Rare-earth Metal Dialkyl Complexes Research Articles

Synthesis, characterization of indol-2-yl-based NCO pincer rare-earth metal alkyl complexes and their catalytic activity towards hydroboration of imines

The reactions of HL (L = 1-(CH3OCH2CH2)-3-(Me2NCH2)-C8H4N) with different equivalent of the RE(CH2SiMe3)3(THF)2 produced a series of novel indol-2-yl-based NCO pincer rare-earth metal dialkyl complexes (κ3NCO-L)RE(CH2SiMe3)2 (RE = Lu(1a), Yb(1b)) and monoalkyl complexes (κ2NC-L)(κ3NCO-L)RE(CH2SiMe3) (RE = Lu(2a), Yb(2b), Er(2c), Y(2d)). These complexes served as catalysts for the hydroboration of imines and exhibited excellent activity with high efficiency under solvent-free and ambient temperature conditions.

Synthesis of bis(oxazoline)-based rare-earth metal complexes and their catalytic performance in the polymerization of isoprene and polar ortho-methoxystyrene.

A series of bis(oxazoline) rare-earth metal dialkyl complexes [(L)Ln(CH2SiMe3)2(THF)n] (L = L1 (dimethyl-substituted bis(oxazoline) ligand), Ln = Y (1-Y), Lu (1-Lu), Sc (1-Sc), n = 1; L = L2 (phenyl-substituted bis(oxazoline) ligand), Ln = Y (2-Y), Lu (2-Lu), Sc (2-Sc), n = 2) was successfully prepared. NMR spectroscopy and X-ray diffraction indicated that all the complexes ligated with a C2 symmetric bis(oxazoline) and two trimethylsilylmethyl ligands. In the presence of borate and triisobutyl aluminium, these complexes exhibited high catalytic activity for the polymerization of isoprene, yielding the polymer with high cis-1,4-regularity (up to 99.9%) and high molecular weight. Moreover, these ternary catalytic systems also served as efficient initiators for the polymerization of polar ortho-methoxystyrene. However, atactic polymers in all the cases were isolated despite the C2 symmetric geometry of bis(oxazoline) ligands.

Rare-earth metal complexes supported by indolyl-based NCN-pincer ligand and their efficient catalysis for isoprene polymerization

Rare-earth metal dialkyl complexes [1-CH2N(CH3)2–3-CH2CH2N(CH3)2C8H4N]RE(CH2SiMe3)2 (RE = 1-Y, 2-Er, 3-Yb and 4-Lu) were synthesized by the well-designed indolyl-based proligand 1-CH2N(CH3)2–3-CH2CH2N(CH3)2C8H4NH with rare-earth metal trialkyl complexes (RE(CH2SiMe3)2(THF)2) underwent direct alkane elimination. Single-crystal X-ray analyses and the NMR spectroscopy revealed these dialkyl complexes were analogous mononuclear NCN-pincer geometry via CH activation of 2-sp2 indole. Employing these complexes, upon activation by aluminum alkyls and borate, initiated isoprene polymerization with high conversion and high stereoselectivity (98% conversion of 2000 equivalent of isoprene, 1,4-cis polymers up to 91.5%).

Rare-Earth Metal Complexes Supported by 1,3-Functionalized Indolyl-Based Ligands for Efficient Hydrosilylation of Alkenes

Two different 1,3-functionalized indolyl-based proligands 1-(2-C4H7O)CH2-3-(2-tBuC6H5N═CH)C8H5N (HL1) and 1-Me2NCH2CH2-3-(2-iPrC6H5N═CH)C8H5N (HL2) were designed, prepared in high yields, and successfully applied to rare-earth metal chemistry showing different reactivities and different bondings with the central metals. The reactions of HL1 with RE(CH2SiMe3)3(THF)2 provided two types of rare-earth metal complexes: the pincer type mononuclear complexes κ3-(L1)RE(CH2SiMe3)2 [L1 = 1-(2-C4H7O)CH2-3-(2-tBuC6H5N═CH)C8H4N, RE = Lu(1), Yb(2)], and the dinuclear rare-earth metal alkyl (per alkyl/per metal) complexes having the ligand in novel coordination modes {(η1:(μ-η2:η1):η1-1-(2-C4H7O)CH2-3-[2-tBuC6H5NCH-(CH2SiMe3)]C8H4N)RECH2SiMe3}2 [RE = Er(3), Y(4), Dy(5), and Gd(6)]. Meanwhile, the reactions of HL2 with RE(CH2SiMe3)3(THF)2 led to the isolation and characterization of only the mononuclear rare-earth metal dialkyl complexes κ3-(L2)RE(CH2SiMe3)2 [L2 = 1-Me2NCH2CH2-3-(2-iPrC6H5N═CH)C8H4N, RE = Lu(7), Gd(8)] bearing the ligand in the pincer chelate form. The mononuclear complexes were formed through the sp2 C-H activation of the 2-indolyl moiety, while the dinuclear complexes were produced unexpectedly through the tandem 2-indolyl sp2 C-H activation and C═N insertion into the RE-CH2SiMe3 bond. These complexes were fully characterized by spectroscopic methods, elemental analyses, and single-crystal X-ray crystallography. The applications of the synthesized complexes as catalysts for the hydrosilylation of terminal alkenes with phenylsilane are described. Anti-Markovnikov addition products were produced by the hydrosilylation of aliphatic olefins, and Markovnikov addition products were isolated with aromatic olefins with high selectivity in the absence of cocatalysts. It is found that the dinuclear rare-earth alkyl complexes exhibited the best catalytic activity with the advantages of mild reaction conditions, short reaction time, low catalyst loading, and wide substrate applicability in comparison with the synthesized mononuclear complexes and the reported catalysts.

DMAO-activated Rare-earth Metal Catalysts for Styrene and Its Derivative Polymerization

The catalytic performance of rare-earth metal dialkyl complexes in combination with DMAO (dry methylaluminoxane) is explored. In the presence of 60 equivalents of DMAO, the half-sandwich complex (C13H8CH2Ph)Sc(CH2SiMe3)2(THF) (1) is inert for styrene polymerization, but (C5Me4Ph)Sc(CH2C6H4NMe2-o)2 (2) converts 18% styrene into syndiotactic polystyrene. Under the same conditions, the constrained-geometry configuration sandium complex (C13H8CH2Py)Sc(CH2SiMe3)2 (3a) displays extremely high catalytic activity (> 6420 kg·molSc−1 h−1) and perfect syndiospecific (rrrr > 99%) for styrene polymerization, and, in contrast, its lutetium (3b) and yttrium (3c) analogues are nearly inactive. Although the binary catalytic system 3a/DMAO exhibits very low activity for 4-methoxystyrene polymerization, it is an efficient catalyst for the syndioselective polymerization of other styrene derivatives such as 2-methoxystyrene, 4-methylthiostyrene, 4-fluorostyrene, 4-dimethylhydrosilylstyrene, alkyne-susbstituted styrenes and 4-methylstyrene. In addition, the binary system 3a/DMAO can copolymerize ethylene and styrene to give alternating copolymers with a single glass transition at 80 °C and 4 bar ethylene pressures. On increasing styrene feed amount from 20 to 60 mmol, the styrene content slight increases from 48.2 mol% to 53.8 mol%, but the polymerization activity is obviously promoted from 240 to 532 kg molSc–1·h–1.

Versatile reactivities of rare-earth metal dialkyl complexes supported by a neutral pyrrolyl-functionalized β-diketiminato ligand.

Herein, rare-earth metal dialkyl complexes supported by a neutral pyrrolyl-functionalized β-diketiminato ligand with the formula LRE(CH2SiMe3)2(thf) (RE = Y (1a), Dy (1b), Er (1c), Yb (1d); L = MeC(NDipp)CHC(Me)NCH2CH2NC4H2-2,5-Me2, Dipp = 2,6-iPr2C6H3) were synthesized via the reactions of the β-diketimine HL with the rare-earth metal trialkyl complexes RE(CH2SiMe3)3(thf)2 in high yields. The reactivities of 1 with pyridine derivatives, unsaturated substrates, and elemental sulfur were investigated, and some interesting chemical transformations were observed. Ligand exchange and activation of sp2 and sp3 C-H bonds occurred during the reactions with pyridine derivatives to afford different types of mononuclear rare-earth metal pyridyl complexes, namely, LEr(CH2SiMe3)2(η1-NC5H4) (2c), LRE(η3-CH2-2-NC5H2-4,6-Me2)2 (RE = Y (3a), Er (3c)), and LRE(CH2SiMe3)(η2-(C,N)-2-(2-C6H4NC5H4)) (RE = Er (4c), Yb = (4d)). Similarly, activation of the sp C-H bond occurred during the reaction of phenylacetylene with 1c to produce the dinuclear erbium alkynyl complex [LEr(CH2SiMe3)(μ-C[triple bond, length as m-dash]CPh)]2 (5c). The mixed amidinate-β-diketiminato ytterbium complex LYb[(Dipp)NC(CH2SiMe3)N(Dipp)](CH2SiMe3) (6d) was obtained by the insertion of bis(2,6-diisopropylphenyl)carbodiimide into a Yb-alkyl bond, as well as via the direct alkane elimination of a CH2SiMe3 moiety with bis(2,6-diisopropylphenyl)formamidine to afford the erbium complex LEr(DippNCHNDipp)(CH2SiMe3) (7c). A rare sp2 C-H bond oxidation of the β-diketiminato backbone with elemental sulfur insertion was detected to provide the unprecedented dinuclear rare-earth metal thiolate complexes (LRE)2(μ-SCH2SiMe3)2(μ-SCC(Me)(NDipp)C(Me)NCH2CH2NC4H2Me2-2,5) (RE = Y (8a), Er (8c)) in the reactions of S8 with 1a and 1c, respectively. The molecular structures of the complexes 1-8 were determined by single-crystal X-ray diffraction analyses.

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.

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).

Novel cationic rare earth metal alkyl catalysts for precise olefin polymerization

ABSTRACTThis mini‐review provides recent progress in the synthesis of rare earth metal dialkyl complexes and their application as highly efficient and regio‐/stereoselective catalysts in the coordination‐insertion (co)polymerization of olefins such as styrene, isoprene, 1,3‐cyclohexadiene, and ocimene. Through modifying the coordination atom, the ligand skeleton, and the substitutent on the skeleton of the chelating ligand, tuning the electron density and the steric environment around the rare earth metal center, the precise control of the activity and regio‐/stereoselectivity of the (co)polymerization as well as the comonomer incorporation and sequence distribution of the resulting copolymers are achieved. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017, 55, 2271–2280

Regio- and Stereochemical Control in Ocimene Polymerization by Half-Sandwich Rare-Earth Metal Dialkyl Complexes.

The polymerization of ocimene has been first achieved by half-sandwich rare-earth metal dialkyl complexes in combination with activator and Al(i) Bu3 . The regio- and stereoselectivity in the ocimene polymerization can be controlled by tuning the cyclopentadienyl ligand and the central metal of the complex. The chiral cyclopentadienyl-ligated Sc complex 1 prepares syndiotactic cis-1,4-polyocimene (cis-1,4-selectivity up to 100%, rrrr = 100%), while the corresponding Lu, Y, and Dy complexes 2-4 and the achiral pentamethylcyclopentadienyl Sc, Lu, and Y complexes 5-7 afford isotactic trans-1,2-polyocimenes (trans-1,2-selectivity up to 100%, mm = 100%).

1,4-Selective Polymerization of 1,3-Cyclohexadiene and Copolymerization with Styrene by Cationic Half-Sandwich Fluorenyl Rare Earth Metal Alkyl Catalysts

The regioselective coordination–insertion polymerization of 1,3-cyclohexadiene (CHD) and copolymerization with styrene (S) could be achieved by cationic half-sandwich fluorenyl rare earth metal alkyl catalysts generated by treating half-sandwich fluorenyl rare earth metal dialkyl complexes Flu′Ln(CH2SiMe3)2(THF)n (1–10) with an activator (such as [Ph3C][B(C6F5)4] (A), [PhNHMe2][B(C6F5)4] (B), or B(C6F5)3 (C)) and AliBu3. The homopolymerization of CHD afforded poly(CHD)s with complete 1,4 selectivity (1,4 selectivity up to 100%). The copolymerization of CHD with styrene gave new random CHD–S copolymers with CHD content ranging from 22 to 74 mol % containing 1,4-linked CHD–CHD, alternating CHD–S, and syndiotactic S–S sequences unavailable previously. The activity of the copolymerization and the comonomer compositions and sequences of the resulting CHD–S copolymers could be easily controlled by changing the substituted fluorenyl ligand, the metal center, the activator, the temperature, and the molar ratio of...

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.

Bis(imino)diphenylamido rare-earth metal dialkyl complexes: synthesis, structure, and catalytic activity in living ring-opening ε-caprolactone polymerization and copolymerization with γ-butyrolactone

Bis(imino)diphenylamido rare-earth metal dialkyl complexes [o-(2,6-(i)Pr(2)-C(6)H(3)-N=C-C(6)H(4))(2)-N]Ln(CH(2)SiMe(3))(2) (1: Ln = Sc; 2: Ln = Lu; 3: Ln = Y) have been synthesized in good yields and structurally characterized by elemental analysis, NMR spectroscopy, and single-crystal X-ray diffraction studies. They serve as highly efficient single-component catalysts both for the living ring-opening ε-caprolactone polymerization and random copolymerization with γ-butyrolactone, with the activity being dependent on the steric hindrance around the metal center, yielding high molecular weight PCLs or P(CL-co-BL)s with narrow molecular weight distributions.

Living 3,4-Polymerization of Isoprene by Cationic Rare Earth Metal Alkyl Complexes Bearing Iminoamido Ligands

Treatment of rare earth metal trialkyl complexes Ln(CH2SiMe3)3(THF)2 (Ln = Sc, Lu, and Y) with 1 equiv of α-diimine ligands 2,6-R2C6H3N═CH−CH═NC6H3R2-2,6 (R = iPr, Me) affords straightforwardly monoanionic iminoamido rare earth metal dialkyl complexes [2,6-R2C6H3N−CH2−C(CH2SiMe3)═NC6H3R2-2,6]Ln(CH2SiMe3)2(THF) (1: Ln = Sc, R = iPr; 2: Ln = Lu, R = iPr; 3: Ln = Y, R = iPr; 4: Ln = Sc, R = Me; 5: Ln = Lu, R = Me; 6: Ln = Y, R = Me) in 65−85% isolated yields. X-ray analyses show these complexes have decreasing steric hindrance in the coordination spheres of the metal centers in the order 1 > 2 > 3 > 4 > 5 > 6. A mechanism involving intramolecular alkyl and hydrogen migration is supported on the basis of DFT calculations to account for ligand alkylation. Activated by [Ph3C][B(C6F5)4], all of these iminoamido rare earth metal dialkyl complexes are active for living polymerization of isoprene, with activity and selectivity being significantly dependent on the steric hindrance around the metal center to yield ho...

Novel polymerization catalysts and hydride clusters from rare-earth metal dialkyls

This Review gives an overview on recent progress in the synthesis and chemistry of rare-earth metal dialkyl complexes bearing monoanionic ancillary ligands, with an emphasis on novel polymerization catalysts. These structurally well-defined and highly reactive compounds are prepared either by alkane elimination reactions between trialkyl rare-earth complexes and acidic neutral ligands, or by the metathetical reactions of rare-earth trihalides with the alkali metal salts of the corresponding ligands. On treatment with an appropriate borate compound, the dialkyl complexes are converted into the corresponding cationic monoalkyl species, which serve as excellent catalysts for the polymerization and copolymerization of a variety of olefins to yield a series of new polymer materials that exhibit novel properties. Alternatively, hydrogenation of the dialkyl rare-earth complexes with H(2) affords a new class of rare-earth polyhydride complexes with unique features in terms of both their structure and reactivity.

Selective ammonolysis of half-sandwich rare-earth metal dialkyl and polyhydride complexes: synthesis of polyamido rare-earth complexes having novel structures

The scandium dialkyl complex [Cp'Sc(CH(2)SiMe(3))(2)(THF)] (1-Sc, Cp' = C(5)Me(4)SiMe(3)) reacts rapidly with ammonia at room temperature to afford selectively a trinuclear hexaamido complex [Cp'Sc(mu-NH(2))(2)](3) (3-Sc) with release of SiMe(4). The reaction of the lutetium dialkyl complex [Cp'Lu(CH(2)SiMe(3))(2)(THF)] (1-Lu) with ammonia under the same conditions gives the analogous hexaamido Lu complex [Cp'Lu(mu-NH(2))(2)](3) (3-Lu) as a major product (92%) together with a tetranuclear octaamido complex [Cp'Lu(mu-NH(2))(2)](4) (4-Lu) as a minor product (8%). In contrast, reaction of tetranuclear rare-earth metal octahydride complexes [Cp'Ln(mu-H)(2)](4)(THF) (Ln = Y (2-Y), Lu (2-Lu)) with ammonia under similar conditions yields selectively the heptaamido/monohydrido complexes [(Cp'Ln)(4)(mu-NH(2))(6)(mu(3)-NH(2))(mu(4)-H)] (Ln = Y (5-Y), Lu (5-Lu)), in which a mu(4)-H ligand remains at the center of the tetrahedral metal framework. Exposure of heptaamido/monohydrido complex 5-Lu to an ammonia atmosphere at room temperature for a long time (two days) affords the octaamido complex 4-Lu quantitatively. The molecular structures of 3-Sc, 3-Lu, 4-Lu, 5-Y, and 5-Lu have been determined by X-ray analyses.

Rare Earth Metal Alkyl Complexes with Methyl-Substituted Triazacyclononane-amide Ligands: Ligand Variation and Ethylene Polymerization Catalysis

A series of rare earth metal dialkyl complexes was prepared with the general formula [Me2TACN-(B)-NR]M(CH2SiMe3)2 (TACN = 1,4,7-triazacyclononane, B = (CH2)2, SiMe2; R = tBu, secBu, nBu; M = Sc, Y, Nd, La). For M = Sc, mixed monoalkyl−monochloro complexes were also accessible. Selected examples of these complexes were structurally characterized and show the metal in a distorted octahedral environment. With Lewis or Bronsted acid activators the dialkyl compounds can be converted to the corresponding monoalkyl cations, which were characterized by NMR spectroscopy. Comparative testing in catalytic ethylene polymerization showed that the catalyst activity is most strongly influenced by the metal ionic radius, but that variations in the ligand backbone and substitution pattern do influence other factors, such as polymer molecular weight and catalyst stability. Catalysts with the intermediately sized rare earth metal yttrium generally showed the highest activity, but some of these catalysts produce polyethylene...