Abstract
The dinickel(II) dihydride complex (1(K) ) of a pyrazolate-based compartmental ligand with β-diketiminato (nacnac) chelate arms (L(-) ), providing two pincer-type {N(3) } binding pockets, has been reported to readily eliminate H(2) and to serve as a masked dinickel(I) species. Discrete dinickel(I) complexes (2(Na) , 2(K) ) of L(-) are now synthesized via a direct reduction route. They feature two adjacent T-shaped metalloradicals that are antiferromagnetically coupled, giving an S=0 ground state. The two singly occupied local dx2-y2 type magnetic orbitals are oriented into the bimetallic cleft, enabling metal-metal cooperative 2 e(-) 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) , suggesting a stabilizing interaction of K(+) with the dihydride unit in 1(K) . H(2) release from 1(K) is triggered by peripheral γ-C protonation at the nacnac subunits, which DFT calculations show lowers the barrier for reductive H(2) elimination from the bimetallic cleft.