Browsing by Author "Makhubela, Banothile C E"

Now showing 1 - 2 of 2
  • Thumbnail Image
    Item
    Open Access
    Alkylated PTA platforms for mono- and polynuclear pre-catalysts for the aqueous biphasic hydroformylation of 1-octene
    (2018) Ramarou, Diteboho Selina; Smith, Gregory S; Makhubela, Banothile C E
    A series of mono-, di- and trimeric alkylated PTA ligands were synthesised. These ligands were reacted with the dimeric rhodium precursor, [RhCl(COD)]2, to produce the corresponding mono-, di- and trinuclear Rh(I)-PTA complexes. These complexes were then reacted with carbon monoxide to substitute the COD ligands with CO ligands, yielding the carbonyl analogues of the complexes. The ligands and complexes were fully characterised using various spectroscopic and analytical techniques, which include 1H, 13C and 31P NMR spectroscopy, FTIR spectroscopy, mass spectrometry, and elemental analysis. The ligands were found to have good solubility in water at room temperature, while the complexes showed water solubility at elevated temperatures. All the complexes were evaluated as catalyst precursors in the aqueous biphasic hydroformylation of 1-octene. The hydroformylation reactions showed that the complexes (6 – 18) were all active when used as catalyst precursors in the aqueous biphasic hydroformylation of 1-octene to yield aldehydes (linear and branched) and iso-octenes as side products. All complexes exhibited good chemoselectivity for aldehydes with the COD complexes displaying better chemoselectivity towards aldehydes than the CO complexes. However, the CO complexes exhibited better regioselectivity for linear aldehydes than the COD complexes. The trinuclear complex displayed accelerated catalytic rates than the dinuclear complexes which, in turn, displayed faster rates than the mononuclear complexes. The complexes could be recycled three times with a marked decrease in the conversion of 1-octene after each run for each catalyst precursor. Leaching studies showed a significant loss of the metal catalysts into the organic layer after each catalytic run. Mercury poisoning studies were conducted and confirmed that, under the catalytic conditions, all complexes behaved entirely as homogeneous catalysts when evaluated as catalyst precursors for the aqueous biphasic hydroformylation of 1-octene.
  • Thumbnail Image
    Item
    Open Access
    Design, synthesis and characterization of water soluble heterobimetallic complexes and their evaluation as aqueous biphasic hydroformylation catalysts
    (2015) Siangwata, Shepherd; Smith, Gregory S; Makhubela, Banothile C E
    A series of new water-soluble N,O-chelating Schiff base ligands were synthesised. These ligands were reacted with ferrocenecarboxaldehyde through Schiff base condensation reactions, leading to new water-soluble ferrocenylimine mononuclear complexes. The mononuclear complexes were reacted with a dimeric rhodium precursor [RhCl(COD)]2 to produce a series of novel ferrocenylimine-Rh(I) heterobimetallic complexes. Both themononuclear and heterobimetallic complexes were found to have good solubility in water of up to 11 mg/mL. The complexes were characterised fully using various spectroscopic and analytical techniques including 1H NMR, 13C NMR spectroscopy, FT-IR spectroscopy, mass spectrometry and elemental analysis. In addition, mononuclear and heterobimetallic complexes were also synthesised as precursors to dendritic DAB-G1 structures. These were found to be water-soluble and they were also characterised using spectroscopic and analytical techniques. The two monometallic and two heterobimetallic complexes were evaluated as pre-catalysts for the aqueous biphasic hydro formylation of 1-octene.The mononuclear ferrocenyl complexes were inactive in the aqueous biphasic hydroformylation experiments. Hydroformylation using the heterobimetallic complexes showed that the pre-catalysts are active in 1-octene conversion, yielding aldehydes (linear and branched) as well as isomerisation products (cis and trans 2- and 3-octene). Linear aldehydes were more favoured with the tertiary-butyl analogue of the heterobimetallic complex. Although loss of metal from the aqueous layer was detected using ICP-OES, the catalysts exhibited good recyclability and could be reused up to 4 times.