Different aluminum complexes were synthesized by the reaction of aluminum alkyls with a hexadentate salen-type Schiff base. The reaction of N,N′-bis(3,5-di-tert-butylsalicylidene)-2,2′-(ethylenedioxy)dianiline (LH2) with one equiv. of AlMe3 in toluene at 100 °C proceeded by methane elimination to produce the intermediate methyl complex [AlMeL] (1), and then subsequent intramolecular methyl migration to give the aluminum complex [AlL′] (2) [L′ = (2-O-3,5-tBu2C6H2)CHNC6H4OCH2CH2OC6H4NCH(Me)(2′-O-3′,5′-tBu2C6H2)]. The reaction of the same ligand with AlEt3 under the same experimental conditions involved ethane elimination, ethylene elimination and intramolecular hydrogen migration, and led to the complex [AlL′′] (3) [L′′ = (2-O-3,5-tBu2C6H2)CHNC6H4OCH2CH2OC6H4NCH2(2′-O-3′,5′-tBu2C6H2)]. However, the interaction of two equivalents of AlMe3 and AlEt3 afforded the corresponding binuclear complexes [(AlMe2)2L] (4) and [(AlEt2)2L] (5), respectively, and no methyl or hydrogen migration was found. The solid-state structures of aluminum complexes 1–3 were determined by single-crystal X-ray diffraction. It was found that complexes 2–5 show a very effective catalytic activity for the cycloaddition of epoxides and CO2 in the presence of NBu4Br as a cocatalyst at atmospheric pressure.

•Synthesis of six new lanthanide complexes stabilized by N-aryl substituted β-ketoiminato ligands.•Lanthanide amides and aryloxides can efficiently initiate the ring-opening polymerization of rac-LA.•The increasing order of activity of Y < Sm < Nd is in agreement with the order of their ionic radii.Several lanthanide complexes supported by N-aryl substituted β-ketoiminato ligands were synthesized by the protonolysis reaction. Reactions of 1-phenyl-3-N-(p-methoxyphenylimino)-1-butanone (HL) with Ln[N(SiMe3)2]3 and Ln(OAr)3(THF) (ArO = 2,6-But2-4-MeC6H2O) in a 2:1 M ratio gave mononuclear lanthanide amides L2Ln[N(SiMe3)2] [Ln = Y (1), Sm (2), Nd (3)] and aryloxides L2Ln(OAr) [Ln = Y (4), Nd (5)], respectively, whereas the same reaction with Yb[N(SiMe3)2]3 afforded an unexpected homoleptic ytterbium complex L3Yb (6). The solid-state structures of lanthanide complexes 1–6 were determined by single-crystal X-ray diffraction. It was found that complexes 1–5 can efficiently initiate the ring-opening of rac-lactide in THF to afford hetereotactic-rich polylactides.Download high-res image (156KB)Download full-size image

•In2Fe2CuO7 nanoparticles were synthesized through the sol-gel method.•In2Fe2CuO7 exhibits excellent visible-light-induced activity to MB degradation.•The excellent photocatalytic activity can be attributed to the narrow band gap.•In2Fe2CuO7 has a good chemical stability and high photocatalytic activities.Transition metal oxide In2Fe2CuO7 nanoparticles were prepared by the sol-gel film coating and subsequent sintering method. The phase formation was investigated by X-ray polycrystalline diffraction (XRD) measurement. The structure refinement confirmed that the sample has a pure hexagonal phase with the space group of P63/mmc. The detailed surface properties were characterized. In2Fe2CuO7 shows an efficient optical absorption in the region of visible wavelength and has a narrow band-gap of 1.91 eV. Particularly, In2Fe2CuO7 presents the efficient photodegradation for methylene blue (MB) solutions under visible-light irradiation. The nanoparticles could be a potential photocatalyst for the photodegradation for organic pollution solutions.

•Synthesis of six new lanthanide complexes stabilized by a novel salen-type Schiff-base ligand.•All lanthanide alkoxide complexes can efficiently initiate the ring-opening polymerization (ROP) of L-LA and rac-LA.•The first-order kinetic dependence on both l-lactide concentration and initiator concentration was found.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 (LH2) with Ln[N(SiMe3)2]3 (Ln = Sm, Nd, La) in a 1:1 M ratio in THF, followed by reactions with 1 equiv of alcohols (tBuOH, EtOH and CH3OCH2CH2OH), produced lanthanide alkoxide complexes LLn(OtBu)(THF) (Ln = Sm (1), Nd (2), La (3)), [LSm(μ-OEt)]2 (4) and [LSm(μ-OCH2CH2OCH3)]2 (5), respectively, whereas the same reaction with Yb[N(SiMe3)2]3 gave an unexpected homoleptic complex L2Yb2(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.

A series of neutral rare-earth metal aryloxides and amides supported by a new pentadentate (N2O3) salen ligand were synthesized, and their catalytic behaviors for the ring-opening polymerization of rac-lactide (rac-LA) were explored. The protolysis reactions of N,N′-bis(3,5-di-tert-butylsalicylidene)-2,2′-diaminodiphenyl ether (LH2) with (ArO)3Ln(THF) (ArO = 2,6-But2-4-MeC6H2O) and Ln[N(SiMe3)2]3 in a 1:1 molar ratio in THF gave the neutral rare-earth metal aryloxides LLn(OAr)(THF)n [n = 0, Ln = Sc (1), Yb (2); n = 1, Ln = Y (3), Sm (4) and Nd (5)] and rare-earth metal amides LLnN(SiMe3)2 [Ln = Yb (6), Y (7)], respectively. X-ray structural determination showed that complexes 1, 2, 6 and 7 have monomeric structures, in which the coordination geometry around the rare-earth metal atom can be best described as a distorted trigonal prism. Complexes 3 and 5 are THF-solvated monomers and each of the rare-earth metal atoms is seven-coordinated to form a distorted capped trigonal prism. It was found that all of these complexes can efficiently initiate the ring-opening polymerization (ROP) of rac-LA to give heterotactic-rich polylactides (PLAs). The highly heterotactic PLA (Pr up to 0.93) was obtained using complex 2 as the initiator at a polymerization temperature of 0 °C. The observed increasing order of activity of 1 < 2 < 3 < 4 ≈ 5 is in agreement with the order of their ionic radii, whereas the order of stereoselectivity is in the reverse order. The rare-earth metal salen amides can initiate rac-LA polymerization in a controlled manner, while polymerization using the rare-earth metal salen aryloxides is less controlled at room temperature.

A series of anionic organo-rare-earth amido complexes stabilized by dianionic phenoxy-amido ligands were prepared and their catalytic behavior for amidation reactions of aldehydes with amines was elucidated. Amine elimination reaction of Ln[N(SiMe3)2]3(μ-Cl)Li(THF)3 with an equimolar of lithium aminophenoxy {[HNO]1Li(THF)}2, which was prepared by the reaction of [HNOH]1 {[HNOH]1 = N-p-fluoro-phenyl(2-hydroxy-3,5-di-tert-butyl)benzylamine} with one equivalent of n-BuLi in tetrahydrofuran (THF) in situ, gave the anionic phenoxy-amido rare earth amido complexes [NO]12Ln[N(SiMe3)2][Li(THF)]2 [Ln = Y (1), Yb (2), Sm (3), Nd (4)] in high isolated yields. Similar reactions of Ln[N(SiMe3)2]3(μ-Cl)Li(THF)3 with {[HNO]2Li(THF)}2, and {[HNO]3Li(THF)}2 in THF gave the anionic rare-earth amides [NO]22Ln[N(SiMe3)2][Li(THF)]2 [Ln = Sm (5), Nd (6)] and [NO]32Ln[N(SiMe3)2][Li(THF)]2 [Ln = Sm (7), Nd (8)] {[HNOH]2 = N-p-chloro-phenyl(2-hydroxy-3,5-di-tert-butyl)benzylamine; [HNOH]3 = N-p-bromo-phenyl(2-hydroxy-3,5-di-tert-butyl)benzylamine}, respectively. All of these complexes were fully characterized. X-ray structural determination revealed that these complexes are isostructural, and have solvated monomeric structures. Each of the rare-earth ions is coordinated by two phenoxy-amido ligands and one N(SiMe3)2 group, and the coordination geometry can be described as a distorted trigonal bipyramid. Each of the lithium atoms is surrounded by one aryloxo group, one amido group and one THF molecule, and the coordination geometry can be described as a trigonal plane. The catalytic behavior of these rare-earth amides for the amidation reaction of aldehyde with amine was elucidated. It was found that these complexes are efficient catalysts for this transformation to produce amides in good to excellent yields under mild reaction conditions, and in some cases, diacylamide compounds can be prepared conveniently.

•Four ytterbium guanidinates bearing bridged bis(phenolate) ligand were prepared.•The solid state structures of all four complexes were determined by X-ray diffraction analysis.•Ytterbium guanidinates showed high activities in catalyzing hydrophosphonylation reactions of aldehydes.A series of ytterbium guanidinato complexes stabilized by an amine-bridged bis(phenolate) ligand were prepared, and their catalytic property for the hydrophosphonylation reaction of aldehydes was explored. Metathesis reactions of amine-bridged bis(phenolate) ytterbium chlorides LYbCl(THF) [L = Me2NCH2CH2N{CH2-(2-OC6H2tBu2-3,5)}2] with corresponding lithium guanidinates in a 1:1 molar ratio in THF gave the expected ytterbium guanidinato complexes LYb[R2NC(NR1)2] [R1 = Cy, R2N = N(TMS)2 (1), N(CH2)5 (2); R1 = iPr, R2N = N(TMS)2 (3), NPh2 (4)]. These ytterbium complexes were well characterized by elemental analyses, IR spectroscopy and single-crystal X-ray structure determination. The metal ion is six-coordinated by two oxygen and two nitrogen atoms from the bis(phenolate) ligand, and two nitrogen atoms from one guanidinato group. The coordination geometry around ytterbium can be described as a distorted octahedron. It was found that these ytterbium guanidinato complexes are highly efficient catalysts for the hydrophosphonylation reaction of various aldehydes under mild conditions.Four ytterbium guanidinato complexes stabilized by an amine-bridged bis(phenolate) ligand were prepared, which showed very high activity for the hydrophosphonylation of aldehydes with diethyl phosphite under mild reaction conditions.

A series of yttrium and ytterbium complexes supported by Salen ligands with different steric and electronic properties were synthesized, and their catalytic performances for the polymerization of rac-lactide (rac-LA) were explored. The phenol elimination reactions of (ArO)3Ln(THF) (ArO = 2,6-But2-4-MeC6H2O) with a number of Salen ligands (CH3)2C[CH2N═CH(C6H2-2-OH-3,5-R2)]2 [L1H2, R = H; L2H2, R = Cl; L3H2, R = But; L4H2, R = CMe2Ph] and CH2[CH2N═CH(C6H2-2-OH-3,5-Cl2)]2 (L5H2), in a 1:1 molar ratio gave yttrium and ytterbium Salen aryloxides L1Ln(OAr)(THF)2 (Ln = Y (1), Yb (2)), L2Ln(OAr)(THF)n (Ln = Y (3), n = 2; Ln = Yb (4), n = 1), L3Y(OAr) (5), L4Y(OAr)(THF) (6), and L5Yb(OAr)(THF) (7), respectively. The amine elimination reactions of L3H2 with Y[N(SiMe3)2]3 in a 1:1 molar ratio and then with 1 equiv of phenol ArOH, and alcohols PhCH2OH and PriOH, produced complex 5 and the yttrium Salen alkoxides [L3Y(μ-OCH2Ph)]2 (8) and [L3Y(μ-OPri)]2 (9), respectively. X-ray structural determination showed that complexes 1–4 and 7 have a THF-solvated monomeric structure, and complex 5 has an unsolvated monomeric structure, whereas complex 8 has an unsolvated dimeric structure. All of these complexes can initiate the ring-opening polymerization of rac-LA at 30 °C in THF. It was found for the first time that the overall coordination environment around the metal center has an obvious influence on the stereoselectivity of these lanthanide Salen complexes. Five-coordinated complex 5 with bulky tert-butyl substituent groups on the phenyl rings displayed apparently lower stereoselectivity than seven-coordinated complex 1, although there is no substituent on the ortho-positions of the Salen ligand L1 in the latter. Complex 7 bearing Cl substituents on the Salen ligand showed the highest stereoselectivity among these lanthanide complexes for rac-LA polymerization, and heterotactic polylactides (Pr up to 0.88) can be obtained at 30 °C in THF.

•Three new lanthanide amides bearing phenoxy(quinolinyl)amide ligand were prepared.•Lanthanide-lithium heterobimetallic complexes were prepared and characterized.•All the lanthanide amides can initiate the ring-opening polymerization of PDO.The amine elimination reaction of quinolinyl aminophenol (LH2) with Ln[N(SiMe3)2]3(μ-Cl)Li(THF)3 in THF afforded lanthanide-lithium aminophenoxy complexes L2LnLi(THF)2 (Ln = Yb (1), Sm (2)), while the similar reaction with Ln[N(SiMe3)2]3 in toluene gave normal monoamido lanthanide complexes LLnN(SiMe3)2(DME) (Ln = Sm (3), Nd (4), La (5)). All complexes have been fully characterized. X-ray structural determination revealed that complexes 1 and 2 have a monomeric C2-symmetric heterobimetallic structure, in which the lanthanide atom is connected to the lithium atom by two oxygen bridges from two phenoxy(quinolinyl)amide ligands. Complexes 4 and 5 have a solvated monomeric structure, and the lanthanide metal centers adopt a distorted octahedral geometry. It was found that complexes 3–5 initiated the ring-opening polymerization of 1,4-dioxan-2-one (PDO) with high activity.Two lanthanide-lithium heterobimetallic complexes and three monoamido lanthanide complexes were synthesized by silylamine elimination reaction of Ln[N(SiMe3)2]3(μ-Cl)Li(THF)3 or Ln[N(SiMe3)2]3 with quinolinyl aminophenol. All the lanthanide amides show highly catalytic activity for the ring-opening polymerization of 1,4-dioxan-2-one.

A series of neutral yttrium guanidinates supported by an amine-bridged bis(phenolate) ligand were synthesized, and their catalytic behaviors for the ring-opening polymerization of 1,4-dioxan-2-one (p-dioxanone, PDO) were explored. Metathesis reactions of amine-bridged bis(phenolate) yttrium chlorides LLnCl(THF) [L = Me2NCH2CH2N{CH2-(2-OC6H2-tBu2-3,5)}2] with corresponding lithium guanidinates generated in situ in a 1:1 molar ratio in THF gave the neutral yttrium guanidinates LY[R2NC(NR1)2] [R1 = −Cy, R2N = −N(TMS)2 (1), −NiPr2 (2), −N(CH2)5 (3); R1 = −iPr, R2N = −NiPr2 (4) −NPh2 (5))]. These complexes were well characterized by elemental analyses, IR, and NMR spectroscopy. The definitive molecular structures of these complexes were determined by single-crystal X-ray analysis. It was found that these complexes can efficiently initiate the ring-opening polymerization (ROP) of PDO, and the catalytic activity is affected by the nature of the guanidinate groups with the active sequence of 1 > 2 ≈ 3 ≈ 4 > 5. The influences of reaction conditions such as polymerization time, polymerization temperature, and molar ratio of monomer to initiator on the polymerization were also investigated. The polymerization kinetics of PDO catalyzed by complex 1 is first-order with respect to monomer concentration, and the apparent activation energy amounts to 30.8 kJ mol–1. The mechanistic investigations showed that the ROP of PDO proceeded through a coordination–insertion mechanism with a rupture of the acyl–oxygen bond of the monomer. MALDI-TOF mass spectrum analysis of the oligomer revealed that there are two kinds of polymer chains in this catalytic system, e.g., the linear chains H–[OCH2CH2OCH2CO]n–OH and the PPDO macrocycles.

The formation of mixed-valent ytterbium and europium complexes L4LnIII2LnII (Ln = Yb (1), Eu (2)) was observed for the first time in the spontaneous reduction reaction system of quinolinyl aminophenol (H2L) with Ln[N(SiMe3)2]3 (Ln = Yb, Eu) in toluene at 90 °C, whereas the same reaction with Sm[N(SiMe3)2]3 gave the expected monoamido samarium complex LSmN(SiMe3)2(DME) (4). The isolation of the binuclear ytterbium complex L3Yb2 (3) under mild conditions demonstrates that the transformation from a trivalent ytterbium complex to the mixed-valent ytterbium species 1 may involve a ligand redistribution reaction and homolysis of the Yb–N bond.

Electronic properties of the aminophenolate groups have obvious effect on the synthesis of aminophenolate lanthanide–lithium complexes. Amine elimination reactions of Ln[N(SiMe3)2]3(μ-Cl)Li(THF)3 with lithium aminophenolates [ArNHCH2(3,5-tBu2C6H2-2-O)Li(THF)]2 (Ar = p-ClC6H4, [ONH]Cl-p; p-BrC6H4, [ONH]Br-p) in tetrahydrofuran (THF) in a 1:2 molar ratio gave the bimetallic lanthanide–lithium amido complexes [NO]Cl-p2Ln[N(SiMe3)2][Li(THF)]2 (Ln = Y (1), Yb (2)), and [NO]Br-p2Ln[N(SiMe3)2][Li(THF)]2 (Ln = Y (3), Yb (4)). When the Ar groups are p-MeOC6H4, ([ONH]MeO-p) and o-MeOC6H4 ([ONH]MeO-o), similar reactions generated the homoleptic lanthanide–lithium complexes [NO]MeO-p3Ln[Li(THF)]3 (Ln = Y (5), Yb (6)) and [NO]MeO-o2Ln[Li(THF)] (Ln = Y (7), Yb (8)) in high isolated yields, respectively. Whereas the bimetallic lanthanide–lithium amido complexes [NO]Cl-o2Ln[N(SiMe3)2][Li(THF)]2 (Ln = Y (9), Yb (10)) can be obtained in good yields, when the Ar group is o-ClC6H4 ([ONH]Cl-o). All of these complexes were well characterized. X-ray structure determination revealed that these complexes have solvated monomeric structures. In complexes 1–4, 9, and 10, the lanthanide atom is five-coordinated by two oxygen atoms and two nitrogen atoms from two aminophenoxy ligands and one nitrogen atom from N(SiMe3)2 group to form a distorted trigonal bipyramidal geometry, whereas in complexes 5–8, the central lanthanide atom is six-coordinated by oxygen atoms, and nitrogen atoms from the aminophenoxy ligands to form a distorted octahedron. It was found that complexes 1–10 are highly efficient initiators for the ring-opening polymerization of 2,2-dimethyltrimethylene carbonate (DTC), affording the polymers with high molecular weights, and the homoleptic heterobimetallic lanthanide complexes showed apparently high activity.

Two dinuclear aluminum alkyl complexes supported by a piperazidine-bridged bis(phenolato) group were prepared, and both complexes exhibited extremely high activity for the ring-opening polymerization of ε-caprolactone. In the presence of benzyl alcohol (BnOH), the polymerization accelerated dramatically.

Polymerization of acrylonitrile was carried out using, for the first time, the lanthanide-sodium alkoxide clusters Ln2(OCH2CH2NMe2)12(OH)2Na8 [Ln=Yb (1), Nd (2) and Sm (3)] as single component catalysts. These heterobimetallic complexes exhibit high activity and give atactic polyacrylonitriles with high molecular weight. The polymerization temperature can be varied over the range −78 to 50°C. The solvent has a substantial effect on the polymerization activity. The order of activity for solvents is DMF>DME≈toluene≈THF>hexane.

Isotactic polypropylene(PP)/glass fiber(GF) composites were modified by grafting polymerization of polyfunctional monomer, pentaerythritol triacrylate (PETA), in the presence of 2,5-dimethyl-2,5-di(tert-butylperoxy) hexane peroxide (DDHP) via melt extrusion. Fourier transform infrared spectroscopy (FTIR), melt strength test (MS), mechanical property test, differential scanning calorimetry (DSC) and X-ray diffraction (XRD) were used to characterize the microstructure and properties of the modified composites. The crystallization kinetics was investigated by Mo method while apparent activation energy of crystallization of the composites was determined by Kissinger method. The FTIR results showed that the acrylic polymers were grafted onto the polypropylene chains. The grafting made the melt strengths and the mechanical properties of the modified composites, and the interfacial adhesion between PP and glass fiber all enhanced. High melting and crystallization temperatures, high crystallization rate and large activation energy of crystallization were also obtained after grafting. In addition, the grafted acrylic polymers recovered the depressed crystallization of polypropylene and restrained α-β transition in fatigue experiment.

A family of neutral and solvent-free bis(amidinate) rare earth metal amide complexes with a general formula [RC(N-2,6-Me2C6H3)2]2LnN(SiMe3)2 (R = phenyl (Ph), Ln = Y (1), Nd (2); R = cyclohexyl (Cy), Ln = Y (3), Nd (4)) were synthesized in high yields by one-pot salt metathesis reaction of anhydrous LnCl3, amidinate lithium salt [RC(N-2,6-Me2C6H3)2]Li, and NaN(SiMe3)2 in THF at room temperature. Single crystal structural determination of complexes 1, 2 and 4 revealed that the central metal adopts distorted pyramidal geometry. In the presence of 1 equivalent of iPr-OH, all these complexes were active for l-lactide polymerization in toluene at 70 °C to give high molecular weight (Mn > 104) polymers.Novel bis(amidinate) rare earth metal amide complexes [RC(N-2,6-Me2C6H3)2]2LnN(SiMe3)2 (R = phenyl, Ln = Y (1), Nd (2); R = cyclohexyl, Ln = Y (3), Nd (4)) were synthesized by one-pot salt metathesis reaction of LnCl3, [RC(N-2,6-Me2C6H3)2]Li, and NaN(SiMe3)2. In the presence of 1 equivalent of iPr-OH, these complexes were active for l-lactide polymerization in toluene at 70 °C.

Two dinuclear aluminum alkyl complexes supported by a piperazidine-bridged bis(phenolato) group were prepared, and both complexes exhibited extremely high activity for the ring-opening polymerization of ε-caprolactone. In the presence of benzyl alcohol (BnOH), the polymerization accelerated dramatically.

Different aluminum complexes were synthesized by the reaction of aluminum alkyls with a hexadentate salen-type Schiff base. The reaction of N,N′-bis(3,5-di-tert-butylsalicylidene)-2,2′-(ethylenedioxy)dianiline (LH2) with one equiv. of AlMe3 in toluene at 100 °C proceeded by methane elimination to produce the intermediate methyl complex [AlMeL] (1), and then subsequent intramolecular methyl migration to give the aluminum complex [AlL′] (2) [L′ = (2-O-3,5-tBu2C6H2)CHNC6H4OCH2CH2OC6H4NCH(Me)(2′-O-3′,5′-tBu2C6H2)]. The reaction of the same ligand with AlEt3 under the same experimental conditions involved ethane elimination, ethylene elimination and intramolecular hydrogen migration, and led to the complex [AlL′′] (3) [L′′ = (2-O-3,5-tBu2C6H2)CHNC6H4OCH2CH2OC6H4NCH2(2′-O-3′,5′-tBu2C6H2)]. However, the interaction of two equivalents of AlMe3 and AlEt3 afforded the corresponding binuclear complexes [(AlMe2)2L] (4) and [(AlEt2)2L] (5), respectively, and no methyl or hydrogen migration was found. The solid-state structures of aluminum complexes 1–3 were determined by single-crystal X-ray diffraction. It was found that complexes 2–5 show a very effective catalytic activity for the cycloaddition of epoxides and CO2 in the presence of NBu4Br as a cocatalyst at atmospheric pressure.

A series of neutral rare-earth metal aryloxides and amides supported by a new pentadentate (N2O3) salen ligand were synthesized, and their catalytic behaviors for the ring-opening polymerization of rac-lactide (rac-LA) were explored. The protolysis reactions of N,N′-bis(3,5-di-tert-butylsalicylidene)-2,2′-diaminodiphenyl ether (LH2) with (ArO)3Ln(THF) (ArO = 2,6-But2-4-MeC6H2O) and Ln[N(SiMe3)2]3 in a 1:1 molar ratio in THF gave the neutral rare-earth metal aryloxides LLn(OAr)(THF)n [n = 0, Ln = Sc (1), Yb (2); n = 1, Ln = Y (3), Sm (4) and Nd (5)] and rare-earth metal amides LLnN(SiMe3)2 [Ln = Yb (6), Y (7)], respectively. X-ray structural determination showed that complexes 1, 2, 6 and 7 have monomeric structures, in which the coordination geometry around the rare-earth metal atom can be best described as a distorted trigonal prism. Complexes 3 and 5 are THF-solvated monomers and each of the rare-earth metal atoms is seven-coordinated to form a distorted capped trigonal prism. It was found that all of these complexes can efficiently initiate the ring-opening polymerization (ROP) of rac-LA to give heterotactic-rich polylactides (PLAs). The highly heterotactic PLA (Pr up to 0.93) was obtained using complex 2 as the initiator at a polymerization temperature of 0 °C. The observed increasing order of activity of 1 < 2 < 3 < 4 ≈ 5 is in agreement with the order of their ionic radii, whereas the order of stereoselectivity is in the reverse order. The rare-earth metal salen amides can initiate rac-LA polymerization in a controlled manner, while polymerization using the rare-earth metal salen aryloxides is less controlled at room temperature.

Electronic properties of the aminophenolate groups have obvious effect on the synthesis of aminophenolate lanthanide–lithium complexes. Amine elimination reactions of Ln[N(SiMe3)2]3(μ-Cl)Li(THF)3 with lithium aminophenolates [ArNHCH2(3,5-tBu2C6H2-2-O)Li(THF)]2 (Ar = p-ClC6H4, [ONH]Cl-p; p-BrC6H4, [ONH]Br-p) in tetrahydrofuran (THF) in a 1:2 molar ratio gave the bimetallic lanthanide–lithium amido complexes [NO]Cl-p2Ln[N(SiMe3)2][Li(THF)]2 (Ln = Y (1), Yb (2)), and [NO]Br-p2Ln[N(SiMe3)2][Li(THF)]2 (Ln = Y (3), Yb (4)). When the Ar groups are p-MeOC6H4, ([ONH]MeO-p) and o-MeOC6H4 ([ONH]MeO-o), similar reactions generated the homoleptic lanthanide–lithium complexes [NO]MeO-p3Ln[Li(THF)]3 (Ln = Y (5), Yb (6)) and [NO]MeO-o2Ln[Li(THF)] (Ln = Y (7), Yb (8)) in high isolated yields, respectively. Whereas the bimetallic lanthanide–lithium amido complexes [NO]Cl-o2Ln[N(SiMe3)2][Li(THF)]2 (Ln = Y (9), Yb (10)) can be obtained in good yields, when the Ar group is o-ClC6H4 ([ONH]Cl-o). All of these complexes were well characterized. X-ray structure determination revealed that these complexes have solvated monomeric structures. In complexes 1–4, 9, and 10, the lanthanide atom is five-coordinated by two oxygen atoms and two nitrogen atoms from two aminophenoxy ligands and one nitrogen atom from N(SiMe3)2 group to form a distorted trigonal bipyramidal geometry, whereas in complexes 5–8, the central lanthanide atom is six-coordinated by oxygen atoms, and nitrogen atoms from the aminophenoxy ligands to form a distorted octahedron. It was found that complexes 1–10 are highly efficient initiators for the ring-opening polymerization of 2,2-dimethyltrimethylene carbonate (DTC), affording the polymers with high molecular weights, and the homoleptic heterobimetallic lanthanide complexes showed apparently high activity.