A DFT-Elucidated Comparison of the Solution-Phase and SAM Electrochemical Properties of Short-Chain Mercaptoalkylferrocenes: Synthetic and Spectroscopic Aspects, and the Structure of Fc–CH₂CH₂–S–S–CH₂CH₂–Fc

Abstract

Facile synthetic procedures to synthesize a series of difficult-to-obtain mercaptoalkylferrocenes, namely, Fc(CH2)nSH, where n = 1 (1), 2 (2), 3 (3), or 4 (4) and Fc = Fe(η(5)-C5H5)(η(5)-C5H4), are reported. Dimerization of 1-4 to the corresponding disulfides 19-22 was observed in air. Dimer 20 (Z = 2) crystallized in the triclinic space group P1̅. Dimers 20-22 could be reduced back to the original Fc(CH2)nSH derivatives with LiAlH4 in refluxing tetrahydrofuran. Density functional theory (DFT) calculations showed that the highest occupied molecular orbital of 1-4 lies exclusively on the ferrocenyl group implying that the electrochemical oxidation observed at ca. -15 < Epa < 76 mV versus FcH/FcH(+) involves exclusively an Fe(II) to Fe(III) process. Further DFT calculations showed this one-electron oxidation is followed by proton loss on the thiol group to generate a radical, Fc(CH2)nS(•), with spin density mainly located on the sulfur. Rapid exothermic dimerization leads to the observed dimers, Fc(CH2)n-S-S-(CH 2)nFc. Reduction of the ferrocenium groups on the dimer occurs at potentials that still showed the ferrocenyl group ΔE = Epa,monomer - Epc,dimer ≤ 78 mV, indicating that the redox properties of the ferrocenyl group on the mercaptans are very similar to those of the dimer. (1)H NMR measurements showed that, like ferrocenyl oxidation, the resonance position of the sulfhydryl proton, SH, and others, are dependent on -(CH2)n- chain length. Self-assembled monolayers (SAMs) on gold were generated to investigate the electrochemical behavior of 1-4 in the absence of diffusion. Under these conditions, ΔE approached 0 mV for the longer chain derivatives at slow scan rates. The surface-bound ferrocenyl group of the metal-thioether, Fc(CH2)n -S-Au, is oxidized at approximately equal potentials as the equivalent CH2Cl2-dissolved ferrocenyl species 1-4. Surface coverage by the SAMs is dependent on alkyl chain length with the largest coverage obtained for 4, while the rate of heterogeneous electron transfer between SAM substrate and electrode was the fastest for the shortest chain derivative, Fc-CH2-S-Au.

(Planar‐Chiral) Ferrocenylmethanols: From Anionic Homo Phospho‐Fries Rearrangements to α‐Ferrocenyl Carbenium Ions

“…It should be noted that for the conversion of ferrocenylmethanol (1a) to the respective thiol derivative, Lawesson's reagent is generally required as a sulfur source. [55] The reaction strongly depends on the concentration of (S p )-27 in the reaction mixture and low- (13), C11-S-C11A 103.0(9); for (S p )-37: P = S 1.954(5)/1.960(5), C11-S2 1.858(17)/1.833(16), S2-C12 1.757(17)/1.724 (19), N-O 1.210(18)-1.235 (19), C11-S2-C12 103.7(8)/104.1 (9). Symmetry operation for generating equivalent atoms [A]: -y, -x, -z + 1/2.…”

Synthesis, Spectroscopy, Electrochemistry and DFT of Electron-Rich Ferrocenylsubphthalocyanines

“…The donating effect is the most prominent on SubPc 10 containing the longest alkyl chain. Propyl (n = 3) is more electron donating than ethyl (n = 2) that is more electron donating then methyl (n = 1) [10,14,25]. Figure 3) is exactly the same, with E • ' = 0.670 V for all five complexes 7-11.…”

“…The neutral axial ferrocenylcarboxylic ligands of SubPcs 7-11 thus have a net electron donating effect on the aromatic ring electrons of SubPcs 7-11 compared to Cl in SubPc 6. The net electron donating effect of the neutral axial ferrocenylcarboxylic ligand is a combination of the electron-withdrawing effect of the carboxyl group [14], the electron donating effect of the alkyl chain [10,14,25] and the electron donating effect of ferrocenyl [26]. Both ring-based reductions of SubPcs 7-11, redox waves II and III in Figure 3 and Table 2, followed the same trend, namely the reduction value decreases near linear as the number of (CH 2 ) groups, n, in the different axially bonded ferrocenyl carboxylic acid moieties (Fc-(CH 2 ) n -CO 2 ) increases in SubPcs 7-10, with the reduction values of SubPc 11 higher than that of SubPc 7, see Figure 4b.…”

“…The Fc + group is highly electronegative [26,28], withdrawing any available electron density from the alkyl groups bonded to it. The first ring-based oxidation of SubPcs 7-11 is consequently influenced by the net electron withdrawing effect of the oxidized axial ferrocenylcarboxylic ligands of SubPcs 7-11 that is a combination of the electron-withdrawing effect of the carboxyl group [14], the electron donating effect of the alkyl chain [10,14,25] and the highly electron withdrawing effect of ferrocenium [26,28], shifting the first ring-based oxidation of SubPcs 7-11 with exactly the same value namely 0.042 V more positive than E • ' of the first ring-based oxidation of SubPcs 6 at 0.628 V. The net electron withdrawing effect of the oxidized axial ferrocenylcarboxylic ligands in 7-11 is thus larger than the electron withdrawing effect of Cl in 6, on the aromatic ring electron density of the SubPcs. It was possible to get chemically reversible ring-based oxidation with peak current ratios approaching 1 and peak current separation ∆E p between 0.080 and 0.084 V, see Table 2.…”

Can Electrochemical Measurements Be Used To Predict X-ray Photoelectron Spectroscopic Data? The Case of Ferrocenyl-β-Diketonato Complexes of Manganese(III)

“…All experiments were performed in a dry cell under an argon atmosphere. Platinum wires were used for the pseudo internal reference electrode as well as the auxiliary electrode, while a glassy carbon working electrode (experimentally determined surface area 7.071 mm 2 ) 25 was utilized. Between each set of scans the working electrode was polished on a Buhler polishing mat with 1 μm and then with 1/4 μm diamond paste.…”