Zirconium complexes ligand exchange reactions

Zirconium complexes, 3, 363-440 acetylacetone, 2,372,377 ligand exchange reactions, 2, 381 rearrangement, 2, 383 alkyl... 

It is generally assumed that MAO firstly undergoes a fast ligand exchange reaction with the metallocene dichloride ( - Me). Either CH or CH3 is further abstracted from the complex by an Al-center from MAO, thus forming a cationic species (step 1). In the step 2, the monomer (alkene) coordinates to the empty orbital of the complex. Step 3 is related to the insertion see Insertion) of the alkene into the zirconium-alkyl bond which generates a new free... 

Furthermore, it is proposed that the active structures of Co " and Co " in anhydrous acetic acid are represented largely by uncharged sixfold-coordinated complexes such as Co (OAc)2(HOAc)4 and Co" (OAc)3(HOAc)3. An addition of water, substituted benzaldehydes, benzoic acids, or phenols might result in exchange reactions with acetic acid ligands, and influence the catalytic properties analogously to the effects observed upon addition of zirconium(IV) acetate [14w]. Thus, only at high cobalt(II) concentrations catalytically less active dimers will play a relevant role. 

Zirconium(IV) and hafnium(IV) tetrakis(tetrahydroborates) M(BH4)4 are of interest as extremely volatile, covalent complexes that contain tridentate BH ligands and exhibit rapid intramolecular exchange of bridging and terminal hydrogen atoms. 4,615 These compounds were prepared initially from NaMF5 (M = Zr or Hf) and excess A1(BH4)3 (equation 53),616 but they are obtained more conveniently from the reaction of the anhydrous metal tetrachloride with excess lithium tetrahydroborate (equation 54), either in the solid state617,618 or in the presence of a small amount of diethyl ether.619... 

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