Metal-alkylidynes electrophile reactions

In Chapter 8 we described how metal carbides (first mentioned in Section 6-1-4) could serve as precursors to carbyne complexes by way of electrophilic addition. Scheme 10.8 revisits a portion of Scheme 8.12, showing Os-carbide complex 72—with its nucleophilic Ccarbide atom—reacting with methyl triflate or tropylium ion to give alkylidynes 73 and 74, respectively. Comparable reactions occur with the corresponding Ru-carbide complex.87 This method may become more general after the synthesis of additional carbide complexes occurs. 

Reactivity modes of the poly(pyrazolyl)borate alkylidyne complexes follow a number of recognised routes for transition metal complexes containing metal-carbon triple bonds, including ligand substitution or redox reactions at the transition metal centre, insertion of a molecule into the metal-carbon triple bond, and electrophilic or nucleophilic attack at the alkylidyne carbon, C. Cationic alkylidyne complexes generally react with nucleophiles at the alkylidyne carbon, whereas neutral alkylidyne complexes can react at either the metal centre or the alkylidyne carbon. Substantive work has been devoted to neutral and cationic alkylidyne complexes bearing heteroatom substituents. Differences between the chemistry of the various Tp complexes have previously been rationalised largely on the basis of steric effects. 

---