Aryloxide complexes

The low spin aryliron complexes Fe(Por)Ar behave differently than their alkyl counterparts toward oxygen. In chloroform the products of the reaction of Fe(Por)Ar with O2 are the iron(IV) alkyl Fe(Por)Ar] and Fe(Por)Cl, while in toluene the aryloxide complexes Fe(Por)OAr are formed with no direct evidence for the formation of arylperoxo intermediates."" The high spin iron(lll) alkynyl complexes which have more ionic character in the Fe—C bond do not react with oxygen, and the order of reactivity of organoiron(lll) complexes toward O2 is given by Fe(Por)(alkyl) > Fe(Por)(aryl) > Fe(Por)(C=CR). ... 

Zinc alkoxide and aryloxide complexes have been of particular interest as enzyme models and catalysts. Tetrameric alkyl zinc alkoxides are a common structurally characterized motif.81... 

Hydrogenation of Aromatics with Well-Defined Nb and Ta Aryloxide Complexes... 

A large number of aryloxide complexes which incorporate lipophilic substituents on a benzenoid moiety have been characterised those which contain singly deprotonated aryloxides are summarised in Table 1. At the simplest level they contain one or two such ligands in conjunction with bulky but otherwise unfunctionalised organoaluminium fragments [44] or else they are homoleptic bis- or tris(aryloxide) systems [86, 120]. However, the... 

Macrocyclic 1,2-diazines were also investigated as ligands <2000AGE1968>. Especially interesting is the reaction of 1,2-diazines (pyridazine 26, phthalazine, and benzo[clcinnoline) with tungsten(ii)aryloxide complexes 33 as the N-N bond is cleaved (Equation 6) <2002CC2482>. 

Stevels et al. studied homoleptic yttrium aryloxide complexes (Fig. 9) [29]. The complexes were rather slow initiators however, in the presence of isopropanol, the rate was accelerated and the polymerization control was excellent. 

The mixed alkoxide/aryloxide complex (tritox)3Ce(OC6H40)Ce(tritox)3 was obtained by reaction of Ce(tritox)3 with benzoquinone [54], Its molecular arrangement resembles that in the pseudomononuclear thulium tritox complex discussed earlier. 

Scheme 7. Alternative routes to homoleptie aryloxide complexes...

The 2,6-diphenyl substituted aryloxide complex Yb(OC6H3Ph2-2,6)3 shows a similarly trigonal pyramidal Ln03 skeleton with Yb 0.33 A above the 03-... 

Corresponding 5-coordinate samarium complexes can also be accomplished (Table 5) [74,75] and heteroatom stabilization of the strongly reducing Sm(II) was observed in the ate complex [KSm(OC6H3tBu2-2,6-Me-4)3(THF)]n [75]. Indefinite chains or higher aggregations by K arene interactions seems to be a common coordination mode in lanthanide aryloxide complexes. 

The reaction product of ytterbium metal with benzophenone in a 1 1 molar ratio could be determined by an X-ray structure [278]. The benzophenone dianion unsymmetrically bridges the ytterbium atoms in the HMPA solvate [Yb(OCPh2)2(HMPA)2]2. The aryl oxygen forms a Yb-O bond with a typical terminal bond length (Table 18), but also donates to the other ytterbium. A Yb-C a-bond involving the a-C-atom (2.59(5) A) balances the charge at Yb (II). Reaction of the dianionic complex with four equivalents of phenol HOC6H3tBu2-2,6-Me-4 afforded the mononuclear aryloxide complex Yb(OAr)2(HMPA)2 (Sect. 4.2) [72],... 

Simple CH-alkoxides continue to reveal surprising new structure chemistry and the composition of Ln(OMe)3 and Ln(OEt)3 is not yet determined. Mononuclear lanthanide aryloxide complexes are well-examined and are the only fully characterized 3-coordinate, homoleptic Ln(OR)3 species. The variation of the steric environment in pure CH- and CHF-alkoxides with respect to volatility (molecular mass optimization) seems to be rather exhausted. It was shown that functionalization can ensure volatility and although the entire MOCVD-busi-ness gets somewhat stuck, CHF- and CHdo-alkoxides are promising alternatives to the /J-diketonates. Sol gel technology can fall back on highly soluble CH- and CHdo-alkoxides. 

Scheme 33 Mechanistic scenario for the formation of differently alkylated lanthanide aryloxide complexes (adopted from [188])...

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. 

An alternative reaction, the addition of an olefinic C—H bond to C=0, is catalyzed by Lewis acidic titanium aryloxide complexes chiral binaphthol ligands give high optical yields.96... 

Deacon, G.B., Fallon, G.D., Forsyth, C.M., Harris, S.C., Junk, PC., Skelton, B.W., and White, A.H. (2006) Manipulation of reaction pathways in redox transmetallation-ligand exchange syntheses of lanthanoid 11/111 aryloxide complexes. Dalton Transactions, 802—812. 

Table 8 Synthetic methods for the preparation of i-block alkoxide and aryloxide complexes.

Alkoxide and aryloxide complexes are moisture-sensitive, and are usually colorless or white solids with melting points substantially above room temperature. An interesting exception to this generalization is provided by the brown barium alkoxides Ba[0(CH2CH20) CH3]2 ( = 2, 3), formed from the reaction of elemental barium with a stoichiometric quantity of the polyether alcohol in THF. They are soluble in diethylether, THF and aromatic hydrocarbons, and are liquid at room temperature. 

With this arrangement of ligands, each lanthanum is seven coordinate and each sodium is five coordinate. In general, a coordination number of 6 or less is the most common for yttrium, lanthanide alkoxide, and aryloxide complexes (4a, 6). A rare example of an alkoxide complex that contains seven-coordinate yttrium is the cyclic decamer [Y(OC2H4OMe)3]10 (see Section V.C.l Fig. 56). 

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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