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.

Oxidative alkylation of (η5-C5Me5)2TiR (R = Cl, Me, Et, CH=CH2, Ph, OMe, N=C(H)tBu) to (η5-C5Me5)2Ti(Me)R by group 12 organometallic compounds MMe2

Oxidative alkylation of Cp*2TiX (Cp*: η5-C5Me5; X = OMe, Cl, N=C(H)tBu) and Cp* 2TiMe by CdMe2 or ZnMe2 gives diamagnetic Cp*2Ti(Me)X and Cp*2TiMe2 respectively, and cadmium or zinc. The reactions of Cp*2TiR (R = Et, CH=CH2, Ph) with MMe2 (M = Cd, Zn) give statistical mixtures of Cp*2Ti(Me)R, Cp*2TiMe2 and Cp*2TiR2. Dimethylmercury does not react with Cp*2TiX.

Synthesis of heteroatom end-functionalized polyethene with lanthanide and transition-metal catalysts

Incorporation of heteroatom functionalities in the catalytic formation of polyolefin materials can be accomplished either by copolymerization of the olefin with an olefinic substrate that has a heteroatom-containing substituent, or by using a heteroatom-containing chain-transfer agent. In the first case the functionalities introduced are located in side-groups on the polyolefin backbone, in the second case the functionality will cap the polymer on one end of the chain. The latter strategy has been applied recently using chain-transfer agents with reactive X-H bonds (X = Si, B) in conjunction with group 3 and group 4 metal catalysts. We have sought to apply the capacity of lanthanide metallocenes to perform ethene polymerization as well as C-H activation to this chemistry, using heteroatom-containing hydrocarbons with activated C-H bonds as chain-transfer agents, and to compare this with analogous cationic group 4 metallocenes