Electrocatalytic proton reduction by an air-stable nickel(ii)-thiolato PNN pincer complex

Synthesis and catalytic performance of nickel phosphinite pincer complexes in deoxygenative hydroboration of amides

A series of imino-POCN^R, amino-POCN^R2, and bis(phosphinite) POCOP pincer complexes of Ni(II) were prepared and tested in catalytic deoxygenative hydroboration of amides with HBPin to the corresponding amines. In contrast to the deoxygenative hydrosilylation approach, primarily developed for tertiary amides, superior reactivity in Ni-catalyzed deoxygenative hydroboration was demonstrated for secondary carboxamides. The bis(phosphinite) hydride complex (POCOP)NiH proved the most active in these reactions, tolerating potentially reducible functionalities such as internal alkenes, esters, nitriles, heteroaromatic compounds, and tertiary amides. Preferable hydroboration of secondary amides was also demonstrated in the presence of primary amide functionalities. The reactions were conducted at 60-80 °C, representing a rare example of a base-metal catalytic system for selective deoxygenation of secondary amides to the corresponding amines under mild conditions. In contrast to secondary amides, deoxygenative hydroboration of primary amides was demonstrated using an iminophosphinite pre-catalyst (POCN^Dmp)Ni(CH₂TMS) (Dmp = 2,6-Me₂C₆H₃). Deoxygenation reactions were suggested to proceed via a direct C-O bond cleavage mechanism, which is triggered by dehydrogenative N-borylation to access more electrophilic N-borylamides amenable to the addition of HBPin to the carbonyl group.

Electrochemical behaviors of a pincer-type NNN-Fe complex and catalytic H2 evolution activity

We describe electrochemical reactivity of a pincer-type [NNN-Fe(tBuNC)3](ClO4)2 complex. Upon electron reduction, the Fe(i) species experienced disproportionation to Fe(0) and Fe(ii). An electron-reduced Fe center dissociated a tBuNC ligand to make an open coordination site, where a proton could be transferred. The low-spin Fe center, assisted by isocyanide and a pyridine-based NNN-pincer ligand, catalyzed efficiently the proton reduction reaction. Also, a Lewis basic amine site in the side 'arm' of the NNN-pincer ligand lowered the free energy for the protonation of an Fe center during the proton reduction process. DFT calculations provided insight into a plausible catalytic pathway.

Selective Carbanion-Pyridine Coordination of a Reactive P,N Ligand to RhI

Ligands with reactive carbon sites in the periphery of a metal center have emerged as a powerful approach for metal-ligand bond activation. These reactive carbon sites are commonly generated by deprotonation strategies. Carbon-silicon bond cleavage is a potential alternative to access such constructs. Herein, the monodesilylation of bis-silyl-substituted P,N scaffold PNSi2 in the coordination sphere of [RhI (Cl)(CO)(PNSi2 )] (1) with sodium azide is disclosed. This affords a unique dinucleating anionic κ2 -C,N-κ1 -P ligand with a carbanionic methine carbon atom directly bound to rhodium as part of a four-membered Rh-N-C-C rhodacycle. This dimer undergoes meta-pyridine C-H activation facilitated by weak bases, which leads to a desymmetrization of the system and provides a σ,π-bridging 3-pyridyl fragment bound to RhI . The facile Si-C cleavage strategy may pave the way to studying the reactivity and functionalization of a variety of κ2 -C,N-coordinated pyridine scaffolds for selective transformations.

Nickel(ii) PE1CE2P pincer complexes (E = O, S) for electrocatalytic proton reduction

The catalytic activity of a series of nickel complexes with different phosphinite/thiophosphinite ligands for electrocatalytic proton reduction strongly depends on the nature of the pincer ligands.