= Solution
<oxidative addition> of an intact Si–H bond initially places \b[H and SiR$_3$ cis] in the <metal> coordination sphere; this is the local arrangement generated by addition of a <sigma bond>. <hydride> and <alkene> must also attain adjacent sites for intramolecular insertion, and the eventual alkyl and silyl groups must be cis for direct <reductive elimination>. Subsequent rearrangements should not be confused with the <stereochemistry> of the bond-addition event itself.
For an alkyl-substituted terminal <alkene>, insertion puts \b[Co on the terminal <carbon> and H on the substituted <carbon>], producing $\mathrm{Co{-}CH_2CH_2R}$. It avoids the more crowded secondary <metal>–alkyl arrangement. Replacement of that Co–C bond by C–Si therefore gives \b[the linear product $\mathrm{RCH_2CH_2SiR_3}$], an <Anti-Markovnikov addition> outcome. Hydrometallation is syn at the coordinated <alkene>, although this simple terminal substrate generally does not retain two substituents whose relative <stereochemistry> could diagnose the complete sequence.
Back to article page
