Reactions of the Phosphinidene-Bridged Complexes [Fe2(η5-C5H5)2(μ-PR)(μ-CO)(CO)2] (R = Cy, Ph, 2,4,6-C6H2tBu3) with Diazoalkanes. Formation and Rearrangements of Phosphadiazadiene-Bridged Derivatives

The phosphinidene complexes [Fe2Cp2(mu-PR)(mu-CO)(CO)(2)](Cp = eta(5)-C5H5; R = Cy, Ph, Mes*; Mes* = 2,4,6-(C6H2Bu3)-Bu-t) react readily with diazoalkanes N2CR'R '' (R' = H, R '' = H, CO2Et, SiMe3; R' = R" = Ph) in dichloromethane solution at room temperature or below to give the corresponding P:P-bridged phosphadiazadiene derivatives [Fe2Cp2(mu-RPN2CR'R '')(mu-CO)(CO)(2)] (2) with high yield. The diazomethane derivative (Fe-Fe = 2.6198(6) angstrom) is protonated selectively with HBF4 center dot OEt2 at the P-bound nitrogen atom to yield the aminophosphide derivative [Fe2Cp2(mu-CyPNHNCH2)-(mu-CO)(CO)(2)](BF4) (Fe-Fe = 2.6126(5) angstrom). Compounds 2 decompose upon heating in toluene solution at 363 K to give the dimer [Fe2Cp2(CO)(4)] as the only monometallic product. The same result was obtained when irradiating with visible-UV light toluene solutions of the phenylphosphinidene-derived compounds. In contrast, relatively selective decarbonylations could be induced photochemically when R = Cy, Mes*. The reaction products, however, were strongly dependent on the nature of all substituents present in compounds 2. The diazomethane derivative yielded a mixture of the P:N-bound phosphadiazadiene complex [Fe2Cp2(mu-CyPN2CH2)(mu-CO)(2)] (major) and the phosphaalkene derivative [Fe2Cp2(mu-CyPCH2)(mu-CO)(CO)] (minor). In contrast, the ethyldiazoacetate derivative gave the paramagnetic complex [Fe2Cp2{mu-CyPN2CH(CO2Et)}(mu-CO)(CO)], possibly containing a mu-P:P,C-phosphadiazadienc ligand, which upon chromatography fully rearranges into the aminophosphide-iminoacyl complex [Fe2Cp2{mu-CyPNHNC(CO2Et)}(mu-CO)(CO)] (Fe-Fe = 2.6261(8) angstrom), possibly through a protonation/deprotonation sequence on the alumina surface. The trimethylsilyldiazomethane derivative instead gave directly the analogous aminophosphide-iminoacyl complex [Fe2Cp2{mu-CyPN(SiMe3)NCH(mu-CO)(CO)], now resulting from an unusual 1,3-shift of the SiMe3 group along the ligand backbone. Finally the photochemical treatment of the ethyldiazoacetate derivative of the supermesithylphosphinidene substrate gave the complex [Fe2Cp2{mu-Mes*PN2CH(CO2Et)}(mu-CO)(2) (Fe-Fe = 2.514(1) angstrom), containing a P:N-bridged phosphadiazadiene ligand bound to the dimetal center in a novel coordination mode, this involving the P-bound nitrogen atom, instead of the C-bound nitrogen.