Mixed Imidazolin-2-iminato–Cp* Thorium(IV) Complexes: Synthesis and Reactivity Toward Oxygen-Containing Substrates

The mixed pentamethylcyclopentadienyl thorium­(IV) imidazolin-2-iminato complexes Cp*₂Th­(Im^DippN)­(Me) (2) and Cp*₂Th­(Im^MesN)­(Me) (3) were synthesized in quantitative yields via rapid protonolysis of Cp*₂Th­(Me)₂ (1) with the respective neutral imidazolin-2-iminato ligand Im^RNH. Cp*₂Th­(Im^DippN)­(Me) (2) and Cp*₂Th­(Im^MesN)­(Me) (3) display short Th–N bond lengths and large Th–N–C angles. The reactivity of complex 2 and 3 toward oxygen-containing substrates was studied, and the catalytic activity of 2 was compared to the dimethyl (bispentamethyl–cyclopentadienyl) thorium complex 1. Complex 2 was applied in the catalytic Tishchenko reaction with aromatic, heteroaromatic, and branched aliphatic aldehydes, displaying a higher catalytic activity than Cp*₂Th­(Me)₂ and Cp*₂Th­(Im^MesN)­(Me). Furthermore, 2 was applied as a catalyst in the crossed Tishchenko reaction and in the oligomerization of bis­(aldehydes), as well as in the ring-opening polymerization of ε-caprolactone. In all reactions, the activity of Cp*₂Th­(Im^DippN)­(Me) (2) and Cp*₂Th­(Im^MesN)­(Me) (3) was higher than that observed for Cp*₂Th­(Me)₂ (1), which can be attributed to the increased electron density introduced by the coordination of the imidazolin-2-iminato ligand.