Organometallic Electrodes: Modification of Electrode Surfaces through Cathodic Reduction of Cyclopentadienyldiazonium Complexes of Cobalt and Manganese

• Published in: Langmuir 2010-09, Vol.26 (18), p.15010-15021
• Main Authors: Laws, Derek R, Sheats, John, Rheingold, Arnold L, Geiger, William E
• Format: Article
• Language: English
• Subjects: Chemistry; Electrochemistry; Electrochemistry: Charge Transfer, Electrocatalysis, Kinetics, Bioelectrochemistry; Exact sciences and technology; General and physical chemistry
• ISSN: 0743-7463; 1520-5827
• DOI: 10.1021/la102579t

Two organometallic complexes having cyclopentadienyldiazonium ligands have been isolated and characterized by spectroscopy, X-ray crystallography, and electrochemistry. Both CoCp(η5-C5H4N2)2+ (2 2+) and Mn(CO)3(η5-C5H4N2)+ (3 +) undergo facile cyclopentadienyldiazonium ligand-based one-electron reductions which liberate dinitrogen and result in strong binding of the cyclopentadienyl ligand to a glassy carbon surface, similar to the processes well established for organic aryldiazonium salts. The organometallic-modified electrodes are robust and have a thickness of approximately one monolayer (Γ = (2−4) × 10−10 mol cm−2). Their voltammetric responses are as expected for a cobaltocenium-modified electrode, [CoCp(η5-C5H4-E)]+, where Cp = cyclopentadienyl and E = electrode, and a “cymantrene”-modified electrode Mn(CO)3(η5-C5H4-E). The cobaltocenium electrode has two cathodic surface waves. The first (E 1/2 = −1.34 V vs ferrocene) is highly reversible, whereas the second (E pc = −2.4 V) is not, consistent with the known behavior of cobaltocenium. The cymantrene-substituted electrode has a partially chemically reversible anodic wave at E 1/2 = 0.96 V, also consistent with the behavior of its Mn(CO)3Cp parent. Many of the properties of aryl-modified electrodes, such as “blockage” of the voltammetric responses of test analytes, are also seen for the organometallic-modified electrodes. Surface-based substitution of a carbonyl group by a phosphite ligand, P(OR)3, R = Ph or Me, was observed when the cymantrene-modified electrode was anodically oxidized in the presence of a phosphite ligand. The successful grafting of organometallic moieties by direct bonding of a cyclopentadienyl ligand to electrode surfaces expands the chemical and electrochemical dimensions of diazonium-based modified electrodes.