Biphenylene Coordination and Ring-Opening by Alkali-Metal Nickelates.

The pre-coordination of substrates to heterobimetallic complexes plays a key role in facilitating challenging bond activations and catalytic reactions. Herein, we report a family of low-valent phenyl-alkali-metal nickelates containing a η4-coordinated biphenylene ligand and demonstrate how the coordination and solvation preferences of the alkali-metal cation (Li, Na or K) influence the rate of C-C bond oxidative addition at nickel through combined structural, spectroscopic and computational studies. The rate of C-C bond cleavage can be further manipulated by replacing the two phenyl-carbanionic ligands with a cyclic 2,2'-biphenyl scaffold, which affords thermally stable and symmetric spirocyclic nickelates upon ring-opening.