Olefin hydrocarboxylation under mild conditions in nickel complex solutions

The hydrocarboxylation of α-olefins into carboxylic acids can be carried out in the presence of the dissolved complex NiCl₂(PPh₃)₂ at comparatively low CO pressures (below 0.8 MPa) with a fairly high product yield. Hexene-1 in acetic acid is converted into a mixture of heptanoic and 2-methylhexanoic acids, whose total yield is 40%. The molar ratio of the isomers is close to unity. However, the normal-chain product dominates at low CO pressures. Under the conditions examined, the catalyst is active only in the presence of a hydrogen (hydride ion) donor. The activity of the nickel complex can be markedly enhanced by preexposure of the reaction mixture to hydrogen pressure in the absence of CO. For the 0.8 MPa CO + 3.2 MPa H₂ gas mixture at 170°C, the turnover frequency of the catalyst is 28.5 and its activity is 4.8 h^?1.