Facile Construction of Yttrium Pentasulfides from Yttrium Alkyl Precursors: Synthesis, Mechanism, and Reactivity

Treatment of the yttrium dialkyl complex Tp^Me2Y­(CH₂Ph)₂­(THF) (Tp^Me2 = tri­(3,5 dimethylpyrazolyl)­borate, THF = tetrahydrofuran) with S₈ in a 1:1 molar ratio in THF at room temperature afforded a yttrium pentasulfide Tp^Me2Y­(κ₄-S₅) (THF) (<b>1</b>) in 93% yield. The yttrium monoalkyl complex Tp^Me2CpYCH₂Ph­(THF) reacted with S₈ in a 1:0.5 molar ratio under the same conditions to give another yttrium pentasulfide [(Tp^Me2)₂Y]⁺­[Cp₂Y­(κ₄-S₅)]⁻ (<b>10</b>) in low yield. Further investigations indicated that the S₅^2– anion facilely turned into the corresponding thioethers or organic disulfides, and released the redundant S₈, when it reacted with some electrophilic reagents. The mechanism for the formation of the S₅^2– ligand has been investigated by the controlling of the reaction stoichiometric ratios and the stepwise reactions

Facile Construction of Yttrium Pentasulfides from Yttrium Alkyl Precursors: Synthesis, Mechanism, and Reactivity

Treatment of the yttrium dialkyl complex Tp^Me2Y­(CH₂Ph)₂­(THF) (Tp^Me2 = tri­(3,5 dimethylpyrazolyl)­borate, THF = tetrahydrofuran) with S₈ in a 1:1 molar ratio in THF at room temperature afforded a yttrium pentasulfide Tp^Me2Y­(κ₄-S₅) (THF) (<b>1</b>) in 93% yield. The yttrium monoalkyl complex Tp^Me2CpYCH₂Ph­(THF) reacted with S₈ in a 1:0.5 molar ratio under the same conditions to give another yttrium pentasulfide [(Tp^Me2)₂Y]⁺­[Cp₂Y­(κ₄-S₅)]⁻ (<b>10</b>) in low yield. Further investigations indicated that the S₅^2– anion facilely turned into the corresponding thioethers or organic disulfides, and released the redundant S₈, when it reacted with some electrophilic reagents. The mechanism for the formation of the S₅^2– ligand has been investigated by the controlling of the reaction stoichiometric ratios and the stepwise reactions

Isoprene Regioblock Copolymerization: Switching the Regioselectivity by the in Situ Ancillary Ligand Transmetalation of Active Yttrium Species

Regioblock copolymers of single alkenes hold great promise for modifying the properties of polymer materials but remain scarce due to the lack of viable synthetic methodologies. Here we describe a method for switching the regioselectivity of the cationic yttrium-catalyzed polymerization of conjugated dienes during chain growth, which leads to the formation of a series of di- and multiregioblock homo/mixed-copolymers with different properties from isoprene and myrcene. Mechanistic data demonstrate that the amidinate yttrium active species [L^bYPIP^3,4]⁺ (L^b = [PhC­(NC₆H₄^<i>i</i>Pr₂-2,6)₂]⁻) changes to the tetramethylaluminate yttrium active center {L^sYPIP^3,4}⁺ (L^s = [AlMe₄]⁻) in situ by amidinate ligand transfer in the presence of AlMe₃. The transformation of active species switches the regioselectivity from 3,4- to <i>cis</i>-1,4 polymerization while the polymer chain keeps propagating. Al^<i>i</i>Bu₃ not only functions as a chain transfer agent but also plays a key role in preventing the chain termination during the amidinate transmetalation. These results highlight the versatility and potential utility of a strategy for the design and precision control of polymer structure and physical properties

Me–Si Bond Cleavage of Anionic Bis(trimethylsilyl)amide in Scorpionate-Anchored Rare Earth Metal Complexes

A novel Tp^Me2-supported (Tp^Me2 = tri­(3,5-dimethylpyrazolyl)­borate) rare earth metal complex promoted Me–Si cleavage of the bis­(trimethylsilyl) amide ligand ([(Me₃Si)₂N]⁻) was observed. Reaction of Tp^Me2LnCl₂ with 2 equiv of K­[(RN)₂CN­(SiMe₃)₂] (KGua) gave the methylamidinate complexes Tp^Me2Ln­[(RN)₂CMe]­[N­(SiMe₃)₂] (R = isopropyl, Ln = Y (<b>1</b>^<b>Y</b>), Er (<b>1</b>^<b>Er</b>); R = cyclohexyl, Ln = Y (<b>2</b>^<b>Y</b>)) in moderate yields. In contrast, Tp^Me2YCl₂(THF) reacted with 1 equiv of KGua to afford a C–N cleavage product Tp^Me2Y­(Cl)­N­(SiMe₃)₂(THF) (<b>4</b>), indicating that this guanidinate ligand is not stable in the yttrium complex with the Tp^Me2 ligand, and a carbodiimide deinsertion takes place easily. The mechanism for the formation of complexes <b>1</b> and <b>2</b> was also studied by controlling the substrate stoichiometry and the reaction sequence and revealed that the bis­(trimethylsilyl)­amine anion N­(SiMe₃)₂^– can undergo two routes of γ-methyl deprotonation and Si–Me cleavage for its functionalizations. All these new complexes were characterized by elemental analysis and spectroscopic methods, and their solid-state structures were also confirmed by single-crystal X-ray diffraction

Reactivity of Scorpionate-Anchored Yttrium Alkyl Complex toward Organic Nitriles

The mixed Tp^Me2/Cp-supported yttrium monoalkyl (Tp^Me2)­CpYCH₂Ph­(THF) (<b>1</b>) reacted with 1 equiv of PhCN in THF at room temperature to afford the imine–enamine tautomer (Tp^Me2)­CpY­(N­(H)­C­(Ph)CHPh)­(THF) (<b>2</b>) and the insertion product (Tp^Me2)­CpY­(NC­(CH₂Ph)­Ph)­(THF) (<b>3</b>), in 61% and 12% isolated yields, respectively. <b>2</b> further reacted with PhCN in toluene at 120 °C to give the N–H bond addition product (Tp^Me2)­CpY­(N­(H)­C­(Ph)­NC­(Ph)CHPh) (<b>4</b>). Treatment of <b>1</b> with 1 equiv of anthranilonitrile produced the dimer [(Tp^Me2)­CpY­(μ-NHC₆H₄CN)]₂ (<b>5</b>). The monomer product (Tp^Me2)­CpY­(NHC₆H₄CN)­(HMPA) (<b>6</b>) can be obtained through the coordination of HMPA (hexamethylphosphoric triamide). The reaction of <b>5</b> with <b>1</b> in THF at room temperature gave the cyano group insertion product [(Tp^Me2)­CpY­(THF)]₂(μ-NHC₆H₄C­(CH₂Ph)N) (<b>7</b>). However, this reaction under the heating conditions gave an unexpected rearrangement product, (Tp^Me2)­CpY­(THF)­(η²-NHC₆H₄C­(CH₂Ph)NH) (<b>8</b>). <b>5</b> further reacted with <i>o</i>-aminobenzonitrile at 120 °C to afford the nucleophilic addition/cyclization product Tp^Me2Y­[κ³-(4-NH(C₈N₂H₄)­(2-NHC₆H₄)]­(HMPA) (<b>9</b>), accompanied with the elimination of the Cp ring. These results indicated that the yttrium alkyl complex exhibits high activity toward organic nitriles and reveals some unusual transformations during the insertion process. All these new complexes were characterized by elemental analysis and spectroscopic methods, and their solid-state structures were also confirmed by single-crystal X-ray diffraction analysis

Rare-Earth-Metal-Catalyzed Addition of Terminal Monoalkynes and Dialkynes with Aryl-Substituted Symmetrical or Unsymmetrical Carbodiimides

A high-efficiency and atom-economic route for the synthesis of N-aryl-substituted propiolamidines was established through the addition of terminal alkynes with aryl-substituted symmetrical or unsymmetrical carbodiimides catalyzed by mixed Tp^Me2/Cp rare-earth-metal alkyl complexes (Tp^Me2)­CpLnCH₂Ph­(THF) (<b>1</b>^<b>Ln</b>). Moreover, the gadolinium alkyl complex <b>1</b>^<b>Gd</b> can also serve as a catalyst for the double addition of dialkynes with carbodiimides. Mechanism studies indicated that the variable coordination modes (κ³ or κ²) of the Tp^Me2 ligand on the rare-earth-metal species may play an important role in the catalytic cycles

Versatile Reactivity of β‑Diketiminato-Supported Yttrium Dialkyl Complex toward Aromatic N‑Heterocycles

The reactions of β-diketiminatoyttrium dialkyl complex LY­(CH₂Ph)₂(THF) (<b>1</b>, L = [{N­(2,6-^<i>i</i>Pr₂C₆H₃)­C­(Me)}₂CH]⁻) with a series of aromatic N-heterocycles such as 2-phenylpyridine, benzothiazole, and benzoxazole were studied and displayed discrete reactivity including C–H activation, C–C coupling, ring-opening/insertion, and dearomatization. The reaction of <b>1</b> with 2-phenylpyridine in 1:2 molar ratio in THF at 30 °C for 14 days afforded a structurally characterized metal complex, LY­(η²-<i>N,C</i>-C₅H₄NC₆H₄-2)­[C₅H₄N­(CH₂Ph-4)­Ph] (<b>2</b>), in 73% isolated yield, indicating the occurrence of phenyl ring C­(sp²)–H activation and pyridine ring 1,4-addition/dearomatization. However, when this reaction was done at 5 °C for 7 days, it gave the pyridine ring 1,2-addition product LY­(η²-<i>N,C</i>-C₅H₄NC₆H₄-2)­[C₅H₄N­(CH₂Ph-2)­Ph] (<b>3</b>) in 54% isolated yield. Further investigations revealed that complex <b>2</b> is the thermodynamic controlled product and complex <b>3</b> is the kinetically controlled product; <b>3</b> converted slowly into <b>2</b>, as confirmed by ¹H NMR spectroscopy. The equimolar reaction of <b>1</b> with benzothiazole or benzoxazole produced two C–C coupling/ring-opening/insertion products, LY­[η²-<i>S,N</i>-SC₆H₄NCH­(CH₂Ph)₂]­(THF) (<b>4</b>) and {LY­[μ-η²:η¹-<i>O,N</i>-OC₆H₄NCH­(CH₂Ph)₂]}₂ (<b>5</b>), in 84% and 78% isolated yields, respectively

Reactivity of Homoleptic Dianionic β‑Diketiminato-Supported Yttrium Complexes toward CS₂: Construction of Neutral or Anionic Dihydropyridinethione

The mixed mono- and dianionic β-diketiminato yttrium complex [η²-N,N-{N­(2,6-^<i>i</i>Pr₂­C₆H₃)­C­(Me)}₂­CH]­Y­[η²-N,N-N­(2,6-^<i>i</i>Pr₂­C₆H₃)­C­(Me)­CHC­(CH₂)­N­(C₆H₃-^<i>i</i>Pr₂-2,6)] (<b>1</b>) was synthesized in almost quantitive yield by the metathesis reaction of β-diketiminato potassium with YCl₃ in a 3:1 molar ratio in THF at room temperature. Complex <b>1</b> reacted with 1 equiv of KCH₂Ph under the same conditions to afford a linear dianionic β-diketiminato-supported Y­(III)/​K­(I) heterobimetallic polymer {Y­[μ-η²:​η¹-N,N-N­(2,6-^<i>i</i>Pr₂­C₆H₃)­C­(Me)­CHC­(CH₂)­N­(C₆H₃-^<i>i</i>Pr₂-2,6)]₂-K­(THF)₃}_∞ (<b>2</b>). Moreover, <b>2</b> can be transformed into the corresponding salt-type complexes [K­([2.2.2]­cryptand)]⁺­{[η²-N,N-N­(2,6-^<i>i</i>Pr₂­C₆H₃)­C­(Me)­CHC­(CH₂)­N­(C₆H₃-^<i>i</i>Pr₂-2,6)]₂­Y}⁻ (<b>3</b>) and [^<i>n</i>Bn₄N]⁺­{[η²-N,N-N­(2,6-^<i>i</i>Pr₂­C₆H₃)­C­(Me)­CHC­(CH₂)­N­(C₆H₃-^<i>i</i>Pr₂-2,6)]₂­Y}⁻ (<b>4</b>) in high yields by the reactions of <b>2</b> with [2,2,2]-cryptand or ^<i>n</i>Bu₄­NCl in THF, respectively. The reaction of <b>3</b> and <b>4</b> with 2 equiv of CS₂ in THF at amibent temperature gave the anionic or neutral aryl-substituted dihydro­pyridine­thione [K­([2.2.2]­cryptand)]⁺­[2-S,4-N­(Ar),6-Me­C₅H₂N­(Ar)]⁻·[2-S,4-N­(H)­Ar,6-Me­C₅H₂N­(Ar)] (<b>5</b>) and 2-S,4-N­(H)­Ar,6-Me­C₅H₂N­(Ar) (<b>6</b>) in moderate yields, accompanied by unidentified materials containing Y³⁺ ions, respectively. The formation of <b>5</b> and <b>6</b> revealed an intermolecular nucleophilic addition/​cyclization and some chemical bond transformations such as C–C and C–N formation, CS cleavage, and 1,3-hydrogen shift occurred in the above reactions. The molecular structures of all of these new complexes <b>1</b>–<b>6</b> have been determined through X-ray single-crystal diffraction analysis

Reactivity of Scorpionate-Anchored Yttrium Alkyl Primary Amido Complexes toward Carbodiimides. Insertion Selectivity of Y–NHAr and Y–CH₂Ph Bonds

The Tp^Me2-supported yttrium dialkyl Tp^Me2Y­(CH₂Ph)₂(THF) (Tp^Me2 = tri­(3,5-dimethylpyrazolyl)­borate) reacted with 1 equiv of ArNH₂ in THF at room temperature to afford the yttrium alkyl primary amido complexes Tp^Me2YNHAr­(CH₂Ph)­(THF) (Ar = Ph (<b>1</b>), C₆H₃-^<i>i</i>Pr₂-<i>2</i>,<i>6</i> (<b>2</b>)) in 84% and 88% isolated yields, respectively. Complex <b>1</b> reacted with ^<i>i</i>PrNCN^<i>i</i>Pr in THF at room temperature to give a yttrium dianionic guanidinate complex, Tp^Me2Y­[(^<i>i</i>PrN)₂CNPh]­(THF)₂ (<b>3</b>, 74%). However, the reaction of <b>1</b> with ArNCNAr (Ar = C₆H₃-^<i>i</i>Pr₂-<i>2</i>,<i>6</i>) in the same conditions produced a Y–C bond insertion product, Tp^Me2Y­[(ArN)₂CCH₂Ph]­(NHPh) (<b>4</b>, 87%). Moreover, treatment of <b>2</b> with 1 equiv of ^<i>i</i>PrNCN^<i>i</i>Pr in THF at room temperature afforded two yttrium complex, Tp^Me2Y­[(^<i>i</i>PrN)­CNAr]­(THF) (<b>5</b>) and Tp^Me2Y­[(^<i>i</i>PrN)₂CCH₂Ph]­(NHAr) (<b>6</b>), in 58% and 19% isolated yields, respectively. These results indicated that carbodiimide can selectively insert into the Y–CH₂Ph and Y–NHAr σ-bonds of Tp^Me2-supported yttrium alkyl primary amido complexes Tp^Me2YNHAr­(CH₂Ph)­(THF), and this selectivity depends on the steric hindrance of the substituent groups <i>R</i> of cabodiimides and the primary amido ligands. All these new complexes were characterized by elemental analysis and spectroscopic methods, and their solid-state structures except <b>1</b> were also confirmed by single-crystal X-ray diffraction analysis

Synthesis, Structural Characterization, and Reactivity of Mono(amidinate) Rare-Earth-Metal Bis(aminobenzyl) Complexes

Three kinds of solvated lithium amidinates with different coordination models were obtained via recrystallization of [PhC­(NC₆H₄^<i>i</i>Pr₂-2,6)₂]­Li­(THF) (<b>1a</b>) in different solvents. Treatment of <i>o</i>-Me₂NC₆H₄CH₂Li with LLnCl₂(THF)_<i>n</i> (<b>2</b>; L = [PhC­(NC₆H₄^<i>i</i>Pr₂-2,6)₂]⁻ (NCN^dipp), [<i>o</i>-Me₂NC₆H₄CH₂C­(NC₆H₄^<i>i</i>Pr₂-2,6)₂]⁻ (NCN^dipp′)) formed in situ from reaction of LnCl₃(THF)_<i>x</i> with LLi­(THF) gave the rare-earth-metal bis­(aminobenzyl) complexes LLn­(CH₂C₆H₄NMe₂-<i>o</i>)₂ (L = NCN^dipp, Ln = Sc (<b>3a</b>), Y (<b>3b</b>), Lu (<b>3c</b>); L = NCN^dipp′, Ln = Sc (<b>3d</b>), Lu (<b>3e</b>)) in high yields. Reactions of complexes <b>3</b> with CO₂, PhNCO, 2,6-diisopropylaniline, and S have been explored. CO₂ inserted into each Ln–C bond of complexes <b>3a</b>–<b>c</b> to form the dual-core complexes [(NCN^dipp)­Sc­(μ-η¹:η¹-O₂CCH₂C₆H₄NMe₂-<i>o</i>)₂]₂ (<b>4a</b>) and [(NCN^dipp)­Ln­(μ-η¹:η²-O₂CCH₂C₆H₄NMe₂-<i>o</i>)­(μ-η¹:η¹-O₂CCH₂C₆H₄NMe₂-<i>o</i>)]₂ (Ln = Y (<b>4b</b>), Lu (<b>4c</b>)). The reaction of <b>3b</b>,<b>c</b>,<b>e</b> with PhNCO produced LLu­[OC­(CH₂C₆H₄NMe₂-<i>o</i>)­NPh]₂(thf) (L = NCN^dipp, Ln = Y (<b>5b</b>), Lu (<b>5c</b>); L = NCN^dipp′, Ln = Lu (<b>5e</b>)). Protonolysis of <b>3a</b>,<b>b</b> by 2,6-diisopropylaniline formed straightforwardly the μ₂-imido complexes [(NCN^dipp)­Ln­(μ-NC₆H₄^<i>i</i>Pr₂-2,6)]₂ (Ln = Sc (<b>6a</b>), Lu (<b>6c</b>)). Reaction of <b>3e</b> with S₈ afforded the sulfur insertion products (NCN^dipp′)­Lu­(CH₂C₆H₄NMe₂-<i>o</i>)­(SCH₂C₆H₄NMe₂-<i>o</i>)­(thf) (<b>7e</b>) and (NCN^dipp′)­Lu­(SCH₂C₆H₄NMe₂-<i>o</i>)₂(thf)₂ (<b>7f</b>) in high yields, respectively, depending on the stoichiometric ratio. All of these complexes were fully characterized by elemental analysis, NMR spectroscopy, and X-ray structural determinations