SYNTHESIS AND CRYSTAL-STRUCTURE OF A PENTACOORDINATE 1,2-OXAGERMETANIDE

A pentacoordinate 1,2-oxagermetanide 1, K+ 18-crown-6{[-C6H4C(CF3)(2)O-]GePh[-CH(CH(2)(t)Bu)C(CF3)(2)O-]}(-), was quantitatively synthesized as a colourless block (m.p. 217-218 degrees C (decomp.)) by deprotonation of the corresponding beta-hydroxygermane 2, [-C6H4C(CF3)(2)O-]GePhCH(CH(2)(t)Bu)C(CF3)(2)OH, which can be prepared by unique cycloelimination of benzene from o-HO(CF3)(2)CC(6)H(4)GePh(2)[CH(CH(2)(t)Bu)C(CF3)(2)OH] (3). On heating in CD3CN at 150 degrees C for 30 days, 1 equilibrates with another diastereomer 4 and then undergoes the Peterson-type reaction to give the corresponding olefin 5, (F3C)(2)C=CHCH(2)(t)Bu (13%), and its double-bond migrated isomer 6, (F3C)(2)CHCH=CH(t)Bu (33%). The yields of the olefins 5 and 6 are not very high, because their polymerization takes place under the reaction conditions. X-ray crystallographic analysis of 1 shows that it has a distorted trigonal bipyramidal structure with two oxygen atoms at apical positions.