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Mechanism of Alkene Insertion

In the Cossee-Arlman mechanism insertion is considered to be direct. The transition state of 6.5 to 6.6 by the Cossee-Arlman mechanism is therefore as designated by 6.8. In 6.8, for clarity the Cl ligands are not shown and represents the growing polymer chain. [Pg.111]

As we saw in Section 2.2.2, an interaction between metal and the a-hydro-gen of an alkyl group is called an agostic interaction. In an extreme situation, where the interaction between the metal atom and the a-hydrogen leads to formal cleavage of the carbon-hydrogen bond, a mechanism involving a metal-carbene intermediate may be invoked. This proposal is known as the Green and Rooney mechanism, and two of the proposed catalytic intermediates are shown by 6.9 and 6.10. [Pg.111]

The heterogeneous character of the conventional Ziegler-Natta catalyst makes studies directed towards mechanistic and structural elucidation at a molecular level extremely difficult. Experimental evidence is therefore sought from homogeneous metallocene and other related catalysts (see Section 6.5). Such evidence does not support the Green-Rooney mechanism. [Pg.112]


Shmidt, A. F., Khalaika, A., Nindakova, L. O., Shmidt, E. Y. Mechanism of alkene insertion into the Pd-Ar bond in the Heck reaction. Kinetics and Catalysis (Translation ofKinetika i Kataliz) 1998, 39, 200-206. [Pg.597]

The mechanisms of alkene insertions are known for some square-planar Pt(II) complexes , but it is difficult to distinguish between pathways in which a four-coordinated alkene/hydride species collapses by migratory insertion to a three-coordinated (perhaps solvated) species, and pathways in which a five-coordinated alkene/hydride collapses to a four-coordinated product. Both pathways occur, depending on the ligands. The rates of insertion of ethylene into the neutral and cationic hydrides trans-PtHX(PEt3)2 and trans-[PtHL(PEt3)2] + (X = Cl , NOj", CN L = acetone, CO, PEtj, AsPha, P(OMe)3 and P(OPh)3) leads to Scheme 1 °. [Pg.566]


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