A divalent ytterbium amidate 1 ([Yb3L6]·2C7H8 for short) was synthesized via amine-elimination of Yb[N(SiMe3)2]2(TMEDA) with an amide proligand N-2,6-diisopropylphenylbenzamide HL (L = 2,6-iPr2C6H3NC(O)Ph) and structurally characterized to be a trinuclear symmetric cluster. Further studies on the reduction of iPrNCNiPr by complex 1 provide Yb(III) complex 2 in hexane–THF ([(YbL2)2(μ-NiPrCNiPr)][YbL3(THF)]·C7H8), which is composed of two subunits in a unit cell, one is a bridged Yb(III) carbene, just the same as complex 4 ([(YbL2)2(μ-NiPrCNiPr)]·3C7H8) obtained in the same reaction in toluene, and the other is a homoleptic monomeric Yb(III) amidate (YbL3). It is also found that complex 2 decomposed to complex 3 ([YbL3]2·2C7H8) and 4 at 90 °C in toluene. Complexes 1–4 were confirmed by X-ray structure determination. Furthermore, complex 4 was proved to be a more active species than its precursor 1 in the catalytic addition of amines to carbodiimides. Finally, complex 1 was found to be an excellent pre-catalyst for the guanylation reaction with a wide scope of substrates.

An asymmetric hydrophosphonylation reaction of diethyl phosphite with α,β-unsaturated amides catalyzed by [(Me3Si)2N]3RE(μ-Cl)Li(THF)3 (RE = Sc (1), Y (2), La (3), Yb (4) and Lu (5)) with H2Ln ((S)-2,4-R2-6-[[2-(hydroxydiphenylmethyl)pyrrolidin-1-yl]methyl]phenol) (R = tBu (H2L1); R = 1-cumyl (H2L2) and R = 1-adm (H2L3)) was disclosed. The effects of different central metals and proligands on the addition reaction were tested and it was found that the combination of Sc complex 1 and ligand H2L2 gave the best results. An excellent chemical yield (up to 99%) and good to high enantioselectivities (varied from 73 to 89%) were achieved with a relatively broad scope of the unsaturated amides. The active species in the current system was also discussed.

Based on three bisamide proligands H2Ln (n = 1–3) (H2L1 = [(Me3C6H2CONHCH2)2CH2], H2L2 = [(Me3C6H2CONHCH2)2C(CH3)2], H2L3 = [Me3C6H2CONH(CH2)2]2NCH3), eight bis(amidato) trivalent rare-earth metal amides {LnRE[N(TMS)2]}2 (n = 1, RE = La (1), Sm (2), Nd (3), Y (4); n = 2, RE = La (5), Nd (6); n = 3, RE = La (7), Nd (8); TMS = SiMe3) were successfully synthesized by treatment of H2Ln with RE[N(TMS)2]3 in a 1:1 molar ratio. Complexes 3, and 5–8 were characterized by single-crystal X-ray diffraction, and NMR characterization was carried out for the La complexes 1, 5, 7 and the Y complex 4. These complexes exhibited high catalytic activities in both the direct amidation of aldehydes and the addition of amines with carbodiimine. It was found that the bis(amidato) rare earth metal amides bearing different linkers have different effects on the transformations and lanthanum and neodymium complexes performed better than others.

A simple, efficient catalytic asymmetric Michael addition of malonates to unsaturated ketones has been successfully developed. This process was promoted by rare earth metal complexes 1–4 bearing a chiral phenoxy functionalized prolinol ligand at room temperature [L1RE(L1H) (H2L1 = (S)-2,4-di-tert-butyl-6-((2-(hydroxydiphenylmethyl)pyrrolidin-1-yl)methyl)phenol, RE = Yb 1, Y 2, Sc 3 and L2Sc(L2H) 4 (H2L2 = (S)-2,4-di-dimethylbenzyl-6-((2-(hydroxydiphenylmethyl)-pyrrolidin-1-yl)methyl)phenol)]. Complex 3 was the best catalyst in the transformation and the products were obtained in up to 99% yield and with 90% ee. In addition, the molecular structures of the catalysts were well characterized, including X-ray determination of complex 3.A simple, efficient catalytic asymmetric Michael addition of malonates to unsaturated ketones has been successfully developed. This process was promoted by rare earth metal complexes 1–4, which is bearing chiral phenoxy functionalized prolinol ligand at room temperature. The Sc complex 3 performed the best and the products reached up to 99% yield and 90% ee.Diisopropyl 2-(3-oxo-1,3-diphenylpropyl)malonateC24H28O5[α]D20 = +18.9 (c 0.925, CHCl3)Source of chirality: synthesisAbsolute configuration: (2S)Diisopropyl 2-(3-(4-methoxyphenyl)-3-oxo-1-phenylpropyl)malonateC25H30O6[α]D20 = +17.8 (c 0.449, CHCl3)Source of chirality: synthesisAbsolute configuration: (2S)Diisopropyl 2-(1-phenyl-3-oxo-3-(4-chlorophenyl)propyl)malonateC24H27ClO5[α]D20 = +14.5 (c 0.932, CHCl3)Source of chirality: synthesisAbsolute configuration: (2S)Diisopropyl 2-(1-phenyl-3-oxo-3-(4-bromophenyl)propyl)malonateC24H27BrO5[α]D20 = +10.4 (c 0.869, CHCl3)Source of chirality: the synthesisAbsolute configuration: (2S)Diisopropyl 2-(1-phenyl-3-oxo-3-(4-trifluoromethylphenyl)propyl)malonateC25H27F3O5[α]D20 = +8.8 (c 0.963, CHCl3)Source of chirality: synthesisAbsolute configuration: (2S)Diisopropyl 2-(1-(4-methoxyphenyl)-3-oxo-3-phenylpropyl)malonateC25H30O6[α]D20 = +23.8 (c 0.126, CHCl3)Source of chirality: synthesisAbsolute configuration: (2S)Diisopropyl 2-(1-naphthyl-3-oxo-3-phenylpropyl)malonateC28H30O5[α]D20 = +23.6 (c 0.742, CHCl3)Source of chirality: synthesisAbsolute configuration: (2S)Diisopropyl 2-(1-(4-fluorophenyl)-3-oxo-3-phenylpropyl)malonateC24H27FO5[α]D20 = +22.0 (c 0.726, CHCl3)Source of chirality: synthesisAbsolute configuration: (2S)Diisopropyl 2-(1-(4-chlorophenyl)-3-oxo-3-phenylpropyl)malonateC24H27ClO5[α]D20 = +17.1 (c 0.703, CHCl3)Source of chirality: synthesisAbsolute configuration: (2S)Diisopropyl 2-(1-(4-nitrophenyl)-3-oxo-3-phenylpropyl)malonateC24H27NO7[α]D20 = +23.6 (c 0.826, CHCl3)Source of chirality: synthesisAbsolute configuration: (2S)Diisopropyl 2-(1-(2-chlorophenyl)-3-oxo-3-phenylpropyl)malonateC24H27ClO5[α]D20 = +29.1 (c 0.808, CHCl3)Source of chirality: synthesisAbsolute configuration: (2S)Diisopropyl 2-(1-(2-methoxyphenyl)-3-oxo-3-phenylpropyl)malonateC25H30O6[α]D20 = +18.3 (c 0.601, CHCl3)Source of chirality: synthesisAbsolute configuration: (2S)Diisopropyl 2-(3-(furan-2-yl)-3-oxo-1-phenylpropyl)malonateC22H26O6[α]D20 = +27.4 (c 0.821, CHCl3)Source of chirality: synthesisAbsolute configuration: (2S)Diisopropyl 2-(3-(thiophen-2-yl)-3-oxo-1-phenylpropyl)malonateC22H26O5S[α]D20 = +14.4 (c 0.766, CHCl3)Source of chirality: synthesisAbsolute configuration: (2S)2-(5-Isopropoxy-4-(isopropoxycarbonyl)-5-oxo-3-phenylpentanoyl)pyridine 1-oxideC23H27NO6[α]D20 = +13.2 (c 0.088, CHCl3)Source of chirality: synthesisAbsolute configuration: (3S)Diisopropyl 2-(2-benzoyl-3-oxo-1,3-diphenylpropyl)malonateC31H32O6[α]D20 = +11.2 (c 0.102, CHCl3)Source of chirality: synthesisAbsolute configuration: (2S)

Three novel bis(amidate) rare-earth metal amides {LRE[N(SiMe3)2]·THF}2 (H2L = N,N′-(cyclohexane-1,2-diyl)bis(4-tert-butylbenzamide); RE = La(1), Nd(2), Y(3)), which were prepared by the treatment of the bridged amide proligand H2L with RE[N(SiMe3)2]3 in tetrahydrofuran, have been characterized by single-crystal X-ray diffraction, elemental analyses, and NMR for complexes 1 and 3. All the complexes were found, for the first time, to be efficient catalysts for the direct carboxylation of terminal alkynes with CO2 at ambient pressure. And the Nd-based catalyst 2 showed the highest reactivity. Various propiolic acids with a good functional group tolerance were successfully synthesized in high-to-excellent yields under mild conditions.

A simple and efficient catalytic enantioselective epoxidation of α,β-unsaturated ketones has been successfully developed, which was catalyzed by rare-earth metal amides [(Me3Si)2N]3RE(μ-Cl)Li(THF)3 (RE = Yb (1), La (2), Sm (3), Y (4), Lu (5)) in the presence of phenoxy-functionalized chiral prolinols at room temperature using tert-butylhydroperoxide (TBHP) as the oxidant. The combination of an Yb-based amide 1 and a chiral proligand (S)-2,4-di-tert-butyl-6-((2-(hydroxydiphenylmethyl)pyrrolidin-1-yl)methyl)phenol) performed very well, and both the yields and the enantiomeric excess of the chiral epoxides reached up to 99% and 99% ee.

Two new bis(amidate) lanthanide amides {LLn[N(SiMe3)2]·THF}2 (H2L = N,N′-(cyclohexane-1,2-diyl)-bis(4-tert-butylbenzamide); Ln = Sm(4), Yb(5)), which were prepared by the treatment of the bridged amide proligand H2L with Ln[N(SiMe3)2]3 in tetrahydrofuran, had been characterized by single-crystal X-ray diffraction and elemental analyses. Both complexes 4 and 5 and the three known isomorphs {LRE[N(SiMe3)2]·THF}2 (RE = La(1), Nd(2), Y(3)) were successfully employed in the addition of amines to carbodiimides for the first time and were found to be efficient catalysts in the transformation at 60 °C under solvent-free conditions. The Nd-based catalyst 2 showed the highest reactivity and provided various guanidines with good functional group tolerance in high to excellent yields.

Eight rare-earth metal guanidinates supported by a versatile family of chelating amine-bridged bis(phenolate) ligands were synthesized. Metathesis reactions of rare-earth metal chlorides [LnClL1(THF)] stabilized by amine-bridged bis(phenolate) ligand L1 with in situ generated lithium guanidinates in a 1:1 molar ratio in THF afforded ytterbium guanidinates YbL1 [R2NC(NR1)2] [R1 = –iPr, R2N = –NiPr2 (1), –N(CH2)5 (2)]. Insertion reactions of the yttrium amides bearing bridged bis(phenolate) ligands with 1 equiv of N,N′-diisopropylcarbodiimide (DIC) yielded six yttrium guanidinates YL1 [(SiHMe2)2NC(NiPr)2] (3), YL2[(SiHMe2)2NC(NiPr)2](THF) (4), YL3[(SiHMe2)2NC(NiPr)2] (5), YL4[(SiHMe2)2NC(NiPr)2] (6), YL5 [(SiHMe2)2NC(NiPr)2] (7), YL6[(SiHMe2)2NC(NiPr)2] (8), respectively. The behaviors of complexes 1–8 in the polymerization of rac-lactide (LA) and rac-β-butyrolactone (BBL) were also explored. It was found that complexes 1–8 efficiently initiated the ring-opening polymerization (ROP) of rac-LA and rac-BBL in a controlled manner, providing highly heterotactic polylactide (Pr up to 0.99) and highly syndiotactic poly(3-hydroxybutyrate) (Pr up to 0.82). The framework of the bridge played a significant role in governing the stereoselectivity, while guanidinate groups work as initiating groups.

Four novel heterobimetallic complexes [REL2]{[(THF)3Li]2(μ-Cl)} stabilized by chiral phenoxy-functionalized prolinolate (RE = Yb (1), Y (2), Sm (3), Nd (4), H2L = (S)-2,4-di-tert-butyl-6-[[2-(hydroxydiphenylmethyl)pyrrolidin-1-yl]methyl]phenol have been synthesized and characterized. These readily available complexes are highly active in catalyzing the epoxidation of α,β-unsaturated ketones, while the enantioselectivity varies according to the ionic radii of the rare earth center. A series of chalcone derivatives were converted to chiral epoxides in 80 → 99% ee at 0 °C using TBHP as the oxidant in the presence of 10 mol % of 1.

Two novel amidate rare-earth metal amides Ln[N(SiMe3)2](κ2-L1)2(THF) (L1 = C6H5C(O)NC6H3(iPr)2) (Ln = Yb (1), Y (2)) were prepared through simple silylamine elimination reactions of the benzamide proligand HL1 with Ln[N(SiMe3)2]3 in tetrahydrofuran at 60 °C. These complexes were well characterized by elemental and single-crystal X-ray diffraction analyses, and the yttrium complex 2 was also characterized by NMR spectroscopic analyses. Investigation on the catalytic behaviors of amidate rare-earth metal amides, including two new complexes 1, 2 and three known amidate divalent rare-earth metal amides {Ln[N(SiMe3)2](μ-O:κ2-L1)(THF)}2 (Ln = Yb (3), Eu (4)), and Eu2[N(SiMe3)2]2(μ-O:κ2-L2)2(THF)3 (L2 = C6H5C(O)NC6H3(Me)2) (5), revealed that all complexes exhibited high catalytic activities toward the hydrophosphonylation of aldehydes and some of them showed moderate to good activities toward unactivated ketones. Complex 1 showed the highest activity, which afforded a series of α-hydroxy phosphonates in good to excellent yields at room temperature after short time with low catalyst loadings.Two novel amidate rare-earth metal amides Ln[N(SiMe3)2](κ2-L1)2(THF) (L1 = C6H5C(O)NC6H3(iPr)2); (Ln = Yb (1), Y (2)) were prepared and well characterized. Investigation on the catalytic behaviors of complexes 1, 2 and three known amidate divalent rare-earth metal amides {Ln[N(SiMe3)2](μ-O:κ2-L1)(THF)}2 (Ln = Yb (3), Eu (4)), and Eu2[N(SiMe3)2]2(μ-O:κ2-L2)2(THF)3 (L2 = C6H5C(O)NC6H3(Me)2) (5), revealed that all complexes exhibited high catalytic activities toward the hydrophosphonylation of aldehydes and some of them showed moderate to good activities toward unactivated ketones, while complex 1 showed the highest activity.

A divalent ytterbium amidate 1 ([Yb3L6]·2C7H8 for short) was synthesized via amine-elimination of Yb[N(SiMe3)2]2(TMEDA) with an amide proligand N-2,6-diisopropylphenylbenzamide HL (L = 2,6-iPr2C6H3NC(O)Ph) and structurally characterized to be a trinuclear symmetric cluster. Further studies on the reduction of iPrNCNiPr by complex 1 provide Yb(III) complex 2 in hexane–THF ([(YbL2)2(μ-NiPrCNiPr)][YbL3(THF)]·C7H8), which is composed of two subunits in a unit cell, one is a bridged Yb(III) carbene, just the same as complex 4 ([(YbL2)2(μ-NiPrCNiPr)]·3C7H8) obtained in the same reaction in toluene, and the other is a homoleptic monomeric Yb(III) amidate (YbL3). It is also found that complex 2 decomposed to complex 3 ([YbL3]2·2C7H8) and 4 at 90 °C in toluene. Complexes 1–4 were confirmed by X-ray structure determination. Furthermore, complex 4 was proved to be a more active species than its precursor 1 in the catalytic addition of amines to carbodiimides. Finally, complex 1 was found to be an excellent pre-catalyst for the guanylation reaction with a wide scope of substrates.

Based on three bisamide proligands H2Ln (n = 1–3) (H2L1 = [(Me3C6H2CONHCH2)2CH2], H2L2 = [(Me3C6H2CONHCH2)2C(CH3)2], H2L3 = [Me3C6H2CONH(CH2)2]2NCH3), eight bis(amidato) trivalent rare-earth metal amides {LnRE[N(TMS)2]}2 (n = 1, RE = La (1), Sm (2), Nd (3), Y (4); n = 2, RE = La (5), Nd (6); n = 3, RE = La (7), Nd (8); TMS = SiMe3) were successfully synthesized by treatment of H2Ln with RE[N(TMS)2]3 in a 1:1 molar ratio. Complexes 3, and 5–8 were characterized by single-crystal X-ray diffraction, and NMR characterization was carried out for the La complexes 1, 5, 7 and the Y complex 4. These complexes exhibited high catalytic activities in both the direct amidation of aldehydes and the addition of amines with carbodiimine. It was found that the bis(amidato) rare earth metal amides bearing different linkers have different effects on the transformations and lanthanum and neodymium complexes performed better than others.