Unprecedented Isospecific 3, 4-Polymerization of isoprene by cationic rare earth metal alkyl species resulting from a binuclear precursor

Cationic alkyl complexes of group 4 metals have been the subject of intensive investigations over the past two decades because of their crucial importance in catalytic olefin polymerization.1 In contrast, cationic alkyl species of rare earth (group 3 and lanthanide) metals are much less developed.2,3 However, recent studies have shown that cationic rare earth metal alkyls are highly efficient olefin polymerization catalysts3 and can show unique activities that differ from those of group 4 metals.3a,b,e Treatment of a neutral di- or trialkyl precursor with an equimolar amount of a borate compound proved to be a convenient route to generate a cationic trivalent rare earth metal alkyl species. Due to the lack of appropriate precursors, the cationic rare earth metal alkyls reported so far were limited solely to mononuclear species, while a binuclear cationic rare earth metal alkyl species remained unknown to date.5 During our investigations on new organo rare earth meta