Reactions of Mono- and Di-substituted acetylenes with planar iridium(I) complexes and carbonylation of the resulting adducts

Abstract

Alk-1-ynes (RC₂H; R = H, Pr, Bu, CH₂CH₂OH, Ph, CO₂Me) undergo irreversible oxidative addition to the iridium(I) complex IrCl(PPh₃)₃ to give six-coordinate hydrido acetylides of iridium(III), IrHCl(C₂R)(PPh₃)₃, the stereochemistry of which is deduced from ¹H N.M.R. and infrared data. Isomers of the corresponding adduct of phenylacetylene with IrCl(PMePh₂)₃ can be isolated. Carbonylation of IrHCl(C₂R)(PPh₃)₃ gives IrHCl(C₂R)(CO)(PPh₃)₂, which can be isolated only when R = H, Ph or CO₂Me; when R = Pr, Bu or CH₂CH₂OH, the complexes immediately decompose to IrCl(CO)(PPh₃)₂ and the alkyne. This reductive elimination also occurs to some extent for R = Ph. Diphenylacetylene and dimethyl acetylenedicarboxylate react with IrCl(PPh₃)₃ to give the known alkyne complex IrCl(PhC₂Ph)(PPh₃)₂ and the known iridiacyclopentadiene complex IrCl-(MeO₂CC₂CO₂Me)₂(PPh₃)₂ respectively. The additions of alk-1-ynes to IrClL₃ and to other lowvalent metal complexes are compared, and the relevance of the oxidative addition to catalysis of linear polymerization of alk-1-ynes is noted.