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.

研究观察到，在室温条件下，同时键合于阳离子钌配合物[Ru]CC(CH2CHCH2)CH(CH2CHCH2)(C14H8Cl)+（6；[Ru] = Cp(PPh3)3Ru）的亚乙烯基配体上的烯丙基与氯蒽基之间，发生了分子内狄尔斯-阿尔德（intramolecular Diels−Alder，IMDA）反应。该亚乙烯基配体充当反应介质，使烯丙基与氯蒽基相互靠近，从而促成反应发生。在配合物6的两个烯丙基中，仅位于Cβ位的烯丙基参与了该反应。在类似的三乙基膦配合物6′中，给电子能力更强的三乙基膦配体反而会降低IMDA反应的速率。针对多款带有非氯代蒽基配体的亚乙烯基配合物中的该IMDA反应，亚乙烯基配体的Cγ位若存在不饱和官能团，尤其是末端炔基取代基，可显著加速反应速率。通过单晶X射线衍射分析，确定了两款IMDA反应产物的固态结构。