Origin of Stability and Inhibition of Cooperative Alkyne Hydrofunctionalization Catalysts

New entries to the [Ru(Cp/Cp*)(P R 2 N R′ 2 )(MeCN)]PF 6 catalyst family were synthesized, including a Cp complex (R=Cy; R′=Ph) and two Cp* complexes (R=Cy, Ph; R′=Ph). These and other derivatives were used for the intramolecular hydroamination of 2‐ethynylaniline to elucidate trends in catalytic lifetime and rate. The readily accessible [Ru(Cp)(P Cy 2 N Ph 2 )(MeCN)]PF 6 derivative showed comparable lifetime to [Ru(Cp)(P t −Bu 2 N Ph 2 )(MeCN)]PF 6 , the previous optimal catalyst. Donor‐free ‘active’ catalysts, [Ru(Cp/Cp*)(P Cy 2 N Ph 2 )]PF 6 , were prepared and their thermal stability was assessed. The relatively high stability of the Cp derivative was explained by the capacity of the P Cy 2 N Ph 2 ligand to coordinate in a κ 3 ‐(P,P,Ar) mode, which protects the low‐coordinate species. This coordination mode is inaccessible with the Cp* derivative. Additionally, [Ru(Cp*)(P Cy 2 N Ph 2 )]PF 6 readily activated the C−Cl bond of the solvent dichloromethane. Variable time normalization analysis (VTNA) revealed that the indole product inhibited the catalyst [Ru(Cp)(P Cy 2 N Ph 2 )(MeCN)]PF 6 , which slowed catalytic rates.