Discrete Ti-O-Ti complexes: visible light-activated, homogeneous alternative to TiO2 photosensitisers

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A series of novel bimetallic TiIV amine bis(phenolate) complexes was synthesised and fully characterised. X-ray crystallography studies revealed distorted octahedral geometries around the Ti centres with single or double oxo-bridges connecting the two metals. These robust, air- and moisture-stable complexes were employed as photosensitisers generating singlet oxygen following irradiation with visible light (420 nm) LED in a commercial flow reactor. All five complexes showed high activity in the photooxygenation of α -terpinene and achieved complete conversion to ascaridole in four hours at ambient temperature. The excellent selectivity of these photosensitisers towards ascaridole ( vs. isomerisation to p -cymene) was demonstrated with control experiments using traditional a TiO2 catalyst. Further comparative studies employing the free pro-ligands as well as a monometallic analogue highlighted the importance of the 'TiO2 -like' moiety in the polymetallic catalysts. Computational studies were used to determine the nature of the ligand to metal charge transfer (LMCT) states and singlet-triplet gaps for each complex, the calculated trends in the UV-vis absorption spectra across the series agreed well with the experimental results.

Original languageEnglish
Pages (from-to)9486-9494
Number of pages9
JournalChemistry - A European Journal
Issue number43
Early online date19 May 2020
Publication statusPublished - 3 Aug 2020


  • amine bis(phenolate)
  • flow chemistry
  • photosensitiser
  • singlet oxygen
  • titanium

ASJC Scopus subject areas

  • Catalysis
  • Organic Chemistry


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