Ambiphilic Nature of Dipyrrolylpyridine-Supported Divalent Germanium and Tin Compounds

We describe the synthesis and characterization of a series of divalent Ge and Sn compounds of the dianionic ligand L (2,6-bis(3,5-diphenylpyrrolyl)pyridine). Forcing base-stabilized divalent group 14 elements (E) into a planar geometry with a sterically constrained pincer-type L ligand is expected to produce LE species possessing ambiphilic properties, as suggested by theoretical calculations. The reactions of LH2 (the acid form of L) with 1 equiv of M(HMDS)2 (HMDS = N(SiMe3)2) yield the dimeric compounds (LE)2 (E = Sn (1) and E = Ge (3)) in benzene or toluene. The dimeric species 1 and 3 react with Lewis bases to yield monomeric LSn(THF)2 (2) and LE(dmap)2 (E = Sn (4), Ge (5); dmap = dimethylaminopyridine) and with the Lewis acidic W(CO)5THF to form LSnW(CO)5 (6). Finally, compounds 1 and 3 undergo insertion reactions with a Sn(I) distannyne to give the triple-decker products 7 and 8.