Cleavage of Carbon Dioxide C=O Bond Promoted by Nickel‐Boron Cooperativity in a PBP‐Ni Complex.

The synthesis and characterization of (tBuPBP)Ni(OAc) (5) by insertion of carbon dioxide into the Ni−C bond of (tBuPBP)NiMe (1) is presented. An unexpected CO2 cleavage process involving the formation of new B−O and Ni−CO bonds leads to the generation of a butterfly‐structured tetra‐nickel cluster (tBuPBOP)2Ni4(μ‐CO)2 (6). Mechanistic investigation of this reaction indicates a reductive scission of CO2 by O‐atom transfer to the boron atom via a cooperative nickel‐boron mechanism. The CO2 activation reaction produces a three‐coordinate (tBuP2BO)Ni‐acyl intermediate (A) that leads to a (tBuP2BO)−NiI complex (B) via a likely radical pathway. The NiI species is trapped by treatment with the radical trap (2,2,6,6‐tetramethylpiperidin‐1‐yl)oxyl (TEMPO) to give (tBuP2BO)NiII(η2‐TEMPO) (7). Additionally, 13C and 1H NMR spectroscopy analysis using 13C‐enriched CO2 provides information about the species involved in the CO2 activation process. [ABSTRACT FROM AUTHOR]