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 cycloaddition 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.

The electrophilic phosphinidene complex PhPW(CO)5 reacts with bis(imine) 5, possessing a single carbon spacer, to give the C−N insertion product 6. B3LYP/6‐31G* calculations indicate that this process occurs by way of a 2,3‐sigmatropic shift from the initially formed phosphane ylide. The alternative, 1,3‐dipolar cycloaddition, followed by ring‐opening of the bicyclic structure, can be ruled out since both steps are energetically much more demanding. Ring‐closure to an azaphosphirane is also less favorable than the C−N insertion, which is in agreement with the absence of such a product in the experiment. (© Wiley‐VCH Verlag GmbH, 69451 Weinheim, Germany, 2002)