Green innovations in C–H bond functionalisation: exploring homogeneous recyclable catalytic systems

C–H bond functionalisation is a pivotal approach in contemporary fabrication of organic compounds, and enables straightforward transformation of inert C–H bonds exempt from needing pre-functionalisation. Homogeneous recyclable catalytic systems upsurge sustainability by empowering catalyst recovery and reuse. This review combines the advantages of both these protocols by exploring a range of recyclable catalytic systems for functionalisation of C–H bonds, concentrating on green and sustainable approaches. We delve into the utilisation of various media and catalytic systems, including polyethylene glycols (PEG), ionic liquids (ILs), deep eutectic solvents (DESs), micellar systems, biphasic systems and systems allowing simple filtration or extraction to enhance catalytic efficiency and recyclability. The discussion encompasses a variety of metal-based catalysts, including rhodium (Rh), ruthenium (Ru), palladium (Pd), copper (Cu) and cobalt (Co), as well as catalyst-free approaches. The recyclability potential of most of these catalytic systems has also been explored. The atom economy and environmental advantages of employing these recyclable systems are highlighted in this review by giving an extensive overview of these innovative methods. Also, this seeks to motivate further exploration in the realm of functionalisation of C–H bonds and foster the progress of sustainable and environmentally conscious synthetic methods.