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

Reaction of the chiral amidine N,NY-bis(1-phenylethyl)benzamidine ((S)-HPEBA), KCH(SiMe3)(2), and MI2 (M = Ca, Sr, Ba) or LnI(2) (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 THE 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.