Stable heterocyclic (Schiff base) divalent Group 14 element species MO-Schiff base-O (M=Ge, Sn, Pb)

The synthesis and characterization of new stable divalent germanium, tin and lead homoleptic species L2M [L2=2,2′-N,N′-bis(salicylidene)ethylenediamine, M=Ge (1), Sn (2), Pb (3); (R,R)-(−)-N,N′-bis(3,5-di-tert-butylsalicylidene)-1,2-cyclohexanediamine, M=Ge (4), Sn (5), Pb (6) and N-methyl-2,2′-imino-bis(8-hydroxyquinoline), M=Ge (7), Sn (8)] are described. Compounds 1–8 were obtained in good yields by alcoholysis of the MN bonds of the divalent precursors [(Me3Si)2N]2M by diols with bis(salicylidene)diamine and 2,2′-imino-bis-quinoline structures. They have been isolated as solids at ambient temperature and are monomeric. NMR, IR and UV spectra are suggestive of N⋯M intramolecular coordination. The chemistry of 1–8 is illustrated through their reactions with iodine and 1,2-benzoquinones. The X-ray structure of the L2Sn-quinone adduct reveals a distorted octahedral coordination geometry around tin with remarkably short SnN distances. Various RCHO insertion reactions into the MO bonds of 1–8 and MO cleavage reactions with organic acids and acyl halides are also described; they provide a convenient procedure for the generation of new heteroleptic divalent species.