Schiff-bases, iron complexes

Activation volumes for aquation of Schiff base complexes [Fe(C5H4NCH=NHR)3]2+ (R = Me, Et, nPr, nBu) are between +11 and +14 cm3 mol-1 (107), and thus within the range established earlier (108) for (substituted) tris-l,10-phenanthroline-iron(II) complexes, viz. +11 to +22 cm3 mol-1. These positive values are consistent with dissociative activation. Kinetic studies of the reaction of a CH2S(CH2)3SCH2 -linked bis(terpy) ligand (L6) with [Fe(terpy)2]2+ showed a very slow two-step process. The suggested mechanism consisted of slow loss of one terpy, rapid formation of [Fe(terpy)(L6)], and finally slow displacement of the second terpy as the partially-bonded L6 becomes hexadentate (109). 

Structures have been determined for [Fe(gmi)3](BF4)2 (gmi = MeN=CHCF[=NMe), the iron(II) tris-diazabutadiene-cage complex of (79) generated from cyclohexanedione rather than from biacetyl, and [Fe(apmi)3][Fe(CN)5(N0)] 4F[20, where apmi is the Schiff base from 2-acetylpyridine and methylamine. Rate constants for mer fac isomerization of [Fe(apmi)3] " were estimated indirectly from base hydrolysis kinetics, studied for this and other Schiff base complexes in methanol-water mixtures. The attenuation by the —CH2— spacer of substituent effects on rate constants for base hydrolysis of complexes [Fe(sb)3] has been assessed for pairs of Schiff base complexes derived from substituted benzylamines and their aniline analogues. It is generally believed that iron(II) Schiff base complexes are formed by a template mechanism on the Fe " ", but isolation of a precursor in which two molecules of Schiff base and one molecule of 2-acetylpyridine are coordinated to Fe + suggests that Schiff base formation in the presence of this ion probably occurs by attack of the amine at coordinated, and thereby activated, ketone rather than by a true template reaction. ... 

Spin cross-over behavior has been established for a number of Schiff base complexes of iron(III) complexes with N402-donor sets. A two-step spin cross-over in the warming direction for [Fe A-(8-quinolyl)salicylaldiminate 2](NCSe) has been ascribed to intermolecular TT-interactions between aromatic rings. Usually spin cross-over in these N402-complexes is... 

There have been very few reports of the Raman spectra of spin-equilibrium complexes. In one experiment the presence of both high-spin and low-spin isomers of an iron(II) Schiff base complex was observed by the resonance Raman spectra of the imine region (11). The temperature dependence of the spectra was recorded for both solid and solution samples. Recently differences were described in the resonance Raman spectra of four- and six-coordinate nickel(II) porphyrin complexes which undergo coordination-spin equilibria. These studies are extensions of a considerable literature on spin state effects on the Raman spectra of iron porphyrins and hemes. There are apparently no reports of attempts to use time-resolved Raman spectra for dynamics experiments. 

Manganese(III) Schiff base complexes, but not those of iron(III), activate dioxygen in the presence of aliphatic aldehydes.33... 

Schiff-base complexes fragment according to the scheme below 25, 196a) labeling experiments were used to determine which phenyl group was lost. The localization of charge on the iron atoms explains loss of benzene by fission of an N—C bond, which is contrary to the usual /8-fission of amines. 

Spin-crossover iron(III)-Schiff base complexes 252... 

Schiff base complex Co(Bzacen)py02 9 Bzacen = JV,JV -ethylenebis(benzoylacetoneiminato) and the diamagnetic iron picket-fence porphyrin Fe TpivPP)(Meim)02 (10) where the iron atom is surrounded by a cage which prevents the dioxygen species from reacting with another iron atom (TpivPP= meso-tetrakis(a,a,a,a-o-pivalamidophenyl)porphyrinato, Meim = 1-methylimid-azole). ... 

The oxidation of Ti " by Fe" and the reaction between TF" and Sn" have been studied using flow and potential-time dependences. An investigation has also been made of the Ag -Ce " reaction. Polarographic studies of planar Schiff base complexes of Co , Ni", and Cu have shown well-defined oxidation waves and in some chelates the two-electron oxidation Co" Co " is postulated. Kinetic studies have also been made on the oxidation of cobalt(ii) dipyridyl complexes by copper(n) and iron(m) perchlorates in anhydrous acetonitrile. Solvent effects have also been investigated in redox reactions of tetrahalogenoplatinum(iv) complexes of the type PtLaX4. ... 

The ky term is assigned to rate-determining dissociation of the iron(u) complex the k term is assigned to bimolecular nucleophilic attack of the cyanide at the iron. For both the phenanthroline and the Schiff base complexes the rate of reaction with cyanide increases greatly as the mole fraction of alcohol increases in methanol- or ethanol-water mixed solvents. 

The base-catalysed hydrophosphonylation of aldehydes or imines (Pudovik reaction) [58] as a convenient method was widely used for the synthesis of 1-hydrox-yalkylphosphonates. Since the pioneering work of Shibuya [50] and Spilling [51] was reported, much attention has been devoted to developing enantioselective catalysts for the synthesis of chiral 1 -hydroxy alkylphosphonates. Chiral aluminium complexes were shown to be more effective chiral catalysts [59-62]. Based on the success of using A1 (salen) and A1 (salcyen) as asymmetric catalysts, Al-Schiff base complexes [63, 64] have been developed to catalyze the asymmetric addition reaction of dial-kylphosphonates and aldehydes. Tridentate Schiff base metal complexes, such as vanadium, chromium, and iron [65], have been successfully applied in many asymmetric synthetic reactions. We noticed that Al(III) complexes could catalyse the asymmetric Pudovik reaction and these ligands could be easily synthesized [66-70]. 

---