Bidentate forms of β-triketimines: syntheses, characterization and outstanding performance of enamine–diimine cobalt complexes in isoprene polymerization

Research output: Contribution to journalArticle

  • Authors:
  • Mohammed Alnajrani
  • Frank Mair


New cationic enamine-β-diimine cobalt complex [LCoBr·THF][BArF] (I) and its neutral analogue [LCoBr2] (II) where L = [(2,4,6-Me3-C6H2)NHCMe[double bond, length as m-dash]C{CMe[double bond, length as m-dash](N-2,4,6-Me3(C6H2))}2] and BArF− = [{3,5-(CF3)2C6H3}4B]−, were synthesised and then characterized by single-crystal X-ray diffraction, MALDI-MS, IR and elemental analysis. These complexes, the first examples reported where putatively tridentate β-triketimines prefer a bidentate coordination mode, were examined as catalysts for the polymerization of isoprene, activated by diethylaluminium chloride (DEAC) or ethylaluminium sesquichloride (EASC). The weakly coordinating BArF anion in I strongly improved activity in comparison to II. Both I and II produced polyisoprene of ca. 80% cis-1,4 and 20% 3,4 enchainment, with trace levels of trans-1,4 and no 1, 2 polymer. A kinetic study for both I and II demonstrated that the polymerization was first-order in monomer and that approximately 46% and 50% of cobalt formed active centres for I and II respectively. EASC was the most active of a range of organoaluminium compounds screened for both I and II. The resulting activities of up to 6 × 105 mol isoprene per mol Co per h are the highest yet recorded for catalysts selective for cis-1,4 enchained polyisoprene.

Bibliographical metadata

Original languageEnglish
Pages (from-to)10435-10446
Number of pages12
JournalDalton Transactions
Issue number25
Early online date24 May 2016
StatePublished - 7 Jul 2016