Organometallic Synthesis and Materials

The Organometallic Synthesis and Materials group, led by Prof M Landman and Dr FP Malan, focusses on the rational design, synthesis and application of transition metal complexes featuring carbon-based ligands. The group continuously apply knowledge and expertise generated to strategically design multi-functional ligands that perform specific function(s) when coordinated to a transition metal, depending on the intended application. Current applications of the isolated complexes include homogeneous catalysis, photoluminescence, and bioactivity studies.

Focus

NHC ligand design

The group specializes in the development of strongly donating N-heterocyclic carbene (NHC) ligands, and their subsequent coordination to transition metal complexes. With specific applications in mind, the N-substituents of the NHC ligands are tailored such that the resulting ligands exhibit specific properties. This allows us to synthesize custom NHC ligands that are not commercially available. To date, the group has reported NHC complexes of Cr, Mn, Ru, Rh, Ir, Ni, Cu and Ag.

Catalysis

A catalyst is a chemical compound that increases the rate of a chemical reaction without itself being consumed, and often allows an otherwise impossible reaction to proceed. All the complexes reported in the group exhibited catalytic activity for a specific transformation reaction. Model reactions investigated include C-O (transfer hydrogenation, alcohol oxidation) and C-C (Suzuki-Miyaura coupling, hydrosilylation) functionalization reactions.

Projects

Catalytically active metal complexes featuring hemilabile NHC ligands

In this project we combine tailored NHC ligands with transition metals to form bench-stable complexes exhibiting catalytic activity in a range of C-O and C-C transformation reactions. Several aspects of the NHC ligands and the effect(s) on the stability and catalytic activity of the resulting complexes are systematically evaluated: variation of the N-substituents (electron-donation vs. electron-withdrawing, normal vs. abnormal coordination, monodentate vs. bidentate coordination, type of tether employed etc.). Successful studies include the Suzuki-Miyaura coupling (CpNiBr(NHC) complexes), base-free glucose dehydration (CpCrBrCl(NHC) complexes), transfer hydrogenation (NHC complexes of Rh, Ir, Ru), alcohol oxidation (NHC complexes of Ni, Ru, Rh, and Ir), domino hydrogenation-epoxidation (Ru-NHC complexes) and hydrosilylation (NHC complexes of Rh and Ir) reactions. Further development of highly active systems are to be immobilized on suitable supports to allow for catalyst recycling studies.

Complexes featuring proton-responsive ligands for small molecule activation

Here we focus on employing ligands that are able to rapidly shuttle protons from suitable molecules to specific substrates to form H₂(g), and then subsequently utilizing this to selectively hydrogenate selected carbonyl-containing substrates. Small molecule activation (eg. CO₂, N₂, H₂O₂) are also investigated using similar ligand frameworks.

Photoluminescent metal-NHC complexes

Here we make use of NHC ligands featuring chromophoric N-substituents to allow the resulting NHC ligands to exhibit photoluminescent properties. The photoluminescence of the imidazolium salts and the corresponding metal-NHC complexes are evaluated and compared, and further developed towards employing the compounds in combination with biological applications for tracking in cell-selective targeting studies.

Biologically active metal-NHC complexes

Apart from investigating the catalytic and photophysical properties of the isolated metal-NHC complexes, we also look at the biological activity of the complexes. In collaboration with the Pharmacology department of the University of Pretoria, among others, the complexes are subjected to a range of anti-cancer, anti-bacterial, and anti-viral studies where several complexes have shown promise. Further tailoring of the NHC ligands and their complexes for these specific studies are currently underway.

Our Group

	Team leaders
Prof Marilé Landman		Dr Frikkie Malan
	Current Students

	Mr Estefan van Vuuren (MSc, submitted). Topic: Complexes of Rhodium and Iridium featuring cyclometallated NHC moieties: Synthesis and catalysis.

	Ms Liza Roos (MSc, submitted). Topic: Naphthalimide-NHC complexes: Synthesis and properties in catalytic, biological and photophysical applications

	Mr Babatunde Awe (PhD) Topic: Synthesis and applications of Ru(II) complexes featuring ONO-pincer ligands.