Group 15 metal aryloxides

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... 

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 ° ). 

There has been an outburst of research interest in the structures, physical properties, and chemistry of the group 2 metal aryloxides. This is particularly true for the elements strontium and barium where work has been stimulated by the possible use of metal aryloxides as precursors (either via sol-gel or MOCVD processes) for the formation of binary and ternary oxides containing these metals.2 Synthetic procedures are based on either the halide (Be) alkyl derivatives (Mg, Grignard derivatives, etc.) or the actual metallic element (Ca, Sr, Ba). Structural studies (Tables 6.14-6.18) show for the smaller elements Be, Mg, and Ca that monomeric and dimeric structural motifs dominate, with rarer examples of trinuclear clusters, e.g. [Ca3(OPh)5(HMPA)6][OPh.2HOPh].2 2 in the case of strontium and barium a more extensive cluster chemistry has been developed for small aryloxide ligands, while monomeric units with terminal aryloxides can be formed with bulky ligands and sufficient additional Lewis bases, e.g. [Ba(OC6H2Bu2-2,6-Me-4)2(THF)3].2 ... 

Table 6.19 Group 3 metal and lanthanide metal aryloxides... 

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... 

Non-metallocene complexes, such as aryloxide 31 and amide 138, have also been utilized as catalyst systems for the polymerization of a-olefins. Moreover, the homogeneous olefin polymerization catalysts have been extended to metals other than those in Group 4, as described in Sect. 7. Complexes such as mono(cyclopentadienyl)mono(diene) are in isoelectronic relationship with Group 4 metallocenes and they have been found to initiate the living polymerization of ethylene. These studies will being further progress to the chemistry of homogeneous polymerization catalysts. 

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