Fe(iv) alkylidenes via protonation of Fe(ii) vinyl chelates and a comparative Mössbauer spectroscopic study

Treatment of cis-Me(2)Fe(PMe(3))(4) with di-1,2-(E-2-(pyridin-2-yl)vinyl)benzene ((bdvp)H(2)), a tetradentate ligand precursor, afforded (bdvp)Fe(PMe(3))(2) (1-PMe(3)) and 2 equiv. CH(4), via C–H bond activation. Similar treatments with tridentate ligand precursors PhCH[double bond, length as m-dash]NCH(2)(E-CH[double bond, length as m-dash]CHPh) ((pipp)H(2)) and PhCH[double bond, length as m-dash]N(2-CCMe-Ph) ((pipa)H) under dinitrogen provided trans-(pipp)Fe(PMe(3))(2)N(2) (2) and trans-(pipvd)Fe(PMe(3))(2)N(2) (3), respectively; the latter via one C–H bond activation, and a subsequent insertion of the alkyne into the remaining Fe–Me bond. All three Fe(ii) vinyl species were protonated with H[BAr(F) (4)] to form the corresponding Fe(iv) alkylidene cations, [(bavp)Fe(PMe(3))(2)][BAr(F) (4)] (4-PMe(3)), [(piap)Fe(PMe(3))(3)][BAr(F) (4)] (5), and [(pipad)Fe(PMe(3))(3)][BAr(F) (4)] (6). Mössbauer spectroscopic measurements on the formally Fe(ii) and Fe(iv) derivatives revealed isomer shifts within 0.1 mm s(–1), reflecting the similarity in their bond distances.