Photochemical and thermal reactions of a 2H-azaphosphirene complex with isonitriles

Photochemical ring opening of {2-[bis(trimethylsilyl)methyl]-3-phenyl-2H-azaphosphirene-kappa P}-pentacarbonyltungsten(0) (1) in diethyl ether in the presence of tert-butyl isocyanide (2) yields the eta(1)-1-aza-3-phosphaallene complex 4 at low temperature (-30 degrees C), the formation of which is explained via a 1,1-addition of 2 with the transiently formed terminal phosphinidene complex 3. Complex 4 decomposed slowly at ambient temperature to furnish the [bis(trimethylsilyl)methyl]-cyanophosphane complex 5 and isobutene. The same result was obtained via thermal ring opening of complex 1 at high temperature. In contrast, thermolysis of 1 in the presence of cyclohexyl isocyanide (7) afforded the N-cyclohexyl-substituted eta(1)-1-aza-3-phosphaallene complex 8. Complexes 4, 5, and 8 were unambiguously characterized by NMR and IR spectroscopy; the structure of complex 5 was established by X-ray crystal structure analysis. The structure of 5 and the energetics of its formation via decomposition of 4 were studied by DFT calculations, thus confirming the proposed reaction course.