Intra- and Intermolecular [3+2] Cycloaddition Reactions ofP-Cp*-Substituted Nitrilium Phosphane-Ylide Tungsten Complexes

Thermal ring opening of {pentacarbonyl[2-pentamethylcyclopentadienyl-3-phenyl-2 H -azaphosphirene-κ P ]tungsten(0)} ( 1 ) in toluene in the presence of either 1-piperidinonitrile or ethyl cyanoformate yields predominantly tricyclic P-heterocycle complexes 4a, b via intramolecular trapping reactions of transiently formed nitrilium phosphane-ylide complexes 3a, b; complex 4a was isolated and fully characterized. On prolonged heating, complexes 4a, b transformed into 2 H -1,3,2-diazaphosphole complexes 5a, b, which were also characterized by NMR spectroscopy. In the case of 1-piperidinonitrile, acyclic dinuclear complex 6 was formed as byproduct via a 2-fold 1,3-addition reaction of complex 3a with water. Furthermore, preliminary studies on ring opening of complex 4a showed retro-[2+1] and retro-[3+2] cycloaddition reactions, depending on the substrate. If dimethyl acetylenedicarboxylate was employed, the tetracyclic phosphorus−carbon cage complex 10 was obtained, and if 1-piperidinonitrile was used, the 2 H -1,3,2-diazaphosphole complex 5a was formed selectively. The structures of 2 H -1,3,2-diazaphosphole complex 5a, the acyclic dinuclear complex 6, and the tetracyclic P-heterocycle complex 10 were determined by single-crystal X-ray diffraction.