A Comparative In Situ HP-FTIR Spectroscopic Study of Bi-and Monodentate Phosphite-Modified Hydroformylation

摘要

The rhodium-catalyzed phosphite-modified hydroformylation of 3,3-dimethyl-1-butene is comparatively studied for a biden-tate and a monodentate phosphite using in situ high-pressure (HP) FTIR spectroscopy and GC analysis. With the bidentate ligand at 70 C, a pseudo-first-order reaction with respect to the olefin takes place, with the pentacoordinate hydrido complex being the only detectable intermediate during the reaction. In contrast, for the monodentate ligand, a zeroth- to pseudo-first-order shift is characteristic with the major intermediate for this system subsequently changing from the coordinatively saturated acyl complex to the respective hydrido complex already at low conversions. Application of the PCD (pure component decomposition) algorithm to the reaction spectra affords the concentration versus time profiles of these intermediates, providing proof that the reaction rate remains controlled by rhodium acyl hydrogenolysis even at medium to high olefin conversions when the corresponding hydrido complex is the major organometallic component. If the reaction is carried out at a temperature of 30 °C in neat olefin, results from both GC and HP-FTIR verify an intermediate regime of saturation kinetics and also the presence of an acyl complex at low olefin conversions for the diphosphite. Initial turnover frequencies of 237 h~(-1) and 1040 h~(-1) are obtained for the mono- and the diphosphite, respectively, at 30 °C, which implies an intrinsically faster hydrogenolysis of the diphosphite-derived acyl rhodium complex at this low temperature.