Hydrogenation of soybean oil with cationic Rh(I)-Phosphine complexes as catalysts — Para-toluene sulfonate and sulfonated styrene resins as counterions

A cationic rhodium(I) complex, viz. Rh NBD diphos⁺ 4-CH₃-C₆H₅SO ₃ ⁻ [NBD = norbornadiene, diphos = (C₆H₅)₂ P-CH₂-CH₂-P(C₆H₅)₂], has been used as a homogeneous catalyst for the hydrogenation of soybean oil in acetone solution. This complex acts almost in the same way as the corresponding ones with ClO ₄ ⁻ or PF ₆ ⁻ as conuterions, i.e., it gives high polyene selectivity and low formation oftrans isomers. Because of the somewhat stronger basic character of the p-toluene-sulfonate ion compared with the perchlorate and hexafluorphosphate ions, the relative proportion of reaction via the so-called monohydride path is larger in the present case. When the ionic complex, Rh NBD diphos⁺, is bound to a solid support, e.g., to the anionic sites of sulfonated polystyrene resins, a nearly total lack of catalytic activity is observed. Possible reasons for these effects are discussed-in terms of π-arene-metal binding and covalent coordination of the sulfonate group.