Insertion of CO2 Mediated by a (Xantphos)NiI -Alkyl Species.

The incorporation of CO2 into organometallic and organic molecules represents a sustainable way to prepare carboxylates. The mechanism of reductive carboxylation of alkyl halides has been proposed to proceed through the reduction of NiII to NiI by either Zn or Mn, followed by CO2 insertion into NiI -alkyl species. No experimental evidence has been previously established to support the two proposed steps. Demonstrated herein is that the direct reduction of (tBu-Xantphos)NiII Br2 by Zn affords NiI species. (tBu-Xantphos)NiI -Me and (tBu-Xantphos)NiI -Et complexes undergo fast insertion of CO2 at 22 °C. The substantially faster rate, relative to that of NiII complexes, serves as the long-sought-after experimental support for the proposed mechanisms of Ni-catalyzed carboxylation reactions.