Synthetic dinuclear complexes

The possibility that Mn catalase possesses a dinuclear center raises the question of whether any synthetic dinuclear complexes can mimic the spectroscopic properties and reactivity of the biological site. A number of dinuclear complexes containing Mn(II), Mn(III), and/or Mn(IV) have been characterized by X-ray diffraction techniques. These... 

UV/Visible Data for Mn Catalase and Synthetic Dinuclear Complexes... 

Macrocyclic Schiff base compartmental ligands (750) (Robson-type ligands) derived from the [2 + 2] condensation of a 2,6-diformyl- or 2,6-diketo-substituted phenol and a diamine are very prominent in dinuclear Ni coordination chemistry.1901-1903 Particular interest lies in magnetic exchange interactions between the adjacent metal ions as well as in bioinorganic chemistry, where such dinuclear complexes have been proposed as synthetic analogues for bimetallosites. 

Dehydrative condensation of transition metal hydroxo complexes is a versatile synthetic method, when the conjugated acid of the incoming ligand (H-A) is a protic compound. There are reports of the synthesis of two types of square-planar hydroxopalladium complexes, mononuclear [TplPr2 x(L)Pd-OH] (X = H, Br) and dinuclear complexes [TplPr2Pd(H20)( -0H)2 (H20)PdTplPr2] (TplPr2 = hydrotris(3,5-diisopropylpyrazolyl)borate), and some dehydrative condensations of them.278... 

As for the dinuclear complexes, one might now ask how closely do the synthetic materials correspond overall to the native site should it contain an Mn4 aggregate. There are Indeed several features which again suggest that close approach to the native site may have been achieved (1) four Mn atoms in two Inequivalent pairs with two distinct Mn...Mn separations (24) ... 

In spite of the abundant work on synthetic, thermodynamic, structural, and spectroscopic aspects of mixed-valence compounds, the dynamic solution behavior toward external redox reagents has not been much addressed. When such compounds are unsymmetrical and valence-localized, several problems arise when a fully reduced dinuclear complex reacts with an oxidant. Haim pioneered a systematic study performed with different systems reacting with a common two-electron oxidant, peroxydisulfate (126). A relevant example is given by reaction (35) ... 

Most nickel(II) complexes with the various Schiff bases derived from salicylaldehyde and different amines have usually been easily prepared by three general methods (i) the reaction of a nickel(II) salt, usually hydrated nickel(II) acetate, with the preformed Schiff base using water, EtOH, MeOH or their mixtures as reaction medium (ii) the condensation reaction of bis(salicylaldehydato)nickel(II) with the appropriate amine in refluxing EtOH or H20/EtOH mixture (iii) the template reaction of the aldehyde with the appropriate amine in the presence of a nickel salt. In Table 97 the formulas, synthetic methods and some physicochemical properties for a number of nickel(II) salicylaldiminato complexes are reported. Examples of dinuclear complexes formed with Schiff bases are specifically reported in Section 50.5.8.5. 

The striking advance since 1973 has been the synthesis of homoleptic isocyanides for vanadium and almost all of the post-group-VIA metals up to group IB (see Table I), and this has been helped in some respects by synthetic rationale. For example, the discovery of the simple reductive or nonreduc-tive cleavage of multiple metal-metal bonds in suitable dinuclear complexes of molybdenum and tungsten has provided a high yield route to W(CNPh)6 and [M(CNR)7]2+ (M = Mo, W) and related complexes (5-14). During these studies the series [M(CNR)7]2+ was completed with the isola-... 

The structures of type II copper sites have not as yet generated as much interest, but the hetero-dinuclear structures of type IIC copper sites and the unusual protein donor ligands found in type IIB copper sites are noteworthy. The synthetic model approach to gain insight into the structures and functions of these types of copper sites will be also described. The diverse functions of a variety of proteins containing type IIA copper sites inspired many chemists to mimic the functions with synthetic copper complexes, even though the spectroscopic properties of the complexes are not unusual. Results of these studies will be reviewed and different aspects of the reactions relating to enzymatic catalysis will be discussed. 

These are formed mainly between metal atoms in d3-cP dinuclear complexes for which perhaps the most important group comprises the ethane-like X3M=MX3 (Dm) compounds, where X = alkyl, amide, alkoxide, thiolate, selenate, and mixtures thereof.115 The synthetic entry into these compounds involves principally the reactions of M2(NMe2)6, as shown in Fig. 18-C-20, and these in turn are made by metathetic reactions involving either MoC13 or WCL, and LiNMe2. 

Similar structural characteristics of the quadruply bridged dinuclear complexes of Pt(II), Pd(II), and Ni(II) indicate that the mixed-metal dinuclear complexes of these metal ions should be stable. However, probably because of the synthetic difficulties, only a few mixed-metal complexes of group 10 elements with such a structure have been prepared so far, although there are a number of examples having a doubly bridged structure (98, 99). For other metals, quadruply bridged mixed-metal complexes are known with the group 6 metal ions Cr, Mo, and W (1, 100, 101). 

Ooi and co-workers adopted an elegant synthetic approach to the mixed-metal complexes of 4-methylpyridine-2-thiolate (4-mpyt). This approach includes the initial preparation of mononuclear complexes [M(4-mpytH)4]Cl2 (M = Pt, Pd), in which all four 4-mpytH ligands coordinate to with sulfur-donor atoms (84,102). The structure of the mononuclear Pd(II) complex with nonsubstituted pyridine-2-thiolate, [Pd(pytH)4]Cl2, is shown in Fig. 16 (84). These mononuclear complexes can be further reacted with the second metal ion to give mixed-metal dinuclear complexes. 

Remarkably, reduced T2D Lc does not react with atmospheric 02. The behavior of the dinuclear T3 center thus contrasts starkly with that displayed by other reduced dinuclear copper sites of enzymes such as hemocyanin and tyrosinase or synthetic model dinuclear complexes (see Chapter 8.15). " These promptly perform a two-electron reduction of O2 to the peroxide level (reversibly, in the case of hemocyanin). 

Matsumoto K, Nagai Y, Matsunami J et al (1998) A synthetic route to alkyl—Pt dinuclear complexes from olefins and its implication on the olefin oxidation catalyzed by amidate-bridged Pt dinuclear complexes. J Am Chem Soc 120 2900-2007, and references therein... 

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