Insertion mechanisms primary 1-alkene insertions

Most recently an example of a ruthenium catalyzed selective addition of primary silanes to alkenes was shown to involve ruthenium silylenes as intermediates (Scheme 5). A remarkable feature of this mechanism is, that the insertion of the alkene does not occur either into a metal-hydride or... 

Possible mechanisms for chain-end stereocontrol for catalytic systems presenting primary and secondary 1-alkene (mainly propene) insertion will be described in Sections 4.1.1 and 4.1.2, respectively. 

According to the Brady-Pettit mechanism (34,35), shown in Scheme 3, chain growth occurs via insertion of CH2 between the surface site and the growing alkyl chain. Termination occurs through H addition or abstraction. According to this mechanism, alkanes and alkenes are predicted to be primary products, as is observed experimentally (91). Moreover, oxygen-containing compounds are predicted to be primary products formed via CO insertion, as discussed in Section 2.1. 

Pioneering studies by Emmet suggested in 1953 that ethylene acts as a chain initiator in Fe-catalyzed Fischer-Tropsch reactions. Many authors have used isotopi-cally labeled olefins to confirm that 1-alkenes are the primary reaction products (although they are thermodynamically instable under the reaction conditions). For instance, Somorjai s group has shown, using a polycrystalline iron sheet (1 cm ), that the addition of ethylene or propene in the syn gas increases the length of the polymer chain. These olefins readsorb and readily form polymers by insertion into adsorbed C fragments. Thus, the Fischer-Tropsch mechanism involves two steps, namelly the formation of olefins and their polymerization ... 

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