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-Pr(i)2)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{mu2-(NSiMe3)}2GeAr' (5), whereas 2 afforded the monoimide bridged Ar'Sn{mu2-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{mu2-CH(SiMe3)}{mu2:eta2-N2CH(SiMe3)}{mu2-N2CH(SiMe3)}GeAr' (9) which contains ligands in three different bridging modes and no Ge-Ge bonding. Reaction of 1 with an excess of N(2)O gave a germanium peroxo species Ar'(HO)Ge(mu2-O)(mu2:eta2-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 PhCPh to give the 1,2-digermacyclobutadiene 12, which has a ring, and with Me(3)SiCCH or PhCC-CCPh to activate a flanking C6H3-2,6-Pr(i)2 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.