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Heterobimetallic Rare Earth–Lithium Complexes with Fewer Than Three Binaphtholates

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Abstract

Heterobimetallic rare earth–alkali metal binaphtholates (REMBs) are exquisite catalysts for asymmetric synthesis (Shibasaki catalysts). All solid-state structures reported so far correspond to the general formula M3RE[(S)-binolate]3 (RE/M/B = 1:3:3 stoichiometry). We have synthesized and characterized crystallographically new complexes of this category, namely Li3RE[(S)-binolate]3·xTHF [RE = Sc (2), Sm (3)] and Li3Nd[(S)-binolate]3·6THF·LiCl (4). The latter is the first reported adduct between a REMB and LiCl. We have also crystallized a rare type of REMB of 1:2:2.5 stoichiometry: Li4Sm2[(S)-binolate]5·6THF·2H2O (5). Such a complex has only one precedent in the literature. The use of (S)-3,3′-dimesityl-1,1′-binaphthyl-2,2′-diol (6) as ligand precursor allowed us to obtain the first X-ray structures of unprecedented REMBs of 1:1:1 and 1:1:2 stoichiometries: {[(S)-6]RECl2(THF)2}[Li(THF)2] [RE = Y (7), Sm (8)] and LiY[(S)-6]2·2THF (9).

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