Intramolecular Diels−Alder Reactions in Ruthenium Vinylidene Complexes Containing Anthracenyl Groups

An intramolecular Diels−Alder (IMDA) reaction was observed at room temperature between an allyl group and a chloroanthracenyl group that were both bonded to the vinylidene ligand of the cationic ruthenium complex [Ru]CC(CH2CHCH2)CH(CH2CHCH2)(C14H8Cl)+ (6; [Ru] = Cp(PPh3)3Ru). The vinylidene ligand functions as a mediator to bring the allyl and the chloroanthracenyl groups in proximity for the reaction to take place. For the two allyl groups in 6, only the one at Cβ underwent the reaction. In the analogous triethylphosphine complex 6′, more electron-donating triethylphosphine ligands lower the rate of the IMDA reaction. For this IMDA reaction in several vinylidene complexes, each with a nonchlorinated anthracenyl ligand, the rate of the reaction is accelerated by the presence of an unsaturated functional group at Cγ of the vinylidene ligand, particularly by a terminal alkynyl substituent. The solid-state structures of two IMDA reaction products have been determined by single-crystal X-ray diffraction analysis.