A sterically hindered N,N,O tripod ligand and its zinc complex chemistry

The new ligand bis(2-picolyl)(2-hydroxy-3,5-di-tert-butylbenzyl)amine (HL) was prepared from bis(2-picolyl)amine and 2,4-di-tert-butyl-6-(chloromethyl)phenol. It acts as a tetradentate N,N,O tripod ligand ensuring 5-fold coordination in all its zinc complexes L.Zn-X. The central complex of the series was [L.Zn(OH(2))]ClO(4) (1) obtained from zinc perchlorate. Together with the more labile complex L.Zn-C(2)H(5) (2), obtained from diethyl zinc, it was used as a starting material for ligand substitutions. In the presence of bases, 1 was converted to L.Zn-OH (3), [L.Zn(py)]ClO(4) (4), and [(L.Zn)(3)(mu(3)-CO(3))]ClO(4) (5). Metathetical reactions produced the neutral complexes L.Zn-X with X = Br (6), OAc (7), OC(6)H(5) (8), SC(6)H(5) (9), OP(O)(OPh)(2) (10), p-nitrophenolate (11), 1-methyluracilate (12), o-formylphenolate (13), and o-hydroxymethylphenolate (14). Structure determinations of 1, 5, 7, 10, 11, 13, and 14 confirmed the strictly monodentate attachment of all units X in L.Zn-X. The hydrolytic cleavage of tris(p-nitrophenyl) phosphate by 1 was investigated preparatively and kinetically. L.Zn-OH was found to be the hydrolytically active nucleophile. The second-order rate constant for the cleavage reaction was found to be slightly lower than the values for related systems, reflecting the steric hindrance in the tert-butyl-substituted ligand L.     

D 3h Al3N: a novel promising ligand for coordination chemistry

Several prior experimental and theoretical studies have been reported on Al₃N and have shown that the D _3h isomer is the global minimum. In this work, we attempt to theoretically design new molecular materials containing the D _3h Al₃N as unit. A novel series of metal complexes with the Al₃N ligand, including [(Al₃N)K(Al₃N)]⁺ (traditional homo-decked sandwich), [(Al₃N)ZnZn(Al₃N)]²⁺ (binuclear metallocene), and [(Al₃N)Zn(C₅H₅)]⁺ (hetero-decked sandwich), are predicted to be local minima on their corresponding potential hyper surfaces at the B3LYP, B3PW91, and BP86 levels of theory with the 6?C311+G(d) basis set. Natural bond orbital and AOMix analyses indicate that the interaction between the metal ions and the Al₃N ligands is mostly electrostatic. This fact suggests that the Al₃N is a promising ligand for coordination chemistry.     

D.I. Mendeleev and physical chemistry: Hundred years after

Among many problems with which D.I. Mendeleev dealt as a physical chemist, the solution concept, the equation of state, and the critical state of matter are chosen for discussion. The author com]municates his thoughts on the state-of-the-art of these fields of knowledge.     

Zinc complex chemistry of N,N,O ligands providing a hydrophobic cavity

Three new highly substituted bis(2-picolyl)(2-hydroxybenzyl)amine ligands were synthesized, and their biomimetic zinc complex chemistry was explored. They have tert-butyl substituents at the 3-and 5-positions of their phenyl rings, and they bear one phenyl group (HL2), two methyl groups (HL3), or two phenyl groups (HL4) at the 6-positions of their pyridyl rings. Their reactions with hydrated zinc perchlorate yield three distinctively different complex types. L2 forms a trigonal-bipyramidal aqua complex, and L3, a square-pyramidal aqua complex. The substituents on L4 leave no room for a water ligand, and the resulting zinc complex is trigonal-monopyramidal with a vacant coordination site. The water ligands on the L2Zn and L3Zn units can be replaced by anionic halide, thiocyanate, p-nitrophenolate, benzoate, and organophosphate as well as uncharged pyridine ligands. The L4Zn unit forms labile halide, p-nitrophenolate, and pyridine complexes. Triethylamine converts the aqua complexes to the labile hydroxides L2Zn-OH and L3Zn-OH, and in polar media [L3Zn-OH2]+ seems to be in equilibrium with L3Zn-OH. The hydroxides, but not the water complexes, effect the hydrolytic cleavage of tris(p-nitrophenyl) phosphate to bis(p-nitrophenyl) phosphate. The kinetic investigation of the cleavage reactions has shown them to be second-order reactions, thereby supporting the proposed four-center mechanism.     

Nitroxide chemistry XXII. Oxidation of N,N-bis(trifluoromethyl)hydroxylamine

A number of cheap oxidising agents have been found to be effective for the conversion of N,N-bis(trifluoromethyl)hydroxylamine into bis(trifluoromethyl)nitroxide. The best of these are cerium(IV) salts either in the solid state or in aqueous acid solution. Efficient, self-indicating processes have been developed using either catalytic amounts of silver(II) picolinate and aqueous potassium persulphate solutions, or electrochemical oxidation with cerium(III) nitrate and sodium nitrate in dilute nitric acid.     

The solid state chemistry of uranium: Part IV. The thermal decomposition and kinetics of tetrachlorobis(N,N, N1, N1-tetramethylurea) uranium(IV)

The thermal decomposition of UCl₄2tmu in an oxygen atmosphere was studied. Decomposition of single crystals begins around 180° C and approximates to UCl₄2tmu_(s) + O_2(g) → UO₂Cl₂tmu_(s) + tmu_(g) + gases and is exothermic (ΔH = −270 ± 5 kJ mol⁻¹). The apparent activation energy for the initial stages (nucleation process) of the reaction was estimated as 362 kJ mol⁻¹. The growth period is described by a one-dimensional diffusion process and the decay period by the contracting-area model.     

Electroanalytical chemistry: Research Developments,Jiang, P.N., Ed., New York: Nova Science Publishers, 2007, 313 p.

Russian Journal of Electrochemistry -