NMR-STUDY OF INTERMEDIATES IN THE BULKY DIPHOSPHITE MODIFIED RHODIUM-CATALYZED HYDROFORMYLATION

The stoichiometric hydroformylation reaction of allyldiphenylphosphine with RhH(CO)(2)(2) (2 is a bulky diphosphite) was studied H-1 and P-3 1 NMR spectroscopy. Reaction of equimolar amounts in benzene resulted in the formation of RhH(CO)(CH2=CHCH2PPh2)(2) in which all three phosp horus ligands are coordinated equatorially (4). When 4 was heated, hyd ride migration occurred leading to two products. Migration to the term inal carbon gave 5, Rh(CO)(PPh2CH2CH2CH2)(2). Migration of the hydride to the internal carbon atom was rapidly followed by CO insertion, res ulting in the acyl compound 6, containing a five-membered rhodacycle. Complex 6 did not undergo reaction with H-2. Reaction of 5 with CO rev ersibly yielded acyl complex 7, containing a six-membered rhodacycle. Hydrogenation of 5 yielded 8, the diphenylpropylphosphine analogue of 4. (C) 1997 Elsevier Science S.A.