Observation of the primary Zr-C insertion products in the reaction of the (butadiene)zirconocene/B(C6F5)3-betaine Ziegler catalyst system with reactive alkynes

The (conjugated diene) group 4 metallocenes 1a-d (diene = butadiene, isoprene; metallocene = Cp2Zr, Cp2Hf, MeCp2Zr) add B(C6F5)(3) to yield the metallacyclic M ... F-C bridged metallocene-borate-betaine complexes 3a-d. These add one equivalent of acetylene to give the chiral metallacyclic insertion products 5a-d that can be described as either intramolecular ion-pair type complexes involving interaction of the negatively polarized terminal -CH=CH-CH2-[B] group of the resulting sigma-ligand system with the positively polarized metallocene moiety of the dipolar betaine product or eta(2)-internal alkene metallocene complexes, respectively, as it is revealed by a comparison with the related acyclic THF-addition products 10 and 12. Propyne inserts unselectively into the terminal Zr-C bond of the complexes 3a-c. In each case a 1:1 mixture of the regioisomers 6a-c (methyl at C2) and 7a-c (methyl group at C1) is obtained. (C) 1998 Elsevier Science B.V.