Alkyl-Substituted Amides as Ligands in Homometallic and Heterobimetallic Calcium Complexes

The reaction of benzylpotassium with anhydrous calcium diiodide and 2,2,6,6-tetramethylpiperidine (Tmp-H) in a molar ratio of 2:1:2 in toluene in the presence of tetramethylethylenediamine yields colorless [(tmeda)Ca(Tmp)2] (1) with an average Ca−Namide bond length of 227.5 pm. The metathesis reaction of CaI2 with 2 equiv of KN(Ph)iPr in tetrahydrofuran (THF) gives [(thf)3Ca{N(Ph)iPr}2] (2) with a Ca−N distance of 234.9 pm. An excess of KN(Ph)R (R = Me, iPr) in the metathesis reaction with CaI2 leads to the formation of calciates of the type K2Ca[N(Ph)R]4 regardless of the applied stoichiometry. The THF-free compound [K2Ca{N(Ph)Me}4]∞ (3) forms a three-dimensional net structure, whereas the amides with the larger isopropyl group lead to the formation of molecular [{(thf)2K(μ-N(Ph)iPr)2}2Ca] (4). In both of these heterobimetallic compounds, the potassium atoms bind to the π systems of the phenyl groups. Heterobimetallic calciates [K2Ca(NPh2)4(thf)3]∞ (5) with R = Ph crystallize with a chain structure. In all of these calciates, the tetra-coordinate calcium atoms are in distorted tetrahedral environments.