Studien zum Vorgang der Wasserstoffübertragung, 71 [1] Tertiäre Phosphine mit ortho-ständigen chelatisierungsfähigen funktionellen Gruppen als Co-Katalysatoren der Homogenhydrierung mit Rh(I)-Komplexen/Studies on the Occurrence of Hydrogen Transfer, 71 [1] Tertiary Phosphines with Functional Groups in the ortho-Position Capable for Chelatization as Co-Catalysts of the Homogeneous Hydrogenation with Rh(I)-Complexes

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Abstract
By systematic variation of the structure of tertiary phosphines with ortho-phenyl substituted groups as co-catalysts of the homogeneous hydrogenation with Rhodium complexes and hexene-1 as a model compound a collection of data is obtained. By investigating the influence of the variation of the Rhodium/Phosphine-Ratio (Rh/P) (1:1,1 and 1:2,2) on the rate of the hydrogentransfer indirect conclusion can be drawn on the composition of the complexes in the equilibria responsible for the hydrogen transfer. Results: 1. Steric effects of substituents linked to the ortho-position of a phenyl group in the co-catalyst are very important (compare the Tables I-V especially Table VI). 2. The rate of hydrogenation is strongly influenced by tertiary phosphines with substituents in a ortho-phenyl group capable for coordination like NR2 and SR. With Rh/P = 1:1,1 the rate of the hydrogenation of hexene-1 is mostly faster as with Rh/P = 1:2,2. Depending on steric effects the rate data can be invers. 3. Tertiary arsines with o-dialkylaminophenyl groups are more effective co-catalyst as the corresponding phosphines (Table V). 4. Tertiary phosphines with an ortho-alkylmercaptophenyl group (38-41) are weakly active cocatalysts using Rh/P = 1:1,1. The thioether 42 (in compounds 12 the diphenylphosphino group is exchanged by the methylmercapto group) is also a moderate active co-catalyst. 5. As a conclusion: it is assumed that complexes of the structure A can coordinate with the substrates hydrogen and olefine . Complexes of the structure B seen to be to stable for the activation of the substrates.

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