Alkali Metallosilicates: Synthesis, Structure and Evaluation in the ROP of ϵ‐Caprolactone

Abstract

A series of metallosilicate complexes ( t BuO) 2 (RO)SiOM (R= t Bu, i Pr, Et, Me; M=Li, Na, K) were prepared from tailor-made silanols. The complexes show different degree of association and feature heterocubane, double-heterocubane or hexagonal prism framework in solid state while ESI-MS shows fragmentation of the oligomers. The steric hindrance around the silicon atom has a direct influence over the association of the alkali derivatives, and the size of the alkali metal influences the shape of the M x O x core. These compounds were studied as initiators in the ROP of ɛ-caprolactone, varying temperature, reaction-time, monomer/ initiator ratio, metal center variation and association degree. The best results were achieved with [{( t BuO) 3 SiO} 4 Li 4 ] (1) producing an almost quantitive yield of polycaprolactone (97 %, M n = 35 kg mol À 1 , M w /M n = 1.72).