Dr Rebecca Melen

Dr Rebecca Melen

Senior Lecturer in Inorganic Chemistry and EPSRC Early Career Fellow

School of Chemistry

Main Group chemistry has undergone a renaissance in recent years with the realisation that the reactivity of main group elements often closely resembles that of transition metals, with recent studies revealing that main group elements can act as homogenous catalysts for a range of transformations.

The development of main group alternatives to conventional transition metal catalysts is an emerging 'hot topic'. Previous research by Melen pioneered the use of Main-Group complexes in the catalytic dehydrocoupling of amino-boranes for which she received the RSC Dalton Young Researcher Award (2013). Her subsequent studies on heterocyclic synthesis via Main Group Lewis acid promoted organic transformations coupled with her dehydrocoupling studies led to her European Young Researcher Award (2014). Amongst her published research, she has several articles designated as 'hot papers' and/or reflected in Front/Inside Cover artwork. Research projects in the Melen group draw together several different areas of chemistry including organic and inorganic synthesis, main group chemistry, catalysis and implement a range of physical characterisation methods (including multinuclear NMR and X-ray diffraction) supported by computational studies.

Links:

Group website: http://www.melengroup.com

BA and MSci (1st Class Honours), University of Cambridge (2004- 2008); PhD, University of Cambridge (2008-2012, Prof. Dominic Wright); Postdoctoral Fellow, University of Toronto, Canada (2012-2013, Prof. Douglas Stephan); Humboldt Fellow, University of Heidelberg, Germany (2013-2014, Prof. Lutz Gade). Appointed as a Lecturer in Chemistry, Cardiff (2014) and promoted to Senior Lecturer (2017). Significant awards: RSC Dalton Young Researchers Award (2013); European Young Researchers Award (2014); Clara Immerwahr Award (2016); Thieme Chemistry Journals Award winner (2018).

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CH3102 Foundations of Inorganic Chemistry

CH3201 Reactivity and Properties of the Elements and their Compounds

CH3402 Frontiers in Ligand Design and Coordination Chemistry

CHT401 Recent Advances in Homogeneous Coordination Chemistry

Details of each module is available in course finder

Research in the Melen group focuses on the use of main group Lewis acids in organic synthesis and catalysis. The research programme includes:

* Main group catalyst design including tuning the steric and electronic effects of the Lewis acid.

* Applications of main group Lewis acids in organic synthesis and catalytic processes.

* Mechanistic studies to determine reaction pathways and the role of the Lewis acid in the reactions using combinations of experimental and theoretical methods.

Lay Summary:

Catalysts are used widely in the industrial setting and provide a lower energy reaction pathway to occur without consumption of the catalyst. To date, many catalysts typically employed are centred on the so called 'precious metals' and, so far, transition metals have dominated homogeneous and heterogeneous catalysis. But is the behaviour of transition metals so notably different from the main group elements? Our research aims to uncover patterns of reactivity which bridge the apparent divide between transition metal and main group chemistry, by demonstrating that p-block elements can catalyse a variety of industrially significant reactions.

Three examples of current research in the Melen group are described below:

The softer side of boron:

Recent contributions by the Melen group to the field of main group mediated organic transformations include the exploration of Lewis acidic main group compounds as reagents for enabling transformations which are typically promoted or catalysed by heavier d-block metals such as Au(I). This includes the use of Lewis acidic boranes to generate a range of pharmaceutically important heterocycles.

Angew. Chem. Int. Ed., 2017, 56, 11995; Angew. Chem. Int. Ed., 2016, 55, 11292; Chem. Eur. J., 2016, 22, 14618.

Beyond BCF:

As main-group chemistry, in particular boron chemistry, has expanded and developed over the past 20 years, one reagent has risen to prominence as well. Tris(pentafluorophenyl)borane, B(C6F5)3 (commonly known as BCF), has demonstrated extensive applications in a wide variety of reactions, including borylation, hydrogenation, hydrosilylation, frustrated Lewis pair (FLP) chemistry, Lewis acid catalysis, and more. However, as main-group chemistry continues to evolve as a field, new reagents are required that go beyond BCF, increasing not only the range of reactions available but also the breadth of compounds attainable. Our research focuses on the development of new borane Lewis acids and advancing novel borane and borocation usage that eclipses that of the stalwart BCF.

Chem. Eur. J., 2017, 23, 10997; Organometallics, 2017, 36, 2381; Inorg. Chem., 2017, 56, 8627; Chem. Eur. J., 2016, 22, 14618.

New Directions in Metal-Free Catalysis:

Recent developments in the Melen group have investigated new directions in metal free catalysis to provide new openings in both the synthesis and applications of main group compounds. This includes enantioselective catalysis using borenium cations, combining FLP hydrogenation with organocatalysis and applications of main group chemistry into flow systems.

ACS Catalysis, 2017, 7, 7748; Adv. Synth. Catal., 2017, 359, 2580; Dalton. Trans., 2016, 45, 15303