A series of neutral and monoanionic nickel dithiolene complexes with (p-methoxyphenyl)-substituted 1,2-dithiolene ligands have been prepared and characterized with physicochemical methods. Two of the complexes -the monoanion of the symmetric [Ni{S 2 C 2 -(-Ph-p-OCH 3 ) 2 } 2 ] (3 -) with NBu 4 + as a counter-ion and the neutral asymmetric [Ni{S 2 C 2 (-Ph)(-Ph-p-OCH 3 )} 2 ] (2)-have been structurally characterized by single crystal X-ray crystallography. All complexes have been employed as proton reducing catalysts in DMF with trifluoroacetic acid as proton source. The complexes are active catalysts with good faradaic yields reaching 83% for 2 but relatively high overpotentials requirements (0.91 V and 1.55 V measured at the middle of the catalytic wave for two processes observed depending on the different routes of the mechanism). The similarity of the experimental data regardless of whether the neutral or anionic form of the complexes is used indicates that the neutral form acts as pre-catalyst. On the basis of detailed DFT calculations the proposed mechanism reveals two main different routes after the protonation of the dianion of the catalyst in accordance with the experimental data, indicating the role of the concentration of the acid and the influence of the methoxy groups. Protonation at sulfur seems be more favorable than at the metal, which is in marked contrast with the catalytic mechanism proposed for analogous cobalt dithiolene complexes.

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A series of homoleptic monoanionic nickel dithiolene complexes [Ni(bdt)2](NBu4), [Ni(tdt)2](NBu4), and [Ni(mnt)2](NBu4) containing the ligands benzene‐1,2‐dithiolate (bdt2−), toluene‐3,4‐dithiolate (tdt2−), and maleonitriledithiolate (mnt2−), respectively, were employed as electrocatalysts in the hydrogen‐evolution reaction with trifluoroacetic acid as the proton source in acetonitrile. All complexes are active catalysts with TONs reaching 113, 158, and 6 for [Ni(bdt)2](NBu4), [Ni(tdt)2](NBu4), and [Ni(mnt)2](NBu4), respectively. The Faradaic yield for the hydrogen evolution reaction reaches 88 % for 2−, which also displays the minimal overpotential requirement value (467 mV) within the series. Two pathways for H2 evolution can be hypothesized that differ in the sequence of protonation and reduction steps. DFT calculations are in agreement with experimental data and indicate that protonation at sulfur follows the reduction to the dianion. Hydrogen evolves from the direduced–diprotonated form via a highly distorted nickel hydride intermediate. The effects of acid strength and concentration in the hydrogen‐evolving mechanism are also discussed.

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The tetrahedral copper(I) diimine complex [Cu(pq)2]BF4 displays high photocatalytic activity for the H2 evolution reaction with a turnover number of 3564, thus representing the first type of a Cu(I) quinoxaline complex capable of catalyzing proton reduction. Electrochemical experiments indicate that molecular mechanisms prevail and DFT calculations provide in-depth insight into the catalytic pathway, suggesting that the coordinating nitrogens play crucial roles in proton exchange and hydrogen formation.

Sustainable transformations towards the production of valuable chemicals constantly attract interest, both in terms of academic and applied research. C–H activation has long been scrutinized in this regard, given that it offers a straightforward pathway to prepare compounds of great significance. In this context, directing groups (DG) have paved the way for chemical transformations that had not been achievable using traditional reactions. Few steps, high yields, selectivity and activation of inert substrates are some of the invaluable assets of directed catalysis. Additionally, the employment of traceless directing groups (TDG) greatly improves and simplifies this strategy, enabling the realization of multi-step reactions in one-pot, cascade procedures. Cheap, abundant, readily available transition metal salts and complexes can catalyze a plethora of reactions employing TDGs, usually under low catalyst loadings—rarely under stoichiometric amounts, leading in greater atom economy and milder conditions with increased yields and step-economy. This review article summarizes all the work done on TDG-assisted catalysis with manganese, iron, cobalt, nickel, or copper catalysts, and discusses the structure-activity relationships observed, by presenting the catalytic pathways and range of transformations reported thus far.

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