Is the Glaser coupling reaction possible with metal alkyne complexes?

Question

As the Glaser coupling reaction is usually done with terminal alkynes with the hydrogen being straight, I wonder if the same reaction can occur in terminal alkynes connected to the backbone of a metal alkyne complexe.

As an example, in the trimerization reaction of acetylene, which happens with the formation of a metal alkyne complete; the hydrogens are bent in a v-shape to the carbon; not straight. Alkyne Trimerisation.

Would it be possible? If it weren’t the case, what would impede this reaction?

Answer 1

The hydrogen being straight corresponds to its sigma bond with carbon having more carbon $2s$ character and less carbon $2p$ character, which makes the covalent overlap somewhat less and the bond more polar. Thus the hydrogen is susceptible to deprotonation by the strong base that initiates the reaction.

If the bond angle becomes bent due to the electronic contributions from the metal, we have lost some $2s$ character in the carbon-hydrogen bond in favor of more $2p$, and the required deprotonation could be inhibited.

Note that in the alkyne trimerization shown in the question, the first two acetylene molecules are effectively reduced before the third one displaces the metal. Such a reduction is not seen in the Glaser coupling.