In contrast to transition metals,rare-earth metal-promoted sp^(2)-sp carbon-carbon coupling through reductive elimination cannot be realized due to the inaccessibility of two-electron metal-based redox couples.Herein,...In contrast to transition metals,rare-earth metal-promoted sp^(2)-sp carbon-carbon coupling through reductive elimination cannot be realized due to the inaccessibility of two-electron metal-based redox couples.Herein,we report that sp^(2)-sp cross-carbanion coupling has been realized in the reaction of rare-earth azametallacyclopentadienes 2 with alkyl and aryl terminal alkynes.The reaction of 2,which are in situ generated from rare-earth metallacyclopropenes 1 and nitriles,with terminal alkynes provides a new class of seven-membered rare-earth metallacycles 3 containing cumulated double bonds.The structures of complexes 3 have been fully characterized.Mechanistic studies using DFT calculations and principal interacting orbital(PIO)analysis reveal that the formation of 3 proceeds through three steps:activation of the alkynyl C-H bond in terminal alkynes,followed by sp^(2)-sp cross-carbanion coupling and subsequent propargyl-to-allenyl isomerization to form a new C-C double bond,providing metallacycles 3.展开更多
基金supported by the National Key R&D Program of China(No.2021YFF0701600)the Natural Science Foundation of China(No.22371006 and 22131001).
文摘In contrast to transition metals,rare-earth metal-promoted sp^(2)-sp carbon-carbon coupling through reductive elimination cannot be realized due to the inaccessibility of two-electron metal-based redox couples.Herein,we report that sp^(2)-sp cross-carbanion coupling has been realized in the reaction of rare-earth azametallacyclopentadienes 2 with alkyl and aryl terminal alkynes.The reaction of 2,which are in situ generated from rare-earth metallacyclopropenes 1 and nitriles,with terminal alkynes provides a new class of seven-membered rare-earth metallacycles 3 containing cumulated double bonds.The structures of complexes 3 have been fully characterized.Mechanistic studies using DFT calculations and principal interacting orbital(PIO)analysis reveal that the formation of 3 proceeds through three steps:activation of the alkynyl C-H bond in terminal alkynes,followed by sp^(2)-sp cross-carbanion coupling and subsequent propargyl-to-allenyl isomerization to form a new C-C double bond,providing metallacycles 3.
