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The complexes of rare-earth metals (Y, La, Sm and Lu) with a chiral tridentate amido-fluorenyl ligand were synthesized and characterized. These complexes demonstrated high efficiency in catalyzing both the intramolecular hydroamination of non-activated olefins and the cyanosilylation of ketones under very mild conditions, however, with no enantiocontrol being achieved. 1 H NMR monitoring of the reaction process suggests the weak coordination capacity of the fluorenyl moiety might be responsible for the lack of asymmetric inducing power of the chiral complexes in such transformations. [ABSTRACT FROM AUTHOR]

A series of neutral lanthanide alkoxide complexes stabilized by a new salen-type Schiff-base ligand were synthesized, and their catalytic behaviors for the ring-opening polymerization of lactide were explored. Amine elimination reactions of N -methyl- N ′, N ″-bis(3,5-di- tert -butylsalicylidene)-2,2′-diaminodiethylamine (LH 2 ) with Ln[N(SiMe 3 ) 2 ] 3 (Ln = Sm, Nd, La) in a 1:1 M ratio in THF, followed by reactions with 1 equiv of alcohols ( t BuOH, EtOH and CH 3 OCH 2 CH 2 OH), produced lanthanide alkoxide complexes LLn(O t Bu)(THF) (Ln = Sm ( 1 ), Nd ( 2 ), La ( 3 )), [LSm( μ -OEt)] 2 ( 4 ) and [LSm( μ -OCH 2 CH 2 OCH 3 )] 2 ( 5 ), respectively, whereas the same reaction with Yb[N(SiMe 3 ) 2 ] 3 gave an unexpected homoleptic complex L 2 Yb 2 ( μ -L) ( 6 ). X-ray structural determination showed that complexes 1 – 3 have a THF-solvated monomeric structure, whereas complexes 4 – 6 have an unsolvated dimeric structure. All lanthanide alkoxide complexes can efficiently initiate the ring-opening polymerization (ROP) of L -LA and rac -LA. The polymerization kinetics of L -LA initiated by complex 1 has been studied in detail and the first-order kinetic dependence on both l -lactide concentration and initiator concentration was found. Furthermore, all complexes showed moderate stereoselectivity for rac -LA polymerization to afford heterotactic-rich polylactides. [ABSTRACT FROM AUTHOR]

Abstract: Linked bis(β-diketiminato) rare-earth metal complexes based on the ethylene-bridged ligand [C2H4(BDIDClP)2]H2 [DClP=2,6-Cl2C6H3] and the cyclohexyl-bridged ligands [Cy(BDIAr)2]H2 [Ar=PMP (= p-MeOC6H4), Mes (=2,4,6-Me3C6H2), DIPP (=2,6-iPr2C6H3)] were prepared via amine elimination starting from [Ln{N(SiMe3)2}3] (Ln=La, Y). The three cyclohexyl-bridged complexes [{(R,R)-Cy(BDIMes)2}YN(SiMe3)2] ((R,R)-3), [{(R,R)-Cy(BDIMes)2}LaN(SiMe3)2] ((R,R)-4), and [{(R,R)-Cy(BDIDIPP)2}LaN(SiMe3)2] ((R,R)-5) were obtained enantiomerically pure. The X-ray crystal structure analysis of the racemic variants of 3 and 4 revealed a distorted square pyramidal coordination geometry around the rare-earth metal, in which the amido ligand occupies the apical position and the two linked β-diketiminato moieties form the basis. The two aromatic substituents adopt a transoid arrangement and both β-diketiminato moieties are bound in a η5 coordination mode with close Ln⋯C contacts. Due to the smaller ionic radius of yttrium vs. lanthanum, the front side of the yttrium complex 3 is sterically more hindered than in the lanthanum complex 4, but there is much more empty coordination space on the rear side, which may rationalize the observed differences in selectivity of 3 in comparison to 4. The catalytic efficiency of the β-diketiminato complexes was strongly affected by steric factors such as ionic radius of the metal and the steric bulk of the aryl substituents, which is an indication for highly steric encumbered catalytic species. The complexes displayed good to moderate catalytic activity in the hydroamination/cyclization of aminoalkenes depending on the steric hindrance around the metal center. The sterically most demanding diisopropylphenyl-substituted complex (R,R)-5 displayed significantly higher enantioselectivities (up to 76% ee), but lower catalytic activity in comparison to the sterically more open mesityl-substituted complex (R,R)-4. The smaller yttrium metal center in complex (R,R)-3 led to reduced activity as well as a reversal in enantioselectivity, which may be rationalized by a change of the approach of the alkene moiety to the Ln-amido bond in the cyclization transition state. [Copyright &y& Elsevier]

Abstract: Asymmetric intramolecular hydroamination reaction is a stately way to prepare chiral nitrogen-containing heterocyclic compounds. We report in this account our personal contribution in this field with the synthesis of chiral amido rare-earth complexes. A new family of structurally defined heterobimetallic rare earth lithium ate complexes based on N-substituted binaphthylamido ligands was discovered that promoted the hydroamination/cyclization of aminoolefins with up to 87% ee. Neutral rare earth amido and amido alkyl complexes could also be prepared and led to very active species. A more simple and reliable synthetic procedure was discovered towards the preparation of heterobimetallic rare earth amido alkyl ate complexes. They proved to be also active and enantioselective catalysts, as a good compromise between efficiency and practicability issues. [ABSTRACT FROM AUTHOR]

Abstract: Reaction of (CH3C5H4)2LnCl(THF) with NaNHAr in a 1:1 molar ratio in THF afforded the amide complexes (CH3C5H4)2LnNHAr(THF) [(Ar=2,6-Me2C6H3, Ln=Yb (I), Y (III); Ar=2,6-iPr2C6H3, Ln=Yb (II)]. X-ray crystal structure determination revealed that complexes I–III are isostructural. The central metal in each complex coordinated to two methylcyclopentadienyl groups, one amide group and one oxygen atom from THF to form a distorted tetrahedron. Complexes I–III and a known complex (CH3C5H4)2YbNiPr2(THF) IV all can serve as the catalysts for addition of amines to nitriles to monosubstituted N-arylamidines. The activity depended on the central metals and amide groups, and the active sequence follows the trend IV ≈ III < I < II. [Copyright &y& Elsevier]