Comparing {Mo<sub>2</sub>O<sub>5</sub>} and {V<sub>2</sub>O<sub>4</sub>} Cores in Aerobic Catalysts for Oxidative Alcohol Dehydrogenation
Multisite molybdenum oxides are key heterogeneous catalysts for oxidative alcohol dehydrogenation (OAD), motivating the development of molecularly defined homogeneous models. Herein, we report a series of dimeric molybdenum(6+) complexes, (A)<sub>2</sub>[Mo<sub>2</sub>(μ-O)(O)<sub>4</sub>(pin<sup>F</sup>)<sub>2</sub>] (pin<sup>F</sup> = perfluoropinacolate), <b>1</b>, which possess a singly bridged, ″open″ {Mo<sub>2</sub>O<sub>5</sub>} core and represent, to the best of our knowledge, the first examples of dimeric complexes for aerobic, homogeneous, Mo-catalyzed OAD. Three salts, where A = NMe<sub>4</sub><sup>+</sup> (<b>1a</b>), {K(18c6)}<sup>+</sup> (<b>1b</b>), and HNEt<sub>3</sub><sup>+</sup> (<b>1c</b>), were prepared from MoO<sub>3</sub> and H<sub>2</sub>pin<sup>F</sup>. Reduction of <b>1</b> yields Mo(5+) dimers, (A)<sub>2</sub>[Mo<sub>2</sub>(μ-O)<sub>2</sub>(O)<sub>2</sub>(pin<sup>F</sup>)<sub>2</sub>] (<b>2a</b>, <b>2b</b>, and <b>2c</b>), which adopt a ″closed″ {Mo<sub>2</sub>O<sub>4</sub>} core featuring a Mo-Mo bond. In catalytic OAD, <b>1a</b> oxidizes activated alcohols whose yield depends on the substrate's C-H BDE. Mechanistic studies using <sup>19</sup>F NMR spectroscopy reveal <b>2</b> to be an off-cycle species, inert to oxidation by O<sub>2</sub> but reoxidized by <i>in-situ-</i>generated H<sub>2</sub>O<sub>2</sub>. The necessity of PCET is confirmed by a +0.9 V anodic shift in the Mo<sup>6+</sup> reduction potential of <b>1a</b> upon protonation and by the catalyst's inertness toward OAT with PPh<sub>3</sub>. SCXRD characterization of <b>1a</b>, <b>1b</b>, and <b>1c</b> and of reduced dimers <b>2a</b>, <b>2b</b>, and <b>2c</b> is reported herein. Comparison with the previously reported vanadium(5+) OAD catalyst [V<sub>2</sub>(μ-O)<sub>2</sub>(O)<sub>2</sub>(pin<sup>F</sup>)<sub>2</sub>]<sup>2-</sup>, <b>{V(5+)}</b><sub><b>2</b></sub>, proposes differences in the mechanisms based on the {M<sub><i>x</i></sub>O<sub><i>y</i></sub>} cores.
Authors
- J R Brown
- Arnold L. Rheingold (ORCID: https://orcid.org/0000-0003-4472-8127)
- Linda H. Doerrer (ORCID: https://orcid.org/0000-0002-2437-6374)
- Jeffrey W. Bacon (ORCID: https://orcid.org/0000-0002-5206-3762)
- Sikyung Choi (ORCID: https://orcid.org/0000-0002-7750-7091)
- John E. Cerritelli (ORCID: https://orcid.org/0009-0006-6945-3667)
- Rana B. Abdu (ORCID: https://orcid.org/0009-0003-5607-9539)
- Mary M. Bussiere (ORCID: https://orcid.org/0000-0002-8231-3021)
- Thor B. Mdalel (ORCID: https://orcid.org/0000-0002-4587-0320)
Institutions
- Boston University (US)
- University of California San Diego (US)
Publication Details
- Journal
- Inorganic Chemistry
- Published
- 2025-09-26
- DOI
- https://doi.org/10.1021/acs.inorgchem.5c03009
- Citations
- 1
- Primary Topic
- Catalysis and Oxidation Reactions
- Type
- article
- Field-Weighted Citation Impact
- 0.39