text: Metal alkyne complexes are intermediates in the semihydrogenation of alkynes to alkenes:
  :CR + H → cis-CRH
  This transformation is conducted on a large scale in refineries, which unintentionally produce acetylene during the production of ethylene. It is also useful in the preparation of fine chemicals. Semihydrogenation affords cis alkenes.
  Metal-alkyne complexes are also intermediates in the metal-catalyzed trimerization and tetramerizations. Cyclooctatetraene is produced from acetylene via the intermediacy of metal alkyne complexes. Variants of this reaction are exploited for some syntheses of substituted pyridines. 
  The Pauson–Khand reaction provides a route to cyclopentenones via the intermediacy of cobalt-alkyne complexes.
  Acrylic acid was once prepared by the hydrocarboxylation of acetylene:
  :CH +  HO + CO → HC=CHCOH
  With the shift away from coal-based (acetylene) to petroleum-based feedstocks (olefins), catalytic reactions with alkynes are not widely practiced industrially. 
  Polyacetylene has been produced using metal catalysis involving alkyne complexes.