Cobaltocenium cation

The observation of radical anions has been confirmed by ESR measurements as illustrated by [Ir4(CO)12], (g = 2.002) 208). Similarly, a toluene solution of Co4(CO)i2 reacts with cobaltocene precipitating a brown compound which is extremely reactive and contains a cobaltocenium cation for each four cobalt atoms of the anion55. With excess cobaltocene (or alkali metals) in THF the reaction proceeds further as shown in Eq. (20),... 

The cathodic shifts of the redox potentials of compounds [68], [69] and [71] on addition of halide anions are due to the stabilization of the cobaltocenium cation by the bound anion which causes the redox couple to shift to a more... 

Bis(cyclopentadienyl)zirconocenes, cationic complexes, 4,896 l,l -Bis(dialkylboryl)cobaltocenium cations, complexation behavior, 7, 88... 

Herberich, G. E., Fischer, A., Wiebelhaus, D., Bis(boryl)metallocenes. 1. 1,1 -bis(diisopropylboryl)cobaltocenium cation A novel anion-binding ligand. Organometallics 1996,15, 3106-3108. 

Figure 26 The DOSY spectrum of a solution containing a tetraureacalix[4]arene host, ferrocene, and cobaltocenium cation in C2D4CI2, recorded at 400 MHz, 298 K. The signal at 5 = 2.72 ppm has the same D as all the signals of the calixarene indicating encapsulation. The signals of the free ferrocene and cobaltocenium cation at 5 = 4.06 and 5.61 ppm, respectively, have much higher diffusion coefficients. (Adapted with permission from Cohen, Y. Avram, L. Frish, L. (2005) Angew. Chem., Int. Ed., 44 520. 2005 Wiley-VCH)...

The power and simplicity of DOSY in probing intermolecular interactions in general and encapsulation in particular, is shown in Fig. 6.10. Upon addition of the cobaltocenium cation (13) to the C2D4CI2 solution of the dimer 12-12, an extra peak at about 2.8 ppm was observed beyond that of 13. When ferrocene (14) was added to the solution, no additional high-field peak was observed. The DOSY spectrum, in Fig. 6.10b, of the C2D4CI2 solution of dimer 12 >12 in the presence of 13 and 14 clearly demonstrates how trivial it is to map the mutual interactions that prevail in the solution between the different molecular species [31c]. Only the peak... 

J. G. Limon-Petersen, E. J. F. Dickinson, S. R. Belding, N. V. Rees, and R. G. Compton. Cychc voltammetry in weakly supported media The reduction of the cobaltocenium cation in acetonitrile. Comparison between theory and experiment, J. Electroanal. Chem. 650, 135-142 (2010). 

Stojanovic RS, Bond AM (1993) Examination of conditions under which the reduction of the cobaltocenium cation can be used as a standard voltammetric reference process in organic and aqueous solvents. Anal Chem 65(l) 56-64. doi 10.1021/ac00049a012... 

Self-Supported Reduction of the Cobaltocenium Cation Problem... 

Figure 31.1 shows the structures of some of the calixarene and calixpyrrole derivatives that were found to self-assemble into dimeric capsules (see structures 2-5). The tetraureacalix[4]arenes (2) were found to from dimeric capsules with internal volumes estimated to be in the range of 160-200 [lib]. These dimeric capsules were found to encapsulate solvent molecules like chloroform and benzene and small ammonium salts [11]. In addition, it was demonstrated with the aid of diffusion NMR [16] that such dimers have a high affinity for charged systems, and it was found that tropylium cation and cobaltocenium cation have higher affinities than benzene and ferrocene, respectively, for the cavity of the dimer of 2 [17]. These and other studies demonstrated that indeed diffusion NMR is an excellent means to probe encapsulation [17, 18], a fact that was instrumental in the study of the large hexameric capsules of resorcin[4]arenes and pyrogallol[4]arenes as will be demonstrated below [18-20]. 

Fig. 4 a Space-filling representation of the tartaric add template in crystalline [Co(t -C5H5)2 + [(Hta)(H2ta)]. b Space-filling representation of the anionic honeycomb framework formed by the [(Hta)(H2ta)]2 units, the cobaltocenium cations stack inside the channels extending along the a-axis (reproduced with permission from [17])... 

The hexameric arene capsules 397 and 401 (Scheme 3.86) have been studied in [82] as potent caging ligands for the encapsulation of cobaltocenium cation. According to NMR data, these ligands form 1 1 cage complexes that result in substantial changes in the CVs the reversible wave characteristic of the free cobaltocenium cation disappears after caging. Tetraalkylammonium halides do not affect this encapsulation process. In the case of hexafluorophosphate, tetrafluo-roborate, and perchlorate salts of these cations. 

Sukardi SK, Zhang J, Burgar I, Home MD, HoUenkamp AF, MacFarlane DR, Bond AM (2008) Prospects for a widely applicable reference potential scale in ionic liquids based on ideal reversible reduction of the cobaltocenium cation. Electrochem Commun 10 250-254... 

Shiddiky MIA, Torriero AAJ, Zhao C, Butgar 1, Kennedy G, Bond AM (2009) Nonadditivity of faradaic currents and modification of capaciteuice currents in the voltammetry of mixtures of ferrocene and the cobaltocenium cation in protic and aprotic ionic liquids. J Am Chem Soc 131 7976-7989... 

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