Synthesis, Spectroscopic and Computational Studies of Rhodium(III) Complexes Bearing N‐Heterocyclic Carbene‐Based C^N^C Pincer Ligand and Bipyridine/Terpyridine

Abstract

Rhodium(III) complexes containing tridentate N‐heterocyclic carbene (NHC)‐based pincer ligand in the form of [Rh(C^N^C)(N^N)X]2+ and [Rh(C^N^C)(tpy)]3+ (C^N^C = (2,6‐bis(1‐butylimidazol‐2‐ylidene)pyridine (C1^N^C1) or 2,6‐bis(3‐butylbenzimidazol‐2‐ylidene)pyridine (C2^N^C2); N^N = bipyridine‐type aromatic diimines; tpy = 2,2':6',2''‐terpyridine; X = Cl or Br) were prepared. Spectroscopic comparisons and time‐dependent density functional theory (TD‐DFT) calculations revealed the lowest‐energy electronic transition associated with these complexes are different from their Ru(II), Os(II) and Ir(III) analogues. The Rh(III) complexes exhibit luminescent behavior at 77 K upon photoexcitation. The impact of the C^N^C pincer ligands on the photophysics of the Rh(III) complexes was investigated.