Lithium aryloxides

A particularly revealing series of aggregates has been discovered for the variously substituted lithiated aryloxides. (For early solution studies on lithium aryloxide aggregation, see Refs 397 and 397a.) The aggregation state of these... 

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). 

It was found that conformationally restricted tertiary amines, preformed lithium aryloxides, and addition of 4 A molecular sieves were essential for accelerating the rate of phenol coupling. As a consequence the reaction could be performed at low temperature (-40 to -20 °C) with high diastereo- and enantioselectivity. 

Other fates are possible for the enolate formed in the initial conjugate addition and an obvious possibility is an aldol reaction. With an asymmetric catalyst, the combination of three simple molecules leads to one enantiomer of one diastereoisomer of the tandem Michael-aldol product14 83. The catalyst 84 is based on a BINOL A1 complex (see chapters 25, 26). It can be drawn either as a lithium salt with an aluminium cation or, better, as a lithium aryloxide with a Lewis-acidic aluminium atom. This is better because both basic ArCT and Lewis acidity are necessary for catalysis. 

The chemistry of rhenium aryloxides is significant. The homoleptic rhenium aryloxides [Re(OAr)4] (OAr = OC6H3Pr -2,6, OC6H3Me2-2,6) have been obtained from [ReCl4(THF)2] and Ihe corresponding lithium aryloxide." " Cyclic voltammetric studies show these square planar d -species can undergo one-electron reduction. As with other transition metal systems (Section 4.2.3) these aryloxides are more difficult to reduce (more negative potential) than their halide counterparts. The 2,6-dimethylphenoxide compound reacts with alkynes to form adducts [(RCCR)Re(OAr)4]. 

Direct catalytic asymmetric Maimich-type reactions of various aromatic and heteroaromatic hydroxyke-tones are catalyzed by a Y N(SiMe3)2 3/TMS-linked-BrNOL complex, whereas a heterobimetallic lanthanum arylox-ide/lithium aryloxide/pybox complex catalyzes direct catalytic asymmetric Mannich-type reactions of a-keto anilides as synthetic equivalents of homoenolates. A La(OTf)3/Me-PyBox/amine base/Bronsted acid combination was found to be effective for direct catalytic asymmetric Maiuiich-type reactions of y-butenolides. ... 

Zirconium dichiorohis(dimethylamide) [87227-57-4] ZrCl2[N(CH2)2]2 h made direcdy from methylamine and zirconium tetrachloride but all of the halogens can be substituted by treating zirconium tetrachloride with the appropriate lithium alkylamide (229). Zirconium arylamines are made from zirconium alkoxides which first are converted to aryloxides (230). 

Hartwig et al. demonstrated that the same combination of iridium precursor and phosphoramidite LI also catalyzes allylic etherifications (Scheme 9) [68]. Lithium and sodium aryloxides were shown to react with cinnamyl and hex-2-enyl carbonates to form the branched allylic ethers in high yield, with high branched-to-linear... 

Core structures of some lithium alkoxides and aryloxides ... 

Although metal alkoxides were successfully used as a synthon for the synthesis (see Scheme 9) of more interesting homo- and heteroleptic metal alkyls, they have not attained the same importance as their sterically hindered aryloxide analogues. This finding might be due to the general solubility of both the products [i.e., desired metal alkyls and alkali metal (generally lithium) alkoxides] in hydrocarbon solvents. This limitation has made a cleaner separation of the products more difficult. 

The unsubstituted para-t-butyl calixarenes themselves complex metals via their aryloxide groups. Since aryloxide complexes are frequently oligomeric, the simple calixarenes do not give monomeric complexes. Aryloxides are hard ligands, therefore they readily form complexes with oxo-philic hard metal ions such as alkali metals, early transition metals, lanthanides, and actinides. Complexation is often inferred because the calixarene acts as a carrier for the metal ion from an aqueous to an organic phase. With the /wa-/-butylcalix[ ]arenes in alkaline solution, a value of n = 6 gives the best carrier for lithium(I), sodium(I), and potassium(I), with a value of n 8 giving the best carrier for rubidium(I) and caesium(I).15,16 Titanium(IV) complexes have been characterized,17-19 as well as those of niobium(V) and tantalum(V).20-22 These complexes are classified as... 

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