Catalyst Pendent‐Base Effects on Cyclization of Alkynyl Amines

Abstract A family of [CpRu(PP)(MeCN)]PF 6 complexes ( 2 a – e and 4 ) were prepared in which the bis‐phosphine ligand contains a pendent tertiary amine in the second‐coordination sphere. 2 a – e contain P Ph 2 N R′ 2 ligands with two amine groups as the pendent base. Complex 4 has the P Ph 2 N Ph 1 ligand with only one pendent amine. The catalytic performance of 2 a – e and 4 were assessed in the cyclization of 2‐ethynyl aniline and 2‐ethynylbenzyl alcohol. It was revealed that the positioning of the pendent amine near the metal active site is essential for high catalyst performance. A comparison of P Ph 2 N R′ 2 catalysts ( 2 a – e ) showed minimal difference in performance as a function of pendent amine basicity. Rather, only a threshold basicity – in which the pendent amine was more basic than the substrate – was required for high performance.