Reactions of functional groups at the periphery of group 4 metallocene frameworks: Selective formation of a Cp-bonded azaboretidine derivative by a hydroboration route

6-Amino-6-methylfulvene has been coupled with benzoic acid by treatment wit h 7-azahydroxybenzotriazole and DCC. Subsequent two-fold deprotonation, at the NH and B-methyl groups, generated the vinylidene-bridged Cp/benzoylamid o ligand 5. Treatment of 5 with ZrCl4(THF)(2) gave the spirometallocene com plex 3a (characterized by X-ray crystal structure analysis), while reaction of 5 with (Et2N)(2)ZrCl2(THF)(2) yielded the bridged half-sandwich complex 3b. Treatment of 3a with two molar equivalents of the strongly electrophil ic borane HB(C6F5)(2) resulted in hydroboration of the exocyclic C=C double bond with concomitant intramolecular N-B adduct formation to yield the aza boretidine-type systems 7 (three diastereoisomers, one of which has been ch aracterized by X-ray diffraction analysis). Similarly, hydroboration of 3b with HB(C6F5)(2) yielded the azaboretidine derivative 9. Activation of the complexes 7 and 9 with methylalumoxane led to active homogeneous Ziegler-ty pe propene polymerization catalysts.