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The Hohloch Group
Non-classical Carbenes and Macrocyclic Systems

Research in the Hohloch group

New (chelating) Cyclic Alkyl Amino Carbenes

Cyclic Alkyl/Aryl Amino Carbenes (CAACs) are part of a new family of N-heterocyclic Carbenes (NHCs), which where first introduced to the literature by Guy Bertrand in 2005. Due to their lower heteroatom stabilization, these carbenes exhibit a higher nucleophilicity as well as a higher electrophilicity compared to classical NHCs. Especially the latter is responsible for their unique electrochemical properties. Our goal is to use these "non-innocent" properties of the CAACs to design new effective and switchable catalysts.

1,2,3-Triazolylidene Complexes of Early Transition Metals and Lanthanides

Besides Cyclic Alkyl Amino Carbenes, another emerging family within the group of carbenes are so called abnormal or mesoionic carbenes. One of the most prominent examples for these mesoionic carbenes are 1,2,3-triazole derived 1,2,3-triazolylidenes. In peculiar, these are interesting because of their high σ-donor strength as well because of their modular synthesis based on the copper catalyzed [3+2] cycloadditon reaction between azides and alkynes. Within the last years, metal complexes of late transition metals have already been shown to be prominent catalysts in various transformations, e.g. proton reduction or the catalytic oxygenation of unactivated C-G bonds. 

However, despite the recent interest in these carbenes, metal complexes of early transition metals and the lanthanides haven't been investigated until now.

Functionalized macrocyclic ligands

Macrocyclic ligands are often also referred to as the building block of lifes. Metal complexes of macrocyclic ligands particularly stand out due to their high kinetic as well as thermodynamic stability and their capability of stabilizing unsual oxidation states of various metal ions, such as Au(II), Cu(IV) etc. 

Our aim is to design functionalized macrocyclic ligands based on the tetramethyltetraazaannulene (TMTAA) ligand, bearing two external and one internal coordination side to build heterotrinuclear metal complexes. The influence of the metals in the "outer" coordination sides towards the chemical and electronic properties of the metal in the "inner" coordination side will be tested and explored.

Dinuclear lanthanide complexes based on makrocyclic ligands

Metal complexes of lanthanides are currently of high interest in the design of single molecular magnets (SMM). However,a currentproblem here is the operating temperature of such sytems, which is often below the temperature of liquid nitrogen. One way to overcome this isue has been the to design multinuclear metal complexes with "non-innocent" bridging ligands. As a spectator ligand on the lanthanides, cyclopentadiened ligands are commonly used. Our focus now is to develop systems which use the tetramethyltetraazaannulene (TMTAA) ligand as a spectator ligand and bridge these building blocks with other macrocyclic ligands (e.g. prophyrines or corroles) and investigate the resulting molecules towards their magnetic and spectroscopic properties.

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