Yttrium Alkyl Research Articles

Reactions of Bis(alkyl)yttrium Complexes Supported by Bulky N,N Ligands with 2,6-Diisopropylaniline and Phenylacetylene

The reactions of bis(trimethylsilylmethyl)yttrium complexes supported by bulky amidopyridinate (Ap) and amidinate (Amd) ligands (LY(CH2SiMe3)2(THF)n: L = Ap, n = 1 (1); L = Amd, n = 1 (2)) with 2,6-diisopropylaniline and phenylacetylene were performed. The reaction of 1 with an equimolar amount of 2,6-diisopropylaniline occurs with TMS elimination and affords an yttrium alkyl anilido species which was isolated as a DME adduct, ApY(CH2SiMe3)(NH-2,6-iPr2C6H3)(DME) (3). The protonolysis of 3 with phenylacetylene results in the alkynyl anilido derivative ApY(C≡CPh)(NH-2,6-iPr2C6H3)(DME) (6). The treatment of complexes 3 and 6 with 2,2′-bipy leads to the formation of the bis(anilido) derivative ApY(NH-2,6-iPr2C6H3)2(bipy) (5). The formation of a dimeric complex containing two ApY fragments linked by two μ2-alkynyl groups and a μ-η2:η2-butatrienediyl fragment, [{AmdY(μ2-C≡CPh)}2(μ2-η2:η2-PhCCCCPh)] (7), was observed in the reaction of 2 with 2 equiv of phenylacetylene.

Synthesis, Structures, and Reactivity of Yttrium Alkyl and Alkynyl Complexes with Mixed TpMe2/Cp Ligands

The structurally characterized Tp(Me2)-supported rare earth metal monoalkyl complex (Tp(Me2))CpYCH(2)Ph(THF) (1) was synthesized via the salt-metathesis reaction of (Tp(Me2))CpYCl(THF) with KCH(2)Ph in THF at room temperature. Treatment of 1 with 1 equiv of PhC≡CH under the same conditions afforded the corresponding alkynyl complex (Tp(Me2))CpYC≡CPh(THF) (2). Complex 1 exhibits high activity toward carbodiimides, isocyanate, isothiocyanate, and CS(2); treatment of 1 with such substrates led to the formation of a series of the corresponding Y-C(benzyl) σ-bond insertion products (Tp(Me2))CpY[(RN)(2)CCH(2)Ph] (R = (i)Pr(3a), Cy(3b), 2,6-(i)Pr-C(6)H(3)(3c)), (Tp(Me2))CpY[SC(CH(2)Ph)NPh] (4), (Tp(Me2))CpY[OC(CH(2)Ph)NPh] (5), and (Tp(Me2))CpY(S(2)CCH(2)Ph) (6) in 40-70% isolated yields. Carbodiimides and isothiocyanate can also insert into the Y-C(alkynyl) σ bond of 2 to yield complexes (Tp(Me2))CpY[(RN)(2)CC≡CPh] (R = (i)Pr(7a), Cy(7b)) and (Tp(Me2))CpY[SC(C≡CPh)NPh] (9). Further investigation results indicated that 1 can effectively catalyze the cross-coupling reactions of phenylacetylene with carbodiimides. However, treatment of o-allylaniline with a catalytic amount of 1 gave only the benzyl abstraction product (Tp(Me2))CpY(NHC(6)H(4)CH(2)CH═CH(2)-o)(THF) (10), without observation of the expected organic hydroamination/cyclization product. All of these new complexes were characterized by elemental analysis and spectroscopic properties, and their solid-state structures were also confirmed by single-crystal X-ray diffraction analysis.

Selective Protonation of the YC Bond in Trinuclear Yttrium Alkyl–Hydrido Clusters and Formation of the Cationic Polyhydrido Core

Selective Protonation of the YC Bond in Trinuclear Yttrium Alkyl–Hydrido Clusters and Formation of the Cationic Polyhydrido Core

Rich C–H bond activations of yttrium alkyl complexes bearing phosphinimino-amine ligands

A series of phosphinimino-amine compounds (2,6– iPr 2–C 6H 3NH)C(Me)CHPPh 2(NAr) (Ar = 2,6– iPr 2–C 6H 3 (HL 1), 2,6–Et 2–C 6H 3 (HL 2), 2,6–Me 2–C 6H 3 (HL 3), C 6H 5 (HL 4), 3–CF 3–C 6H 4 (HL 5)) that existed in imine and amine forms were synthesized and fully characterized. Treatment of HL 1−5 with Y(CH 2SiMe 3) 3(THF) 2 afforded the corresponding yttrium mono- or bis(alkyl) complexes that depended significantly on the ancillary ligands. The reactions between HL 1−3 and Y(CH 2SiMe 3) 3(THF) 2 at room temperature generated mononuclear monoalkyl complexes 1– 3 via deprotonation and C–H bond activation. However, when compounds HL 4,5 were used, the dialkyl complexes 4 and 5 were isolated by deprotonation only. The molecular structures of complexes 1– 4 were characterized with X-ray crystallography and discussed.

Synthesis and Structural Features of Boratabenzene Rare-Earth Metal Alkyl Complexes

A series of solvent-free boratabenzene rare-earth metal alkyl complexes (C5H5BR)(2)LnCH (SiMe3)(2) (9: R = NEt2, Ln = Y; 10: R = NPh2, Ln = Y; 11: R = CH3, Ln = Y; 12: R = NPh2, Ln = Sm; 13: R = NPh2, Ln = Dy; 14: R = NEt2, Ln = Lu; 15: R = NPh2, Ln = Lu; 16: R = Me, Ln = Lu) were synthesized. The solid-state structures of 10, 13, and 15 were determined by single-crystal X-ray diffraction. The crystal structures of 10,13, and 15 feature highly unsymmetrical coordination of the alkyl ligands and short Ln-C(alkyl) distances. The diamagnetic yttrium and lutetium alkyl complexes, 9-11 and 14-16, were characterized by (H-1, C-13, B-11) NMR spectroscopy. The Ln-C alpha H alpha, (H-1 NMR: delta 0.68-0.99 ppm) and Ln-C alpha H alpha (C-13 NMR: delta 33.9-39.1 ppm) resonances of these boratabenzene rare-earth metal alkyl complexes are rather downfield in comparison with those of the bis-Cp rare-earth metal alkyl complexes. Y-89 NMR spectra of the boratabenzene yttrium alkyl complexes 9-11 and the Cp complex (C5H4Me)(2)YCH(SiMe3)(2) were recorded. The Y-89 NMR chemical shifts for 9, 10, and 11 are 176.1, 170.0, and 162.2 ppm, respectively, which are significantly downfield in comparison with that of (C5H4Me)(2)YCH(SiMe3)(2) (44.0 ppm).

Facile Synthesis of Hydroxyl-Ended, Highly Stereoregular, Star-Shaped Poly(lactide) from Immortal ROP of rac-Lactide and Kinetics Study

Triethanolamine (TEA) reacted with 3 equiv of yttrium alkyl complex 1 bearing O,N,N,O-tetradentate Salan ligand to give a trinuclear yttrium alkoxide counterpart 2 via metathesis reaction. Complex 2 initiated the ring-opening polymerization of rac-lactide in a livingness mode under mild conditions. Remarkably, 2 was so tolerant of the protic TEA that under various TEA-to-yttrium molar ratios ranging from 1:3 up to 81:1, the polymerization performed smoothly, suggesting an immortal characteristic. The resultant polylactides had variable molecular weights (Mn = 1.36 × 104to 32.54 × 104) but narrow molecular weight distributions (PDI = 1.02−1.09), and, especially, pure heterotactic (Pr = 0.99), hydroxyl-functionalized and star-shaped architecture, which were fully characterized by NMR spectroscopy and MALDI−TOF mass spectrum analyses and confirmed further by calculating the contraction factor value g′ (g′ = 0.96) via Mark−Houwink equations. Detailed investigation of the “immortal” polymerization gave a unique kinetics law of −d[LA]/dt = kp[LA][TEA]−0.352.

Reactions of alkali metal and yttrium alkyls with a sterically demanding bis(aryloxysilyl)methane: Formation of aryloxide complexes by Si-O bond cleavage

Abstract Reaction of bis(bromodimethylsilyl)methane (BrSiMe2)2CH2 (1) with two equivalents of 2,6-diisopropylphenol (Ar′OH) in the presence of the auxiliary base NEt3 affords the bis(aryloxysilyl)methane (Ar′OSiMe2)2CH2 (2) as a colourless oil following work-up. The reaction of 2 with [Li(Bun)] in the presence of [K(OBut)] promoted Si-O bond cleavage and the sole isolable product from this reaction was found to be the colourless, crystalline heterobimetallic complex [{Li(OAr′)}2{K(OAr′)}2(THF)4] (3). The in situ reaction of 2 with one equivalent of [Li(Bun)] in the presence of one equivalent of [K(OBut)] and subsequent addition to one equivalent of [Y(I)3(THF)3.5] afforded colourless, crystalline [Y(OAr′)(I)2(THF)3] (4) as the only isolable product. No reaction was observed between [Y(Bn)3(THF)3] (Bn = CH2C6H5) and one equivalent of 2 in toluene at room temperature; heating solutions led to decomposition and recovery of 2. In THF, the reaction between 2 and one equivalent of [Y(Bn)3(THF)3] resulted in Si-O bond cleavage with concomitant Si-C bond formation to give (BnSiMe2)2CH2 (5) as a colourless oil and the colourless, crystalline compounds [Y(OAr′)2(Bn)(THF)] (7), and [Y(OAr′)3(THF)2] (8) which were separated by fractional crystallisation. In an attempt to prepare 7 by a rational route, [Y(OAr′)2(I)(THF)2] (6) was prepared from the reaction of [Y(I)3(THF)3.5] with two equivalents of [K(OAr′)]. However, although 6 could be prepared by a rational salt elimination route, attempts to convert it to 7 resulted instead in 8 being recovered as the only isolable product. This is proposed to be the result of Schlenk-type equilibria, which is supported by the observation that dissolution of pure 6 in benzene results in the additional presence of 8 in the 1H NMR spectrum over 12 h. Compound 7 was prepared rationally from the reaction between [Y(Bn)3(THF)3] and two equivalents of HOAr′. However, although crystalline 7 could be isolated in sufficient quantities for analysis, NMR spectra were consistent with the formation of 8 in solution from Schlenk-type equilibria. Compounds 2–8 have been variously characterised by X-ray diffraction, NMR and FTIR spectroscopy, and CHN microanalyses.

Yttrium‐Amidopyridinate Complexes: Synthesis and Characterization of Yttrium‐Alkyl and Yttrium‐Hydrido Derivatives

AbstractAryl‐ or heteroaryl‐substituted aminopyridine ligands (N2HAr) react with an equimolar amount of [Y(CH2SiMe3)3(thf)2] to give yttrium(III)‐monoalkyl complexes. The process involves the deprotonation of N2HAr by a yttrium alkyl followed by a rapid and quantitative intramolecular sp2‐CH bond activation of the aryl or heteroaryl pyridine substituents. As a result, new Y complexes distinguished by rare examples of CH bond activations have been isolated and completely characterized. Selective σ‐bond metathesis reactions take place on the residual Y–alkyl bonds upon treatment with PhSiH3. Unusual binuclear metallacyclic yttrium(III)‐hydrido complexes have been obtained and characterized by NMR spectroscopy and X‐ray diffraction analysis.

Trimethylsilylmethyl complexes of the rare-earth metals with sterically hindered N-heterocyclic carbene ligands: adduct formation and C–H bond activation

Tris(trimethylsilylmethyl) complexes of yttrium and lutetium [LnR(3)(THF)(2)] (R = CH(2)SiMe(3)) were treated with sterically bulky N-heterocyclic carbenes (NHC) 1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene (IPr) and 1,3-bis(2,4,6-trimethylphenyl)imidazol-2-ylidene (IMes). IPr gave labile mono-adducts [LnR(3)(NHC)], isolated as thermally robust crystals and fully characterized by NMR spectroscopy and X-ray diffraction. IMes gave a similar lutetium mono-adduct [LuR(3)(IMes)] with the lutetium alkyl [LuR(3)(THF)(2)], whereas the yttrium alkyl [YR(3)(THF)(2)] resulted in the formation of an ortho-metalated product. This compound, isolated as a crystalline bis(THF) adduct, contains a strained six-membered chelate ring that has been formed by the C-H bond activation of one of the ortho-methyl groups of the mesityl group. In contrast [LuR(3)(IMes)] only slowly underwent a similar C-H bond activation.

Synthesis, characterization of amine-bridged bis(phenolate) yttrium alkyl complex and its catalytic behavior for the Tishchenko reaction

Reaction of homoleptic yttrium tris-alkyl complex YR3(R=CH2C6H4NMe2-o) with 1 equivalent of amine bis(phenol)s LH2 (L=Me2NCH2CH2N(CH2-(2-O-C6H2-Bu2 2-3,5))2) afforded the solvent-free yttrium alkyl complex LYR (1), which has been characterized with elemental analysis, 1H NMR and IR spectra, and structural determination. The coordination geometry around the center metal atom can be best described as a distorted octahedron. It was found that complex 1 can be used as an efficient catalyst for the Tishchenko reaction.

Ring-Opening Reactions of Aromatic N-Heterocycles by Scandium and Yttrium Alkyl Complexes

The C-N bond in aromatic N-heterocycles is a strong bond, its cleaving involving mostly examples of metal-element multiple bonds. We report on the C-C coupling of two molecules of an aromatic N-heterocycle mediated by scandium and yttrium benzyl complexes supported by a ferrocene 1,1'-diamide ligand. The reaction with 1-methylimidazole leads, ultimately, to the formation of a ring-opened imidazole coupled to a 1-methylimidazole fragment, a structure showing extended conjugation of double bonds. The experimental evidence agrees with involvement of only sigma bonds in these transformations.

Synthesis and structural characterisation of an yttrium–alkyl–alkylidene

The first structurally authenticated yttrium-alkyl-alkylidene is reported; structural, spectroscopic, and theoretical analyses show that whilst the yttrium-alkylidene bond is short, it possesses a bond order less than one and is comparable to the Y-C(alkyl) single bond within the same molecule.

O2 activation and hydrolysis of Salan rare-earth metal alkyl complexes

Salan ligated yttrium alkyl complex , L(1)Y(CH(2)SiMe(3))(THF) (Salan = L(1): [2-O-3,5-tBu(2)-C(6)H(2)CH(2)N(CH(3))CH(2)](2)), was exposed to an oxygen/nitrogen atmosphere to give a bimetallic alkoxide complex , [L(1)Y(mu-OCH(2)SiMe(3))](2). Whilst the lutetium counterparts (L(1)Lu(CH(2)SiMe(3))(THF)) and (L(2)Lu(CH(2)SiMe(3))(THF); L(2): [2-O-3-tBu-C(6)H(2)CH(2)N(CH(3))CH(2)](2)) were hydrolysed with moist nitrogen to afford mixed hydroxy/silyloxy complexes and ([L(1,2)Lu(mu-OSiMe(3))(mu-OH)LuL(1,2)]), respectively.

Intramolecular (sp3-hybridized) C−H Activation: Yttrium Alkyls versus Transient Yttrium Hydrides

Intramolecular sp3-hybridized C−H activation of novel yttrium alkyl and hydrido complexes supported by bulky aminopyridinato ligands derived from deprotonated 2,6-(diisopropylphenyl)-[6-(2,6-dimethylphenyl)pyridin-2-yl]amine (Ap‘-H) is reported. Reaction of YCl3 with a 2-fold molar excess of Ap‘K in THF afforded complex [Ap‘2YCl(thf)] (1). Alkylation of 1 with an equimolar amount of LiCH2SiMe3 in hexane allowed isolation of the alkylyttrium derivative [Ap‘2YCH2SiMe3(thf)] (2) in 65% yield. Unexpectedly treatment of complex 2 with PhSiH3 (toluene, 20 °C) afforded the product of intramolecular sp3-hybridized C−H bond activation, Ap‘(Ap‘-H)Y(THF) (3). Most likely a hydrid species is formed in the course of this reaction, which undergoes rapid C−H activation since 3 is formed from 2 directly about 500 times slower than in the presence of 1 equiv of PhSiH3. Molecular structures of complexes 2 and 3 have been confirmed by X-ray crystal structure analysis.

Mixed ligands supported yttrium alkyl complexes:: Synthesis, characterization and catalysis toward lactide polymerization

Treatment of yttrium tris(alkyl)s, Y(CH 2SiMe 3) 3(THF) 2, by equimolar H(C 5Me 4)SiMe 3(HCp′) and indene (Ind-H) afforded (η 5-Cp′)Y(CH 2SiMe 3) 2(THF) ( 1) and (η 5-Ind)Y(CH 2SiMe 3) 2(THF) ( 2) via alkane elimination, respectively. Complex 1 reacted with methoxyamino phenols, 4,6-(CH 3) 2-2-[(MeOCH 2CH 2) 2-NCH 2]-C 6H 2-OH (HL 1) and 4,6-(CMe 3) 2-2-[(MeOCH 2CH 2) 2-NCH 2]-C 6H 2-OH (HL 2) gave mixed ligands supported alkyl complexes [(η 5-Cp′)(L)]Y(CH 2SiMe 3) ( 3: L = L 1; 4: L = L 2). Whilst, complex 2 was treated with HL 2 to yield [(η 5-Ind)(L 2)]Y(CH 2SiMe 3) ( 5). The molecular structures of 3 and 5 were confirmed by X-ray diffraction to be mono(alkyl)s of THF-free, adopting pyramidal and tetragonal-bipyramidal geometry, respectively. Complexes 3 and 5 were high active initiators for the ring-opening polymerization of l-lactide to give isotactic polylactide with high molecular weight and narrow to moderate polydispersity.

Achiral Lanthanide Alkyl Complexes Bearing N,O Multidentate Ligands. Synthesis and Catalysis of Highly Heteroselective Ring-Opening Polymerization of rac-Lactide

Alkane elimination reactions of amino-amino-bis(phenols) H2L1-4, Salan H2L5, and methoxy-beta-diimines HL6,7 with lanthanide tris(alkyl) s, Ln(CH2SiMe3)(3)(THF)(2) (Ln = Y, Lu), respectively, afforded a series of lanthanide alkyl complexes 1-8 with the release of tetramethylsilane. Complexes 1-6 are THF-solvated mono( alkyl) s stabilized by O, N, N, O-tetradentate ligands. Complexes 1-3 and 5 adopt twisted octahedral geometry, whereas 4 contains a tetragonal bipyramidal core. Bearing a monoanionic moiety L-6 (L-7), complex 7 ( 8) is a THF-free bis(alkyl). In complex 7, the O, N, N-tridentate ligand combined with two alkyl species forms a tetrahedral coordination core. Complexes 1, 2, and 3 displayed modest activity but high stereoselectivity for the polymerization of rac-lactide to give heterotactic polylactide with the racemic enchainment of monomer units P-r ranging from 0.95 to 0.99, the highest value reached to date. Complex 5 exhibited almost the same level of activity albeit with relatively low selectivity. In contrast, dramatic decreases in activity and stereoselectivity were found for complex 4. The Salan yttrium alkyl complex 6 was active but nonselective. Bis(alkyl) complexes 7 and 8 were more active than 1-3 toward polymerization of rac-LA, however, to afford atactic polylactides due to di-active sites. The ligand framework, especially the bridge between the two nitrogen atoms, played a significant role in governing the selectivity of the corresponding complexes via changing the geometry of the metal center.

Pyrrolide-Ligated Organoyttrium Complexes. Synthesis, Characterization, and Lactide Polymerization Behavior

The N,N-bidentate ligand 2-{(N-2,6-diisopropylphenyl)iminomethyl)}pyrrole (L-1) and the N,N,P-tridentate ligand 2-{(N-2-diphenylphosphinophenyl)iminomethyl)}pyrrole (L-2) have been prepared. Their reactions with homoleptic yttrium tris(alkyl) compound Y(CH2SiMe3)(3)(THF)(2) have been investigated. Treatment of Y(CH2SiMe3)(3)(THF)(2) with 1 equiv of L-1 generated a THF-solvated bimetallic (pyrrolylaldiminato)yttrium mono(alkyl) complex (1) of central symmetry. In this process, L-1 is deprotonated by metal alkyl and its imino CN group is reduced to C-N by intramolecular alkylation, generating dianionic species that bridge two yttrium alkyl units in a unique eta(5)/eta(1):kappa(1) mode. The pyrrolyl ring behaves as a heterocyclopentadienyl ligand. Reaction of Y(CH2SiMe3)(3)(THF)(2) with 2 equiv of L-1 afforded the monomeric bis(pyrrolylaldiminato)yttrium mono(alkyl) complex (2), selectively. Amination of 2 with 2,6-diisopropylaniline gave the corresponding yttrium amido complex (3). In 3 the pyrrolide ligand is monoanionic and bonds to the yttrium atom in a eta(1):kappa(1) mode. The homoleptic tris(eta(1):kappa(1)-pyrrolylaldiminato)yttrium complex (4) was isolated when the molar ratio of L-1 to Y(CH2SiMe3)(3)(THF)(2) increases to 3:1. Reaction of L-2 with equimolar Y(CH2SiMe3)(3)(THF)(2) afforded an asymmetric binuclear complex (5).

Mono(amidinate) Yttrium Alkyl Complexes: The Effect of Ligand Variation on Ethene Polymerization Catalysis

AbstractYttrium dialkyl complexes were prepared for three different 2,6‐diisopropylphenyl‐substituted benzamidinate ligands. The electron‐donating ability of the parent ligand (L1) was decreased by a pentafluorophenyl backbone substituent (L2), and enhanced by addition of a pendant Lewis base (L3). The corresponding cationic monoalkyl species were generated and compared in catalytic ethene polymerization.

The 6-amino-6-methyl-1,4-diazepine group as an ancillary ligand framework for neutral and cationic scandium and yttrium alkyls

The 6-amino-6-methyl-1,4-diazepine framework is a readily available neutral 6-electron ligand moiety, suitable to support cationic group 3 metal alkyl catalysts; it also provides convenient access to tri- and tetradentate monoanionic ligand derivatives.

Yttrium Alkyl Complexes with Triamino−Amide Ligands

Two new monoanionic tetradentate triamino−amide ligands, [(Me2NCH2CH2)2N-B-N(t-Bu)]- (B = (CH2)2, L1; SiMe2, L2) were prepared. Reaction of L1H with Y(CH2SiMe3)3(THF)2 yielded L1Y(CH2SiMe3)2 (1), which was structurally characterized. Compound 1 decomposes at ambient temperature via metalation of one of the NMe2 methyl groups to give {[(CH2)MeN(CH2)2][Me2N(CH2)2]N(CH2)2N(t-Bu)}Y(CH2SiMe3) (2). Attempts to prepare L2Y(CH2SiMe3)2 resulted in very rapid ligand metalation. Both 1 and 2 react with [PhNMe2H][B(C6F5)4] to generate the cation [(L1)YCH2SiMe3]+. The combination of 1 and [Ph3C][B(C6F5)4] is active in catalytic ethene polymerization, but with a short catalyst lifetime. The metalated complex 2 reacts with ethene and with pyridine by stoichiometric insertion into the Y−CH2N bond, and the latter product was structurally characterized. In L1Y(X)(CH2SiMe3) complexes, the Y−amine distance trans to X is very sensitive to the nature of X, suggesting the presence of a trans influence.