A Well-Defined NHC-Ir(III) Catalyst for the Silylation of Aromatic C–H Bonds: Substrate Survey and Mechanistic Insights
A well-defined NHC-Ir(III) catalyst, [Ir(H)2(IPr)(py)3][BF4] (IPr = 1,3-bis-(2,6-diisopropylphenyl)imidazol-2-ylidene), that provides access to a wide range of aryl- and heteroarylsilanes by intermolecular dehydrogenative C–H bond silylation has been prepared and fully characterized. The directed and non-directed functionalisation of C–H bonds has been accomplished successfully using the arene as the limiting reagent and a variety of hydrosilanes in excess, including Et3SiH, Ph2MeSiH, PhMe2SiH, Ph3SiH and (EtO)3SiH. Examples that show unexpected selectivity patterns that stem from the presence of aromatic substituents in hydrosilanes are also presented. The selective bisarylation of bis(hydrosilane)s by directed or non-directed silylation of C–H bonds is also reported herein. Theoretical calculations at the DFT level shed light on the intermediate species of the catalytic cycle and the role played by the ligand system on this Ir(III)/Ir(I) mechanism.