Computational Organometallic Chemistry

Research uses computational chemistry to model reaction mechanisms in transition metal organometallic chemistry. Methods employed include density functional theory, hybrid QM/MM calculations and molecular dynamics. We aim to understand challenging bond activation processes (C-H and C-F bond cleavage), rationalise unusual reactivity patterns and model multi-step catalytic cycles. Research is usually carried out in close collaboration with experimental chemists.

1. Ambiphilic Metal-Ligand Assisted (AMLA) C-H Activation

We have developed the concept of Ambiphilic Metal-Ligand Assisted (AMLA) C-H activation. In this process an agostic interaction to an unsaturated metal centre combines with H-bonding to a basic co-ligand to facilitate C-H bond cleavage. With aromatic C-H activation at [Pd(OAc)₂] this mechanism supersedes the long-proposed Wheland-type intermediate.  AMLA can account for facile C-H bond cleavage of both e^--deficient and e^--rich aromatic substrates at a range of late transition metal centres.

Figure 1. Computed agostic Intermediate in the AMLA-6 C-H Activation of dimethylbenzylamine at [Pd(OAc)₂].

2. Metallophosphoranes and Aromatic C-F Bond Activation

We have defined novel ligand-assisted mechanisms for breaking the strong C-F bond of fluoroaromatics. This process involves nucleophilic attack by an e^--rich metal centre with addition of a C-F bond over the M-L moiety, where L can be PR₃, SiR₃ or BR₂. For L= PR₃metallophosphoranes, [L_nM-(PFR₃)], are formed as intermediates or transition states. Metallophosphoranes also play a role in the unusual M-F/P-R exchange reactions, such as the interconversion of [RhF(PPh₃)₃] to [Rh(Ph)(PFPh₂)(PPh₃)₂].

Figure 2. The central role of metallophosphoranes in phosphine-assisted C-F bond activation and F/R exchange processes.

3. Ruthenium N-Heterocyclic Carbene (NHC) Complexes in Catalysis

NHC ligands often confer enhanced reactivity on metal complexes. An example is the hydrodefluorination of C₆F₅H to give 1,2-C₆F₄H₂ catalysed by [Ru(H)₂(CO)(NHC)(PR₃)₂] species. Calculations show this unusual ortho-selectivity arises from a nucleophilic attack mechanism where the hydride ligand (and not the metal) acts as the reacting species. Calculations also aim to understand the stability of NHC ligands towards metal-based decomposition reactions such as C-H, C-C and C-N activation.

Figure 3. Nucleophilic attack of a hydride ligand at the ortho position of C₆F₅H.

• Head of Institute, Institute of Chemical Sciences
• Programme Director - Chemistry with a Year in Australia

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