Methyl iodide oxidative addition to monocarbonylphosphine [Rh((C4H3S)COCHCOR)(CO)(PPh3)] complexes utilizing UV/vis and IR spectrophotometry and NMR spectroscopy to identify reaction intermediates: R = C6H5 or C4H3S

The chemical kinetics, studied by UV/vis and IR, of the oxidative addition of CH3I to [Rh((C4H3S)COCHCOR)(CO)(PPh3)], with R = C6H5 (Ph) or C4H3S, consists of three definite reaction steps and involves isomers of two distinctly different classes of a RhIII-alkyl and two distinctly different classes of a RhIII–acyl species according to the following reaction scheme: lecular formulas of all the RhIII–alkyl and RhIII–acyl species are [Rh((C4H3S)COCHCOR)(CH3)(CO)(PPh3)(I)] and [Rh((C4H3S)COCHCOR)(COCH3)(PPh3)(I)] respectively, but the geometry is different due to different co-ordination positions of the ligands. The equilibrium K2 was fast enough to be maintained during the RhI depletion in the first reaction step and during the RhIII–alkyl2 formation in the second reaction step. A 1H and 31P NMR study of the oxidative addition of CH3I to the different isomers of [Rh((C4H3S)COCHCOC6H5)(CO)(PPh3)], containing an unsymmetrical β-diketonato ligand, reveals the existence of at least two structural isomers for each reaction intermediate according to the following reaction scheme: served rate of formation and depletion of the two RhI isomers of the [Rh((C4H3S)COCHCO(C6H5))(CO)(PPh3)] complex, as well as the different isomers of each reaction intermediate, are the same, contrary to what was previously found for the formation of the alkyl2 isomers when R = CF3. All reaction intermediates are identified spectroscopically.