Nickel salicylaldehyde complex

The Schiff bases have contributed to a large extent to the development of the coordination chemistry of nickel(II), particularly those obtained by the condensation of salicylaldehyde with various mono- and poly-dentate amines. A large number of nickel(II) complexes have been synthesized with these ligands exhibiting all of the possible coordination geometries, spin states and spectromagnetic properties. The early complexes of nickel(II) with different salicylal-dimines have been covered extensively in a number of review articles.2246-2252... 

Most nickel(II) complexes with the various Schiff bases derived from salicylaldehyde and different amines have usually been easily prepared by three general methods (i) the reaction of a nickel(II) salt, usually hydrated nickel(II) acetate, with the preformed Schiff base using water, EtOH, MeOH or their mixtures as reaction medium (ii) the condensation reaction of bis(salicylaldehydato)nickel(II) with the appropriate amine in refluxing EtOH or H20/EtOH mixture (iii) the template reaction of the aldehyde with the appropriate amine in the presence of a nickel salt. In Table 97 the formulas, synthetic methods and some physicochemical properties for a number of nickel(II) salicylaldiminato complexes are reported. Examples of dinuclear complexes formed with Schiff bases are specifically reported in Section 50.5.8.5. 

Table 97 Nickel(ll) Complexes with Bi- and Poly-dentate Schiff Base Ligands Derived from Salicylaldehyde or Related Aldehydes and Various Amines... 

Several nickel(II) complexes have been reported with Schiff bases derived from the condensation of salicylaldehyde and various amino acids. The structures of the complexes were investigated by means of electronic and NMR spectra as well as X-ray crystallography.2336-2341 Recently the X-ray structure of complex (321), prepared by the reaction of pyridoxal-HCl, o-phospho-DL-threonine and N NOsVfiHaO at pH 5, has been reported.2341... 

The effect of the charge may also be seen in some nickel(n) complexes. The neutral complex 4.7, containing two anionic ligands obtained by the deprotonation of the salicylaldehyde derivative, is completely stabilised towards hydrolysis. In contrast, the monocationic complex 4.8, containing two neutral 1,10-phenanthroline ligands, is rapidly hydrolysed to the corresponding salicylaldehyde complex (Fig. 4-25). Presumably, the overall positive charge of the complex promotes the attack of the nucleophile upon the electrophilic carbon centre. 

New and more selective homogeneous catalysts continue to be developed. Very few catalysts for the homogeneous reduction of aromatic compounds are known but this year two have been reported. The first is the readily prepared rhodium complex [Rh(r -C5Me5)Cl2]2 which will reduce benzene (50°C/50atm) in the presence of a base to cyclohexane " with this catalyst a high stereospecificity for all ci5-addition is observed. The other report" concerns the use of salicylaldehyde complexes of copper and nickel for the catalytic reduction of aromatic rings, but there is some doubt as to whether the active catalysts are homogeneous or not. 

By means of the NMR examination of nickel(II) complexes of SchifFs bases of salicylaldehyde with N,N-substituted ethylenediamines, Thwaites et al [Th 66a, Th 66b] demonstrated that, in addition to the diamagnetic square planar and the paramagnetic octahedral complexes, other paramagnetic species containing a nickel(II) atom with a coordination number of five are also formed in chloroform solution. No difference between the two types of paramagnetic complex can be established by means of magnetic moment measurements, and only the NMR spectra provide a possibility for distinguishing between them. 

The coordination process may either stabilize or destabilize aromatic Schiff bases. If nickel (II) salts are added to ammoniacal solutions of salicylaldehyde, the precipitate obtained is the inner complex salt of nickel (II) and salicylaldimine (61). If beryllium chloride is added to the Schiff base derived from 2-hydroxy-l-naphthaldehyde and ethylamine, however, the Schiff base is decomposed and the inner complex of beryllium (II) and 2-hydroxy-1-naphthaldehyde is obtained (59). Here the strength of the coordinate bonds formed with the metal seems to determine which complex will be formed. 

In 1992, Crabtree and co-workers reported the first nickel catalyst effective for silane alcoholysis.161 The complex, [Ni(tss)]2 (tss = salicylaldehyde thiosemicarbazone), bears a ligand that contains O and N donor groups and a semicarbazide sulfur. Alcoholysis of Et3SiH with ethanol or methanol occurs at room temperature in 50% dimethyl sulfoxide-benzene. However, the reaction is inhibited in the presence of strong donor ligands, H2, or atmospheric pressure of CO. 

Simple macrocyclic quadridentate complexes can be synthesized by template reactions from ethers derived from salicylaldehyde and diamines in the presence of appropriate metal ions such as nickel(II) (equation 3).35>36 However, these reactions can also be carried out quite effectively in the absence of metal ions to yield the free ligands, which can be obtained by hydrolysis of the complexes. An iron(II) macrocyclic quinquedentate chelate of this type has been produced by template synthesis (equation 4).37... 

It has been known for many years that the rate of hydrolysis of a-amino acid esters is enhanced by a variety of metal ions such as copper(II), nickel(II), magnesium(H), manganese(II), cobalt(II) and zinc(II).338 Early studies showed that glycine ester hydrolysis can be promoted by a tridentate copper(II) complex coupled by coordination of the amino group and hydrolysis by external hydroxide ion (Scheme 88).339 Also, bis(salicylaldehyde)copper(II) promotes terminal hydrolysis of the tripeptide glycylglycylglycine (equation 73).340 In this case the iV-terminal dipeptide fragment... 

Condensation of ketones or aldehydes with the methyl ester of dithiocarbazic acid produces hgands with S,N,0 or S,N donor sets. An example is (142), which acts as both a didentate and a tridentate to ReO. Nickel(II)-templated reactions of pentanedione or salicylaldehyde with aminoethanethiol produce N,0,S ligands such as (143) and (144) these form simple mononuclear complexes or else dinuclear species with thiolate bridging two Ni centers. Mixed donor Schiff-base hgands including other heteroatoms such as P (145) and Te (146) have appeared. 

Simple macrocyclic quadridentate complexes can be synthesized by template reactions from ethers derived from salicylaldehyde and diamines in the presence of appropriate metal ions such as nickel(II) (equation However, these reactions can also be carried out quite effectively... 

The complexes Nin(L), where L = 3,10-di(/>-X-benzoyl)-2,4,9,11 -tetrame-thyl-l,5,8,12-monobenzotetraazcyclo[14]annulene, X = Me, H, Cl, N02, OMe, show H deshielding effects due to the benzoyl groups.401 The 111 and 13C NMR spectra of Ni(II) and Zn(II) complexes with the Schiff base from 1,2-bis(o-aminophcnoxy)cthanc and salicylaldehyde are consistent with 0,N,N,0-coordination of the ligand.402 The 3H NMR spectra of aqueous solutions of [Ni(L-0)]+ and [Ni(L-NH)(H20)3]2+, where L = flexidentate 5-substituted salicylaldimino Schiff bases based on l-(2-aminoethyl)piperazine, show that these exist as planar and octahedral forms in equilibrium.403 H NMR signals from the ortho-protons in bis[2-(2,4-dichlorophenylmethyleneamino)benzene-thiolato]nickel(II) are consistent with Ni. . . H-C interactions in solution.404... 

In alkaline media in the presence of Ni " ", condensation takes place between salicylaldehyde thiosemicarbazone or selenosemicarbazone and salicylaldehyde to give complexes of (165) in which the ligands do not co-ordinate via the X atom. The structures of both cis- and trans-bis(dithiosemicarbazido)-bis(dinitrato)-nickel(ii) have been determined. The Ni—S bond lengths are longer in the trans-isomer than in the cis-form. The structures of the... 

The nickel complex 11, with a fluorous Schiff base as ligand, was prepared from salicylaldehyde and 4-perfluorodecylaniline (Scheme 15). This fluorous Ni complex was used as a catalyst for the conjugate addition of -diketones to diethyl azodicarboxylate (DEAD). The mixture was stirred at 60 C in a mixture of... 

A wide variety of nickel chelates, e.g, Ni complexes of dithioic acids (NiDRC and NiDRP), salicylaldehyde oximes (33), thiobisphenolates (cyasorb UV 1084, 31) and hydroxybenzyl phos-phonates (Irgastab 2001 30), all of which are good UV stabilizers, " are substantially lost during the photooxidative induction period (Figure 5, where R = butyl). 

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