CO₂‐to‐Cyclic Carbonate Transformation at Ambient Pressure Using a Mechanochemically Prepared Ti(III) Catalyst

A readily accessible Ti(III) complex, [Li(thf) 4 ][Ti( Mes PDA) 2 ] ( 4 ) ( Mes PDA = N, N′‐bis(2,4,6‐trimethylphenyl)‐ o ‐phenylenediamide), has been synthesized mechanochemically, offering a sustainable route to Ti(III) species. Complex 4 , combined with [NBu 4 I] (TBAI), efficiently catalyzes the cycloaddition of CO 2 (1 bar) with terminal and internal epoxides, bio‐resourced diepoxides, and the tri‐substituted limonene oxide. This work represents the first example of a Ti(III)‐based catalyst capable of efficiently synthesizing cyclic carbonates from CO 2 and epoxides under atmospheric pressure, and demonstrates the superior catalytic activity of Ti(III) compared to its Ti(IV) analog [Ti( Mes PDA) 2 ] ( 3) . A detailed mechanistic study is conducted through density functional theory analysis to explore the catalytic pathways mediated by Ti(III) and Ti(IV). Key steps include epoxide coordination to Ti, iodide‐mediated ring‐opening to form a Ti‐alkoxide species, and CO 2 insertion into the Ti–O bond. The superior performance of Ti(III) arises from its lower oxophilicity, which weakens Ti–O interactions, enhancing CO 2 insertion. Electron Paramagnetic Resonance (EPR) spectroscopy confirms epoxide coordination and supports the formation of a Ti(III)‐alkoxide intermediate. Further evidence for the latter species comes from X‐ray crystallography of the Ti(IV)‐alkoxide analog [Li(4‐crown‐12) 2 ][Ti( Mes PDA) 2 ( O i Pr)] ( 17 ), providing indirect structural evidence. These findings advance the development of Ti(III) systems in CO 2 valorization and highlight the key role of oxidation state in catalytic efficiency.