Kinetics of the substitution of β-Diketones in β-diketonato(1,5-cyclooctadiene)rhodium(I) complexes by benzoyl-1,1,1-trifluoroacetone

Article abstract of DOI:10.1016/0022-328X(89)87187-6

The kinetics and mechanism of the reactions between and trifluorobenzoylacetone (TFBA) to give have been studied in a petroleum-ether medium at various temperatures with UV spectroscopy.The rate law is -d/dt=(k_s+k_y) and the reaction is shown to proceed via an associative mechanism.The value of k_s and k_y were determined for various β-diketone complexes with β-diketone=acac, BA, DBM, TFAA and HFAA.The reactivities of the complexes fall as the β-diketone is varied in the sequence BA>acac>DBM>TFAA>HFAA, indicating that electronegative substituents in the β-diketone increase the trans-effect and therefore the strength of the Rh-O bonds.Since the ring opening is the rate-determining step in the reaction.It can be concluded that the complex containing the β-diketone with the largest trans-effect, which gives rise to the strongest Rh-O bonds, will undergo the slowest substitution.The effect of the substituents of the β-diketone (CF3, phenyl and CH3) on the trans-effect is discussed.