Iron complexes heterocyclic ligands

Fe-Heterocycles and iron complexes with heterocyclic ligands 93 JOM(457)63. Ruthenium and osmium complexes with heterocyclic ligands, clusters including Ru- and Os-heterocyclic fragments 93JOM(457)121. 

Bis (jU-oxo)dimetal diamond cores in copper and iron complexes with heterocycles as ligands relevant to biocatalysis 02AG(E)1114. 

One must realize that it would be very difficult to recover the free ligand from Co(III),Rh(III),Ir(III),Pt(IV),and Pt(II)-ammonia or cyanide coitplexes only the smooth continuity to less irreversibly bonded Cr(III),Pd(II),and Hg(II) complexes makes this taxonomy almost palatable.Organisms can produce iron complexes like cytochrome c, hemoglobin,cobalt(III) in vitamin B 12,and plants can produce Mg(II) conplexes like chlorophyll-For some years,it was considered difficult to remove the central atom from the planar,heterocyclic systems with strong absorption bands in the visible (like phthalocyanine),and much... 

A catalytic cycle shown above has been proposed. The reaction begins with the oxidation of the iron complex to form the oxo-iron species by reaction with oxygen. An electrophilic attack of this oxo-iron complex on C-2 position of heteroarenes is aided by the heteroatom. Following a consequential deprotonation, a tertiary complex comprising iron, heterocycle, and MCPA ligand is formed. With the introduction of arylboronic acid, transmetalation and then elimination of the iron complex can yield the desired product. 

Besides complexes of thiosemicarbazones prepared from nitrogen heterocycles, iron(III) complexes of both 2-formylthiophene thiosemicarbazone, 26, and 2-acetylthiophene thiosemicarbazone, 27, have been isolated [155]. Low spin, distorted octahedral complexes of stoichiometry [Fe(26)2A2]A (A = Cl, Br, SCN) were found to be 1 1 electrolytes in nitromethane. Low spin Fe(27)3A3 (A = Cl, Br, SCN) complexes were also isolated, but their insolubility in organic solvents did not allow molar conductivity measurements. Infrared speetra indicate coordination of both via the azomethine nitrogen and thione sulfur, but not the thiophene sulfur. The thiocyanate complexes have spectral bands at 2065, 770 and 470 cm consistent with N-bonded thiocyanato ligands, but v(FeCl) and v(FeBr) were not assigned due to the large number of bands found in the spectra of the two ligands. 

The copper(II) complexes of 3-ethoxy-2-oxobutyraldehyde bis(thiosemicarbazone) and related compounds are active in vivo agents [151, 158, 159]. The metal complexes of 2-heterocyclic thiosemicarbazones were evaluated for their cytotoxicities [160, 161]. Further studies have revealed that these ligand s iron and copper complexes are effective inhibitors of DNA synthesis at much lower concentrations than the free thiosemicarbazones without apparent cytotoxicity [127]. Although the iron(III) complex of 2-isoformylquinoline thiosemicarbaz-one, 21, is considerably more active than free 21, the copper(II) complex is only moderately more active [127]. 

As highly reactive heterocycles, the thietes are well suited for the formation of metal complexes. Takahashi and Dittmer both individually and in collaboration have been involved with the interaction of thietes and iron or cobalt carbonyls. During the thermally or photochemically induced complexation process, ring opening takes place so that the resultant thioacrolein is the actual ligand in the organometallic compound (Scheme i7)/ 3-203,204... 

Ferrocene, bis(cyclopentadienide)iron, was the first transition metal complex with aromatic ligands, and its discovery induced extensive research on complexes of different transition metals and different aromatic ligands. It is therefore not surprising that borinate ion complexes of this type are known. Some complexes with five-membered heterocycles were mentioned in Section 1.21.7. In this section borinate complexes are considered in greater detail because of their formal relationship to benzene. An extensive review on transition metal complexes with boron heterocycles has recently been published (80MI12100). 

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