aThe Guelph-Waterllo Center for Graduate Work in Chemistry,
University of Waterloo, Ontario, Canada N2L 3G1 bInstituto de Quimica - Universidade de Sao Paulo, Av. Prof.
Lineu Prestes 748, CEP05599-970, Sao Paulo, Brazil
Preparation of alkyl-ferrocenyl tellurides
Alkyl-ferrocenyl tellurides may be prepared by treatment of differrocenyl
ditelluride with NaBH4 and alkyl bromides in ethanol or by alkylation of
ferrocenyl-lithium with RTeBr in THF.
Transmetalation reaction of butyl-ferrocenyl telluride
Butyl-ferrocenyl telluride, upon treatment with BuLi, leads to
ferrocenyl-lithium which undergoes reaction with many electrophiles to afford
monosubstituted ferrocenes in good yields thereby overcoming the formation of
disubstituted products which always accompanies direct metalation of ferrocene.
Ferrocenyl tellurides with a direct ortho metalation group (DMG)
May be prepared in high yield by of deprotonation (1.5 equiv. of BuLi/1.5
equiv. of TMEDA/ THF) of N,N-diisopropylferrocene carboxamide followed by
quenching with BuTeBr.
The treatment of this telluride with RLi may, in theory, lead to two
reactions: deprotonation ortho to the carboxamide group (directed ortho
metalation) or transmetalation of the TeBu group. Preliminary results are
summarized below
Summary
Alkyl-ferocenyl tellurides can be prepared by reaction of lithiated ferrocene
with tellurium electrophiles.
The reaction of these tellurides with BuLi leads to monolithioferrocene
which can be quenched with several electrophiles.
Initial metalation results on a 2-caboxamido ferrocenyl telluride indicates
that competite directed ortho metalation and transmetalation occurs.
References
Tellurium chemistry: N.Petragnani, Tellurium in Organic
Chemistry, Academic Press, 1994.
