Abstract
Treatment of N,N-chelated germylene [(iPr)(2)NB(N-2,6-Me2C6H3)(2)]Ge (1) with ferrocenyl alkynes containing carbonyl functionalities, FcC equivalent to CC(O)R, resulted in [2+2+2] cyclization and formation of the respective ferrocenylated 3-Fc-4-C(O)R-1,2-digermacyclobut-3-enes 2-4 [R = Me (2), OEt (3) and NMe2 (4)] bearing intact carbonyl substituents. In contrast, the reaction between 1 and PhC(O)C equivalent to CC(O)Ph led to activation of both C equivalent to C and C=O bonds producing bicyclic compound containing two five-membered 1-germa-2-oxacyclopent-3-ene rings sharing one C-C bond, 4,8-diphenyl-3,7-dioxa-2,6-digermabicyclo[3.3.0]octa-4,8-diene (5).
With N-methylmaleimide containing an analogous C(O)CH=CHC(O) fragment, germylene 1 reacted under [2+2+2] cyclization involving the C=C double bond, producing 1,2-digermacyclobutane 6 with unchanged carbonyl moieties. Finally, 1 selectively added to the terminal double bond in allenes CH2=C=CRR' giving rise to 3-(=CRR')-1,2-digermacyclobutanes [R/R' = Me/Me (7), H/OMe (8)] bearing an exo-C=C double bond.
All compounds were characterized by (1)H, (13)C{1)H} NMR, IR and Raman spectroscopy and the molecular structures of 3, 4, 5, and 8 were established by single-crystal X-ray diffraction analysis. The redox behavior of ferrocenylated derivatives 2-4 was studied by cyclic voltammetry.