Siloxides alkoxides

Organozinc Compounds Bearing Alkoxides, Siloxides, Boryloxides,... 

Most of the knowledge about aluminate and alkylaluminum coordination stems from X-ray crystallographic studies. The basic idea of this section is to compile a rare-earth metal aluminate library categorizing this meanwhile comprehensive class of heterobimetallic compounds. Main classification criteria are the type of homo- and heterobridging aluminate ligand (tetra-, tri-, di-, and mono alkylaluminum complexes), the type of co-ligand (cyclopen-tadienyl, carboxylate, alkoxide, siloxide, amide), and the Ln center oxidation state. In addition, related Ln/Al heterobimetallic alkoxide complexes ( non-alkylaluminum complexes) are surveyed. Emphasis is not put on wordy structure discussions but on the different coordination modes (charts) and important structural parameters in tabular form. An arbitrary collection of molecular structure drawings complements this structural report. 

A combination of 89Y and 29Si has been used to observe the fluxionality of some yttrium alkoxides, siloxides, and adducts. Large 89Y chemical shift changes have been observed on changing the coordination number of the yttrium.79... 

Most of the remaining examples of supramolecular alkali metal compounds involving r-coordination are alkoxides, siloxides, and thiolates. In polymeric sodium phenolate ( NaOC6H4Me-4 2]n, 79 [78], the / -arene interaction of the phenolate ligands with sodium plays a crucial role, because it restricts the structure of the resulting polymer to a one-dimensional stack of [NaOC6H4Me-4]2 dimers and prevents the formation of a fully extended three-dimensional network. 

Two principle strategies have been employed for the synthesis of siloxide-containing molecular precursors. The first involves a silanolysis, or condensation, reaction of the Si - OH groups with a metal amido, alkyl, hahde, or alkoxide complex. The second method involves salt metathesis reactions of an alkali metal siloxide with a metal hahde. Much of our work has been focused on formation of tris(tert-butoxy)siloxide derivatives of the early transition metals and main group elements. The largely imexplored regions of the periodic table include the lanthanides and later transition metals. 

The polarity of the Al-C bond allows easy derivatization of the five-coordinate aluminum alkyls by alkane elimination (Figure 9). For example, Salen aluminum alkyls LAlMe could be converted to dimeric or polymeric Salen aluminum phosphinates [LAl 02P(H)Ph ] 98 (n = 2 or oo, depending on the Salen ligand backbone)98,99 by reaction with phenyl phosphinic acid, Salen aluminum siloxides LA10SiPh3 by reaction with triphenyl silanol,96 or Salen aluminum alkoxides LAIOR by reaction with an alcohol.100... 

According to the general idea presented by Wolczanski [4], alkoxide and siloxide (alternative to cyclopentadienyl complexes) of transition metals are bonded through a o-type orbital such as the sp hybrid and via Jt-donation of two pjt orbitals perpendicular to the M-O direction (Figure 7.1). 

Hydrido alumimun alkoxides and siloxides are primarily Lewis acids due to the three-valent aluminum atom and therefore tend to compensate the elec-... 

An important area in the chemistry of titanium alkoxides is with the siloxides, Ti(OSiR3)4and their derivatives containing Hal, OR, oxoligands and the related polymers. The latter find rather broad applications as dielectric and isolation materials. They are briefly considered in the book by Feld and Cowe [560], a detailed review being included in the monograph by Andrianov [48]. Table 12.12 presents the properties of only certain simplest derivatives. 

Routes to monomeric , mononuclear , monolanthanide alkoxides, enolates, siloxides and aryloxides - an expanded title which will put the scope of the article in a more concrete form. The synthesis of mononuclear alkoxides, in particularly homoleptic derivatives [1], was decisively stimulated by the discovery of high temperature superconducting ceramics based on YBa2Cu307<, where yttrium represents the lanthanide elements [2]. The support of volatile and highly soluble molecular precursors is a prerequisite for synthesizing thin films of these materials by means of MOCVD [3] and sol gel processes [4], respectively. More recently, lanthanide alkoxide reagents became established in... 

Heterogeneous diene polymerization catalysts based on modified and unmodified silica-supported lanthanide complexes are known as efficient gas-phase polymerization catalysts for a variety of support materials and activation procedures (see Sect. 9). Metal siloxide complexes M(()SiR3 )x are routinely employed as molecular model systems of such silica-immobilized/ grafted metal centers [196-199]. Structurally authenticated alkylated rare-earth metal siloxide derivatives are scarce, which is surprising given that structural data on a considerable number of alkylated lanthanide alkoxide and aryloxide complexes with a variety of substitution patterns is meanwhile available. 

The preparation and structures of siloxanediol derivatives has been reviewed29,184 but some representative examples of reactions are given below. Two general methods have been used to make metal siloxides from silanols one involves the direct reaction of a silanol with the metal derivative, usually an amide, alkoxide, halide or alkyl (to give amine, alcohol, HX or alkane byproducts respectively), while the second involves the preparation of a simple alkali metal derivative which can then be used as a siloxide transfer reagent for further synthesis. Only the direct route will be considered here. Two of the most useful siloxide transfer species, (MOPh2Si)20 (M = Li or Na), are... 

Most of the triorganoantimony(V) alkoxides are monomeric, moisture sensitive and are volatile products. Both infrared and H NMR spectral data for triorganoantimony(V) alkoxides and siloxides have been interpreted in terms of trigonal bipyramidal geometry around antimony atom278"281). 

Alkoxides and aryloxides have been intensively studied because of their interest, especially for Ba, as precursors to oxide materials having desirable electronic properties this development was stimulated by the discovery of superconducting materials such as YBajG CVx. The same interest applies to other volatile complexes like /3-diketonates. The alkyl or aryl oxides (also siloxides) are readily obtained by a variety of methods, notably (a) direct interaction of the metals with ROH in THF, toluene saturated with NH3,22 or other ether solvents (b) the interaction of... 

The siloxides of aluminum can be prepared in the same maimer as the alkoxides and exhibit similar stractural features. Interest in these compounds arose from a desire for sol-gel or polymeric precursors for aluminosilicates. Unfortunately, these compounds extensively hydrolyze, losing most of the silicon as the silanol. However, the investigation of the hydrolysis of (Et3SiO)3Al has generated considerable insight into the stracture and composition of aUcoxy- and siloxy-substitutedalumoxanepolymers, (ROAIO) These macromolecules are now believed to have a structure related to that of boehmite. 

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