Novel N,O,N-Supported Tetracoordinate Aluminum Complexes for the Highly Controlled and Immortal ROP of Trimethylene Carbonate (TMC) under Mild Conditions: Access to Narrowly Disperse poly-TMC and Derived Copolymers

The novel N,O,N-supported tetracoordinate amidoaluminum complexes {eta(3)(N,O,N}-(C5H9)N-C6H4}(2)O-AlNMe2 (2a, R = C5H9; 2b, R = C6H(11)) have been synthesized and structurally characterized. In the solid state, as determined from X-ray crystallographic studies, complex 2a consists of a four-coordinate Al species in which the Al center adopts a distorted-trigonal-monopyramidal (tmp) geometry with the nitrogens of the three amido groups (defining the pyramidal base) being nearly coplanar with Al. Such Al species, when combined with an alcohol source such as benzyl alcohol, effectively polymerize trimethylene carbonate (TMC) at room temperature in a highly controlled manner to yield narrowly disperse poly(trimethylene carbonate), as deduced from polymer characterizations with various kinetic studies. The high degree of molecular chain length control of the present system was further exploited to access narrowly dispersed PEG-functionalized amphiphilic copolymers. The attractive features of the system lie in the combination of an excellent activity, a high level of chain length control, and mild reaction conditions.