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 [L-2 = 2,2'-N,N'-bis-(salicylidene)ethylenediamine, M = Ge (1), Sn (2), Pb (3); (R,R)-(-)-N,N'-bis(3,5-di-tert-butylsalicylidene) amine, 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 [(Me,Si)(2)N](2)M 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. (C) 1999 Elsevier Science S.A. All rights reserved.