Phospha[3]radialenes. Syntheses, Structures, Strain Energies, and Reactions

Abstract

In situ-generated terminal phosphinidene complex PhPW(CO)5 adds in a 1,2-fashion to the terminal double bond of tetramethylcumulene and cyclic 1,2,3-cyclodecatriene. The resulting alkenylidenephosphiranes 19A and 20A, which are three-membered phosphiranes containing an exocyclic allenic group, subsequently rearrange to the corresponding phospha[3]radiales 19B and 20B, which are phosphiranes having two exocyclic double bonds. All four organophosphorus compounds were characterized by single-crystal X-ray structure determinations. Bicyclic 20A contains a significantly bent (171.5(7)°) and twisted (14.2(8)°) allenic unit in contrast to 19A. The rearrangement to the thermodynamically favored radialenes is considered to occur by a phosphirane ring opening/closure sequence. On using a second equivalent of PhPW(CO)5, insertion takes place into a PC bond of 20B, but not of 19B, to give two new phospha[4]radialene isomers, viz. cis-20C and trans-20C, both of which were characterized by crystal structure determinati...