Cyclometalated Iridium(III) Complexes Featuring Disubstituted Cyanamides

Abstract

AbstractThe neutral cyclometalated iridium(III) complexes [Ir(ppy)2Cl(NCNR2)] [ppy=2‐phenylpyridinato‐C2,N, R=Me 3 a, Et 3 b, C5H10 3 c] were prepared via the reaction of the chloro‐bridged dimer [Ir2(ppy)4(μ‐Cl)2] (1) with corresponding dialkylcyanamides NCNR2 (2 a–c) and 3 a–c were isolated in 74–85% yields. The cationic cyclometalated iridium(III) complex [Ir(ppy)2(NCNMe2)2](OTf) (4) was obtained by replacement of chloride ligands with NCNMe2 in 1 in the presence of AgOTf. UV/Vis absorption and emission properties of 3 a−c and 4 were studied; these complexes exhibit luminescence in the solid state upon photoexcitation (340 nm, 77 K). The characteristic feature of the X‐ray structures of 3 a–c is a deviation of the fragment Ir–N–C from linearity by 13.8(5)–22.8(3)°. Quantum chemical DFT calculations and topological analysis of the electron density distribution within the formalism of Bader's theory (AIM method) performed for 3 a–c demonstrated that the Ir–N–C fragments in the optimized equilibrium structures of [Ir(ppy)2Cl(NCNR2)] significantly deviate from the linearity (by 19.8–30.7°) and indicated that the Ir–N contacts between the metal centers and dialkylcyanamide ligands are relatively weak (24–30 kcal/mol) and have a closed‐shell dative interactions character. The charge decomposition analysis (CDA) shows existence of {M}←L donation with almost negligible contribution of the {M}→L back‐donation in 3 a–c.