Electronic Bite Angle Effect and Activity

The rate of dissociation of CO was studied separately via CO exchange in a rapid scan IR spectroscopy study under pressure [16]. In this study, no influence of the natural bite angle on the rate of formation of the unsaturated (diphosphine)Rh(CO)H complexes was found for ligands 2,4, and 6. Ligand 10 shows a sharp increase in CO 

In a series of electronically distinct but sterically equal ligands 4, it was found that the overall selectivity for linear aldehyde was constant, whereas the linear branched ratio and the rate increased concomitantly with the ee/ea ratio in the hydrido isomers (Table 1.2) [20]. The higher 1/b ratio was because of an increase in the 2-octene formation - the escape route for the formed branched alkylrhodium intermediate. 

In summary, a wider bite angle increases the concentration of unsaturated (diphosphine)Rh(CO)H and, other effects being absent or insignificant, the overall effect will result in an acceleration of the hydroformylation reaction. 

When the backbone of a ligand allows both ee and ea coordination, the basicity of the phosphine has a pronounced effect on the chelation mode [22]. One of the first 

Ligand R ee ea ratio l/b ratio % linear aldehyde % isomer tof  

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