Multimetallic Lithium Complexes Derived from the Acids Ph2C(X)CO2H (X=OH, NH2): Synthesis, Structure and Ring Opening Polymerization of Lactides and Lactones. Issue 2 (18th January 2017)

• Record Type: Journal Article
• Authors: Al‐Khafaji, Yahya F.; Prior, Timothy J.; Horsburgh, Lynne; Elsegood, Mark R. J.; Redshaw, Carl
• Is Part Of: ChemistrySelect. Volume 2:Issue 2(2017)
• Page Start: 759
• Page End: 768
• Publication Date: 2017-01-18
• Subjects: Benzilic acid -- Diphenylglycine -- Lithium -- Ring Opening Polymerization -- Structures; Chemistry -- Periodicals; 540.5
• DOI: 10.1002/slct.201602029
• Languages: English
• ISSNs: 2365-6549

Abstract

Abstract: Reaction of LiOR (R= t‐ Bu, Ph) with the acids 2, 2 / ‐Ph2 C(X)(CO2 H), X=OH (benzH), NH2 (dpgH) was investigated. For benzH, one equivalent LiO t‐ 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 LiO t‐ Bu (2 equivalents) led to {Li8 (O t ‐Bu)2 [(benz)](OCPh2 CO2 CPh2 CO2 t ‐Bu)2 (THF)4 } (3 ), the core of which comprises two open cubes linked by benz ligands. For dpgH, two equivalents of LiO t‐ Bu in THF afforded [Li6 (O t ‐Bu)2 (dpg)2 (THF)2 ] (4 ), which contains an Li2 O2 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. Abstract : We report here our investigations on the use of lithium complexes bearing ligands derived from Ph2 (X)CO2 H, i. e. benzilic acid (X=OH) and 2, 2 / ‐diphenylglycine (X=NH2 ) which, on interaction with lithium alkoxides, as well as resulting in some unusual structural motifs incorporating lithium‐oxygen rings and ladders, has afforded ROP systems (of ϵ‐caprolactone, rac ‐lactide and δ‐valerolactone) exhibiting reasonable activities and low polydispersities.