Synthesis of Dianionic β-Diketiminate Lanthanide Amides L′LnN(SiMe₃)₂(THF) by Deprotonation of the β-Diketiminate Ligand L (L = {[(2,6-<i>i</i>Pr₂C₆H₃)NC(CH₃)]₂CH}⁻) and the Transformation with [HNEt₃][BPh₄] to the Cationic Samarium Amide [LSmN(SiMe₃)₂][BPh₄]

Reaction of β-diketiminate lanthanide dichlorides LLnCl₂(THF)₂ (L = {[(2,6-<i>i</i>Pr₂C₆H₃)­NC­(CH₃)]₂CH}⁻) with 2 equiv of NaN­(SiMe₃)₂ in toluene afforded lanthanide amide complexes supported by a dianionic β-diketiminate ligand L′, L′LnN­(SiMe₃)₂(THF) (L′ <b>=</b>{(2,6-<i>i</i>Pr₂C₆H₃)­NC­(CH₂)­CHC­(CH₃)­N­(2,6-<i>i</i>Pr₂C₆H₃)}^2–, Ln = Yb (<b>1</b>), Y (<b>2</b>), Gd (<b>3</b>), Sm (<b>4</b>)), in moderate yields via deprotonation of L. Addition of a small amount of THF led to an increase of the yields of <b>1</b>–<b>4</b>. Lanthanide metals have a great influence on the deprotonation of L. The same reaction with LNdCl₂(THF)₂ did not afford the analogous complex L′NdN­(SiMe₃)₂(THF), but the normal diamide complex LNd­[N­(SiMe₃)₂]₂ (<b>5</b>) was isolated instead. The metathesis reaction of the triply bridged dichlorides of Sm, LSmCl­(μ-Cl)₃SmL­(THF), with 2 equiv of NaN­(SiMe₃)₂ yielded the diamide complexes LSm­[N­(SiMe₃)₂]₂ in toluene, while complex <b>4</b> was formed instead in a mixture of toluene and THF. In contrast, the same reactions with LYbCl­(μ-Cl)₃YbL­(THF) either in toluene or in a mixture of toluene and THF both afforded <b>1</b>. Treatment of <b>4</b> with [HNEt₃]­[BPh₄] in THF at room temperature gave the novel cationic Sm β-diketiminate amide complex [LSmN­(SiMe₃)₂(THF)₂]­[BPh₄] (<b>7</b>) in good yield. Complexes <b>1</b>–<b>5</b> and <b>7</b> have been confirmed by single-crystal X-ray structural analyses. The mechanism of deprotonation of L was discussed

Highly Enantioselective Epoxidation of α,β-Unsaturated Ketones Catalyzed by Rare-Earth Amides [(Me₃Si)₂N]₃RE(μ-Cl)Li(THF)₃ with Phenoxy-Functionalized Chiral Prolinols

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 (<b>1</b>), La (<b>2</b>), Sm (<b>3</b>), Y (<b>4</b>), Lu (<b>5</b>)) in the presence of phenoxy-functionalized chiral prolinols at room temperature using <i>tert</i>-butylhydroperoxide (TBHP) as the oxidant. The combination of an Yb-based amide <b>1</b> and a chiral proligand (<i>S</i>)-2,4-di-<i>tert</i>-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

RE[N(SiMe₃)₂]₃‑Catalyzed Guanylation/Cyclization of Amino Acid Esters and Carbodiimides

The example of rare-earth metal-catalyzed guanylation/cyclization of amino acid esters and carbodiimides is well-established, forming 4­(3<i>H</i>)-2-alkylaminoquinazolinones in 65–96% yields. The rare-earth metal amides RE­[N­(TMS)₂]₃ (RE = Y, Yb, Nd, Sm, La; TMS = SiMe₃) showed high activities, and La­[N­(TMS)₂]₃ performed best for a wide scope of the substrates

Dinuclear Aluminum Poly(phenolate) Complexes as Efficient Catalysts for Cyclic Carbonate Synthesis

A series of dinuclear aluminum complexes <b>1</b>–<b>4</b> stabilized by amine-bridged poly­(phenolato) ligands have been synthesized, which are highly active in catalyzing the cycloaddition of epoxides and CO₂. In the presence of 0.3 mol % complex <b>3</b> and 0.9 mol % NBu₄Br at 1 bar CO₂ pressure, terminal epoxides bearing different functional groups were converted to cyclic carbonates in 60–97% yields. Complex <b>3</b> is one of the rare examples of Al-based catalysts capable of promoting the cycloaddition at 1 bar pressure of CO₂. Moreover, reactions of more challenging disubstituted epoxides also proceeded at an elevated pressure of 10 bar and afforded cyclic carbonates in 52–90% yields

Control of Conformations of Piperazidine-Bridged Bis(phenolato) Groups: Syntheses and Structures of Bimetallic and Monometallic Lanthanide Amides and Their Application in the Polymerization of Lactides

A series of bimetallic and monometallic lanthanide amides stabilized by a piperazidine-bridged bis­(phenolato) ligand were successfully prepared, and the factors controlling the formation of these lanthanide amides were elucidated. Reactions of Ln­[N­(TMS)₂]₃(μ-Cl)­Li­(THF)₃ (TMS = SiMe₃; THF = tetrahydrofuran) with a piperazidine-bridged bis­(phenol), H₂[ONNO]­[4-bis­(2-hydroxy-3,5-di-<i>tert</i>-butylbenzyl)­piperazidine], in a 2:1 molar ratio in THF at 60 °C gave the anionic bimetallic bis­(phenolato) lanthanide amido complexes [ONNO]­{Ln­[N­(TMS)₂]₂­(μ-Cl)­Li­(THF)}₂ [Ln = Y (<b>1</b>), Er (<b>2</b>), Eu (<b>3</b>), Sm (<b>4</b>)], whereas the same reactions conducted at room temperature gave the monometallic bis­(phenolato) lanthanide amides [ONNO]­LnN­(TMS)₂(THF) [Ln = Y (<b>5</b>), Sm (<b>6</b>)]. Complex <b>1</b> can be transformed to a neutral bimetallic bis­(phenolato) yttrium amido complex, [ONNO]­{Y­[N­(TMS)₂]₂}₂ (<b>7</b>), by heating a toluene solution to 80 °C. Complex <b>7</b> can also be conveniently prepared by the reaction of the yttrium amide Y­[N­(TMS)₂]₃ with H₂[ONNO] in a 2:1 molar ratio at 60 °C. For neodymium and praseodymium, only the monometallic lanthanide amido complexes [ONNO]­LnN­(TMS)₂(THF) [Ln = Nd (<b>8</b>), Pr (<b>9</b>)] were isolated, even when the reactions were conducted at 60 °C. Furthermore, reaction of H₂[ONNO] with the less bulky lanthanide amides Ln­[N­(SiMe₂H)₂]₃(THF)₂ in a 2:1 molar ratio at 60 °C gave the monometallic lanthanide amido complexes [ONNO]­Ln­[N­(SiMe₂H)₂]­(THF) [Ln = Yb (<b>10</b>), Y­(<b>11</b>), Nd (<b>12</b>)] as neat products; no bimetallic species were formed. All of these complexes were characterized by IR, elemental analyses, and single-crystal X-ray diffraction. Complexes <b>1</b>, <b>5</b>, <b>6</b>, <b>7</b>, and <b>11</b> were further confirmed by NMR spectroscopy. These complexes are highly efficient initiators for the ring-opening polymerization of l-lactide. In addition, complexes <b>1</b>, <b>3</b>, <b>5</b>, <b>7</b>, and <b>11</b> can initiate <i>rac</i>-lactide polymerization with high activity to give heterotactic-rich polylactides

Chemo- and Regioselective Hydroarylation of Alkenes with Aromatic Amines Catalyzed by [Ph₃C][B(C₆F₅)₄]

A nonmetal catalyst [Ph₃C]­[B­(C₆F₅)₄] has been developed to catalyze hydroarylation reaction of alkenes with aromatic primary, secondary, and tertiary amines, which generated aniline derivatives in 32–98% yields. This method is applicable to a wide range of substrates, is highly chemo- and regioselective, and provides a simple and efficient approach for aniline derivative preparation

Enantioselective Reduction of Ketones Catalyzed by Rare-Earth Metals Complexed with Phenoxy Modified Chiral Prolinols

Enantioselective reduction of ketones and α,β-unsaturated ketones by pinacolborane (HBpin) has been well-established by using chiral rare-earth metal catalysts with phenoxy modified prolinols. A number of highly optically active alcohols were obtained from reduction of simple ketones catalyzed by ytterbium complex <b>1</b> [L⁴Yb­(L⁴H)] (H₂L⁴ = (<i>S</i>)-2- <i>tert</i>-butyl-6-((2-(hydroxydiphenylmethyl)­pyrrolidin-1-yl)­methyl)­phenol). Moreover, α,β-unsaturated ketones were selectively reduced to a wide range of chiral allylic alcohols with excellent yields, high enantioselectivity, and complete chemoselectivity, catalyzed by a single component chiral ytterbium complex <b>2</b> [L¹Yb­(L¹H)] (H₂L¹ = (<i>S</i>)-2,4-di-<i>tert</i>-butyl-6-((2-(hydroxydiphenylmethyl)­pyrrolidin-1-yl)­methyl)­phenol)

Synthesis of Group 4 Metal Complexes Stabilized by an Amine-Bridged Bis(phenolato) Ligand and Their Catalytic Behavior in Intermolecular Hydroamination Reactions

Zirconium and titanium complexes <b>1</b> and <b>2</b>, bearing an amine-bridged bis­(phenolato) ligand, have been synthesized and characterized. Although <b>1</b> and <b>2</b> were inactive in catalyzing intermolecular hydroamination reactions, cationic complexes generated in situ from treatment of <b>1</b> and <b>2</b> with borate [Ph₃C]­[B­(C₆F₅)₄], respectively, were found to be highly active. In general, excellent yields (up to >99%) and 100% regioselectivity for a broad range of terminal alkynes and anilines were observed within a reaction time of 1 h. Reactions with internal alkynes of moderate sterics also led to good yields and moderate regioselectivity. A kinetic study was also conducted, which provided some insights into the mechanism of hydroamination reactions

Synthesis and Characterization of Salalen Lanthanide Complexes and Their Application in the Polymerization of <i>rac</i>-Lactide

A series of neutral lanthanide complexes supported by ONNO Salalen-type ligands were synthesized, and their catalytic activity for the polymerization of <i>rac</i>-lactide (<i>rac</i>-LA) was explored. The amine elimination reactions of Ln­[N­(SiMe₃)₂]₃(μ-Cl)­Li­(THF)₃ with the ONNO Salalen-type ligand L¹H₂ (L¹ = (2-O-C₆H₂-Bu^t₂-3,5)­CHNCH₂CH₂N­(Me)­CH₂(2-O-C₆H₂-Bu^t₂-3,5)) in a 1:1 molar ratio in tetrahydrofuran (THF) gave the neutral lanthanide amides L¹Ln­[N­(SiMe₃)₂]­(THF) (Ln = Y (<b>1</b>), Sm (<b>2</b>), Nd (<b>3</b>)). Reaction of the lanthanide amides with benzyl alcohol produces the dimeric lanthanide alkoxo complex (L^<b>1</b>LnOCH₂Ph)₂ (Ln = Y (<b>4</b>), Sm (<b>5</b>)) in high isolated yield. Y­[N­(SiMe₃)₂]₃(μ-Cl)­Li­(THF)₃ reacted with the Salalen-type ligand L²H₂ (L² = (2-O-C₆H₂-Bu^t₂-3,5)­CHNCH₂CH₂N­(Me)­CH₂{2-O-C₆H₂-(CPhMe₂)₂-3,5}) in a 1:l molar ratio in THF also gave the desired yttrium amide, but this complex could not be separated because of its very good solubility even in <i>n</i>-pentane. The proton exchange reactions of L¹H₂ and L²H₂ with (C₅H₅)₃Ln­(THF) in a 1:1 molar ratio in THF and then with 1 equiv of benzyl alcohol gave the desired lanthanide alkoxides [L^<b>1</b>Ln­(OCH₂Ph)]₂ (Ln = Y (<b>4</b>), Sm (<b>5</b>), Yb (<b>6</b>)) and [L^<b>2</b>Y­(OCH₂Ph)]₂ (<b>7</b>), respectively. Complexes <b>1</b>–<b>7</b> were well characterized by elemental analyses, IR spectra, X-ray single-crystal structure determination, and NMR spectroscopy in the case of complexes <b>1</b>, <b>4</b>, and <b>7</b>. Complexes <b>1</b>–<b>3</b> are isostructural and have a solvated monomeric structure. The coordination geometry around the lanthanide atom can be best described as a distorted trigonal bipyramid. Complexes <b>4</b>–<b>7</b> are dimeric species in the solid state. They all contain a Ln₂O₂ core bridging through the oxygen atoms of the two OCH₂Ph groups. Each of the lanthanide atoms is also six-coordinated to form a distorted octahedron. It was found that all the complexes are efficient initiators for the ring-opening polymerization of <i>rac</i>-LA, giving PLA with good heterotacticity (<i>P</i>_r up to 0.85). The observed order of increase in activity is in agreement with the order of the ionic radii, whereas the stereoselectivity is in reverse order. The steric bulkiness of the substituents on the phenol ring has no obvious impact on the rate and stereocontrolability of the polymerizations. The Ln–O species resulted in more controllable polymerization than the corresponding Ln–N species, and complex <b>4</b> can initiate <i>rac</i>-LA polymerization in a controlled manner

Synthesis of Group 4 Metal Complexes Stabilized by an Amine-Bridged Bis(phenolato) Ligand and Their Catalytic Behavior in Intermolecular Hydroamination Reactions

Zirconium and titanium complexes <b>1</b> and <b>2</b>, bearing an amine-bridged bis­(phenolato) ligand, have been synthesized and characterized. Although <b>1</b> and <b>2</b> were inactive in catalyzing intermolecular hydroamination reactions, cationic complexes generated in situ from treatment of <b>1</b> and <b>2</b> with borate [Ph₃C]­[B­(C₆F₅)₄], respectively, were found to be highly active. In general, excellent yields (up to >99%) and 100% regioselectivity for a broad range of terminal alkynes and anilines were observed within a reaction time of 1 h. Reactions with internal alkynes of moderate sterics also led to good yields and moderate regioselectivity. A kinetic study was also conducted, which provided some insights into the mechanism of hydroamination reactions