Carboxylation of the Ni–Me Bond in an Electron-Rich Unsymmetrical PCN Pincer Nickel Complex

The
synthesis of a new unsymmetrical PCN ligand bearing tert-butyl groups on the phosphorus atom and isopropyl groups
on the nitrogen donor atom is presented. It reacts with the commercially
available Ni­(DME)­Br2 precursor to offer the corresponding t‑BuPCNi‑Pr pincer
nickel bromide complex 1 together with a paramagnetic
species, which was characterized as a tetrahedral nickel complex.
Complex 1 reacts with MeMgCl to give the corresponding
methyl complex 3. Carboxylation of complex 3 using 4 atm of CO2 gave the PCN nickel acetate complex 4 under mild reaction conditions comparable to those for the
corresponding palladium complexes with PCP ligands.