HOMOGENEOUS CATALYSIS - MECHANISM OF CATALYTIC HYDROACYLATION - THE CONVERSION OF 4-PENTENALS TO CYCLOPENTANONES

The mechanism of catalytic hydroacylation of 4-pentenal to cyclopentanone using the catalysts left bracket Rh-(diphos) right bracket ** plus and left bracket Rh((S,S)-chiraphos) right bracket ** plus has been investigated by multinuclear NMR spectroscopy. The catalytic precursors exist as arene-bridging dimers, left bracket Rh(diphosphine) right bracket //2**2** plus , in CH//3NO//2 solutions. These dimers are not catalytically active and require to be split by the substrate before catalysis occurs. The left bracket Rh(diphos) right bracket //2**2** plus dimer exists as two isomers; the minor isomer reacts with the substrate approximately 100 times faster than the major isomer. Numerous rapidly equilibrating catalyst-substrate adducts are observed.