[14405-49-3] · C45H33FeO6 · Tris(dibenzoylmethide)iron(III) · (MW 725.63)
(FeIII complex containing b-diketonate ligands serves as catalyst precursor for the cross coupling of Grignard reagents with vinyl bromide1 and for the intramolecular alkylation of ketones to give bicyclic alcohols2)
Alternate Name: tris(dibenzoylmethanato)iron.
Physical Data: mp 240 °C (dec).
Solubility: insol hexane; sol benzene; slightly sol alcohol.
Form Supplied in: red powder.
Analysis of Reagent Purity: visible spectrum 408, 500 (sh) nm.
Preparative Methods: Iron(III) Chloride and excess dibenzoylmethane in ethanol give a red solid; add 50% aq. ammonia; filter the red solid, wash with water, and dry.
Purification: precipitate from hot benzene by addition of hot hexanes.
Handling, Storage, and Precautions: store tightly sealed in a cool, dry place.
Tris(dibenzoylmethide)iron(III), Fe(dbm)3, is an effective catalyst in the stereospecific cross coupling of vinyl bromides with primary, secondary, and tertiary Grignard reagents (eq 1 and Table 1). Improved yields were observed when dimethoxyethane replaced THF as the solvent and lower reaction temperatures were employed.1b The cross coupling of vinyl sulfones with Grignard reagents was also successfully accomplished in the presence of Fe(dbm)3.1c,d
The superior performance compared to other FeIII catalysts has been attributed to its resistance to deactivation.1a It is superior to other organometallic catalysts, particularly Ni, because it is used at lower concentrations and temperatures and isomerization of the Grignard reagent does not occur.3 In general, FeIII catalysts are proposed to be readily reduced to FeI or Fe0 species, which serve as the active catalyst in the cross coupling reactions.3
Intramolecular Barbier-type reactions2 using magnesium have typically failed when used to construct six-membered cycloalkanols.6 Fe(dbm)3 used in combination with lanthanide reducing reagents, namely Samarium(II) Iodide, has been shown to overcome this shortcoming. The reaction was shown to be quite stereoselective when n = 1 (m = 1 or 2), but gives poor stereoselectivity when n > 1 (eq 2 and Table 2).
Indeed, numerous other organometallic reagents have been utilized to construct the desired bicycloalkanols (m = 0-2), including Pd,7 Ni,8 and other alkali metals.9 The Barbier-type reaction with SmI2 has also proved to be quite general for the efficient, simple construction of a variety of complex, bicyclic ring systems including bridgehead, bicyclic alcohols (eqs 3-5).2b
Mark W. Zettler
The Dow Chemical Company, Midland, MI, USA