Multimetallic Lithium Complexes Derived from the Acids Ph2C(X)CO2H (X=OH, NH2): Synthesis, Structure and Ring Opening Polymerization of Lactides and Lactones

Abstract

AbstractReaction of LiOR (R=t‐Bu, Ph) with the acids 2,2/‐Ph2C(X)(CO2H), X=OH (benzH), NH2 (dpgH) was investigated. For benzH, one equivalent LiOt‐Bu in THF afforded [Li(benz)]2⋅2THF (1⋅2THF), which adopts a 1D chain structure. If acetonitrile is used (mild conditions), another polymorph of 1 is isolated; LiOPh also led to 1. Robust work‐up afforded [Li7(benz)7(MeCN)] 2MeCN THF (2⋅2MeCN⋅THF). Use of LiOt‐Bu (2 equivalents) led to {Li8(Ot‐Bu)2[(benz)](OCPh2CO2CPh2CO2t‐Bu)2(THF)4} (3), the core of which comprises two open cubes linked by benz ligands. For dpgH, two equivalents of LiOt‐Bu in THF afforded [Li6(Ot‐Bu)2(dpg)2(THF)2] (4), which contains an Li2O2 6‐step ladder. Similar reaction of LiOPh afforded [Li8(PhO)4(dpg)4(MeCN)4] (5). Complexes 1–5 were screened for their potential as catalysts for ring opening polymerization (ROP) of ϵ‐caprolactone (ϵ‐CL), rac‐lactide (rac‐LA) and δ‐valerolactone (δ‐VL). For ROP of ϵ‐CL, conversions > 70 % were achievable at 110 °C with good control. For rac‐LA and δ‐VL, temperatures of at least 110 °C over 12 h were necessary for activity (conversions > 60 %). Systems employing 2 were inactive.