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-( t Bu) 2 -1,8-(PPh 2 ) 2 -carbazole), reacted with rare-earth-metal tris(aminobenzyl) complexes (Ln(CH 2 C 6 H 4 N(Me) 2 - o ) 3 ) to afford the first PNP-carbazolide rare-earth-metal bis(alkyl) complexes, LLn(C 6 H 4 CH 2 N(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 Y 3+ ion in a κP:κN:κP′-tridentate mode and the two aminobenzyl groups coordinate to the Y 3+ ion in η 1 C:κN-bidentate modes. Complexes 1 − 3 combined with [Ph 3 C][B(C 6 F 5 ) 4 ] gave cationic catalyst systems that initiated cis-1,4-polymerizations of 1,3-conjugated dienes with high activities. Especially, the system 1 /[Ph 3 C][B(C 6 F 5 ) 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 ( M n = (10−70) × 10 4 ) and narrow polydispersity (PDI = 1.15−1.47).