Projects

Homogeneous Catalysis with Mono- and Multinuclear

Transition Metal Complexes

1. Compounds with reactive M-P or M=P bonds

New P-functionalised (chiral) phosphine ligands can be incorporated in the coordination sphere of transition metal complexes by insertion of polar multiple-bond systems into M-P or M=P bonds. The resulting phosphorus systems are not (or hardly) available using other synthetic routes. (Chiral) phosphine ligands are of essential importance for homogeneous catalysis. In the long term, the goal is to conduct these reactions catalytically.

Insertion of isonitrile into the Ta=P bond of a tantalum phosphinidene complex

2. Complexes with bifunctional ligands, H-X-bridge-Y-H (or X-R, Y-R; with X, Y = O, S, PR, NR, Cp; bridge = alkylene, arylene, etc.)

Heterometallic Cu-La-salen complex

Complexes containing early (electron-poor) and late (electron-rich) metals connected by bridging ligands are of high interest because they can display cooperative synergistic effects between the metals.

We are interested in substituted (bifunctional) ligands of the type H-X-bridge-Y-H (or R) (with X, Y = O, S, PR, NR, Cp; bridge = alkylene, arylene, etc.) and phosphanylalkyl- or -arylcyclopentadienides.

"Switchable" bisphosphine ligand

Furthermore, functionalised bridging ligands (ferrocene, aromatics, heterocycles, conjugated systems, etc.) are used to modify in situ the donor-acceptor properties of phosphines (i.e. electrochemically, UV-Vis spectroscopically, by modifying the temperature or the pH, etc.) and to develop in this way "switchable" phosphines with possible catalytic application.

Dimeric ((RP,SP)-1,2-bis(1-adamantyl-(-)-menthyl-phosphonito)-ortho-dicarbaborane(12))rhodium(I)-chlorid

3. Electron-poor carbaboranylphosphine ligands

The cluster framework of ortho-carbaboranes (three-dimensional electron-poor aromatic analogues) can be functionalised at the C-H groups through phosphorus-containing groups. The newly formed carbaboranylphosphines, -phosphonites, etc., are potential electron-poor (chiral) ligands for use in homogeneous catalysis.

4. Bioorganometallic chemistry-biomimetic complexes
Mono- and multinuclear transition metal complexes as models for metallo-enzymes are used in homogeneous catalysis, i.e. oxidation and CO2 activation reactions.

Biological and Medicinal Chemistry with Inorganic Compounds

1. Carbaboranes for BNCT

Boron derivatives are important in Boron Neutron Capture Therapy (BNCT) for selective tumour targeting in the presence of healthy cells. Cluster compounds, especially meta- and para-carbaboranes are used to deliver boron to the target cells. Carbaboranes exhibit a high boron content, low toxicity and very high kinetic stability. Additionally, they can be easily incorporated into (bio)chemical structures.

New boron compounds are designed by a combination of tumor-targeting strategies: use of phosphonato groups as phosphate mimetics and galactosyl groups that allow specific bonding to lectins on the surface of tumour cells. A further strategy is the incorporation of carbaborane-containing amino acids into carrier peptides.

Asborin

2. Carbaboranes as phenyl ring analogues

Besides their three-dimensional aromaticity, carbaboranes also exhibit extremely high hydrophobicity. Therefore, they can be incorporated instead of phenyl groups as pharmacophoric moieties in biologically active structures, e.g., aspirin.

3. Phosphine-containing amino acids

Phosphine-substituted amino acids are synthesised and coordinated to catalytically active transition metals after incorporation in proteins. The protein pockets should enable stereoselective catalysis.

Precursors for Materials Science

1. Phosphorus-rich transition metal complexes as precursors for binary metal phosphides MPx

[Cu4(P4Ph4)2(PCyp3)3]

Binary metal phosphides MPx often exhibit interesting optical, electronic and/ or magnetic properties. We have developed an approach to this class of compounds starting with volatile phosphorus-rich metal complexes as molecular precursors.

2. Functionalised (chiral) building blocks for MOFs (metal-organic frame-works)

[Zn4O{(4,4´-(CO2)2-2,2´-(OMe)2-1,1´-C6 H3)2}3]n(IRMOF-Wit-1)

Catalytic reactions at the metal centres in MOFs can result in destruction of the three-dimensional framework (catalysis = labile complexes with free coordination sites). Therefore, we use functionalised (chiral) bridging ligands able to build defined three-dimensional frameworks and in addition coordinate metal complex fragments. Furthermore, the (electronic) influence of the framework's metal ions on the second metal centre is of interest.

last modified: 28.10.2019