Activation of C-H and B-H bonds through sigma-bonding to Cobalt complexes

Lead Research Organisation: University of Oxford
Department Name: Oxford Chemistry

Abstract

By applying knowledge gained from the extensive research into 4d and 5d metal complexes for C-H activation and dehydrocoupling of amino borane, to 3d metals, especially cobalt. A range of novel catalysts will be synthesised, characterised and used in catalysis with a focus upon dehydrocoupling and C-H activation processes and in particular the generation of sigma-alkane complexes. The use of 3d metals in these processes is relatively unexplored and offers many scientific and technological opportunities. Amine boranes have received considerable recent attention due to the range of their potential uses: as a hydrogen storage and transport vector, as precursors for ceramic BN thin-films, and as precursors to polymers with potentially interesting properties. The majority of reported catalysts for dehydrocoupling of amine boranes are based on 4d and 5d metals, with limited research addressed towards finding examples of cobalt complexes. The few cobalt examples investigated have low activity and selectivity for the polyaminoborane target product and are ill defined. By applying previous research into rhodium and iridium based catalysts to cobalt based systems new, highly active, complexes will be isolated, characterised and used in catalysis. Following this with detailed mechanistic studies will lead to insight into this previously under investigated class of catalyst. These same complexes should also display interesting behaviour in C-H activation. Due to its potential applications in the transformation of natural gas into chemical feedstocks, and in natural product synthesis, C-H activation has been the focus of extensive research. Again, most of this work has been carried out using 4d and 5d metal complexes. A focus within the Weller group has been on the isolation of the low valent sigma-alkane complexes as an intermediate in C-H activation processes. The group has carried out single-crystal solid-gas reactions which have led to the isolation of a number of rhodium based sigma-alkane complexes. Application of this same methodology to cobalt could allow the synthesis of 3d sigma-alkane complexes, which would be a significant landmark discovery in the area. This project falls within the EPSRC Physical Science research area, more specifically within the focus of catalysis. It is estimated that catalysis currently contributes over £50 billion/year to the UK economy, and further development is essential for transformation towards a sustainable society.

Publications

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Boyd TM (2020) A Structurally Characterized Cobalt(I) s-Alkane Complex. in Angewandte Chemie (International ed. in English)

Studentship Projects

Project Reference Relationship Related To Start End Student Name
EP/N509711/1 01/10/2016 30/09/2021
1949556 Studentship EP/N509711/1 01/10/2017 31/03/2021 Timothy Morgan Boyd
 
Description Amine boranes have received considerable recent attention due to the range of their potential uses: as a hydrogen storage and transport vector, as precursors for ceramic BN thin-films, and as precursors to polymers with potentially interesting properties.[1] The majority of reported catalysts for dehydrocoupling of amine boranes are based on 4d and 5d metals, with limited research addressed towards finding examples of cobalt complexes.[2]
By research funded through this award a simple Co(II)-based amine-borane dehydropolymerisation catalyst system was reported that operates at low loadings, to selectively give (H2BNMeH)n polymer on scale, with catalyst control over Mn, narrow dispersities and low residual metal content.[3] This will enable processing and properties testing of these novel amine borane polymers.
Due to its potential applications in the transformation of natural gas into chemical feedstocks, and in natural product synthesis, C-H activation has been the focus of extensive research. A focus within the Weller group has been on the isolation of the low valent s-alkane complexes as an intermediate in C-H activation processes. The group has carried out single-crystal solid-gas reactions which have led to the isolation of a number of rhodium based s-alkane complexes.[4]
Application of this same methodology to cobalt, as part of this award, allowed the synthesis of a cobalt salkane complex, [Co(Cy2P(CH2)4PCy2)(norbornane)][BArF4], the first of its kind to be prepared by any route, a landmark discovery within the field.[5] Magnetic characterisation of this s-alkane complex revealed a triplet electronic state, a remarkable result as previous calculations show a 3Co(CO)Cp···HCH3 interaction would be repulsive.[6] Periodic DFT and electronic structure analyses revealed weak C-H?Co sinteractions, stabilised by dispersive interactions between the alkane and the anion microenvironment.

References:
[1] Staubitz, A.; Robertson, A. P. M.; Manners, I. Chem. Rev. 2010, 110 (7), 4079-4124.
[2] Pagano, J. K.; Stelmach, J. P. W.; Waterman, R. Dalt. Trans. 2015, 44 (27), 12074-12077.
[3] Boyd, T.M.; Andrea, K.A.; Baston, K., Johnson, A.; Ryan, D.E.; and Weller A.S. Chem. Commun., 2020,56, 482-485
[4] Chadwick, F. M.; Rees, N. H.; Weller, A. S.; Krämer, T.; Iannuzzi, M.; Macgregor, S. A. Angew. Chemie Int. Ed. 2016, 55 (11), 3677-3681.
[5] Boyd, T.M.; Tegner, B.E.; Tizzard, G.J.; MartínezMartínez, A.J.; Neale, S.E.; Hayward, M.A.; Coles, S.J.; Macgregor, S.A. and Weller, A.S. Angew. Chem. Int. Ed. in the press.
[6] J. L. Carreón-Macedo and J. N. Harvey, J. Am. Chem. Soc., 2004, 126, 5789-5797.
Exploitation Route The production of a simple Co(II)-based amine-borane dehydropolymerisation catalyst system which allows the synthesis of the novel amine borane polymer on scale enables further investigation into these materials. Previously the materials properties of these polymers were unexplored due to synthesis only being possible on small scale (50 mg), making materials properties investigations impossible. Preliminary investigation into these properties has begun through collaboration with a material chemistry group.
It is possible propene to be generated from ethene/butenes, via isomerization from 1-butene to 2-butenes followed by metathesis with ethene. Given the world-wide demand for propene, the energy efficient isomerization of butenes is thus particularly important in an industrial context.[1] Within the group single crystalline catalysts based upon the s-alkane complexes of rhodium promote the efficient double bond isomerization of 1-butene to 2-butenes under flow-reactor conditions.[2] Investigation into applying this methodology to more earth abundant cobalt based systems has both cost and environmentally beneficial implications.
References:
[1] Sattler, J. J. H. B.; Ruiz-Martinez, J.; Santillan-Jimenez, E.; Weckhuysen, B. M. Chem. Rev. 2014, 114, 10613-10653.
[2] Martínez-Martínez, A.J.; Royle, C.G.; Furfari, S.K.; Suriye, K. and Weller, A.S. ACS Catalysis 2020 10 (3), 1984-1992
Sectors Chemicals

URL https://pubs.rsc.org/en/Content/ArticleLanding/2019/CC/C9CC08864D#!divAbstract,https://onlinelibrary.wiley.com/doi/10.1002/anie.201914940