Rhodium phosphine complexes immobilized on silica as active catalysts for 1-hexene hydroformylation and arene hydrogenation

• Published in: Journal of molecular catalysis. A, Chemical Chemical, 2004-03, Vol.210 (1), p.179-187
• Main Authors: Standfest-Hauser, Christina M., Lummerstorfer, Thomas, Schmid, Roland, Hoffmann, Helmuth, Kirchner, Karl, Puchberger, Michael, Trzeciak, Anna M., Mieczyńska, Ewa, Tylus, Włodzimierz, Ziółkowski, Józef J.
• Format: Article
• Language: English
• Subjects: Alkylsiloxanes; Catalysis; Catalytic reactions; Chemistry; Exact sciences and technology; General and physical chemistry; Hydroformylation; Hydrogenation; Rhodium complexes; Surface confined catalysts; Theory of reactions, general kinetics. Catalysis. Nomenclature, chemical documentation, computer chemistry
• ISSN: 1381-1169; 1873-314X
• DOI: 10.1016/j.molcata.2003.09.012

Rhodium complexes [Rh(acac)(CO)(Ph 2PCH 2CH 2Si(OMe) 3)] and [Rh(acac)(Ph 2PCH 2CH 2Si(OMe) 3) 2] were immobilized at silica as [Rh(O-{SiO 2}(HO-{SiO 2})(CO)(P-{SiO 2})] ( 1a) and [Rh(O-{SiO 2})(HO-{SiO 2})(P-{SiO 2}) 2] ( 2a), respectively, after removal of acac ligands protonated by acidic proton of silica-OH group. Complexes 1a and 2a were characterized with 31 P -CP/MAS, XPS and IR methods and used as pre-catalysts in hydroformylation of 1-hexene. The pre-catalyst 1a produced up to 54% of aldehydes with Ph 2PCH 2CH 2Si-{SiO 2} co-catalyst and up to 94% with PPh 3 and it was found more active compared to 2a. Additionally 1a catalyzes hydrogenation of aromatic hydrocarbons (benzene and toluene). In immobilizing the rhodium complexes [Rh(acac)(CO)(P)] ( 1) and [Rh(acac)(P) 2] ( 2) (P = Ph 2PCH 2CH 2Si(OMe) 3) onto SiO 2, acetylacetone is found to be released through protonation of the acac ligand by the acidic silica-OH groups. The resulting complexes [Rh(O-{SiO 2}(HO-{SiO 2})(CO)(P-{SiO 2})] ( 1a) and [Rh(O-{SiO 2})(HO-{SiO 2})(P-{SiO 2}) 2] ( 2a) were successfully tested with respect to their catalytic action on 1-hexene hydroformylation as well as benzene and toluene hydrogenation. The reaction outcome, viz. the formation of aldehydes versus isomerization, depends strongly on the presence and concentration of a phosphine co-catalyst. Thus, while 1a gave only a 17% yield of aldehyde in the absence of phosphines, the yield is increased to 54% in the presence of phosphinated silica P-{SiO 2} or even 94% if PPh 3 is added to the solution. Without extra added phosphine, both 1a and 2a effect mainly the isomerization of 1-hexene to 2-hexene. Pre-catalyst 1a catalyzes also the hydrogenation of benzene at 10.5 atm H 2 and 90 °C to give cyclohexane with a TOF of 608 h −1.