432538 Computational Screening of Metal-Ligand Systems for Methanol Carbonylation

Monday, November 9, 2015: 9:10 AM
255A (Salt Palace Convention Center)
Nathan Duff, Department of Chemical and Biomolecular Engineering, North Carolina State University, Raleigh, NC and Erik E. Santiso, Department of Chemical and Biomolecular Engineering, North Carolina State University, Raleigh, NC

Acetic acid is produced industrially by methanol carbonylation with iridium or rhodium based catalysts. The expense of iridium, and rhodium has led to attempts to improve catalytic activity by designing ligands for iridium and rhodium metal complexes.[1] Alternatively, the cost of the catalyst can be reduced, by designing ligands to improve the catalytic activity of a less expensive metal center.[2] Unfortunately, the methyl iodide promoter necessary for the reaction can often preferentially alkylate the ligands bound to the metal center. As a result, carefully designed catalysts often degrade to their unligated form in the reactor. Identification of metal/ligand pairs that are resistant to alkylation by methyl iodide as well as improve catalytic activity is necessary for a commercially viable catalyst.

        Density functional theory (DFT) is used to screen ligands-metal pairs for stability and reactivity for methanol carbonylation. Metal centers with cobalt, rhodium, and nickel were examined with nitrogen, phosphorous, arsenic, and antimony based ligands. The bond dissociation energy of metal-ligand bonds are compared to ligand bonds in the undesired ligand salts that result from ligand alkylation by methyl iodide. Ligands that bond more strongly to the metal than in the salt are more likely to result in a stable ligated catalyst. The relative performance of metal-ligand pairs is also estimated by computing the activation barrier for the rate-limiting step of methyl iodide addition in the catalytic cycle. Our results are validated for some systems by existing experimental results, and suggest new metal-ligand combinations for further study.


1. Thomas CM, Suss-Fink G. Ligand effects in the rhodium-catalyzed carbonylation of methanol. Coord. Chem. Rev. 2003; 243:125-142.

2. Moser WR, Marshik-Guerts BJ, and Okrasinski SJ. The mechasnism of the phosphine-modified nickel-catalyzed acetic acid process.  J. Mol. Catal. A: Chem. 1999; 143:71-83.

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