Ligand Protonation Triggers H₂ Release from a Dinickel Dihydride Complex to Give a Doubly “T”‐Shaped Dinickel(I) Metallodiradical

Abstract

The dinickel(II) dihydride complex (1 K)o fap yrazolate-based compartmental ligand with b-diketiminato (nacnac) chelate arms (L À), providing two pincer-type {N 3 }binding pockets,has been reported to readily eliminate H 2 and to serve as amasked dinickel(I) species.Discrete dinickel(I) complexes (2 Na , 2 K)ofL À are now synthesized via adirect reduction route. They feature two adjacent T-shaped metalloradicals that are antiferromagnetically coupled, giving an S = 0g round state. The two singly occupied local d x 2 Ày 2 type magnetic orbitals are oriented into the bimetallic cleft, enabling metal-metal cooperative 2e À substrate reductions as shown by the rapid reaction with H 2 or O 2 .X-ray crystallography reveals distinctly different positions of the K + in 1 K and 2 K ,s uggesting as tabilizing interaction of K + with the dihydride unit in 1 K .H 2 release from 1 K is triggered by peripheral g-C protonation at the nacnac subunits,w hich DFT calculations showl owers the barrier for reductive H 2 elimination from the bimetallic cleft.

Ligand Protonation Triggers H2 Release from a Dinickel Dihydride Complex to Give a Doubly “T”‐Shaped Dinickel(I) Metallodiradical

“…the anion of 2 M and 2' ')a re in good agreement with metric parameters observed experimentally (Table S3). Energies of the S = 1a nd the antiferromagnetically coupled broken symmetry state differ by less than 0.2 kcal mol À1 [24] Angewandte Chemie Forschungsartikel (Table S5) and optimized structures are almost identical. A single point calculation based on the atomic coordinates taken from the X-ray crystallographic analysis of 2 K confirms an antiferromagnetically coupled ground state (J % À100 cm À1 ;T able S5).…”

“…K + •••C pz contacts < 3.5 are shown as dashed lines. [24] Angewandte Chemie Forschungsartikel (Table S5) and optimized structures are almost identical. A single point calculation based on the atomic coordinates taken from the X-ray crystallographic analysis of 2 K confirms an antiferromagnetically coupled ground state (J % À100 cm À1 ;T able S5).…”

“…2 ] + (cation of 3;t hermal ellipsoids set at 30 %probability).T he BAr F 4 counteranion and most hydrogen atoms (except for those at the g-C of the b-diimine subunits) are omitted for clarity. [24] Figure 6. UV/Vis spectra of dinickel(II) complex 1 K and dinickel(I) complexes 2 K and 3 in THF at room temperature.…”

“…When the dideuteride analogue of 2 K ,[ KL(Ni II -D) 2 ]( 1 K -D), was protonated with 2equivalents of [H(Et 2 O) 2 ]BAr F 4 in THF and the reaction monitored by 2 HNMR spectroscopy, clean formation of D 2 was detected, without any signs of HD 2 ] + (cation of 3;t hermal ellipsoids set at 30 %probability).T he BAr F 4 counteranion and most hydrogen atoms (except for those at the g-C of the b-diimine subunits) are omitted for clarity. [24] Figure 6. UV/Vis spectra of dinickel(II) complex 1 K and dinickel(I) complexes 2 K and 3 in THF at room temperature.…”

Molecularly Controlled Catalysis – Targeting Synergies Between Local and Non‐local Environments

“…Because of this process's reversibility, a powerful 2‐electron reductant can be unmasked and react with substrates such as benzaldehyde. In another related study, the authors could isolate the moderately stable dinickel(I) complex featuring two adjacent T‐shaped metalloradicals 25 M (Scheme 10b) [36] . Such pincer‐based T‐shaped nickel(I) metalloradicals represent powerful reductants capable of bond activation [37] .…”