Group 12 mixed complexes

As a result of strong electronic interactions between the two metalloporphyrin units, there is a substantial uncertainty in assigning oxidation states in mixed-valence group 2 complexes of redox-active metals, such as Co. Thus, although reduced neutral C02 derivatives can be reasonably well described as those of Co the location (metal versus porphyrin) of the electron hole(s) in the singly and doubly oxidized derivatives is not known definitively, and may be very sensitive to the medium [LeMest et al., 1996, 1997]. For example, in benzonitrile, the UV-vis spectmm of [(FTF4)Co2]" ... 

Note that this reaction can also be used for the preparation of complexes with mixed substituents if the alkylating agent has a different group. Such complexes have also been generated by ring cleavage of trinuclear complexes, for example, with acyl halides (Equation (47)).2... 

The deoxyheme of the PLL system assumes two states, (a) and (ft) in Scheme 11, and equilibrium is established between diem. The first state (a) is the stable chelate structure, where the heme complex is relatively inactive to oxygen molecules or carbon monoxide, and the helical structure of PLL is partially destroyed. In the second state (ft) chelate formation by the two e-amino side chains of PLL is not perfect, and the heme complex is more active in (ft) than in (a). But the PLL chain is cofled up in an a-helix in (ft). As illustrated in (c), a PLL molecule contains many heme complexes (a) (in our PLL system, [heme]/[residual group of amino acid of PLL] = 1/7.5 and [heme]/[PLL molecule] = 47). When one of the heme complexes combines with molecular oxygen, the chelate structure of heme changes to that of die mixed complex, —NH2—Fe—02, according to Eqs. (12) or (13). The formation of the mixed complex reduces the strain in the PLL chain and the helical structure... 

Of special interest is the comparison of the inactivity of bipyridine-Cu(II) as a catalyst in salicyl phosphate hydrolysis, with its strong catalytic effect on the hydrolysis of dicarboxyphenyl-2-phosphate. A comparison of formulas XXVII with XXXIV and XXXVI shows that mixed complex formation of Cu+2 with salicyl phosphate and bipyridine would prevent attack of the phosphate group via the proposed mechanism. The formation of the analogous mixed chelate with DCPP (XXXIV and XXXVI) would produce a reaction intermediate for the reaction, since the metal ion would tie up one of the carboxylate ions but leave... 

The coordinated phenanthroline ligand is almost planar while the two pyridyl groups in coordinated bipyridyl are twisted with respect to each other (less than 10°) as a consequence of steric repulsion between non-bonded atoms. Mixed complexes of the type [Ni(bipy)(phen)2]2+ and [Ni(bipy)2(phen)]2+ have been also reported.849... 

When a sample of TS-1 interacts with a stoichiometric amount of H202, a strong band appears at 25,000 cm-1 in the UV-visible spectrum upon addition of a stoichiometric amount of ammonia, the band shifts to 27,500 cm-1 and slowly declines. This sequence has been interpreted as evidence of formation of a mixed complex in which both NH3 and the peroxo group are coordinated to the TiIv. This mixed complex could be the precursor of NH2OH (Geobaldo et al., 1992). 

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