The synthesis and physicochemical properties of the new molybdenum dinitrogen complexes [Mo(N 2 )(tdppme)-(dmpm)] (2) and [Mo(N 2 )(tdppme)(dppm)] (3) are reported. Complexes 2 and 3 are facially coordinated by the tripodal ligand 1,1,1-tris(diphenylphosphanylmethyl)ethane (tdppme) and contain the bidentate coligands bis(dimethylphosphanyl)methane (dmpm) and bis(diphenylphosphanyl)-methane (dppm), respectively. They are accessible by amalgam reduction of the Mo III precursor [MoBr 3 (tdppme)] (1) under nitrogen in the presence of dppm and dmpm, respectively. Protonation of 2 with trifluoromethanesulfonic acid

A series of density functional theory (DFT) calculations on the full [Mo(HIPT)N3N] catalyst are performed to obtain an energy profile of the Schrock cycle. This is a continuation of our earlier investigation of this cycle in which the bulky hexaisopropyterphenyl (HIPT) substituents of the ligand were replaced by hydrogen atoms (Angew. Chem., Int. Ed. 2005, 44, 5639). In an effort to provide a treatment that is as converged as possible from a quantum-chemical point of view, the present study now fully takes the HIPT moieties into account. Moreover, structures and energies are calculated with a near-saturated basis set, leading to models with 280 atoms and 4850 basis functions. Solvent and scalar relativistic effects have been treated using the conductor-like screening model and zeroth-order regular approximation, respectively. Free reaction enthalpies are evaluated using the PBE and B3LYP functionals. A comparison to the available experimental data reveals much better agreement with the experiment than preceding DFT treatments of the Schrock cycle. In particular, free reaction enthalpies of reduction steps and NH3/N2 exchange are now excellently reproduced.

Conflicting results have been reported with respect to the photoinduced switching of the magnetic properties of [FeIII(salten)]+ complexes [salten = 4‐azaheptamethylene‐1,7‐bis(salicylideneiminate)] coordinated by photoisomerizable ligands. In order to address this problem, two FeIII complexes [Fe(salten)(3‐azpy)]BPh4 (1) and [Fe(salten)(4‐azpy)]BPh4 (2) have been synthesized and characterized by various physicochemical methods (azpy = phenylazopyridine). Both 1 and 2 exhibit a low spin (S = 1/2) to high spin (HS, S = 5/2) transition in the solid state. In solution at room temperature both complexes are predominantly HS. Upon exposure to 310 (trans → cis) and 440 nm radiation (cis → trans) the free and coordinated 3‐ and 4‐azpy ligands undergo a reversible cis–trans isomerization. For 2 a corresponding reduction of the HS fraction 2 % is observed, whereas in 1 no effect is observed. Extensive DFT calculations, which employ different functionals and basis sets, explain this experimental result. The consequences of these findings with respect to the design of spin‐switchable iron(III) complexes with photoactive ligands are discussed.

A new tyrosinase model based on the mononuclear copper(I) complex CuL bzm 1 is synthesized and characterized. The ligand L bzm 1 of this system contains a combination of an imine and a benzimidazole function which renders the system more biomimetic in comparison to the recently published L py 1 model of tyrosinase (M. Rolff, J. Schottenheim, G. Peters, F. Tuczek, Angew. Chem. Int. Ed. 2010, 122, 6583). As shown by UV/Vis and NMR spectroscopy, the CuL bzm 1 complex catalytically mediates the conversion of the monophenol DTBP-H to the o-quinone DTBQ with a TON of 31. This reac-

The active site of galactose oxidase (GOase) contains a copper atom coordinated by a tyrosyl radical. This enzyme catalyzes the two‐electron oxidation of alcohols to aldehydes. We present a GOase model system, which catalytically mediates the conversion of ethanol to acetaldehyde with a TON of 74. The crystal structure of the mononuclear copper complex [CuII(L6‐H)(CH3CN)](ClO4)2 coordinated by acetonitrile reveals an apical position for the phenol group. Furthermore we prepared the dimeric complex [(CuII)2(L6)2](PF6)2, which was structurally characterized as well. Cleavage of the dimer along with formation of the phenoxyl radical was effected by cerium(IV) ammonium nitrate. The dimer could also be cleaved by treatment with pyridine. In order to obtain information about the interaction between the unpaired electron in the d‐orbital of CuII to the electron in the half‐occupied orbital of the tyrosyl radical DFT is employed. In the ground state a ferromagnetic coupling (S = 1) is obtained.