Carbon Dioxide Capture and Functionalization from a Molecular Ti(III) Oxo Anion

Carbon dioxide capture and functionalization sequesters carbon dioxide in more robust products and offers a viable route to reducing greenhouse gas emissions. We present herein a unique molecular Ti^III oxo anion that reversibly binds CO₂ to allow both its sequestration and functionalization. The reduction of [(PN)₂Ti═O] (1) [PN = (2-PⁱⁱPr₂-4-methylphenyl)(mesityl)amide] with KC₈ and 2.2.2-cryptand (crypt) resulted in formation of [K(crypt)][(PN)₂Ti═O] (2), which was fully characterized and shown to contain a Ti-centered radical. Complex 2 reacts with Al(CH₃)₃ to form [K(crypt)][(PN)₂Ti{O(Al(CH₃)₃}] (3), which can be independently prepared from [K(crypt)][(PN)₂Ti(OCP)] and Al(CH₃)₃. Whereas 1 does not react with CO₂, 2 rapidly captures the gas (1 atm, 25 °C) to produce a Ti^III carbonate [K(crypt)][(PN)₂Ti(κ²-O₂C═O)] (4). Chemical and electrochemical oxidation of 4 releases CO₂ to regenerate 1 while a soluble organic carbonate [Me₃SiOC(O)OSiMe₃, Me = CH₃] is obtained from reaction of 4 with ClSiMe₃.