Mixed complexes, bimetallic

The first closo metaHaborane complexes prepared (159) were the nickelaboranes [< /(9j 0-( q -C H )Ni(B22H22)] and closo-l]l- r]-Q ]) -l]l-53i] pri Q [55266-88-1] (Fig. 13). These species are equivalent to closo-C ]]ri ][ i closo-Q, p5 2 by tbe electron-counting formaUsm. The mixed bimetallic anion [ /(9j (9-(Tj -C H )2CoNi(B2QH2Q)] and other related species were reported later (160). These metallaboranes display remarkable hydrolytic, oxidative, and thermal stabiUty. 

Fig. 8 Structure of some mixed bimetallic allenylidene complexes...

Petit-Ramel MM, Khalil I (1974) Mixed bimetallic complexes II. Determination of the stability constants ofyttrium citrates of the bimetallic copper yttrium citrate. Bull Soc Chim (Fr) 1259-1263... 

The "mixed" bimetallic complex RhCl(PBu Pr2)2(u-Cl)2PtCl(PBu Pr2) in which the phosphines are axial and trans shows J(Rh,P) = 95.6 Hz [128], Many of the molecules mentioned represent new and interesting molecular types, e.g. XXII, which contains a rhodium-mercury bond, and we shall return to these at a later point. 

By judicious choice of reaction conditions an acyclic Ni11 complex (784) could be isolated, which serves as a valuable starting material for the preparation of unsymmetrical and mixed metal complexes by subsequent reaction with various amines. Also, a symmetrical Schiff base macrocycle of larger size has been obtained as a minor byproduct upon condensation of (784) with 1,3-diaminopropane. The resulting Ni11 complex (785) is again bimetallic, although room to bind four metal ions is in principle available.1367... 

Natta s bimetallic mechanism stipulates that when the catalyst and cocatalyst components are mixed, the chemisorption of the aluminium alkyl (electropositive in nature) occurs on the titanium chloride solid surface which results in the formation of an electron-deficient bridge complex of the structure shown... 

Other recent reports have also indicated that mixed-metal systems, particularly those containing combinations of ruthenium and rhodium complexes, can provide effective catalysts for the production of ethylene glycol or its carboxylic acid esters (5 9). However, the systems described in this paper are the first in which it has been demonstrated that composite ruthenium-rhodium catalysts, in which rhodium comprises only a minor proportion of the total metallic component, can match, in terms of both activity and selectivity, the previously documented behavior (J ) of mono-metallic rhodium catalysts containing significantly higher concentrations of rhodium. Some details of the chemistry of these bimetallic promoted catalysts are described here. 

Pd/Sn bimetallic nanoparticles were synthesized from SnCl2 and Pd(N03)2 (47). In this case, the authors presented the pretreatment of the mixed solution. This pretreatment may produce the double complexes of Sn and Pd ions. The procedure is as follows Separate boiled clear solutions of SnCl2 and Pd(N03)2 with a small portion of concentrated HC1 were mixed and evaporated to dryness. The dry solids were digested with concentrated HNOj and HC1, forming an orange-red solution, which was again evaporated. The dry solid was then extracted with water and reduced by borohydride in the presence of surfactant. In the Pd-Sn bimetallic nanoparticles thus prepared, tin exists as Sn11 or Sn,v ions, as confirmed by XPS. 

In some cases, alkoxide displacements at a metal center proceed sequentially and at different rates so that, if redistribution processes do not intervene, mixed diketonates can be obtained by adjusting the ratios of reactants.190,191 Recently, bimetallic / -diketonates of the type M2(diketonate)2(OR)4 (M = Mo, W R = alkyl) have been prepared from diketones and M2(OR)6. X-Ray studies show that one diketonate is attached to each metal atom so that unbridged M=M units are retained although rapid rotation about this multiple bond can occur.192 Diketonate complexes with metal-metal multiple bonds are rather uncommon, one other example being C2v CK-Mo2(Me-COCHCOMe), (02 CMe)2.193... 

The interaction of the metal alkoxides with the salts of carboxylic acids or with p-diketonates of other metals is especially attractive for the synthesis of bimetallic molecular precursors in the cases, when the preparation of the alkoxide of the other metal is somehow hindered or it is insoluble or irreactive under the conditions applied. This method has been widely used for the sol-gel preparation of HTSC materials (because of low solubility and reactivity of Cu(OR)2) and lead-containing ferroelectrics (in the view of difficult synthesis and low stability of Pb(OR)2). It should be mentioned that the reaction between a metal alkoxide and a functional derivative does far not always lead to the formation of a mixed-ligand bimetallic complex ... 

It should be mentioned that in many cases it turns out to be impossible to isolate the bimetallic mixed-ligand complex. The isolable reaction products appear to be homometallic heteroleptic species. The composition of the reaction products is often dependent on the polarity and donor properties of the solvent as the molecules of the latter compete with the bridging alkoxo-, car-boxylato-, or p-diketonatoligands for the place in the coordination sphere of metal atoms. Thus if the reaction of Pb(OAc)2 with Sn(OBu )4 mentioned above is carried out in pyridine, it gives Sn(OBu )3(OAc)Py and Pb(OAc)(OBu ) as the major products and not the bimetallic complex [298]. Sn(OBu )3(OAc)Py turns also to be the major product of the reaction of Sn(OBu )4with Me3SiOAc... 

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