New divalent samarocenes for butadiene polymerisation: influence of the steric effect and the electron density on the catalytic activity

Two new divalent samarocenes, Cp*′2Sm(THF) (1) and (CpPh3)2Sm(THF) (2) (Cp*′=C5Me4nPr, CpPh3=H2C5Ph3-1,2,4), were synthesized and characterized by 1H NMR and elemental analysis. The activity of 1 and 2 as butadiene polymerisation catalysts was studied, in the presence of MAO and MMAO, and compared to this of Cp*2Sm(THF)2 (3) and (Cp4i)2Sm (4) (Cp*=C5Me5, Cp4i=C5HiPr4), in the same conditions. The 1/MAO system presents the highest activity. The less active 2/MAO system leads to a high cis-1,4 regular structure up to 97%. The MMAO cocatalyst is found very sensitive to the steric hindrance of the samarocenes: the activity decreases from 1/MAO to 1/MMAO, and no activity is observed in the case of complexes 2 and 4, associated to MMAO. Complexes 1 and 2 can be both oxidized with AlMe3 to give the corresponding Sm/Al bimetallics and , respectively.