MECHANISTIC ASPECTS OF A HIGHLY REGIOSELECTIVE CATALYTIC ALKENE HYDROFORMYLATION USING A RHODIUM CHELATING BIS(PHOSPHITE) COMPLEX

The rhodium-catalyzed hydroformylation of 1-octene using the bis(phosp hite) ligand bbmb was studied using in situ, high-pressure H-1 and P-3 1 NMR and FT-IR spectroscopy. Four species, Rh(bbmb)(acac), Rh(bbmb)(C O)(2)H, and two dimeric complexes, appeared sequentially during differ ent stages of the catalysis when Rh(acac)(CO)(2) was used as the catal yst precursor. These were independently synthesized and their reactivi ty studied. The major species present during catalysis was determined to be Rh(bbmb)(CO)(2)H (1), which was fully characterized. This hydrid e complex was shown to be an effective alkene isomerization catalyst. Using magnetization transfer, the rate of exchange between 1 and the t erminal and internal vinyl hydrogens of 3,3-dimethylbutene were 0.62 a nd 0.51 s(-1) respectively. The rapid, reversible nature of the alkene insertion establishes that the regiochemistry of the final aldehyde i s not determined at the alkene insertion step or any event prior to it . The dimeric species were shown to convert to 1 via reversible additi on of dihydrogen.