Ligand cooperation in the formal hydrogenation of N2O using a PC(sp2)P iridium pincer complex.

A new PC(carbene)P pincer ligand with 2,3-benzo[b]thiophene linkers connecting the flanking dialkyl phosphine donors to the central carbene can be attached to Ir(I). The chloro derivative reacts with N2O with loss of N2 to form an iridaepoxide species by addition of an oxygen atom to the Ir═C linkage. This compound reacts with H2 to afford the oxidative addition product, in which the hydride ligands are trans to the Ir-O bond. Heating this dihydride results in slow release of H2O; kinetic and spectroscopic studies show that conversion of the dihydride to its isomer, in which the hydrides are cis to the Ir-O bond, is required for H2O elimination to take place. Together, these reactions constitute the stoichiometric conversion of N2O and H2 to N2 and H2O; further mechanistic studies suggest ways to make the system catalytic.