Arnaldo Cinquantini

The redox behaviour of ferrocene derivatives: VI. Benzylferrocenes. The crystal structure of decabenzylferrocenium tetrafluoroborate☆

The electrochemical behaviour of the benzyl-substituted ferrocenes [(η5-C5Bz5)2Fe] and [(η5-C5Bz5)Fe(η5- C5H5)] in non-aqueous solutions has been examined. As expected, they undergo reversible one-electron removal more easily than ferrocene itself, but with significantly more difficulty than [(η5-C5R5)2Fe] (R = Me or Et). In dichloromethane solution, the formal electrode potentials (vs. SCE) are as follows: E°′([(C5Bz5)2Fe]+/0) = +0.38 V, E°′([(C5Me5)2Fe] +/0) = −0.10 V, E°′([(C5Et5)2Fe]+/0) = −0.06 V, E°′([(C5H5)2Fe]+/0) = +0.45 V. The electrochemical properties suggest that the [(C5Bz5)2Fe]+/0 redox change should be accompanied by minor, but detectable geometrical strains. In order to define more quantitatively the geometrical reorganization accompanying such electron removal processes, the X-ray structure of [(C5Bz5)2Fe][BF4] has been determined. Comparison with the previously determined structure of neutral [(C5Bz5)2Fe] shows an elongation of about 0.05 A of the FeC(cyclopentadienyl) distances, which is a common feature of all ferrocene/ferrocenium couples, but this is also accompanied by reorganization of the peripheral benzyl substituents. In the neutral precursor, the methylene fragments are tilted away from the plane of the cyclopentadienyl rings towards the iron atom, whereas in the monocation they become coplanar.

Electrochemical behaviour of acyclic and macrocyclic complexes of nickel(II), copper(II) and uranyl(VI)

Abstract The electrochemical behaviour of a series of mono-nuclear, homo- and hetero-dinuclear complexes of dioxouranium(VI), nickel(II) and copper(II) ions with acyclic and cyclic compartmental ligands, derived from the condensation of 2,6-diformyl-4-chlorophenol and polyamines of the type NH 2 (CH 2 ) 2 X(CH 2 ) 2 NH 2 (XNH, S), is reported. The kinetic and thermodynamic aspects governing the electrode mechanism are also discussed with respect to the different ligand designs and their differences in the donor atom sets.

Electrochemical behaviour of a series ofN,N′-1,2-Phenylenebis(salicylideneimin)ato transition metal complexes

SummaryThe electrochemistry of a series of nickel(II), copper(II), cobalt(II), manganese(II) and oxovanadium(IV) complexes with theN,N′-1,2-phenylenebis(salicylideneimin)ate ligand has been studied in dimethyl sulfoxide solution. Kinetic and thermodynamic aspects of the electron-transfer processes are discussed, also with respect to those of the correspondingN,N′-ethylenebis(salicylideneimin)ate and bis(salicylideneiminate-3-propyl)amine derivatives

The redox behaviour of the cluster anion [Fe4N(CO)12]−. Electron transfer chain catalytic substitution reactions. Crystal structure of [Fe4N(CO)11PPh3)]−

Abstract The electrochemical investigation of the redox properties of the monoanion [Fe4N(CO)12]− points out its ability to undergo sequentially two one-electron reductions. The first step leads to the quite stable dianion [Fe4N(CO)12]:2−; the EPR results indicate that in frozen solution an equilibrium exists between two different molecular geometries of such a dianion. The second electron addition produces the relatively short-lived trianion [Fe4N(CO)12]3−. In the presence of monodentate phosphines, the redox change [Fe4N(CO)12]−/2− triggers the electrocatalytic substitution of one CO group to afford the substituted monoanions [Fe4N(CO)11(PR3)]−. As a matter of fact, sub-stoichiometric amounts of Ph2CO − produce [Fe4N(CO)11(PPh3)]−, the crystal structure of which has been solved. Crystal data for [N(PPh3)2][Fe4N(CO)11(PPh3)]: triclinic, space group P 1 (No. 2), a=11.009(6), b=17.285(4), c=17.380(2) A, α=103.11(3), β=91.18(2), γ=105.26(3)°, Z=2, Dc=1.444 g cm−3, Mo Kα radiation (λ=0.71073 A), μ(Mo Kα)=10.5 cm−1, R=0.048 (Rw=0.054) for 5010 independent reflections having I > 3σ(I). Preliminary evidence is given that in the presence of bidentate phosphines one CO ligand substitution occurs at room temperature, whereas two CO groups are replaced at higher temperatures.

Electrochemical behaviour of a series of iron(II), nickel(II) and copper(II) complexes with linear pentadentate schiff-base ligands

Abstract The electrochemical behaviour of iron(II), nickel(II) and copper(II) complexes with a number of derivatives of the pentadentate ligand bis(salicylideneimine-3-propyl)amine (X-SALRDPT) has been investigated in non-aqueous solvent. The one-electron anodic oxidation of all the metal(II) complexes has been characterized and correlated, as well as the frequency shifts of their d–d transitions, to the inductive effect of the various substituents on the salicylic moieties. Crystal field stabilization energies involved in the redox change are discussed. The cathodic charge transfer II/I and I/0 for nickel(II) and copper(II) chelates have been also investigated. On the basis of electrochemical measurements, some considerations on the reactivity of the complexes towards dioxygen are made.

Electrochemical behaivour of uranyl(VI) ion in different non-aqueous solvents

Abstract The electrochemical reduction of uranyl(VI) ion at platinum and/or mercury microelectrodes has been studied in different non-aqueous media by voltammetric techniques (cyclic voltammetry, de voltammetry at elactrodes with periodical renewal of diffusion layer, chronoamperometry, controlled-potential coulometry). Reproducible voltammetric responses have been obtained in dimethyl sulfoxide, N,N -dimethylformamide, acetic anhydride, pyridine, morpholine and ethylenediamine solvents. The mechanistic aspects involved have been studied. the solvation process of uranyl(VI) ion in the various solvents has been discussed in terms of dependence of the redox potential for the U(VI)/U(V) couple on the electron—pair donor properties of the solvents.

Voltammetric behaviour of uranyl-diethyldithiocarbamate complexes in aprotic medium

Abstract The polarographic investigation of the reaction between uranyl and diethyldithiocarbamate ions in DMSO evidentiates two prevailing complex species: UO 2 (DEDTC) + and UO 2 (DEDTC) − 3 . The two species exhibit one reversible cathodic wave (E 1 2 = −0.662V and −1.170V, respectively) both involving the reaction of the uranyl complex to uranium(V) complex. The formation of one reversible well-shaped anodic wave in the presence of diethyldithiocarbamate ion, due to the formation of mercury(II) complexes, has been already reported; in the present case, however, also the UO 2 (DEDTC) − 3 species gives an anodic wave associated with the following electrode process: Cyclic voltammetric tests suggest that the mentioned cathodic processes are to be considered quasi-reversible, while the anodic one, involving the ligand exchange between UO 2+ 2 and Hg 2+ , is not reversible. The stability constants of UO 2+ 2 and Hg 2+ , diethyldithiocarbamate complexes are also estimated.

Polarographic Investigations on Uranyl(VI) Complexes in Dimethylsulfoxide. 1. Monocarboxylic Ligands.

Abstract The formation of acetate, glycolate, chloroacetate and β-chloropropionate complexes of uranium(VI) in dimethylsulfoxide has been investigated by the polarographic method. 0.1 M tetrabutylammonium perchlorate was used as supporting electrolyte. The 3:1 acetate and the 1:1 glycolate complexes give distinct cathodic waves; the polarographic behaviour allows to evidentiate also the 1:1 and 2:1 acetate, the 1:1 chloroacetate and β-chloropropionate complex formation. The formed complexes are stronger in DMSO than in water and the more so the harder the ligand. The (a)-character of uranyl ion is more marked in DMSO than in aqueous media.

Complexes of magnesium(II) and other divalent metal ions with adenosine 5′-triphosphate and 2,2′-dipyridylamine in aqueous solution

Abstract Binary and ternary systems involving adenosine 5′-triphosphate (ATP), 2,2′-dipyridylamine (DPA) and magnesium, calcium, strontium, manganese, cobalt, copper, and zinc(II) metal ions have been investigated in aqueous media by potentiometric titrations. The analysis of the titration curves shows the existence of M(ATP)2−, M(ATP)(H)−, and M(ATP)2(H)24− species for alkaline-earth metal ions, while no ternary complex can be detected. For transition metal ions both binary and ternary species are found. Binary M(ATP)2(H)24− complexes are present in solutions containing manganese and cobalt(II) metal ions but these species cannot be revealed in the case of copper and zinc(II). Ternary complexes as M(ATP)(DPA)2− and M(ATP)(DPA)(H)− are common to all transition metals. Binuclear and hydroxo complexes as M2(ATP)(OH)− and M(ATP)(OH)3− are found only for copper and zinc(II). A hypothesis on the possible role of the species M-ATP in 1:2 ratio in the dephosphorylation mechanism is advanced on the basis of a comparison between the equilibrium data in the solution phase and the solid state structures of the magnesium, calcium, and manganese(II)- ATP-DPA systems.

3,3-Diethyl-and 3,3-dibenzyl-1,2-diferrocenylcyclopropenes.

Reactions of 2,3-diferrocenylcyclopropenone 1 with ethyl- and benzylmagnesium chlorides afford 3,3-diethyl-and 3,3-dibenzyl- 1,2-diferrocenylcyclopropenes 2 and 3, respectively, and products of nucleophilic opening of the three-membered ring resulting from the addition of RMgCl to the carbonyl group, viz., saturated ketones(4,5-diferrocenylheptan-3-ones 4a,b and 3,4-diferrocenyl-1,5-diphenylpentan-2-ones 5a,b as ca. 3: 1 mixtures of two diastereomers) and other products. The spatial structures of compounds 2 and 4a were established by X-ray diffraction analysis of single crystals. Protonation of the cyclopropenes 2 and 3 with tetrafluoroboric acid at -40 degrees C yields the corresponding 3,3-dialkyl-1 ,2-diferrocenylcyclopropylium tetrafluoroborates. Transformation of the latter into diferrocenylallylic cations upon increasing the temperature to 20 degrees C and their eprotonation under the action of N,N-dimethylaniline were studied. Electrochemical investigation of 1 and 2 shows that in both complexes the cyclopropene spacer allows electronic communication between the two outer ferrocenyl groups, this being notably greater for 2 than for 1.