Dimeric n-Alkyl Complexes of Rare-Earth Metals Supported by a Linked Amido−Cyclopentadienyl Ligand:  Evidence for β-Agostic Bonding in Bridging n-Alkyl Ligands and Its Role in Styrene Polymerization

The dimeric rare-earth hydrides [Ln(η^5:η^1-C_5Me_4SiMe_2NCMe_3)(THF)(μ-H)]_2 (Ln = Y, Yb) react with excess α-olefin H_2C ═ CHR (R = Et, ^nPr, ^nBu) in a 1,2-insertion to give the series of THF-free dimeric n-alkyl complexes [Ln(η^5:η^1-C_5Me_4SiMe_2NCMe_3)(μ-CH_2CH_2R)]_2 as isolable crystals. Single-crystal X-ray diffraction studies on the five derivatives [Y(η^5:η^1-C_5Me_4SiMe_2NCMe_2R‘)(μ-CH_2CH_2R)]_2 (R‘ = Me, R = Et, ^nBu; R‘ = Et, R = Et, ^nPr) and [Yb(η^5:η^1-C_5Me_4SiMe_2NCMe_3)(μ-CH_2CH_2^nBu)]_2 revealed that the centrosymmetric dimeric complexes consist of two trans-arranged [Ln(η^5:η^1-C_5Me_4SiMe_2NCMe_2R‘)] fragments connected by two μ-alkyl ligands. Most strikingly, there…

Rare earth metal-based catalysts for the polymerization of nonpolar and polar monomers

Abstract The synthesis of rare earth metal half-sandwich hydrido complexes [Ln (h5:h1-C5Me 4SiMe2NCMe3) (THF) (µ-H) ] 2 (Ln = Y, Lu) through s-bond metathesis of the easily accessible alkyl complexes [Ln (h5:h1-C5Me 4SiMe2NCMe3) (CH2 SiMe3) (THF) ] was developed. The dimeric yttrium hydrido complexes are highly fluxional, and a monomer-dimer equilibrium is present. They were tested as single-site, single-component catalysts for the polymerization of ethylene and styrene, as well as alkyl acrylate and acrylonitrile. The hydrido complexes polymerize ethylene slowly and form isolable mono (insertion) products with styrene. The yttrium n-alkyl complexes [Y (h5:h1-C5Me 4SiMe2NCMe3) (R) (THF) ] […

Rare Earth Half-Sandwich Catalysts for the Homo- and Copolymerization of Ethylene and Styrene

The synthesis of rare earth metal half-sandwich hydrido complexes [Ln(η5:η1-C5Me4SiMe2NCMe3)(THF)(μ-H)]2(Ln = Y, Lu, Yb, Er, Tb) through σ-bond metathesis of the alkyl complexes [Ln(η5:η1- C5Me4SiMe2NCMe3)(CH2SiMe3)(THF)], easily accessible by the reaction of the amino-cyclopentadiene with [Ln(CH2SiMe3)3(THF)2], was developed. The dimeric lanthanide hydrido complexes are highly fluxional involving THF dissociation and cis-trans isomerization of the linked amidocyclopentadienyl ligand. The presence of a monomer-dimer equilibrium is suggested by cross-over experiments. They were tested as single-site, single-component catalysts for the polymerization of ethylene, α-olefin, and styrene, as wel…

Single-Component Polymerization Catalysts for Ethylene and Styrene:  Synthesis, Characterization, and Reactivity of Alkyl and Hydrido Yttrium Complexes Containing a Linked Amido−Cyclopentadienyl Ligand

Yttrium alkyl complexes Y(η5:η1-C5Me4SiMe2NCMe2R)(CH2SiMe3)(THF) (R = Me, Et) and Y(η5:η1-C9H6SiMe2NCMe3)(CH2SiMe3)(THF) can be prepared in high yields by a σ-bond metathesis reaction between Y(CH2SiMe3)3(THF)2 and amino-functionalized cyclopentadienes or indene. The structure of Y(η5:η1-C5Me4SiMe2NCMe2Et)(CH2SiMe3)(THF) was shown by single-crystal X-ray diffraction to be that of a three-legged piano stool. Reaction of Y(CH2SiMe3)3(THF)2 with the tridentate linked amido−cyclopentadienyl ligands (C5Me4H)SiMe2NHR (R = CH2CH2OMe, CH2CH2NMe2, CH2CH2CH2OMe, CMe2CH2OMe), which contain an additional donor site, results in the cleavage of the silicon−cyclopentadienyl bond and the formation of the t…

Hydrogenolysis of the dialkyl complexes [Y(η5-C5Me4SiMe2R)(CH2SiMe3)2(THF)] (1a, R = Me; 1b, R = Ph) results in the formation of the tetranuclear dihydrido complexes [{(η5-C5Me4SiMe2R)Y}4(μ-H)4(μ3-H)4(THF)2] (2a, R = Me; 2b, R = Ph), characterized by NMR spectroscopy. 2a was studied by single crystal X-ray diffraction. In the solid state, an unsymmetrical tetrahedral configuration of four [Y(η5-C5Me4SiMe3)] units is observed, two of which contain each one molecule of THF. Each yttrium atom is bonded to two μ2- as well as three μ3-bridging hydrido ligands. Synthese und Charakterisierung eines vierkernigen Hydrid-Clusters von Yttrium [{η5-(C5Me4SiMe3)Y}4(μ-H)4(μ3-H)4(THF)2] Die Hydrogenolyse …

Dimeric Hydrido Complexes of Rare-Earth Metals Containing a Linked Amido−Cyclopentadienyl Ligand:  Synthesis, Characterization, and Monomer−Dimer Equilibrium

Dimeric hydrido complexes of lutetium, ytterbium, and yttrium containing a linked amido−cyclopentadienyl ligand, [Ln(η5:η1-C5Me4SiMe2NCMe2R)(L)(μ-H)]2 (Ln = Lu, Yb, Y; R = Me, Et; L = THF, PMe3), w...

Yttrium Alkyl and Hydrido Complexes Containing a Tridentate-Linked Amido-Cyclopentadienyl Ligand

A tridentate-linked amido-cyclopentadienyl ligand (C5Me4CH2SiMe2NCH2CH2NMe2)2- (L) was coordinated at yttrium to give the alkyl complex [Y(L)(CH2SiMe3)(THF)] (2), which reacts with H2 to give the T...

Group 3 and 4 metal alkyl and hydrido complexes containing a linked amido-cyclopentadienyl ligand: “constrained geometry” polymerization catalysts for nonpolar and polar monomers

Abstract In order to understand the nature of the putative cationic 12-electron species [M(η 5 :η 1 -C 5 R 4 SiMe 2 NR′)R″] + of titanium catalysts supported by a linked amido-cyclopentadienyl ligand, several derivatives with different cyclopentadienyl C 5 R 4 and amido substituents R′ were studied systematically. The use of tridentate variants (C 5 R 4 SiMe 2 NCH 2 CH 2 X) 2− (C 5 R 4 =C 5 Me 4 , C 5 H 4 , C 5 H 3 t Bu ; X=OMe, SMe, NMe 2 ) allowed the NMR spectroscopic observation of the titanium benzyl cations [Ti(η 5 :η 1 -C 5 Me 4 SiMe 2 NCH 2 CH 2 X)(CH 2 Ph)] + . Isoelectronic neutral rare earth metal complexes [Ln(η 5 :η 1 -C 5 R 4 SiMe 2 NR′)R″] can be expected to be active for pol…