| Popis: |
The most common homogeneous Ziegler type catalysts for ring-opening metathesis polymerization (ROMP) of cycloolefins are composed of salts or complexes of W or Mo (usually WCl6) and organometallic derivatives of Al, Sn, Li or Mg [1]. The main role of the latters is to alkylate the transition metal with the formation of σ-metal-carbon bond of relatively low stability. Although the decomposition of such organometallic compounds proceeds mostly via β-H-elimination or β-disproportionation reactions, recent data shows [2] that these reactions are always accompanied, if only to a small extent, by α-elimination (or disproportionation) giving metal-carbene complexes - the active centres of the ROMP. |
