Electrophilic Chemistry of Tetraphosphacubane: Novel Monophosphonium Ions of Ethylation, Benzylation, Acylation, and Adamantylation, Di- and Triphosphonium Ions of Acylation/Alkylation and Alkylation/Protonation, and Monoprotonation of Tetraoxo- and Tetrathioxotetraphosphacubane

Article abstract of DOI:10.1021/jo00106a013

Ethyl triflate and benzyl triflate (via PhCH2Cl/AgOTf) react with the tetraphosphacubane 2a at room temperature to give the phosphonium salts 6 and 7.The P-adamantylated monocation 8 was obtained by the ambient temperature reaction of 2a with 1-Ad(1+)SbCl6(1-).P-Acylation of 2a with MeCO(1+)SbCl6(1-) gives 9, whereas the diphosphonium salt 11 is cleanly obtained by ambient temperature acylation of 6, adamantylation of 6 with 1-Ad(1+) is less selective, forming 13 in a mixture.Protonation of 6 with FSO3H*SbF5 (1:1) (magic acid)/SO2 gives a ca. 1:1 mixture of dication 14 and trication 15.The trication becomes more prominant with time or by an increase in temperature.Protonation of 5 similarly gives a mixture of 16 and 17, but the disappearance of 16 is very rapid.With HF/SbF5 (1:1)/SO2ClF only triphosphonium cation 17 is detected.Protonation of 6 with FSO3H*SbF5 (1:1)/SO2 leads to near exclusive formation of 14; only traces of 15 are detected.Tetraoxo- and tetrathioxotetraphosphacubanes 4a, 4b are only monoprotonated in Magic acid/SO2 (-> 18 and 19).PM3 calculations on protonation of tetramethyltetraphosphacubane 21 as model are also reported.