The effect of the amido substituent on polymer molecular weight in propene homopolymerisation by titanium cyclopentadienyl-amide catalysts

In the homopolymerisation of propene by the cyclopentadienyl-amide titanium catalyst systems [η5,η1-C5H4(CH2)2NR]TiCl2/MAO and [η5,η1-C5H4(CH2)2NR]Ti(CH2Ph)2/B(C6F5)3 (R = tBu, iPr, Me), the catalyst with the smallest substituent (Me) on the amido moiety consistently gives the highest polymer molecular weight. This differs from the trend usually observed in related catalysts with tetramethylcyclopentadienyl-amide ancillary ligands, where larger amide substituents result in higher molecular weights. Based on the present information a hypothesis is formulated in which an increased cation-anion interaction for the less sterically hindered catalyst is responsible for disfavouring chain transfer relative to chain growth.

Carbon-bridged cyclopentadienyl amido group 4 metal complexes : ligand tuning and olefin polymerization

De organometaalchemie en vooral die van overgangsmetalen en lanthaniden heeft zich in 40-50 jaar buitengewoon sterk ontwikkeld. Niet alleen werd een breed gebied van synthese en karakterisatie van nieuwe verbindingen en uitgebreid reactiviteitsonderzoek ontsloten maar ook werd de ontwikkeling van nieuwe methoden en inzichten in meer toepassingsgerichte gebieden zoals de organische synthese maar vooral de (homogene en heterogene) katalyse door de organometaalchemie sterk gestimuleerd. ... Zie: Samenvatting

Competitive CH Activation in (Pentamethylcyclopentadienyl)(cyclooctatetraene)alkylzirconium Compounds Cp*Zr(COT)R. Selective Formation of Fulvene or Cyclooctatrienyne Ligands. Molecular Structure of Cp*Zr(μ-η8:η2-C8H6)ZrCp*(η4-C8H8), a Dinuclear Zwitt

Thermolysis of Cp*Zr(COT)R (Cp* = η5-C5Me5, COT = η8-C8H8, R = CH2SiMe3, Me) proceeds via a double hydrogen abstraction from a cyclooctatetraene ligand to give RH and Cp*Zr(μ-η8:η2-C8H6)ZrCp*(η4-C8H8) as the kinetic product. Cp*Zr(μ-η8:η2-C8H6)ZrCp*(η4-C8H8) undergoes a thermally induced hydrogen transfer from the pentamethylcyclopentadienyl ligands to the cyclooctatetraenediyl ligand to give the thermodynamic product FvZrCOT (Fv = η6-C5Me4CH2). For Cp*Zr(COT)R (R = CH2Ph) a different thermolysis reaction was observed, in which FvZrCOT was the major product at low temperatures, together with some Cp*Zr(μ-η8:η2-C8H6)ZrCp*(η4-C8H8). The latter does not convert into the thermodynamic product at the temperature of thermolysis, indicating an alternative, direct, thermal decomposition pathway to FvZrCOT for R = CH2Ph, with preferred hydrogen abstraction from the sp3 carbon of the pentamethylcyclopentadienyl ligand. Cp*Zr(μ-η8:η2-C8H6)ZrCp*(η4-C8H8) crystallizes in the monoclinic space group P21/n with a = 8.324 (2) Å, b = 15.966 (3) Å, c = 22.647 (3) Å, β = 92.56 (1)° , V = 3007 (1) Å3, and Z = 4. The molecular structure shows an unprecedented cyclooctatrienyne ligand, bridged asymmetrically between the Zr atoms. The formulation as a cyclooctatrienyne complex is formal; the actual bonding of the ligand is as a dimetalated η8-cyclooctatetraene-1,2-diyl. The diamagnetism of Cp*Zr(μ-η8:η2-C8H6)ZrCp*(η4-C8H8) implies a zwitterionic complex in which a 16-electron zirconium center [Cp*Zr(COT)]+ is connected to another 16-electron center [Cp*Zr(η4-C8H8)R2]- through a bridging η8-cyclooctetraene-1,2-diyl ligand.

Linked cyclopentadienyl-amido complexes of zirconium; ligand dependence of cation-anion interactions and ethene polymerisation activity

A range of zirconium dichloride complexes [C5H4(CH2)nNR]ZrCl2 (n = 2, R = iPr, tBu; n = 3, R = Me, Et, iPr) with linked cyclopentadienyl-amide ancillary ligands were prepared by amine elimination routes. Their dibenzyl derivatives [C5H4(CH2)nNR]Zr(CH2Ph)2 react with B(C6F5)3 to give the ionic species {[C5H4(CH2)nNR]Zr(CH2Ph)}[PhCH2B(C6F5)3]. In bromobenzene solvent, the position of the equilibrium between the solvent-separated ion pair and the species in which the anion is η6-coordinated to the metal centre through the B-benzyl phenyl group is strongly dependent on ligand bridge length and substitution. This gives an indication of the overall steric requirement of the ligand system. The activity of the [C5H4(CH2)nNR]ZrCl2/methylaluminoxane catalysts in the homopolymerisation of ethene was probed. The [C5H4(CH2)nNiPr]Zr-system found to be several times more efficient for n = 3 than for n = 2, with the [C5H4(CH2)3NMe]Zr-system being the most active of the compounds studied.

Titanium Dichloro, Bis(carbyl), Aryne, and Alkylidene Complexes Stabilized by Linked Cyclopentadienyl-Amido Auxiliary Ligands

Thermal decomposition of the carbyl compounds {C5H4(CH2)2NR}TiR´2 proceeds through α- and β-H elimination to give stable aryne, alkylidene, and olefin complexes in the presence of PMe3. Reaction of the dibenzyl compound {C5H4(CH2)2N-t-Bu}Ti(CH2Ph)2 with B(C6F5)3 gives the cationic [{C5H4(CH2)2N-t-Bu}TiCH2Ph]+, which is an active catalyst for the polymerization of ethene and propene.