Half-sandwich Rare-earth Metal Complexes Research Articles

Half-Sandwich Rare-Earth metal complexes bearing 4,5,6,7-Tetrahydroindenyl ligands for highly Syndiospecific (Co)Polymerization of styrene

As Cp-derived ligands, substituted 4,5,6,7-tetrahydroindene (THI) ligands with tunable steric bulk have been synthesized, and their ligated half-sandwich rare-earth metal complexes were also sucessfully prepared and tested for styrene (co)polymerization. In conjunction with [Ph3C][B(C6F5)4], the THI-ligated scandium complexes exhibited high catalytic activity for highly syndiotactic polymerization of styrene (>99% rrrr). THI3Me-Sc/[Ph3C][B(C6F5)4] binary system also promoted the copolymerization of styrene and isoprene/butadiene by both the concurrent addition and sequentical addition of monomers, affording the copolymers with block microstructure as deterimined by NMR (1H and 13C) spectra. The huge difference in reactivity ratios betewen styrene and isoprene/butadiene (rIP / rSt = 31.1 and rBD / rSt = 173.6) revealed in kinetics investigation further proved the predominantly block structure of resultant copolymers.

Synthesis, characterization and ε-caprolactone polymerization properties of ferrocenyl modified half-sandwich rare-earth metal complexes

Salt metathesis of RECl3 with FcC5Me4Li followed by the addition of LiCH2C6H4NMe2-o in THF gave the ferrocenyl functionalized half-sandwich rare-earth metal bis(o-dimethylaminobenzyl) complexes (FcC5Me4)RE(CH2C6H4NMe2-o)2 (RE = Sc, Y, Lu) in good isolated yields.

Diastereodivergent [3 + 2] Annulation of Aromatic Aldimines with Alkenes via C-H Activation by Half-Sandwich Rare-Earth Catalysts.

Stereodivergent catalysis is of great importance, as it can allow efficient access to all possible stereoisomers of a given product with multiple stereocenters from the same set of starting materials. We report herein the first diastereodivergent [3 + 2] annulation of aromatic aldimines with alkenes via C-H activation by half-sandwich rare-earth catalysts. This protocol provides an efficient and general route for the selective synthesis of both trans and cis diastereoisomers of multisubstituted 1-aminoindanes from the same set of aldimines and alkenes, featuring 100% atom efficiency, excellent diastereoselectivity, broad substrate scope, and good functional group compatibility. The diastereodivergence is achieved by fine-tuning the sterics or ligand/metal combination of the half-sandwich rare-earth metal complexes.

Syndiotactic polymerization of styrene and copolymerization with ethylene catalyzed by chiral half-sandwich rare-earth metal dialkyl complexes

The syndiotactic polymerization of styrene (St) and the copolymerization of St with ethylene (E) were carried out by using a series of chiral half-sandwich rare-earth metal dialkyl complexes (Cp x *) as the catalysts. The complexes are Ln(CH2SiMe3)2(THF) (1−4: Ln = Sc (1), Ln = Lu (2), Ln = Y (3), Ln = Dy (4)) bearing chiral cyclopentadienyl ligand containing bulky cylcohexane derivatives in the presence of activator and Al i Bu3. For the St polymerization, a high activity up to 3.1 × 106 g of polymer molLn−1·h−1 and a high syndiotactic selectivity more than 99% were achieved. The resulting syndiotactic polystyrenes (sPSs) have the molecular weights (Mn) ranging from 3700 g·mol−1 to 6400 g·mol−1 and the molecular weight distributions (Mw/Mn) from 1.40 to 5.03. As for the copolymerization of St and E, the activity was up to 2.4 × 106 g of copolymer molSc−1·h−1·MPa−1, giving random St-E copolymers containing syndiotactic polystyrene sequences with different St content in the range of 15 mol%−58 mol%. These results demonstrate that the bulky cyclopentadienyl ligands of the chiral half-sandwich rare-earth metal complexes effectively inhibit the continued insertion of St monomers into the (co)polymer chain to some extent in comparison with the known half-sandwich rare-earth metal complexes.

Computational Analyses of the Effect of Lewis Bases on Styrene Polymerization Catalyzed by Cationic Scandium Half-Sandwich Complexes

The styrene polymerizations catalyzed by cationic half-sandwich rare-earth metal complexes [(η5-C5Me5)Sc(CH2SiMe3)(THF)n]+ (n = 0 (A), 1 (thfA)), [(η5-C5Me5)Sc(CH2C6H4NMe2-o)]+ (B), and [(η5-C5Me5)Sc(C6H4OMe-o)]+ (C) have been computationally studied. It has been found that THF as an external Lewis base has no effect on the regioselectivity in the chain initiation step. However, it can make activity lower toward styrene insertion. THF is computationally proposed to move away from the Sc center during chain propagation and thus has no effects on stereoselectivity. Aminobenzyl as an internal Lewis base in B results in no regioselectivity at the chain initiation stage and has no effect on syndioselectivity during chain propagation. The internal Lewis base anisyl induces high-isotactic chain-end microstructure. The discrepancy in chain-end microstructures induced by aminobenzyl and anisyl groups could be ascribed to the different coordination capability of oxygen and nitrogen atoms to Sc metal. The size of th...

Half-Sandwich Rare Earth Metal Complexes as Novel Catalysts for Olefin Polymerization and Other Chemical Transformations

Abstract This article describes our recent studies on the synthesis and chemistry of mono(cyclopentadienyl)-ligated rare earth metal alkyl and hydride complexes. The half-sandwich mono- and dialkyl rare earth metal complexes are prepared either by alkane elimination reactions between trialkyl rare earth complexes and the neutral cyclopentadiene derivatives or by metathetical reactions of rare earth trichlorides with the alkali metal salts of the corresponding ligands. The reaction of the dialkyl complexes with an equivalent of a borate compound such as [Ph3C][B(C6F5)4] or [PhNMe2H][B(C6F5)4] generates easily the corresponding cationic monoalkyl species, which serve as excellent catalysts for the polymerization and copolymerization of a variety of olefins to yield a new family of polymer materials that show novel properties but are difficult to prepare by other catalysts. The half-sandwich monoalkyl rare earth complexes bearing the silylene-linked cyclopentadienyl–arylamido ligands act as excellent catalysts for the catalytic dimerization of terminal alkynes, cross coupling of terminal alkynes with isocyanides, and the catalytic addition of terminal alkyne C–H, amine N–H, and phosphine P–H bonds to carbodiimides. The hydrogenolysis of the dialkyl rare earth complexes with H2 affords a new class of polynuclear rare earth metal polyhydride complexes, which show unique features in both structure and reactivity.

Half-Sandwich Indenyl Rare Earth Metal Dialkyl Complexes: Syntheses, Structures, and Catalytic Activities of (1,3-(SiMe3)2C9H5)Ln(CH2SiMe3)2(THF)

Reactions of 1,3-bis(trimethylsilyl)indene with Ln(CH2SiMe3)3(THF)2 gave half-sandwich rare earth metal complexes (1,3-(SiMe3)2C9H5)Ln(CH2SiMe3)2(THF) (Ln = Y, Lu, Dy). These complexes were characterized by single-crystal X-ray diffraction, which showed the η5 hapticity of indenyl ligands in all of the complexes. The catalytic behaviors of the complexes for intramolecular hydroamination of aminoalkenes were investigated. The catalytic activity increased with increasing the metal ion size, and the Y and Dy complexes showed excellent activities to a variety of aminoalkenes.

Catalytic Addition of Terminal Alkynes to Carbodiimides by Half-Sandwich Rare Earth Metal Complexes

The catalytic addition of terminal alkynes to carbodiimides has been achieved for the first time by use of half-sandwich rare earth metal complexes, such as {Me2Si(C5Me4)(NPh)}Y(CH2SiMe3)(THF)2, which offers a straightforward, atom-economic route to the N,N'-disubstituted propiolamidines which contain a conjugated C-C triple bond, a new family of amidines which were difficult to prepare by other means. A rare earth metal amidinate species was confirmed to be a true catalytic species in this process, thus demonstrating for the first time that an amidinate unit, though being often used as an ancillary ligand for various organometallic complexes, can itself participate in a catalytic reaction under appropriate conditions.