HYDROFORMYLATION WITH A RHODIUM BULKY PHOSPHITE MODIFIED CATALYST - CATALYST COMPARISON FOR OCT-1-ENE, CYCLOHEXENE, AND STYRENE

The rhodium-catalyzed hydroformylation of oct-1-ene, cyclohexene, and styrene has been studied using Rh(CO)(2)Acac as the catalyst precursor and tris(2-tert-butyl-4-methyphenyl) phosphite as the Ligand (T = 40- 100 degrees C, P-CO = 2.5-44 bar, P-H2 = 2.5-50 bar, toluene as a solv ent). For oct-1-ene, very high hydroformylation rates are obtained (39 .8 x 10(3) mol [mol Rh](-1) h(-1)) under mild conditions (P-CO = 10 ba r, P-H2 = 10 bar, T = 80 degrees C). The concentration dependencies of the reaction rate show that the rate-determining step is the reaction of Ha with the acylrhodium complex. A negative order in the CO concen tration is observed. For cyclohexene, the reaction rate is lower under the same conditions (512 mol [mol Rh](-1) h(-1), [cyclohexene] = 0.91 M), the addition of cyclohexene to the starting rhodium hydride compl ex now being rate-limiting. In the hydroformylation of styrene, the ra te is 3 times lower than that of oct-1-ene. For the formation of the l inear 3-phenylpropanal, the rate-determining step is the reaction of H -2 with the rhodium acyl. species. CO inhibits the reaction. In contra st with the formation of the secondary 2-octyl species from oct-1-ene, the formation of the secondary (1-phenylethyl)rhodium species is reve rsible. For the formation of the branched aldehyde, the kinetics depen d strongly on the CO partial pressure. At low CO pressures, addition o f CO to the proposed (eta(3)-1-phenylethyl)rhodium intermediate is slo w. At higher CO pressures, hydrogenolysis of the rhodium acyl intermed iate is the rate-determining step and the rate decreases with increasi ng CO.