Mn-catalysed C-H activation breakthrough

Posted on 8 September 2016

A significant breakthrough in understanding the mechanisms involved in manganese-catalysed C-H bond activation

Scheme of Mn-catalysed C-H activation

Working collaboratively, the research groups of Duckett, Fairlamb and Lynam, have investigated the mechanism of C-H bond activation in organic substrates involving manganese(I) carbonyl species (Angewandte Chemie International Edition 2016, DOI: 10.1002/anie.201606236). 

Direct web link: http://onlinelibrary.wiley.com/doi/10.1002/anie.201606236/epdf

Using a combined computational and experimental approach the team have been able to identify and characterise a highly reactive intermediate 7-membered manganacycle which acts as an anvil point to either reductive elimination or protonation, delivering different organic products (see figure). 

The team have been able to understand the origin of the organic product selectivity by working with 2-pyrone derivatives, which possess a unique reactivity profile in the experimental mechanistic study.  Furthermore, a highly unusual Mn-mediated Diels-Alder cycloaddition reaction and fragmentation process on a 2-pyridyl moiety was identified, when running reactions in neat terminal acetylene.  Generally, Diels-Alder reactions of 2-pyridines are quite rare, and thus the findings offer much potential and scope for future studies.

The most pleasing element of the study was that so many students contributed: Nasiru Yahaya (an overseas student from Nigeria, recently graduated) and Kate Appleby (recently moved to being a PDRA with Simon Duckett), supported by a key discoveries by an undergraduate student (Magdalene Teh), Erasmus exchange students (Conrad Wagner, Erik Troschke), and other PhD students playing a supporting role in the laboratory (Jonathan Ward, Joshua Bray and Lars 'Anders' Hammarback). We also gratefully acknowledge the X-ray crystallographic work done by Adrian Whitwood, Natalie Pridmore and Jessica Milani.

The paper was jointly dedicated to Professor Michael Bruce of the University of Adelaide and Professor Robin Perutz of the University of York.  Bruce pioneered the Mn-carbonyl C-H bond activation chemistry in the year Ian Fairlamb was born (1975), an interesting coincidence.  Perutz has been a pioneer in studying organometallic photochemical processes and when we needed to employ photochemical methods and NMR for the characterisation of the highly reactive manganacycle intermediate, it presented a warm and timely opportunity to recognise his significant contributions to the field.