Formation and Reactions of Small Ring Compounds of Germanium and Lead

Abstract

Hexa-fe/i-butylcyclotrigermane, the only peralkylcyclotrigermane reported to date, reacts with the heavier chalcogens or aryl isocyanides by insertion into one GeGe bond to provide the ring-enlarged four-membered cycles. Hexakis(2,4,6-triisopropylphenyl)cyclotristannane (21), first described by Masamune and Sita, is now easily accessible by treatment of tin(II) chloride with 2,4,6-triisopropylphenylmagnesium bromide. Heating of 21 to ca. 80°C leads to an equilibrium between 21 and its cleavage products bis(2,4,6-triisopropylphenyl)stannylene (22) and tetrakis-(2,4,6-triisopropylphenyl)distannene (23), both of which can be trapped by various addition reactions. The reactions of 23 with the heavier chalcogens provide strong evidence for a true tin-tin double bond in distannene 23. With transition metal substrates stannylene 22 reacts by substitution or insertion to give some new stannylene complexes. Treatment of the intermediate zirconocene with 21 leads to a very air-sensitive product, whose spectral data indicates the formation of the first transition metal complex of a distannene. Attempts to prepare a more stable distannene of type 23 by replacement of the 2,4,6-triisopropylphenyl groups by the bulkier 2,4,6-tri-ie/ibutylphenyl groups remained unsuccessful as yet, because in this case aryl/alkyl rearrangements take place.