Tetracarbonylhydridoferrate salts: NaHFe(CO)4 and KHFe(CO) 4

Abstract

(A) Brunet and co-workers showed that KHFe(CO)4 is a selective reducing agent for the reduction of electron deficient ketones as well as a highly selective reducing agent for the mono-reduction of the keto group in α-ketocarbonyl compounds. Ester, amide and nitrile groups, as well as other unactivated carbonyl functions, remain intact under the reaction conditions. (B) In the presence of NaHFe(CO)4 or KHFe(CO) 4, azides or acyl azides can be converted into the corresponding primary amines or amides. (C) HFe(CO)4 salts are convenient and general hydride sources for reductive amination reactions. This method can be applied to aromatic as well as aliphatic amines and aldehydes. When dialdehydes are employed, cyclic amines are obtained. (D) Selective reduction of α,β-unsaturated carbonyl compounds is another typical reaction of NaHFe(CO)4 or KHFe(CO)4. Under these conditions, a wide variety of functional groups such as ketones, esters, nitriles, amides, etc. are tolerated and the reaction can be performed in the presence of other olefins. One exception are α,β-unsaturated diketones that undergo deacylative reduction under the reaction conditions, affording saturated monoketones. (E) Umani-Ronchi and co-workers described a formal 'α-alkylation' of carbonyl compounds (aldol reaction/elimination/reduction) with aldehydes, in the presence of KHFe(CO)4. The yields depend upon the steric requirements of the aldehyde. (F) Shin and co-workers used KHFe(CO)4 to convert carboxylic acid chlorides into the corresponding esters under mild and neutral conditions. (G) The reagent, formed by combining in situ NaHFe(CO)4 and MeI, reacts with alkynes. After CuCl2 oxidation, cyclobutenediones can be obtained in moderate yields. Similarly, the reagent generated in situ from NaHFe(CO)4/CH2Cl2 reacts with alkynes and, after CuCl2 oxidation, leads to α,β-unsaturated acids. The reaction using NaHFe(CO)4/TMSCl system gives the corresponding α,β-unsaturated carboxylic acids at room temperature and the corresponding cyclobutenediones at 60 °C. © Georg Thieme Verlag Stuttgart.