Switching from Dimerization to Cyclotrimerization Selectivity by FeCl3 in the Y[N(TMS)2]3-Catalyzed Transformation of Terminal Alkynes: A New Strategy for Controlling the Selectivity of Organolanthanide-Based Catalysis
journal contributionposted on 23.08.2010 by Xiuli Bu, Zhengxing Zhang, Xigeng Zhou
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Y[N(TMS)2]3/FeCl3 has been found to be an efficient bimetallic catalyst system for the cyclotrimerization of terminal alkynes, which cannot be achieved by either trivalent iron or trivalent lanthanide catalysts. Furthermore, this reaction also occurs efficiently in the presence of Fe[N(TMS)2]3 and YCl3. Both aromatic and aliphatic alkynes are compatible with this catalytic system. It is postulated that the catalytic cyclotrimerization proceeds through a tandem intermolecular diinsertion of alkynes into the yttrium−alkynyl bond and intramolecular electrophilic addition of a π-coordinated alkyne moiety, and the π-coordination of Fe3+ to alkyne may play an important role in controlling the insertion degree of advancement and selectivity. The observed catalytic reaction is sharply in contrast with the cyclotrimerization of alkynes, known to proceed through a typical metallacyclopentadiene intermediate.