Low-Coordinate Germylene and Stannylene Heterocycles featuring Sterically Tunable Bis(amido)silyl Ligands

A series of monomeric heterocyclic metallylenes [{iPr2Si(NR)2}M:] (M = Ge and Sn; R = Dipp = 2,6-iPr2C6H3 or SiPh3) have been prepared. Preliminary atom-transfer chemistry involving the new low-valent germylenes with the chalcogen sources Me3NO and S8 yielded the corresponding dimeric oxo- and sulfido complexes (e.g., [{iPr2Si(NDipp)2}Ge(μ-E)]2; E = O and S). Structural analyses of the metallylenes and their oxidized products reveal that incorporation of the umbrella-shaped triarylsilyl groups (SiPh3) within the NSiN chelate confers additional steric protection about the group 14 centers relative to a Dipp group. The inclusion of sterically modifiable −SiAr3 (Ar = aryl) units as part of a bis(amido) ligand array represents a new approach in this field and holds considerable promise with regard to attaining increasingly higher degrees of steric bulk.