Ligand trans-effect in octahedral complexes of 3d metals and its manifestation in the synthesis of metalloporphyrins in solution

We study features of the indicator kinetic reaction of meso(tetraphenyl)tetrabenzoporhine with cobalt(II), nickel(II), and manganese(II) acetates in electron-donating organic solvents (N,N-dimethylformamide (DMF), dimethyl sulfoxide (DMSO), and pyridine (Py)) and in their binary mixtures at temperatures in the range 348–368 K. Specific features of the trans-effect of solvent molecules on the rate and activation parameters of formation of manganese(II), cobalt(II), nickel(II), and copper(II) complexes with porphyrin are noted.     

Reactivity of 3d-metal salt solvates in reactions with porphyrins: Influence of the trans effect

The reactivity of 3d-metal salt solvates [MX₂(S)₄] and [MX₂(S₁) _m (S₂)_4?m ] has been studied in reactions with different porphyrins: meso-tetraphenylporphine (H₂TPP), N-methyloctaethylporphine (H(N-Me)(β-Et)₈P), and meso-tetraphenyltetrabenzoporphine (H₂TBP(ms-Ph)₄). Solvents S, S₁, and S₂ are dimethyl sulfoxide (DMSO), dimethylformamide (DMF), and pyridine (Py), respectively. The strong catalytic effect of the solvents and ligands with π orbitals on the reaction rates due to the trans influence in the coordination sphere of the salt solvates has been observed and explained. A possible activation mechanism of the trans influence was considered. A strong dependence of the trans effect on the nature of the metal and porphyrin was shown.     

Effects of the ligand structure and electronic properties of the central atom on the kinetics of complex formation of N-methyloctaethylporphyrine with solvate complexes in binary solvents

The reactivity of 3d-metal solvates [MX₂(S)₄] and [MX₂(S₁)_m(S₂)_4?m ] (where S, S₁, and S₂ are solvent molecules: pyridine, N,N-dimethylformamide, and dimethyl sulfoxide) toward porphyrins with different structures, N-methyloctaethylporphyrin and meso-tetraphenyltetrabenzoporphyrin, is discussed. A strong catalytic effect of solvents and ligands having π orbitals was found and rationalized in terms of trans effect in the coordination sphere of solvate salts. A probable activation mechanism of the trans effect was proposed, and its magnitude was shown to strongly depend on the metal nature.     

Palladium(II) octaalkylporphyrinates: Synthesis and spectral properties

Palladium 3,7,13,17-tetramethyl-2,8,12,18-tetrabutylporphyrinate (I) and its 5,15-diaza (II), diphenyl (III), and di(4-bromophenyl) (IV) derivatives were synthesized by the complex formation reaction of palladium(II) chloride with corresponding tetrapyrrole ligands in dimethylformamide, and their spectral properties were studied.     

Synthesis and design of tetrapyrrole molecular receptors for alkali metal cations

meso-Phenylporphyrins containing at the benzene ring a conformationally labile polyether fragment with a terminal pyridine ring were synthesized, and their spectral and physicochemical properties were studied. The relations found between the spectral parameters of the tetrapyrrole chromophore, on the one hand, and acid-base equilibria and complex formation with alkali metal cations, on the other, showed the possibility for design of porphyrin-based molecular ensembles possessing useful properties.     

Trans-Effect in Kinetics of Reactions of Mixed Solvates of Cu(II) Acetate with Tetraphenyltetrabenzoporphine in Organic Solvents

The kinetics of complex formation of tetraphenyltetrabenzoporphine with Cu(II) and Zn(II) acetates is studied in individual and mixed coordinating solvents on the basis of DMSO, DMF, and Py. The substantial increase in CuAc₂ reactivity in mixed solvents is explained by the trans-effect of ligands in composition of the metal solvate sphere.     

Complexation of Tetraphenyltetrabenzoporphine with Cu(II), Cd(II), Zn(II), and Co(II) Salts in Organic Solvents

The rate and activation parameters of tetraphenyltetrabenzoporphine (H₂TPTBP) complexation with 3d-metal acetates and acetylacetonates are shown to be determined by the solvent nature. With an increase in the electron-donor properties of a solvent, the reaction rate increases due to protonation of N–H bonds and decreases as MA _m (Solv) _{n – m} salt solvates become more stable. As the result, the rate of a reaction with ZnAc₂ increases in the series: DMF < dmso=">< py=">< proh-1="><>₃CN <>₆H₆. In inert and weakly coordinating solvents, the transition state of a reaction is supposed to be formed according to the mechanism of contraction of the salt coordination sphere. The rate of H₂TPTBP reaction with metal acetates in pyridine changes in the series: Cu(II) > Cd(II) > Zn(II) > Co(II), while the stability of the obtained complexes decreases in the series Cu(II) > Co(II) > Zn(II) > Cd(II). It is shown that the spectral criterion of the complex stability can be used in the series of metal complexes with one ligand, but it is violated if the ligand structure is changed.     

Trans-effect in the kinetics of reactions of mixed Cu(II) acetate solvates with N-methyloctaethylporphine

The kinetics of complex formation reaction of N-substituted octaethylporphine (H(N-Me)(β-Et)₈P] with copper(II) acetate in individual and mixed solvents based on DMSO, DMF, and Py is studied by spectrophotometry. An increase in the complex formation rate of this porphyrin with CuAc₂ in mixed solvents is explained in terms of the trans-effect of the ligands in the solvate sphere of the salt.     

Complex Formation and Spectral Properties of meso-Phenyltetrabenzoporphyrins in Pyridine and N,N-Dimethylformamide

Contributions of structural (macroring distortion) and polarization (in asymmetrically substituted derivatives) effects into the reactivity and chromophoric properties of substituted porphyrins were revealed on the basis of the kinetics of complex formation of nona-, deca-, undeca-, and dodecasubstituted porphyrins (meso-phenyltetrabenzoporphyrins) with Zn(OAc)₂ in pyridine and the electronic absorption spectra of the ligands and their complexes with Zn(II) and Cu(II) in pyridine and N,N-dimethylformamide (DMF). Dodecaphenyl substitution produces a weaker ring distortion in the more aromatic tetrabenzoporphyrin compared with porphyrins themselves. Irrespective of the degree of macroring nonplanarity, the Zn (II) and Cu complexes of tetrabenzoporphyrins with increasing degree of meso-phenyl substitution meet a spectral stability criterion.     

Synthesis of 2,8,12,18-tetrabutyl-3,7,13,17-tetramethyl-5-{3-[11-(pyridin-4-yloxy)-3,6,9-trioxaundecyloxy]phenyl}-porphyrin and study on the effect of its molecular conformation on physicochemical properties

2,8,12,18-Tetrabutyl-3,7,13,17-tetramethyl-5-{3-[11-(pyridin-4-yloxy)-3,6,9-trioxaundecyloxy] phenyl}porphyrin was synthesized, and its complexation with zinc and potassium cations in the system toluene-methanol (5:1) was studied by spectrophotometric titration and ¹H NMR spectroscopy. Spatial preorganization of the meso-aryl substituent due to complex formation of potassium cation with the polyether fragment accelerates the reaction of zinc with the title compound approximately threefold. A probable scheme of the interaction was proposed, and formation constants of the corresponding complexes were determined.