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Dr Graeme Hogarth

Research Overview

Transition metal chemistry is an increasingly diverse area of study. We are interested in applying our expertise in small molecule organometallic-inorganic chemistry in a number of areas, as well as gaining further insight into fundamental transformations at transition metal centres. A number of projects are currently running within the group, some of which are detailed below. All involve the synthesis of new complexes and rely on extensive use of NMR spectroscopy and X-ray crystallography. We apply a hands-on approach so students are involved with all aspects of the work

A: Models of the iron-only hydrogenase enzyme

In the late 1990s it was determined by protein crystallography that the active site of the iron-only hydrogenase enzyme (responsible for the reduction of protons to hydrogen) contained an organometallic diiron centre (Fig.1a). Due to the importance of hydrogen production to the future of the planet, tremendous effort has been focused on developing biomimetics of this catalytic centre; that is isolated molecular complexes which efficiently catalyse the conversion of protons to hydrogen. Our work in this area has focussed on the development of biomimetics in which the diiron centre is made unsymmetrical by virtue of the coordination of multidentate phosphines (Fig.1b-c). We work closely in collaboration with Alex Lewis and Katherine Holt in this multidisciplinary research area.

Chemical structures of iron-only hydrogenase enzyme with and without added multidentate phosphines

B: Binuclear and cluster chemistry

A range of transformations can occur at binuclear and small cluster centres which are not possible at mononuclear centres. We are interested in looking at both the fundamental aspects of such transformations, while also preparing small heterometallic clusters which are capable of displaying unique reactivity traits. Current examples include the reactivity of a range of furyl-bridged diruthenium complexes (Fig. 2) which unusually undergo CO substitution via an associative process resulting from the facile interconversion of bridging and monodentate furyl ligands and some novel osmium-tin clusters which show a range of novel reactivity patterns. This work is in collaboration with Derek Tocher and Professor Shariff Kabir ( Jahangirnagar University, Bangladesh).

Reaction scheme involving CO substitution of a furyl-bridged diruthenium complex

C: Homogeneous and heterogeneous catalysis

The development of new catalysts is a key challenge for the synthetic chemist. We work in two areas in this respect. In the area of homogeneous catalysis, we have shown that a range of low-valent copper complexes are highly active catalysts for the aziridination of alkenes. This is an important process since these small molecules can be readily functionalised via ring-opening to give a range of important amino-containing organics. Very recently we have diversified our efforts into the heterogeneous catalysis domain, taking up the challenge to develop active nanoparticulate catalysts for a range of oxidation processes. We have adopted a bottom-up approach, impregnating small molecular gold clusters into and onto inorganic supports and testing their catalytic properties after carefully “driving off” the supporting ligands. We can follow this process by EXAFS and other techniques to carefully characterise the resulting nanoparticles. This work is carried out in collaboration with Gopinathan Sankar and promising preliminary results have been obtained.

D: Dithiocarbamates and smart dithiocarbamates

Dithiocarbamates are an extremely well-developed class of ligand which are easy to prepare and form stable complexes with all the transition metals (and most other elements). We have worked in this area over a number of years and Hogarth is the author of the definitive review (Transition Metal Dithiocarbamates: 1978-2003, Prog. Inorg. Chem., 2005, 53 , 71-561). Recent efforts have focussed on using palladium dithiocarbamate complexes (Fig. 3a) as volatile precursors to palladium sulfides and the development of smart dithiocarbamates whereby secondary functionalisation is incorporated in order to develop applications in a range of areas including the stepwise synthesis of multimetallic arrays (Fig. 3b) and the functionalisation of gold nanoparticles. Much of the work in the area of smart dithiocarbamates is done in collaboration with Dr James Wilton-Ely ( Oxford University).

Reaction scheme to form multimetallic arrays from palladium dithiocarbamate complexes

E: Small bite-angle diphosphines

Diphosphines find widespread use as co-ligands in homogeneous catalysis. Most frequently, examples with more than one backbone atom, as exemplified by dppe, are utilised since small bite-angle diphosphines (with a single backbone atom) tend towards forming binuclear complexes whereby the diphosphine spans the dimetal centre. Over the past 5 years, however, homogeneous catalysts containing small bite-angle diphosphines have been shown to be extremely active in a range of processes including the important industrial process whereby ethylene is trimerised to give hex-1-ene. In our work we have explored the functionalisation of both the aryl groups and the backbone carbon of the well-known diphosphine bis(diphenylphosphino)methane (dppm) (Fig. 4a; Ar = Ph, X = CH2). Thus, changes to the aryl groups has been carried out, together with the on-metal functionalisation of the backbone carbon (Fig. 4b-c). Attempts are now underway to test these small bite-angle diphosphines in a range of catalytic processes.

Chemical structure of modified diphosphines

F: Imido and oxo chemistry

Over the past 15 years we have been active in the area of metal oxo and imido chemistry. Early goals were the development of oxo and imido transfer agents for applications in organic synthesis, while more recently we have focussed on the reversible carbon-nitrogen bond cleavage and formation at a dimolybdenum centre (Fig. 5). A clear understanding of the factors affecting these processes, especially carbon-nitrogen bond formation, is clearly important for the development of imido-transfer reagents. We find that the insertion of an arylisocyanate occurs selectively into the bridging rather than the terminal imido ligands (discounting the myth that the latter are always more reactive than the former) and have used a combination of NMR and X-ray studies to show that the process occurs with full regioselectivity.

Reversible carbon-nitrogen bond cleavage and formation at a dimolybdenum centre

Some recent publications

  1. Multifunctional dithiocarbamates as ligands towards the rational synthesis of polymetallic arrays: an example based on a piperizine-derived dithiocarbamate ligand, J. D. E. T. Wilton-Ely, D. Solanki, and G. Hogarth, Eur. J. Inorg. Chem., 2005, 4027-4030.
  2. Multiple Nitrene Insertions into the Metal-Sulfur Bonds of Dithiocarbamates: Synthesis Zwitterionic Diamido and Tetraamido Complexes [M{TsNSC(NR2)S}2] and [M{TsNSC(NR)SNTs}2] (M=Cu, Ni, Co), G.Hogarth, K.T.Holman, A.Pateman, I.Richards, A.Sella and J.W.Steed, Dalton Trans., 2005, 2688-2695.
  3. Regioselective and Reversible Carbon-Nitrogen Bond Formation: Synthesis, Structure and Reactivity of Ureato-Bridged Complexes [Mo2(NAr)2(m-X){m-ArNC(O)NAr}(S2CNR2)2] (X = NAr, S; Ar = Ph, p-tolyl; R = Me, Et, Pr), G. Hogarth and I. Richards, Dalton Trans., 2005, 760-773.
  4. Small bite-angle diphosphines: Synthesis and structure of low-valent complexes of bis(di-ortho-tolylphosphino)methane (dotpm) and related ligands, M. Cullen, A. J. Deeming, G. Hogarth and M.-Y. Lee, Can. J. Chem., 2006, 84, 319-329.
  5. A dithiocarbamate-stabilized copper(I) cube, D. Cardell, G. Hogarth and S. Faulkner, Inorg. Chim. Acta, 2006, 359, 1321-1324.
  6. Synthesis, crystal structure and protonation of the asymmetric iron-only hydrogenase model [Fe2(CO)3(m-SCH2CH2CH2S){mh2-Ph2PCH2CH2P(Ph)CH2CH2PPh2}], G. Hogarth and I. Richards, Inorg. Chem. Commun., 2007, 10, 66-70.
  7. Allyl palladium dithiocarbamate and related complexes as precursors to palladium sulfides, A. Birri, B. Harvey, G. Hogarth, E. Subasi and F. Ugar, J. Organomet. Chem., 2007, 692, 2448-2455.
  8. Models of the iron-only hydrogenase: Structural studies of chelating diphosphine complexes [Fe(CO)4(-pdt)(2-diphosphine)], F.I. Adam, G. Hogarth, I. Richards and B.E. Sanchez, Dalton Transactions, 2007, 2495-2498.
  9. Synthesis and crystal structure of [Ru8(m5-S)2(m4-S)(m3-S)(m-CNMe2)2(m-CO)(CO)15] formed via the double sulphur-carbon bond cleavage of dithiocarbamate ligands, A. J. Deeming, C. Forth and G. Hogarth, J. Organomet. Chem., 2007, 692, 4000-4004.
  10. Models of the iron-only hydrogenase: Reactions of [Fe2(CO)6(m-pdt)] with small bite-angle diphosphines yielding bridge and chelate diphosphine complexes [Fe2(CO)4(diphosphine)(m-pdt)], F. I. Adam, G. Hogarth and I. Richards, J. Organomet. Chem., 2007, 692, 3957-3968.
  11. Small bite-angle diphosphines: Synthesis and molecular structures of [M(CO)4{X2PC(R1R2)PX2}] (M = Mo, W; X = Ph, Cy; R1 = H, Me, Et, Pr, allyl; R2 = Me), G. Hogarth and J. Kilmartin, J. Organomet. Chem., 2007, 692, 5655-5670.
  12. Chelate and bridge diphosphine isomerization: Triosmium and triruthenium clusters containing 1,1΄-bis(diphenylphosphino)ferrocene (dppf), N. Begum, U.K. Das, M. Hassan, G. Hogarth, S.E. Kabir, E. Nordlander, M.A. Rahman and D.A. Tocher, Organometallics, in press.
  13. Bimetallic osmium-tin clusters: Addition of triphenyltinhydride to unsaturated [Os3(CO)8{-Ph2PCH2P(Ph)C6H4}(m-H)] and saturated [Os3(CO)10(m-dppm)], M.R. Hasan, G. Hogarth, G. M. Golzar Hossain, S.E Kabir, A.K. Raha, M.S. Saha and D.A. Tocher,Organometallics, in press.
  14. Reaction of Ru3(CO)12 with tri(2-furyl)phosphine: Di-and tri-substituted triruthenium and phosphido-bridged diruthenium complexes, N. Begum, M.A. Rahman, M.R. Hassan, S.E. Kabir, E. Nordlander, G. Hogarth and D.A. Tocher, J. Organomet. Chem., in press.