Why propene is not polymerized by (Cp*2YH)2: reactions of yttrium alkyl complexes with alkenes produce allyl and vinyl yttrium complexes

Yttrium alkyl complexes Cp*2YR react with C&z.sbnd;H bonds of alkenes to form either yttrium allyl complexes or yttrium vinyl complexes. Less substituted alkenes react faster, consistent with prior alkene coordination. The selectivity of the reaction of Cp*2YR with C&z.sbnd;H bonds is allylic CH3≫vinyl C&z.sbnd;H≫allylic CH2. Propene is readily metallated by Cp*2YR giving the η3-allyl complex Cp*2Y(η3-CH2<f>⋯¯</f>CH<f>&z.sbnd;&z.tDot;</f>CH2) which does not react further with propene. This explains why Cp*2YR (R=alkyl, H) complexes make poor propene polymerization catalysts. [Copyright &y& Elsevier]