We present new ideas underlying a self-modelling factor analytical method which allows to extract pure component spectra and the associated concentration profiles from a set of spectroscopic measurements. The usefulness of the method is demonstrated and compared with established tools for model problems and for a system from catalytic hydroformylation by Rhodium complexes both with overlapping component spectra. Self-modelling methods tend to minimize the overlap of the recovered spectra, which can result in an unwanted distortion of the spectra and concentration profiles. For strongly overlapping spectra a penalty condition on a specific singular value of the absorptivity matrix factor and a global decomposition approach are appropriate tools to construct improved factorizations.
The rhodium‐catalyzed phosphite‐modified hydroformylation of 3,3‐dimethyl‐1‐butene is comparatively studied for a bidentate 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.
A detailed quantitative study of
phosphine-modified hydrido iridium
complexes relevant for the hydroformylation reaction has been performed
using HP-FTIR and HP-NMR spectroscopy. The equilibrium composition
under typical reaction conditions has been characterized. Investigation
of the temperature dependency allowed even for a distinction between
both configurational isomers of [HIr(CO)2(PPh3)2]. The trihydride complex [H3Ir(CO)(PPh3)2] is part of the investigated equilibrium depending
on the ratio of p(H2)/p(CO). Single rate constants for the sequence of corresponding equilibrium
reactions have been estimated from stopped-flow experiments and conventional
measurements, monitoring the concentrations after changing reactant
concentrations.
Going up! n‐Selectivity and activity can be increased simultaneously in hydroformylation by the use of novel hybrid ligands such as 1 containing O‐acylphosphite groups. For the first time these ligands deliver impressively n‐selective rhodium‐catalyzed hydroformylation of internal octenes, and this with an industrial relevant catalytic activity.
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