Binding , release , and functionalization of CO 2 at a nucleophilic oxo anion complex of titanium †

The titaniumoxoanion complex [(Et2O)2Li][OTi(N[ tBu]3,5-Me2C6H3)3] ([(Et2O)2Li][1]) reactswithCO2 indiethyl ether to form the carbonate complex ([Li][O2COTi(N[ tBu]3,5-Me2C6H3)3])6 ([Li][2]). The solidstate structure of complex [Li][2] is a hexamer with a hexagonal prismatic core comprised of six lithium cations bridgedby the carbonate functionality. In themonomeric subunits of [Li][2], the carbonate ligand is bound kto the titanium metal center and pseudo kto the lithium countercation. The hexameric structure persists in benzene solutions as determined by HDOSYNMRtechniques. The binding ofCO2 in complex [Li][2] is reversible and can be effected by the introductionof the lithium sequestration reagent 12-crown-4 to diethyl ether solutions of [Li][2]. Complex [Li][2] is readily functionalized with Me3SiOS (O)2CF3 to yield the silyl carbonate complexMe3SiOC(O)OTi(N[ tBu]3,5-Me2C6H3)3 (3), the solid-state structure of which is presented. Functionalization with pivaloyl chloride results in the rapid loss of CO2 and formation of the pivalate complex tBuC(O)OTi(N[tBu]3,5-Me2C6H3)3 (4).