Kinetics of the substitution of the cyclooctadiene ligand in β-diketonatocyclooctadienerhodium(I) complexes by triphenylphosphite

Article abstract of DOI:10.1016/0022-328X(90)80242-R

The reaction between complexes and triphenylphosphite was studied for various β-diketones in a dichloroethane medium.The observed rate law is R = k.The reaction rate increases in the order acac < BA < DBM < TFAA < TFBA < HFAA (acac = acetyloacetone, BA = benzyloacetone, DBM = dibenzoylacetone, TFAA = 1,1,1-trifluoro-2,4-pentanedione, TFBA = 1,1,1-trifluoro-5-phenyl-2,4-pentanedione, HFAA = 1,1,1-trifluoro-5,5,5-trifluoro-2,4-pentanedione), indicating that electronegative substituents of the β-diketoneincrease the reactivity of these complexes towards substitution reactions.A good linear free energy relationship was obtained.The large negative values for the entropy of activation, as well as the order of reactivity of the different β-diketone complexes, point towards an associative mechanism.