C-F center dot center dot center dot M+ interaction in anionic alpha-fluorovinyl rhenium oxycarbene complexes and their beta-fluoroenolate analogsстатья
Информация о цитировании статьи получена из
Web of Science,
Scopus
Статья опубликована в журнале из списка Web of Science и/или Scopus
Дата последнего поиска статьи во внешних источниках: 18 июля 2013 г.
Аннотация:The C-F center dot center dot center dot M+ interaction in anionic sigma-(alpha-fluorovinyl)rhenium oxycarbene complexes, [RCF=CFRe=C(O)R'(CO)(4)]M (1-6), M = Na, Li, K is studied by F-19 NMR in THF and Et2O. The coordination of alpha-F to M+ results in an upheld shift of the corresponding F-19 NMR signal and a decrease of (1)J(CF). The maximum shift is found for the Li salt of complex 4 in Et2O (Delta delta(F alpha) = 36.4 ppm), in which case a Li-7-F-19 spin-spin coupling is also observed (J(LiF): = 40 Hz). The Delta E of C-F center dot center dot center dot M. interaction and its effect on F-19 shielding was further studied by DFT calculations using beta-fluoroenolates as models, which confirmed a strong impact of CF-bond environment on the coordination ability of fluorine in these F,O-chelates. A compound with a beta-fluoroenolate backbone but without rhenium, o-(alpha-fluorovinyl)phenolate 12, was prepared and studied by F-19 NMR, and similarly showed indications of C-F center dot center dot center dot M+ interaction in THF solution. It is concluded that the donor ability of fluorine in the studied system is enhanced because of the conjugation of alpha-fluorovinyl group with the enolate pi-system and back donation from the transition metal. (C) 2011 Elsevier B.V. All rights reserved.