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

Cross-coupling catalysts are prone to unproductive side reactivity that 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, CyJohnPhos-bound Ni 0 complex following product-forming reductive elimination. In the absence of substrate, free phosphine ligand, or π-accepting additives, dimerization of (CyJohnPhos)Ni 0 occurs, followed by C-P bond activation of the ligand to form a phosphido-bridged Ni 0 /Ni II dimer; both the Ni 0 /Ni 0 and Ni 0 /Ni II dimers were structurally characterized. Monomeric (CyJohnPhos)Ni 0 must be intercepted by substrate or free ligand to prevent irreversible dimerization and catalyst deactivation.