Investigating Reductive Elimination and Ligand Exchange Pathways from Homoleptic Lithium Nickelate Acetylide Complexes

Alkali-metal nickelates have been shown to be key intermediates in a range of Ni-catalyzed transformations involving polar organometallics, but mechanistic studies into elementary reaction steps are limited. Herein, we assess reductive elimination pathways from homoleptic lithium nickelates, Li₂Ni^II(C≡C–R)₄, (where R = Ph, ^tBu, or SiMe₃), to give 1,3-diynes. We find that the rate of reductive elimination varies depending on the R substituent (fast for R = Ph, slow for ^tBu), and that the resulting Li/Ni⁰ complex, in which the 1,3-diyne product remains coordinated, can adopt different structural motifs. For R = SiMe₃ derivatives, competing ligand exchange pathways have been identified and spectroscopically interrogated.