Investigation of the Purity of Alkali Metal Diphenylphosphides and Their Reactions with Organic Halides. Evidence for Single Electron Transfer

Article abstract of DOI:10.1021/jo00073a051

For the first time the purity of lithium, sodium, and potassium diphenylphosphide, prepared by various methods, has been evaluated using (31)P NMR spectroscopy.A method was developed to prepare each of the phosphides in a high state of purity.Highly pure potassium diphenylphosphide was then allowed to react with p-iodotoluene in order to determine the effect of purity on the S_RN1 nature of this reaction.The results were then compared with literature reports which used less pure KPPh2.The mechanism of reaction of alkyl halides with pure alkali metal diphenylphosphides, using the radical probes 6-halo-5,5-dimethyl-1-hexenes and 1-halo-2,2-dimethylhexanes, was investigated.The results provide the first evidence to support single electron transfer (SET) in the reaction of an alkali metal diphenylphosphide with an alkyl halide.SET was found to be the major reaction pathway in the reaction of hindered alkyl iodides (neopentyl type).On the other hand, SET was found to be a minor pathway in the reaction of the corresponding alkyl bromides and chlorides with PPh2(1-).There was no evidence found for SET in the reactions of unhindered alkyl halides with PPh2(1-) although SET participation cannot be rigorously excluded.