Stereochemistry of the reaction products of the oxidative addition reaction of methyl iodide to [Rh((C4H3S)COCHCOR)(CO)(PPh3)]: A NMR and computational study. R = CF3, C6H5, C4H3S

A NMR study of the reaction mixture of the square planar [Rh((C₄H₃S)COCHCOR)(CO)(PPh₃)] complex and CH₃I, where R = CF₃, C₆H₅ or C₄H₃S, revealed that two types of alkyl and one (R = CF₃) or two (R = C₆H₅ or C₄H₃S) types of acyl species exist in the system. Two isomers of each species with an unsymmetrical β-diketonato ligand were observed. ¹H-¹H NOESY NMR unambiguously showed that the PPh₃ group is in the apical position in the more stable Rh^III-alkyl product. Theoretical computations of the equilibrium geometry of the possible reaction products, consistent with experimental observations, revealed that the first alkyl product results from trans addition to Rh^I and that the second thermodynamic alkyl product adopts an octahedral geometry with the PPh₃ group and the iodide above and below the square planar plane. Theoretical computations also revealed that the thermodynamic acyl product adopts a square-pyramidal geometry with the COCH₃ group in the apical position.