Zirconium acetyl complexes

Figure 4 shows the remarkable structural similarity between the bimetallic carbene (1 2) and alkoxy complexes formed from diverse paths 1,2 addition of Zr-H to a carbonyl bound to tungsten (eq. 1) and 1,1 addition of Re-H to a zirconium-bound acetyl (eq. 2). 

Zirconium and hafnium tetraalkoxides are highly reactive compounds. They react with water, alcohols, silanols, hydrogen halides, acetyl halides, certain Lewis bases, aryl isocyanates and other metal alkoxides. With chelating hydroxylic compounds HL, such as j8-diketones, carboxylic acids and Schiff bases, they give complexes of the type ML (OR)4 these reactions are discussed in the sections dealing with the chelating ligand. 

Good -selectivity (a as high as 1 16) was found on reaction of 4-Q-acetyl-6-deoxy-2,3-di-Q-methyl-/9-D-allopyranosyl fluoride (D-mycinosyl fluoride) with alcohols in the presence of silver perchlorate and bis(cyclopentadienyl)zirconium dichloride in benzene,and in related fashion a desosamine fluoride has been used to produce -glycosides under mild conditions involving a hafnium complex and the methods have been combined in a total synthesis of the macrocyclic glycoside mycinamycin IV. 

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