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 oxo anion that reversibly binds CO to allow both its sequestration and functionalization. The reduction of [(PN)Ti═O] (1) [PN = (2-PPr-4-methylphenyl)(mesityl)amide] with KC and 2.2.2-cryptand (crypt) resulted in formation of [K(crypt)][(PN)Ti═O] (2), which was fully characterized and shown to contain a Ti-centered radical. Complex 2 reacts with Al(CH) to form [K(crypt)][(PN)Ti{O(Al(CH)}] (3), which can be independently prepared from [K(crypt)][(PN)Ti(OCP)] and Al(CH). Whereas 1 does not react with CO, 2 rapidly captures the gas (1 atm, 25 °C) to produce a Ti carbonate [K(crypt)][(PN)Ti(κ-OC═O)] (4). Chemical and electrochemical oxidation of 4 releases CO to regenerate 1 while a soluble organic carbonate [MeSiOC(O)OSiMe, Me = CH] is obtained from reaction of 4 with ClSiMe.