Actinide-Alkylidenes

Lead Research Organisation: University of Manchester
Department Name: Chemistry

Abstract

Building on our prior work where we prepared uranium-carbon double bonds that are heavily stabilised by two phosphorano groups and then evolved this to a less stabilised silyl-phosphino combination, we aim to target genuine actinide-carbon bonds that are not stabilised at all, other than by the actinide (uranium and/or thorium). Thence, this would then secure one of the long-standing goals in synthetic actinide chemistry to provide a type of complex called an actinide-alkylidene, pure variants of which have thus far only been prepared in cryogenic (5 K) matrix isolation spectroscopic experiments. The objectives are therefore to: (1) extend the range of silyl-phosphino systems to include oxidation states of uranium other than +4; (2) prepare thorium analogues; (3) with the knowledge from (1) and (2) systematically decrease the stabilisation at carbon by exchanging the silyl for alkyl and phosphino for aryl in different combinations; (4) if successful, extend the range of oxidation states for uranium and probe the inherent reactivity and electronic structure of these compounds. This project will involve organic and inorganic synthesis methods es, structural, spectroscopic, and magnetic characterisation techniques, and computational techniques. The student will be trained in handling radiochemicals, highly sensitive compounds, and developing novel synthetic methodologies to construct the actinide-carbon double bonds which are anticipated to be novel compared to established d-block analogues.

Publications

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Studentship Projects

Project Reference Relationship Related To Start End Student Name
EP/N509565/1 01/10/2016 30/09/2021
1935621 Studentship EP/N509565/1 03/09/2017 30/09/2021 Josef Boronski
 
Description Metal-ligand multiple bonding has evolved into a vast field of research over the past five decades. Complexes of transition metals with multiple bonds to ligands have been used for critical industrial chemistry, as well as implicated in vital biochemical processes. Furthermore, over recent decades, a number of winners of The Nobel Prize in Chemistry have been awarded the honour (at least partially) in recognition of their investigations into the reactivity of complexes containing metal-ligand multiple bonds.

Although the synthesis and reactivity of transition metal complexes with multiply-bound ligands is very well developed, the chemistry of actinide-element multiple bonds has historically lagged significantly behind. In recent years, however, research into complexes with actinide-ligand multiple bonds has advanced rapidly, leading to great developments within the field and contributing considerably to the fundamental understanding of actinide chemistry. The past decade has seen the synthesis of the first molecular terminal uranium nitride [U=N], selenide [U=Se], telluride [U=Te], parent phosphinidene [U=PH], arsinidene [U=AsH] and arsenido [U=AsK2] complexes, amongst many other complexes with novel uranium-element linkages. These species have provided insights into the degree of covalency exhibited by uranium complexes and the extent to which the "chemically-active" electrons of this element participate in these covalent interactions.

We have discovered new uranium-carbon bonding linkages and explored their unique reactivities. This has provided new insight into the bonding and electronic structure of uranium. This is particularly important as it may inform the reprocessing of uranium waste from the nucelar fuel cycle. This is critical, as refinements to the cycle may reduce environmental concerns regarding the reprocessing of nuclear fuel. Furthermore, the fundamental understanding of this element has been greatly enhanced by this work. Thus, its potential uses in the synthesis of novel molecules, or those which require expensive/rare metals to make, are somewhat better understood. Finally, a greater understanding of the reductive and oxidative chemistry of uranium has been acquired. The uranium-alkylidene complexes synthesised in this study are particularly stable in oxidation states (specifically the +5 oxidation state, in which uranium has lost 5 electrons), which are often otherwise very reactive and difficult to stabilise. This provides further insight into the nature of the uranium-carbon bonding interaction.
Exploitation Route Developing collective understanding of actinide bonding is crucial as it informs research into the separation of actinide and lanthanide fission products in spent nuclear fuel. This work may inform separations science (for separating uranium from other elements) and understanding of the industrial applications of uranium complexes for the synthesis of new molecules.
Sectors Chemicals,Energy,Environment

URL https://www.nature.com/articles/s41557-019-0306-x