Osaka, Japan – The arrangement of small molecules – known as ligands – around transition metal atoms affects how the metal atoms behave. This is important because transition metals are used as catalysts in the synthesis of a wide range of important materials.
Now, in a study published in the
Journal of the American Chemical Society,
researchers from The University of Osaka have reported a chemical bond that hadn’t been reported before: complexes of nickel(0), a metal, with simple ligands containing boron, a non-metal.
Transition metals are known to form complexes with ligands containing atoms from group 13 elements, including aluminum, gallium, and indium. These are known as Z-type ligands, and they can accept electrons from a metal. However, boron, the smallest element in group 13, has only been shown to do this with the support of additional ligands that help approach metals to the boron center.
The University of Osaka researchers used a mixture of experimental and theoretical methods to show the first formation of a direct bond between nickel and boron without structural constraint by additional ligands.
“We used bulky tris(perfluoroaryl)boranes as the boron-containing ligands,” explains the lead author of the study, Yutaka Mondori. “They were able to attach at one site on the nickel center – known as being monodentate – and accept a pair of electrons from the nickel atom.”
The resulting complex had what is known as square-planar geometry. This means that the nickel is in the center and the ligands are arranged around it at the four compass points, all in the same plane. This can be useful as it allows other potential reactants to approach the nickel from above or below.
Although the square-planar geometry is more common for the 2+ oxidation state of nickel, spectroscopic analysis confirmed this unusual electronic structure in this new complex. The new nickel-boron interaction was found to have both covalent and dative bonding characteristics. In addition, the bulky borane ligand interacted noncovalently with the L-type electron-donating ligands also present in the complexes, forming what the researchers describe as “frustrated L/Z-ligand pairs.”
“Nickel is an important material that is used in a wide range of catalytic processes,” says senior author Yoichi Hoshimoto. “By establishing that nickel-boron bonds can be formed with monodentate Z-type ligands, we have extended the possibilities for tuning nickel complexes for specific processes.”
It is hoped that the findings will contribute to the design of new catalysts to improve the efficiency and selectivity of syntheses for high-value products such as polymers and pharmaceuticals.
###
The study, “Monodentate σ‑Accepting Boron-Based Ligands Bearing Square-Planar Ni(0) Centers,” was published in the
Journal of the American Chemical Society at DOI: https://doi.org/10.1021/jacs.4c15892.
About The University of Osaka
The University of Osaka was founded in 1931 as one of the seven imperial universities of Japan and is now one of Japan's leading comprehensive universities with a broad disciplinary spectrum. This strength is coupled with a singular drive for innovation that extends throughout the scientific process, from fundamental research to the creation of applied technology with positive economic impacts. Its commitment to innovation has been recognized in Japan and around the world. Now, The University of Osaka is leveraging its role as a Designated National University Corporation selected by the Ministry of Education, Culture, Sports, Science and Technology to contribute to innovation for human welfare, sustainable development of society, and social transformation.
Website:
https://resou.osaka-u.ac.jp/en