Intra- and intermolecular [3+2] cycloaddition reactions of P-Cp*-substituted nitrilium phosphane-ylide tungsten complexes

Thermal ring opening of {pentacarbonyl[2-pentamethylcyclopentadienyl-3-phenyl-2H- azaphosphirene-kappa 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 2H-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 2H-1,3,2-diazaphosphole complex 5a was formed selectively. The structures of 2H-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.