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-BuPCN^i-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.