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

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(CNBu^t)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)}{μ₂:η²-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.