Formation of C_NHC^∧C_alkyl and C_NHC^∧C_aryl κ²-Chelate Complexes through Competitive sp³- and sp²-CH Activations: An...

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 sp²-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.