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

Reversing Conventional Reactivity of Mixed Oxo/Alkyl Rare-Earth Complexes: Non-Redox Oxygen Atom Transfer

International audienceThe preferential substitution of oxo ligands over alkyl ones of rare-earth complexes is commonly considered as "impossible" due to the high oxophilicity of metal centers. Now, it has been shown that simply assembling mixed methyl/oxo rare-earth complexes to a rigid trinuclear cluster framework cannot only enhance the activity of the Ln-oxo bond, but also protect the highly reactive Ln-alkyl bond, thus providing a previously unrecognized opportunity to selectively manipulate the oxo ligand in the presence of numerous reactive functionalities. Such trimetallic cluster has proved to be a suitable platform for developing the unprecedented non-redox rare-earth-mediated oxygen atom transfer from ketones to CS2 and PhNCS. Controlled experiments and computational studies shed light on the driving force for these reactions, emphasizing the importance of the sterical accessibility and multimetallic effect of the cluster framework in promoting reversal of reactivity of rare-earth oxo complexes

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