Nickel monophosphine arene adducts have been proposed as highly reactive intermediates capable of difficult C–O bond activation steps in Ni catalyzed cross-coupling reactions. The addition of N-methylmorpholine N-oxide to arene solutions of ([Cy₃P)₂Ni]₂N₂ allows for the synthesis of stable (η⁶-arene)Ni(PCy₃) complexes. The isolation of these species demonstrates their viability as intermediates and provides an experimental means to test the hypothesized importance of the Ni(PCy₃) moiety in bond activation and catalysis.