Homoleptic Chiral Benzamidinate Complexes of the Heavier Alkaline Earth Metals and the Divalent Lanthanides

Reaction of the chiral amidine N,N′-bis­(1-phenyl­ethyl)­benzamidine ((S)-HPEBA), KCH­(SiMe3)2, and MI2 (M = Ca, Sr, Ba) or LnI2 (Ln = Eu, Yb) in a 2:2:1 stoichiometric ratio resulted in the chiral homoleptic monomeric alkaline earth metal compounds [Ca­(PEBA)2­(THF)2] (1) and [Sr­(PEBA)2­(THF)2] (2), the dimeric barium complex [Ba­(PEBA)2]2 (3), and the monomeric divalent lanthanide compounds [Eu­(PEBA)2­(THF)2] (4), and [Yb­(PEBA)2­(THF)2] (5). The solid-state structures of all compounds were established by single-crystal X-ray diffraction. Three different structures are observed in the solid state. Compounds 1, 2, 4, and 5 form distorted coordination octahedra. For the alkaline earth element complexes 1 and 2, the two THF molecules are located in a trans-position, whereas, for the lanthanide compounds 4 and 5, they are arranged in a cis-position. In contrast, the barium complex 3 is dimeric with two amidinate ligands in an unusual “side-on” bridging mode. All five complexes were used as catalysts for hydrophosphination reactions of styrene and substituted analogues.