Organotellurium heterocycles, notably tellurazoles and related compounds, exhibit a propensity for self-assembly into supramolecular structures as a result of intermolecular secondary bonding interactions between tellurium and other heteroatoms. A further investigation of such assemblies is greatly aided by improved synthetic access to ortho substituted aryltellurium halides, which serve as intermediates in the preparation of organotellurium heterocycles. Regiospecific ortho tellurination of aromatic substrates occurs when tellurium tetrachloride coordinates to moieties such as amide, urea or carbamate, resulting in ortho substituted aryltellurium trichlorides rather than sterically favored para substitution products. As an example, phenyl dimethyl urea undergoes tellurination in position 2 rather than 4. At this time the full scope of ortho tellurination reactions remains unknown. Potential candidates for effective coordination include a wide range of functional groups such as amides, ureas, carbamates, esters, ketones, as well as their sulfur analogs. Computational modeling of transition state energy profiles for such reactions and geometries around hypervalent tellurium in the resulting products has provided important insights into structural features and conditions that favor regioselective ortho tellurination. Modeling has emerged as an advantageous alternative to a purely empirical approach for identifying suitable precursors, which would require a large number of substrates to be tested for their suitability. Results of ab-initio calculations obtained with density functional theory will be presented.

Examples of regiospecific ortho tellurination reactions

Thomas Junk

University of Louisiana at Monroe

Appearances