Molecular and crystal structure of ortho-tellurated azomethines with intramolecular N → Te coordination

Abstract

Novel reactions have been discovered and studied of C aliph.–Te bond scission in o-butyltellurobenzalanilines under the action of halogens, which afford 2-halogenotellurenyl- and 2-trihalogenotellurobenzalanilnes in high yields. The series of azomethines have been synthesized with different tellurium-containing groups in o-positions with respect to the CN bond. The effects of structural factors upon the length of N → Te intramolecular coordination bonds have been studied by the following methods: X-ray structural determinations, dipole moments, 1H and 125Te NMR spectroscopy and IR spectroscopy. In Te II derivatives, the shortest intramolecular N→ Te contact (2.23 Å) is formed in 2-chlorotellurenyl derivatives XIIIb. Bis(2-formylphenyl)tellurium imines XIVa exist in the crystal form as 10-Te-3 telluranes, in which long intramolecular fractional N → Te bonds (2.70–2.72 Å) have been detected, with the basicity of the imine N atom no practical effect on their length. The 125Te NMR spectrum of the 15N labelled bis[2-(phenyl)iminomethinylphenyl]telluride shows that in solution of this compound a very fast (on an NMR timescale), Te–N and Te ← N bond scrambling occurs owing to a dynamic equilibrium between the topomeric 10-Te-3 structures that apparently takes place via the 12-Te-4 tellurane intermediates. The intramolecular coordination bond in the Te iv derivative, (2-phenyliminomethinyl-phenyl)butylmethyl telluronium perchlorate, belongs to the longest Te → N bonds (2.75 Å). For the first time, the 125Te– 15N spin-spin coupling constants are reported for a number of o-tellurated azomethines.