Free-base meso-tetra(pentafluorophenyl)porphyrin, 1, is electrocatalytically active for hydrogen gas generation in the presence of p-toluenesulfonic acid.

10,corrole [C-3H] has been shown to be electrocatalytically active towards hydrogen evolution in acetonitrile under acidic conditions. We observed hydrogen gas generation at −1.22 V vs Fc/Fc + in acetonitrile when [C-3H] was used as a catalyst and p-toluenesulfonic acid was used as the proton source, with an overpotential of 0.57 V. This activity is comparable to other metalated and metal-free macrocycles. From a combination of experimental observations and density functional theory calculations, a mechanistic pathway was obtained when a strong acid was used as the proton source (p-toluenesulfonic acid). The favored mechanism for hydrogen gas generation when p-toluenesulfonic acid is used is a protonation, reduction, reduction, protonation (CEEC) pathway. On the other hand, when a weaker acid (benzoic acid) was used, the metal-free corrole could not catalyze the proton reduction reaction.

We report the synthesis and characterization of a series of dimolybdenum paddlewheel complexes of the type Mo 2 (DAniF) 4−n (hpp) n (n = 1−3), where DAniF is the anion of N,N′-di-p-anisyl-formamidine and hpp is the anion of 1, 3,4,6,7,8hexahydro-2H-pyrimido[1,2-a]pyrimidine. The effect on the electronic structure of these tetragonal paddlewheel dimolybdenum compounds was studied upon systematic substitution of formamidinate ligands by the more basic guanidinates. Mo−Mo distances in the paddlewheel structures decreased upon guanidinate ligand substitution, and were found to be 2.0844(6) and 2.0784(6), for Mo 2 (DAniF) 3 (hpp) (1 ) and trans-Mo 2 (DAniF) 2 (hpp) 2 (2), respectively. Electrochemical studies show that the half-wave potential of the Mo 2 5+ /Mo 2 4+ couple shifts cathodically upon ancillary ligand substitution ranging from −0.286 V for the tetraformamidinate complex to −1.795 V for the tetraguanidinate analogue and with redox potentials of −0.75, −1.07, and −1.14 V for 1, 2, and 3 (Mo 2 (DAniF)(hpp) 3 ), respectively. The presence of a second redox event assigned to the Mo 2 6+ /Mo 2 5+ couple was not observed until two guanidinate ligands were introduced. Raman spectroscopy shows that the v(M−M) stretch gets systematically strengthened upon formamidinate ligand substitution by the guanidinate ligand hpp. The induced delta bond destabilization by the basic hpp ligand was measured using DFT calculations by tracking the energy of the frontier orbitals. The decrease in the HOMO−LUMO energy gap was supported by the red shift in the UV−vis spectra of the compounds: 412, 442, and 450 nm for 1, 2, and 3, respectively.