2,5-Bis{N-(2,6-diisopropylphenyl)iminomethyl}pyrrolyl Complexes of the Heavy Alkaline Earth Metals: Synthesis, Structures, and Hydroamination Catalysis

The heteroleptic iodo complexes [(DIP(2)pyr)MI(THF)(n)] (M = Ca, Sr (n = 3); Ba (n = 4); (DIP(2)pyr)(-) = 2,5-bis{N-(2,6-diisopropylphenyl)iminomethyl}pyrrolyl) were synthesized by reaction of [(DIP(2)pyr)K] with anhydrous, alkaline earth metal diiodides. All complexes are monomeric in the solid state. A kappa(3)-coordination mode of the (DIP(2)pyr)(-) ligand was observed for the strontium and the barium compounds, while the analogous calcium derivative is kappa(2)-coordinated in the solid state. However, VT-H-1 NMR studies of [(DIP(2)pyr)CaI(THF)(3)] indicate a symmetrically coordinated (DIP(2)pyr)(-) ligand in solution. Computational studies confirm the different coordination modes in solution and in the solid state. The preferred kappa(2)-coordination mode observed in the solid state might be a result of temperature or/and crystal packing effects. Furthermore, the calcium and strontium amido complexes [(DIP(2)pyr)M{N(SiMe3)(2)} (THF)(2)] (M = Ca, Sr) were prepared by reaction of [(DIP2pyr)MI(THF)(n)] (M = Ca, Sr (n = 3)) with [K{N(SiMe3)(2)}]. Both compounds were investigated for the intramolecular hydroamination of aminoalkenes. Both catalysts showed a good activity, and the best results were obtained for the calcium complex [(DIP(2)pyr)Ca{N(SiMe3)(2)}(THF)(2)].