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-2(i))(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 ArGe{mu(2)-(NSiMe3)}(2)GeAr (5), whereas 2 afforded the monoimide bridged Ar'Sn{mu(2)-N(SiMe3)}SnAr' (6). Reaction of 1 with t-BuNC or PhCN yielded the adduct Ar'GeGe(CNBu7Ar (7) or the ring compound AI'Ge-N(Ph)CC(Ph)N-GeAr' (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{mu(2)-CH(SiMe3)}{mu(2):eta(2)-N2CH(SiMe3)}{mu(2)-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(mu(2)-O)(mu(2):eta(2)-O-2)Ge(OH)Ar' (10) which features a Ge-O-Ge-O-O 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 equivalent to CPh to give the 1,2-digermacyclobutadiene 12, which has a Ge-C-C-Ge ring, and with Me3SiC=CH or PhC equivalent to C-C equivalent to CPh to activate a flanking C(6)H(3-)2,6-Pr-2(i) 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.