An aluminium(I) complex originally reported by Roesky and coworkers (ref) was prepared and showed that it undergoes extremely facile oxidative addition reactions with fluorocarbons. These reactions proceed quantitatively and cleanly at room temperature or below and result in breaking the carbon–fluorine bond by oxidative addition to the Al(I) centre. The aforementioned reaction does not require a catalyst and is highly selective for C–Al bond formation (>99:1). To date we have applied it to 8 substrates including fluoroarenes, fluoroolefins and fluoroalkanes. Our initial results have been published in a communication (Chem. Commun. 2015, 51, 15994).
In parallel we have developed catalytic methods that originate from a structurally related aluminium(III) dihydride. While inefficient catalysts based on zirconium (Angew. Chem., Int. Ed. 2012, 51, 12599) and rhodium (Organometallics 2014, 33, 7027) formed the basis of our proposal. Over the course of our study we discovered a new palladium catalyst that was highly effective and selective. This catalyst operates at 1 mol% loading or less with TOFs ~10 h-1 and has been applied to 12 substrates. Again the catalyst is selective for the formation of C–Al bonds, but in this case C–H bond formation is competitive and selectivity for C–Al versus C–H bond formation ranges from 4.4:1 to 27:1.
During our original investigation of the Zr-catalysed method we discovered that the aluminium reagent coordinates to the zirconium complex. This new heterobimetallic contains two distinct metals that are bridged by a hydrogen atoms and is capable of breaking carbon–fluorine bonds and acting as a catalyst for the process described above. As an extension of these studies we investigated new types of coordination complexes in which main group metal hydrides (M = Zn, Mg, Al) act as ligands for transition metals. As part of our preliminary results we described coordination and bond breaking in a series of Rh-complexes (Chem. Sci. 2015, 6, 5617). During the grant period we discovered a whole host of new complexes, including 10 crystallographically characterised heterobimetallics and through a combination of experiment and theory (DFT calculations) described the trajectory of approach of zinc hydrides to transition metals (Angew. Chem., Int. Ed. 2016, 55, 16031) and the solution dynamics of new types of complexes containing three metal atoms bridged by two hydrogen atoms (Chem. Eur. J. 2017, 23, 5682).
Exploitation and Dissemination:
The majority of the work carried out during this fellowship has been published in top quality journals within the chemistry community. A final manuscript is being prepared on the Pd-catalysed methods for C–F bond activation. Key findings have formed the basis of new grant applications and this includes successful funding applications to horizon2020. These include, an ERC starting grant for the host group (FluoroFix) which centers on extension of the development of the catalytic methods but applied to remediation of environmentally persistent HFCs and HFOs, and a Marie Curie Fellowship (FluoroCross) which aims to develop related synthetic methods but based entirely on magnesium reagents recently reported by the host group (J. Am. Chem. Soc., 2016, 138, 12763). The groups work on heterobimetallic complexes was recently recognised by award of the Harrison-Meldola Memorial Prize from the RCS and our findings will be used to form the basis of a further grant application to the UK funding body the EPSRC developing new types of catalysts based on two metals held in close proximity.
