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}2Ln-μ-Cl)n] (Ln = Sc, Y, Nd, Sm, Lu), and the tris­(amidinate)
compound [{(S)-PETA}3Y] 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}2Ln­{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.