Isolation of Ruthenium–Indoline and −Indole Zwitterion Complexes: Insight into the Metal-Induced Cyclization of Aniline-Tethered Alkynes and Strategy to Lower the Activation Barrier of Metal−Vinylidene Formation

Isolation of the first examples of Ru­(II)–indoline and −indole zwitterion complexes derived from reactions between [Ru([14]­aneS4)­Cl2] ([14]­aneS4 = 1,4,8,11-tetrathiacyclotetradecane) and aniline-tethered alkynes has been achieved. Mechanistic studies regarding the selectivity between a “vinylidene-involving pathway” and a “direct nucleophilic ring closure mechanism” for these reactions have been conducted experimentally and theoretically. Employment of 1,2-silyl shift as a strategy to lower the activation barrier for the formation of Ru–vinylidene species has also been proved to be successful.