Iron complexes diketones

Unlike the corresponding iron complexes, aroylnickel carbonylates give acyloins instead of aldehydes by hydrolysis with aqueous methanol containing hydrochloric acid. In reactions at higher temperature, or by treatment with bromine, a-diketones are formed 85L... 

Scattered examples of incorporation of the two CO groups into organic compounds using iron complexes to afford 1,2-diketones and acyl lactones are known.t Hioi]... 

Another useful reaction of these complexes is alkene insertion. This works well with electron-poor alkenes and may be drawn as a Michael addition. One application is in the synthesis of the perfumery compound, CM-jasmone 4.205 (Scheme 4.73). The initial acyl iron complex reacted with methyl vinyl ketone to give a 1,4-diketone 4.204, which underwent a subsequent intramolecular aldol reaction on treatment with a base. 

Tris(2,4-pentanedionato)iron(III) [14024-18-1], Fe(C H202)3 or Fe(acac)3, forms mby red rhombic crystals that melt at 184°C. This high spin complex is obtained by reaction of iron(III) hydroxide and excess ligand. It is only slightly soluble in water, but is soluble in alcohol, acetone, chloroform, or benzene. The stmcture has a near-octahedral arrangement of the six oxygen atoms. Related complexes can be formed with other P-diketones by either direct synthesis or exchange of the diketone into Fe(acac)3. The complex is used as a catalyst in oxidation and polymerization reactions. 

In 1968 the first reports of spin crossover in iron(III) monothio-y8-diketo-nates appeared [84, 85] and reviews on metal complexes of monothio-/ -diketones were published shortly afterwards [86, 87]. The monothio-/ -dike-tones can be considered as a ligand system intermediate between acetylace-tone and dithioacetylacetone (Fig. 4). 

S-Methyl-A-(2-pyridyl)methylenedithiocarbazate (nns) can be prepared by the condensation of S-methyldithiocarbazate and pyridine-2-aldehyde. The low-spin complexes [Fe(nns)2].X (X = CIO or FeCl ) have both been isolated.2,1.3-Benzothiodiazole. 2,1,3-benzoselenodiazole, and their derivatives (L) form the octahedral complexes FeL2Cl3. and morpholine-4-carbodithioate (mdtc) forms the complex [Felmdtclj]. Mossbauer and magnetic data for a series of monothio- -diketonate-iron(iii) complexes have been interpreted in terms of a thermal equilibrium between the sextet and doublet states. 

The Ns-terdentate ligand bis(2-pyridylcarbonyl)amine, Hbpca = (54), is also a / -diketone, and ean therefore act as a bridging ligand. In the complexes [Fe(bpca)2][M (hfac)2]2, where = Fe, Mn, or Ni, the central iron, in its high ligand field Ng environment, is low-spin, while the iron eoordinated to hfac in the first complex is, as expected for its tris-/3-diketonate environment, high-spin." ... 

In the above examples, the nucleophilic role of the metal complex only comes after the formation of a suitable complex as a consequence of the electron-withdrawing effect of the metal. Perhaps the most impressive series of examples of nucleophilic behaviour of complexes is demonstrated by the p-diketone metal complexes. Such complexes undergo many reactions typical of the electrophilic substitution reactions of aromatic compounds. As a result of the lability of these complexes towards acids, care is required when selecting reaction conditions. Despite this restriction, a wide variety of reactions has been shown to occur with numerous p-diketone complexes, especially of chromium(III), cobalt(III) and rhodium(III), but also in certain cases with complexes of beryllium(II), copper(II), iron(III), aluminum(III) and europium(III). Most work has been carried out by Collman and his coworkers and the results have been reviewed.4-29 A brief summary of results is relevant here and the essential reaction is shown in equation (13). It has been clearly demonstrated that reaction does not involve any dissociation, by bromination of the chromium(III) complex in the presence of radioactive acetylacetone. Furthermore, reactions of optically active... 

The idea of an one-center template mechanism was initially supported by first-order kinetics in iron. Moreover, intermediates 3a, 43 and 44 ands also their transition states in the catalytic cycle (Scheme 8.18) were proved by computational studies [71]. Moreover, mass spectrometric (ESI) [72] and spectroscopic (EXAFS and Raman) studies indicated complex 45 with two equatorial [3-diketonate ligands to be the catalytically active species in solution (Scheme 8.19) [73]. Actually, 4equiv. of FeCl3-6H20 are needed to generate 1 equiv. of complex 45 under reaction conditions ... 

Precisely the last condition explains the fact that mainly ICC have been obtained by the immediate interaction of ligands and zero-valent metals. Thus, a large series of metal p-diketonates was synthesized in the absence of a solvent [513,634-638], for example, iron bis- and tra-acetylacetonates [635]. It was shown that other ligands can serve as activators or promoters in these processes. In particular, the introduction of a,a or y,y -bipy into the reaction mixture gives the possibility of isolating copper acetylacetonates and adducts of similar complexes of cobalt and nickel [636], meanwhile the p-diketonates of the metals above are not formed under conditions similar to those reported in Ref. 635. Under dissolution of more active metallic barium in the mixture of another p-dikctone - dipivaloyl-methane (DPM) - with dyglime (DG) or tetraglime (TG) in absolute pentane, the mononuclear complex [Ba(DPM)2(TG)] and binuclear complex [Ba2(DPM)4 ( t-H20)(DG)] were isolated and structurally characterized [637]. 

The reaction, of metal carbonyls with 1,3-diketones generally results in a complete displacement of carbon monoxide accompanied by oxidation of the metal to yield 1,3-diketonato complexes. For example, iron pentacarbonyl, chromium hexa-carbonyl, and molybdenum hexacarbonyl afford FefCgHjOOs,1 Cr(CsHr02)8,2 and Mo(CgH702)s,2,s respectively, when allowed to react with 2,4-pentanedione. 

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