Physical Sciences ︱ Professor Connie Lu

Decreasing M-Cr bond order

Coniguring new bonds 28 25 26 27 Ni between irst-row Mn Fe Co

24 24 24 24 transition metals Cr Cr Cr Cr

Transition metals are some of the B.O.= 5 3 2 1 most important elements in the Periodic Table for their wealth of applications, spanning catalysis to biology. The rich chemistry of molecules composed of ten or more Building metal-metal bonds can be like building blocks – chemical bonding to chromium (Cr) the transition metals arises from atoms. Ligands can be diverse not just can change from quintuple to single by varying the other light transition metal partner. their remarkable ability to form in their chemical structure, but also in multiple chemical bonds, a process how they attach to the metal centre. Professor Lu wants to ind ways to exploit that is still not fully understood Some ligands just bind directly to the and remains a major challenge in metal whereas others bind through Professor the properties of the more common light fundamental chemistry. multiple sites on the ligand, or in the Connie Lu at the University of case of metal complexes with more than transition metals, to replace their heavier, Minnesota has been tackling this one metal centre, the ligands can act as question by synthesising the irst a bridge between the centres by binding scarcer counterparts mixed-metal complex containing the two metals together. synthesis and carbon dioxide activation, This is why Professor Lu wants to only the irst-row transition metals an important step in the development ind ways to exploit the properties to explore the fundamental nature It is the variety and the complexity of this of sustainable energy technologies. of the more common light transition of a chemical bond. chemical behaviour that makes Professor metals, to replace their heavier, Connie Lu at the University of Minnesota DOUBLE-DECKER METALS scarcer counterparts. so fascinated by transition metals and Professor Lu’s research predominantly he transition metals are a series their associated ligands. With her focuses on the lighter transition metals. One series of complexes that Professor of elements mostly located in research group, she has designed over At present, many industrial processes Lu’s group have been making are Tthe middle of the Periodic Table. ifty new metal-ligand complexes, with that rely on catalysts make use of the dicobalt complexes, two cobalt centres This includes elements such as cobalt, iron, a variety of different metal centres. heavier transition metal elements. joined together by some unusual ligands, and manganese. What makes transition Now, she wants to use this knowledge However, the heavier transition metals also designed by her group, called metals so interesting, and gives rise to the not just to address fundamental are signiicantly less abundant on Earth ‘double-decker’ ligands. These ligands thousands of different ways in which they questions in chemistry, but to design and there is the imminent danger of are named as such because they act can react, is their electronic structure, or next-generation catalysts for chemical shortages of many of these elements. as scaffolds for stacking together two the arrangement of the electrons in the metal-metal centres, allowing the metal element. As chemical bonding is all about centres to form multiple bonds with each electron sharing between two different other. The more bonds formed between chemical species, the electronic structure two species, the shorter and stronger of an element dictates how an element will the bond but such multiple bonding is react with other species and how many and very rare between two metals of different what type of chemical bonds it can form. kinds. The design and properties of these ligands has allowed Professor Lu Transition metals typically have a large to achieve several world-irsts by making number of electrons available for a molecule with triple bonds between chemical bonding, but also space to two different light transition metals, receive electrons from possible ligands, iron and chromium and a quintuple bond molecules which bind to the central between manganese and chromium. metal atom to form the inal metal While quintuple bonds are rare in complex. These ligands can vary in size, Bimetallic complexes can also deliver "ready-made" bimetallic active sites onto a solid support, themselves, the manganese-chromium from single atoms, to highly complex as shown for the metal-organic framework material, NU-1000. complex remains the only example of

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E: [email protected] T: +1 612 625 6983 W: http://www1.chem.umn.edu/groups/lu/

Research Objectives Collaborators with Karl Wieghardt. In 2009, she Professor Lu’s lab seeks to develop • Professor Laura Gagliardi, University began independent research at the homogeneous catalysts for converting of Minnesota University of Minnesota, where she abundant small molecules, such as • Dr Eckhard Bill, Max Planck Institute is currently an Associate Professor. N2 and CO2, into useful chemical for Chemical Energy Conversion feedstocks, such as ammonia and • Collaborators in the Inorganometallic Contact methanol, respectively. The group is Catalyst Design Center, University of Professor Connie Lu interested in creating, understanding Minnesota, http://www1.chem.umn. Laboratory of Inorganic Synthesis and exploiting new chemical bonding. edu/icdc/ and Catalysis University of Minnesota Funding Bio 207 Pleasant St SE, • National Science Foundation (NSF) Connie Lu received a BS in Chemistry Minneapolis, MN 55405 • US Department of Energy, Basic from MIT and a PhD from Caltech with USA Energy Science Jonas Peters. She was a Humboldt postdoctoral fellow at the Max-Planck- Institute for Bioinorganic Chemistry

a quintuple bond between two different The dificult conversion of nitrogen to silylamine, when catalysed by the dicobalt complex, can metal centres. occur at room temperature and at ambient pressure of nitrogen. Theoretical calculations predict transition metals and main group that the hardest step is the formation of the second N-Si bond, which is shown on the right. Do you think your bimetallic Q&A elements, which are to the right on the catalysts will be scalable for THE NITROGEN PROBLEM What allows the double decker Periodic table. This is a new, exciting industrial processes? Making bonds between metal centres industry for drug manufacture as well in solid supports, that can later be used ligands to bring together two direction for us because we have found The bimetallic catalysts contain of different transition metals is a as for agricultural usages and in water in catalysis. By using the bimetallic different metal centres? that nickel-gallium pairings make great specialised ligands, which will be powerful tool for exploring the chemistry puriication. The possibility of being molecules as a delivery vehicle for Transition metals have certain catalysts for hydrogenating CO2. We expensive to make for an industrial and bonding of transition metals and able to use nitrogen, rather than more the metal centres, it should be possible preferred geometries for binding are curious about some of the heaviest process. Rather, these catalysts are forming an extensive library of such polluting chemical synthesis routes, as to make a greater variety of catalytic ligands. We take advantage of the well- elements, the rare earth metals, which wonderful demonstrations of what compounds is important to further our a way of manufacturing these chemicals supports and develop new systems that known fact that a single metal centre reside at the very bottom of the Periodic light transition metals can achieve understanding of catalysis design and would be a huge development towards make use of the more abundant lighter often prefers to form a ive-membered table. While our current ligands are too together. To be scalable, we will need synthesis. However, such compounds more sustainable chemical synthesis. transition metals. By bringing together ring with ligands. Our double-decker small for these metals, we have designed cheaper methods to place two metals are not so commonly found in nature, chemical identiication techniques used ligand design scaffolds just the right new ligands which we hope will allow us together on a solid support and to ind whereas bimetallic complexes, where the LOOKING AHEAD in other areas of chemistry, Professor number of donor atoms such that to explore bonding in the nether regions a support that will preserve the unique two metal centres are the same transition Given the success of Professor Lu’s Lu also hopes to further characterise both metals are each part of three of the Periodic table. bimetallic reactivity. metal, are found in many enzymes, group at making many metal-metal the unique bonding in the compounds approximate pentagons. As I write this, nature’s catalysts for biological reactions. compounds with a variety of transition synthesised in her group and develop I think it would fun to ask grade school Do you think that it will be possible What’s the greatest number of metal species, the plan is to ind other models to further our understanding of children to see how many irregular to replace all heavy transition metal chemical bonds you’ve been able to Professor Lu has found that one of exciting applications of this chemistry. how different metals bond and interact. pentagons they can ind in one of our catalysts with lighter metal catalysts? create between two metals? the dicobalt species her group has The bimetallic molecules made by the molecules. Absolutely, it is just a matter of time. Five. Quintuple bonds are still quite synthesised is an incredibly eficient group can be used to install the metals Note: These are irregular pentagons We all want sustainable catalysts, and rare and are only known for transition catalyst in turning nitrogen (N2) to because the sides and angles are researchers all over the world are working metals. My collaborator Laura Gagliardi

N(SiMe3)3, an amide species. Nitrogen not all equal. to replace heavy, precious metals with has predicted that the maximum is an incredibly inert species that makes lighter, earth-abundant ones for all types number of bonds between two metals up most of our atmosphere so getting Professor Lu has achieved several world- Do you think these ligands can be of catalytic applications. As a community, is six. Isolating a molecule with a it to react to form new compounds used for all transition metals and we are generating knowledge about how sextuple bond would be spectacular, is very dificult. However, amines are irsts by making a molecule with triple pairings? to better control the properties of the and it remains an exciting challenge very valuable chemicals, with a global bonds between two different light We can use these ligands to study light transition metals. for synthetic chemists. market worth billions of dollars; they other pairings, for example between are widely used in the pharmaceutical transition metals

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