Reactivity Studies on Lanthanum and Cerium Hydrido Metallocenes

The alkyl complexes [5-1,3-(Me3C)2C5H3]2Ln(CH2C6H4-o-NMe2) (Ln = La 1, Ce 2) react with 9-borabicyclo[3.3.1]nonane (9-BBN) in THF to afford the lanthanum boroxide complex [5-1,3-(Me3C)2C5H3]2La(µ-OBC8H14)(THF) (3) and cerium boroxide complex [5-1,3-(Me3C)2C5H3]2Ce(µ-OBC8H14)(THF) (4)....

Synthesis and characterisation of an enantiomerically pure scandium pentadienyl complex and its application in the polymerisation of rac-lactide

The alkyl-functionalised scandium complex [(pdl*SiMe₂N^tBu)Sc(thf)(CH₂SiMe₃)] (2) was synthesised in enantiomerically pure form and characterised by NMR spectroscopy and X-ray diffraction analysis. Complex 2 features a chiral constrained geometry ligand derived from the natural compound (1R)-(-)-myrtenal, in which the pentadienyl (pdl*) fragment coordinates in η³:η²-allyl-en fashion to the scandium atom. Compound 2 catalyses the polymerisation of rac-lactide at 30 °C and 50 °C yielding amorphous poly(lactide) with slightly heterotactic enchainment (P_m = 0.36 and 0.37). In agreement with the data obtained from GPC and DSC measurements, a chain-end control mechanism is proposed with fast chain propagation relative to the initiation, which leads to broad molecular weight distributions (Đ ≈ 1.80) and higher than expected molecular weights. Furthermore, chain transfer processes are observed, but only small amounts of transesterification and racemisation occur. Kinetic studies reveal a second-order dependence in rac-lactide (monomer) concentration and a first-order dependence in the concentration of catalyst 2.

Enantiomerically Pure Constrained Geometry Complexes of the Rare-Earth Metals Featuring a Dianionic N-Donor Functionalised Pentadienyl Ligand: Synthesis and Characterisation

We report the preparation of enantiomerically pure constrained geometry complexes (cgc) of the rare-earth metals bearing a pentadienyl moiety (pdl) derived from the natural product (1R)-(-)-myrtenal. The potassium salt 1, [Kpdl*], was treated with ClSiMe₂ NHtBu, and the resulting pentadiene 2 was deprotonated with the Schlosser-type base KOtPen/nBuLi (tPen=CMe₂ (CH₂ Me)) to yield the dipotassium salt [K₂ (pdl*SiMe₂ NtBu)] (3). However, 3 rearranges in THF solution to its isomer 3' by a 1,3-H shift, which elongates the bridge between the pdl and SiMe₂ NtBu moieties by one CH₂ unit. This is crucial for the successful formation of various monomeric C₁ - or dimeric C₂ -symmetric rare-earth cgc complexes with additional halide, tetraborohydride, amido and alkyl functionalities. All compounds have been extensively characterised by solid-state X-ray diffraction analysis, solution NMR spectroscopy and elemental analyses.

l- and rac-lactide polymerisation using scandium and aluminium permethylindenyl complexes

Scandium and aluminium constrained geometry permethylindenyl complexes are reported and their lactide polymerisation study discussed.

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.

Lanthanocene and Cerocene Alkyl Complexes: Synthesis, Structure, and Reactivity Studies

Lanthanocene and cerocene alkyl complexes [η⁵-1,3-(Me₃C)₂C₅H₃]₂Ln(CH₂C₆H₄-o-NMe₂) (Ln = La 3 and Ce 4) were obtained from the salt metathesis of {[η⁵-1,3-(Me₃C)₂C₅H₃]₂Ln(μ₃-κ³-O₃SCF₃)₂K(THF)₂}₂·THF (Ln = La 1·THF and Ce 2·THF) with LiCH₂C₆H₄-o-NMe₂. Reactivity of 3 and 4 toward various small molecules provides access to a series of lanthanide derivatives. For example, reactions of 3 and 4 with elemental chalcogens (sulfur and selenium) in 1:1 molar ratio give the lanthanide thiolates {[η⁵-1,3-(Me₃C)₂C₅H₃]₂Ln(μ-SCH₂C₆H₄-o-NMe₂)}₂ (Ln = La 5 and Ce 6) and selenolates {[η⁵-1,3-(Me₃C)₂C₅H₃]₂Ln(μ-SeCH₂C₆H₄-o-NMe₂)}₂ (Ln = La 7 and Ce 8). The compounds 3 and 4 react with two equivalents of elemental chalcogens (sulfur and selenium) to afford the lanthanide disulfides {[η⁵-1,3-(Me₃C)₂C₅H₃]₂Ln}₂(μ-η²:η²-S₂) (Ln = La 9 and Ce 10) and diselenides {[η⁵-1,3-(Me₃C)₂C₅H₃]₂Ln}₂(μ-η²:η²-Se₂) (Ln = La 11 and Ce 12). The lanthanide disulfides (9 and 10) or diselenides (11 and 12) can also be readily obtained through oxidation of the corresponding lanthanide thiolates (5 and 6) or selenolates (7 and 8) by elemental chalcogens concomitant with the (Me₂N-o-C₆H₄CH₂)₂E₂ (E = S or Se) release. Treatment of 3 and 4 with one equivalent or two equivalents of benzonitrile produces the serendipitous lanthanum and cerium-1-azaallyl complexes [η⁵-1,3-(Me₃C)₂C₅H₃]₂Ln[N(H)C(Ph)═CHC₆H₄-o-NMe₂] (Ln = La 13 and Ce 14) or amidine complexes [η⁵-1,3-(Me₃C)₂C₅H₃]₂Ln[N(H)C(Ph)NC(Ph)═CHC₆H₄-o-NMe₂]·C₇H₈ (Ln = La 15·C₇H₈ and Ce 16·C₇H₈), respectively. The compound 15 or 16 can also be readily synthesized by further insertion of one benzonitrile molecule into the 1-azaallyl complex 13 or 14. Insertion of N,N'-dicyclohexylcarbodiimide or phenyl isothiocyanate into Ln-C bonds within 3 and 4 results in the formation of the amidine complexes [η⁵-1,3-(Me₃C)₂C₅H₃]₂Ln[CyNC(CH₂C₆H₄-o-NMe₂)NCy] (Cy = cyclohexyl, Ln = La 17 and Ce 18) or thioamidato complexes [η⁵-1,3-(Me₃C)₂C₅H₃]₂Ln[SC(CH₂C₆H₄-o-NMe₂)NPh] (Ln = La 19 and Ce 20). All of the new compounds were characterized by various spectroscopic methods, and their solid-state structures were further confirmed by single-crystal X-ray diffraction analyses.

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.

Zirconium complexes based on an ethylene linked amidinate–amido ligand: synthesis, characterization and ethylene polymerization

Monomer/dimer zirconium complexes 4–6 were synthesized by changing the molar ratio of ZrCl4 : ligand. The catalytic behaviors of these zirconium complexes were investigated in the presence of MAO as a cocatalys.

Group IV compounds bearing a novel tridentate N-donor ligand: synthesis, structures and ethylene polymerization

In this paper, treatment of [PhN(CH₂)₃NC(Ph)NSiMe₃]₂Li₄·2Et₂O with group IV metal chlorides yields corresponding compounds 3–5. The catalytic behaviors of 3–5 were investigated in the presence of MAO as co-catalyst for ethylene polymerization.

Metallacyclic yttrium alkyl and hydrido complexes: synthesis, structures and catalytic activity in intermolecular olefin hydrophosphination and hydroamination

Metallacyclic neutral and ionic yttrium alkyl complexes coordinated by a dianionic ene-diamido ligand ([2,6-iPr2C6H3NC(Me)=C(Me)NC6H3iPr2-2,6] = L(1)) [L(1)]Y(CH2SiMe3)(THF)2 (2), {[L(1)]Y(CH2SiMe3)2}(-){Li(THF)4}(+) (3), [L(1)]Y(OEt2)(μ-Me)2Li(TMEDA) (4) were synthesized using a salt-metathesis approach starting from the related chloro complex [L(1)]Y(THF)2(μ-Cl)2Li(THF)2 (1) in 70, 85 and 72% yields respectively. The reactions of 2 with H2 or PhSiH3 afford the dimeric hydride {[L(1)]Y(THF)(μ-H)}2(μ-THF) (5) containing two μ-bridging hydrido and one μ-bridging THF ligands (91 and 85% yields). The X-ray studies of complexes 2, 3 and 5 revealed η(2)-coordination of the C=C fragment of an ene-diamido ligand to a Y cation. DFT calculations were carried out to give an insight into the metal-ligand bonding and especially the interaction between the metal and the ene-diamido ligand. The observed bonding of the ene-diamido fragment is found to reflect the acidity of the metal center in the complex that is partially overcome by a better donation from the double bond (better overlap with an empty d orbital at the yttrium center). The treatment of complex 4 with DME resulted in the C-O bond cleavage of DME and afforded a three nuclear methoxide oxide complex [{[L(1)]Y}3(μ(2)-OMe)3(μ(3)-O)](2-)[Li(DME)3](+)2 (6). Complexes 2, 3, 5 and 7 proved to be efficient precatalysts for the intermolecular hydrophosphination of styrene, 4-vinylpyridine, and 1-nonene with PhPH2 and Ph2PH as well as hydroamination of styrene and pyrrolidine.

Synthesis, structure and reactivity of rare-earth metallacarborane alkyls [η(1):η(5)-O(CH2)2C2B9H9]Ln(σ:η(1)-CH2C6H4-o-NMe2)(THF)2

Rare-earth metallacarborane alkyls can be stabilized by the incorporation of a functional sidearm into both π and σ ligands. Reaction of [Me3NH][7,8-O(CH2)2-7,8-C2B9H10] with one equiv. of Ln(CH2C6H4-o-NMe2)3 gave metallacarborane alkyls [η(1):η(5)-O(CH2)2C2B9H9]Ln(σ:η(1)-CH2C6H4-o-NMe2)(THF)2 (Ln = Y (), Gd (), Er ()) via alkane elimination. They represent the first examples of rare-earth metallacarborane alkyls. Treatment of with RN[double bond, length as m-dash]C[double bond, length as m-dash]NR (R = Cy, (i)Pr) or 2-benzoylpyridine afforded the corresponding mono-insertion products [η(1):η(5)-O(CH2)2C2B9H9]Y[η(2)-(RN)2C(CH2C6H4-o-NMe2)](DME) (R = Cy (), (i)Pr ()) or [η(1):η(5)-O(CH2)2C2B9H9]Y[C5H4NC(Ph)(CH2C6H4-o-NMe2)O](THF)2 (), respectively. Complex also reacted with ArNCO or ArNC (Ar = 2,6-diisopropylphenyl, 2,6-dimethylphenyl) to give di-insertion products [η(1):η(5)-O(CH2)2C2B9H9]Y[OC([double bond, length as m-dash]NC6H3Me2)N(C6H3Me2)C(CH2C6H4-o-NMe2)O](THF)2 () or [η(1):η(5)-O(CH2)2C2B9H9]Y[C([double bond, length as m-dash]NC6H3(i)Pr2)C([double bond, length as m-dash]NC6H3(i)Pr2)(CH2C6H4-o-NMe2)](DME) (). These results showed that the reactivity pattern of the Ln-C σ bond in rare-earth metallacarborane alkyls was dependent on the nature of the unsaturated organic molecules. New complexes were characterized by various spectroscopic techniques and elemental analysis. Some were further confirmed by single-crystal X-ray analysis.

Half-sandwich scandium boryl complexes bearing a silylene-linked cyclopentadienyl-amido ligand

A boryl scandium complex supported by the silylene-linked cyclopentadienyl-amido ligand was synthesized for the first time.

Trinuclear alkyl hydrido rare-earth complexes supported by amidopyridinato ligands: synthesis, structures, C–Si bond activation and catalytic activity in ethylene polymerization

[(Ap^9MeLu)₃(μ²-H)₃(μ³-H)₂(CH₂SiMe₃)(thf)₂] was synthesized. For Y and Yb C–Si bond activation occurs affording [(Ap^9MeLu)₃(μ²-H)₃(μ³-H)₂(CH₂SiMe₃)(thf)₂] and [(Ap^9MeLn)₃(μ²-H)₃(μ³-H)₂(CH₂SiH₂Ph)(thf)₂].

A double addition of Ln-H to a carbon-carbon triple bond and competitive oxidation of ytterbium(II) and hydrido centers

Addition of two Ln-H bonds of an Yb(II) hydrido complex supported by bulky amidinate ligand to a C≡C bond lead to the formation of 1,2-dianionic bibenzyl fragment. Both Yb(II) and hydrido centers are oxidized under the reaction conditions. The resulting Yb(II)-η(6) -arene interaction is surprisingly robust: the arene cannot be replaced from the metal coordination sphere when treated with Lewis bases.