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