RESEARCH


Research in the Weller group is based upon synthetic organometallic chemistry, and in particular the generation and stabilisation of transition metal complexes with a low coordination number or which are “operationally unsaturated”.  Through this we are interested in topics related to catalysis (e.g. weakly coordinating anions, hemi-labile ligands), C-H and C-C complexes and activation (via agostic interactions) and the self-assembly of metal fragments to form novel clusters that show promise as models for hydrogen on metal surfaces and new hydrogen storage devices. Our research themes broadly encompass organometallic, inorganic chemistry and catalysis. Close links with members of the organic section gives the possibility that joint inorganic/organic projects related to this area can be pursued. Collaborations with theoretical chemists (especially
Professor Stuart Macgregor, Heriot–Watt, and Professor Jennifer Green, Oxford) also lead to a deeper understanding of structures and reactivity of many of the new complexes made.


Overview



Selected recent highlights of this research include:

The synthesis and definitive characterisation of late transition metal C-C and B-H  and C–H sigma and agostic complexes. These complexes also undergo C-C, B-H and C-H activation in solution, making them genuine intermediates in these transformations of growing synthetic utility. Highlights include the isolation of complexes with C–C agostic interactions, [1, 2] alkyl dehydrogenation and C-H activation, [3,4] and the unraveling of the mechanism of dehydrocoupling of amine boranes: precursors to chemical hydrogen stores for fuel cell applications and novel B–N polymeric materials.[5,6,7]

C-C and C-H


The role of hemilabile ligands in stabilising latent vacant coordination sites on transition metal systems. A recent important result from this work is the development (with Willis, Oxford) of hydroacylation catalysts for challenging substrates (C-H activation) in which each steps on the catalytic cycle has been characterized.[8, 9]

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The synthesis of a new class of unsaturated metal clusters [10,11,12], by a kinetically-controlled self-assembly process, which have an extraordinarily high hydride content; are models for hydrogen attachment on a metal surface; uptake and release H2; undergo a variety of electrochemical processes due their unsaturated electronic structure and act as redox-switchable hydrogen storage materials.

Cluster

References

[1] A. B. Chaplin and A. S. Weller, C-C bond activation of a cyclopropyl phosphine: Isolation and reactivity of a tetrameric rhodacyclobutane, Organometallics, 2010, 29, 2332

[2] S. K. Brayshaw, E. Sceats, G. Kociok-Köhn, J. C. Green, A. S. Weller Rhodium complexes with agostic C-C bonds Proc. Nat. Acad. Sc. 2007, 104, 6921

[3] T. M. Douglas, S. K. Brayshaw, R. Dallanegra, S. A. Macgregor, G. L. Moxham, G. Kociok-Köhn, P. Vadivelu, A. S. Weller and T.Wondimagegn, Intramolecular Alkane Dehydrogenation in Cationic Rhodium Complexes of Tris-Cyclopentylphosphine, Chem. Eur. J. 2008, 14, 1004

[4] N. S. Townsend, A. B. Chaplin, M. A. Naser, A. L. Thompson, N. H. Rees, S. A. Macgregor and A. S. Weller, Reactivity of the Latent 12-Electron Fragment [Rh(PiBu3)2]+ with Aryl Bromides. Aryl-Br and Phosphine Ligand C-H Activation, Chem. Eur. J. 2010, 16, 8378

[5] A. B. Chaplin and A. S. Weller B-H Activation at a Rh(I) centre: A Missing Link in the Transition Metal Catalysed Dehydrocoupling of Amine-Boranes, Angew. Chem. Int. Ed. 2010, 49, 581.

[6] T. M. Douglas, A. B. Chaplin, A. S. Weller, X. Yang and M. B. Hall Monomeric and Oligomeric Amine-Borane σ-complexes of Rhodium. Intermediates in the Catalytic Dehydrogenation of Amine-Boranes. J. Am. Chem. Soc. 2009, 131, 15440

[7] R. Dallanegra, A. B. Chaplin, A. S. Weller Bis-Amine Boranes: A New Binding Mode at a Transition Metal Centre Angew. Chem. Int. Ed.  2009, 48, 6875

[8] R.J. Pawley, G. L. Moxham, R. Dallanegra, A. B. Chaplin, S. K. Brayshaw, A. S. Weller and M, C. Willis Controlling Selectivity in Intermolecular Alkene or Aldehyde Hydroacylation Reactions Catalysed by {Rh(L2)}+ Fragments. Organometallics, 2010, 29, 1717

[9] G. M. Moxham, H. Randell-Sly, S. K. Brayshaw, A. S. Weller and M. C. Willis, Intermolecular Alkene Hydroacylation using b-S-substituted Aldehydes. Mechanistic Insight into the Role of a Hemilabile P-O-P ligand. Chem. Eur. J. 2008, 14, 8383

[10]R. M. Hiney, A. B. Chaplin, J. Harmer, J. C. Green and A. S. Weller Using EPR to follow the reversible dihydrogen addition to a paramagnetic cluster of high hydride count: [Rh6(PCy3)6H12]+ and [Rh6(PCy3)6H14]+, Dalton Transactions, 2010, 39, 1726

[11]S. K. Brayshaw, J. C. Green, R. Edge, E. J. L. McInnes, P. R. Raithby, J. E. Warren and A. S. Weller, [Rh7(PiPr3)6H18][BArF2]4 – A Molecular Rh(111) Surface Decorated with 18 Hydrogens, Angew. Chem. 2007, 46, 7844

[12]S.K. Brayshaw, J. S.McIndoe, F. Marken, P. R. Raithby, J. E. Warren and A. S. Weller Sequential Reduction of High Hydride Count Rhodium Octahedral Clusters [Rh(PR3)6H12][BArF4]2: Redox-Switchable Hydrogen Storage, J. Am. Chem. Soc. 2007, 129, 1793