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Although there has been much development in the field of uranium coordination and organometallic chemistry, the role of f-orbital participation in uranium coordination compounds is not been studied in depth. Therefore, it can be very informative to perform studies on the electronic communication between U–U and U–M metal centers. The Diaconescu and Meyer group are both interested in synthesizing complexes that possess U–U and U–M bonds and characterizing them with various methods such as SQUID magnetization, EPR spectroscopy, cyclic voltammetry (CV), and Mössbauer spectroscopy. While these spectroscopic techniques are all available in the Meyer laboratory at the University of Erlangen-Nuremberg, the Diaconescu group at UCLA will contribute to this joint project by offering their know-how of synthetic organometallic chemistry techniques to lead this proposed project to and transfer of this knowledge for the proposed chemistry of uranium is very desirable.
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Final report:
Ferrocene is widely incorporated in pharmaceutical candidates, materials, and redox agents. In addition, ligand scaffolds make use of ferrocene groups because of their steric, electronic, and redox properties. We pursued the study of 1,1’-disubstituted, ferrocene-based chelating ligands as versatile frameworks in supporting metal complexes. Cerium is the only lanthanide that has accessible the +4 oxidation state.
In order to understand how important the ability of uranium f orbitals to engage in covalent bonding is, a project was started to investigate the chemistry of cerium complexes supported by ferrocene-based chelating ligands (publication 1). In order to be able to differentiate between redox-active and redox-inactive metal centers, yttrium complexes were also studied. All these metal complexes were applied to redox-switchable catalysis. Redox-switchable catalysis is an atom-economical method that generates multiple catalytically active species with different reactivity; because these species originate from a single precursor, the cost of chemical synthesis is reduced. We applied metal complexes supported by ferrocene-derived ligands to two types of redox-switchable catalysis: (1) redox control of ligand-based processes and (2) redox control of the metal undergoing catalysis.
(1) An yttrium derivative, which is supported by a Schiff base analogue (phosfen), showed orthogonal reactivity toward the ring-opening polymerization of cyclic esters when the ferrocene backbone was in its reduced or oxidized form (Figure 1, publication 2). The reactivity toward lactide of the oxidized complex was lower than that of the reduced form.
(2) The first example of a metal-based redox switch, which is not a part of a supporting ligand, to be used for the polymerization of lactide was reported (publication 3). The activity of cerium alkoxide complexes supported by a Schiff base ligand was controlled using redox reagents during the ring-opening polymerization of L-lactide. The rate of L-lactide polymerization was modified by switching in situ between the cerium(III) and cerium(IV) species.
Publications supported by the BaCateC grant:
1. Synthesis and Characterization of Cerium(III/IV) Alkoxide Complexes Supported by Chelating-Ferrocene Ligands. Broderick, E. M.; Thuy-Boun, P.; Guo, N.; Vogel, C.; Sutter, J.; Miller, J. T.; Meyer, K.; Diaconescu, P. L. Inorg. Chem. 2011, 50(7), 2870-2877, http://dx.doi.org/10.1021/ic102076g
2. Redox Control of a Ring-Opening Polymerization Catalyst. Broderick, E. M.; Guo, N.; Vogel, C.; Xu, C.; Sutter, J.; Miller, J. T.; Meyer, K.; Mehrkhodavandi, P.; Diaconescu, P. L. J. Am. Chem. Soc. 2011, 133(24), 9278–9281, http://pubs.acs.org/doi/abs/10.1021/ja2036089
3. Redox control of a polymerization catalyst by changing the oxidation state of the metal center. Broderick, E. M.; Guo, N.; Wu, T.; Vogel, C.; Xu, C.; Sutter, J.; Miller, J. T.; Meyer, K.; Cantat, T.; Diaconescu, P. L. Chem. Commun. 2011, 47, 9897-9899, http://dx.doi.org/10.1039/C1CC13117F
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