Our research interests focus on understanding the structure, synthesis and reactivity of mixed-metal organometallic compounds and nanocatalysts.
Organometallics for synthesis
We are interested in the activities of molecular organometallic reagents and have used homo- and heterometallic reagents including Li-Al and Li-Zn systems to fabricate hydridic clusters and to function as chemoselective bases. We work on this with teams in Tokyo, Rennes and Manchester. Recent major advances include:
1) the first demonstration that directed benzylic lithiation can be used to generate tertiary carbanions (below right) and,
2) the combination of CuCN with organolithium reagents to give bimetallic bases such as (TMP)2Cu(CN)Li2.THF (TMP = 2,2,6,6-tetramethylpiperidide; below left) that have applications in directed cupration and C–C bond formation.
For the first tertiary carbanion syntheses by directed metalation and a comparison of anion structures in the solid state and in solution see Chem. Eur. J., 2011, 17, 8078 and 2012, 18, 11036.
See J. Am. Chem. Soc., 2007, 129, 15102, Organometallics, 2009, 28, 38 and Angew. Chem. Int. Ed., 2012, 51, 12081 for advances in lithium amidocuprate structural and mechanistic chemistry and Chem. Eur. J., 2011, 17, 13284 for the applications of lithium cuprates in the elaboration of halopyridines.
Recently we have established the existence of adducts that may help to explain how cuprates of the type (amide)2Cu(Cl)Li2.L (below left; amide = TMP, L = Et2O) can exclude LiX to give highly active (amide)2CuLi.L. Steric effects associated with the amide ligand are thought to be crucial to controlling structure and are suggested if DMP (= cis-2,6-dimethylpiperidide) is used in place of TMP (below right).
See Chem. Eur. J., 2014, 20, 3908 for lithium amidocuprate adducts in directed aromatic cupration and for a recent review see Dalton Trans., 2014, DOI: 10.1039/C4DT01130A.
The ability to access stable and compositionally and dimensionally controllable metallic nanoparticles promises applications in catalysis. We prepare metal nanoparticles (e.g. Au, Cu, Pd, CuM, PdM, M = Sn, Zn…) and use them to achieve controllably functional surfaces by deposition or encapsulation in mesostructured thin films (illustrated below). In collaboration with the Technical University of Eindhoven and Queen's University, NI, applications of the resulting microreactors have been developed in the areas of selective hydrogenation, nanotube growth, and fine chemicals synthesis.
See Lab Chip, 2009, 9, 503 for capillary microreactors wall-coated with mesoporous catalyst supports. For the immobilization of Cu catalysts (see below) and microfluidic Ullmann SNAr-type C-O coupling reactions see Chem. Eur. J., 2012, 18, 1800.
We are also interested in fundamental aspects of nanoparticle synthesis and structure. Recently, we have successfully fabricated oxidatively stable Cu-based nanocatalysts as evidenced by XRD and XPS (below). By introducing Zn we have also achieved CuZn nanoparticles with differing intermetallic ratios and predicted upper d-band energies for Cu. Cu-based catalysts were successfully deployed in multicomponent 1,3-dipolar cycloaddition reactions, yielding 1,2,3-triazoles using unprecedentedly low catalyst loadings and under facile conditions.
See Dalton Trans., 2010, 6496 for the development of new routes towards Cu-based nanosystems and Nanoscale, 2013, 5, 342 for further advances in particle synthesis and stability and the application of Cu-based catalysts to triazole formation.
Our interest in Cu-based nanoparticles, including how they progressively oxidize, has been reflected in work on the passivation of metal nanoparticles towards degenerative processes. As part of a new study into the preparation of magnetic nanoparticles for applications in catalysis we have recently fully characterized monodisperse Co seeds encapsulated by Fe3O4 and established the presence of a sub-surface carbon layer:
The presence of this layer may have implications for core stability (the Co has been shown to be oxidatively stable for up to a year and counting) and the ability to favour the synthesis of core-shell heterostructures. This is the subject of ongoing work that seeks to establish the generality of this encapsulation procedure.
See Nanoscale, 2013, 5, 5765 for the synthesis and detailed characterization of Co-Fe3O4 nanoparticles, including using EFTEM and EELS point scan data (below) that proves the existence of intraparticle carbon. For the extension of detailed characterization of multimetallic core-shell architectures to the Fe3O4-encapsulation of more complex seeds see also Carbon, 2014, 76, 464.
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