Transition metal mediated C–H functionalization has been highly relevant in organic synthesis for decades. However, sustainability as an inherent feature in such transformations remains under-developed. Through a varied approach, we have explored metal-centered catalysis practiced via mechanochemistry and under microwave-irradiation, both strictly without the use of any toxic organic solvents. In some sections of this report, we shed light upon C–H functionalizations carried out in the universal and clean solvent water, as well as in neat, solvent-devoid conditions. Different metal centers like Pd, Rh, Ru, Cu, Fe, Co and a spectrum of mechanistic pathways that have accomplished these reactions in an unconventional but green protocol, are discussed extensively. This serves as an attempt to address the challenges in environmental preservation while carrying out organic reactions, and to encourage innovative versatile ideas. Our review collectively presents the endeavours that have introduced hazard-free methodologies in these C–H activation pathways.