Synthesis and Characterization of Co(II) Substituted Keggin-Type Polyoxometalates as Novel Catalysts for the Hydroformylation of 1-Hexene in a Thermomorphic Solvent System

Polyoxometalates (POMs) are a unique class of metal oxides, being of huge interest for the catalysis society. CoII-substituted phosphomolybdate POMs (namely H7[PCoMo11O40], H11[PCo2Mo10O40] and H15[PCo3Mo9O40]) have been successfully synthesized for the first time. The structure of the new CoII substituted POMs was solved by single-crystal X-ray diffraction as well as vibrational (FT-IR and Raman) and nuclear magnetic/electron paramagnetic resonance (NMR and EPR) spectroscopy and found to be of the Keggin-type. The Co-POMs were then applied as molecular catalysts for the hydroformylation of 1-hexene in a thermomorphic solvent mixture of water and 1-butanol. This is the very first example of a 1st row transition metal POM acting as a hydroformylation catalyst achieving 46 % heptanal yield. The best results were obtained using H11[PCo2Mo10O40] as a catalyst at 140 degrees C, 150 bar CO/H2 1 : 2, and a reaction time of 4 h, paving the way for new POM-based catalysts in hydroformylation reactions. Especially from the IR data it is visible that the vibrational bands are shifted to lower wavenumbers with increasing CoII substitution degree, indicating that CoII is successfully incorporated into the Keggin structure. image