Hydroformylation of olefins by water soluble and asymmetric cobalt and platinum complexes
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Hydroformylation of olefins (OXO synthesis), one of the oldest organometallic catalytic reactions, continues to be of interest because of its commercial significance. Great interest recently has been placed on the development of immobilized homogeneous catalysts that combine the virtues of conventional heterogeneous and homogeneous catalysts. The objective of this dissertation is to investigate novel phosphine modified water soluble cobalt and platinum complexes as homogeneous and immobilized hydroformylation catalysts. The ligands include (1) Monodentate phosphines: P[ (CH2 ) n-C6H4-S03Na] 3 (n = 0-3) and P[C6H4-NMe3+BF4-]3; (2) Bidentate asymmetric phosphines: CHlRAPHOS(NMe2)4 (CHlRAPHOS = 2, 3-bis (diphenylphosphino) butane) , SKEWPHOS (NMe2) 4 (SKEWPHOS = 2,4-bis(diphenylphospino)pentane), and DlOP(NMez)4 (DlOP = 2,2-dimethyl-4,5-bis(diphenyl(phosphinomethyl)-1,3- dioxolane) ). These complexes were immobilized and/or recycled by four different methods: (1) Two phase catalysis; (2) Supported aqueous phase catalysis; (3) Catalyst supported on ion exchange resins; (4) Extraction of the catalyst from an organic phase into an aqueous phase. Catalytic results for the hydroformylation of a-olefins shows that nib (normal:branch of aldehyde product) ratio can be increased if proper alkyl-phosphine ligands are chosen. For example, as high as 18.5 of nib ratio was obtained in Ptcl[P(C6Hs)3]2-snC13 system and 5.6 in CO₂ (CO) 6 [TRlMAPP] 2 (TRlMAPP = trimethylamino-phenylphosphine) system. Metal leaching, from the aqueous phase to the organic phase during the catalytic reaction, was reduced by supporting the water soluble cobalt and platinum complexes onto a high surface area glass (CGP-350). For instance, 5.7% cobalt metal was found in the organic phase when CO2(CO)6(TPPTS)2 was used under reaction conditions (TPPTS = triphenylphosphine trisulphonated salt). When the same cobalt complex was immobilized on glass, no cobalt metal leaching was observed. Asymmetric hydroformylation of styrene catalyzed by PtCl [SKEWPHOS (NMe2) 4] -SnCl3 shows a very strong temperature dependence on optical selectivity. Enantiomeric excess (ee's) switches sign fromS toR form at 57°C. At 25°C, there is 60.6% ee of S product, whereas 56.7% ee in favor of R product is observed at 100°C.
- Doctoral Dissertations