Binuclear and Trinuclear Complexes

Diruthenium(II,III) tetraacetate reacts with triphenyl phosphine, in THF or toluene solution, to give mononuclear and binuclear [Ru(III)2] products. Spectroscopic evidence was obtained for a diamagnetic violet tetranuclear intermediate. Diruthenium(II,III) tetrapropionate reacts with oxalate in a three-stage kinetic sequence. The first rapid step is the replacement of one of 

8 Inert-Metal Complexes Other Inert Centers 

Substitutions at triangular trinuclear oxo-carboxylato complexes which M3(/i3-0) cores, which may be simple or may be mixed metal or mixed valence species, are often slow. The third step in water replacement in Ru(III)30(OH2)3 derivatives by acetate has a half-life of several minutes at ambient temperatures, while replacement of water by CDjOD in [Ru2Rh ( 3-0)(0Ac)g(0H2)3] has rate constants of 6.0x10 and 1.2x10 for reaction at the Ru and Rh, respectively, at 21 °C in CD30D. Further examples of kinetic studies at trinuclear centers M3O where the metal atoms are molybdenum or tungsten can be found in Section 8.2.2 earlier in this chapter. 

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Magnetic susceptibility data for the binuclear and trinuclear complexes [79-86]. 

The complete redox series relative to reduction of the bipyridine ligands, in the binuclear and trinuclear complexes, should be constituted by eigth and twelve one-electron redox processes, respectively, since each bpy carries one redox orbital [10]. At room temperature and in non strictly aprotic conditions, chemical reactions, involving one of the members of the redox series, can take place, causing the termination of the redox series. The reduction processes for these species were therefore studied in strictly anhydrous DMF solutions at -54 C [8]. 

The extension of the redox series both for the binuclear and trinuclear complexes, does not reach, under the conditions utilized, the maximum number of redox steps predicted, probably due to the high negative potentials expected for the last steps. Although one or two steps of the ligand based redox series are missing, the redox series, reported in this work, are among the most extended ever observed. 

The second example to be discussed here belongs to a series of polychromophoric complexes synthesized in the context of some intercomponent energy transfer studies (see Section 5) [70]. These are cyano-bridged binuclear and trinuclear complexes of formula... 

A multiple-path mechanism has been elaborated for dissociation of the mono- and binuclear tris(hydroxamato)-iron(III) complexes with dihydroxamate ligands in aqueous solution. " Iron removal by edta from mono-, bi-, and trinuclear complexes with model desferrioxamine-related siderophores containing one, two, or three tris-hydroxamate units generally follows first-order kinetics though biphasic kinetics were reported for iron removal from one of the binuclear complexes. The kinetic results were interpreted in terms of discrete intrastrand ferrioxamine-type structures for the di-iron and tri-iron complexes of (288). " Reactivities for dissociation, by dissociative activation mechanisms, of a selection of bidentate and hexadentate hydroxamates have been compared with those of oxinates and salicylates. ... 

The reaction of dioxygen with laccase or ascorbate oxidase was reviewed in Section IX and in Messerschmidt et al. (74), where the possible binding modes of dioxygen to binuclear and trinuclear copper centers are discussed. A novel mode of dioxygen binding to a binuclear copper complex was found in a compound synthesized by Kitajima et al. (165). The complex contains peroxide in the mode, i.e., side-on between... 

Earlier, Herrmann et al. (1976 a, 1976 b) found that the mononuclear (pentacar-bonyl)(hydrido)manganese complex 10.74 forms a 10 1 mixture of the di- and trinuclear complexes 10.75 and 10.76 with diazomethane, if the reagents are mixed in THF at - 85 °C and the system is allowed to reach room temperature (10-34). In the same reaction with the analogous rhenium complex, only the binuclear complex... 

Both binuclear and trinuclear oxalamidinate palladium complexes were employed by Rau, Walther and coworkers [79] in copper-free Sonogashira reactions. The peculiarity of the system was seen to reside in the presence of chemical bridges that allowed electronic communication between metal centers (Scheme... 

Electrochemical behaviour of binuclear complex 1 and trinuclear complexes 2 and 3... 

In cyclic voltammetry (CV) the binuclear complex 1 and trinuclear complexes 2 and 3, show two and three one-electron reversible processes respectively, that can be attributed confidently to the oxidation of Ru(II) to RuGII). The results, obtained at 25 C, are summarized in Fig.l in terms of the half-wave potentials for the various steps. The E of the Ru(bpy)2(CN)j... 

Figure 1. Comparison of values relative to the oxidation of RuGD centres for 5x10 M ACN solution in 0.1 M (C2Hj) NBF of Ru(bpy)2(CN)2 binuclear complex 1 and trinuclear complexes 2 and3.T=25T.

The solution chemistry and water oxidation of a trinuclear complex [(bpy)2(H20)RuIIIORuIV (bpy)20Ruln(OI I2)(bpyh]6+ 489 and of a (nonisolated) binuclear Ru -terpyridine complex [ (terpy)(H20)2Rum 20] f+ 490 have also been reported. However, these complexes, as well as mononuclear [Ru(bpy)2(H20)2]2+,491 arenotcatalystsasaconsequenceoftheirfastdecomposition. 

A series of binuclear bicarbonato and trinuclear carbonato complexes have been isolated (34j) when [M(tren)(0H2)](C104)2 (M = Cu(II), Zn(II)) was allowed to react with NaHC03 at pH 6.5 and... 

In 1959, the coordinated mercaptide ion in the gold(III) complex (4) was found to undergo rapid alkylation with methyl iodide and ethyl bromide (e.g. equation 3).9 The reaction has since been used to great effect particularly in nickel(II) (3-mercaptoamine complexes.10,11 It has been demonstrated by kinetic studies that alkylation occurs without dissociation of the sulfur atom from nickel. The binuclear nickel complex (5) underwent stepwise alkylation with methyl iodide, benzyl bromide and substituted benzyl chlorides in second order reactions (equation 4). Bridging sulfur atoms were unreactive, as would be expected. Relative rate data were consistent with SN2 attack of sulfur at the saturated carbon atoms of the alkyl halide. The mononuclear complex (6) yielded octahedral complexes on alkylation (equation 5), but the reaction was complicated by the independent reversible formation of the trinuclear complex (7). Further reactions of this type have been used to form new chelate rings (see Section 7.4.3.1). 

Crystal data for the trinuclear (structure 5) and tetranuclear (structures 6, 7a, and 8) complexes reveal bond distances and angles which are comparable to those observed in the mono- and dihydroxo-bridged binuclear complexes (40, 42, 49, 50, 53, 54, 62, 87). 

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