Heavy Alkali Metal Amides: Role of Secondary Interactions in Metal Stabilization

The coordination chemistry of the bis(diphenylmethylsilyl)amine ligand, HN(SiMePh(2))(2), with the heavy alkali metals potassium and rubidium has been investigated to study its effect on the structure of the resulting compounds. The compounds exhibit extensive intra- and intermolecular M-pi interactions, creating 1-D coordination polymers, [K{N(SiMePh(2))(2)}](infinity) (1) and [Rb{N(SiMePh(2))(2)}](infinity) (3). This motif is maintained in the presence of tetrahydrofuran (THF), as seen in [K{N(SiMePh(2))(2)}thf](infinity) (2). In contrast, use of the tridentate PMDTA allows isolation of a monomeric species, K(pmdta)N(SiMePh(2))(2) (4), which exhibits both agostic and M-pi interactions. The incorporation of macrocyclic 18-crown-6, results in the formation of a rare non-metal bound amido species, {[K(18-crown-6)N(SiMePh(2))(2)]}(infinity) (5), stabilized by M-pi interactions from adjacent [N(SiMePh(2))(2)](-) ligands propagating 1-D coordination polymers.