Highly Cis-1,4-Selective Living Polymerization of 1,3-Conjugated Dienes and Copolymerization with ε-Caprolactone by Bis(phosphino)carbazolide Rare-Earth-Metal Complexes

Bis(phosphino)carbazole, HL (HL = 3,6-(tBu)2-1,8-(PPh2)2-carbazole), reacted with rare-earth-metal tris(aminobenzyl) complexes (Ln(CH2C6H4N(Me)2-o)3) to afford the first PNP-carbazolide rare-earth-metal bis(alkyl) complexes, LLn(C6H4CH2N(Me)2)2 (Ln=Y (1), Sc (2), Er (3)). The yttrium complex 1 was characterized by X-ray diffraction analysis as a solvent-free monomer, in which the carbazolide ligand coordinates to the Y3+ ion in a κP:κN:κP′-tridentate mode and the two aminobenzyl groups coordinate to the Y3+ ion in η1C:κN-bidentate modes. Complexes 1−3 combined with [Ph3C][B(C6F5)4] gave cationic catalyst systems that initiated cis-1,4-polymerizations of 1,3-conjugated dienes with high activities. Especially, the system 1/[Ph3C][B(C6F5)4] displayed excellent cis-1,4-selectivity (>99%) and living mode at a broad range of polymerization temperatures (0−80 °C). Remarkably, the living yttrium−polydiene active species could further initiate the ring-opening polymerization of ε-caprolactone to give selectively poly(cis-1,4-diene)-b-polycaprolactone block copolymer with controllable molecular weight (Mn = (10−70) × 104) and narrow polydispersity (PDI = 1.15−1.47).