Design, Synthesis, and Evaluation of Chalcogen Interactions

Abstract

Contributions in the area of cationic chalcogen-chalcogen and chalcogen-π interactions as well as chalcogen mediated Group 14-iron interactions have been made. This work reports the electrochemical oxidation of 8- and 10-membered ring dichalcogenides appended with β-silicon and tin substituents. The heterocycles with tellurium undergo reversible oxidation but those with sulfur or selenium are irreversibly oxidized. The ionization energies of these mesocyclic chalcogenoethers were determined by photoelectron spectroscopy. These lowest ionization energies reflect substantial (0.53-0.75 eV) orbital destabilizations due to the neighboring C-Si or C-Sn bonds. In particular, a novel Si-Si effect on the ionization of these β-disilyl sulfides and selenides was found by PES measurements. Fe₂S₂(CO)₆ clusters with a C-Sn or C-Sn-C moiety bridging the sulfur atoms or a CH₂SnMe₃ group attached to each sulfur have also been studied by photoelectron spectroscopy. Stannylation lowers the ionization energy of sulfur lone pair orbitals in these systems owing to a geometry dependent interaction as well as the Fe-Fe HOMO. Additionally, various sulfur and phosphine substituted hydroquinone and catechol redox ligands have been synthesized to append to iron sulfur clusters. Lastly, model m-terphenyl methyl and phenyl chalcogenoethers that will be further used to study cationic aromatic-chalcogen interactions have been synthesized in either of two ways. Suzuki couplings of 2,6-dibromoaniline and (2,6-diiodo-4-methylphenyl)(methyl)sulfane afford m-terphenyl methyl thioethers in 27-42% yield. Deprotonation of 1,3-dichlorobenzene and treatment with substituted aryl Grignard reagents generated m-terphenyl anions which were quenched with alkyl or aryl dichalcogenides to give m-terphenyl chalcogenoethers in 16-74% yields. A new synthesis of phenyl m-terphenyl chalcogenoethers was found. Treatment of substituted iodo-m-terphenyls with diphenyl dichalcogenides using CsOH⋅H₂O in DMSO affords phenyl m-terphenyl chalcogenoethers in 19-84% yields. Extending the scope of this methodology to other 2,6-blocked aryl halides as well as the use of aliphatic and aromatic thiols or secondary alicyclic amines has been initially explored. Finally, o-methoxy substituted m-terphenyl chalcogenoethers show atropisomerism, with barriers in the range of 66-80 kJ/mol, as determined by variable temperature ¹H NMR spectroscopic studies.