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

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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.

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