Periodic Reporting for period 4 - ENTANGLED-TM-ALKANE (Entangled pincer ligand architectures and their application in the transition-metal-mediated activation of alkanes)
Período documentado: 2019-10-01 hasta 2020-09-30
The selective activation of alkanes under mild conditions by well-defined molecular complexes of the transition elements is a frontier challenge, with the potential to revolutionise the way in which we exploit these vast and low-cost chemical feedstocks. The fundamental organometallic chemistry of these processes is, however, poorly understood and a much greater understanding is required before their full potential in chemical synthesis can be realised. In particular, the characterisation and reaction chemistry of sigma–alkane complexes, metal-alkane adducts formed through coordination of an intact C–H bond to the metal centre, have proven to be exceedingly difficult to investigate using conventional experimental approaches as a consequence the weakly interacting nature of alkanes and their otherwise transient presence in reactions between alkanes and highly reactive metal-based compounds.
To address this knowledge gap and inspired from supramolecular chemistry, the objective of ENTANGLED-TM-ALKANE was to develop and study of systems containing alkane substrates held in close proximity to reactive metal centres through mechanical entanglement within supporting tridentate macrocyclic ‘pincer’ ligands. These Interlocked macrocyclic Pincer–Alkane Systems (IPAS) are highly challenging synthetic targets and their realisation within the timescale of the project ultimately proved to be overly ambitious, with the exception of two pybox-based systems that are less amenable to formation of the intermolecular M∙∙∙H-C bonding interactions of interest. Nevertheless, whilst the destination may not have been reached the journey was filled with adventure and resulted in the discovery of some interesting and impactful science, which we hope will simulate further research at the interface between organometallic and supramolecular chemistry (see below).
To address this knowledge gap and inspired from supramolecular chemistry, the objective of ENTANGLED-TM-ALKANE was to develop and study of systems containing alkane substrates held in close proximity to reactive metal centres through mechanical entanglement within supporting tridentate macrocyclic ‘pincer’ ligands. These Interlocked macrocyclic Pincer–Alkane Systems (IPAS) are highly challenging synthetic targets and their realisation within the timescale of the project ultimately proved to be overly ambitious, with the exception of two pybox-based systems that are less amenable to formation of the intermolecular M∙∙∙H-C bonding interactions of interest. Nevertheless, whilst the destination may not have been reached the journey was filled with adventure and resulted in the discovery of some interesting and impactful science, which we hope will simulate further research at the interface between organometallic and supramolecular chemistry (see below).
I feel the most impactful outcomes from this project are associated with advances in the organometallic chemistry of macrocyclic pincer ligands. During this project we have demonstrated how the unique steric profile of these ligands can be used to augment metal-based reactivity. For instance, changing the selectivity of terminal alkyne homocoupling reactions (DOI = 10.1002/anie.201807028 10.1002/chem.202002962 10.1039/d0dt03550e) and promoting the otherwise unfavourable oxidative addition of a C(sp)-C(sp) bond (DOI = 10.1002/anie.202009546).
Outcomes form the project can summarized under the following headings:
✪ Methods for the preparation of macrocyclic PXEXP pincer ligands (DOI = 10.1039/c9dt04474d 10.1039/c9dt04835a).
✪ Methods for the preparation of late-transition-metal-based rotaxanates and catenates (DOI = 10.1002/anie.201807028 10.1002/chem.202002962 10.1002/anie.202009546 10.1039/d0dt03550e; unpublished)
✪ Mechanistic insights and control of terminal alkyne homocoupling reactions (DOI = 10.1002/anie.201807028 10.1002/chem.202002962 10.1039/d0dt03550e).
✪ Development of a shape changing tandem catalyst for the one-pot preparation of bicyclo[4.2.0]octa-1,5,7-trienes from terminal aryl alkynes (involving formation of 5 C-C bonds in one experimental operation; DOI = 10.1039/c9sc06153c).
✪ The structure and reactivity of low coordinate (acyclic) PXNXP complexes (DOI = 10.1039/c8dt05049j 10.1021/acs.inorgchem.9b00957) with the isolation and characterisation of nitrous oxide derivatives practicably notable (DOI = 10.1002/anie.201908333).
✪ Advancing the organometallic chemistry of NHC-based CNC pincer complexes (DOI = 10.1039/c6dt01263a 10.1016/j.poly.2017.08.001 10.1021/acs.organomet.8b00595 10.1039/d0dt01137a 10.1002/ejic.202000780).
✪ Quantifying the donor properties of pincer ligands (DOI = 10.1002/ejic.201900727).
Outcomes form the project can summarized under the following headings:
✪ Methods for the preparation of macrocyclic PXEXP pincer ligands (DOI = 10.1039/c9dt04474d 10.1039/c9dt04835a).
✪ Methods for the preparation of late-transition-metal-based rotaxanates and catenates (DOI = 10.1002/anie.201807028 10.1002/chem.202002962 10.1002/anie.202009546 10.1039/d0dt03550e; unpublished)
✪ Mechanistic insights and control of terminal alkyne homocoupling reactions (DOI = 10.1002/anie.201807028 10.1002/chem.202002962 10.1039/d0dt03550e).
✪ Development of a shape changing tandem catalyst for the one-pot preparation of bicyclo[4.2.0]octa-1,5,7-trienes from terminal aryl alkynes (involving formation of 5 C-C bonds in one experimental operation; DOI = 10.1039/c9sc06153c).
✪ The structure and reactivity of low coordinate (acyclic) PXNXP complexes (DOI = 10.1039/c8dt05049j 10.1021/acs.inorgchem.9b00957) with the isolation and characterisation of nitrous oxide derivatives practicably notable (DOI = 10.1002/anie.201908333).
✪ Advancing the organometallic chemistry of NHC-based CNC pincer complexes (DOI = 10.1039/c6dt01263a 10.1016/j.poly.2017.08.001 10.1021/acs.organomet.8b00595 10.1039/d0dt01137a 10.1002/ejic.202000780).
✪ Quantifying the donor properties of pincer ligands (DOI = 10.1002/ejic.201900727).
In the context of the approach adopted, I feel that the work conduced in this project has showcased the potential of research at the interface between organometallic and supramolecular chemistry. I would consider our use of the mechanical bond to promote otherwise unfavourable metal-based reactivity a breakthrough (DOI = 10.1002/anie.202009546).