Reactions of the Phosphinidene-Bridged Complexes [Fe<sub>2</sub>(η<sup>5</sup>-C<sub>5</sub>H<sub>5</sub>)<sub>2</sub>(μ-PR)(μ-CO)(CO)<sub>2</sub>] (R = Cy, Ph, 2,4,6-C<sub>6</sub>H<sub>2</sub><i><sup>t</sup></i>Bu<sub>3</sub>) with Diazoalkanes. Formation and Rearrangements of Phosphadiazadiene-Br
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The phosphinidene complexes [Fe2Cp2(μ-PR)(μ-CO)(CO)2] (Cp = η5-C5H5; R = Cy, Ph, Mes*; Mes* = 2,4,6-C6H2tBu3) 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(μ-RPN2CR′R′′)(μ-CO)(CO)2] (2) with high yield. The diazomethane derivative (Fe−Fe = 2.6198(6) Å) is protonated selectively with HBF4·OEt2 at the P-bound nitrogen atom to yield the aminophosphide derivative [Fe2Cp2(μ-CyPNHNCH2)(μ-CO)(CO)2](BF4) (Fe−Fe = 2.6126(5) Å). Compounds 2 decompose upon heating in toluene solution at 363 K to give the dimer [Fe2Cp2(CO)4] as the only organometallic 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(μ-CyPN2CH2)(μ-CO)2] (major) and the phosphaalkene derivative [Fe2Cp2(μ-CyPCH2)(μ-CO)(CO)] (minor). In contrast, the ethyldiazoacetate derivative gave the paramagnetic complex [Fe2Cp2{μ-CyPN2CH(CO2Et)}(μ-CO)(CO)], possibly containing a μ-P:P,C-phosphadiazadiene ligand, which upon chromatography fully rearranges into the aminophosphide-iminoacyl complex [Fe2Cp2{μ-CyPNHNC(CO2Et)}(μ-CO)(CO)] (Fe−Fe = 2.6261(8) Å), possibly through a protonation/deprotonation sequence on the alumina surface. The trimethylsilyldiazomethane derivative instead gave directly the analogous aminophosphide-iminoacyl complex [Fe2Cp2{μ-CyPN(SiMe3)NCH}(μ-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{μ-Mes*PN2CH(CO2Et)}(μ-CO)2] (Fe−Fe = 2.514(1) Å), 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.
