Titanium complexes phenoxides

Certain half-sandwich phenoxides have been shown to be highly active olefin polymerization catalysts. For example, the zirconium complex (60) polymerizes ethylene with an activity of 1,220 gmmol-1 h-1 bar-1.181 A similar titanium complex (61) displays an activity of 560gmmol ll bar 1 at 60°C.182-189 Comparable activities were also recorded for the copolymerization of ethylene with 1-butene and 1-hexene. 

Scheme 350 shows the structures of a number of mono-Cp titanium complexes with more elaborately substituted aryloxo ligands. The compounds are formed by the reaction of Cp TiCl3 with 1 equiv. of the substituted phenol in the presence of an excess of pyridine or by treatment of the lithium phenoxide with Cp TiCl3 some of them have been... 

Chmura et al. also prepared air and moisture resistant chiral imino phenoxide complexes of zirconium and titanium, 14 [16]. They envisioned to study the effect of supporting ligand chirality on the stereoselectivity of LA ROP reaction. But at the end, they did not gain acceptable evidence enable to support any relationship. They showed that all isolated polymers had similar and moderate heterotactic microstructure which implied simple chain end control mechanism and resulted to the selective racemic enchainment during the propagation process. First, they investigate polymerization in toluene at 80°C and ambient temperature in which titanium complexes were absolutely inactive and zirconium coxmterparts showed moderate activity after 2 and 24 hours, respectively. Then they checked out solvent free conditions at 130°C and received almost complete conversion after 30 minutes for both titanium and zirconium alkoxide complexes (Table 7.2, entry 33-36). In this condition, titanium coxmterpart, in contrast to zirconium, resulted to full atactic polymer. Their investigation also showed that zirconium complex retained its activity in moisture or with lactic acid impurity in crude monomer which is deleterious for most metal alkoxide catalysts. 

Sarazin and co-workers prepared calcium, magnesium, zinc, titanium, and sodium-titanium amino phenoxide as potential catalysts in CL ROP [28]. But only calcium, 26, and sodium-titanium, 27, complexes were active in this reaction with poor results (Table 7.3, entry 18-19). 

Crocker and co-workers reported the use of 108 as starting material in the preparation of monomeric titanasilsesquioxane phenoxide derivatives. Heating of the isopropoxide precursor with phenols resulted in elimination of i-PrOH and formation of the corresponding titanium phenoxide complexes (Scheme 36). 

The addition of a base, typically ammonia, to mixtures of transition metal halides and alcohols allows the synthesis of homoleptic alkoxides and phenoxides for a wide range of metals. Anhydrous ammonia was first used in the preparation of titanium alkoxides where the reaction is forced to completion by the precipitation of ammonium chloride.41 Although useful for the synthesis of simple alkoxides and phenoxides of Si, Ge, Ti, Zr, Hf, V, Nb, Ta and Fe, as well as a number of lanthanides,42-47 the method fails to produce pure /-butoxides of a number of metals.58 Presumably, secondary reactions between HC1 and Bu OH take place. However, mixing MC14(M = Ti, Zr) with the Bu OH in the presence of pyridine followed by addition of ammonia proves successful, giving excellent yields of the M(OBul)4 complexes.59... 

A compound similar to (XIII) has also been prepared from the pyrocatechol compound Ti(02C6H4)Cl2 by reduction with sodium amalgam in THF, and has been formulated to be similar to (XIII) with the two phenoxide groups at each titanium being replaced by the pyrocatecholate dianion. The ESR signal from both these complexes suggests the presence of one unpaired electron per dimer (50). 

The hydroxyalkylation of phenols with chiral glyoxylates, followed by hydrolysis, gives regioselectively 2-hydroxymandelic acids with high enantioselectivity (eqnation 28). The crystal-structure determination of the titanium phenoxide complex shows evidence for chelation-controlled reaction giving the observed high enantioselectivities . ... 

Standard synthetic procedures for the synthesis of Cp-type titanium monophenoxide complexes from their trichloride precursors involve the use of either lithium phenoxides [47] or phenols in conjunction with an organic base in order to absorb the HCl released [48]. 

The preparation of Tbf titanium phenoxides involved the development of a suitable type of chlorotitanium aryloxides as starting material since most complexes of the general formula ClTi(OAr)3Xn (Ar = any phenyl, X = Lewis... 

---