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

Abstract

Cyclic polyamine 1,4,7-trimethyl-1,4,7,10-tetraazacyclododecane, (Me₃TACD)H (= Me₃[12]aneN₄), reacted with [K{N(SiHMe₂)₂}] in benzene-d₆ to give [K{(Me₃TACD)SiMe₂N(SiHMe₂)}] (1) under hydrogen evolution. Single-crystal X-ray diffraction of 1 shows a dinuclear structure in the solid state, featuring a bridging μ-amido and a weak β-agostic Si–H bond. 1,7-Dimethyl-1,4,7,10-tetraazacyclododecane (Me₂TACD)H₂ (= Me₂[12]aneN₄) and (Me₃TACD)H were reacted with [Sc{N(SiHMe₂)₂}₃(thf)] in benzene-d₆ to give [{(Me₂TACD)SiMe₂N(SiHMe₂)}Sc{N(SiHMe₂)₂}] (2) and [(Me₃TACD)Sc{N(SiHMe₂)₂}₂SiMe₂] (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(Me₃TACD)(CH₂SiMe₃)₂] (4) was obtained by reacting (Me₃TACD)H with [Sc(CH₂SiMe₃)₃(thf)] in benzene-d₆. The scandium amide complexes 2 and 3 catalyzed the ring-opening polymerization (ROP) of meso-lactide to give syndiotactic polylactides.