Paramagnetic Cobalt Complexes Research Articles

Highly linear polyethylenes tailored with 2,6-bis[1-(p-dibenzo-cycloheptylarylimino)ethyl]pyridylcobalt dichlorides.

A novel family of 2,6-bis[1-(p-dibenzocycloheptylarylimino)ethyl]pyridylcobalt dichlorides Co1-Co4 were synthesized and fully characterized by FT-IR, 1H NMR, and elemental analysis as well as X-ray diffraction analysis. The 1H NMR spectra of these paramagnetic cobalt complexes Co1-Co3 showed similar spectra with one set of signals, while Co4 possessed two sets of signals due to the different conformations caused by different substituents on the ortho-position of the N-aryl group. Crystal structures of Co1, Co2 and Co4 revealed similar square-pyrimidal geometry around the cobalt ion, in which two dibenzocycloheptyl groups adapted as cis-conformers, whereas Co3 possessed bistrigonal geometry and the two dibenzocycloheptyl groups were adapted as trans-conformers. On activation with methylaluminoxane (MAO) or modified MAO (MMAO), all these cobalt complexes displayed high catalytic activities towards ethylene polymerization (up to 1.21 × 107 g (PE) mol-1 (Co) h-1) and produced polyethylenes with narrow molecular distributions (PDI ≈ 2.0). Co3 bearing bulkier isopropyl substituents on the ortho-position gave much higher molecular weight of resultant polyethylene than the other cobalt complexes reported herein. The microstructure analysis of the PEs demonstrated that they are highly linear and contain a vinyl end group as the major group and saturated methyl as the minor group, in which the content of the unsaturated polymer chain relied on the ortho-substituent of the N-aryl group.

Radio-frequency superradiance induced by the rheological explosion of polymer composites containing paramagnetic cobalt complexes

Superradiance induced by the rheological explosion of composites based on polystyrene, cobalt acetylacetonate, and/or 3,5-di-tert-butylcatechol has been investigated. The superradiance intensity is determined by solid-phase chemical reactions induced by the rheological explosion. EPR, X-ray diffraction, and electron microscopic characterization of stable products resulting from the rheological explosion in the polymer matrix has demonstrated that the superradiance intensity is related to the electronic properties and structure of two-spin intermediates, namely, radical pairs and organoelement biradicals.

Peculiarities of molecular structure of 1-vinylimidazole: High resolution NMR study

The peculiarities of molecular structure of 1-vinylimidazoles were studied using 1Н and 13С NMR spectra of its complexes. Mechanisms of delocalization of unpaired electron spin density in the complex CoCl2⋅4(1-vinylimidazole) were revealed. Characteristic features of 1-vinylimidazole coordination with (C2H5)3SnCl were established. Unlike paramagnetic cobalt complex, the structure of VIM diamagnetic complex with triethylhalogenstananne R represents a trigonal bipyramid. The Sn atom in this complex has sp3d-hybridization and three alkyl moieties trend towards coplanarity interacting with sp2-orbitals of tin. The long-range spin–spin interaction between protons of 1-vinylimidazole and the vinyl group coupled with the pyrrole nitrogen N1, typical for coplanar arrangement the imidazole cycle and vinyl moiety was found.

Molecular and Electronic Structures of Homoleptic Nickel and Cobalt Complexes with Non‐Innocent Bulky Diimine Ligands Derived from Fluorinated 1,4‐Diaza‐1,3‐butadiene (DAD) and Bis(arylimino)acenaphthene (BIAN)

AbstractThe diimine complexes with bulky fluorinatedN‐substituents [NiII(FDAD)2]1and [CoII(FDAD)2]2[FDAD =N,N′‐bis(pentafluorophenyl)‐2,3‐dimethyl‐1,4‐diaza‐1,3‐butadiene]as well as diimine complexes with extended π system [NiII(FBIAN)2]3and [CoI(FBIAN)3]4(FBIAN = bis[N‐{3,5‐bis(trifluoromethyl)phenyl}imino]acenaphthene) were synthesized. Compound4represents the first complex with three bis(imino)acenaphthene ligands synthesized so far. The molecular structures of the complexes1–4were determined by X‐ray crystallography at 193 K. Complexes1,2and3comprise the divalent metal ions with pairs of radical monoanionic ligands, whereas4is best described as a cobalt(I) complex with two neutral (FBIAN)0and one (FBIAN)1–ligand in the radical monoanionic form. The electronic structures of the paramagnetic cobalt complexes2and4were investigated by SQUID measurements and X‐band EPR spectroscopy. Both complexes possess a doublet ground state, with electron density located mostly in the metal d‐orbitals. The doublet–quartet energy gap for4was established to be 159 cm–1. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006)

One-Electron Transformations of Paramagnetic Cobalt Complexes. Synthesis and Structure of Cobalt(II) Amidodiphosphine Halide and Alkyl Complexes and Their Reaction with Alkyl Halides

Complexes of the type CoX[N(SiMe2CH2PPh2)2], where X = Cl, Br, or I, can be prepared via reaction of CoX2 with LiN(SiMe2CH2PPh2)2; these derivatives are tetrahedral high-spin d7 systems. Reaction o...

ESR study of ?-allyl Co(II) complexes in Ziegler type catalytic systems

ESR study of the interaction between the components of the catalytic system Co(acac)2- PBu3-LiBu in the presence of butadiene revealed the formation of stable paramagnetic cobalt complexes containing a PBu3 ligand and butadiene molecules. Complexes (η3-R)2CoPBu3 (where R is allyl, crotyl, benzyl) have been synthesized by ordinary methodsin situ, in order to identify the structures of the complexes. ESR parameters and geometry of the central core have been determined. The influence of the nature of phosphine ligands on the parameters of the ESR spectra has been studied. The general regularities in the ESR spectra of (η3-R)2CoPBu3 and the complexes formed in the catalytic system have been revealed.

“[Cp*CoCoCp*]” is a Hydride

The supposed synthesis of the cobalt complex [Cp*CoCoCp*] was in the spotlight at the end of last year (Angew. Chem. Int. Ed. Engl. 1991, 30, 1124). But the compound described at that time is actually the mixed‐valent cobalt hydride 2. The reaction of the dinuclear complex 1 with LiAlH4 yields two paramagnetic cobalt complexes (2 and 3), which have been fully characterized by X‐ray crystallography and spectroscopic methods, as well as by protonation and carbonylation. See also the Corrigendum on p. 1392. equation image

NMR chemical shift method in magnetic susceptibility measurements applied to studies of the reaction of cobalt complexes with cumene hydroperoxide

AbstractThe NMR chemical shift method was applied for the determination of the magnetic susceptibility of paramagnetic transition metal complexes in solution. The method was found to be very useful for the determination of magnetic susceptibility changes during a chemical reaction in which one paramagnetic compound produced another. The concentrations of two paramagnetic cobalt complexes [Co3O(O2CCH3)6(HO2CCH3)3] and Co(O2CCH3)2, were calculated from the chemical shift value observed during their reaction with cumene hydroperoxide. The results are consistent with those obtained from electronic spectra.

The cleavage of the carbon--cobalt bond in vitamin B12 and coenzyme B12 by reduction with electrons in gamma-irradiated frozen solutions.

Abstract The one-electron reduction of vitamin B1 2 and its coenzyme has been studied by γ-irradiating the frozen methanolic solutions of these compounds. A new optical absorption spectrum was obtained by γ-irradiation of aqueous methanol solution of vitamin B1 2 at 77°K; this spectrum changed by slight warming to that of B1 2 r. ESR spectra were also recorded. The ESR signal at g ≈ 2.3 for the irradiated solution at 77°K was ascribed to the vitamin B1 2 anion, in which an unpaired electron is localized in the σ★ orbital of the cobalt-ligand bond. Upon slight warming the ESR signal changed to that of B1 2 r. In contrast to the vitamin, the ESR spectrum of irradiated coenzyme B1 2 solution in C2 H3 O2 H3 + 2H2 O at 77°K showed no signal due to a paramagnetic cobalt complex but an asymmetric signal of g ≈ 2.0, which is attributable to an organic radical presumably derived from the adenosyl group. The optical spectrum indicates the formation of B1 2 s (diamagnetic) by the CoC bond cleavage. Upon slight warming the optical and ESR spectra changed to those ascribed to B1 2 r. The present study thus revealed that the one-electron reduction of vitamin B1 2 and its coenzyme B1 2 gives rise to the heterolytic cleavage of the CoC bonds by the selective attack of electrons, and the former produces B1 2 r and the latter, B1 2 s.

Reactions of tris(triphenylphosphine)dinitrogencobalt hydride with ethyl vinyl ether, vinyl acetate and methyl acrylate and general remarks on its reaction with terminal olefins

Tris(triphenylphosphine)dinitrogencobalt hydride (I) reacts with vinyl ethyl ether and vinyl acetate to yield products of hydrogenation. A diamagnetic binuclear cobalt complex is formed in the reaction with vinyl acetate and a paramagnetic binuclear cobalt complex with vinyl ethyl ether. Methyl acrylate reacts with (I) to give methyl α- (d, l)-methylpropionylacetate, dimethyl α- d,l-methylglutarate, methyl adipate and dimethyl cyclobutane-1,2-dicarboxylate. In this reaction a paramagnetic cobalt complex is also formed and interaction of the unpaired electron with 1H is observed. The nature of the cobalt complexes in solution is discussed. Changes in the direction of reaction of (I) with substituted oleflns RCH=CH 2, when R is varied, are also discussed.

Electron spin resonance studies of the reaction product between hydridodinitrogentris(triphenylphosphine)cobalt(I) and olefins. I.

During the reaction of hybridodinitrogentris(triphenylphosphine)cobalt(I) with styrenes a paramagnetic cobalt complex is formed. The ESR spectrum of this complex is believed to contains 15 hf lines. On the grounds of the chemical reactivity of the compound and computer analysis of its ESR spectrum it is shown to be a binuclear cobalt complex. The influence of different Lewis bases, protic substances and cobalt oxidation reagents on ESR spectra is reported.

Structure of the Second Coordination Sphere of Transition Metal Complexes. II. Substituted Anilines as Ligands

The role of substituted anilines as second coordination sphere ligands of cobalt(II) complexes has been investigated. Chemical shifts of the ligand nuclear magnetic resonance (n.m.r.) spectra arising from pseudo-contact interaction with the paramagnetic cobalt complex have been utilized for this purpose. It has been found that in each case the aniline preferentially occupies a position perpendicular to the three fold symmetry axis of the complex and tends to be aligned with the amino group directed towards the cobalt atom. Electron withdrawing substituents para to the amino group enhance the second coordination sphere binding and electron donating substituents diminish it. These results are consistent with the idea that the structure of the second coordination sphere is determined by electrostatic interaction with the negatively charged ligands comprising the first coordination sphere. There is competition between aniline molecules and solvent molecules for a position in the second sphere with the solvent competing with increasing effectiveness in the series carbon tetrachloride, benzene, and methylene chloride.