Implications of Indenyl Substitution for the Structural Chemistry of Rare-Earth Metal (Half-)Sandwich Complexes and Performance in Living Isoprene Polymerization

Abstract

Lanthanum indenyl half-sandwich complexes of the composition (IndR)­La­(AlMe4)2 were synthesized in high crystalline yields by a salt-metathesis protocol applying La­(AlMe4)3 and Li­(IndR). In the solid state, the parent indenyl (Ind) and 2-ethylindenyl (IndEt) complexes exhibit a dimeric structural motif with the methyl groups of the linearly aligned La­(μ-CH3)Al moieties being cis-positioned to the indenyl ligand. In contrast, 1-trimethylsilyl indenyl (IndSi) directs the η1-coordinated methyl group of the bridging aluminato ligand into a trans-position, while 2-tert-butyl indenyl afforded the monomeric half-sandwich complex (Ind tBu)­La­(AlMe4)2. The reactions of Lu­(AlMe4)3 with 1 or 2 equiv of Li­(IndR) gave predominantly bis­(indenyl) sandwich complexes (IndR)2­Lu­(AlMe4). All (half-)­sandwich complexes were characterized by X-ray structure analysis, 1H/13C­{1H} NMR and FTIR spectroscopy, and microanalysis. The performance of all half-sandwich complexes in isoprene polymerization was assessed upon activation with [Ph3C]­[B­(C6F5)4], [Ph­NMe2H]­[B­(C6F5)4], or B­(C6F5)3. The choice of indenyl ligand and cocatalyst had a major impact on the polymerization efficiency and stereospecificity. The highest selectivities could be achieved with the binary catalyst systems (IndEt)­La­(AlMe4)2/​[Ph3C]­[B­(C6F5)4] (cis/trans content 10.4/85.9) and (IndSi)­La­(AlMe4)2/​B­(C6F5)3 (cis/trans content 77.0/13.0).

Cerium Fluorenyl Complexes Including CC Coupling Reactions

“…This indicates some magnetic inequality of the ring and t Bu protons, which has also been detected for substituted indenyl ligands due to prochiral effects. Considering the steric constraints of the fluorenyl ligands, which clearly hinder rotation, similar effects might apply for 2 …”

“…Considering the steric constraints of the fluorenyl ligands, which clearly hinder rotation, similar effects might apply for 2. 38 Salt Metathesis Reactions Promoted by Flu-CeCl 2 (THF) 3 (1 Ce,Cl ). Given the preferred formation and stability toward ligand redistribution of compound Flu-CeCl 2 (THF) 3 (1 Ce,Cl ), we next aimed at salt metathesis ligand exchange.…”

Cationic Half-Sandwich Tetrahydrofluorenyl Rare-Earth Metal Complexes as Stable Single-Site Catalysts for (Co)Polymerization of Styrene and Butadiene

“…For example, the TMS-Y/[Ph 3 C][B(C 6 F 5 ) 4 ] binary system converted 500 equiv of styrene in a yield of 41% within 240 min (entry 12 in Table 1). Also, all the polystyrene produced by the yttrium-and lutetium-based catalytic systems were perfectly syndiotactic (>99% rrrr), which could be evidenced by their 13 C NMR spectra as well as their high melting points around 260 °C in the DSC traces (Figures S27 and S28). Noticeably, all the values of measured molecular weights of polystyrene are higher than those in theory, suggesting low to moderate catalytic efficiencies (14−65%).…”

“…5d,e NMR spectroscopy was performed to character the detailed microstructure of generated copolymers. The 1 H and 13 C NMR spectra of the selected sample (entry 4 in Table 2) with styrene feeding of 50% are shown in Figure 5. The peaks at δ 6.52−7.05 ppm in 1 H NMR spectrum were assigned to phenyl protons in the styrene units, while the peaks at δ 4.90−5.34 ppm arose from the olefinic protons in the butadiene units.…”

Analysis of the Rare Earth Mineral Resources Reserve System and Model Construction Based on Regional Development

“…On the basis of the research on the whole rare earth resources, they found that there were some problems in the rare earth industry, such as serious resource waste, severe environmental pollution, and chaotic industry supervision, and put forward some measures to improve the utilization efficiency of rare earth resources and turn the advantages of rare earth resources into economic advantages [ 12 ]. Diether et al thought that the upstream and downstream enterprises of rare earth industry are all self-interested, and the main bodies in the industry chain are in their own way, and there is no sufficient information communication between them, ignoring the government's policy guidance, which leads to the low comprehensive performance of the rare earth industry chain [ 13 ]. Zhai et al studied the important role of rare earth in iron and steel production and pointed out that rare earth elements can improve the shape and distribution of inclusions, refine grains, and then significantly improve the impact toughness, tensile strength, and oxidation resistance of products [ 14 ].…”