CO2 activation by metal−ligand-cooperation mediated by iridium pincer complexes

Abstract

Herein we report the reversible activation of CO2 by the dearomatized complex [(tBuPNP*)Ir(COE)] (1) and by the aromatized complex [(tBuPNP)Ir(C6H5)] (2) via metal-ligand cooperation (MLC) (tBuPN = 2,6-bis-(di-tert-butylphosphinomethyl)pyridine; tBuPNP* = deprotonated PNP; COE = cyclooctadiene). The [1,3]-addition of CO2 to 1 and 2 is reversible at ambient temperature. While the dearomatized complex 1 reacts readily at ambient temperature with CO2 in THF or benzene, complex 2 reacts with CO2 upon heating in benzene at 80 °C or at ambient temperature in THF. The novel aromatized complex [(tBuPNP)IrCl] (10) does not react with CO2. Based on the reactivity patterns of 1, 2, and 10 with CO2, we suggest that CO2 activation via MLC takes place only via the dearomatized species, and that in the case of 2 THF plays a role as a polar solvent in facilitating formation of the dearomatized hydrido phenyl complex intermediate (complex II).