Paramagnetic carbenemetal complexes. Part 2. Synthesis and spectroscopic studies of stable electron-rich olefin-derived paramagnetic carbenecarbonyl- and carbenenitrosyl-iron(I) complexes

Abstract

The synthesis of some new electron-rich olefin-derived carbeneiron(0) complexes (1)–(11) of the type [Fe(CO)₃(L^Me)L′][L^Me= C[graphic omitted]Me; L′= PMePh₂, PEt₂Ph, PPh₂H, PPh₃, AsPh₃, P(C₆H₁₁)₃, or P (OPh)₃], [{Fe(CO)₃(L^Me)}₂(µ-dppe)], (8), and [Fe₂(CO)₆(L^Me)(dppe)] is described, from the appropriate ligand with [Fe(CO)₄(L^Me)]. These complexes have then been used to produce paramagnetic carbeneiron(I) salts (12)–(38) by one-electron oxidation, generally by use of Ag[BF₄]. The iron (I) salts are often chemically and thermally stable, nine examples, e.g.[Fe(CO)₃(L^Me)₂][BF₄], being fully characterised as crystalline materials. Oxidation of complex (8) yields the novel di-iron(I) dication [{Fe(CO)₃(L^Me)}₂(µ-dppe)]²⁺ which contains two independent, non-interacting, low-spin d⁷ iron atoms. The tricarbonyliron(I) complexes react with various neutral ligands to afford [Fe(CO)₂(L^Me)(L′)L″]⁺ cations and CO; such reactions are often followed by disproportionation, e.g.[Fe(CO)₃(L^Me)(PPh₃)]⁺ gives [Fe(CO)₂(L^Me)(PPh₃)₂]⁺ and [Fe(CO)₄(L^Me)]⁺, which may have synthetic utility. The ligand L^Me assists stabilisation of the cationic iron(I) state by delocalising positive charge. Infrared and e.s.r. data provide an insight into the structure and stereochemistry of the iron(0)(trigonal-bipyramidal) and iron(I)(distorted square-pyramidal) complexes and suggest that the L^Me ligand is a better acceptor of the unpaired electron density than a tertiary phosphine.