Hydrogenation of carbon dioxide to formate by α-diimine RuII, RhIII, IrIIIcomplexes as catalyst precursors Journal of Organometallic Chemistry

The conversion of CO2 into valuable chemicals has been of major interest because it is cheap and readily
available. The concept of reducing CO2 pollution via its utilization into valuable products has inspired us
to synthesise novel 4,4'-((1Z)-butane-2,3-diylidenebis(azanylylidene))dibenzoic acid (L) metal complexes
{[(L)RuII] (C1), [(L)RhIII] (C2), [(L]IrIII (C3)} complexes for catalytic hydrogenation of CO2. The adiimine
metal complexes (C1eC3) were characterised using several analytical techniques, including:
NMR spectroscopy and single crystal X-ray crystallography. In a mixture of THF/H2O and a base, all three
catalyst precursors were able to hydrogenate CO2 cleanly to formate as a product. However, the best
combination of catalyst precursor and a base was C1 and DBU that selectively produced formate at a
moderate temperature of 120 ?C and at 60 bar. The best productivity under these conditions is TOF of 35
h?1 within 2 h and a TON of 322. This work is significant because it provides a one-step synthesis for
formate from CO2 using a-diimine-based complexes which can be synthesised in a one-step reaction. The
density functional theory calculations on C1 supports that RueH is the active species in the process of
CO2 hydrogenation to formate with the insertion of the CO2 to RueH being the rate determining step.