The major thrust of the work being carried out under this project is to prepare and characterize pentacoordinate and hexacoordinate phosphorus compounds. The chemical and physical properties of these compounds are then determined. Extensive use of 1H, 19F, 13C and 31P NMR spectroscopy is used in characterizing these substances. A relatively general method has been developed for the preparation of pentacoordinated phosphorous compounds in which two alkoxy groups are bonded to phosphorus. The method involves allowing a trivalent phosphorus compound to react with two moles of an alkyl benzene-sulfenate. The products are the pentacoordinate phosphorus compound and a mole of diphenyl disulfide. Another relatively general method involves allowing a trivalent phosphorus compound to react with a cyclic 4-membered ring unsaturated disulfide. The products of these reactions are pentacoordinated phosphorous compounds containing an unsaturated 5-membered ring with two sulfurs bonded to the phosphorus. A number of the above prepared pentacoordinated phosphorus compounds have been allowed to react with various nucleophiles such as alkoxide and fluoride ions. Often relatively stable hexacoordinated phosphorus compounds are formed. These compounds and others are being submitted for testing for anti-tumor activity.