Hydroformylation catalysts, selective coordinative bonding

As mentioned above, most published papers and patent applications deal with ligands and their influence on activity and selectivity in the oxo synthesis. When alkylphosphine-modified cobalt catalysts were introduced by Shell [135], high n/i selectivities were reported. However, coordination of phosphine ligands makes the metal-hydrogen bond more hydridic, therefore leading to substantial formation of hydrogenation products. Hydroformylation of 1-pentene yielded hex-anol with 91 % linearity. 

The mechanism of olefin hydroformylation catalyzed by rhodium complexes has been extensively studied. For TPP as a ligand, it corresponds to Wilkinson s dissociative mechanism, which involves the four-coordinated active intermediate HRh(CO)L2 (L = TPP, Figure 14.2). Coordination of olefin with HRh(CO)L2 yields the 7t-complex 2. The insertion of coordinated olefin to the Rh-H bond leads to the formation of alkyl complexes 3a or 3b, respectively, via the anti-Markovnikov or the Markovnikov path. Subsequently, the alkyl migration to the CO affords the acyl complexes 4a or 4b, which leads to linear or branched aldehyde and HRh(CO)L2 via hydrogenolysis, eventually. The water-soluble catalyst HRh(CO)(TPPTS)3 is considered to react according to the dissociative mechanism [10]. However, the reaction occurs at the liquid phase or the gaseous-Hquid interface [11], and the activity and selectivity are remarkably different from those... 

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