In this thesis, we first examine the application of Pd(II) anionic, square planar complexes of the type [RPPh3]2[Pd2X2Cl4], where X= Cl, Br, for the first time as a catalyst precursor for the Heck reaction carried out in DMF at 140 ?C. It was found that during the reaction, phosphonium halide stabilized Pd(0) nanoparticles of about 10 nm, which have been formed in situ from the palladium(II) precursor and Pd(0) colloidal nanoparticles acts as the reservoir for Pd(II) species via activation of the metal surface through the oxidative addition of aryl halides. Second goal was the immobilization of this phosphonium salts simultaneously as phosphonium-palladium complex/phase transfer catalyst matrix on the surface of silica nanoparticles and the application of the resulting catalyst in the Heck and Suzuki reactions of a variety of different haloarenes in neat aqueous media was investigated. In the next section, supported palladium nanoparticles on TRIS (tris(hydroxymethyl)aminomethane) and thiethanol amin modified silica gel, and their catalytic application for Heck coupling was investigated. The catalysts were characterized by a combination of XRD, TEM, FESEM, and SEM/EDX thechniques. In the next step, An environmentally friendly iron-based catalyst supported on acac-functionalized silica was successfully prepared and evaluated as heterogeneous catalysts for Mizoroki–Heck reaction of aryl iodides and olefins. This catalytic system showed good activities that were comparable to that of palladium catalysts. The catalyst was simply recovered from the reaction mixture and recycled five times. The reactions were carried out in poly(ethylene glycol) as a green solvent. Interestingly, using this catalyst, aryl iodides were selectively olefinated in the presence of aryl bromides. next, CuFe2O4 nanoparticles were synthesized and their application in thioetherification of aryl halide and potassium thiocyanate under ligand-free conditions was studied. A variety of symmetrical diarylthioethers were synthesized. This catalyst was magnetically separated, recycled, and reused up to five cycles. Afterwards, An efficient, mild, and simple protocol for iron-catalyzed Suzuki–Miyaura cross-coupling reaction between iodo- or bromoaryl derivatives and arylboronic acids was developed in the presence of iron(III) chloride (5 mol%) and NaHCO3 as the base, aryl iodides and bromides reacted with arylboronic acids in ethanol at reflux temperature under air to give the corresponding bis-aryl compounds with good to excellent yields. finally, silica core- shell magnetic nanoparticles were prepared and Pd(acac)2 was immobilized on the surface of these particles and their application in Suzuki type coupling of boronic acids and acyl halides was studied.