Catalyst Deactivation of a Monoligated CyJohnPhos-Bound Nickel(0) Complex

Cross-coupling catalysts are prone to unproductive side reactivity, which can limit their practical use in synthetic chemistry. A detailed understanding of these pathways and the conditions that enable them is important for reaction optimization and rational catalyst design. In this work, we report the off-cycle reactivity of a monoligated, (2-biphenyl)dicyclohexylphosphine (CyJohnPhos)-bound Ni0 complex following product-forming reductive elimination. In the absence of substrate, free phosphine ligand, or π-accepting additives, dimerization of (CyJohnPhos)Ni0 occurs, followed by C–P bond activation of the ligand to form a phosphido-bridged Ni0/NiII dimer; both the Ni0/Ni0 and Ni0/NiII dimers were structurally characterized. Monomeric (CyJohnPhos)Ni0 must be intercepted by the substrate or free ligand to prevent irreversible dimerization and catalyst deactivation.