Scandium Aminopyridinates: Synthesis, Structure and Isoprene Polymerization

Alkane elimination reactions of [Sc(CH2SiMe3)(3)(thf)(2)] or [Sc(CH2Ph)(3)(thf)(3)] with aminopyridines (1a = (2,6-diisopropylphenyl)-[6-(2,4,6-triisopropylphenyl)pyridin-2-yl]amine, 1b = [6-(2,4,6-triisopropylphenyl)pyridin-2-yl]-(2,4,6-trimethylphenyl)amine, 1c = (2,6-diisopropylphenyl)-[6-(2,6-dimethylphenyl)pyridin-2-yl]amine) led to selective formation of dialkyl complexes of scandium stabilized by one aminopyridinato (Ap) ligand. The reaction of these compounds with anilinium borate leads to the elimination of one of the two alkyl functions and affords organoscandium cations. The amine elimination reaction of [Sc{N(SiHMe2)(2)}(3)(thf)] with the aminopyridine la yields the corresponding mono(aminopyridinato) complex. Single-crystal X-ray analyses were carried out for [Ap center dot Sc(CH2Ph)(2)(thf)] (3a), [Ap center dot Sc(CH2Ph)(thf)(3)][B-(C6H5)(4)] (4a) and [Ap center dot Sc{N(SiHMe2)(2)}(2) (6a) (Ap center dot-H = 1a). The aminopyridinato-stabilized dialkylscandium complexes [ApScR(2)(thf)] (R = CH2SiMe3, CH2Ph) are initiators for controlled 3,4-selective isoprene polymerization after activation with perfluorinated tetraphenyl borates. Variation of the polymerization temperature as well as the addition of different alkylaluminium compounds influence the microstructure of the obtained polymer. Bis(dimethylsilyl)amides of scandium polymerize isoprene in the presence of anilinium borate and alkylaluminium compounds with high cis-1,4-selectivity. ((C) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)