Insertion propene into metal-carbon bond

Since the 1960s the syndiospecific chain-end controlled polymerization of propene in the presence of homogeneous vanadium-based catalytic systems has been known. For these systems, it has been well established by the work of Zambelli and co-workers that the polymerization is poorly regioselective and the stereoselective (and possibly syndiospecific) step is propene insertion into the metal secondary carbon bond with formation of a new secondary metal-carbon bond.133134... 

Stereospecific Inserting propene or other w-olefins into a metal carbon bond, a chiral carbon is formed by the tertiary carbon atom M-CH2-CH(CH3)-R. There are two enantiomers (configuration) possible (by Fis-cherprojection methyl group to the top or to the bottom). Different catalysts can synthesize the different configurations (see Fig. 15). 

Iron complex (55) also reacts with H2 to produce methane and ethene to afford propene <80JA1752>. Both reactions appear to involve insertion into a metal-carbon bond followed by elimination. When osmium complex (56) adds ethene, the diosmacyclopentane which results from ethene addition is isolated. When terminal alkynes react with (55), an alkene-substituted ring carbon results... 

On the basis of the fact that (R)-BMPP coordinated to the metal center can induce asymmetric addition of methyldichlorosilane across the carbon-carbon double bond of 2-substituted propenes to afford an enantiomeric excess of (R)-2-substituted propylmethyldichlorosilanes, the following processes should be involved in these reactions (a) insertion of the metal center into the silicon-hydrogen bond (oxidative addition of the hydrosilane) (b) addition of the resulting hydridometal moiety to the coordinated olefin preferentially from its re face (in a cis manner) to convert the olefin into an alkyl-metal species and (c) transfer of the silyl group from the metal center to the alkyl carbon to form the product. Since process (b) most likely involves diastereomeric transition states or intermediates, the overall asymmetric bias onto the R configuration at the chiral carbon would have already been determined prior to process (c). A schematic view of such a process is given in Scheme 1. 

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