A CoCl2·6H2O/Zn reagent using 2-(2,6-diisopropylphenyl)iminomethylpyridine (dipimp), 1,2-bis(diphenylphosphino)ethane (dppe), or 1,2-bis(diphenylphosphino)benzene (dppPh) as a ligand effectively catalyzed the cross-addition reaction of silylacetylene to internal alkynes. The reaction of some unsymmetrical internal alkynes, such as 3-arylpropargyl alcohols, proceeded in a highly regioselective manner in the presence of dppe or dppPh but gave a nearly 1:1 mixture of regioisomers in the presence of dipimp. The results of reactions using 1-deuterated 2-silylacetylene revealed that the reaction involves a direct oxidative addition of the silylacetylenic C-H bond to cobalt.

A cobalt-catalyzed alkyne [2 + 2 + 2] cycloaddition reaction has been applied to polymerizations yielding linear polymers via selective cross-cyclotrimerization of yne-diyne monomers, which occurs in a chain-growth manner. Additionally, through control of the alkyne reactivity of the two monomers, this method was efficiently applied to the spontaneous block copolymerization of their mixture. Here we present the proposed mechanism of the catalyst transfer process of this cycloaddition polymerization.

In the presence of FeCl(n)-(bisphosphine) or FeCl(n)-(2-iminomethylpyridine) (n = 2 or 3), 2-substituted oxetanes reacted with Grignard reagents undergoing reductive magnesiation at the 2-position to afford substituted 3-oxidopropylmagnesium compounds, which are useful nucleophiles in reactions with a variety of electrophiles.

Several systems consisting of a ligand, a metal compound, and zinc have been developed as catalysts for alkyne cycloaddition reactions and alkyne-nitrile co-cycloaddition reactions. N-Heterocyclic carbene (NHC)-iron(III) chloride-zinc, NHC-cobalt(II) chloride-zinc, and 2-{ [(2,6-diisopropylphenyl)imino]meth-yl}pyridine (dipimp)-iron(III) chloride hexahydrate-zinc systems catalyzed intramolecular cyclotrimerization reactions of alkynes. The dipimp-cobalt(II) chloride hexahydrate-zinc system catalyzed cycloaddition reactions of a variety of alkynes in intramolecular, partially intramolecular, and fully intermolecular fashions. The ethane-1,2-diylbis(diphenylphosphine)-cobalt(II) chloride hexahydrate-zinc system was effective in catalyzing the [2 + 2 + 2] cocycloaddition of diynes with nitriles. Nickel complexes with an ionic liquid-tagged ligand converted 1,6-diynes into the corresponding cyclooctatetraenes in a toluene-ionic liquid biphasic system in the presence of zinc. The dipimp-nickel(II) chloride hexahydrate-zinc catalyst polymerized 1,6-diynes to form conjugated polyene cyclic polymers. These results and their applications in synthesis, including controlled polymerization reactions, are described. 1 Introduction 2 Alkyne [2+2+2] Cycloaddition 2.1 Development of N-Heterocyclic Carbene-Cobalt or Iron Compound-Zinc Catalyst Systems 2.2 Development of 2-{[(2,6-Diisopropylphenyl)imino]meth-yl}pyridine-Cobalt or Iron Salt-Zinc Catalyst Systems 2.2.1 Development of 2-{[(2,6-Diisopropylphenyl)imino]meth-yl}pyridine-Iron Chloride-Zinc Catalyst Systems 2.2.2 Development of the 2-{[(2,6-Diisopropylphenyl)imino]methyl}pyridine-Iron Chloride Hexahydrate-Zinc Catalyst System 2.3 The 2-{[(2,6-Diisopropylphenyl)imino]methyl}pyridine-Cobalt(II) Chloride Hexahydrate-Zinc Catalyst System 2.3.