Diastereocontrolled synthesis of cis-olefins by selective C–C bond formation between alkyl and alkynyl groups coordinated to “Ir(CHCHPPh3)(CO)(PPh3)2”

Abstract

cis,cis-1,4-Dipropenylbenzene (cis,cis-p-C₆H₄(CHCHCH₃)₂, cis-DPB) and cis,cis,cis-1,3,5-tripropenylbenzene (cis,cis,cis-m,m-C₆H₃(CHCHCH₃)₃, cis-TPB) are obtained in high yields by reactions of di- and tri-nuclear alkyl–alkenyl–alkynyl iridium(III) compounds, [p-C₆H₄(CC–Ir(CH₃)(CHCHPPh₃)(CO)(PPh₃)₂)₂]²⁺1 and [m,m-C₆H₃(CC–Ir(CH₃)(CHCHPPh₃)(CO)(PPh₃)₂)₃]³⁺3 with HCl. The reaction of the mono-nuclear alkyl–alkenyl–alkynyl iridium(III) complex, [Ir(CH₃)(CHCHPPh₃)(CC-p-C₆H₄CH₃)(CO)(PPh₃)₂]⁺7a with DCl selectively gives cis-CD₃CDCD(p-C₆H₄CH₃) 8a-d₅ while two isomers, cis-C₆H₅CD₂CDCD(p-C₆H₄CH₃) 8b-d₄ and cis-C₆H₅CDCDCD₂(p-C₆H₄CH₃) 8b′-d₄ are obtained from the reaction of [Ir(CH₂Ph)(CHCHPPh₃)(CC-p-C₆H₄CH₃)(CO)(PPh₃)₂]⁺7b with DCl. Plausible reaction pathways containing the initial attack of H⁺ on the β-carbon of the alkynyl ligands to produce cis-alkenyl complexes that give η²-allene complexes are suggested for the selective and diastereocontrolled C–C bond forming reactions between alkyl and alkynyl groups to give cis-olefins, 8, cis-DPB, and cis-TPB.