Aryl Isocyanate, Carbodiimide, and Isocyanide Prepared from Carbon Dioxide. A Metathetical Group-Transfer Tale Involving a Titanium−Imide Zwitterion

Carbon dioxide can be readily converted quantitatively and under mild conditions into the aryl isocyanate and symmetrical carbodiimide via a metathetical reaction involving a zwitterionic titanium imide (nacnac)TiNAr(CH₃B(C₆F₅)₃) (nacnac^- = [ArNC(^tBu)]₂CH, Ar = 2,6-ⁱPr₂C₆H₃). The metathetical process to generate isocyanates allows also for facile formation of sterically demanding aryl isocyanide, by a deoxygenation route. Labeling studies using enriched ¹³CO₂ are also described.