Metal aryloxides reactions

Lewis acids of chiral metal aryloxides prepared from metal reagents and optically active binaphthol derivatives have played a significant role in asymmetric synthesis and have been extensively studied.23 However, in Diels-Alder reactions, the asymmetric induction with chiral metal aryloxides is, in most cases, controlled by steric interaction between a dienophile and a chiral ligand. This kind of interaction is sometimes insufficient to provide a high level of enantioselectivity. 

Lanthanide aryloxides have proved to be excellent precursors to homoleptic lanthanide alkyls (B, Eq. 13) [140], The reaction can be conducted in non-polar solvents because of the good solubility of the starting compounds. The formation of insoluble alkali metal aryloxides is the driving force (kinetic control). Complexes derived from aliphatic alcohols [141] and acetylacetonates [131] are... 

In this section, we will highlight the development in the use of metal alkox-ides for the synthesis of new and interesting organometallic compounds, many of these are either inaccessible or difficult to synthesize by common synthetic procedures. We will not discuss (a) the chemistry of organometallic compounds containing alkoxides as supporting ligands, for which excellent reviews by Chisholm and co-workers (154, 513, 514) are available and (b) intramolecular cyclometalation (i.e., C—H bond activation) reactions of metal aryloxides due to the availability of an excellent account of this topic in a review article by Rothwell (515). Furthermore, a brief mention of the use of a related metal derivative (i.e., metal aryloxide) will be made merely for comparison. 

For this type of transformation, the insolubility of one of the products (i.e., lithium aryloxide) in pentane appears to be the driving force. Another distinct feature of metal aryloxides is their susceptibility to undergo intramolecular C—H bond activation (i.e., cyclometalation) reactions to afford new organometallic systems supported by aryloxide ligands (515). 

A much more widely used synthetic method entails the metathetical exchange reaction between alkali metal aryloxides and the metal halide. This procedure has been applied to the synthesis of lanthanide, actinide, and d-block metal aryloxides as well as derivatives of the main group metals (Eqs 6.23, 6.24, ° 6.25, " 6.26, 6.27, 6.28, 6.29, and 6.30 ° ). 

The homoleptic metal dialkylamides are an important class of compounds in inorganic chemistry. They are typically synthesized by treatment of the corresponding halide with lithium or sodium dialkylamide. Although involving an extra synthetic step, there are numerous examples where metal dialkylamide intermediates are useful in the synthesis of metal aryloxide compounds. The reaction normally involves the simple addition of the parent phenol to the metal dialkylamide in a nonprotic, typically hydrocarbon, solvent (Eqs 6.36, 6.37, and 6.38 ). 

Transition metal aryloxides undergo a number of insertion reactions with small molecules. Some of this reactivity is of fundamental importance, and in a number of cases important mechanistic studies have been carried out. 

The insertion of carbon monoxide into metal aryloxide bonds appears to be restricted to later transition metal complexes. The initial products of these reactions are aryloxy-carbonyls, which may be stable or undergo further reaction. Three examples of this type of reaction are shown in Eqs (6.66)-(6.68). ... 

This is a very general reaction for metal aryloxides, and has been observed for both early and late d-block metal centres as well as for the p-block metals. 

The metals thorium and uranium (as with the chemistry in general of these elements) dominate actinide aryloxide chemistry. Synthetic strategies normally focus on the halides reacting with group 1 metal aryloxides or reaction of metal amides with phenols. An important piece of early work was the demonstrated interconversion of eight-coordinate [UMe4(dmpe)2] and [M(OPh)4(dmpe)2] (M = Th, U Table 6.20) by addition of phenol or MeLi to each substrate respectively. The reaction of the cyclometallated... 

Metal exchange reactions have been used in the preparation of heavy alkali organometallics by reaction of alkali metal alkoxide or aryloxide with an organolithium reagent under precipitation of lithium alkoxide/aryloxide. For these reactions, careful ligand choice enables the separation of the two solid reaction products. Two variants of this reaction for alkaline-earth metal organometallics... 

REACTIONS OF METAL ALKOXIDES AND ARYLOXIDES 15.3.5.1 Ligand Coordination... 

The reaction must involve an alkoxide or aryloxide of a highly electropositive metal, i.e. the M—O bond must have high ionic character. Alkoxides of molybdenum and tungsten of formula M2 (OR)6, which have strong M—O a- and re-bonds will not, for example, react with alkyl halides to yield ether.261... 

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