A series of monomeric heterocyclic metallylenes [{(Pr2Si)-Pr-i(NR)(2)}M:] (M = Ge and Sn; R = Dipp = 2,6-(Pr2C6H3)-Pr-i or SiPh3) have been prepared. Preliminary atom-transfer chemistry involving the new low-valent germylenes with the chalcogen sources Me3NO and S-8 yielded the corresponding dimeric oxo- and sulfido complexes (e.g., [{(Pr2Si)-Pr-i(NDipp)(2)}Ge(mu-E)](2); E = 0 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,