In a 2-liter four-necked flask equipped with an effective condenser, stirrer, and dropping funnel, 500 mL of anhydrous tetrahydrofuran (THF) was added and deoxygenated by drying nitrogen for 1 hour. Subsequently, 100 g (0.382 mol) of triphenylphosphine was added and the mixture was stirred until a clarified solution was formed. During this process, 6 g (0.856 mol) of freshly prepared, ultrafine lithium rinsed with THF was added in small amounts in batches while keeping the reaction temperature below 50 °C to control the exothermic nature of the reaction. After the lithium addition was completed, the resulting dark red solution was cooled to 0 °C and a THF solution (50 mL) of 50 g (0.442 mol) of 1,5-dichloropentane was prepared and similarly cooled to 0 °C. This solution was added dropwise to the reaction mixture, keeping the temperature at 0°C. Upon completion of the dropwise addition, the color of the reaction mixture changed to light brown. Subsequently, the mixture was refluxed at 80°C for 3 hours. After completion of the reaction, it was cooled to room temperature and 750 ml of deoxy methanol was added. The mixture was again cooled to 0 °C and 125 ml of oxygen-free water was added rapidly and dropwise to the vigorously stirred mixture. After standing at 0 °C for some time, the upper solution was decanted. The residue was filtered under nitrogen protection, washed with 5 x 25 ml of cold ether and dried under vacuum for 20 hours. 29.4 g (35% yield as triphenylphosphine) of 1,5-bis(diphenylphosphino)pentane was finally obtained as a white amorphous powder with a melting point of 41-44 °C, which is consistent with literature data. The 1H and 31P NMR spectra of the product were consistent with the structure, and the data are listed in Table 3.If the synthesis is carried out using undeoxygenated methanol and water, the oxidation of 1,5-bis(diphenylphosphino)pentane to 1,5-bis(diphenylphosphino)pentoxide is observed, at which point the product is a caramelized, amorphous mixture, which needs to be separated by graded recrystallization from the mixed benzene/methanol solvent.
