R. Streubel et al., Intra- and intermolecular [3+2] cycloaddition reactions of P-Cp*-substituted nitrilium phosphane-ylide tungsten complexes, ORGANOMETAL, 19(4), 2000, pp. 475-481
Thermal ring opening of {pentacarbonyl[2-pentamethylcyclopentadienyl-3-phen
yl-2H- azaphosphirene-kappa P]tungsten(0)} (1) in toluene in the presence o
f either 1-piperidinonitrile or ethyl cyanoformate yields predominantly tri
cyclic P-heterocycle complexes 4a,b via intramolecular trapping reactions o
f transiently formed nitrilium phosphane-ylide complexes 3a,b; complex 4a w
as isolated and fully characterized. On prolonged heating, complexes 4a,b t
ransformed into 2H-1,3,2-diazaphosphole complexes 5a,b, which were also cha
racterized by NMR spectroscopy. In the case of 1-piperidinonitrile, acyclic
dinuclear complex 6 was formed as byproduct via a 2-fold 1,3-addition reac
tion of complex 3a with water. Furthermore, preliminary studies on ring ope
ning of complex 4a showed retro-[2+1] and retro-[3+2] cycloaddition reactio
ns, depending on the substrate. If dimethyl acetylenedicarboxylate was empl
oyed, the tetracyclic phosphorus-carbon cage complex 10 was obtained, and i
f 1-piperidinonitrile was used, the 2H-1,3,2-diazaphosphole complex 5a was
formed selectively. The structures of 2H-1,3,2-diazaphosphole complex 5a, t
he acyclic dinuclear complex 6, and the tetracyclic P-heterocycle complex 1
0 were determined by single-crystal X-ray diffraction.