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 readilyavailable. The concept of reducing CO2 pollution via its utilization into valuable products has inspired usto 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 adiiminemetal 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 threecatalyst precursors were able to hydrogenate CO2 cleanly to formate as a product. However, the bestcombination of catalyst precursor and a base was C1 and DBU that selectively produced formate at amoderate temperature of 120 ?C and at 60 bar. The best productivity under these conditions is TOF of 35h?1 within 2 h and a TON of 322. This work is significant because it provides a one-step synthesis forformate from CO2 using a-diimine-based complexes which can be synthesised in a one-step reaction. Thedensity functional theory calculations on C1 supports that RueH is the active species in the process ofCO2 hydrogenation to formate with the insertion of the CO2 to RueH being the rate determining step.