The first quaternary ammonium-group-containing [FeFe]-hydrogenase models [(μ-PDT)Fe (CO) {κ -(Ph P) N(CH ) NMe BzBr}] (2; PDT=propanedithiolate) and [(μ-PDT)Fe (CO) {μ-(Ph P) N(CH ) NMe BzBr}] (4) have been prepared by the quaternization of their precursors [(μ-PDT)Fe (CO) {κ -(Ph P) N(CH ) NMe }] (1) and [(μ-PDT)Fe (CO) {μ-(Ph P) N(CH ) NMe }] (3) with benzyl bromide in high yields. Although new complexes 1-4 have been fully characterized by spectroscopic and X-ray crystallographic studies, the chelated complexes 1 and 2 converted into their bridged isomers 3 and 4 at higher temperatures, thus demonstrating that these bridged isomers are thermodynamically favorable. An electrochemical study on hydrophilic models 2 and 4 in MeCN and MeCN/H O as solvents indicates that the reduction potentials are shifted to less-negative potentials as the water content increases. This outcome implies that both 2 and 4 are more easily reduced in the mixed MeCN/H O solvent than in MeCN. In addition, hydrophilic models 2 and 4 act as electrocatalysts and achieve higher i /i values and turnover numbers (TONs) in MeCN/H O as a solvent than in MeCN for the production of hydrogen from the weak acid HOAc.

A new series of the structural and functional models for the active site of [NiFe]-Hases has been prepared by a simple and convenient synthetic route. Thus, treatment of diphosphines RN(PPh) (1a, R = p-MeCHCH; 1b, R = EtOCCH) with an equimolar NiCl·6HO, NiBr·3HO, and NiI in refluxing CHCl/MeOH or EtOH gave the mononuclear Ni complexes RN(PPh)NiX (2a, R = p-MeCHCH, X = Cl; 2b, R = EtOCCH, X = Cl; 3a, R = p-MeCHCH, X = Br; 3b, R = EtOCCH, X = Br; 4a, R = p-MeCHCH, X = I; 4b, R = EtOCCH, X = I) in 67-97% yields. Further treatment of complexes 2a,b-4a,b with an equimolar mononuclear Fe complex (dppv)(CO)Fe(pdt) and NaBF resulted in formation of the targeted model complexes [RN(PPh)Ni(μ-pdt)(μ-X)Fe(CO)(dppv)](BF) (5a, R = p-MeCHCH, X = Cl; 5b, R = EtOCCH, X = Cl; 6a, R = p-MeCHCH, X = Br; 6b, R = EtOCCH, X = Br; 7a, R = p-MeCHCH, X = I; 7b, R = EtOCCH, X = I) in 60-96% yields. All the new complexes 3a,b-4a,b and 5a,b-7a,b have been characterized by elemental analysis and spectroscopy, and particularly for some of them (3a,b/4a,b and 5b/6b) by X-ray crystallography. More interestingly, the electrochemical and electrocatalytic properties of such halogenido-bridged model complexes are first studied systematically and particularly they have been found to be pre-catalysts for proton reduction to H under CV conditions.

As the oxidized state models for the active site of [FeFe]-H2ases, a series of new diphosphine-chelated dinuclear FeII(μ-X)­FeII (X = Cl, Br, I) complexes have been prepared using a simple and convenient one-pot synthetic method. Thus, treatment of the diphosphine dppv-chelated Fe dithiolate (dppv)­Fe­(CO)2(pdt) with equimolar amounts of the dppv-chelated Fe dihalides (dppv)­Fe­(CO)2X2 in the presence of a 2-fold excess of NaBF4 at room temperature gave the corresponding homodiphosphine dppv/dppv-chelated dinuclear Fe complexes [(dppv)2(CO)2Fe2(μ-pdt)­(μ-X)]­(BF4) ([1(μ-X)]­(BF4)), whereas their dppe analogues [(dppe)2(CO)2Fe2(μ-pdt)­(μ-X)]­(BF4) ([2(μ-X)]­(BF4)) could be prepared by treatment of the dppe-chelated Fe complex (dppe)­Fe­(CO)2(pdt) with dppe-chelated Fe dihalides (dppe)­Fe­(CO)2X2 and NaBF4 under similar conditions. Furthermore, the heterodiphosphine dppv/dppe-chelated dinuclear Fe complexes [(dppv)­(dppe)­(CO)2Fe2(μ-pdt)­(μ-X)]­(BF4) ([3(μ-X)]­(BF4)) could be similarly prepared by the one-pot reactions of the dppv-chelated Fe dithiolate (dppv)­Fe­(CO)2(pdt) with equimolar dppe-chelated Fe dihalides (dppe)­Fe­(CO)2X2 and a 2-fold excess of NaBF4. All the prepared new complexes [1(μ-X)]­(BF4)–[3(μ-X)]­(BF4) were fully characterized by elemental analysis and various spectroscopic techniques and particularly for some of their representatives by X-ray crystallography. In addition, on the basis of an electrochemical study, complexes [1(μ-X)]­(BF4) were found to be catalysts for H2 production from Cl3CCO2H under CV conditions.

Precision tracking control for electro-hydraulic servo systems is a critical but difficult issue to be addressed, especially in the situation of large friction torques and low velocities. To address this problem, a novel control scheme is proposed in this paper based on a sliding-mode variable structure controller and a friction observer. The sliding-mode variable structure control law and the sliding-mode friction observer are detailed. The bristle dynamic friction model is adopted to estimate the friction torques and reduce the effects caused by the nonlinear frictions. The proposed control scheme is verified and validated through experimental results. The results show that good position tracking performance with high precision is attained in the presence of dynamic friction even with large friction torques and very low velocities.