A class of electrochemical mediators is described for electrocatalytic oxidation reactions that are catalyzed by metal hydrides. The octahedral ruthenium complex [Ru­(acac)2(pyimN)] (RuIIIN 3) is shown to abstract a hydrogen atom from the ruthenium hydride [RuH­(CNN)­(dppb)] (RuH 2, CNN = 2-aminomethyl-6-tolylpyridine, dppb = 1,4-bis­(diphenylphosphino)­butane) to generate [Ru­(acac)2(pyimNH)] (RuIINH 4) and a reduced Ru­(CNN)­(dppb) complex. As RuIIIN 3 can be electrochemically regenerated from RuIINH 4 under appropriately basic and oxidizing conditions, we envisioned using RuIIIN 3 as a suitable electrochemically regenerable hydrogen atom acceptor in a tandem electrocatalytic cycle to reduce the overpotential for electrocatalytic alcohol oxidation by 450 mV. In the presence of a strong base, the previously reported alcohol oxidation electrocatalyst [RuX­(CNN)­(dppb)] (1, X = Cl, 2, X = H) catalyzes the oxidation of isopropanol to acetone with a turnover frequency (TOF) greater than 3 s–1 at −0.70 V versus ferrocenium/ferrocene (Fc+/0) in tetrahydrofuran. Upon adding RuIINH 4, RuCl 1 electrocatalytically oxidizes isopropanol to acetone at −1.20 V versus Fc+/0 in tetrahydrofuran with a TOF of ca. 1 s–1. Cyclic voltammetry and chemical hydrogen atom transfer studies suggest that the predominant electrocatalytic pathway involves hydrogen atom abstraction from RuH 2 by electrochemically generated RuIIIN 3.

The synthesis, structural characterization, and electrochemical behavior of the neutral Mn­(azpy)­(CO)3(Br) 4 (azpy = 2-phenylazopyridine) complex is reported and compared with its structural analogue Mn­(bipy)­(CO)3(Br) 1 (bipy = 2,2′-bipyridine). 4 exhibits reversible two-electron reduction at a mild potential (−0.93 V vs Fc+/0 in acetonitrile) in contrast to 1, which exhibits two sequential one-electron reductions at −1.68 V and −1.89 V vs Fc+/0 in acetonitrile. The key electronic structure differences between 1 and 4 that lead to disparate electrochemical properties are investigated using a combination of Mn–K-edge X-ray absorption spectroscopy (XAS), Mn–Kβ X-ray emission spectroscopy (XES), and density functional theory (DFT) on 1, 4, their debrominated analogues, [Mn­(L)­(CO)3­(CH3CN)]­[CF3SO3] (L = bipy 2, azpy 5), and two-electron reduced counterparts [Mn­(bipy)­(CO)3]­[K­(18-crown-6)] 3 and [Mn­(azpy)­(CO)3]­[Cp2Co] 6. The results reveal differences in the distribution of electrons about the CO and bidentate ligands (bipy and azpy), particularly upon formation of the highly reduced, formally Mn(−1) species. The data show that the degree of ligand noninnocence and resulting redox-activity in Mn­(L)­(CO)3 type complexes impacts not only the reducing power of such systems, but the speciation of the reduced complexes via perturbation of the monomer–dimer equilibrium in the singly reduced Mn(0) state. This study highlights the role of redox-active ligands in tuning the reactivity of metal centers involved in electrocatalytic transformations.

An electrocatalytic system for the hydrogenation of benzaldehyde to benzyl alcohol and dibenzyl ether is described. The molybdenum hydride (C5Ph4OH)­Mo­(CO)3(H) (3) is shown to be the actively hydrogenating species. This hydride is demonstrated to be remarkably acid-stable, leading to a ca. 67% Faradaic efficiency for aldehyde reduction over hydrogen evolution despite strongly acidic and reducing conditions. Hydride 3 is prepared via 1-proton-2-electron reduction of cation [(C5Ph4OH)­Mo­(CO)3(CH3CN)]­[OTf] ([2]­[OTf]), which is generated by protonation of the Mo(0) precursor [(C5Ph4O)­Mo­(CO)3(L)]­(1).

The first synthesis of anion capped cerium corrole complexes is reported. Unusual clustering of the lanthanide corrole units has been found and the degree of aggregation can be controlled by the choice of the capping ligand. A polymeric structure 1a, with the general formula [Cor-Ce(THF)-Cp-Na]n (Cor = 5,15-bis(2,4,6-trimethylphenyl)-10-(4-methoxyphenyl)-corrole, THF = tetrahydrofuran), is formed using sodium cyclopentadienide (NaCp) and a dimeric structure 2a, with the general formula [Cor-Ce-Tp]2, is formed when potassium tris(pyrazolyl)borate (KTp) is used. Encapsulation of the counter-cation leads to the isolation of the monomeric structures 1b and 2b, with the generual formulas [AM(2.2.2.-Cryptand)][Cor-Cp-X] (AM = Na or K, X = Cp or Tp). The structural and spectroscopic properties of the complexes have been investigated.