Formation of C NHC ∧ C alkyl and C NHC ∧ C aryl κ 2 -Chelate Complexes through Competitive sp 3 - and sp 2 -CH Activations: An Experimental and Computational Study.

Depending on the chelate ring present, cyclometalated complexes are useful catalysts for various reactions. The reactivity of Ir III and Rh III NHC complexes bearing aliphatic or aromatic N,N'-substituents and thus featuring various metalation sites toward cyclometalation has been investigated. The Rh III complex bearing an N -mesityl- N '-benzyl-NHC does not participate in any cyclometalation, while the Ir III complex reacts under metalation of an ortho -methyl group of the Mes substituent to give complex [ 3 ] with a six-membered chelate ring. The Rh III and Ir III complexes bearing an N - o -tolyl, N -benzyl-NHC undergo sp 2 -CH activation to yield the cyclometalated complexes [ 4 ] and [ 5 ] featuring a five-membered C NHC ∧ C chelate ring. Density functional theory (DFT) studies corroborated the experimental findings.