Hydroformylation reaction Hydrogen, homogeneous activation

In general, homogeneous catalysts based on HPANs consist of complex equilibrium mixtures of polyanions of different compositions with products of the deg-radative dissociation of the heteropolyanion. All these species can function as the active form or as ligands of a transition metal complex [16]. The HPAN + Pd(II) and HPAN + Rh(I) systems are also used in carbonylation, hydroformylation, and hydrogenation reactions [17]. Other redox systems based on HPANs are also known. Their second component is Tl(III)/Tl(I) [18], Pt(IV)/Pt(II) [19], Ru(IV)/ Ru(II), or Ir(IV)/Ir(III) [20]. 

The olefin-metal carbonyl complex is the only immediate source of hydrogen and carbon monoxide in the hydroformylation reaction and the transfer of hydrogen and carbon monoxide to the olefin takes place within this complex. This mechanism of reaction is general in these homogeneously catalyzed reactions after the molecules are activated and suitably situated in the complex, a fast reaction occurs with formation and desorption of the products. It is not difficult to picture a similar activated adsorption, reaction, and desorption taking place on a metal surface. 

The polymers were converted to supported catalysts corresponding to homogeneous complexes of cobalt, rhodium and titanium. The cobalt catalyst exhibited no reactivity in a Fischer-Tropsch reaction, but was effective in promoting hydroformylation, as was a rhodium analog. A polymer bound titanocene catalyst maintained as much as a 40-fold activity over homogeneous titanocene in hydrogenations. The enhanced activity indicated better site isolation even without crosslinking. 

This section is concerned with the activation of hydrocarbon molecules by coordination to noble metals, particularly palladium.504-513 An important landmark in the development of homogeneous oxidative catalysis by noble metal complexes was the discovery in 1959 of the Wacker process for the conversion of ethylene to acetaldehyde (see below). The success of the Wacker process provided a great stimulus for further studies of the reactions of noble metal complexes, which were found to be extremely versatile in their ability to catalyze homogeneous liquid phase reaction. The following reactions of olefins, for example, are catalyzed by noble metals hydrogenation, hydroformylation, oligomerization and polymerization, hydration, and oxidation. 

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