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Reactions of the Heavier Group 14 Element Alkyne Analogues Ar‘EEAr‘ (Ar‘ = C6H3-2,6(C6H3-2,6-Pri2)2; E = Ge, Sn) with Unsaturated Molecules:  Probing the Character of the EE Multiple Bonds

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posted on 2005-12-14, 00:00 authored by Chunming Cui, Marilyn M. Olmstead, James C. Fettinger, Geoffrey H. Spikes, Philip P. Power
Reactions of the alkyne analogues Ar‘EEAr‘ (Ar‘ = C6H3-2,6(C6H3-2,6-Pri2)2; E = Ge (1); Sn (2)) with unsaturated molecules are described. Reaction of 1 and 2 with azobenzene afforded the new hydrazine derivatives Ar‘E{(Ph)NN(Ph)}EAr‘ (E = Ge (3); Sn (4)). Treatment of 1 with Me3SiN3 gave the cyclic singlet diradicaloid Ar‘Ge{μ2-(NSiMe3)}2GeAr‘ (5), whereas 2 afforded the monoimide bridged Ar‘Sn{μ2-N(SiMe3)}SnAr‘ (6). Reaction of 1 with t-BuNC or PhCN yielded the adduct Ar‘GeGe(CNBut)Ar‘ (7) or the ring compound (8). In contrast, the tin compound 2 did not react with either t-BuNC or PhCN. Treatment of 1 with N2CH(SiMe3) generated Ar‘Ge{μ2-CH(SiMe3)}{μ22-N2CH(SiMe3)}{μ2-N2CH(SiMe3)}GeAr‘ (9) which contains ligands in three different bridging modes and no GeGe bonding. Reaction of 1 with an excess of N2O gave a germanium peroxo species Ar‘(HO)Ge(μ2-O)(μ2:η2-O2)Ge(OH)Ar‘ (10) which features a ring. Oxidation of 1 by tetracyanoethylene (TCNE) led to cleavage of the GeGe bond and formation of a large multiring system of formula Ar‘Ge3+{(TCNE)2-}3{(GeAr‘)+}3. The digermyne 1 also reacted with 1 equiv of Ph⋮CPh to give the 1,2-digermacyclobutadiene 12, which has a ring, and with Me3SiC⋮CH or PhC⋮CC⋮CPh to activate a flanking C6H3-2,6-Pri2 ring and give the tricyclic products 13 and 14. The “distannyne” 2 did not react with these acetylenes. Overall, the experiments showed that 1 is highly reactive toward unsaturated molecules, whereas the corresponding tin congener 2 is much less reactive. A possible explanation of the reactivity differences in terms of the extent of the singlet diradical character of the GeGe and SnSn bonds is discussed.