Synthesis and structure of N-arylimines of β-tellurocyclohexenals with the intramolecular coordination N → Te bonds

A series of N-arylimines of β-tellurocyclohexenals 11 have been synthesized and the molecular and crystal structures of the compounds 11a–e and also β-(dimethyltelluronium)cyclohexenal perchlorate 12 studied by X-ray crystallography. All the compounds contain strong intramolecular coordination N → Te (O → Te) bonds of the hypervalent type. In 11a–e, the lengths of the N → Te bonds are within the range of 2.690–2.147 Å and are 1.0–1.5 Å shorter than the sum of the van der Waals radii of respective atoms. In the N-arylimines 11b–e with the electronegative groups attached to the tellurium center, the lengths of the N → Te bonds are very close to that characteristic of a standard covalent N–Te bond. The experimental observed geometries are well reproduced by the DFT calculations performed at B3LYP/LanL2DZ level of approximation. The energies of the intramolecular coordination N → Te bonds vary from 23 kJ mol−1 for 11a to 119 kJ mol−1 for 11e. The calculated energy of the O → Te bond in 12 was found to be 50 kJ mol−1. The 125Te NMR chemical shifts of compounds 11 span the wide range of 734.3–1622.4 ppm. The largest downfield 125Te NMR chemical shifts are observed in the case of the compounds 11e, f in which the most electronegative atoms are attached to the tellurim centers.