Mechanistic studies of the hydroformylation of 1-alkenes using a monodentate phosphorus diamide ligand

The mechanism of the rhodium-catalyzed hydroformylation reaction using a mo nodentate phosphorus diamide ligand has been investigated. The system prese nts an ideal case to illustrate the basics of hydroformylation. A detailed kinetic study and (in situ) spectroscopic techniques revealed that several of the elementary reaction steps are involved in the hydroformylation rate control. Which step is rate-determining depends strongly on the conditions used. Deuterioformylation showed that alkene coordination followed by hydri de migration is irreversible under the conditions studied. The rhodium hydr ide complex HRhL2(CO)(2) and several rhodium-acyl complexes were observed d uring the hydroformylation reaction. The structures of the rhodium-acyl com plexes have been characterized using P-31, C-13, and Rh-103 NMR spectroscop y. The major rhodium-acyl complex formed, RC(O)RhL2(CO)(2), has a trigonal- bipyramidal structure with the two phosphorus ligands coordinated in the eq uatorial plane. The exchange rates of the equatorial and apical carbonyl li gands with dissolved carbon monoxide differ significantly, the equatorial c arbon monoxide being much more labile.