CYCLOTRIMERIZATION OF ACETYLENES CATALYZED BY (η5-CYCLOPENTADIENYL)RHODIUM COMPLEXES

Article abstract of DOI:10.1016/0022-328X(85)80250-3

The comparative rates of cyclotrimerization of dimethylacetylenedicarboxylate (DMAD) and hex-3-yne have been studied with the catalysts <(η⁵-C5R5)Rh(COD)> (R=H, Me, Cl; COD=cycloocta-1,5-diene), <(η⁵-C5R5)Rh(CO)2> (R=H, Me), <(η⁵-C5Me5)RhL2> (L=C2H4, PF3) and <(η⁵-C5H4PPh3)Rh(CO)2>⁺ PF6^- under pseudo-first-order conditions.In these reactions, which all obey the rate law, rate=k_obs, the rate of cyclotrimerization of DMAD decreases as the ?-acceptor strength of the cyclopentadienyl ligand increases, and this trend is reversed in reactions of hex-3-yne.The rates of cyclotrimerization also appear to vary with the nature of the ligand L (where L=C2H4, CO, PF3, 1/2COD) implying that L remains bound to the rhodium atom through the catalytic cycle.Preliminary studies have shown that in some cases selective co-oligomerization occurs with mixtures of two different acetylenes using the catalysts <(η⁵-C5H5)Rh(COD)> and <(η⁵-C9H7)Rh(COD)>.