Peter Voth

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 polymerization. To arrive at neutral 12-electron hydride and alkyl species of the rare earth metals, we employed a lanthanide tris(alkyl) complex [Ln(CH 2 SiMe 3 ) 3 (THF) 2 ] (Ln=Y, Lu, Yb, Er, Tb), which allows the facile synthesis of the linked amido-cyclopentadienyl complex [Ln(η 5 :η 1 -C 5 Me 4 SiMe 2 NCMe 3 )(CH 2 SiMe 3 )(THF)]. Hydrogenolysis of the linked amido-cyclopentadienyl alkyl complex leads to the dimeric hydrido complex [Ln(η 5 :η 1 -C 5 Me 4 SiMe 2 NCMe 3 )(THF)(μ-H)] 2 . These complexes are single-site, single-component catalysts for the polymerization of ethylene and a variety of polar monomers such as acrylates and acrylonitrile. Nonpolar monomers such as α-olefins and styrene, in contrast, give isolable mono-insertion products which allow detailed studies of the initiation process.

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

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) ] [R = (CH2) nCH3, n = 3-9], prepared by the mono (insertion) of a-olefins, initiate polymerization in a relatively controlled manner. Thus, styrene was polymerized by the n-alkyl complex to give atactic polystyrenes with somewhat enriched syndiotacticities.

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 well as alkyl acrylate and acrylonitrile. The hydrido complexes polymerize ethylene slowly, whereas they form isolable mono(insertion) products with α-olefins and with styrene. The yttrium n-alkyl complexes [Y(η5:η1,-C5Me4SiMe2NCMe3)(R)(THF)n] (R = (CH2)nCH3, n = 3-9), prepared by the mono(insertion) of α-olefins, initiate polymerization of styrene in a relatively controlled manner. Thus, styrene was polymerized by the in-situ formed n-hexyl complex to give atactic polystyrenes with narrow molecular weight distributions and somewhat enriched syndiotacticities. Sequential addition of terf-butyl acrylate allows the synthesis of poly(styrene-block- tert-butyl acrylate).