Stereospecific polymerizations of conjugated dienes by single site iron complexes having chelating N,N,N-donor ligands

Iron-terpyridine complexes, [Fe(terpyridine)(2)](FeCl4)(2) (1), FeCl3(terpyridine) (4), and FeCl3-(4,4',4"-tri-tert-butylterpyridine) (5), were found to display high catalytic activities for 1,2/3,4-polymerizations of isoprene and trans-1,4-polymerization of 1,3-butadiene in the presence of MMAO (modified methylalumoxane), whereas FeCl2(6,6"-diarylterpyridine) complexes 2 and 3 exhibit no catalysis for polymerizations of these two monomers even in the presence of MMAO. The N,N,O-ligated N-(2-pyridyl)-methyl-2-hydroxy-3,5-di-tert-butylbenzaldimine complex (6) of FeCl2 and the corresponding N-(2-pyridyl)-2-oxy-3,5-di-tert-butylbenzaldimine/FeCl (7) revealed more efficient catalysis for polymerization of isoprene and 1,3-butadiene. In sharp contrast to these N,N,N-donor or N,N,O-donor ligated complexes, N,N-ligated FeCl2(sparteine) complex 8 shows much lower catalytic activities, although the stereospecifity is much higher.