Small Molecule Activation by Polyoxovanadate-Alkoxide Clusters

The development of homogeneous catalysts for multi-electron transformations remains a major challenge due to the impact of the harsh reaction conditions needed in the catalyst durability. For example, common industrial reductions of small molecules such as the Haber-Bosch and Fischer-Tropsch processes take advantage of solid-state catalysts at high temperatures and pressures. Chemists realized that metal-surface interactions play a key role in the activity of heterogeneous systems and have investigated the deposition of catalytic metal centers in the surface of various inert metal-oxides. Functionalized metal-oxide surfaces can be seen as a metal-oxide ligand environments coordinating catalytically active sites, facilitating multi-electron transformations (e.g., as electron reservoir) occurring in the deposited metal center. In consequence, functionalized molecular metal oxides can serve as homogeneous mimics of metal-oxide materials. Mixed-valent hexanuclear polyoxovanadate-alkoxide (POV-alkoxide) clusters, with a chemical formula [(FeIICl)(VV5-nVIVnO5)(O)(O-R)12](1+n)-, have emerged as redox reservoirs for multi-electron processes due to the VV/VIV redox couple and the iron open metal site. This approach has led to the successful activation of nitrogen-containing oxyanions relevant to the nitrogen cycle.

An iron open metal site can be easily created through the cleavage of the chloride ligand in the Fe-Cl bond; therefore, we propose to study the activation of small molecules such as molecular oxygen by iron functionalized POV-alkoxide clusters using a combination of density functional theory, complete active space, and domain-based local pair natural orbital coupled cluster calculations. We hypothesize that upon coordination, the O2 oxidizes one of the five VIV centers to VV (electron reservoir) rather than oxidizing the FeII center. Following this coordination and redox event, the radical M-O-O· group is sufficiently activated that it can be protonated and reduced to form an hydroperoxide OOH group. This group can be subsequently protonated form a water molecule and further oxidize the POV-alkoxide cluster to form a Fe=O group. This study aims to determine if the oxidation state of the iron center remains unchanged while the POV-alkoxide electrons are the ones being using in the activation of molecular oxygen and the overall energetics for this small molecule activation. Once activated, the catalytic activity of the Fe=O in the POV-alkoxide cluster will be explored.

Selected Publications

1. Meyer, R. L.; Miró, P.; Brennessel, W. W.; and Matson, E. M. O2 Activation with a Sterically Encumbered, Oxygen-Deficient Polyoxovanadate-Alkoxide Cluster. Inorg. Chem. 2021, 60, 18, 13833–13843. DOI:10.1021/acs.inorgchem.1c00887

2. Rabbani, S. M. G.; Achazi, A. A.; and Miró, P. Computational Insights into the Nucleation of Mixed-Valent Polyoxovanadate Alkoxide Clusters. Inorg. Chem. 2021, 60 (10), 7262. DOI:10.1021/acs.inorgchem.1c00337

3. Fertig, A. A.; Rabbani, S. M. G.; Koch, M. D.; Brennessel, W. W.; Miró, P.; and Matson, E. M. Physicochemical Implications of Surface Alkylation of High-valent, Lindqvist-type Polyoxovanadate-alkoxide Clusters. Nanoscale 2021, 13, 6162. DOI:10.1039/D0NR09201K