Mild, reversible reaction of iridium(III) amido complexes with carbon dioxide

Unlike some other Ir(III) hydrides, the aminopyridine complex [(2-NH 2-C5NH4)IrH3(PPh3) 2] (1-PPh3) does not insert CO2 into the Ir-H bond. Instead 1-PPh3 loses H2 to form the cyclometalated species [(κ2-N,N-2-NH-C5NH4)IrH 2(PPh3)2] (2-PPh3), which subsequently reacts with CO2 to form the carbamato species [(κ2-O,N-2-OC(O)NH-C5NH4)IrH 2(PPh3)2] (10-PPh3). To study the insertion of CO2 into the Ir-N bond of the cyclometalated species, a family of compounds of the type [(κ2-N,N-2-NR-C 5NH4)IrH2(PR′3)2] (R = H, R′ = Ph (2-PPh3); R = H, R′ = Cy (2-PCy 3); R = Me, R′ = Ph (4-PPh3); R = Ph, R′ = Ph (5-PPh3); R = Ph, R′ = Cy (5-PCy3)) and the pyrimidine complex [(κ2-N,N-2-NH-C4N 2H3)IrH2(PPh3)2] (6-PPh3) were prepared. The rate of CO2 insertion is faster for the more nucleophilic amides. DFT studies suggest that the mechanism of insertion involves initial nucleophilic attack of the nitrogen lone pair of the amide on CO2 to form an N-bound carbamato complex, followed by rearrangement to the O-bound species. CO2 insertion into 1-PPh 3 is reversible in the presence of H2 and treatment of 10-PPh3 with H2 regenerates 1-PPh3, along with Ir(PPh3)2H5. © 2012 American Chemical Society.