Synthesis and Reactivity of Rare-Earth-Metal Monoalkyl Complexes Supported by Bidentate Indolyl Ligands and Their High Performance in Isoprene 1,4-cis Polymerization

Synthesis and Reactivity of the Rare-Earth Metal Complexes Bearing the Indol-2-yl-Based NCN Pincer Ligand

The pincer rare-earth dialkyl complexes [κ3-LRE(CH2SiMe3)2 (RE = Lu(1a), Yb(1b), Er(1c), Y(1d), Dy(1e))] with the indol-2-yl-based NCN pincer ligand were synthesized by the reactions of the proligand HL (L = 1-Me2NCH2CH2-3-(2-iPrC6H5N═CH)C8H4N) with RE(CH2SiMe3)3(THF)2. These complexes exhibited a variety of reactivities toward organic compounds such as amines, triphenylphosphine ylide, N-phenylimidazole, pyridine derivatives, and o-carborane leading to σ-bond metathesis, migration insertion, and redox reaction products. The reactions of the dialkyl rare-earth metal complexes with o-carborane afforded the novel NCN pincer-ligated carboryne-based metallacyclopropanes which reacted with diphenyl ketone to give insertion products of the RE-C2-ind and one of the RE-Ccage bonds, while the reaction of the carboryne-based metallacyclopropanes with diphenyldiazomethane produced the di-aza-metallacyclopentanes via the insertions of the N═N bond of the diphenyldiazomethane into two RE-Ccage bonds and the RE-C2-ind bond. The reactions of the dialkyl complexes with 2 equiv of 2,2'-bipyridine afforded the pincer-ligated bis(2,2'-bipyridyl monoanionic radical) complexes via the homolytic redox reaction.

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.

Synthesis and characterization of rare-earth metallate amido complexes bearing 2-amidate-functionalized indolyl ligand and their application in the hydroboration of esters with pinacolborane

The reactions of 2-amidate-functionalized indolyl proligand 2-(2,6-iPr2C6H3NHC=O)C8H5NH (H2L) with [(Me3Si)2N]3RE(μ-Cl)Li(THF)3 were studied leading to the synthesis and characterization of a series of novel discrete trinuclear rare-earth metal metallate amido complexes...

Half-sandwich rare-earth metal complexes bearing a C5Me4-C6H4-o-CH2NMe2 ligand: synthesis, characterization and catalytic properties for isoprene, 1-hexene and MMA polymerization

A new ortho-dimethylaminomethylphenyl-tetramethylcyclopentadienyl ligand C₅Me₄H-C₆H₄-o-CH₂NMe₂ (HL) and a series of rare-earth metal complexes bearing this ligand were synthesized. Of these complexes, two binuclear alkyl complexes [(C₅Me₄-C₆H₄-o-CH₂N(Me)CH₂-μ)Ln(CH₂SiMe₃)]₂ (Ln = Sc (1a) and Y (1b)) were obtained from the alkane elimination reaction of the free ligand with Ln(CH₂SiMe₃)₃(THF)₂, followed by an intramolecular C-H activation process of a NMe group in the ligand with a CH₂SiMe₃ group, two binuclear dichloro complexes (C₅Me₄-C₆H₄-o-CH₂NMe₂)₂Y₂Cl₄[LiCl(THF)₂] (2a) and [(C₅Me₄-C₆H₄-o-CH₂NMe₂)LuCl(μ-Cl)]₂ (2b) were synthesized by the reaction of anhydrous yttrium or lutetium trichloride with the lithium salt of the ligand LiL, and the binuclear bis(borohydrido) complexes [(C₅Me₄-C₆H₄-o-CH₂NMe₂)Ln(μ-BH₄)BH₄]₂ (Ln = Sm (3a) and Nd (3b)) were synthesized by the reaction of Ln(BH₄)₃(THF)₃ (Ln = Sm and Nd) with the lithium salt of the ligand. The molecular structures of all complexes 1a, 1b, 2a, 2b, 3a and 3b were determined by single-crystal X-ray crystallography. Upon activation with AlR₃/Ph₃CB(C₆F₅)₄, MAO or MMAO, the binuclear alkyl complexes 1a and 1b show good catalytic activity for isoprene cis-1,4 enriched regioselective polymerization and moderate catalytic activity for 1-hexene polymerization. Complexes 3a and 3b were studied as catalysts for methyl methacrylate polymerization reaction under different conditions and were found to show moderate to high catalytic activity.

Aluminum complexes with Schiff base bridged bis(indolyl) ligands: synthesis, structure, and catalytic activity for polymerization of rac-lactide

A series of Schiff base bridged bis(indolyl) ligands were developed for aluminum chemistry. The reactions of AlEt3 or AlMe3 with the Schiff base bridged bis(indolyl) proligands R1(-N[double bond, length as m-dash]CHC8H5NH)2 (R1 = -CH2CH2- (H2L1); -CH2CH2CH2- (H2L2); -CH2CMe2CH2- (H2L3); rac-Cy (H2L4); and R,R-Cy (H2L5)) were studied leading to the synthesis of a series of aluminum alkyl complexes L1AlEt (1)-L5AlEt (5) and L3AlMe (3b) in good yields, while the reaction of H2L3 with Al(OiPr)3 gave the aluminum alkoxide complex L3AlOiPr (3a). These aluminum complexes were characterized by spectroscopic methods and elemental analyses. The solid state structures of the aluminum complexes 1-5 and 3a were confirmed by the X-ray diffraction study. X-ray analyses revealed that the aluminum centre in these complexes is five-coordinated. The coordination geometry is between square pyramidal and trigonal bipyramidal. In the presence of 1 equiv. of isopropanol, the aluminum alkyl complexes exhibited notable activity towards the ring-opening polymerization of rac-lactide at 70 °C in toluene, with good control over molecular weights and dispersities. The substituents and the length of the bridging part between the two Schiff base nitrogen atoms have an influence on either the tacticity of isolated polymers or the rate of polymerization. The kinetics of complex L3AlOiPr (3a) in C6D6 was also investigated, and the experimental results revealed that the rate of polymerization was first-order with respect to rac-lactide.

Synthesis, characterization, and reactivity of dinuclear organo-rare-earth-metal alkyl complexes supported by 2-amidate-functionalized indolyl ligands: substituent effects on coordination and reactivity

Two series of new dinuclear organo-rare-earth-metal alkyl complexes supported by 2-amidate-functionalized indolyl ligands with different haptic modes were synthesized and characterized. The treatment of [RE(CH2SiMe3)3(THF)2] with 1 equiv. of 2-(2,6-iPr2C6H3NHC[double bond, length as m-dash]O)C8H5NH (H2L1) and 2-(2-tBuC6H4NHC[double bond, length as m-dash]O)C8H5NH (H2L2) in toluene yielded the dinuclear organo-rare-earth-metal alkyl complexes {[η1:(μ2-η1:η1)-L1]RE(CH2SiMe3)(THF)2}2 [RE = Gd (1a), Dy (1b), Y (1c), Er (1d), and Yb (1e)] and {[η1:(μ2-η1:η1):η1-L2]RE(CH2SiMe3)(THF)2}2 [RE = Gd (2a), Dy (2b), Y (2c), Er (2d), and Yb (2e)] in good yields. When [RE(CH2SiMe3)3(THF)2] were treated with 2 equiv. of H2L1 or H2L2 in THF, the dinuclear organo-rare-earth-metal complexes {(η1:η1-HL)[η1:(μ2-η1:η1):η1-L]RE(THF)}2 (1ca: RE = Y, L = L1; 2ea: RE = Yb, L = L2) were obtained. The complexes could react with small organic molecules such as N,N'-diisopropylcarbodiimide (DIC), phenyl isocyanate, N-methylallylamine, phenylacetylene, pyridine, N-phenylimidazole, or 4-dimethylaminopyridine (DMAP) to yield a series of new complexes with different reactivity patterns along with the reported rare-earth-metal alkyl complexes. In the presence of cocatalysts, these dinuclear organo-rare-earth-metal alkyl complexes could initiate isoprene polymerization with high activity (100% conversion of 2000 equiv. of isoprene in 12 h), yielding polymers with high regioselectivity (1,4 polymers up to 96.1%).

Anilido-oxazoline-ligated rare-earth metal complexes: synthesis, characterization and highly cis-1,4-selective polymerization of isoprene

Anilido-oxazoline-ligated rare-earth metal dialkyl complexes have been synthesized and structurally characterized. The complexes exhibited strong fluorescence emissions and good catalytic performance on isoprene polymerization with high cis-1,4-selectivity. The treatment of anilido-oxazoline precursors ortho-C6H4[NH(2,6-R12C6H3)][C[double bond, length as m-dash]NC(R2,R3)CH2O] (R1 = R2 = R3 = Me (HL1); R1 = iPr, R2 = R3 = Me (HL2); R1 = R2 = iPr, R3 = H (HL3); and R1 = iPr, R2 = R3 = H (HL4)) with an equimolar amount of Ln(CH2SiMe3)3(THF)2 (Ln = Sc, Y) afforded rare-earth metal complexes L1-4-Ln(CH2SiMe3)2(THF)n (L1-Sc (1), n = 1; L2-Sc (2), n = 0; L1-Y (3), n = 1; L2-Y (4), n = 1; L3-Y (5), n = 1; and L4-Y (6), n = 1) in good yields. The complexes are stable in both the solid state and solution. Single crystal X-ray diffraction study showed that complexes 1, 3 and 4 exhibit a distorted trigonal bipyramidal configuration, while complex 2 is pseudo-tetrahedral without coordinated THF. The luminescence properties of complexes 1-4 were investigated and the emission maxima were found in the range of 465-477 nm. DFT and TD-DFT studies were carried out to explore their characteristic electronic structures and gain insight into their optical properties. Upon activation with organic borates, the reported complexes exhibited high activity and cis-1,4-selectivity for isoprene polymerization. The nature of the central metal and substituent groups in oxazoline have an influence on the cis-1,4-selectivity.

Synthesis and characterization of 2-t-butylimino-functionalized indolyl rare-earth metal amido complexes for the catalytic addition of terminal alkynes to carbodiimides: the dimeric complexes with the alkynide species in the μ–η1:η2 bonding modes

Dimeric complexes [(μ–η¹:η²-RCC)REL2]₂ (L = 2-(^tBuNCH)C₈H₅N), with alkynyl in the μ–η¹:η² modes, were isolated in the study of the catalytic reaction.

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.

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).

Reactivity of 1,3-Disubstituted Indoles with Lithium Compounds: Substituents and Solvents Effects on Coordination and Reactivity of Resulting 1,3-Disubstituted-2-Indolyl Lithium Complexes

Reactivity of 1,3-disubstituted indolyl compounds with lithium reagents was studied to reveal the substituents and solvent effects on coordination modes and reactivities resulting in different indolyl lithium complexes. Treatment of 1-alkyl-3-imino functionalized compounds 1-R-3-(R'N═CH)C₈H₅N [R = Bn, R' = Dipp (HL¹); R = Bn, R' = ^tBu (HL²); R = CH₃OCH₂, R' = Dipp (HL³); Dipp = ⁱPr₂C₆H₃] with Me₃SiCH₂Li or ⁿBuLi in hydrocarbon solvents (toluene or n-hexane) produced 1,3-disubstituted-2-indolyl lithium complexes [η¹:(μ₂-η¹:η¹)-1-Bn-3-(DippN═CH)C₈H₄NLi]₂ (1), {[η¹:(μ₃-η¹:η¹:η¹)-1-Bn-3-(^tBuN═CH)C₈H₄N][η²:η¹:(μ₂-η¹:η¹)-1-Bn-3-(^tBuN═CH)C₈H₄N][η¹:(μ₂-η¹:η¹)-1-Bn-3-(^tBuN═CH)C₈H₄N]Li₃} (2), and [η¹:η¹:(μ₂-η¹:η¹)-1-CH₃OCH₂-3-(DippN═CH)C₈H₄NLi]₂ (3), respectively. The bonding modes of the indolyl ligand were kept in 1 by coordination with donor solvent, affording [η¹:(μ₂-η¹:η¹)-1-Bn-3-(DippN═CH)C₈H₄NLi(THF)]₂ (4). The trinuclear complex 2 was converted to dinuclear form with a change of bonding modes of the indolyl ligand by treatment of 2 with donor solvent THF, producing [η¹:(μ₂-η¹:η¹)-1-Bn-3-(^tBuN═CH)C₈H₄NLi(THF)]₂ (5). X-ray diffraction established that compounds 1, 3, 4, and 5 crystallized as dinuclear structures with the carbanionic sp² carbon atoms of the indolyl ligands coordinated to lithium ions in a μ₂-η¹:η¹ manner, while compound 2 crystallized as a trinuclear structure and the carbanionic atoms of the indolyl moieties coordinated to lithium ions in μ₂-η¹:η¹ and μ₃-η¹:η¹:η¹ manners. When the lithiation reaction of HL¹ with 1 equiv of ⁿBuLi was carried out in THF, the monomeric lithium complex {η¹:η¹-1-Bn-3-(DippN═CH)-2-[1'-Bn-3'-(DippNCH)C₈H₅N]C₈H₄NLi(THF)} (6) having coupled indolyl moieties was obtained. The compound 6 can also be prepared by the reaction of 1 with 0.5 equiv of HL¹ with a higher isolated yield. Accordingly, the lithium complexes [η¹:η⁴-1-Bn-3-^tBuN═CH-2-(1'-Bn-3'-^tBuNCHC₈H₅N)C₈H₄NLi(L)] (L = THF, 7a; L = Et₂O, 7b) with the coupled indolyl moieties in η⁴ mode were isolated by treatment of HL² with 2 in THF or Et₂O. All complexes were characterized by spectroscopic methods, and their structures were determined by X-ray diffraction study.

Rare earth metal bisamido complexes with an NNO tridentate ligand and catalytic activity for the selective polymerization of isoprene

A series of rare earth metal bisamido complexes was synthesized, which could effectively initiate the polymerization of isoprene to afford polyisoprene with high regio- and stereo-selectivity in the presence of cocatalysts.

Rare-earth metal hydrides supported by silicon-bridged boratabenzene fluorenyl ligands: synthesis, structure and reactivity

The first boratabenzene derivatives of rare-earth metal hydrides were synthesized, and their reactivity was studied.

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.

Alpha and beta diimine cobalt complexes in isoprene polymerization: a comparative study

Isoprene was polymerized by diimine cobalt catalyst in the presence of DEAC to produce cis-1,4 and 3,4 polyisoprene.