Controlling Chemoselectivity in Ruthenium(II)‐Induced Cyclization of Aniline‐Functionalized Alkynes

The cyclization of heteroatom‐functionalized alkynes induced by d6‐transition‐metal centers has traditionally been associated with the vinylidene pathway. However, recent evidence suggests that d6‐transition‐metal centers can also activate alkynes through non‐vinylidene pathways. In this study, we conducted a comprehensive experimental and theoretical investigation into the reactions between the Ru(II) complex [Ru([9]aneS3)(bpy)(OH2)]2+ and 2‐alkynylanilines. Our study revealed that the selectivity between the vinylidene and non‐vinylidene pathways can be tuned by reaction temperature, substrate, and solvent polarity. This strategic control allows for the preferential formation of either C2‐ or C3‐metalated indole zwitterion complexes. Additionally, we identified a rare decyclization mechanism that enables the conversion of C2‐metalated indoles to C3‐metalated indoles, underscoring the significance of product stability in these pathways. Overall, this work demonstrates practical approaches to control the preference between vinylidene and non‐vinylidene pathways, which is crucial for the design of new catalysts and metalated heterocyclic complexes.