A series of heteroleptic copper(I) photosensitizers of the type [(P^P)Cu(N^N)] with an extended π-system in the backbone of the diimine ligand has been prepared. The structures of all complexes are completely characterized by NMR spectroscopy, mass spectrometry, and X-ray crystallography. These novel photosensitizers were assessed with respect to the photocatalytic reduction of protons in the presence of triethylamine and [Fe (CO) ]. Although the solid-state structures and computational results show no significant impact of the π-extension on the structural properties, decreased activities were observed. To explain this drop, a combination of electrochemical and photophysical measurements including time-resolved emission as well as transient absorption spectroscopy in the femto- to nanosecond time regime was used. Consequently, shortened excited state lifetimes caused by the rapid depopulation of the excited states located at the diimine ligand are identified as a major reason for the low photocatalytic performance.

Organometallic complexes containing non-innocent ligands of the type Cp*Ir(tBAFPh)(1), where H2tBAFPh is 2-(2-trifluoromethyl)anilino-4,6-di-tert-butylphenol, were found to activate H2 in a redox-switchable manner. The 16e- complex 1 was inert with respect to H2, CO, as well as conventional basic substrates until oxidation. Oxidation of 16-electron 1 with 1 equiv of Ag+ resulted in ligand-centered oxidation affording salts of [1]+, which were characterized by crystallographically, EPR, and elemental analyses. [1]+ was reduced to 1 in the presence of H2 and the sterically hindered base, 2,6-(tBu)2C5H3N, via a pathway that is first-order in both metal and dihydrogen. Compound [1]+ forms adducts with MeCN, which inhibits catalysis. The catalytic oxidation of H2 was established by electrochemical methods to be associated with the monocation.

The magnetic properties of the title complexes were studied by EPR spectroscopy, magnetometry and ab initio calculations.

Incorporation of a biotinylated Hoveyda-Grubbs catalyst within (strept)avidin affords artificial metalloenzymes for the ring-closing metathesis of N-tosyl diallylamine in aqueous solution. Optimization of the performance can be achieved either by chemical or genetic means.

Artificial metalloenzymes result from combining a catalytically active organometallic moiety with a macromolecular host. The resulting hybrid catalysts combine attractive features of both homogeneous and enzymatic systems. Herein we summarize the recent progress in this emerging field and outline the challenges ahead.