Phosphonium describes a univalent radical, PH4. Quaternary phosphonium salts, obtained from tertiary alkyl phosphines with the treatment with alkyl or aromatic halides, are replacing phase transfer catalysts and biocides functions for quaternary phosphonium salts due to more effective performance and higher thermal stability. Phosphonium salts are used as epoxy curing agents. A variety of phosphine transition metal complexes including chiral complexes are synthesized as the very reactive and versatile homogeneous catalysts and stereospecific as well.