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

Abstract

The heteroleptic iodo complexes [(DIP2pyr)MI(THF)n] (M = Ca, Sr (n = 3); Ba (n = 4); (DIP2pyr)− = 2,5-bis{N-(2,6-diisopropylphenyl)iminomethyl}pyrrolyl) were synthesized by reaction of [(DIP2pyr)K] with anhydrous alkaline earth metal diiodides. All complexes are monomeric in the solid state. A κ3-coordination mode of the (DIP2pyr)− ligand was observed for the strontium and the barium compounds, while the analogous calcium derivative is κ2-coordinated in the solid state. However, VT-1H NMR studies of [(DIP2pyr)CaI(THF)3] indicate a symmetrically coordinated (DIP2pyr)− ligand in solution. Computational studies confirm the different coordination modes in solution and in the solid state. The preferred κ2-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 [(DIP2pyr)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 [(DIP2pyr)Ca{N(SiMe3)2}(THF)2].