Enantiopure Amidinate Complexes of the Rare-Earth Elements

The synthesis of the new chiral amidine (S,S)-N,N'-bis(1-phenylethyl)pivalamidine ((S)-HPETA) and its corresponding lithium salt (S)-LiPETA are reported, and their solid-state structures were investigated by single-crystal X-ray diffraction. Depending on the stoichiometric ratio and the ion radius of the rare-earth metal, the reaction of (S)-LiPETA with anhydrous lanthanide trihalides (Ln = Sc, Y, La, Nd, Sm, Lu) afforded mono-, bis-, and tris(amidinate) complexes. The mono(amidinate) compound [{(S)-PETA}LaI4Li2(thf)(4)], the bis(amidinate) complexes [({(S)-PETA}(2)Ln-mu-Cl)(n)] (Ln = Sc, Y, Nd, Sm, Lu), and the tris(amidinate) compound [{(S)-PETA}(3)Y] were isolated and structurally characterized by single-crystal X-ray diffraction. For the bis(amidinate) compounds, either monomeric or chloro-bridged dimeric structures were observed in the solid state. Furthermore, chiral bis(amidinate)-amido and-alkyl complexes [{(S)-PETA}(2)Ln{E(SiMe3)(2)}] (E = N, Ln = Y; E = CH, Ln = Sc, Y, Lu) were synthesized by salt metathesis and their catalytic activity and enantioselectivities were investigated in hydroamination/cyclization reactions. All of these compounds showed very good catalytic activity, and all of the investigated substrates were converted regiospecifically into their corresponding cyclic products under mild reaction conditions within good reaction times. The lutetium alkyl compound combined a high activity with good enantioselectivity.