Dinuclear site complex

Love and coworkers have reported a series of dinuclear cobalt complexes derived from a rigid binucleating macrocycle H4L 18 as shown in Fig. 26 (150). The synthesis of the dicobalt complex [Co2(L18)] (36) was achieved by an anaerobic transamination reaction between H4L18 and [Co(thf) N(SiMe3)2 2] in THF. The unsaturated species 36 forms a bis(pyridine) adduct, 36 py2 (py — pyridine), which has a cleft-like structure reminiscent of pacman diporphyrin complexes (151,152). Both cobalt ions are square pyramidal, with Col and Co2 displaced out of the N4-basal planes by 0.17 and 0.18 A, respectively. The apical sites are occupied by pyridine nitrogen atoms that are exo and endo to the cleft. Interestingly the endo pyridine is canted and reflects the... 

For the hydrolysis of phosphate esters under mild conditions, metal ions and metal complexes are the most efficient nonenzymatic reagents currently available. However, they do not reach the catalytic efficiency of enzymes, and higher reactivities are desirable in view of applications. To mimic enzymatic dinuclear sites is a strategy to generate more efficient artificial phosphoesterases. 

Newer types of the dinuclear vanadium(IV) complex catalysts 84 have been developed. The abovementioned dinuclear vanadium complexes possess a VO V linkage whereas the ESR study on the catalyst 84 revealed no V—O—V linkage. The sense of enantioselection by the catalyst 84 of the (R,5,5)-structure is opposite to that of the binuclear complex 78a of the same (R,5,5)-structure. These results suggested two active sites attached to the binaphthyl skeleton in the catalyst 84 performed the dual activation of 2-naphthols in the oxidative couphng to achieve high enantioselectivity ... 

Copper (continued) cynates, 17 322, 323 diaminodithioether complexes, 17 185 diazene complexes, 27 232 difluoride, structure, 27 85, 86, 87, 88 dinuclear sites, 40 362-367 diphosphine complexes of, 14 235-239 electron-density distributions of complexes, 27 34, 41... 

Dinuclear clusters ferrous site distortion, 38 175 spin ladder, 38 182-183 Dinuclear cobalt complex, 45 291-293 Dinuclear complexes osmium, electrochemistry, 37 321-323 quadruply bridged, 40 187-235 axial ligand substitution properties, 40 232-234... 

Molecular hysteresis results when the interconversion between the states does not follow the same pathway on sweeping the external stimulus or field in one or the opposite directions [8.240a, 8.241]. A hysteresis loop has, for instance, been described for the electrochemical interconversion of redox states in a dinuclear metal complex it involves the switching between two different binding sites [8.240b]. Spin... 

These masked enolate complexes also react smoothly with carbonyl compounds, in reactions surprisingly reminiscent of the reaction of dimedone with formaldehyde (Fig. 5-13). The dinuclear products are of some interest as models for the dinuclear sites of some metalloproteins. 

Regarding the structure and function of nitrogenases in producing ammonia from N2, Sellmann has studied several model systems wherein heterolytic activation of H2 occurs on sulfur ligands (87). A core geometry based on a hybrid of the FeMoco active site structure with a dinuclear diazene complex, [Fe( NHS4 )]2(p-N2H2), is a proposed model (Scheme 4). 

Phosphates bridge dinuclear metal centers in the active sites of some phosphoes-terases [1-3]. Dinuclear metal complexes should be able to provide double Lewis acid activation for hydrolyzing phosphates. To quantify double Lewis acid activation for cleaving phosphate diesters, we studied the reaction of 24 (Figure 6.16), which has... 

Mononuclear vs. Dinuclear Sites. All molybdenum enzymes contain two molybdenum atoms. Dinuclear molybdenum complexes are well... 

There have been a few reports of first generation coordination complex structural models for the phosphatase enzyme active sites (81,82), whereas there are some examples of ester hydrolysis reactions involving dinuclear metal complexes (83-85). Kim and Wycoff (74) as well as Beese and Steitz (80) have both published somewhat detailed discussions of two-metal ion mechanisms, in connection with enzymes involved in phosphate ester hydrolysis. Compared to fairly simple chemical model systems, the protein active site mechanistic situation is rather more complex, because side-chain residues near the active site are undoubtedly involved in the catalysis, i.e, via acid-base or hydrogenbonding interactions that either facilitate substrate binding, hydroxide nucleophilic attack, or stabilization of transition state(s). Nevertheless, a simple and very likely role of the Lewis-acidic metal ion center is to... 

Dinuclear Manganese Complexes as Models for the Manganese Catalase. As discussed previously, the manganese catalase has a dinuclear active site that is thought to function by cycling redox states between Mn(II)2 and Mn(III)2. Although the [Mn(IV)(salpn)(/z2-0)]2 chemistry nicely explains the alternate catalase reactions of the OEC, this system is an inappropriate model for the Mn catalase because the redox cycle in that enzyme is lower and the core structure is believed to be dramatically different. In fact, a [Mn(III/IV)(/z2-0)]2 superoxidized state of the Mn catalase has been identified and shown to be inactive. 

Iron-Sulfur Proteins Manganese Proteins with Mono- Dinuclear Sites Manganese The Oxygen-evolving Complex Models Superconductivity. 

Pope, S.J.A., Kenwright, A.M., Heath, S.L., and Faulkner, S. (2003) Synthesis and luminescence properties of a kinetically stable dinuclear ytterbium complex with differentiated binding sites. Chemical Communications, 1550. 

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