Scandium alkyl and amide complexes containing a cyclen-derived (NNNN) macrocyclic ligand: synthesis, structure and ring-opening polymerization activity toward lactide monomers

Cyclic polyamine 1,4,7-trimethyl-1,4,7,10-tetraazacyclododecane, (Me(3)TACD)H (= Me-3[12]aneN(4)), reacted with [K{N(SiHMe2)(2)}] in benzene-d(6) to give [K{(Me(3)TACD)SiMe2N(SiHMe2)}] (1) under hydrogen evolution. Single-crystal X-ray diffraction of 1 shows a dinuclear structure in the solid state, featuring a bridging mu-amido and a weak beta-agostic Si-H bond. 1,7-Dimethyl-1,4,7,10-tetraazacyclododecane (Me(2)TACD)H-2 (= Me-2[12]aneN(4)) and (Me(3)TACD)H were reacted with [Sc{N(SiHMe2)(2)}(3)(thf)] in benzene-d(6) to give [{(Me(2)TACD) SiMe2N(SiHMe2)}Sc{N(SiHMe2)(2)}] (2) and [(Me(3)TACD)Sc{N(SiHMe2)(2)}(2)SiMe2] (3), respectively. Both compounds are monomeric in solution and X-ray diffraction studies showed the scandium metal centers to be six-coordinate. The scandium alkyl complex [Sc(Me(3)TACD)(CH2SiMe3)(2)] (4) was obtained by reacting (Me(3)TACD)H with [Sc(CH2SiMe3)(3)(thf)] in benzene-d(6). The scandium amide complexes 2 and 3 catalyzed the ring-opening polymerization (ROP) of meso-lactide to give syndiotactic polylactides.