Acetylacetonate and Acetate Complexes of Nickel(II) Catalyse the Air Oxidation of Phosphines

The polymeric complex trans‐[Ni(acac)2(µ2‐dppe)]n·2MeCN {1a, dppe = 1,2‐ethylenebis(diphenylphosphine)} is sometimes transiently deposited from the reaction of [Ni(acac)2] with dppe in MeCN prior to its facile onwards air oxidation to final crystallization of a doubly‐oxygenated relative, cis‐[Ni(acac)2(µ2‐dppeO2)]n {2, dppeO2 = 1,2‐ethylenebis(diphenylphosphineoxide)}. A similar unsolvated phase of the initial polymer, trans‐[Ni(acac)2(µ2‐dppe)]n (1b), can be isolated from toluene. The oxidation of dppe by O2 is catalytic and dppeO2 was isolated in close to stoichiometric yields from solutions containing 5 % Ni(acac)2 relative to dppe. The reaction rate slows after a few turnovers due to inhibition by the product. The relative yields of dppeO2 are higher than those from catalytic air oxidation of methyldiphenylphosphine and triphenylphosphine and we speculate that a pathway for this reaction involves a dimetallic cooperativity enabled specifically by dppe. Dppe is air‐oxidized in turnover reactions catalyzed by Ni(acac)2 and Ni(OAc)2. The metastable 1D polymeric trans‐[Ni(acac)2(µ2‐dppe)]n·2MeCN and cis‐[Ni(acac)2(µ2‐dppeO2)]n are isolated at the start and end of the reaction respectively. Higher yields compared to reactions using the analogous monophosphine suggest a dimetallic O2 activation process.