Highly electrophilic metallocenes and their role in alkene polymerizations

This summary explores three main topics: (1) zwitterionic alternatives to c ationic metallocene alkyl complexes as olefin polymerization catalysts, bas ed on borato (-BR3-) and boryl (-BR2) substituted cyclopentadienyl ligands (R=C6F5); including zwitterionic zirconium allyl complexes of the type CpZr (eta(3)-allyl){eta(3)-allyl-CH2B(C6F5)(3)}; (2) reactions which contribute to catalyst deactivation, notably aluminum alkyl mediated C6F5 transfer rea ctions as well as C-H activation reactions including an unusual case of cat alyst self-reactivation; (3) the role of highly electrophilic metallocene c omplexes of aluminum, zirconium and yttrium in combination with weakly coor dinating anions as initiators for the carbocationic polymerization of isobu tene and isobutene-isoprene copolymerizations is discussed.