Structure and Electrochemical Properties of Directly Bound Dinuclear Cobaltadithiolene Complexes. Substituent Effect on Reduction Potentials and Mixed-Valence States

Abstract

The X-ray structures and electrochemical properties of the dinuclear cobaltadithiolene complexes, μ-(1,4-disubstituted 1,3-butadiene-1,2,3,4-tetrathiolato)-bis[(η5-cyclopentadienyl)cobalt(III)], have been investigated. In the diphenyl derivative, two benzene rings in the same molecule are located face to face with the distance of 3.5 Å, while in the dimethyl derivative, two methyl groups are in remote positions. However, in the electrically neutral dinuclear complexes, there is no evidence for the intramolecular interaction between two aryl groups in solutions. Electrochemical and spectrochemical investigations revealed that in electrically neutral state, the interaction between two cobaltadithiolene moieties is small, while in monoanioic state it becomes greater. The Hammett’s plot for ΔEr1/2 (ΔEr1/2 = Er1/2(red.1) − Er1/2(red.2)) shows that the electron-attracting substituents can stabilize the mixed-valence state, [Co(II)–Co(III)]−. The smaller ΔEr1/2 values for the complexes having aryl substituents are due to the smaller interactions between the anioic and neutral moieties, because of the steric hindrance of aryl groups which inhibit the conjugation of the two cobaltadithiolene rings.

Dinuclear Cp* Cobalt Complexes of the 1,2,4,5-Benzenetetrathiolate Bischelating Ligand

“…The difference of two reduction potentials (Δ E 1/2 ) in complex 1 is equal to 269 mV (Table ), suggesting the existence of a stable mixed-valence Co III –Co II state. Note also that this Δ E 1/2 value is larger or comparable to those observed in the dinuclear CpCo dithiolene complexes [CpCo(S 2 C 2 (R))] 2 ( 9 ) shown in Chart where the two metallacycles are linked through a single covalent bond (Δ E 1/2 = 160–222 mV for R = Me, Ph, p -C 6 H 4 COMe, p -C 6 H 4 NO 2 ; Δ E 1/2 = 262–285 mV for R = H, SiMe 3 ) . Comparison with the trinuclear cobaltadithiolene complex 10 is also interesting because it possesses a similar rigid coplanar benzene center.…”

“…In this work, we have investigated a dinuclear cobalt dithiolene complex with the 14-electron π-conjugated btt 4− ligand (Chart ), that is, [Cp*Co(btt)CoCp*] ( 1 ). Most reported cobalt dithiolene complexes are mononuclear complexes, either heteroleptic monodithiolene complexes, such as CpCo(dithiolene), or homoleptic bis(dithiolene) complexes of the general formula [Co(dithiolene) 2 ] n − . – Only a few examples of the dinuclear cobalt dithiolene complex have been reported until recently. Guyon et al have described the dinuclear cobalt dithiolene complexes [CpCo(tto)CoCp] and [Cp*Co(tto)CoCp*], incorporating the 10-electron π-conjugated tto 4− ligand (Chart ) .…”

“…Guyon et al have described the dinuclear cobalt dithiolene complexes [CpCo(tto)CoCp] and [Cp*Co(tto)CoCp*], incorporating the 10-electron π-conjugated tto 4− ligand (Chart ) . In other dimeric cobalt dithiolene complexes reported by Sugimori et al and formulated as [CpCo(S 2 C 2 (R))] 2 (R = H, Me, SiMe 3 , Ph, p -C 6 H 4 COMe, p -C 6 H 4 NO 2 ), two cobaltadithiolene metallacycles are linked by a single C–C bond (Chart ). These are formal 14π-electron systems, but the two dithiolene rings are not located on the same plane, hence limiting the extent of conjugation between the two rings.…”

Coupling Reactions of Alkynylsilanes Mediated by a Cu(I) Salt: Novel Syntheses of Conjugate Diynes and Disubstituted Ethynes

“…Bulb-to-bulb distillation (200−210 °C/3 Torr) gave 1a in 86% yield as a colorless solid (GC yield; >99%). The following symmetrical conjugate diynes were prepared by literature procedures: 1,4-di(4-methoxyphenyl)-1,3-butadiyne ( 3b ), 1,4-di(4-acetylphenyl)-1,3-butadiyne ( 3c ), and 7,9-hexadecadiyne ( 4 ) …”

Rare direct imidation of aromatic metallacycle by reaction of CpCo(dithiolene) complex with N-halosuccinimide

“…The ORTEP drawing of 1a clearly indicates the substitution of succinimide group to the dithiolene carbon. Concerning the homo-coupling products, 1b and 2b have been obtained by another synthetic procedure [13]. The only homo-coupling product 3b is a new product and here it can be characterized by some spectroscopic data and elemental analysis.…”