Nucleophilic attack by unsaturated carbon

The propargyl ligand is electronically analogous to the allyl if both are bound to the metal via 7 -coordination. If bound in the 7 -form, the former may generate considerably higher strain compared to the 7 -allyl system. The 7 -propargyl ligand 

When making bond with the allyl carbon, the nucleophile can approach it from both sides of the allyl plane (opposite to and same as the metal atom), with this dichotomy being analogous to that encountered in the reaction of alkene/alkyne 

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