Klaus H. Moock

Stabilization of high oxidation states in transition metals. An electrochemical and computational study of structurally comparable molybdenum and tungsten complexes

Molybdenum and tungsten chlorides, chloride oxides and chloride nitrides as well as thiazene and phosphazene metallacycles were studied by electrochemical methods in CH2Cl2. The different ligand systems have a profound influence on the redox potentials. The stabilization of high valency increases from the hexachloro to pentachlorooxo to chloronitrido complexes and the metallacycles. There is a systematic difference in the electrode potentials between molybdenum and tungsten redox couples. The geometries of the d1 and d0 species, optimized using density functional methods, are in good agreement with the available experimental data and trends in redox data are reproduced by the computed energy difference between the appropriate d1/d0 pair. The relative stability of the higher oxidation state is directly linked to the donor properties of the ligands present, and increases in the order: Cl6 < F6 < Cl5O < Cl4(N3S2) < Cl3(N3P2) < Cl4N.

A dimer of 4-(4-methoxyphenyl)-1,2,3,5-diselenadiazole

The analysis of the title compound, C 8 H 7 N 2 OSe 2 , shows that its crystals are composed of weakly linked dimers, with intramolecular Se-Se distances of 2.343(3) and 2.345(2)A, intermolecular Se...Se distances of 3.193(3) and 3.316(3)A, and lateral Se...Se interactions of 3.514(2) and 3.579(3)A.

Organometallic thiazenes. Oxidative addition of S4N4 to low-valent metals; electrochemistry and 15N NMR of CpCoS2N2 and Cp*CoS2N2

The reactions of S4N4 with CpM(CO)x and Cp★M(CO)x(M = Mn, Fe, Co, Ni and Rh) result in tractable products only when M = Co. The electrochemical behaviour of the previously known complexes CpCoS2N2 and Cp★CoS2N2 has been investigated by DC and AC cyclic voltammetry. Each has a single one-electron reduction process occurring at −0.65 V (Cp) and −0.99 V (Cp★), vs. SCE, in CH2Cl2 solution. For the Cp complex, chemical reduction using cobaltocene has also been achieved. 15N NMR spectra were recorded for 99% 15N enriched samples: 550 (broad singlet) and 431 (singlet) for Cp, 518 (broad singlet) and 404 ppm (singlet) for Cp★, referenced to liquid NH3. The electronic absorption spectra are also reported, and interpreted in the light of EHMO calculations.

3,7-Di-tert-butyl-1,5,2,4,6,8-dithiatetrazocine

The eight-membered ring in the title compound, C 10 H 18 N 4 S 2 , lies about an inversion centre and is essentially planar with normal bond lengths and angles [mean C-S 1.569 (2) and mean C-N 1.326(3)A].

Synthesis and characterization of new fluorosulfinate : NH4SO2F

Abstract Sulfur dioxide reacts with dry ammonium fluoride to give ammonium fluorosulfinate. The infrared and low temperature Raman spectra of the new salt are described.

Heterocycles from Silylated Amidines. Preparation of 1,3,2,4,6-Dithiatriazines; Preparation and E.S.R. Characterization of New 1,2,3,5-Dithia- and Diselenadiazolyl Radicals; the Conversion of Dithiadiazolyls to 1,5,2,4,6,8-Dithiatetrazocines by Reaction With O2

Abstract The synthesis of 3- and 4-substituted aryl dithiatriazines, {XC6H4CN3S 2}2, (X = 4-CH3,4-Cl, 3-CF3,4-CF3, 4-C3O, 4-C6H5); dithiadiazolyl radicals 4-X-C6H4CN2S2 (X = CH3, CH3O, Cl, NO2 and CF3) and their dimers in the solid state and four new diselenadiazolyl radicals 4-X-C6H4CN2Se2 (X = CH3, CH3O, Cl, and CF3) as well as CF3CN2Se2 and their dimers are reported. The crystal structure of the 4-Cl dithiatriazine dimer was determined. The sulphur radicals, either in bulk or in higher yield when produced in situ with Ph3Sb, react with O2 to give the corresponding 3- and 4-substituted 1,5,2,4,6,8-dithiatetrazocines, {X-C6H4CN2}2S2, X = 4-H, 4-CH3,4-CH3O,4-Cl, 3-CF3,4-CF3. Physical properties (mp, colour, IR andNMR data) of the derivatives withX = CH3 and 4-CF3 differ substantially from those in a previow report.

The Electrochemistry and Electronic Structure of High-Valent Molybdenum and Tungsten Metallacycles

Abstract The metallacycles , W have been studied in CH2Cl2 using cyclic voltammetry. The observed redox potentials indicate that the cyclic π-base ligand, [NPPh2NPPh2N]3−, is capable of stabilising high oxidation states in both molybdenum and tungsten complexes. Empirical MO calculations are presented which rationalize the electronic structure of the metallacycles.

Electrochemical Studies on C,N,S and C,N,Se Ring Systems—An Overview

Abstract Electrochemical studies of 5, 6, 7 and 8-membered rings containing catenated C-N-S and C-N-Se groups have been undertaken using cyclic and a.c. voltammetry. The results find a satisfying interpretation using semi-empirical MO theory. The results provide an important insight into the utility of such ring systems for the design of molecular metals.

Redox reactions of metallocenes with tungsten and molybdenum hexafluoride

Tungsten and molybdenum hexafluoride react in acetonitrile with a series of metallocenes to give coloured salts. Oxidation of iodo-, bromo- and 1,1′-dibromo-ferrocene with both hexafluorides resulted in the formation of 1 : 1 halogenoferrocenium hexafluoro-tungstate(V) and -molybdate(V) compounds, [Fe(η-C5H5)(η-C5H4Br)][MF6], [Fe(η-C5H5)(η-C5H4I)][MF6] and [Fe(η-C5H4Br)2][MF6](M = W or Mo). Cobaltocene reduced MoF6 in a two-electron step to give a 2 : 1 adduct, [Co(η-C5H5)2·2MeCN]2[MoF6], while with WF6 the 1 : 1 product [Co(η-C5H5)2·2MeCN][WF6] was formed. The redox reactions involving metallocenes and the hexafluorides are in agreement with the thermodynamic stabilities of their oxidation states found by electrochemical methods. The electrode potentials obtained for the metallocene hexafluorometalates consist of the two one-electron reduction steps for [MF6]0/–/2–(M = W or Mo) and the reversible one-electron steps for the metallocene–metallocenium couples.