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Copper-mediated aromatic and aliphatic C-H hydroxylations using benign oxidants (O 2 and H 2 O 2 ) have been studied intensively in recent years to meet the growing demand for efficient and green C-H functionalizations. Herein, we report an enantioselective variant of the so-called clip-and-cleave concept for intramolecular ligand hydroxylations by the application of chiral diamines as directing groups. We tested the hydroxylation of cyclohexanone and 1-acetyladamantane under different oxidative conditions (Cu I /O 2 ; Cu I /H 2 O 2 ; Cu II /H 2 O 2 ) in various solvents. As an outstanding example, we obtained ( R )-1-acetyl-2-adamantol with a yield of 37% and >99:1 enantiomeric excess from hydroxylation in acetone using Cu I and O 2 . Low-temperature stopped-flow UV-vis measurements in combination with density functional theory (DFT) computations revealed that the hydroxylation proceeds via a bis(μ-oxido) dicopper intermediate. The reaction product represents a rare example of an enantiopure 1,2-difunctionalized adamantane derivative, which paves the way for potential pharmacological studies. Furthermore, we found that 1-acetyladamantane can be hydroxylated in a one-pot reaction under air with isolated yields up to 36% and enantiomeric ratios of 96:4 using Cu II /H 2 O 2 in MeOH.

We report the preparation of a new organic σ-donor with a C 6 H 4 -linker between an N-heterocyclic carbene (NHC) and an exocyclic methylidene group, which we term N-heterocyclic quinodimethane (NHQ). The aromatization of the C 6 H 4 -linker provides a decisive driving force for the reaction of the NHQ with an electrophile and renders the NHQ significantly more basic than analogous NHCs or N-heterocyclic olefins (NHOs), as shown by DFT computations and competition experiments. In solution, the NHQ undergoes an unprecedented dehydrogenative head-to-head dimerization by C-C coupling of the methylidene groups. DFT computations indicate that this reaction proceeds via an open-shell singlet pathway revealing the diradical character of the NHQ. The product of this dimerization can be described as conjugated N-heterocyclic bis-quinodimethane, which according to cyclic voltammetry is a strong organic reducing agent (E 1/2 =-1.71 V vs. Fc/Fc + ) and exhibits a remarkable small singlet-triplet gap of ΔE S→T =4.4 kcal mol -1 ., (© 2023 The Authors. Angewandte Chemie International Edition published by Wiley-VCH GmbH.)

Nitride complexes are key species in homogeneous nitrogen fixation to NH 3 via stepwise proton-coupled electron transfer (PCET). In contrast, direct generation of nitrogenous organic products from N 2 -derived nitrides requires new strategies to enable efficient reductive nitride transfer in the presence of organic electrophiles. We here present a 2-step protocol for the conversion of dinitrogen to benzonitrile. Photoelectrochemical, reductive N 2 splitting produces a rhenium(V) nitride with unfavorable PCET thermochemistry towards ammonia generation. However, N-benzoylation stabilizes subsequent reduction as a basis for selective nitrogen transfer in the presence of the organic electrophile and Brønsted acid at mild reduction potentials. This work offers a new strategy for photoelectrosynthetic nitrogen fixation beyond ammonia-to yield nitrogenous organic products., (© 2022 The Authors. Angewandte Chemie International Edition published by Wiley-VCH GmbH.)

Transition metal halide complexes are used as precursors for reductive N 2 activation up to full splitting into nitride complexes. Distinct halide effects on the redox properties and yields are frequently observed yet not well understood. Here, an electrochemical and computational examination of reductive N 2 splitting with the rhenium(III) complexes [ReX 2 (PNP)] (PNP = N(CH 2 CH 2 P t Bu 2 ) 2 and X = Cl, Br, I) is presented. As previously reported for the chloride precursor ( J. Am. Chem. Soc. 2018, 140, 7922), the heavier halides give rhenium(V) nitrides upon (electro-)chemical reduction in good yields yet with significantly anodically shifted electrolysis potentials along the halide series. Dinuclear, end-on N 2 -bridged complexes, [{ReX(PNP)} 2 (μ-N 2 )], were identified as key intermediates in all cases. However, while the chloride complex is exclusively formed via 2-electron reduction and Re III /Re I comproportionation, the iodide system also reacts via an alternative Re II /Re II -dimerization mechanism at less negative potentials. This alternative pathway relies on the absence of the potential inversion after reduction and N 2 activation that was observed for the chloride precursor. Computational analysis of the relevant Re III/II and Re II/I redox couples by energy decomposition analysis attributes the halide-induced trends of the potentials to the dominating electrostatic Re-X bonding interactions over contributions from charge transfer.