization
All reactions were carried out under a dry nitrogen atmosphere using Schlenk techniques or in a glove box. Lithium dicyclohexylamide was synthesized by treatment of dicyclohexylamine with one equivalent of n-butyllithium (2.5 M in nhexane). Solvents were dried according to standard proce-   Representative for the three different molecules of 1 in the asymmetric unit, the molecular structure of complex Zr3 is displayed. Displacement ellipsoids correspond to the 50% probability level. H atoms have been omitted for clarity.  Bruker, 2015), SHELXS (Sheldrick, 2008), SHELXL (Sheldrick, 2015), DIAMOND (Brandenburg, 2006) and publCIF (Westrip, 2010).

Special details
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. Refinement. Refined as a 2-component inversion twin.