Addition of a phosphinidene complex to C=N bonds: P-ylides, azaphosphiridines, and 1,3-dipolar cycloadditions

The terminal phosphinidene complex PhPW(CO)₅ adds to the imine bond of PhHC=N-Ph to give 3-membered ring azaphosphiridines, which undergo ring-expansion with an additional imine to yield a set of four isomeric five-membered ring diazaphospholanes. Treatment with the diimines PhHC=N(CH₂)_n-N=CHPh (n=2,3,4) results instead - in all three cases - in only a single isomer of the (CH₂)_n, bridged diazaphospholane. For n = 2 or 3, this aminal group is easily hydrolyzed to afford new 6- and 7-membered ring heterocycles. No intermediate azaphosphiridine complex is observed during the addition reaction to the diimines. B3LYP/6-31G* calculations on an unsubstituted, uncomplexed system suggest that the initially formed P,N-ylide of the H₂C=N-(CH)₂-N=CH₂ diimine both kinetically and thermodynamically favors an intramolecular 1,3-dipolar cyclo-addition over an imine insertion into the CPN ring of an intermediate azaphosphiridine. Single-crystal X-ray structures for the (CH₂)₂-bridged azaphospholane complex and the HCl adduct of the 7-membered hydrolysis product are presented.