Small ring compounds containing highly coordinate Group 14 elements

Syntheses, structures, thermolyses of pentacoordinate 1,2-oxasiletanides (1), K+, 18-crown-6, {[C6H4C(CF3)2O]SiPh[CHRCR1R2O]}−, pentacoordinate1,2-oxastannetanides (2), K+, 18-crown-6, {Ph3Sn[CH(SPh)CR1R2O]}−, pentacoordinate 1,2-oxagermetanide (3), K+, 18-crown-6, {[C6H4C(CF3)2O]GePh[CH(CH2-t-Bu)C(CF3)2O]}−, germylalkoxide (4), K+, 18-crown-6, Ph3GeCH(CH2-t-Bu)C(CF3)2O−, pentacoordinate siprobi[1,2-oxasiletanide] (5), DBU·H+, {PhSi[-CH2C(CF3)2O]2}− are summarized. All compounds except for spirobi[1,2-oxasiletanide] 5, which underwent homo-Brook rearrangement, gave the corresponding olefins upon heating, indicating that they are intermediates of Peterson-type reactions. However, it was found that 1,2-oxasiletanides bearing the Martin ligand, which usually undergo the Peterson reaction, can afford the homo-Brook rearrangement products depending on the substituent at the 3-position and the reaction conditions, demonstrating that the Peterson reaction and homo-Brook rearrangement proceed via a common intermediate, a pentacoordinate 1,2-oxasiletanide. Crystal structures of these compounds are also presented.