The physical and chemical properties, and in particular, the nucleophilicity and nuclear magnetic resonance spectra of iminophosphoranes I-V have been studied in detail. Nmr measurements of 31p chemical shifts have indicated that electronic effects of substituents on the nitrogen atom in iminophosphoranes are transmitted to phosphorus whereas such interaction is prevented in N-alkylated salts such as VI. Basic hydrolysis of salts of iminophosphoranes _-I. and III gave high yields of secondary arylamines uncontaminated by the extraneous products usually formed during direct alkylation of primary amines and this method has been developed as a new synthetic route. Although the relative rates of formation of salts from iminophosphoranes and alkyl halides were found to be RI > Or > RC1, tertiary halides often underwent elimination rather than substitution by the iminophosphoranes. Whereas iminophosphoranes III and IV gave mono and bisalkylated products, depending on the halide used, iminophosphoranes II were alkylated on the pyridine ring only. Novel complexes between iminophosphoranes I and II and Group VI transition metal carbonyls have been prepared and their structures elucidated. Their chemical reactions have been studied to discover whether the reactivity of the free ligands is significantly modified, to an extent useful in organic synthesis, by the transition metal atoms. Electrophilic aromatic substitution reactions and oxidative coupling studies of iminophosphoranes have been investigated to provide access to substituted amines and biphenyls.