Another significant advantage of our system is that it is compatible with some substrates that have not been traditionally used in CEC. For example, aryl halides with sterically demanding substituents in the ortho-position are a challenging class of substrates in conventional CEC. This is likely because oxidative addition of the sterically hindered aryl electrophile is difficult relative to the activation of the alkyl halide coupling partner, which results in incompatible rates of substrate activation in catalysis. We hypothesized that our system could overcome this challenge through modulation of catalyst loadings (vide supra). Consistent with this proposal, mono-orthosubstituted aryl bromides with significant steric bulk (4p & 4q) could be coupled in high yield using increased loadings of bpy Ni compared to reactions between bromobenzene (4a) and 1-bromo-3-phenylpropane. In particular, the coupling of 4q is significant, as Weix et al. previously reported that it was difficult to couple aryl halides with bulky ortho-directing groups. By further increasing the loading of bpy Ni and decreasing the loading of Co Pc , this strategy could be extended to di-ortho-substituted aryl iodides (4r & 4s), for which there is virtually no precedent in the CEC literature. Heteroaryl halides are important substrates because heteroaromatic groups are common structures in medicinal chemistry, but are traditionally difficult substrates in CEC. In particular, it has proven challenging to use 2-halofurans and 2-halothiophenes as substrates in CEC, especially when there is no substitution in the 5-position. Our system can couple several heteroaryl substrates in high yield, including 2-bromofuran (4t), 2-bromothiophene (4u), and 3bromopyridine (4v). Importantly, the same optimization strategy that was utilized for simple arenes can be applied to heteroaryl substrates to overcome potential challenges associated with substrates binding to catalysts (see SI). We note, however, that we can only couple 2bromopyridine (4w) in 41% yield using 10 mol% bpy Ni and 10 mol% of Co Pc .