Periodic Reporting for period 4 - FeREDCOUPLS (FeREDCOUPLS - Reduced Iron Catalysts for Reduction and Coupling Reactions)
Berichtszeitraum: 2021-04-01 bis 2022-12-31
The aerobic conditions on our planet have enabled the accumulation of oxidized matter whereas reduced chemicals constitute the most valuable energy carriers. The future shortages of energy-rich resources make efficient reductive conversions of available and stable chemicals into valuable chemicals and fuels one of the greatest challenges of modern societies. Over the past decades, metal-catalyzed reductions and related reductive processes have emerged as key synthetic methods for the preparation of diverse building blocks, fine chemicals, pharmaceuticals, agrochemicals and materials. Such reactions are mostly operated with noble or toxic catalyst metals (Pd, Ni, Cu, Co, Rh, Pt). However, the commonly employed catalysts exhibit detrimental effects on the environment and generate high operational costs. Iron catalysts are a promising yet under-utilized alternative in the context of reductive transformations. This ERC project combines organometallic synthesis with modern analytical, theoretical and technological tools to provide new iron catalysts for challenging chemical transformations. The work covers four packages that aim at the development of iron catalysts in low oxidation states, the formation of C-C bonds by iron-catalyzed cross-couplings, the formation of C-C bonds by radical processes, and the formation of C-H bonds by hydrogenation processes. The targeted reaction classes bear great relevance to the construction of fine chemicals, pharmaceuticals and energy carriers.
This project successfully provided new insight into the preparation and stabilization of reduced iron complexes in the presence of organic ligands, the synthesis of hitherto unknown nanoclusters and unusual hydride complexes. All iron complexes were evaluated in a wide range of coupling and reduction reactions that bear great relevance to fine chemicals, materials and pharmaceuticals production. The comparison of Fe catalysts with its closest neighbours Mn and Co led to additional new insight into the formation of nanoclusters and molecular complexes and their applications to reduction processes. We significantly expanded the art of synthesis of iron complexes, iron clusters and iron nanoparticles, we expanded and tremendously enhanced the performance of iron catalysts in various reduction processes. Hitherto unknown metal-metal ensembles could be stabilized by bulky amido and bridging hydride ligands, a general building principle that was not known before but will see major applications in catalyst development and materials synthesis. The knowledge and the synthesis of iron hydride complexes, the key precursors to all hydroprocesses with iron catalysts, was greatly pushed forward. New radical addition reactions were developed that led to the preparation of highly functionalized alkenes bearing halogen, silicon and ester functionalities. We developed the most active halofluoroalkylation procedures and identified a new carbene-extended radical addition method that delivers highly functional molecules by a hitherto unknown mechanism. Such densely functionalized molecules are key precursors to materials syntheses and pharmaceuticals. In the context of hydrogenations, metallate catalysts and nanoparticle catalysts were prepared that displayed very high activity in hydrogenations of various alkenes, alkynes, imines, and carbonyl compounds. Recently, unprecedentedly high activities were achieved in hydrogenations of aromatic building blocks.
After 6 years of intensive research, this action delivered a wide range of new synthetic methods and prepared new types of iron catalysts. Among the diverse chemical processes studied, five achievements have or will have tremendous impact onto the art of modern synthesis of fine chemicals and materials:
1) We discovered a new method of metal nanocluster synthesis that constitute snapshots of the growth of nanoparticles from molecular precursors to larger particles. The synthesis of well-defined nanoclusters with Mn and Fe centers in our group already pioneered the art of cluster and catalyst design. Our works significantly propelled the state of the art by virtue of the unexpected arrangements of metal-metal bonds, the unknown ligand geometries, novel magnetic properties, and high catalytic activities observed in these nanoclusters. Never before has such information been gained for 3d metal species. We identified small nanocluster with unusal arrangements of Fe, Co, Mn metal ions surrounded by labile ligand architectures. Such materials bear utmost importance as catalysts, nanoparticle precursors, and as model species for spectroscopic and theoretical investigations into metal layers, metallic materials, and metal catalysts.
2) Our explorations of the synthesis and properties of iron hydride complexes for catalytic reductions and hydrogen technologies were very fruitful. New classes of hydride complexes were discovered that display unusual structures and unique reactivities. This field of research is highly under-utilized but is now given a major push forward with the availability of new model species for further studies.
3) Iron-catalyzed reductions of a wide range of stable organic substrates were developed to great maturity. Highly active catalysts were prepared for hydrogenations of alkenes, alkynes, and arenes. The latter reaction, the transformation of stable and easily available aromatic molecules into highly energetic hydrocarbons is a major breakthrough in the strive for sustainability. Never before has an inexpensive, non-toxic, and abundant metal such as iron been shown to enable facile hydrogenation of very stable arenes; an area of synthesis and manufacture that is limited to very expensive, toxic and rare noble metals. This discovery holds great potential for implementations into chemical production settings. Further, we reported environmentally friendly catalysts for stereoselctive hydrogenations of alkynes.
4) In the context of cross-coupling reactions, this project introduced new directing groups that enable highly selective and rapid cross-couplings of arenes with organometallic reagents. For the first time, simple carbonyl-derived substituents were shown to exert an accelerate effect onto C-C bond formations. This general method has not been fully explored so far, but a major impact on pharmaceutical, fine chemicals, and materials syntheses is easily foreseen.
5) The detailed study of Fe complexes, catalysts, and their reactivity profiles led to model studies with their neighbors Co and Mn. Both metals were investigated for their performance to draw general conclusions. And many of these efforts were met with huge success: Cobalt-catalyzed radical atom transfer addition reactions were reported that complement the state of the art. Cobalt-catalyzed reductions of organic substrates, incl the greenhouse gas CO2, were reported to even outperform the efficiency of iron in selected cases. Mn clusters were demonstrated to originate from the very same nanocluster synthesis method that was developed for Fe. Therefore, this project has given many inspirations to related fields of research.
It is important to note that several projects were brought to full fruition in the final stages of this action. Currently, the groundbreaking findings in the areas of metal nanoclusters, iron hydride complexes, arene hydrogenation methods, and directed cross-couplings are being concluded and prepared for publications.
1) We discovered a new method of metal nanocluster synthesis that constitute snapshots of the growth of nanoparticles from molecular precursors to larger particles. The synthesis of well-defined nanoclusters with Mn and Fe centers in our group already pioneered the art of cluster and catalyst design. Our works significantly propelled the state of the art by virtue of the unexpected arrangements of metal-metal bonds, the unknown ligand geometries, novel magnetic properties, and high catalytic activities observed in these nanoclusters. Never before has such information been gained for 3d metal species. We identified small nanocluster with unusal arrangements of Fe, Co, Mn metal ions surrounded by labile ligand architectures. Such materials bear utmost importance as catalysts, nanoparticle precursors, and as model species for spectroscopic and theoretical investigations into metal layers, metallic materials, and metal catalysts.
2) Our explorations of the synthesis and properties of iron hydride complexes for catalytic reductions and hydrogen technologies were very fruitful. New classes of hydride complexes were discovered that display unusual structures and unique reactivities. This field of research is highly under-utilized but is now given a major push forward with the availability of new model species for further studies.
3) Iron-catalyzed reductions of a wide range of stable organic substrates were developed to great maturity. Highly active catalysts were prepared for hydrogenations of alkenes, alkynes, and arenes. The latter reaction, the transformation of stable and easily available aromatic molecules into highly energetic hydrocarbons is a major breakthrough in the strive for sustainability. Never before has an inexpensive, non-toxic, and abundant metal such as iron been shown to enable facile hydrogenation of very stable arenes; an area of synthesis and manufacture that is limited to very expensive, toxic and rare noble metals. This discovery holds great potential for implementations into chemical production settings. Further, we reported environmentally friendly catalysts for stereoselctive hydrogenations of alkynes.
4) In the context of cross-coupling reactions, this project introduced new directing groups that enable highly selective and rapid cross-couplings of arenes with organometallic reagents. For the first time, simple carbonyl-derived substituents were shown to exert an accelerate effect onto C-C bond formations. This general method has not been fully explored so far, but a major impact on pharmaceutical, fine chemicals, and materials syntheses is easily foreseen.
5) The detailed study of Fe complexes, catalysts, and their reactivity profiles led to model studies with their neighbors Co and Mn. Both metals were investigated for their performance to draw general conclusions. And many of these efforts were met with huge success: Cobalt-catalyzed radical atom transfer addition reactions were reported that complement the state of the art. Cobalt-catalyzed reductions of organic substrates, incl the greenhouse gas CO2, were reported to even outperform the efficiency of iron in selected cases. Mn clusters were demonstrated to originate from the very same nanocluster synthesis method that was developed for Fe. Therefore, this project has given many inspirations to related fields of research.
It is important to note that several projects were brought to full fruition in the final stages of this action. Currently, the groundbreaking findings in the areas of metal nanoclusters, iron hydride complexes, arene hydrogenation methods, and directed cross-couplings are being concluded and prepared for publications.