Kinetic Study of the Oxidative Addition Reaction between Methyl Iodide and [Rh(imino-β-diketonato)(CO)(PPh)3] Complexes,Utilizing UV–Vis,IR Spectrophotometry,NMR Spectroscopy and DFT Calculations |
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Authors: | Hendrik Ferreira Marrigje Marianne Conradie Jeanet Conradie |
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Institution: | 1.Department of Chemistry, University of the Free State, Bloemfontein 9300, South Africa; (H.F.); (J.C.);2.Department of Chemistry, UiT The Arctic University of Norway, N-9037 Tromsø, Norway |
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Abstract: | The oxidative addition of methyl iodide to Rh(β-diketonato)(CO)(PPh)3] complexes, as modal catalysts of the first step during the Monsanto process, are well-studied. The β-diketonato ligand is a bidentate (BID) ligand that bonds, through two O donor atoms (O,O-BID ligand), to rhodium. Imino-β-diketones are similar to β-diketones, though the donor atoms are N and O, referred to as an N,O-BID ligand. In this study, the oxidative addition of methyl iodide to Rh(imino-β-diketonato)(CO)(PPh)3] complexes, as observed on UV–Vis spectrophotometry, IR spectrophotometry and NMR spectrometry, are presented. Experimentally, one isomer of Rh(CH3COCHCNPhCH3)(CO)(PPh3)] and two isomers of Rh(CH3COCHCNHCH3)(CO)(PPh3)] are observed—in agreement with density functional theory (DFT) calculations. Experimentally the Rh(CH3COCHCNPhCH3)(CO)(PPh3)] + CH3I reaction proceeds through one reaction step, with a rhodium(III)-alkyl as the final reaction product. However, the Rh(CH3COCHCNHCH3)(CO)(PPh3)] + CH3I reaction proceeds through two reaction steps, with a rhodium(III)-acyl as the final reaction product. DFT calculations of all the possible reaction products and transition states agree with experimental findings. Due to the smaller electronegativity of N, compared to O, the oxidative addition reaction rate of CH3I to the two Rh(imino-β-diketonato)(CO)(PPh)3] complexes of this study was 7–11 times faster than the oxidative addition reaction rate of CH3I to Rh(CH3COCHCOCH3)(CO)(PPh3)]. |
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Keywords: | rhodium imino-β -diketonato oxidative addition DFT |
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