Iron and oxygen play essential roles in many biological processes. One of the most familiar examples is hemoglobin, the protein that transports oxygen through the bloodstream. In hemoglobin, iron binds dioxygen—an oxygen molecule made of two bonded oxygen atoms.
Iron can also form highly reactive compounds called iron oxos. These molecules support important chemical reactions in the body, including processes performed by liver enzymes that break down pharmaceutical drugs and other substances.
Discovering New Oxygen Chemistry Beyond Iron
Rice University chemist Raúl Hernández Sánchez set out to determine whether oxygen could form similar compounds with another class of metals located near the bottom of the periodic table. These elements are known as f-block metals, which include lanthanides in the upper row and actinides below them.
Hernández Sánchez proposed that lanthanides capable of binding oxygen in the right configuration might produce highly reactive lanthanide oxo compounds. These molecules could provide synthetic alternatives to iron oxos and give chemists new tools for investigating biologically relevant reactions.
However, researchers faced a significant challenge. F-block metals—especially lanthanides—were not generally thought to interact with small molecules such as oxygen through pi bonding. Pi interactions are important in numerous biological systems, including proteins and other biomolecules.
In a study published in the Journal of the American Chemical Society, Hernández Sánchez and his research team demonstrated that dioxygen can form pi interactions with neodymium, a lanthanide metal. The discovery enabled the formation of previously inaccessible lanthanide oxo compounds.
Using a Molecular Basket to Control Neodymium
“We had a ligand platform that we developed a few years ago,” said Hernández Sánchez, an assistant professor of chemistry. “You can think of it as a basket that allows us to capture metals and position them in ways to encourage specific types of bindings.”
Each molecular basket was designed to hold one f-block metal atom. The researchers positioned two baskets opposite each other and arranged six atoms between them, including a dioxygen molecule that connected the two neodymium centers.
This structure created an octacoordinate ligand environment, allowing the researchers to precisely control the position and reactivity of the neodymium atoms.
“Once we had the lanthanide in our ligand basket, we started to explore its reactivity to small molecule substrates until we found the right conditions to find dioxygen in an unprecedented fashion,” said Hong-Lei Xu, a postdoctoral researcher and first author of the study.
Revealing an Unprecedented Type of Oxygen Bonding
Under carefully controlled conditions, neodymium and dioxygen formed pi interactions that scientists had previously considered unlikely. The reaction generated a new lanthanide oxo molecule, expanding the known chemistry of f-block metals.
The discovery gives researchers an opportunity to investigate whether highly reactive lanthanide oxos could serve as alternatives to iron oxos in synthetic chemistry. Scientists can also explore whether lanthanide-based compounds offer chemical properties and reactivity that iron compounds cannot provide.
Although the research focused on neodymium, Hernández Sánchez and his colleagues believe the same ligand framework could enable comparable reactions with many other lanthanides—and potentially with actinides.
“The ability to bind dioxygen to f-block metals and cleave the bond between the two oxygen atoms allows us to potentially unveil highly reactive lanthanide oxos and form high value-added chemicals. We could open a new chapter in the chemistry of lanthanides,” Hernández Sánchez said.
The research received support from Rice University startup funding, the Robert A. Welch Foundation and Welch Foundation Grant C-2142-20230405.
Source: www.sciencedaily.com