Synthesis and structural characterization of solvated calcium amides containing bulky silylamide ligands

A series of solvated calcium bis(amides) with the general formula Ca[N(R)(SiMe3)]2(solv)x (R = –SiMe2t-Bu, –SiPh2t-Bu, and –SiPh3) was prepared from the reaction of CaI2 with 2 equiv of the corresponding potassium amide. Solvent ligands used in this study include THF, pyridine (py), hexamethylphosphoranide (HMPA), and 4-dimethylaminopyridine (DMAP). The coordinated THF in Ca[N(SiMe2t-Bu)(SiMe3)]2(THF)2 could be replaced by stronger donating ligands. When –N[(SiPh3)(SiMe3)] was used as the amide ligand again a bis(THF) adduct was formed. Quite interestingly, when the more sterically-demanding ligand –N[(SiPh2t-Bu)(SiMe3)] ligand was used only one THF molecule could coordinate to Ca, leading to a rare example of a tri-coordinate Ca bis(amide). One of the starting amides, [KN(SiMe2t-Bu)(SiMe3)]2, was isolated and found to adopt a dimeric structure in the solid state. All complexes were characterized with 1H NMR, 13C NMR, elemental analyses, and X-ray crystallography when appropriate.