Zirconium compounds aryl derivatives

Three classes of hybrid HPA are known to be stable to hydrolysis 1. Organometallic derivatives of the type RM (M = Si, Ge, Sn, Pb and R = alkyl or aryl). 2. Cyclopentadienyl-titaninm derivatives. 3. Zirconium alkoxide or phosphate derivatives, all of which are illustrated in Figure 2. We have tested phenyl model compounds of all of these for stability by boiling them in 6M HCl or H2O2 solution. This study showed that only PhP-O-HPA moieties are stable under conditions likely to be encountered in a fuel cell. Never the less we continue to study model compounds of the type RSi-O-HPA due to the large diversity of available ethoxy- and chloro- silanes. 

The instability of Ti reagents with branched alkyl groups is due to their tendency to decompose by 3-elimination. For this type of compounds the corresponding zirconium reagents are more suitable, since they do not undergo decomposition. For example, r-butylzirconium tributoxide (58b) is readily prepared from r-butyllithium and chlorozirconium tributoxide (58a) (equation 24). Alkyl- and aryl-zirco-nium(lV) tributoxides add to carbonyl compounds (Table 3) in the same fashion as Ti derivatives, with the advantage of low basicity, as is shown by their reactions with enolizable carbonyl compounds (Section 1.5.3.1.2). 

Negishi and his co-workers have developed several approaches to allylated arenes involving cross-coupling reactions. Preliminary studies established that aryl-aluminium, zirconium, or zinc compounds readily undergo palladium-catalysed cross-coupling with allylic halides or acetates (Scheme 19). Later in the year it was shown that allylic alcohol derivatives containing OAlR2,... 

A great number of norbornene-like monomers [e.g., m = 1-3, R] and R2 = alkyl and aryl groups, Eqs. (103) and (104)] with or without substituents have been employed in polymerization reactions induced by Ziegler-Natta and ROMP catalysts derived from ruthenium, osmium, iridium, palladium, platinum, molybdenum, and tungsten halides or vanadium and zirconium halides or acetylacetonate associated with organometallic compounds [162, 163]. Both addition and ring-opened polymers have been obtained by this way depending on the catalyst employed [Eqs. (103) and (104)]. 

---