PENTAMETHYLCYCLOPENTADIENYL TRANSITION-METAL COMPLEXES. ELECTROCHEMISTRY OF TRANSITION-METAL pi -COMPLEXES. 7. CYCLOPENTADIENYL(ARENE)COBALT CATIONS: PREPARATION, ELECTROCHEMICAL REDUCTION, AND SPECTROSCOPIC INVESTIGATION OF THE PARAMAGNETIC D**7 MONOCATIONS.

U. Koelle, B. Fuss, M. V. Rajasekharan, B. L. Ramakrishna, J. H. Ammeter, M. C. Boehm

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Abstract

A novel halogen/arene exchange reaction starting from left bracket Co(pmco)X//2 right bracket //2 (pmcp equals eta **5-1,2,3,4,5-pentamethylcyclopentadienyl, X equals Cl, Br) makes accessible the Co(pmcp)(arene)**2** plus dications. A series of these sandwich cations substituted to a varying degree by methyl groups in either ligand ring was prepared. Electrochemical (cyclic voltammetry and polarography at the DME) reduction of Co(cp)(arene)**2** plus and Co(pmcp)(arene)**2**30 (cp equals eta **5-cyclopentadienyl, pmcp equals eta **5-pentamethylcyclopentadienyl; arene: bz equals eta **6-benzene, mes equals eta **6-mesitylene, pmbz equals eta **5-cyclopentadienyl, and hmbz equals // eta **6-hexamethylbenzene) salts (BF//4** minus , PF//6** minus ) in propylene carbonate revealed two reversible one-electron reduction steps of nearly constant separation for each compound ( plus 0. 4 to minus 0. 12 v and minus 0. 56 to minus 1. 1 vs. SCE respectively). These results are compared to the reduction potentials determined for the two-step reduction of Co(hmbz)//2**2** plus in the same solvent and to potentials for related sandwich systems in the literature. A regular displacement of both reduction potentials with the number and the position of the methyl substituents at either ring on comparison with the results of an INDO-SCF calculation yields a relation between the electrochemical substituent effect and the bonding of the ligand.

Original languageEnglish (US)
Pages (from-to)4152-4160
Number of pages9
JournalJournal of the American Chemical Society
Volume106
Issue number15
StatePublished - Jan 1 1984
Externally publishedYes

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Electrochemistry
Coordination Complexes
Metal complexes
Cobalt
Transition metals
Cations
Positive ions
Polarography
Ligands
Halogens
Benzene
Salts
Electrons
Polarographic analysis
Cyclic voltammetry
Propylene
Carbonates
mesitylene
propylene carbonate
hexamethylbenzene

ASJC Scopus subject areas

  • Chemistry(all)

Cite this

@article{6b3c2bc7650a49a48c6931811639777b,
title = "PENTAMETHYLCYCLOPENTADIENYL TRANSITION-METAL COMPLEXES. ELECTROCHEMISTRY OF TRANSITION-METAL pi -COMPLEXES. 7. CYCLOPENTADIENYL(ARENE)COBALT CATIONS: PREPARATION, ELECTROCHEMICAL REDUCTION, AND SPECTROSCOPIC INVESTIGATION OF THE PARAMAGNETIC D**7 MONOCATIONS.",
abstract = "A novel halogen/arene exchange reaction starting from left bracket Co(pmco)X//2 right bracket //2 (pmcp equals eta **5-1,2,3,4,5-pentamethylcyclopentadienyl, X equals Cl, Br) makes accessible the Co(pmcp)(arene)**2** plus dications. A series of these sandwich cations substituted to a varying degree by methyl groups in either ligand ring was prepared. Electrochemical (cyclic voltammetry and polarography at the DME) reduction of Co(cp)(arene)**2** plus and Co(pmcp)(arene)**2**30 (cp equals eta **5-cyclopentadienyl, pmcp equals eta **5-pentamethylcyclopentadienyl; arene: bz equals eta **6-benzene, mes equals eta **6-mesitylene, pmbz equals eta **5-cyclopentadienyl, and hmbz equals // eta **6-hexamethylbenzene) salts (BF//4** minus , PF//6** minus ) in propylene carbonate revealed two reversible one-electron reduction steps of nearly constant separation for each compound ( plus 0. 4 to minus 0. 12 v and minus 0. 56 to minus 1. 1 vs. SCE respectively). These results are compared to the reduction potentials determined for the two-step reduction of Co(hmbz)//2**2** plus in the same solvent and to potentials for related sandwich systems in the literature. A regular displacement of both reduction potentials with the number and the position of the methyl substituents at either ring on comparison with the results of an INDO-SCF calculation yields a relation between the electrochemical substituent effect and the bonding of the ligand.",
author = "U. Koelle and B. Fuss and Rajasekharan, {M. V.} and Ramakrishna, {B. L.} and Ammeter, {J. H.} and Boehm, {M. C.}",
year = "1984",
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day = "1",
language = "English (US)",
volume = "106",
pages = "4152--4160",
journal = "Journal of the American Chemical Society",
issn = "0002-7863",
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T1 - PENTAMETHYLCYCLOPENTADIENYL TRANSITION-METAL COMPLEXES. ELECTROCHEMISTRY OF TRANSITION-METAL pi -COMPLEXES. 7. CYCLOPENTADIENYL(ARENE)COBALT CATIONS

T2 - PREPARATION, ELECTROCHEMICAL REDUCTION, AND SPECTROSCOPIC INVESTIGATION OF THE PARAMAGNETIC D**7 MONOCATIONS.

AU - Koelle, U.

AU - Fuss, B.

AU - Rajasekharan, M. V.

AU - Ramakrishna, B. L.

AU - Ammeter, J. H.

AU - Boehm, M. C.

PY - 1984/1/1

Y1 - 1984/1/1

N2 - A novel halogen/arene exchange reaction starting from left bracket Co(pmco)X//2 right bracket //2 (pmcp equals eta **5-1,2,3,4,5-pentamethylcyclopentadienyl, X equals Cl, Br) makes accessible the Co(pmcp)(arene)**2** plus dications. A series of these sandwich cations substituted to a varying degree by methyl groups in either ligand ring was prepared. Electrochemical (cyclic voltammetry and polarography at the DME) reduction of Co(cp)(arene)**2** plus and Co(pmcp)(arene)**2**30 (cp equals eta **5-cyclopentadienyl, pmcp equals eta **5-pentamethylcyclopentadienyl; arene: bz equals eta **6-benzene, mes equals eta **6-mesitylene, pmbz equals eta **5-cyclopentadienyl, and hmbz equals // eta **6-hexamethylbenzene) salts (BF//4** minus , PF//6** minus ) in propylene carbonate revealed two reversible one-electron reduction steps of nearly constant separation for each compound ( plus 0. 4 to minus 0. 12 v and minus 0. 56 to minus 1. 1 vs. SCE respectively). These results are compared to the reduction potentials determined for the two-step reduction of Co(hmbz)//2**2** plus in the same solvent and to potentials for related sandwich systems in the literature. A regular displacement of both reduction potentials with the number and the position of the methyl substituents at either ring on comparison with the results of an INDO-SCF calculation yields a relation between the electrochemical substituent effect and the bonding of the ligand.

AB - A novel halogen/arene exchange reaction starting from left bracket Co(pmco)X//2 right bracket //2 (pmcp equals eta **5-1,2,3,4,5-pentamethylcyclopentadienyl, X equals Cl, Br) makes accessible the Co(pmcp)(arene)**2** plus dications. A series of these sandwich cations substituted to a varying degree by methyl groups in either ligand ring was prepared. Electrochemical (cyclic voltammetry and polarography at the DME) reduction of Co(cp)(arene)**2** plus and Co(pmcp)(arene)**2**30 (cp equals eta **5-cyclopentadienyl, pmcp equals eta **5-pentamethylcyclopentadienyl; arene: bz equals eta **6-benzene, mes equals eta **6-mesitylene, pmbz equals eta **5-cyclopentadienyl, and hmbz equals // eta **6-hexamethylbenzene) salts (BF//4** minus , PF//6** minus ) in propylene carbonate revealed two reversible one-electron reduction steps of nearly constant separation for each compound ( plus 0. 4 to minus 0. 12 v and minus 0. 56 to minus 1. 1 vs. SCE respectively). These results are compared to the reduction potentials determined for the two-step reduction of Co(hmbz)//2**2** plus in the same solvent and to potentials for related sandwich systems in the literature. A regular displacement of both reduction potentials with the number and the position of the methyl substituents at either ring on comparison with the results of an INDO-SCF calculation yields a relation between the electrochemical substituent effect and the bonding of the ligand.

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