Stable paramagnetic carbenemetal complexes; syntheses and properties of low spin d7(1,3-dimethylimidazolidin-2-ylidene)iron(I) tetrafluoroborates

Abstract

Stable (at ca. 20 °C), green, crystalline, paramagnetic carbeneiron(I) salts (a)[Fe(CO)₂(L^Me)(L′)(L″)]⁺[BF₄]^–[L^Me=–[graphic omitted]Me](2; L′= L^Me, PPh₃ or PEt₃, and L″= CO), (3; L′= PPh₃, L″= L^Me), and [4; L′= L″= PPh₃, PEt₃, or P(OPh)₃], and (b)[Fe₂(CO)₆-(L^Me)₂(µ-Ph₂PCH₂CH₂PPh₂)]²⁺[BF₄]^–₂(6) are obtained by AgBF₄ oxidation of an appropriate Fe⁰ precursor (1) or (5), or from (2) by CO–PPh₃ exchange or disproportionation; i.r. [ν(CO)] and e.s.r. (g) and a(P)] measurements on (2)–(4) and (6), and cyclic voltammetric data (E_½) on a neutral Fe⁰ complex indicate that while the odd electron is substantially metal-centred, the carbene ligand L^Me contributes to stability by its strong Fe–C bond and delocalisation of positive charge.