Electron-Deficient Borinic Acid Polymers: Synthesis, Supramolecular Assembly, and Examination as Catalysts in Amide Bond Formation

Monika K. Baraniak, Roger A. Lalancette, Frieder Jäkle

Research output: Contribution to journalArticle

Abstract

The Lewis acidic character of borinic-acid-functionalized polymers suggests broad potential applications in supramolecular materials, chemo- and biosensors, as well as supported catalysts. Two highly electron-deficient borinic acid copolymers (3 a and 3 b) with variable steric hindrance at the boron center were prepared by reaction of aryldibromoboranes ArBBr2 (2, Ar=2,4-Cl2Ph, 3,5-Cl2Ph) with a 10 % stannylated polystyrene random copolymer, followed by conversion to the desired PS-B(Ar)OH functionalities. The supramolecular assembly of these polymers through Lewis acid–Lewis base interactions and reversible covalent B−O−B bond formation was investigated. Exposure of a polymer solution of 3 a to pyridine triggered spontaneous gelation, whereas 3 b only gelled upon addition of molecular sieves to favor formation of boroxane crosslinks. The crosslinking process was readily reversed by addition of small amounts of water or wet solvent. The dynamic processes were studied in detail by variable-temperature (VT) NMR by using molecular model compounds. The polymers and their corresponding model compounds were also examined as catalysts in the amide bond formation reaction between phenylacetic acid and benzylamine. The 3,5-dichlorophenyl borinic acid derivatives proved to be the more effective catalysts. Mechanistic studies suggested that the borane Lewis acid-catalyzed coupling involves initial acid-induced protodeboronation to release the dichlorophenyl boronic acid as the active catalyst.

Original languageEnglish (US)
Pages (from-to)13799-13810
Number of pages12
JournalChemistry - A European Journal
Volume25
Issue number60
DOIs
StatePublished - Oct 28 2019

    Fingerprint

All Science Journal Classification (ASJC) codes

  • Catalysis
  • Organic Chemistry

Keywords

  • B−N Lewis pairs
  • Lewis acid catalyst
  • borinic acids
  • boroxanes
  • supramolecular polymers

Cite this