L. E. Nivorozhkin

Structural variations in nickel(II) and copper(II) MN4 Schiff-base complexes with deprotonated tetradentate N,N′-bis(5-aminopyrazol-4-ylmethylene)polymethylenediamine ligands

Two series of copper(II) and nickel(II) complexes [ML1]–[ML6] containing deprotonated tetradentate N,N′-bis(5-aminopyrazol-4-ylmethylene)polymethylene diamine ligands L1–L6 with varying n(2–4) of the bride –HCN(CH2)nNCH– have been prepared and investigated by 1H NMR, UV/VIS and ESR spectroscopy and cyclic voltammetry measurements. Complexes [CuL4]–[CuL6] display a gradual alteration of the configuration at the metal centre from planar to pseudo-tetrahedral when going from n= 2 to 4 as indicated by the variations in their ESR spectral parameters. This was also reflected in the electronic spectra which exhibited a red shift of the ligand-field bands in this series. The nickel(II) complexes with n= 2 or 3 possess a planar structure both in solution and in the solid state, whereas in the case of [ML6](n= 4), diamagnetic in the solid state, a rapid (on the NMR time-scale) equilibrium between planar low-spin (S= 0) and tetrahedral high-spin (S= 1) forms was found in chloroform solution with 45% of the high-spin species at 331 K. At low temperatures the planar ⇄ tetrahedral interconversion is not accompanied by R⇄S enantiomerization at the metal centre due to the higher barriers to inversion of the seven-membered metallocycle which was followed at elevated temperatures by coalescence of the diasterotopic NCH2 and CCH2 protons. The crystal structure of [NiL6][H2L6=N,N′-bis(5-amino-1,3-diphenylpyrazol-4-ylmethylene)butane-1,4-diamine] revealed a planar-to-tetrahedral distorted metal configuration with an angle between the N(1)NiN(2) and N(5)NiN(8) planes of 21° and twist-chair conformation of the seven-membered metallocycle. Cyclic voltammetry showed a reversible NiII→ NiIII oxidation at potentials 0.47–0.51 V and irreversible CuII→ CuI transformations.

Bis[4-(2,6-dimethylphenyliminomethyl)-5-pyrazolethiolato]nickel(II) complexes with an unusual trans-planar structure

Abstract The nickel(II) complexes bis[1-phenyl-3-methyl-4-(2,6-dimethylphenyl)iminomethyl-5-pyrazolethiolato]nickel(II) (1) and bis[1,3-diphenyl-4-(2,6-dimethylphenyl)iminomethyl-5-pyrazolethiolato]nickel(II) (2), based on the 4-imino-methyl-5-thiopyrazole ligands containing a 2,6-xylyl substituent at the coordinating imino nitrogen atom, have been prepared and their structures investigated. Complex 1 is tetrahedral and high-spin in solution as indicated by its temperature-independent μeff value of 2.75 BM whereas 2 displays magnetic behaviour and 1H NMR spectra consistent with a fast planar (LS)-tetrahedral (HS) equilibrium (ΔH° = 11.8 kJ mol−1, ΔS° = 34.6 J mol−1 K−1). 1 and 2 are low-spin in the solid state. An X-ray diffraction study of 1 revealed a trans-square-planar coordination geometry which is unusual for bis-chelate N2S2 metal complexes, in comparison to cis-planar geometry.

Synthesis and structure of tetracoordinated nickel(II) complexes of deprotonated chelated aminoazo ligands: X-ray crystal structure of bis[1-isopropyl-3-methyl-4-(4-methylphenylazo)-5-(4-methoxyphenylamidato) pyrazole] nickel(II)

SummaryTetracoordinate nickel(II) complexes NiL2 derived from the deprotonated forms of aminoazoligands HL were prepared and investigated by spectroscopy and magnetic susceptibility measurements. The magnetic moments, which lie in the 3.1–3.6 B.M. range correspond to the occurrence both in solution and in the solid state of the high spin (S = 1) form and a tetrahedral configuration at the metal centre. The u.v. spectra exhibit three ligand field bands at 1020–1280 nm characteristic of high spin nickel(II) complexes. The large isotropic chemical shifts found in the 1H n.m.r. spectra are consistent with partial delocalization of unpaired electron spin density to the ligand HOMO. The X-ray single crystal structure of NiL24[L4= 1-isopropyl-3-methyl-4-(4-methylphenylazo)-5-(4-methoxyphenylamino)-pyrazole] reveals that the metal is coordinated by four nitrogen atoms in tetrahedral configuration with an angle of 90° between the N(1)NiN(2) and N(6)NiN(7) planes belonging to the different almost planar metallocycles. The rates of R⇄S interconversion of the tetrahedral configuration for NiL24and NiL25[L5 = 1-isopropyl-3-methyl-4-phenylazo-d5-5-(4-methoxyphenylamino)pyrazole] are slow on the n.m.r. timescale. In contrast to NiL21-Ni26, NiL27], which contains coordinated NH-groups instead of NAr-groups, is planar.

Photo- and thermochromic spirans

New spiropyrans with π-acceptor azomethine and ketovinyl substituents in the 8′ position were synthesized using the functional possibilities of the carbonyl group. The structures of the compounds obtained and their photochromic properties in 2-propanol at −70°C were studied.

Photochromic and thermochromic spirans

The preparation of 1,3-dithiolanium salts from 1,2-ethanedithiol and carboxylic acid chlorides, the subsequent condensation of which with aromatic o-hydroxy aldehydes leads to spiropyrans of the dithiolane series, is described. The PMR spectra were studied, and the photochromic properties are discussed.

Photochromic and thermochromic spiranes. 19. 2-thioxo-3-phenyl-5,5-diivietiiylspiro (1,3-oxazolidine-4,2′-[2h]chromenes)

We have synthesized and characterized by IR, UY,1H, and13C NMR spectroscopy new spiropyrans based on 2-thioxo-3 phenyl-5,5-dimethyl-1,3-oxazolidine. We have studied their photochromic properties in 2 propanol at -80°C. In the electronic spectra of photo-induced farms, we have detected two long-wavelength absorption bands in the 370–438 and 480–677 nm region.

Energy barriers for the enantiotopomerization of tetrahedral boron chelates

The enantiotopomerization of diarylboron salicylideneaminato-chelates proceeding via a transition state with planar tetraco-ordinate boron is associated with thermally accessible energy barriers which have been determined by use of dynamic n.m.r. spectroscopy.

Formyl and formylvinyl derivatives of 2-methylenebenzo-1,3-dithiole

Abstract2,5-Dimethyl- and 2-ethyl-5-methyl-1,3-benzodithiolium perchlorates react with dimethylformamide and N-phenyl-N-methylaminoacrolein to give monoiminium salts, the hydrolysis of which yields the corresponding aldehydes. The trans-transoid structure ofβ-formylvinyl-substituted 2-methylenebenzo-1,3-dithioles was established by a comparison of the experimental and calculated dipole moments, absorption maxima, and intensities of the electron transitions and also by analysis of the PMR spectra.

Synthesis of new spiropyrans from 2,5-dimethyl-1,3-benzodithiolium salts

New spiropyrans that have thermochromic properties were obtained by the condensation of 2,5-diniethyl-1,3-benzodlthiolium perchlorate with o-hydroxy aromatic aldehydes and subsequent treatment of the resulting 2-styryl derivatives with ammonia in ether.

Formylation and vinylformylation of 2,3-cycloalkenobenzopyrylium salts

Heating of 2,3-cycloalkenobenzopyrylium salts in acetic anhydride with excess formylating agent (dimethylformamide, formanilide, N-formylmorpholine, and N-phenyl-N-methyl-aminoacrolein) gives monoiminium salts, the hydrolysis of which yields aldehydes or, in the presence of hydrosulfide, thioaldehydes. On treatment with the Vilsmeier complex, 1-methylquinaldinium salts give diiminium salts, which are hydrolyzed to the corresponding aldehydes.