Transition metals complexes with Schiff bases

Schiff base complexes of transition metal ions have occupied a central role in the development of coordination chemistry. In particular, the tetradentate ligands acacenH2 (46) and salenH2 (47), prepared from ethylenediamine and acetylacetone or salicylaldehyde, have been thoroughly investigated since their discoveries in 1889 and 1931. Most of these studies have dealt with divalent metal ions such as Co , Ni or Cu and there are relatively few reports concerning silver(I) complexes. ... 

A versatile starting material for the preparation of compounds belonging to the second class of polymers is (19) (R = Br) via a lithiation step numerous compounds have been prepared (19) (R = PPh2) readily forms complexes with transition metal compounds. Reduction of (19) (R = NO2) gives (19) (R = NH2), that can be used in diazotization and subsequent diazo coupling reactions. Another application of (19) (R = NH2) involves Schiff base... 

Homogeneous catalyst systems include transition metals, for example, Schiff base complexes with cobalt [59]. Unfortunately, there is no protocol known to recover and recycle the expensive Schiff base. Many copper complexes have been employed for the oxidation of phenols to 1,4-benzoquinones [60]. Copper salts such as CUCI2 and CuBr2 are widely used for the oxidation of trimethylphenol with molecular oxygen at larger scale [61]. In addition, applications of the halides of Cr, Mn, Fe, Ni, and Zn as catalysts have been described [58]. Copper halides have also been combined with earth metal halides, for example, MgCl2 [62] or LiCl, in the presence of a phase transfer catalyst [63]. 

In gas chromatography, thermotropic hquid crystals belonging to such groups of chemical compounds as Schiff s base, azo- and azoxy-compounds, esters, derivatives of biphenyls and terphenyls, organic complexes with transition metals, and organic polymers are used. Siloxane polymers of liquid-crystaUine properties are stable within the wide range of temperatures from 50°C to 300°C. 

The rates, selectivities, and stabilities of transition-metal-substituted poly-oxometalates in olefin epoxidation are compared with those of metallopor-phyrins, Schiff base complexes, and triflate salts, as follows (320b) ... 

A new type of octaazamacrobicyclic Schiff bases was synthesized in high yields via a template condensation on Group 2 metal ions in ethanol at 40-50°C (Scheme 92) [196], The resultant kinetically labile complexes readily transmetallize when reacted with transition metal (cobalt, nickel, iron, copper(II)) salts to form the corresponding mononuclear [M(imBT)]X2 complexes (where X is BF4 and C104 ). 

Rh2(55-mepy)4] was first used for cyclo-propanation. Enantioselective cyclopropana-tion is industrially important since synthetic pyrethroids, which are used as insecticides, contain substituted three-membered rings, whose configuration is crucial for their biological effect. [9] Enantioselective cyclopropa-nation has tradition. It was this reaction type which in 1966 opened up the field of enantioselective homogeneous catalysis with transition metal complexes. The copper(II) complex of the Schiff base from salicylaldehyde and optically active 1-phenylethylamine at that time reached 6% ee. [10] With optimized opti-... 

Virtually all types of metal ions have been complexed with macrocyclic ligands. " Complexes of transition metal ions have been studied extensively with tetraaza macrocycles (Chapter 21.2). Porphyrin and porphyrin-related complexes are of course notoriously present in biological systems and have been receiving considerable investigative attention (Chapter 22). Macrocyclic ligands derived from the Schiff base and template-assisted condensation reactions of Curtis and Busch also figure prominantly with transition metal ions. The chemistry of these ions has been more recently expanded into the realm of polyaza, polynucleating and polycyclic systems. Transition metd complexes with thioether and phosphorus donor macrocycles are also known. ... 

Schiff bases play an important role in coordination chemistry as they readily form stable complexes with most of the transition metals. The development of bioinorganic chemistry has increased interest in Schiff base complexes as it has been recognised that many of these complexes may serve as models for the metal-containing sites in metallo-proteins and -enzymes. Schiff also discovered the experimental technique of preparing... 

Thermal Analysis Curves of Complexes of Transition Metals with Schiff Bases... 

Pd-cataly2ed reactions of butadiene are different from those catalyzed by other transition metal complexes. Unlike Ni(0) catalysts, neither the well known cyclodimerization nor cyclotrimerization to form COD or CDT[1,2] takes place with Pd(0) catalysts. Pd(0) complexes catalyze two important reactions of conjugated dienes[3,4]. The first type is linear dimerization. The most characteristic and useful reaction of butadiene catalyzed by Pd(0) is dimerization with incorporation of nucleophiles. The bis-rr-allylpalladium complex 3 is believed to be an intermediate of 1,3,7-octatriene (7j and telomers 5 and 6[5,6]. The complex 3 is the resonance form of 2,5-divinylpalladacyclopentane (1) and pallada-3,7-cyclononadiene (2) formed by the oxidative cyclization of butadiene. The second reaction characteristic of Pd is the co-cyclization of butadiene with C = 0 bonds of aldehydes[7-9] and CO jlO] and C = N bonds of Schiff bases[ll] and isocyanate[12] to form the six-membered heterocyclic compounds 9 with two vinyl groups. The cyclization is explained by the insertion of these unsaturated bonds into the complex 1 to generate 8 and its reductive elimination to give 9. 

The coordination shell comprises three fac-S and three fac-N-donor atoms in [Fe(6mp)3] [FeClJCl, where 6mp = 6-thiopurine, (189). Both iron(II) and iron(III) complexes are included in a review of transition metal complexes of thiosemicarbazones. " 5,5 -Dimethyl-l,2,3-cyclohex-anetrione-l,2-dioxime-3-thiosemi-carbazone, dcdt (190), acts as an A, A, 5 -donor to Fe +, giving a bis-ligand complex (contrast [Fe(7V,7V -dcdt)3] with Fe " "). The Schiff bases from pyridine 2-carboxaldehyde and thiosemicarbazide or 4-phenyl thiosemicarbazide also act as A, VV, 5 -donors, both to Fe " " and to Fe " ". The antibacterial activity of these complexes was assessed, in... 

The use of a Schiff s base complex as a chelating ligand has been extensively studied for transition metals (31). An analogous complex has been produced for sodium perchlorate with two molecules of Cu(salen) (where salen = N,N -ethylenebis(salicylidene-iminato)). Each sodium, Fig. 4, is surrounded octahedrally by two oxygens from a perchlorate ion and four from the two chelating Cu(salen) ligands (32). 

Transition metal complexes encapsulated in the channel of zeolites have received a lot of attention, due to their high catalytic activity, selectivity and stability in field of oxidation reactions. Generally, transition metal complex have only been immobilized in the classical large porous zeolites, such as X, Y[l-4], But the restricted sizes of the pores and cavities of the zeolites not only limit the maximum size of the complex which can be accommodated, but also impose resistance on the diffusion of substrates and products. Mesoporous molecular sieves, due to their high surface area and ordered pore structure, offer the potentiality as a good host for immobilizing transition complexes[5-7]. The previous reports are mainly about molecular sieves encapsulated mononuclear metal complex, whereas the reports about immobilization of heteronuclear metal complex in the host material are few. Here, we try to prepare MCM-41 loaded with binuclear Co(II)-La(III) complex with bis-salicylaldehyde ethylenediamine schiff base. 

Template and capping reactions feature in recent work. A number of sterically hindered H20 and N4 ligands have been prepared in which a quadridentate Schiff base is capped by condensation of salicylaldehyde or pyrrole-2-carbaldehyde with a series of bis(8-aminonaphthyl)alkyl ethers. These ligands combine the versatility of the Schiff base with the protective features well known for certain model porphyrin systems, and appear to be of some interest. The zinc(II) complex and other transition metal complexes have been prepared.340... 

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