Dr Simon Aldridge

Academic History

2010-present Professor of Main Group Chemistry, Fellow in Inorganic Chemistry and Tutor for

Graduates, The Queen’s College.

2007-2010 University Lecturer in Inorganic Chemistry and Fellow of the Queen’s College.

1998-2006 School of Chemistry, Cardiff University. Senior lecturer from 2004.

1997-1998 Post-doctoral associate, Imperial College London (with Prof DMP Mingos FRS).

1996-1997 Fulbright Scholar and post-doctoral associate, Notre Dame, Indiana, USA

(with Prof TP Fehlner).

1996 DPhil, Inorganic Chemistry Laboratory, University of Oxford (with Prof AJ Downs).

Research Interests / Highlights

Main Group and Transition Metal Organometallic Chemistry

Current research encompasses projects which are more fundamental in nature (‘discovery driven’) – such as studies aimed at systematically uncovering the chemistry of new types of chemical bond, as well as those which are targeted at specific applications - such as sensors for toxic environmental contaminants and catalysts for hydrogen production from B/N containing materials. An over-arching theme of much of the work is the stabilization and application of compounds with potent Lewis acidity.

Three main areas encompass a significant proportion of recent research efforts:

(i) The synthetic, structural and reaction chemistry of transition metal complexes containing multiple bonds to group 13 elements;

(ii) Structure/bonding studies of transition metal boryl/borane and related complexes and investigation of their implication in amine-borane activation and C-H functionalization chemistries; and

(iii) The design and synthesis of novel Lewis acids with applications in sensors and catalysis.

Recent highlights in these areas include the first example of a transition metal complex containing a BN alkene analogue (Angew. Chem., Int. Ed. 2010, 49, 921; J. Am. Chem. Soc. 2010, 132, 10578), the first trapping of group 13/group 17 analogues of N₂ and CO (Angew. Chem., Int. Ed. 2009, 48, 3669; J. Am. Chem. Soc. 2008, 130, 5449; J. Am. Chem. Soc. 2008, 130, 16111; also the subject of two highlight articles in Angew. Chem., Int. Ed. 2008, 47, 6326 and 2010, 49, 3412), the first Fe=B double bond (J. Am. Chem. Soc. 2003, 125, 6356; J. Am. Chem. Soc. 2010, 132, 4586,), the first examples of metathesis chemistry involving M=B bonds (Angew. Chem., Int. Ed. 2005, 44, 7457; highlighted in Science 2005 310, 747); functionalization of organic substrates by borylene transfer and/or cycloaddition (Angew. Chem., Int. Ed. 2006, 45, 3513; Angew. Chem., Int. Ed. 2006, 45, 6118), and novel Lewis acid sensors for F^-/HF and CN^-/HCN (Angew. Chem., Int. Ed. 2005, 44, 3606; Inorg. Chem. 2008, 47, 793; Chem. Eur. J. 2008, 14, 7525; Inorg. Chem. 2010, 49, 157). Fuller details of current work can be found at http://users.ox.ac.uk/~quee1989 (research group webpage).

The Aldridge group specialises in a range of techniques for the synthesis and manipulation of air-sensitive compounds, and uses a variety of approaches (multinuclear NMR, X-ray crystallography, computational chemistry) to characterize new molecules. Active collaborations exist with Ian Fallis (Cardiff), Cameron Jones (Monash, Australia), E. Jemmis (Bangalore, India), Philip Mountford and John McGrady (both Oxford), the Defence Science and Technology Laboratory (Porton Down) and BP (Hull).

Recent highlighted work on M=B double bonds (left) and chemical sensors (right)

FUNDAMENTAL STUDIES OF NOVEL CHEMICAL BONDS:

The coordination chemistry of CO at low-valent transition metals remains one of the cornerstones of organometallic chemistry, and that of the dinitrogen molecule underpins synthetic attempts to mimic biological activation of N₂. By contrast coordination of the isoelectronic 10 valence electron molecule BF has not previously been achieved. Recent studies in the Aldridge group have addressed this deficiency, allowing for the first time the structural characterization of a transition metal complex of BF (Angew. Chem., Int. Ed. 2009, 48, 3669; highlight: Angew. Chem., Int. Ed. 2010, 49, 3412). Moreover, a terminal mode of coordination can be accessed by the use of the heavier group 13 monohalide fragment GaI (J. Am. Chem. Soc. 2008, 130, 5449; J. Am. Chem. Soc. 2008, 130, 16111; also subject of a highlight article in Angew. Chem., Int. Ed. 2008, 47, 6326). These synthetic and structural studies have been complemented by in-depth analyses of electronic structure revealing, for example, weaker pi bonding and readier heterolytic cleavage for the BF diatomic molecule over CO (our work in this area was recently reviewed in a feature article: Chem. Commun. 2009, 1157).

These studies form part of a broader programme aimed at developing versatile synthetic routes to complexes containing unsaturated group 13 ligand systems (e.g. metal boron double bonds), evaluating their electronic structure, and exploiting their fundamental patterns of reactivity – ultimately towards the catalytic functionalization of organic substrates. These studies have led to the landmark results such as the first Fe=B double bond (J. Am. Chem. Soc. 2003, 125, 6356), the first examples of metathesis chemistry involving M=B bonds (Angew. Chem., Int. Ed. 2005, 44, 7457; highlighted in Science 2005 310, 747); and to the functionalization of organic substrates by borylene transfer and/or cycloaddition (Angew. Chem., Int. Ed. 2006, 45, 3513; Angew. Chem., Int. Ed. 2006, 45, 6118). Aspects of this fundamental chemistry have been included in recent editions of undergraduate chemistry textbooks.

Analysis of compounds containing M=B multiple bonds by crystallography (left) and quantum chemistry (right).

Highly electrophilic rhodium and iridium complexes in B-H, C-H and N-H activation chemistry:

Recent work sponsored by the EPSRC has examined synthetic and stabilization strategies for cationic 14-electron group 9 metal complexes stabilized by strongly electron donating N-heterocyclic carbene ligands. One of the prime motivating forces for our work in this area is to examine the possibility for using such systems in catalytic processes, and in particular for the trapping and characterization of potential intermediates in CC and BN dehydrogenation chemistry. With this in mind the trapped metathesis intermediate [(IMes)₂M(H)₂Cl(Na)]⁺[BAr^f₄]^-, for example, serves as a convenient source of [(IMes)₂M(H)₂]⁺ (by loss of NaCl) and has been exploited in the synthesis of the first examples of transition metal aminoborane complexes (Angew. Chem., Int. Ed. 2010, 49, 921; J. Am. Chem. Soc. 2010, 132, 10578). Systems of this sort are of interest as model intermediates in the metal-catalysed dehydrogenation of amineboranes and provide an interesting contrast – in coordination chemistry terms – with isoelectronic alkene donors (‘end-on’ vs. ‘side-on’). Ongoing work has revealed the formation (and structural characterization) of 14-electron primary boryl hydride species under catalytic conditions and is examining approaches to the key technological problem of B/N fuel rehydrogenation using high energy sources of the H₂ fragment.

ANION AND NEUTRAL MOLECULE SENSORS:

The binding of anions by receptor molecules is an area of enormous recent research interest, which is not only relevant to biological systems, but has widespread applications, for example in catalysis and sensor systems. From the viewpoint of sensor design, key features are selectivity (i.e. the recognition of the target anion over possible contaminants) and signalling (i.e. the triggering of a measurable response on anion binding). A wide variety of chemical strategies have been employed to selectively bind anions, and we have been using group 13 based Lewis acids in this area – with the selectivity for given anions based, for example, on the strength of the donor/acceptor bond formed (e.g. for fluoride, F^-) or on the complementary geometry of the binding sites and target anion (e.g. for CN^-or [CH₃CO₂]^-)

More applied work has targeted the use of redox-active Lewis acids in the development of highly sensitive, highly selective sensors for F^-/HF and CN^-/HCN. This facet of the group’s research efforts has led to the realization of new synthetic methodologies for ferrocene-derivatized Lewis acids and ultimately to the development of a simple colorimetric swab technology which allows for the detection of chemical warfare agents (CWAs) in both the (weaponized) liquid and vapour phases. This work has been funded by back-to-back EPSRC grants and the resulting patented IP is the basis for current commercialization negotiations. Despite the commercial sensitivities, some aspects of this work have recently been published: Angew. Chem., Int. Ed. 2005, 44, 3606; Dalton Trans. 2007, 3486; Inorg. Chem. 2008, 47, 793; Chem. Eur. J. 2008, 14, 7525; Inorg. Chem. 2010, 49, 157.

A key future target in this area, ultimately aimed at improving device sensitivity, is the development of catalytic sensors. The aim is to identify host/guest complexes formed between receptor and target analyte which will catalyze an orthogonal reaction. Our approach utilizes electron transfer chemistry as the basis for catalysis, e.g. of a dye bleaching reaction.

Colorimetric fluoride ion sensing by polyborylated ferrocenes: structural influences on thermodynamics and kinetics.

J.K. Day, C. Bresner, N.D. Coombs, I.A. Fallis, L.-L. Ooi, R.W. Harrington, W. Clegg and S. Aldridge.

Inorg. Chem., 2008, 47, 793-804 (selected as cover article).

A Group 13 / Group 17 Analogue of CO and N₂: Coordinative Trapping of the GaI Molecule.

N.D. Coombs, W. Clegg, D.J. Willock and S. Aldridge.

J. Am. Chem. Soc., 2008, 130, 5449-5451.

Additionally this paper was the subject of a Highlight article in Angew. Chem., Int. Ed. (2008, 47, 6326-6328).

AND/NOT Sensing of Fluoride and Cyanide by Ferrocene Derivatized Lewis Acids.

A.E.J. Broomsgrove, D. Addy, C. Bresner, I.A. Fallis, A.L. Thompson and S. Aldridge.

Chem. Eur. J., 2008, 14, 7525-7529.

Cationic Terminal Gallylene Complexes by Halide Abstraction: Coordination Chemistry of a Valence Isoelectronic Analogue of CO and N₂.

N.D. Coombs, D. Vidovic, J.K. Day, A.L. Thompson, A. Stasch, W. Clegg, L. Russo, L. Male, M.B. Hursthouse, D.J. Willock and S. Aldridge

J. Am. Chem. Soc., 2008, 130, 16111-16124.

Transition Metal Borylene Complexes: Boron Analogues of Classical Organometallic Systems.

D. Vidovic, G.A. Pierce and S. Aldridge.

Chem. Commun., 2009, 1157-1171.

Structures and Aggregation of the Methylamine-Borane Molecules, Me_nH_3–nN.BH₃ (n = 1-3), Studied by X-ray Diffraction, Gas-phase Electron Diffraction, and Quantum Chemical Calculations.

S. Aldridge, A.J. Downs, C.Y. Tang, S. Parsons, M.C. Clarke, R. Johnstone, H.E. Robertson,D.W.H. Rankin, and D.A. Wann.

J. Am. Chem. Soc., 2009, 131, 2231-2243.

Half-sandwich group 8 borylene complexes: synthetic and structural studies, and oxygen atom abstraction chemistry.

G.A. Pierce, D. Vidovic, D.L. Kays,N.D. Coombs, A.L. Thompson, D.J. Willock, E.D. Jemmis, S. De and S. Aldridge.

Organometallics, 2009, 28, 2947-2960.

Reactivity of cationic terminal borylene complexes: Novel mechanisms for insertion and metathesis chemistry involving strongly Lewis acidic ligand systems.

S. De, G.A. Pierce, D. Vidovic, D.L. Kays,N.D. Coombs, E.D. Jemmis and S. Aldridge

Organometallics, 2009, 28, 2961-2975.

Sterically encumbered iridium bis(N-heterocyclic carbene) systems: Multiple C-H activation processes and isomeric normal/abnormal carbene complexes.

C.Y. Tang, W. Smith, D. Vidovic, A.L. Thompson, A.B. Chaplin and S. Aldridge.

Organometallics, 2009, 28, 3059-3066.

Coordination and activation of the BF molecule.

D. Vidovic and S. Aldridge.

Angew. Chem., Int. Ed., 2009, 48, 3669-3672.

Additionally this paper was the subject of a Highlight article in Angew. Chem., Int. Ed. (2010, 49, 3412).

Facile syntheses of dissymmetric ferrocene-functionalized Lewis acids and acid/base pairs.

I.R. Morgan, A. Di Paolo, D. Vidovic, I.A. Fallis and S. Aldridge

Chem. Commun., 2009, 7288-7290.

Evaluation of electronic, electrostatic and hydrogen bond co-operativity in the binding of cyanide and fluoride by Lewis acidic ferrocenylboranes.

A.E.J. Broomsgrove, D. Addy, A. Di Paolo, I.R. Morgan, C. Bresner, V. Chislett, I.A. Fallis, A.L. Thompson, D. Vidovic, S. Aldridge.

Inorg. Chem., 2010, 49, 157-173.

Rhodium and Iridium Aminoborane Complexes: Coordination Chemistry of BN Alkene Analogues.

C.Y. Tang, A.L. Thompson, S. Aldridge.

Angew. Chem., Int. Ed., 2010, 49, 921-925.

Fluoride Sensing by Lewis Acidic Boranes.

C.R. Wade, A.E.J. Broomsgrove, S. Aldridge, F.P. Gabbaï.

Chem. Rev. 2010, 110, 3958–3984.

Generation of Cationic Two-Coordinate Group 13 Ligand Systems by Spontaneous Halide Ejection: Remarkably Nucleophile Resistant (Dimethylamino)borylene Complexes.

D.A. Addy, G.A. Pierce, D. Vidovic, D. Mallick, E.D. Jemmis, J.M. Goicoechea, S. Aldridge.

J. Am. Chem. Soc. 2010, 132, 4586–4588.

Dehydrogenation of saturated CC and BN bonds at cationic N-heterocyclic carbene stabilized M(III) centers (M = Rh, Ir).

C.Y. Tang, A.L. Thompson, S. Aldridge.

J. Am. Chem. Soc., 2010, 132, 10578-10591.

Research Guides

Professor Simon Aldridge

Research

Selected Publications