Alternating and random copolymerization of isoprene and ethylene catalyzed by cationic half-sandwich scandium alkyls

Cationic half-sandwich rare-earth metal alkyl species catalyzed polymerization and copolymerization of aryl isocyanides possessing polar, bulky, or chiral substituents

Cationic half-sandwich rare-earth metal alkyl species were first used for the coordination–insertion polymerization and copolymerization of aryl isocyanides.

Scandium-catalyzed copolymerization of myrcene with ethylene and propylene: convenient syntheses of versatile functionalized polyolefins

A novel family of myrcene-based polyolefins and functionalized polyolefins was prepared by the copolymerization of myrcene with ethylene and propylene catalyzed by half-sandwich scandium complexes.

A displacement-type fluorescent probe reveals active species in the coordinative polymerization of olefins

The correct identification of active species is an important prerequisite to study the mechanism of coordinative polymerization of olefins, which can afford important theoretical guidance for the design and synthesis of new organometallic catalysts and high-performance polyolefin materials.

α-C-H Alkylation of Methyl Sulfides with Alkenes by a Scandium Catalyst

The C-H addition of sulfides to alkenes is an atom-efficient route for the functionalization and modification of sulfide compounds through C-C bond formation, but this transformation is highly challenging. We report here the regioselective α-C(sp³)-H addition of a wide range of methyl sulfides to a variety of olefins and dienes by a half-sandwich scandium catalyst. This protocol provides a unique route for the synthesis of diverse sulfide derivatives through C-C bond formation at a sulfur-adjacent carbon atom in a 100% atom efficient fashion.

Cis-1,4-Polymerization of Isoprene by 1,3-Bis(oxazolinymethylidene)isoindoline-Ligated Rare-Earth Metal Dialkyl Complexes

A series of novel chiral nonmetallocene pincer-type rare-earth metal dialkyl complexes bearing the chiral monoanionic tridentate C₂-symmetric 1,3-bis(oxazolinymethylidene)isoindoline (BOXMI-H) ligand (BOXMI)Ln(CH₂SiMe₃)₂ 1⁻3 (1: Ln = Sc, yield = 57%; 2: Ln = Lu, yield = 55%; 3: Ln = Y, yield = 62%) have been prepared in moderate yields via the acid-base reaction between the BOXMI ligand and rare-earth metal tri(trimethylsilylmethyl) complexes. The X-ray diffractions show that both of the complexes 1 and 2 contain one BOXMI ligand and two trimethylsilylmethyl ligands, adopting a distorted trigonal bipyramidal configuration. In the presence of a cocatalyst such as borate and AlR₃, these complexes 1⁻3 exhibit high activities of up to 6.8 × 10⁴ (g of polymer)/(molLn h) and high cis-1,4 selectivities of up to 97% in the polymerization of isoprene in toluene, yielding the cis-1,4-polyisoprenes with heavy molecular weights (Mn of up to 710,000 g/mol) and bimodal molecular weight distributions (Mw/Mn = 2.0⁻4.5).

DFT Studies on cis-1,4-Polymerization of Dienes Catalyzed by a Cationic Rare-Earth Metal Complex Bearing an Ancillary PNP Ligand

Dnsity functional theory (DFT) calculations have been carried out for the highly selective cis-1,4-polymerization of butadiene catalyzed by a cationic rare-earth metal complex bearing an ancillary PNP ligand. It has been found that the chain initiation and propagation of butadiene polymerization occurs via the favorable cis-1,4-insertion route. The trans-1,4 and 1,2-insertion are unfavorable both kinetically and thermodynamically. The chain growth follows the π-allyl-insertion mechanism. The analyses of energy decomposition of transition states indicate that the likelihood of rival insertion pathways is predominantly controlled by the interaction energy of butadiene with a metal center and the deformation energy of butadiene moiety. The electronic factor of the central metal has a decisive influence on the cis- vs. trans-insertion and the regioselectivity (cis-1,4- vs. cis-1,2-insertion) is mainly determined by steric hindrance. Tetrahydrofuran (THF) coordination made monomer insertion less favorable compared with THF-free case and had more noticeable impact on the trans-monomer insertion compared with the cis case. During the chain propagation, cis-insertion of monomer facilitates THF de-coordination and the THF molecule could therefore dissociate from the central metal.

Copolymerization of propylene with styrene and ethylene by a THF-containing half-sandwich scandium catalyst: efficient synthesis of polyolefins with a controllable styrene content

A novel family of multi-block propylene–styrene copolymers with syndiotactic styrene–styrene blocks and random propylene–ethylene–styrene terpolymers with a broad composition range were obtained by using (C₅Me₄SiMe₃)Sc(CH₂SiMe₃)₂(THF).

The terpolymerization of ethylene and propylene with isoprene via THF-containing half-sandwich scandium catalysts: a new kind of ethylene–propylene–diene rubber and its functionalization

A novel family of ethylene–propylene–isoprene terpolymers was prepared by the terpolymerization of ethylene and propylene with isoprene catalyzed by the half-sandwich scandium complexs.

Controlled polymerization of isoprene promoted by a type of hemilabile XPN3 (X = O, S) ligand supported cobalt(ii) complexes: the role of a hemilabile donor on the level of control

Cobalt dichloride complexes (Co1–Co9) carrying a novel type of hemilabile donor PN³ (L1–L3) or XPN³ (L4–L6, X = O; L7–L9, X = S) are reported as precursors for controlled polymerization of isoprene.

Di and trinuclear rare-earth metal complexes supported by 3-amido appended indolyl ligands: synthesis, characterization and catalytic activity towards isoprene 1,4-cis polymerization

Different di and trinuclear rare-earth metal complexes supported by 3-amido appended indolyl ligands were synthesized and their catalytic activities towards isoprene polymerization were investigated. Treatment of [RE(CH₂SiMe₃)₃(thf)₂] with 1 equiv. of 3-(CyN[double bond, length as m-dash]CH)C₈H₅NH in toluene or in THF afforded dinuclear rare-earth metal alkyl complexes having indolyl ligands in different hapticities with central metals {[η²:η¹-μ-η¹-3-(CyNCH(CH₂SiMe₃))Ind]RE-(thf)(CH₂SiMe₃)}₂ (Cy = cyclohexyl, Ind = Indolyl, RE = Yb (1), Er (2), Y (3)) or {[η¹-μ-η¹-3-(CyNCH(CH₂SiMe₃))Ind]RE-(thf)₂(CH₂SiMe₃)}₂ (RE = Yb (4), Er (5), Y (6), Gd (7)), respectively. These two series of dinuclear complexes could be transferred to each other easily by only changing the solvents in the process. Reaction of [Er(CH₂SiMe₃)₃(thf)₂] with 1 equiv. of 3-t-butylaminomethylindole 3-(^tBuNHCH₂)C₈H₅NH in THF afforded the unexpected trinuclear erbium alkyl complex [η²:η¹-μ-η¹-3-(^tBuNCH₂)Ind]₄Er₃(thf)₅(CH₂SiMe₃) (8), which can also be prepared by reaction of 3 equiv. of [Er(CH₂SiMe₃)₃(thf)₂] with 4 equiv. of 3-(^tBuNHCH₂)C₈H₅NH in THF. Accordingly, complexes [η²:η¹-μ-η¹-3-(^tBuNCH₂)Ind]₄RE₃(thf)₅(CH₂SiMe₃) (RE = Y (9), Dy (10)) were prepared by reactions of 3 equiv. of [RE(CH₂SiMe₃)₃(thf)₂] with 4 equiv. of 3-(^tBuNHCH₂)C₈H₅NH in THF. Reactions of [RE(CH₂SiMe₃)₃(thf)₂] with 1 equiv. of 3-t-butylaminomethylindole 3-(^tBuNHCH₂)C₈H₅NH in THF, followed by treatment with 1 equiv. of [(2,6-ⁱPr₂C₆H₃)N[double bond, length as m-dash]CHNH(C₆H₃ⁱPr₂-2,6)] afforded, after workup, the dinuclear rare-earth metal complexes [η¹-μ-η¹:η¹-3-(^tBuNCH₂)Ind][η¹-μ-η¹:η³-3-(^tBuNCH₂)Ind]RE₂(thf)[(η³-2,6-ⁱPr₂C₆H₃)NCHN(C₆H₃ⁱPr₂-2,6)]₂(RE = Er (11), Y (12)) having the indolyl ligands bonded with the rare-earth metal in different ligations. All new complexes 1-12 were fully characterized by spectroscopic methods and elemental analyses, and their structures were determined by X-ray crystallographic analyses. It was found that, except for complexes 1, 4, 11 and 12, all complexes were highly efficient catalysts for selective isoprene polymerization (up to 99% 1,4-cis selectivity) with the cooperation of co-catalysts, and the trinuclear complexes displayed advantages over dinuclear complexes in terms of molecular weight of polymers.

Scandium-catalysed intermolecular hydroaminoalkylation of olefins with aliphatic tertiary amines

A homoleptic scandium trialkyl complex in combination with a borate compound served as an excellent catalyst for the C–H addition of aliphatic tertiary amines to various olefins.

A homoleptic scandium trialkyl complex in combination with a borate compound served as an excellent catalyst for the C–H addition of aliphatic tertiary amines to olefins. This highly regiospecific, 100% atom efficient C–H bond alkylation reaction was applicable to a wide variety of tertiary amines and olefins, including functionalised styrenes and unactivated α-olefins. This work represents the first example of rare-earth catalysed olefin hydroaminoalkylation and also the first example of catalytic C–H addition of aliphatic tertiary amines to olefins with any catalyst.

ortho-Selective C-H addition of N,N-dimethyl anilines to alkenes by a yttrium catalyst

The efficient and selective ortho-alkylation of N,N-dimethyl anilines via C-H addition to alkenes was achieved for the first time using a cationic half-sandwich yttrium catalyst. This protocol constitutes a straightforward and atom-economical route for the synthesis of a new family of tertiary aniline derivatives with branched alkyl substituents, which are otherwise difficult to obtain. DFT calculation studies suggest that the interaction between the yttrium atom and the NMe₂ group plays an important role and the intramolecular C-H activation through a σ-bond metathesis pathway is the rate-determining step, which is consistent with the experimental KIE observations.

Synthesis of Copolymers by Living Carbanionic Alternating Copolymerization

The synthesis and characterization of copolymers from styrene and 1,3-pentadiene (two isomers) are reported. Styrene/1,3-pentadiene (1:1) copolymerization with carbanion initiator yield living, well-defined, alternating (r1 = 0.037, r2 = 0.056), and highly stereoregular copolymers with 90%-100% trans-1,4 units, designed Mn s and low ÐM s (1.07-1.17). The first-order kinetic resolution and NMR spectra demonstrate that the copolymers obtained possess strictly alternating structure containing both 1,4- and 4,1-enchaiments. Also a series of copolymers with varying degrees of alternation are synthesized from para-alkyl substituted styrene derivatives and 1,3-pentadiene. The degree of alternation is strongly dependent on the polarity of solvent, reaction temperature, type of trans-cis isomer of 1,3-pentadiene and para-substituted group in styrene. The macro zwitterion forms (SPC) through the distribution of electronic charges from the donor (1,3-pentadiene) to the acceptor (styrenes) are proposed to interpret the carbanion alternating copolymerization mechanism. Owing to the versatility of the carbanion-initiating reaction, the present alternating strategy based on 1,3-pentadiene (especially cis isomer) can serve as a powerful tool for precise control of polymer chain microstructure, architecture, and functionalities in one-pot polymerization.

Highly Active and Isospecific Styrene Polymerization Catalyzed by Zirconium Complexes Bearing Aryl-substituted [OSSO]-Type Bis(phenolate) Ligands

[OSSO]-type dibenzyl zirconium(IV) complexes 9 and 10 possessing aryl substituents ortho to the phenoxide moieties (ortho substituents, phenyl and 2,6-dimethylphenyl (Dmp)) were synthesized and characterized. Upon activation with dMAO (dried methylaluminoxane), complex 9 was found to promote highly isospecific styrene polymerizations ([mm] = 97.5%–99%) with high molecular weights M_w up to 181,000 g·mmol⁻¹. When the Dmp-substituted pre-catalyst 10/dMAO system was used, the highest activity, over 7700 g·mmol(10)⁻¹·h⁻¹, was recorded involving the formation of precisely isospecific polystyrenes of [mm] more than 99%.

Bis(alkyl) rare-earth complexes coordinated by bulky tridentate amidinate ligands bearing pendant Ph2PO and Ph2PNR groups. Synthesis, structures and catalytic activity in stereospecific isoprene polymerization

Replacement of Ph₂PO group by Ph₂PNPh leads to a switch of stereoselectivity from cis-1,4 to trans-1,4.

Half-sandwich rare-earth-catalyzed olefin polymerization, carbometalation, and hydroarylation

The search for new catalysts for more efficient, selective chemical transformations and for the synthesis of new functional materials has been a long-standing research subject in both academia and industry. To develop new generations of catalysts that are superior or complementary to the existing ones, exploring the potential of untapped elements is an important strategy. Rare-earth elements, including scandium, yttrium, and the lanthanides (La-Lu), constitute one important frontier in the periodic table. Rare-earth elements possess unique chemical and physical properties that are different from those of main-group and late-transition metals. The development of rare-earth-based catalysts by taking the advantage of these unique properties is of great interest and importance. The most stable oxidation state of rare-earth metals is 3+, which is difficult to change under many reaction conditions. The oxidative addition and reductive elimination processes often observed in catalytic cycles involving late transition metals are generally difficult in the case of rare-earth complexes. The 18-electron rule that is applicable to late-transition-metal complexes does not fit rare-earth complexes, whose structures are mainly governed by the sterics (rather than the electron numbers) of the ligands. In the lanthanide series (La-Lu), the ionic radius gradually decreases with increasing atomic number because of the influence of the 4f electrons, which show poor shielding of nuclear charge. Rare-earth metal ions generally show strong Lewis acidity and oxophilicity. Rare-earth metal alkyl and hydride species are highly reactive, showing both nucleophilicity and basicity. The combination of these features, such as the strong nucleophilicity and moderate basicity of the alkyl and hydride species and the high stability, strong Lewis acidity, and unsaturated C-C bond affinity of the 3+ metal ions, can make rare-earth metals unique candidates for the formation of excellent single-site catalysts. This Account is intended to give an overview of our recent studies on organo rare-earth catalysis, in particular the synthesis and application of half-sandwich rare-earth alkyl complexes bearing monocyclopentadienyl ligands for olefin polymerization, carbometalation, and hydroarylation. Treatment of half-sandwich rare-earth dialkyl complexes having the general formula CpMR2 with an equimolar amount of an appropriate borate compound such as [Ph3C][B(C6F5)4] can generate the corresponding cationic monoalkyl species, which serve as excellent single-site catalysts for the polymerization and copolymerization of a wide range of olefin monomers such as ethylene, 1-hexene, styrene, conjugated and nonconjugated dienes, and cyclic olefins. The cationic half-sandwich rare-earth alkyl complexes can also catalyze the regio- and stereoselective alkylative alumination of alkenes and alkynes through insertion of the unsaturated C-C bond into the metal-alkyl bond followed by transmetalation between the resulting new alkyl or alkenyl species and an alkylaluminum compound. Moreover, a combination of deprotonative C-H bond activation of appropriate organic compounds such as anisoles and pyridines by the rare-earth alkyl species and insertion of alkenes into the resulting new metal-carbon bond can lead to catalytic C-H bond alkylation of the organic substrates. Most of these transformations are unique to the rare-earth catalysts with selectivity and functional group tolerance different from those of late-transition-metal catalysts.

Mono(boratabenzene) rare-earth metal dialkyl complexes: synthesis, structure and catalytic behaviors for styrene polymerization

Four mono(boratabenzene) rare-earth metal dialkyl complexes, [(3,5-Me2-C5H3BR)Ln(CH2SiMe3)2(THF)] (1: R = NEt2, Ln = Sc; 2: R = NEt2, Ln = Lu; 3: R = Ph, Ln = Sc; 4: R = Ph, Ln = Lu), were synthesized efficiently via a one-pot strategy with Li[3,5-Me2-C5H3BR] (R = NEt2, Ph), LnCl3(THF)x (Ln = Sc, x = 3; Ln = Lu, x = 0), and LiCH2SiMe3. The solid-state structures of 1 and 2 were determined by single-crystal X-ray diffraction. Variable-temperature NMR studies indicated that the energy barrier for the rotation of aminoboratabenzene in 1 (ΔG‡ ≈ 71 kJ mol−1) is higher than that of phenylboratabenzene in 3 (ΔG‡ ≈ 59 kJ mol−1). These mono(boratabenzene) rare-earth metal dialkyl complexes’ catalytic behaviors for styrene polymerization were investigated, and found that mono(boratabenzene) scandium dialkyl complexes show high catalytic activities for syndiotactic polymerization upon activation with cocatalysts.

Rare-earth–iridium heterobimetallic complexes with bridging imido and silylmethyl ligands: synthesis, structure and reactivity

The reaction of [(C₅Me₅)IrN^tBu] with [(C₅Me₄R)Ln(CH₂SiMe₃)₂(THF)] (Ln = Lu, Sc; R = Me, SiMe₃) afforded novel heterometallic rare earth–iridium imido complexes, which show unique structural features and reactivities.

Bis(alkyl) rare-earth complexes supported by a new tridentate amidinate ligand with a pendant diphenylphosphine oxide group. Synthesis, structures and catalytic activity in isoprene polymerization

The introduction of a pendant Ph₂P(O) group into an amidinate ligand resulted in high 1,4-cis selectivity (96.6%) while maintaining very high activity.