A silica-supported, switchable, and recyclable hydroformylation-hydrogenation catalyst

A homogeneous hydroformylation catalyst, designed to produce selectively li near aldehydes, was covalently tethered to a polysilicate support. The immo bilized transition-metal complex [Rh(A)CO](+) (1(+)), in which A is N-(3-tr imethoxysilane-n-propyl)-4,5-bis(diphenylphosphino)phenoxazine, was prepare d both via the sol-gel process and by covalent anchoring to silica. 1(+) wa s characterized by means of P-31 and Si-29 MAS NMR FT-IR, and X-ray photoel ectron spectroscopy. Polysilicate immobilized Rh(A) performed as a selectiv e hydroformylation catalyst showing an overall selectivity for the linear a ldehyde of 94.6% (linear to branched aldehyde ratio of 65). In addition 1-n onanol, obtained via the hydrogenation of the corresponding aldehyde, was f ormed as an unexpected secondary product (3.6% at 20% conversion). Under st andard hydroformylation conditions, 1(+) and HRh(A)(CO)(2) (1) coexist on t he support. This dual catalyst system performed as a hydroformylation/hydro genation sequence catalyst (Z), giving selectively 1-nonanol from 1-octene; ultimately, 98% of 1-octene was converted to mainly 1-nonanal and 97% of t he nonanal was hydrogenated to 1-nonanol. The addition of 1-propanol comple tely changes Z in a hydroformylation catalyst (X), which produces 1-nonanal with an overall selectivity of 93%, and completely suppresses the reductio n reaction. If the atmosphere is changed from CO/H-2 to HZ the catalyst sys tem is switched to the hydrogenation mode (Y), which shows a clean and comp lete hydrogenation of 1-octene and 1-nonanal within 24 h. The immobilized c atalyst can be recycled and the system can be switched reversibly between t he three "catalyst modes" X, Y, and Z, completely retaining the catalyst pe rformance in each mode.