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Titanium compounds in low oxidation states are highly reducing species and hence powerful tools for the functionalization of small molecules. However, their potential has not yet been fully realized because harnessing these highly reactive complexes for productive reactivity is generally challenging. Advancing this field, herein we provide a detailed route for the formation of titanium(III) orthophenylendiamido (PDA) species using [LiBHEt 3 ] as a reducing agent. Initially, the corresponding lithium PDA compounds [Li 2 ( Ar PDA)(thf) 3 ] (Ar = 2,4,6-trimethylphenyl ( Mes PDA), 2,6-diisopropylphenyl ( i Pr PDA)) are combined with [TiCl 4 (thf) 2 ] to form the heterobimetallic complexes [{TiCl( Ar PDA)}(μ- Ar PDA){Li(thf) n }] ( n = 1, Ar = i Pr 3 and n = 2, Ar = Mes 4 ). Compound 4 evolves to species [Ti( Mes PDA) 2 ] ( 6 ) via thermal treatment. In contrast, the transformation of 3 into [Ti( i Pr PDA) 2 ] ( 5 ) only occurs in the presence of [LiNMe 2 ], through a lithium-assisted process, as revealed by density functional theory (DFT). Finally, the Ti(IV) compounds 3 - 6 react with [LiBHEt 3 ] to give rise to the Ti(III) species [Li(thf) 4 ][Ti( Ar PDA) 2 ] (Ar = i Pr 8 , Mes 9 ). These low-valent compounds in combination with [PPN]Cl (PPN = bis(triphenylphosphine)iminium) are proved to be highly selective catalysts for the copolymerization of CO 2 and cyclohexene epoxide. Reactions occur at 1 bar pressure with activity/selectivity levels similar to Salen-Cr(III) compounds.

Two new derivatives of the bis(3,5-dimethylpyrazol-1-yl)methane modified by introduction of organosilyl groups on the central carbon atom, one of which bearing a chiral fragment, have been easily prepared. We verified the potential utility of these compounds through the reaction with [Zr(NMe 2 ) 4 ] for the preparation of novel zirconium complexes in which an ancillary bis(pyrazol-1-yl)methanide acts as a robust monoanionic tridentate scorpionate in a κ 3 -NNC chelating mode, forming strained four-membered heterometallacycles. These κ 3 -NNC-scorpionate zirconium amides were investigated as catalysts in combination with tetra- n -butylammonium bromide as cocatalyst for CO 2 fixation into five-membered cyclic carbonate products. The study has led to the development of an efficient zirconium-based bicomponent system for the selective cycloaddition reaction of CO 2 with epoxides. Kinetics investigations confirmed apparent first-order dependence on the catalyst and cocatalyst concentrations. In addition, this system displays very broad substrate scope, including mono- and disubstituted substrates, as well as the challenging biorenewable terpene derived limonene oxide, under mild and solvent-free conditions.