Electronic Effects on the Synthesis, Structure, Reactivity, and

27

Downloaded by CHINESE UNIV OF HONG KONG on March 1, 2016 | http://pubs.acs.org Publication Date: March 1, 1992 | doi: 10.1021/ba-1992-0230.ch027

Electronic Effects on the Synthesis, Structure, Reactivity, and Selectivity of Rhodium Hydroformylation Catalysts Alexis A. Oswald , Dan E . Hendriksen , Rodney V. Kastrup , and Edmund J. Mozeleski 1,†

2

3

4

Enimont America, Inc., R & D Center, Monmouth Junction, NJ 08852 Exxon Chemical Company, Baytown, TX 77522-4900 Exxon Research and Engineering Company, Annandale, NJ 08801 Exxon Chemical Company, Annandale, NJ 08801

1 2 3 4

Steric effects of phosphine and phosphite ligands on carbonylhydridorhodium catalysts have been considered. However, the electronic effects were not considered systematically. We studied rhodium com­ plexes of phosphorus ligands of varying strengths of coordination via sigma donation and pi back-donation. For example, we compared complexes of Ph P, Ph PEt, PhPEt , Et P, and (EtO) P. In general, complexes of strongly σ-donating aliphatic phosphine ligands re­ quired a high temperature for their activation by ligand dissociation and showed a high total (normal plus iso) aldehyde selectivity. In contrast, pi back-donation by triarylphosphines and particularly by phosphite esters led to a very high normal-to-iso ratio of aldehydes derived from α-olefins but also led to more undesired olefin hydro­ genation and isomerization. The results can be explained with a con­ sistent, overall framework of rhodium hydroformylation mechanisms involving complexes of different carbonylation degrees. 3

1

2

2

3

3

ERTIARY PHOSPHINE AND PHOSPHITE ESTER COMPLEXES

of rhodium hy­ droformylation catalysts are attractive candidates for studying electronic and steric effects on catalyst activity and selectivity. Both the electronic and steric environments of rhodium can be greatly changed by an appropriate choice of phosphorus ligands. The electronic and sometimes the steric effects f

Deceased

0065-2393/92/0230-0395$07.00/0 © 1992 American Chemical Society

In Homogeneous Transition Metal Catalyzed Reactions; Moser, William R., et al.; Advances in Chemistry; American Chemical Society: Washington, DC, 1992.

396

H O M O G E N E O U S TRANSITION M E T A L C A T A L Y Z E D REACTIONS

of phosphorus ligands will be considered here from the viewpoint of catalyst activity-selectivity and equilibrium between the two carbonylhydridorhodium catalyst precursors. (R P) Rh(CO)H ^ 3

3

[(R P) Rh(CO)H] ± * 3

2

(R P) Rh(CO) H