Metal aryloxides mixed

The method can also be applied to the synthesis of transition metal aryloxides, with mixed hydrido, aryloxides sometimes being observed and isolated (Eqs 6.51 and... 

Alkoxides and aryloxides demonstrate similar chemistry to that of hydroxides in that it is possible to prepare mixed metal or double metal derivatives similar to hydroxo salts such as Na2[Sn(OH)6]. The formation of mixed metal alkoxides, e.g. Na2[Zr(OEt)6] and Ln[Al(OPri)4]3, is typically a result of the electron deficiency (Lewis acidity) of the metal centers in units of the type M(OR)x or M(OAr)JC (x < 5). This then leads either to oligomerization via alkoxide bridges or, in the presence of other alkoxides, to the formation of mixed metal compounds. 

The coordination of an alkoxide or aryloxide can lead to a mixed metal derivative.149 In some cases, ligand exchange can take place to generate a neutral adduct (equation 55).IS4... 

Yb(tritox)2]2 is readily formed [150]. The strongly reducing and thermally unstable Sm(II) amides tend to get oxidized by alcohols under the usual conditions [268], However, aryloxides have been isolated, especially when they are stabilized by ate complexation as in the case of [KSm(OC6H3-2,6-tBu2)3 (THF)]n [269]. In addition, the latter complex represents another approach of the silylamide route, namely the generation of mixed metallic complexes by retention of the original metal composition of the amide. 

The alkali metal is typically bound to the aryloxide oxygen atoms, although in a number of cases it has been shown that interactions between sodium and the phenoxy ring of aryloxide ligand are an important aspect of the bonding in the mixed metal cluster (Eq. 6.34 ). 

This method has been used to produce a variety of homoleptic aiyloxide complexes and has also been applied to the synthesis of mixed alkyl, aryloxide derivatives of metals. Partial substitution is typically achieved by simple control of the stoichiometry or by using sterically demanding aryloxides (Eqs 6.49, 6.50, and 6.51 ). 

Table 6.1 Metal-ligand bond lengths for mixed alkyl, aryloxides of niobium and tantalum...

It is also common that mixed metal derivatives of the lanthanides and group 1 metals are the products of synthesis. This can occur for small aryloxides leading to clusters, e.g. [La2Na3(/r4-OAr)3(/z2-OAr)6(dioxane)5] (OAr = OQH4Me-4), as well as in the generation of more discrete species with bulkier aryloxides, e.g. [(thf)Li(/i2-OAr)2La(OAr)2(THF)] (OAr = OC6H3Pr -2,6). In some situations the alkali metal interacts with the aryloxide jr-nucleus, e.g. [Cs( 7r-Ar-0)2La(OAr)2] (OAr = OC6H3P1I-... 

The reaction of mixed alkyl, aryloxides of the group 4 metals with CO has not yielded simple insertion products. However, final products are clearly the result of subsequent reactivity of y/ -acyl intermediates. The compound [(ArO)2Ti(t/ -R NCR)(R)] undergoes reaction with CO to produce the non-planar oxa-aza-metallacycle [(ArO)2Ti OC(R)=C(R)N(R ) ]. Carbonylation of [(ArO)2MR2] in the presence of pyridine remarkably leads to pyridine-di-melhoxide complexes. The threo and erythro isomeric mixture can be rationahzed on the basis of nucleophilic attack of acyl groups on coordinated pyridine figands. ... 

A large number of mixed alkyl, aryloxides of aU four metals have been obtained by reacting [MR3] with phenols. Monomeric bis(aryloxides) of aluminium, e.g. 

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