Copper complexes of the hybrid guanidine ligands 1,3-dimethyl-N-(quinolin-8-yl)-imidazolidin-2-imine (DMEGqu) and 1,1,3,3-tetramethyl-2-(quinolin-8-yl)-guanidine (TMGqu) have been studied comprehensively with regard to their structural and electrochemical properties and their activity in atom transfer radical polymerization (ATRP). A simple analysis of the molecular structures of the complexes gives no indication about their activity in ATRP; however, with the help of DFT and NBO analysis the influence of particular coordinating donors on the electrochemical properties could be fully elucidated. With an adequate DFT methodology and newly applied theoretical isodesmic reactions it was possible to predict the relative position of the redox potentials of copper complexes containing DMEGqu and TMGqu ligands. In addition, predictions could be made as to whether the complexes of DMEGqu or TMGqu are more active in ATRP. Four new Cu(I) complexes were tested in standard ATRP reactions and kinetically investigated both in bulk and in solution. It could be proven that complexes featuring DMEGqu possess a lower redox potential and are more active in ATRP, although the tetramethylguanidine moiety represents the stronger donor.

The enzyme tyrosinase contains a reactive side‐on peroxo dicopper(II) center as catalytically active species in C−H oxygenation reactions. The tyrosinase activity of the isomeric bis(μ‐oxo) dicopper(III) form has been discussed controversially. The synthesis of bis(μ‐oxo) dicopper(III) species [Cu2(μ‐O)2(L1)2](X)2 ([O1](X)2, X=PF6−, BF4−, OTf−, ClO4−), stabilized by the new hybrid guanidine ligand 2‐{2‐((dimethylamino)methyl)phenyl}‐1,1,3,3‐tetramethylguanidine (L1), and its characterization by UV/Vis, Raman, and XAS spectroscopy, as well as cryo‐UHR‐ESI mass spectrometry, is described. We highlight selective oxygenation of a plethora of phenolic substrates mediated by [O1](PF6)2, which results in mono‐ and bicyclic quinones and provides an attractive strategy for designing new phenazines. The selectivity is predicted by using the Fukui function, which is hereby introduced into tyrosinase model chemistry. Our bioinspired catalysis harnesses molecular dioxygen for organic transformations and achieves a substrate diversity reaching far beyond the scope of the enzyme.

The synthesis of the new hybrid guanidine ligands DMEGdmap, DMEGdeae, TMGdmab, DMEGdmab, TMGdeab and DMEGdeab is reported. These ligands were combined with zinc chloride, and the six obtained new complexes were structurally characterised by X-ray crystallography and NMR spectroscopy. Further six new zinc chloride complexes were obtained from the hybrid guanidine ligands TMGdmae, DMEGdmae, TMGdeae, TMGdmap, TMGdeap and TEGdeap. Each of the twelve com- [a]

Ligands DMEG6etqu, TMG6etqu, DMEG6buqu, and TMG6buqu were developed on the basis of guanidine quinoline (GUAqu) ligands 1,3-dimethyl-N-(quinolin-8-yl)imidazolidin-2imine (DMEGqu) and 1,1,3,3-tetramethyl-2-(quinolin-8-yl)guanidine (TMGqu). These ligands feature an alkyl substituent at the C6 of the quinoline backbone. The synthetic strategy developed here enables inexpensive syntheses of any kind of C6-substituted GUAqu ligands. On one hand, the alkylation increases the solubility of corresponding copper complexes in apolar atom transfer radical polymerization (ATRP) monomers like styrene. On the other hand, it has a significant electronic influence and thus an effect on the donor properties of the new ligands. Seven Cu I and Cu II complexes of DMEG6etqu and TMG6etqu [a]

Guanidines are highly useful ligands which have conquered coordination chemistry within the last 20 years. Their CN 3 moiety allows multiple substitution patterns which enables tailoring them to a large variety of applications, ranging from bioinorganic coordination chemistry via medicinal chemistry to polymerisation catalysis. In bioinorganic chemistry, guanidines gave important stimuli in the modelling of copper type 1, 2 and 3 enzymes. This review provides with a comprehensive overview on complexes which have been reported with neutral guanidine ligands. Peralkylated guanidines as well as bicyclic or more complex guanidine-comprising entities are described in their coordination chemistry with transition and main-group metals. The structural features of the complexes as well as their most prominent features in bioinorganic chemistry or polymerisation catalysis are highlighted. Hereby, the role of the delocalisation of the positive charge within the guanidine unit gained during coordination is discussed in its importance for efficient and robust coordination. The delocalisation within the CN 3 unit can be measured by the structural value ρ which is discussed for numerous systems. The charge delocalisation makes neutral guanidines versatile and efficient for the stabilisation of highly different coordination modes and a large variety of oxidation states.