Thorium(IV) trialkyl complexes of non-carbocyclic ligands as highly active isoprene polymerisation catalysts

A series of mono-anionic non-carbocyclic ligands, including bidentate benzamidinate [PhC(NDipp)2] (Dipp = C6H3-2,6-iPr2), iminophosphinamide [Ph2P(NDipp)2], and phosphinoamide [Ph2PNDipp], and tridentate hydrotris(3,5-dimethyl-1-pyrazolyl)borate (TpMe2) were used to stabilize the corresponding thorium(IV) trialkyl complexes [PhC(NDipp)2]Th(CH2SiMe3)3 (1), [Ph2P(NDipp)2]Th(CH2SiMe3)3 (2), [Ph2P(NDipp)]Th(p-CH2-C6H4-Me)3 (3) and (TpMe2)Th(CH2SiMe3)3 (4), which were characterized by NMR spectroscopy and single-crystal X-ray analysis. Complexes 1-4 in combination with [Ph3C][B(C6F5)4] and AliBu3 form the non-Cp-ligated actinide catalyst systems to show high activity and high cis-1,4-selectivity (89.9%) or trans-1,4-selectivity (91.4%) for the polymerization of isoprene.