The mounting pressure of environmental degradation and climate change has intensified the search for sustainablechemicalprocesses. Transition metal complexes (TMCs) occupy a central position in green chemistry owing to their tuneable electronicstructures,diverse coordination geometries, and remarkable catalytic versatility. These coordination compounds can activate a widerangeofsubstrates under mild conditions, reducing energy consumption and hazardous by-product generation. Despite their potential,thewidespread adoption of TMC-based catalysts faces several formidable challenges: achieving high selectivity in complexsubstrateenvironments, preventing metal leaching into products, designing robust recyclable systems, and developing atom-economical syntheticpathways for the complexes themselves. Balancing reactivity with stability under diverse reaction conditions remains apersistentbottleneck. This study presents the rational design, synthesis, and characterisation of a series of novel TMCs incorporatingmultidentateN,N-, N,O-, and P,P-donor ligands coordinated to Cu(II), Pd(II), Ru(II), Fe(III), Ni(II), and Mn(III) centres. Complexeswerefullycharacterised using IR, UV-Vis, NMR, ESI-MS, XRD, and magnetic susceptibility measurements. Catalytic performancewasevaluatedin aerobic oxidations, C–C coupling, photocatalytic water splitting, epoxidation, and hydrogenation reactions under greensolventconditions. The synthesised complexes demonstrated excellent catalytic activity with yields ranging from 85–97%and turnovernumbers(TON) up to 30 × 10³. The [Pd(PPh₃)₄] and [Cu(bpy)₂]²⁺ systems exhibited outstanding recyclability over tenreactioncycles.Photocatalytic hydrogen evolution with [Ru(bpy)₃]²⁺ achieved a quantum efficiency of 12.4%, while [Fe(salen)Cl] gave91%enantioselectivity in asymmetric epoxidation. This work demonstrates that judicious ligand engineering and metal selection can produce highly active, selective, and recyclable catalytic systems fully aligned with the principles of green chemistry, providinga robust platformfor next-generation sustainable catalytic processes. Keywords: Transition metal complexes, green chemistry, homogeneous catalysis, ligand design, sustainable synthesis, photocatalysis