The bridge towards a more stable and active side-on-peroxido (Cu2II(µ-η2:η2-O2)) complex as a tyrosinase model system.

A novel dinucleating bis(pyrazolyl)methane ligand was developed for tyrosinase model systems. After ligand synthesis, the corresponding Cu(I) complex was synthesized and upon oxygenation, formation of a µ-η2:η2 peroxido complex could be observed and monitored using UV/Vis-spectroscopy. Due to the high stability of this species even at room temperature, a molecular structure of the complex could be characterized via single-crystal XRD. Additional to its promising stability, the peroxido complex showed catalytic tyrosinase activity which was investigated via UV/Vis-spectroscopy. Products of the catalytic conversion could be isolated and characterized and the ligand could be successfully recycled after catalysis experiments. Furthermore, the peroxido complex was reduced by reductants with different reduction potentials. The characteristics of the electron transfer reactions were investigated with the help of the Marcus relation. The combination of the high stability and catalytic activity of the peroxido complex with the new dinucleating ligand, enables the shift of oxygenation reactions for selected substrates towards green chemistry, which is furthered by the efficient ligand recycling capability.

Evaluation of Pd→B Interactions in Diphosphinoborane Complexes and Impact on Inner-Sphere Reductive Elimination.

The dative Pd→B interaction in a series of R DPBR' Pd0 and PdII complexes (R DPBR' =(o-PR2 C6 H4 )2 BR', diphosphinoborane) was analyzed using XRD, 11 B NMR spectroscopy and NBO/NLMO calculations. The borane acceptor discriminates between the oxidation state PdII and Pd0 , stabilizing the latter. Reaction of lithium amides with [(R DPBR' )PdII (4-NO2 C6 H4 )I] chemoselectively yields the C-N coupling product. DFT modelling indicates no significant impact of PdII →B coordination on the inner-sphere reductive elimination rate.