SYNTHETIC, STRUCTURAL, AND REDOX STUDIES OF ARENE ALKYL COMPLEXES OF TANTALUM(III) SUPPORTED BY ARYLOXIDE AND ARENETHIOLATE LIGANDS

A series of η6-hexamethylbenzene alkyl and aryl complexes of tantalum(III) supported by aryloxide and arenethiolate ligands have been prepared, characterized, and compared to their halide analogues. Thus, (η6-C6Me6)Ta(OAr)2Cl (1, Ar = 2,6-C6H3iPr2) reacts with MeMgBr at low temperature to afford (η6-C6Me6)Ta(OAr)2Me (3). Low-temperature alkylation of (η6-C6Me6)Ta(OAr)Cl2 (2) with 2 equiv of RMgBr forms (η6-C6Me6)Ta(OAr)R2 (4, R = Me; 5, R = Et) and with 2 equiv of RLi affords (η6-C6Me6)Ta(OAr)R2 (6, R = CH2SiMe3; 7, R = Ph). Complexes 3−7 are more stable than their halide precursors; no products arising from α- or β-H elimination processes were identified upon thermolysis. In addition to NMR studies of these compounds, cyclic voltammetry experiments show two oxidation processes; the Ta(III) ⇄ Ta(IV) couple is quasi-reversible, and the Ta(IV) → Ta(V) process is irreversible. Molecules of 5 exhibit a folded arene ligand with π-electron localization (diene−diyl structure) and normal ethyl ligands (no evidenc...