High-Oxidation-State Neutral and Cationic Tantalum(IV) Alkyl Complexes That Are Stable toward β-Hydrogen and β-Methyl Eliminations

The synthesis and solid-state structural characterization of a family of homoleptic and mixed dialkyl dTa(IV) complexes of the formula, (η5-C5Me5)TaR1R[N(i-Pr)C(Me)N(i-Pr)], where R1 = R2 = i-Bu (3), n-Bu (4), and Et (7), and R1 = Me, R2 = i-Bu (10), neopentyl (Np) (11), are reported, along with those for the cationic d1Ta(IV) complex, {(η5-C5Me5)TaNp[N(i-Pr)C(Me)N(i-Pr)]}[B(C6F5)4] (12). All of the new compounds displayed a remarkably high degree of solution stability toward β-hydrogen and β-methyl eliminations/abstractions. Thermolysis of 3 in toluene at 80 °C for 18 h provided the Ta(IV) trimethylenemethane (TMM) complex 13.