Bimetallic alkoxide synthesis

The electrochemical technique can be used also for direct synthesis of bimetallic alkoxides. For instance, the anodic dissolution of rhenium in the methanol-based electrolyte that already contained MoO(OMe)4, permitted to prepare with a good yield (60%) a bimetallic complex RevMov,02(OMe)7, with a single Re-Mo bond [904], Application of the same procedure permitted the preparation of complex alkoxide solutions with controlled composition for sol-gel processing of ferroelectric films [1777]. 

The synthesis of bimetallic alkoxides can be achieved using the 2 routes first described by Meerwein and Bersin [1101] complex formation of2 alkoxides and the methathesis of a metal halide with an alkali metal alkoxide. 

The obtaining of tin(IV) alkoxides was first reported in a well-known publication by Meerwein and Bersin [1101] devoted to bimetallic alkoxides. At the end of the 1950s Bradley [222] and Make [1049] practically simultaneously devoted the synthetic approaches to and described the properties of nearly all major representatives of the Sn(OR)4homologous series. During the last 10 to 20 years interest in these compounds was renewed due to the prospect of their application in the synthesis of optically transparent and conducting films based on Sn02, and also of related ceramic materials. The alkoxides of Sn(IV) were considered in detail in a review by Hampden-Smith etal. [702],... 

The compounds of these two elements belong apparently to the most studied and most fully characterized alkoxoderivatives of metals. The particular features of their synthesis and physicochemical properties are discussed in detail in a large number of review publications authored by Chisholm [370] who made tremendous contributions to the development of the chemistry of these substances. The synthetic routes to the bimetallic alkoxide derivatives of molybdenum and tungsten (VI) along with the discussion of their physicochemical properties and application prospects are also reviewed in [1638, 908],... 

Lewis acid-base reactions between component alkoxides have been used primarily for the synthesis of bimetallic alkoxides involving (1) alkali alkoxides and less basic alkoxides, and (2) between binary alkoxides of other metals. 

SYNTHESIS OF BIMETALLIC ALKOXIDE FOR THE PREPARATION OF BIMETALLIC OXIDE NANOPOWDER... 

The synthesis of new and novel bimetallic alkoxide was carried out by applying a molecular structure design concept based on the choice of a proper metal-oxygen core and its completion with hgands to provide the necessary number of donor atoms and sterical protection around the core simultaneously. The freshly prepared alkoxide is highly soluble in mother alcohol, but the solubility decreases on ageing due to the loss of solvating molecules and air hydrolysis which leads to the formation of hydrated oxides [92-97]. 

Athar T, Bohra R, Mehrotra. RC. Synthesis and properties of some bimetallic alkoxides of antimony (III). Main Group Met Chem 1987 10(6) 399-410. 

Following the procedure of Meerwein and Bersin and others, - - this method has been extended to the bimetallic alkoxides of alkali metals (Lewis bases) with those of less basic metals and metalloids, beryllium, zinc, - boron, aluminium, gallium,tin(n), " tin(iv), antimony(iii), bismuth, titanium," niobium(iv), zirconium, " thorium, niobium(v), tantalum(v) and copper. Equations (3.1)-(3.3) reflect a few typical reactions used in the synthesis of bimetallic alkoxides involving alkali metals (M) ... 

This is really a modification of the earlier procedures in which the alkoxides of two metals formed in situ by the reactions of the respective metal halides with alkali alkoxides interact together to yield the bimetallic alkoxide the method can be illustrated by the one-pot synthesis of Ln Al(OPr )4 3 by the reaction shown in Eq. (3.47) ... 

Johansson A., Kessler V.G. Molecular structure design based on Lewis acid-base interaction in the preparation of bimetallic alkoxides derived from two electronegative elements. The synthesis and X-ray single crystal study of Mo2Ta40g(OMe)i6 andMo4Ta208(0 Pr)i4. Inorg. Chem. Commun. 

Johansson A., Roman M., Seisenbaeva GA., Kloo L., Szabo Z., Kessler V.G. The solution thermolysis approach to molybdenum(V) alkoxides synthesis, soUd state and solution structures of the bimetallic alkoxides of molybdenum(V) and niobium(V), tantalum(V) and tungsten(VI). J. Chem. Soc., Dalton Trans. 2000 387... 

Because the process is associated with the breakdown of an oxide barrier layer at the anode, it requires usually impressively high voltage (30-200 V). The products of electrochemical synthesis are always contaminated with halides and, for early transition elements, also with bimetallic alkoxides with Li when lithium salts are used as electrolytes. It means that the products after separation need to be purified by additional recrystallization or distillation. High-yield electrochemical synthesis has been proved to be an attractive approach to such precursors as Nb(OMe)s [96], Ta(OMe)s [104], MoO(OMe)4 [117], WO(OMe)4 [117], Mo (OMe)6 and W(OMe)6 [118], and Re406(0Me)12 [60]. 

A useful application of the silver-mediated additions is 1,3 -diene synthesis by three-carbon elongation of aldehydes [48,51,53]. The bimetallic reagent 3-trimethylsilyl-l-propenylzirco-nocene chloride (A Scheme 8.23) reacts with aldehydes under the influence of a catalytic amount of Ag+ to give the intermediate zirconocene-alkoxide B, which then undergoes a Peterson-type 1,4-elimination of TMS alkoxide to stereoselectively afford ( )-dienes (fc/Z > 96 4) (Scheme 8.23). A Wittig reaction yields the same products without stereoselectivity (ca. 1 1 mixtures of E- and Z-isomers). 

For more than 30 years at Lomonosov Moscow State University, later at Karpov Institute of Physical Chemistry, and recently at the Swedish University of Agricultural Sciences, Uppsala (V. G. Kessler), the authors of this book have systematically studyiedthe synthesis and properties of homometallic alkoxides of Groups I-Vm of the Periodic Table, the bimetallic derivatives (alkox-oaluminates, -titanates, -zirconates, -niobates, -tantalates, -molybdates, -tung-... 

In conclusion it is necessary to note the considerable change in chemical activity occurring on transformation from the alkoxides into oxocomplexes. An example is the synthesis of a bimetallic Bi-Ti complex. The complex formation of 2 isopropoxides occurs only in the presence of water (h = 0.2-0.7), which leads to the formation of Bi-oxoisopropoxide, which then reacts with Ti(OPr )4 already at room temperature providing BiTi20(0Pr% [447] (see also Chapter 8). Teyssie et al. [760] have proposed a large group of alkoxides of 3d-transition metals, and also those of Zn, Al, and Mo as highly effective selective catalysts for polymerization of lactones, isocyanates, and so on. 

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 ... 

The metatheis of acetates with the alkali alkoxides (method 5) can be used for the preparation of the methoxides and ethoxides of all three elements and is the only reaction leading to Hg(OR)2 [1623]. The trans-esterification of Zn(OMe)2 (method 6), according to [1121], can be carried out only in the presence of LiOR (forming soluble bimetallic complexes). The direct electrochemical synthesis on the anodic oxidation of metals in alcohols has been described for Zn(OEt)2 and a series of cadmium derivatives (Cd(OR)2 — obtained in the presence of such donor ligands as Dipy, Phen, and Dmso [98]) (method 2). 

Studies of the alkoxides of this group started in the middle of 1960s when Funk [602], Mehrotra [1129], and Reinmann [1349] nearly simultaneously reported the synthesis of Ga(OR)j. Indium isopropoxide was first described by Mehrotra in 1972 [1106] (the preparation ofIn(OMe)3 on reaction of InC13 with 50 equivalents of NaOMe reported by Runge et al. [1374] should apparently be questioned). Of the modem studies of primary interest are the preparation of indium (I) phenoxides stabilized by bulky ligands, reported by Roesky etal. [1362,1434], and that of the bimetallic butoxide, In Sn(OBu )3, described byVeith etal. [1685],... 

The synthesis of the alkoxides of tin(II) was first reported at the beginning ofthe 1960s when the preparation ofthe cyclic derivatives of diatomic phenols (Zuckermann et al.) [1814] and also that of their precursor methoxide was described. Recently it has also been reported that the synthesis and structural characterization of Sn(OBu )2, derivatives of sterically hindered phenols, and also ofthe bimetallic complexes (mainly with alkaline and alkaline earth metals) (Veith) [1682-1685, 1688, 1692-1695]. 

The inverse-micelle approach may also offer a generalized scheme for the preparation of monodisperse metal-oxide nanoparticles. The reported materials are ferroelectric oxides and, thus, stray from our emphasis on optically active semiconductor NQDs. Nevertheless, the method demonstrates an intriguing and useful approach the combination of sol-gel techniques with inverse-micelle nanoparticle synthesis (with OTO erafe-temperature nucleation and growth). Monodisperse barium titanate, BaTiOs, nanocrystals, with diameters controlled in the range from 6-12nm, were prepared. In addition, proof-of-principle preparations were successfully conducted for Ti02 and PbTiOs. Single-source alkoxide precmsors are used to ensure proper stoichiometry in the preparation of complex oxides (e.g. bimetallic oxides) and are commercially available for a variety of systems. The... 

E. Vandenbergh (1) and with the mode of preparation of different active systems, polynuclear structures are clearly a key feature for the design of catalysts able to polymerize substituted oxlranes into very high molecular weight polyethers. In an exploratory approach based on these premises and aimed at the synthesis of well characterized and versatile specie of that type, we have shown indeed (2) that soluble p-oxo-bimetallic trinuclear alkoxides having the general formula RO) m1-0-m2-0-m1 (OR)0 rank cunong the best known... 

The synthesis of transition metal alkyls usually involves the interaction of a very reactive metal alkyl, with a transition metal halide or alkoxide. This approach necessarily involves having two metals in the system which considerably complicates the problem of isolation of single pure compounds. In addition, low-valence transition metal compounds are electron-deficient molecules, and, for this reason, they will attempt to expand their coordination number by sharing ligands (halogen, alkyl, etc.) between two metal centers with the formation of bimetallic complexes. 

Campion, J, F., Payne, D. A., Choe, H. K., Maurin, J. K., and Wilson, S. R., Synthesis of bimetallic barium titanium alkoxides as precursors for electrical ceramics. Molecular structure of the new barium titanium oxide alkoxide Ba4Tii30i2(OC2H40Me)24, Inorg. Chem., 30, 3245 (1991). 

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