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

Abstract

The iridium complex 1 based on a metalated CNP ligand containing an imidazolin-2-ylidene fragment has been prepared by treatment of the ligand precursor 4 with Ag2O followed by reaction with [IrCl(COE)2]2. The chlorohydride imidazolidin-2-ylidene complex 6, which is isostructural to 1, was synthetized by reaction of the previously reported dihydride derivative 3 with CH2Cl2. Complexes 1 and 6 exhibit luminescence arising from a 3MLCT/ILCT state involving the metalated CNP ligand, which is particularly intense for 1 in the solid state at 298 K. Furthermore, the reactivity of complexes 1 and 6 towards bases was compared. Deprotonation of 1 with KOtBu produced the selective formation of the dinuclear complex 7; meanwhile, the reaction of 6 led to a complex mixture of products. The same reactions carried out in the presence of PPh3 produced the selective deprotonation of the P-bonded methylene bridges of 1 and 6, yielding the isostructural derivatives 9 and 10. DFT calculations performed on the uNHC-containing tautomers I and II, and the sNHC-based isomers III and IV, showed that the NHC-deprotonated derivatives II and IV are more stable by 3.20 and 2.73 kcal mol–1, respectively, than their P-deprotonated counterparts (I and III). However, a reverse stability order was observed for hexacoordinated tautomers I·L and II·L, and III·L and IV·L (L = PPh3, CO, MeCN). Finally, the catalytic activity of complex 3 in the transfer hydrogenation of ketones has been assessed.