Periodic Reporting for period 4 - multiBB (Boron-boron multiple bonding)
Période du rapport: 2020-11-01 au 2021-04-30
The ERC Advanced Grant project “Boron-Boron Multiple Bonding” (MULTIBB) is based on the poorly-understood and little-studied ability of boron atoms to form multiple bonds among themselves. While the more common elements of the first row of the periodic table’s “main block” (i.e. carbon, nitrogen, oxygen) all have well-understood multiple bonding abilities, boron’s have remained little understood until recently. While filling this knowledge gap is a fundamental goal of this project, the inherently electron-rich and highly reactive nature of compounds with boron-boron multiple bonds make them fascinating reagents for further chemistry, suggesting the possibility of novel reactions with inert molecules and bond-forming processes. Our 2012 discoveries of high-yielding, reliable routes to compounds with B-B double and triple bonds, in conjunction with funding as part of the ERC Advanced Grant, have allowed us to comprehensively explore the possibilities of B-B multiple bonding in main-group, organic and coordination chemistry. The objectives of the project were: (a) a massive expansion of the structural diversity of compounds with B-B double and triple bonds by variation of their components, and studies of their properties, (b) testing the reactivity of compounds with B-B double and triple bonds, including their small-molecule activation abilities, 1,2-addition reactions, cycloaddition, metathesis and ring-opening reactions, coordination chemistry, and redox chemistry, (c) synthesis and study of unusual and novel B-B multiply bonded systems with functional components, and (d) synthesis of poly- and oligomeric species containing B-B multiple bonds. Taken together, the project aimed to explore the synthesis, diversity, and reactivity of B-B multiple bond systems, as well as determining how B-B multiple bonds interact in an intramolecular sense with other functional components.
The project involved a comprehensive experimental and computational study of the structural limits and properties of compounds containing boron-boron multiple bonds, and the mapping and exploitation of the synthetic abilities of these highly reactive compounds.
The first part of the project involved a wide-scope expansion of the structural diversity of diborenes and diborynes, by altering the two variable components of the compounds, the anionic substituent and the Lewis base unit. While some components were chosen for their stability-enhancing characteristics, others were chosen as they were the opposite, i.e. destabilising and reactivity enhancing. Other units were incorporated as leaving groups, i.e. to direct reactivity of the compound away from the B-B multiple bond and towards other bonds of the molecule. In other cases, functional components were incorporated that allowed us to study the interactions between the B-B multiple bond and the functional unit, such as electronically-conducting, wire-like units, units with empty orbitals, strongly electron-accepting/donating units and units with multiple redox states.
The second part of the project was based on a comprehensive exploration of the reactivity of diborenes and diborynes, taking advantage of their highly electron-rich and reactive nature. Thereby, diborenes and diborynes were subjected to a wide range of reagents in a strategic fashion, ranging from highly reactive species such as strong oxidants to relatively inert molecules of societal and industrial importance, such as carbon dioxide, alkynes, amines, etc. The results of these reactions have radically broadened our understanding of the reactivity of B-B multiple bonds, leading to a long list of bond activation processes. Many of these reactions gave the simple addition product of two groups across the B2 unit or reactions known with their organic counterparts. However, many others gave completely unexpected products, such as C-C bond cleavage products, diborabenzenes, additions across a single boron atom, etc.
The results of the project have been published in 42 peer-reviewed articles, with three further papers currently submitted. A number of manuscripts are in preparation, and many more are planned from the work amassed in this project. 31 of the published articles have appeared in top general science or general chemistry journals with impact factors above nine (e.g. Journal of the American Chemical Society (5), Angewandte Chemie (20), Nature Communications (1), Chemical Science (4), Chemical Reviews (1)) and the average journal impact factor of the articles is 11.7. The published papers have already attracted over 700 citations (Web of Science), with an average number of citations per paper of ca. 18, and two are designated Highly Cited Papers by the Web of Science (top 1% in citations for its field). The publication output includes three major reviews that have been published in premier chemistry journals (one in Chemical Reviews, two in Angewandte Chemie). Eight of the papers emerging from this project have been the subject of highlights by other scientific journals and magazines (Nature Communications, Chemistry World, Angewandte Chemie, Synfacts, Nachrichten aus der Chemie), resulting in ten highlights in total. Results of the project have been communicated in a range of other ways, such as conference participation (ca. 40 oral and poster presentations from the PI, students and postdocs working on the project), lecture tours and award lectures. Overall, the publication output and dissemination from the project is outstanding, leading to an extraordinary amount of attention for the research, the group, the PI, and the host institution. A number of major scientific awards, award lectureships, and fellowships of scientific societies received by the PI have also been based in part on the excellent results of the project.
The first part of the project involved a wide-scope expansion of the structural diversity of diborenes and diborynes, by altering the two variable components of the compounds, the anionic substituent and the Lewis base unit. While some components were chosen for their stability-enhancing characteristics, others were chosen as they were the opposite, i.e. destabilising and reactivity enhancing. Other units were incorporated as leaving groups, i.e. to direct reactivity of the compound away from the B-B multiple bond and towards other bonds of the molecule. In other cases, functional components were incorporated that allowed us to study the interactions between the B-B multiple bond and the functional unit, such as electronically-conducting, wire-like units, units with empty orbitals, strongly electron-accepting/donating units and units with multiple redox states.
The second part of the project was based on a comprehensive exploration of the reactivity of diborenes and diborynes, taking advantage of their highly electron-rich and reactive nature. Thereby, diborenes and diborynes were subjected to a wide range of reagents in a strategic fashion, ranging from highly reactive species such as strong oxidants to relatively inert molecules of societal and industrial importance, such as carbon dioxide, alkynes, amines, etc. The results of these reactions have radically broadened our understanding of the reactivity of B-B multiple bonds, leading to a long list of bond activation processes. Many of these reactions gave the simple addition product of two groups across the B2 unit or reactions known with their organic counterparts. However, many others gave completely unexpected products, such as C-C bond cleavage products, diborabenzenes, additions across a single boron atom, etc.
The results of the project have been published in 42 peer-reviewed articles, with three further papers currently submitted. A number of manuscripts are in preparation, and many more are planned from the work amassed in this project. 31 of the published articles have appeared in top general science or general chemistry journals with impact factors above nine (e.g. Journal of the American Chemical Society (5), Angewandte Chemie (20), Nature Communications (1), Chemical Science (4), Chemical Reviews (1)) and the average journal impact factor of the articles is 11.7. The published papers have already attracted over 700 citations (Web of Science), with an average number of citations per paper of ca. 18, and two are designated Highly Cited Papers by the Web of Science (top 1% in citations for its field). The publication output includes three major reviews that have been published in premier chemistry journals (one in Chemical Reviews, two in Angewandte Chemie). Eight of the papers emerging from this project have been the subject of highlights by other scientific journals and magazines (Nature Communications, Chemistry World, Angewandte Chemie, Synfacts, Nachrichten aus der Chemie), resulting in ten highlights in total. Results of the project have been communicated in a range of other ways, such as conference participation (ca. 40 oral and poster presentations from the PI, students and postdocs working on the project), lecture tours and award lectures. Overall, the publication output and dissemination from the project is outstanding, leading to an extraordinary amount of attention for the research, the group, the PI, and the host institution. A number of major scientific awards, award lectureships, and fellowships of scientific societies received by the PI have also been based in part on the excellent results of the project.
Thanks almost exclusively to this project, B-B multiple bonding has truly come of age, and the combined results of the project will likely stand as the authoritative work of the post-discovery period of the field. The first part of the project, regarding the synthesis of new diborenes and diborynes, resulted in a massive expansion of the diversity of these multiply-bound species, from relatively stable examples to highly reactive and unstable species, extensive insights into their photophysical properties and the mechanisms of their formation, as well as a range of new synthetic routes to prepare them. The second part of the project, focused on the reactivity of diborenes and diborynes, amounts to a tour de force of the power of these highly electron-rich species to activate bonds of reagents. These multiply-bonded species, made internationally visible through the dissemination activities arising from the project, will now be in the minds of a wide community of scientists across scientific fields, countries and continents. At the centre of this, the research group of the PI has cemented its place as the world-leading group for B-B multiple bonding and low-oxidation-state boron chemistry, befitting its place as the founding group of the Institute for Sustainable Chemistry & Catalysis with Boron at the University of Würzburg. It should also be noted that work on these projects and the communication of the results is ongoing even after the project’s official completion, as the results have opened up a wide range of exciting new research avenues for which new funding has been obtained and/or is currently being sought from other sources.