Lanthanide Heteroatom-Stabilised Alkylidenes: A New Approach to Multiply Bonded Lanthanide Chemistry

Lead Research Organisation: University of Nottingham
Department Name: Sch of Chemistry

Abstract

One of the most exciting and challenging areas of contemporary lanthanide chemistry (lanthanides are the 14 elements at the bottom of the periodic table) is the isolation of lanthanide alkylidenes (compounds which feature a carbon atom doubly bonded to a lanthanide, Ln=C), and only a very limited number are known. Therefore, enduring fundamental questions regarding the stability, structure, bonding, and reactivity of lanthanide alkylidenes remain. Such species are scarce because they lack sufficiently good orbital interactions to stabilise the Ln=C double bond in the way numerous transition metals can. However, if heteroatoms (phosphorus or silicon) are appended to the alkylidene they can help stabilise the electrons in the Ln=C double bond. This First Grant will build on preliminary results the applicant has obtained, which exploits alkylidene heteroatom stabilisation, and utilises his expertise in lanthanide chemistry, to effect a significant and rapid expansion of this field to address the new chemistry of lanthanide alkylidenes. New lanthanide alkylidenes will be subjected to a detailed structural and spectroscopic interrogation, which will be combined with theoretical computational calculations to comprehensively establish their stability, structure and bonding. The reactivity patterns of these complexes will be screened in reactions which parallel transition metal alkylidene reactions (cycloadditions, Wittig-type). Importantly, the applicants preliminary results include a system which exhibits not only a formal Ln=C double bond, but also a reactive Ln-C single bond. This places two very reactive fragments in close proximity at the same metal centre, and presents a unique opportunity to exploit the synergy resulting from them being harnessed together. We will use this synergy to attempt access to previously unknown structural motifs, such as the first terminal lanthanide imides (Ln=N double bond) and the first lanthanide tetrylenes (Ln=Si and Ln=Ge double bonds). These will be highly interesting inorganic versions of unsaturated organic olefins and allenes (C=C, C=C=C), and given the extensive use of transition metal alkylidenes and imides by academia and industry for the synthesis of fine chemicals, pharmaceutical drugs, and commodity plastic polymers, they promise novel new reactivities.
 
Description Compounds which contain a meta-carbon double bond (alkylidenes = carbenes), where the metal is a transition metal, have many important applications in synthesis and are central to Nobel Prize winning chemistry. However, the corresponding f-block chemistry is poorly developed, but could deliver promising new synthetic applications because of the ability of f-block metals to activate unreactive chemical bonds.



This project investigated the synthesis of new f-block carbenes and has begun to investigate their intrinsic reactivity. To do this, we required new precursor molecules. We have prepared these new precursors and they have potential applications for the preparation of rare earth complexes in a wide variety of areas which are of interest to researchers generally. Since the area was poorly developed we have developed several new methodologies to access new f-block carbene compounds. Now we have several synthetic methodologies in hand we have employed these to successfully expand the work from our preliminary results and we have prepared many new rare earth and uranium carbenes which has opened up the area.



By preparing rare earth and uranium carbenes we have been able to directly compare the differences in bonding between the rare earths and uranium and have observed significant and important differences in the covalency of metal-carbene bonding. Furthermore, we have demonstrated that the uranium-carbenes perform metallo-Wittig chemistry. However, the corresponding rare earth carbenes exhibit distinct reactivity, namely regioselective C-H bond activations of organic ketones. This activation is followed by C-C and C-O bond formation reactions, which can be controlled, to give more complex organic products that are part of a class of compound which forms a potential basis for the synthesis of antibiotics. By pursuing rare earth and uranium carbenes in parallel in an interweaved project we have been able to elucidate structure-bonding-reactivity relationships and start to apply this knowledge. We have also discovered that some of the uranium carbene complexes can be converted into compounds which display magnetism of purely molecular origin. This is a particularly significant result within the field of nanomagnetism, and could lead to applications in ultra-high density data storage and quantum computing in a broader context.



This Project has been extremely successful and cost effective. Most of the original objectives have been achieved, and significant progress has been made towards accomplishing the others. Several new and exciting avenues of research have arisen from this work and these together with the outstanding objectives form part of the future research direction and effort of the PI's research group. This Project provided the basis for subsequent funding from EPSRC, the Royal Society, and a highly competitive and prestigious ERC Starter Grant. This Project has resulted in 13 publications detailing results of major fundamental importance and the 5 highlighted publications are particularly impactful. Furthermore, at least 8 more publications from this work will emerge in the near future. This Project has enabled the PI to become established and internationally recognised in what has become a competitive and vibrant area and 17 conference presentations have been given. This Project has resulted in several fruitful collaborations internationally which will be fostered in the future. Key results have been highlighted in the hugely popular, multi-award winning YouTube project Periodic Videos which has ensured broad dissemination of this work. This Project has been excellent training for the appointed PDRA Dr Mills, who has gone on to be an academic at Manchester. This project also supported several PhDs, whom have all gone on to work in chemical industry or academia.



Postscript - Dr Mills was appointed to an academic lectureship position at Manchester University (December 2012) which shows that this grant provided excellent training and supported the academic skills pipeline. In 2016 a paper was published in Chemical Science detailing work founded on this grant, it described a world record energy barrier for a single molecule magnet and gave experimental confirmation of a theory proposed as to how to make single molecule magnets better.
Exploitation Route We have developed the fundamental knowledge of f block carbenes, and more recently this work formed the basis for successful follow-on funding for single molecule magnets that could one day find uses in data storage and quantum computing.
Sectors Chemicals,Digital/Communication/Information Technologies (including Software),Other

 
Description Designing highly axial lanthanide single molecule magnets
Amount £706,000 (GBP)
Funding ID EP/P002560/1 
Organisation Engineering and Physical Sciences Research Council (EPSRC) 
Sector Public
Country United Kingdom
Start 12/2016 
End 11/2019
 
Description EPSRC
Amount £270,564 (GBP)
Funding ID EP/G051763/1 
Organisation Engineering and Physical Sciences Research Council (EPSRC) 
Sector Public
Country United Kingdom
Start 03/2009 
End 02/2011
 
Description EPSRC Established Career
Amount £1,422,792 (GBP)
Funding ID EP/M027015/1 
Organisation Engineering and Physical Sciences Research Council (EPSRC) 
Sector Public
Country United Kingdom
Start 10/2015 
End 09/2020
 
Description European Commission (EC)
Amount £180,000 (GBP)
Funding ID Marie Curie IIF THOR 297888 
Organisation European Commission 
Sector Public
Country European Union (EU)
Start 07/2012 
End 06/2014
 
Description European Research Council
Amount £1,900,000 (GBP)
Funding ID 612724 
Organisation European Research Council (ERC) 
Sector Public
Country Belgium
Start 10/2014 
End 09/2019
 
Description European Research Council
Amount £850,000 (GBP)
Funding ID 239621 
Organisation European Research Council (ERC) 
Sector Public
Country Belgium
Start 01/2009 
End 09/2014
 
Description High Intensity High Sensitivity X-ray Diffraction Equipment
Amount £1,100,000 (GBP)
Funding ID EP/P001386/1 
Organisation Engineering and Physical Sciences Research Council (EPSRC) 
Sector Public
Country United Kingdom
Start 10/2016 
End 10/2021
 
Description Royal Society of London
Amount £265,000 (GBP)
Funding ID UF110005 - URF Renewal 
Organisation The Royal Society 
Sector Charity/Non Profit
Country United Kingdom
Start 10/2012 
End 09/2015
 
Description Royal Society of London
Amount £12,737 (GBP)
Funding ID RG110238 - Equipment Grant 
Organisation The Royal Society 
Sector Charity/Non Profit
Country United Kingdom
Start 10/2011 
End 09/2012
 
Description EPR 
Organisation University of Manchester
Country United Kingdom 
Sector Academic/University 
PI Contribution We provide materials for study.
Collaborator Contribution UK EPR service provides multi frequency and temperature experiments to spectroscopically probe our molecules.
Impact Publications in Science, Nature Family, JACS, Angewandte Chemie, see publication list for details.
Start Year 2009