Direct Functionalization of White Phosphorus to Cyclotetraphosphanes: Selective Formation of Four P-C Bonds

Converting elemental white phosphorus directly into organophosphorus or polyphosphorus is meaningful, challenging and attractive. The ate-complexes of aluminacyclopentadienes 1a,b react with P₄ to afford selectively the cyclotetraphosphanes 2a,b featuring four newly formed P-C bonds and a planar square cyclo-P₄ ring. Density functional theory calculations show that the conversion of tetrahedral P₄ to planar cyclo-P₄ moiety undergoes through an unexpected 1,1- P-insertion/Diels-Alder reaction/isomerization cascade process. The reaction of 2a with iodomethane or p-benzoquinone afforded the P-methylation product 3 and the metal-free cyclotetraphosphane 4, respectively. Interestingly, reduction of 4 generated the phospholyl anions 5 and 6 while treatment of 4 with iodomethane afforded the phospholyl cation 7.