Table 2.
Electrocatalytic H2 evolution peak potentials (V vs. Fc+/0) in the presence of Co and Ni complexes measured at a GC electrode by cyclic voltammetry (100 mV·s−1) in the presence of 3 equiv of various acids in CH3CN (nBu4NBF4 0.1 mol·L−1)
| Acid | p-Cyanoanilinium | Tosic acid | Anilinium | TFA | Et3NHCl |
|---|---|---|---|---|---|
| pKa | 7.6 | 8.7 | 10.7 | 12.65 | 18.7 |
| E0(H+/H2) in CH3CN* | −0.59 | −0.66 | −0.77 | −0.89 | −1.25 |
| [Co((DO)2BF2)pnBr2] | −0.82 | −0.85 | −0.88 | −0.89 | — |
| [Co(DO)(DOH)pnBr2] | −0.78 | −0.83 | −0.97 | −1.10 | — |
| [Ni(DO)(DOH)pn](ClO4) | −0.95 | −1.01 | −1.09 | −1.20 | −1.54 |
| [Ni((DO)2BF2)pn](ClO4) | −0.95 | −0.94 | −0.98 | −1.00 | — |
| [Ni(MO)(MOH)pnCl] | −0.97 | † | −1.0 | −1.00 | — |
| [Co(dmgBF2)2(CH3CN)2] | −0.80 | −0.93 | −0.89 | −0.90 | |
| [Co(dmgH)2pyCl] | — | — | — | — | −1.48 |
*These calculated values do not take into account the homoconjugation reaction (self-association of the the acid with its conjugated base) that may increase the effective acidity of these acids, in particular for tosic acid and TFA.
†The species is unstable in the presence of high concentrations of acid.