Synthesis, characterisation and reactivity of water-soluble ferrocenylimine-Rh(I) complexes as aqueous-biphasic hydroformylation catalyst precursors

Water-soluble complexes based on monosodium 5-sulfonato salicylaldimine (3) and 3-^tbutyl-5-sulfonatosalicylaldimine have been synthesised via sulfonation and Schiff base condensation reactions. The ligand (3) and the new water-soluble mononuclear 5-sulfonatosalicylaldimine-ferrocenylimine complexes (4 and 5) have been synthesised and characterised fully using ¹H NMR, ¹³C{¹H} NMR, and FT-IR spectroscopy, elemental analysis as well as mass spectrometry. Subsequently, the Rh(I) heterobimetallic complexes (6 and 7) were synthesised from [RhCl(COD)]₂ (COD = 1,5-cyclooctadiene) and the ferrocenylimine metalloligands (4 and 5) and characterised using various analytical and spectroscopic techniques. These complexes were applied as catalyst precursors in aqueous biphasic hydroformylation reactions. Optimal conditions were established at 95 °C (40 bar), showing the best chemoselectivity for aldehydes. The mononuclear ferrocenyl pre-catalysts (4 and 5) were inactive in the aqueous-biphasic hydroformylation of 1-octene. The heterobimetallic catalyst precursors (6 and 7) displayed good activity and could be recycled for at least 4 runs under the investigated conditions for the aqueous biphasic hydroformylation of 1-octene.