Design, synthesis and characterization of water soluble heterobimetallic complexes and their evaluation as aqueous biphasic hydroformylation catalysts
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.
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