Periodic Reporting for period 1 - BAIPFeOTC (Bis(alkyl-imidazolyl)propionate (BAIP) based bio-inspired mono-nuclear non-heme iron(II) complexes that catalyze challenging oxidative transformations of organic compounds)
Période du rapport: 2015-09-01 au 2017-08-31
In this project, we developed a new class of facial triad N,N,O ligands based on the bis(alkyl-imidazolyl)propionate (BAIP) architecture for the synthesis of bio-inspired mono-nuclear non-heme iron(II) complexes. The reactivities of the synthesized iron complexes towards the oxidative transformation of bio-relevant bidentate substrates have been examined.
Beside that, we have investigated the ligand-based redox chemistry of homoleptic cobalt and zinc complexes derived from a b-diiminate ligand (bis(1-methyl-4,5-diphenyl-1H-imidazol-2-yl)methane anion; an intermediate in the synthesis of the bulky BAIP ligand) that is structurally very similar to widely studied b-diketiminate ligands. These complexes show four reversible/quasi-reversible single-electron oxidations that are all ligand based. The anionic and oxidized pi-radical ligand containing cobalt complexes were synthesized and characterized by a number of spectroscopic and computational techniques that corroborated their ligand-based redox chemistry.
The design and development of highly efficient as well selective catalysts is one of the major goals of research in chemistry. During the last decades, transition metal-catalysed transformations have been dominated by the use of precious metals, for example, Pt, Pd, Rh, and Ir, which are expensive, toxic and scarce. The desire to replace these noble metals by base metals such as iron and cobalt, which are earth-abundant and have no toxicity issues, as catalytic materials represent one on the biggest challenges in the fields of catalysis and synthesis. As part of the general endeavors of creating sustainable chemical production methods, the development and use of catalysts and catalytic reaction procedures is vital. The search for new homogeneous catalysts based on non-noble metals also includes the design of new organic ligands that allow the properties of the catalysts to be tuned and optimized.
Protocols for the design of new sterically encumbered BAIP-ligands for the generation of highly reactive 1:1 Fe/ligand complexes that mimic the bio-inspired mono-nuclear non-heme iron(II) enzymes are the first objective of this project. Next, the physical properties of the resulting iron complexes are an important objective, as these provide insight in the nature of the overall complex and help to correlate their chemical reactivity to their structural design. Another important objective is the study of the chemical reactivity of the iron complexes towards organic substrates. Insight in this reactivity provides a means to link the properties of the iron complexes to those of the non-heme iron enzymes, which they are meant to mimic, and also to investigate their properties as man-made catalysts for important oxidation reactions.
As a subproject, we have also studied a bidentate N,N ligand which is an intermediate molecule in the synthesis of the bulky BAIP ligand. This N,N ligand framework bears an extended imidazole-based pi-system in conjugation with a formal b-diketimine backbone. Bis-ligated cobalt and zinc complexes featuring this anionic ligand have been synthesized and characterized by several spectroscopic techniques including single crystal X-ray analysis. The homoleptic bis-ligated cobalt and zinc complexes were studied by cyclic voltammetry, which showed that these complexes undergo series of four consecutive single-electron oxidations that are all assigned to ligand-based oxidations. The singly and doubly oxidized complexes have been synthesized on a preparative scale and have been fully characterized by various spectroscopic techniques.