Titanium alkoxides alcoholysis reactions

Reaction of tris(neopentyl) complexes of titanium, zirconium and hafnium with molecular oxygen furnishes the corresponding tris(neopentoxy) complexes [42, 43, 51]. A peroxo complex is an intermediate in this reaction, being relatively stable in the case of titanium [42]. The alkoxide species can also be formed upon reaction with alcohols under mild conditions [42, 52]. The alcoholysis reaction is fast, with a low dependence on the steric hindrance of the alkyl chain [42]. Hydrolysis leads to ](=SiO)M(OH)3] or ](=SiO)2M(OH)2], depending on the precursor species. Deu-... 

Sato and coworkers have reported an asymmetric synthesis of Baylis-Hillman-type allylic alcohols 48, 49 via a chiral acetylenic ester titanium alkoxide complex (Scheme 9) [41]. These reactions rely on the use of the novel acetylenic ester titanium alkoxide complex 44 with a camphor-derived chiral auxiliary. Optically active, stereodefined hydroxy acrylates 46, 47 were obtained in high yields and with excellent regio- and diastereoselectivities. The chiral auxiliary was subsequently cleaved off by alcoholysis. 

In general, the facility for interchange of alkoxy groups increases from tertiary to secondary to primary groups. Verma and Mehrotra tried to determine the extent of such equilibria in the case of titanium alkoxides, Ti(OR)4 and found the following order in the interchangeability of alkoxo groups in alcoholysis reactions MeO > EtO > Pr 0 > Bu 0. ... 

In a comparative study of the alcoholysis reactions of titanium alkoxides, the facility of replacement reactions appears to follow the trend OBu > OPr > OEt > OMe. This type of comparative trend appears to be particularly marked in the alkoxides of some later 3d transition metals. For example, primary alkoxides of d nickel(n) do not appear to undergo alcoholysis reactions with secondary or tertiary and other primary alcohols, whereas the reactions of nickel(n) tert-butoxide with primary alcohols are highly facile. 

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