Suthamalli K. Ramalingam

Cyclic voltammetric and e.s.r. studies of a tetraaza 14-membered macrocyclic copper(II) complex derived from 3-salicylideneacetylacetone ando-phenylenediamine: stabilization and activation of unusual oxidation states

SummaryA 14-membered macrocyclic Schiff base derived from 3-salicylideneacetylacetone ando-phenylenediamine acts as a tetradentate and strongly conjugated ligand to form a cationic solid complex with CuCl2. U.v.-vis. and e.s.r. spectral data reveal a strong ligand to metal π-interaction in the square planar complex. C.v. data reveal that the title ligand is able to stabilize the copper(III) oxidation state more effectively than comparable saturated or partially unsaturated macrocyclic ligands and confers a weaker tendency for reduction of copper(II) to copper(I) and copper(0). While the inclusion of a PPh3 ligand suppresses the Cu0 → CuI → CuII oxidation, imidazole and pyridine strongly enhance the CuII → CuIII oxidation of the complex.

Spectral and redox models for blue copper proteins: copper(II) complexes of β-diketonimines from a Knoevenagel condensate

Abstract Low molecular weight and low symmetric solid copper complexes have been synthesised, in an attempt to simulate the spectral and redox properties of blue copper proteins, in a template manner via an unisolable ligand system. The Knoevenagel condensate, 3-salicylideneacetylacetone (salac: C 12 H 12 O 3 ), reacts with the primary amines, aniline, p-Cl-aniline, and methyl amine and copper salts in an in situ manner, producing neutral copper complexes. The complexes thus synthesised are: ( A ) Cusalac(aniline) 2 Br 2 , ( B ) Cusalac(aniline) 2 Cl 2 , ( C ) Cusalac(p-Cl-aniline) 2 Br 2 , ( D ) Cusalac(MeNH 2 ) 2 Cl 2 , ( E ) Cusalac(aniline) 2 (OAc) 2 , and ( F ) Cusalac(MeNH 2 ) 2 (OAc) 2 . The ethanolic solution of A exhibits high extinction value (3000 M −1 , cm −1 (Type I) and the acetonitrile solution of D has normal extinction value of 100 M −1 , cm −1 (Type II). The copper hyperfine data (cm −1 ) and reduction potential (vs Ag/AgCl) of A ( A ‖ =0.0115 and E 1/2 =+605 mV) and B ( A ‖ =0.0117 and E 1/2 =+595 mV) correspond well with typical blue copper protein models. But the complex E ( A ‖ =0.0177 and E 1/2 =−555 mV) and F ( A ‖ =0.016 and E 1/2 =−910 mV) widely deviate from the model systems.

Bis(benzotriazol-1-yl) methylimine as a novel cyanating agent for labile β-diketonates

Abstract Bis(benzotriazol-l-yl) methylimine was used as a novel electrophilic cyanating agent for labile β-diketonates (M = Cu II , Ni II , Co II , Zn II and Cd II ). The actual cyanating species was 1 -cyanobenzotriazole formed in situ with the elimination of benzotriazole. The labile metal-oxygen bond in the chelates possibly induced debenzotriazolation. The inert and less labile β-diketonates did not undergo this reaction. The final product of the reaction, however, was the mixed-ligand complex of cyano-β-diketone and benzotriazole, identified by spectral and analytical methods. Copyright

New β-diketon-(2-phenylethyl)imine Schiff base chelates of copper(II), nickel(II) and cobalt(III) and their electrophilic substitution products

Abstract New Schiff base chelates of nickel(II), copper(II) and cobalt(III) derived from acac/bzac and 2PEA (acac = 2,4-pentanedionate, bzac = 1-phenyl-1,3-butanedionate anions; 2PEA = 2-phenylethylamine) have been synthesized and characterized. The nickel(II) and copper(II) complexes are non-planar, cobalt(II) does not form any isolable complex and the cobalt(III) complex has an octahedral structure as indicated from UV-vis, IR, 1H and 13C NMR and analytical data. Steric factors arising from the flexible CH2CH2Ph substituent on the nitrogen atom of 2PEA force the less hindered, non-planar, tetrahedral geometry for copper(II) and nickel(II) and the meridional octahedral geometry for cobalt(III) to predominate. Electrophilic substitution reactions of these chelates, like γ-halogenation and γ-phenylisocyanation, are also reported.

Phenylisocyanation and bromination studies on lanthanide β-diketonates

SummaryPhenylisocyanation and bromination of some twenty lanthanide β-diketonates: Ln(acac)3, Ln(bzac)3 and Ln(dbzm)3 where Ln=PrIII, NdIII, SmIII, GdIII, DyIII and YIII and Ce(acac)4, Ce(bzac)4 and Ce(dbzm)4 have been investigated. While phenylisocyanation gives the expected 3-substituted phenylamido product, bromination, for the first time, has been observed to yield a substituted product with flipping of one (or two) six-membered diketone ring to give a five-membered ring in which the entering bromine electrophile is bonded to the metal and a carbon atom. The other diketone rings, although γ-substituted, remain intact with respect to metal coordination. The substituted complexes have been characterised by i.r., u.v. and n.m.r. spectroscopy.

Selective cyanation/bromination of coordinated β-diketones using CNBr as a new reagent

Abstract Cyanogen bromide was used as a new twin purpose reagent for bromination or cyanation of β-diketonates of many transition and some non-transition metals. Whereas inert and less labile chelates of Cr III , Co III , Al III and Be II yielded γ-brominated reaction products, the labile ones of Co II , Ni II , Mg II and Cu II gave γ-cyanated diketonates. VO IV and Fe III chelates yielded γ-bromo products in methanol and γ-cyano products in chloroform. The reagent is the first cyanating agent for β-diketonates. CNI was also used as a new reagent for β-diketonates and the reactions were compared with those of CNBr.

Linkage isomerization resulting from phenylisocyanation of unsubstituted and γ-halogenated β-diketonates

Abstract Linkage isomerization in β-diketonates resulting from sterically induced intramolecular rearrangement in metal-ligand bonding have been observed during phenyl isocyanation of β-diketonato and β-ketonimino complexes of chromium(III), cobalt(III), cobalt(II), nickel(II) and copper(II). Steric repulsions operating between γ-CO·NH·Ph and α-C6H5 or between γ-CO·NX·Ph (γ-halogenated substrate) and α-CH3/C6H5 of the rings, probably lead to rearrangement changing the metal-ligand bonding from MO (diketone oxygen) to MO (amide oxygen).

Cobalt(II), nickel(II), copper(II) and zinc(II) complexes of conjugated 3-(benzylidene/salicylidene)-β-diketones (having no enolisable γ-carbon proton) and their reactions

SummaryThe synthesis and structural characterization of new metal(II) chelates (M = CoII, NiII, CuII and ZnII) of neutral conjugated bidentate β-diketone ligands, having no enolisable γ-carbon proton, and their reactions are reported. The ligand systems chosen are Knoevenagal condensates of aromatic aldehydes with β-diketones, such as 3-(benzylidene/salicylidene) acetylacetone/benzoylacetone. The general composition of the chelates is [M(AA)B2C2] for 6-coordinate complexes and [M(AA)B2] for 4-coordinate complexes. (AA) is a neutral bidentate aldehyde-β-diketone condensate ligand; B is a mono-dentate anion and C is monodentate neutral ligand (H2O/Py). Bromination at α-methyl groups by NBS and PyHBr3, Schiff base condensation at β-carbonyl groups by amine bases and 1,2-addition reaction at the γ-carbon double bond are reported.

Transition metal complexes of the Schiff bases from 2-phenylethylamine and 2-hydroxyarylcarbonyl compounds

SummaryA series of complexes of the type CoIIIL3, NiL2, Ni(HL)2(OAc)2 and CuL2 where HL is a Schiff base derived from 2-phenylethylamine and 2-hydroxy-1-naphthaldehyde, salicylaldehyde, 2-hydroxyacetophenone and its 5-methyl and 5-chloro-derivatives and 2-hydroxypropiophenone and its 5-methyl and 5-chloro-derivatives have been synthesised and characterized. The cobalt(III) complexes are octahedral, the copper complexes are planar, the complexes NiL2 of Schiff bases derived from aldehydes are also planar, whereas those derived from ketones formulated Ni(HL)2(OAc)2 are octahedral.

N.m.r. characterisation of linkage isomers

SummaryHalogenation of LnIII, CeIV and ZrOII β-diketone/β-ketoester derivatives and their mixed ligand complexes of the types Ln(AA)2(Sal) and Ln(AA)(Sal)2 by NCS, NBS and PyHBr3 yield different isomeric products depending on the nature of the solvent medium, the reagent and the reaction time. The halogenation, if carried out in glacial acetic acid, irrespective of the reagent, yields the stable S-hall, product wherein the three chelate rings remain imperturbed in respect of metal coordination. When the reaction is carried out in 5% v/v DMF-CHCl3 employingN-halosuccinimide and maintaining correct reaction times, it is possible to isolate individually three other isomeric products. The isomers prepared are Ln(OO)3, Ln(OO)2(OX), Ln(OO)(OX)2 and Ln(OX)3 where (OO) represents diketone oxygen linkage and (OX) represents diketone oxygen and substituted halogen linkage to the central metal ion. The four linkage isomers have been identified by a comparison of the number of observed3H n.m.r. or13C n.m.r. signals with those expected for a given isomer on the basis of symmetry considerations in the tris-chelated octahedral structures.