Three [FeFe]‐hydrogenase model complexes [(μ‐dmedt){Fe(CO)3}2] [1; dmedt = SCH(CH3)CH(CH3)S], [(μ‐dmedt){Fe(CO)3}{Fe (CO)2PPh3}] (1‐PPh3), and [(μ‐dmest){Fe(CO)3}2] [1‐O; dmest = SCH(CH3)CH(CH3)S(O)], 1‐O were synthesized and characterized. These model complexes, which are generally used as the functional biomimics of the hydrogen‐producing dinuclear active site in [FeFe]‐hydrogenase, were used as efficient catalysts for the selective hydroxylation of aromatic compounds to phenols under mild conditions. Because both the dithiolato‐sulfur site and the Fe–Fe bond in the model complexes were possible active oxidation sites, DFT calculations were used to investigate the oxygenated products, that is, the S‐oxygenated products or the Fe‐oxygenated forms of the model complexes, which may be involved in the catalytic cycle. The experimental and computational results indicate that the thermodynamically favored Fe‐oxygenated intermediates dominate the hydroxylation of the aromatic compounds. A possible mechanism for the hydroxylation is also proposed.

No abstract

A mononuclear iron(II) complex, Et 4 N[Fe(C 10 H 6 NO 2 ) 3 ], coordinated by three 1-nitroso-2-naphtholate ligands in a fac-N 3 O 3 geometry, was initiated to catalyze the direct hydroxylation of aromatic compounds to phenols in the presence of H 2 O 2 under mild conditions. Various reaction parameters, including the catalyst dosage, temperature, mole ratio of H 2 O 2 to benzene, reaction time and solvents which could affect the hydroxylation activity of the catalyst, were investigated systematically for benzene hydroxylation to obtain ideal benzene conversion and high phenol distribution. Under the optimum conditions, the benzene conversion was 10.2% and only phenol was detected. The catalyst was also found to be active towards hydroxylation of other aromatic compounds with high substrate conversions. The hydroxyl radical formed due to the reaction of the catalyst and H 2 O 2 was determined to be the crucial active intermediate in the hydroxylation. A rational pathway for the formation of the hydroxyl radical was proposed and justified by the density functional theory calculations.

The frequency of a nonlinear vibration system is nonlinearly related to its amplitude, and this relationship is critical in the design of a packaging system and a microelectromechanical system (MEMS). This paper proposes a straightforward frequency prediction method for nonlinear oscillators with arbitrary initial conditions. The tangent oscillator, the hyperbolic tangent oscillator, a singular oscillator, and a MEMS oscillator are chosen to elucidate the simple solving process. The results, when compared with those obtained by the homotopy perturbation method, exhibit a good agreement. This paper introduces a very convenient procedure for attaining quick and accurate insight into the vibration property of a nonlinear vibration system.

No abstract