Hydroformylation of 1-hexene and propene with in situ formed rhodium phosphine catalysts

A series of triphenylphosphines modified with different heteroatom groups ( -SCH3. -N(CH3)(2), -OCH3, -CF3) in ortho or para position of the phenyl rin g(s) were synthesised and tested for their catalytic behaviour in the rhodi um catalysed hydroformylation of l-hexene (80 degreesC, 15 bar) and propene (100 degreesC, 10 bar). Hydroformylation results for 1-hexene and propene differed markedly. With 1-hexene, the differences in activity and in chemo- and regioselectivity obtained with the various ligands were minor. Among t he heterodonor ligands, the strong sigma -donor ligands yielded higher hydr oformylation activity than the less basic ligands. In the case of propene, heterodonor bidentate ligands suppressed the hydroformylation reaction. In addition, 1,4-bis(diphenylphosphino)butane and (o-thiomethylphenyl)bis(1-na phthyl)phosphine favoured the formation of n-butanal, Only the -CF3 modifie d ligands behaved similarly with the two alkenes. The influence of the stru cture of the ligand in hydroformylation was studied by using molecular mode lling methods. The steric size of the ab initio energy minimised free ligan d structures was evaluated by Tolman's cone angle method. Co-ordination pro perties of -CF3 group modified phosphines were studied in reaction with Rh- 2(CO)(4)Cl-2, and the structure of Rh(CO)CI(P(o-CF3C6H4)Ph?)2 (1) was deter mined crystallographically. (C) 2001 Elsevier Science B.V. All rights reser ved.