| Research Abstract |
Biphasic catalysis is a well-established method for effective catalyst separation and recycling. The Ruhrchemie/Rhone-Poulenc process for the hydroformylation of propene catalyzed by a water-soluble rhodium complex with triphenylphosphane trisulfonate (TPPTS) as a ligand has been repeatedly discussed in the literature, because it allows the exclusive use of water as the reaction medium. However, its application is limited to olefins which have appreciable water solubility. Furthermore, the key issue in this process, where linear aldehydes are the most desired products, is the control of regioselectivity. In this research project, our attention was focused on the design and preparation of novel water-soluble diphosphine ligands for metal-complex catalysts which function inverse phase-transfer catalysts and induce high regioselectivity.
First of all, we have designed sulfonated derivative of 4,5-diphosphino-9,9-dimethylxanthene possessing one p-(p-alkyloxyphenyl) phenylalkyl group on each
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two phosphorus atoms, such as 4,5-bis{[p-(p-methoxyphenyl)-phenylethyl]-phenylphosphino}-9,9-dimethylxanthene and 4,5-bis{tert-butyl[p-(p-methoxyphenyl)phenylethyl]-phosphino}-9,9-dimethylxanthene. The sulfonated derivatives would be expected not to form aggregates in water, while syntheses of *eir precursors are generally difficult owing to P-chirogenic bisphosphines with tree different substituent groups on the two phosphorus atoms.
As one of intermediates, we have prepared 4,5-bis(boranato-terf-butylphosphino)-9,9-dimethylxanthene as a mixture of (rac)-diphosphine and (meso)-one, and separated it to two diastereomers. However, it was unsuitable as a intermediate, because the treatment with BuLi afforded no lithio derivative. Also, removal of the boranato group was difficult by treatment with amines or acids such as tetrafluoroboric acid. Then, to obtained precursors of the target compounds, one-pot reaction starting from dichlorophenylphosphine was conducted with (p-methoxyphenyl)phenylethylmagnesium chloride, where 4,5-bis(chlorophenylphosphino)-9,9-dimethylxanthene would be formed selectively as an intermediate. Finally, the precursor, 4,5-bis{[p-(p-methoxyphenyl)phenylethyl]-phenylphosphino}-9,9-dimethylxanthene, was obtained as a mixture of (rac)-diphosphine and (meso)-one, and separated to two diastereomers. After sulfonation of the precursor, we will conduct hydroformylation of higher olefins in aqueous biphasic system using Rh-complexes with the sulfonated ligands to realize high regioselectivity. Less
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