Influence of Thiolate versus Alkoxide Ligands on the Stability of Crystallographically Characterized Mn(III)-Alkylperoxo Complexes
| Autor: | Alexandra N. Downing, Penny Chaau Yan Poon, Michael K. Coggins, Julie A. Kovacs |
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| Rok vydání: | 2021 |
| Předmět: |
Coordination sphere
General Chemistry Electronic structure 010402 general chemistry Antibonding molecular orbital 01 natural sciences Biochemistry Catalysis 0104 chemical sciences Ion Crystallography chemistry.chemical_compound Colloid and Surface Chemistry chemistry Alkoxide Reactivity (chemistry) Mulliken population analysis Derivative (chemistry) |
| Zdroj: | Journal of the American Chemical Society. 143(16) |
| ISSN: | 1520-5126 |
| Popis: | The work described herein demonstrates the exquisite control that the inner coordination sphere of metalloenzymes and transition-metal complexes can have on reactivity. We report one of few crystallographically characterized Mn-peroxo complexes and show that the tight correlations between metrical and spectroscopic parameters, established previously by our group for thiolate-ligated RS-Mn(III)-OOR complexes, can be extended to include an alkoxide-ligated RO-Mn(III)-OOR complex. We show that the alkoxide-ligated RO-Mn(III)-OOR complex is an order of magnitude more stable (t1/2298 K = 6730 s, kobs298 K = 1.03 × 10-4 s-1) than its thiolate-ligated RS-Mn(III)-OOR derivative (t1/2293 K = 249 s, k1293 K = 2.78 × 10-3 s-1). Electronic structure calculations provide insight regarding these differences in stability. The highest occupied orbital of the thiolate-ligated derivative possesses significant sulfur character and π-backdonation from the thiolate competes with π-backdonation from the peroxo π*(O-O). DFT-calculated Mulliken charges show that the Mn ion Lewis acidity of alkoxide-ligated RO-Mn(III)-OOR (+0.451) is greater than that of thiolate-ligated RS-Mn(III)-OOR (+0.306), thereby facilitating π-backdonation from the antibonding peroxo π*(O-O) orbital and increasing its stability. This helps to explain why the photosynthetic oxygen-evolving Mn complex, which catalyzes O-O bond formation as opposed to cleavage, incorporates O- and/or N-ligands as opposed to cysS-ligands. |
| Databáze: | OpenAIRE |
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