Metalated Ir-CNP Complexes Containing Imidazolin-2-ylidene and Imidazolidin-2-ylidene Donors - Synthesis, Structure, Luminescence, and Metal-Ligand Cooperative Reactivity

The iridium complex1based on a metalated CNP ligand containing an imidazolin-2-ylidene fragment has been prepared by treatment of the ligand precursor4with Ag2O followed by reaction with [IrCl(COE)(2)](2). The chlorohydride imidazolidin-2-ylidene complex6, which is isostructural to1, was synthetized by reaction of the previously reported dihydride derivative3with CH2Cl2. Complexes1and6exhibit luminescence arising from a(3)MLCT/ILCT state involving the metalated CNP ligand, which is particularly intense for1in the solid state at 298 K. Furthermore, the reactivity of complexes1and6towards bases was compared. Deprotonation of1with KOtBu produced the selective formation of the dinuclear complex7; meanwhile, the reaction of6led to a complex mixture of products. The same reactions carried out in the presence of PPh(3)produced the selective deprotonation of the P-bonded methylene bridges of1and6, yielding the isostructural derivatives9and10. DFT calculations performed on theuNHC-containing tautomersIandII, and thesNHC-based isomersIIIandIV, showed that the NHC-deprotonated derivativesIIandIVare more stable by 3.20 and 2.73 kcal mol(-1), respectively, than their P-deprotonated counterparts (IandIII). However, a reverse stability order was observed for hexacoordinated tautomersI center dot LandII center dot L, andIII center dot LandIV center dot L(L = PPh3, CO, MeCN). Finally, the catalytic activity of complex3in the transfer hydrogenation of ketones has been assessed.