Zwitterionic nickel(II) complexes: Synthesis, characterization, decomposition, and stoichiometric and catalytic reactivities.

Zwitterionic nickel(II) compounds with a borate-containing anionic bidentate phosphine ligand (PBP − ) have been synthesized and some of them crystallographically characterized. The methyl complex, (PBP − )Ni + CH 3 (NCCH 3 ), reacts with H 2 to form an 12-membered macrocycle containing three Ni nuclei and reacts with carbon monoxide (CO) to afford the acetyl complex (PBP − )Ni + COCH 3 (CO). The square planar acetyl complex is stable in solution under 1 atm of CO but undergoes irreversible decomposition under high CO pressure at room temperature. X-Ray crystallographic characterization of a decomposition product revealed fragmentation of the anionic borate under high pressure. (PBP − )Ni + COCH 3 (CO) is an active catalyst for ethylene-CO copolymerization, but its productivity is low likely due to its instability under high CO pressure. [ABSTRACT FROM AUTHOR]