While the above approach tolerates a wide range of coupling partners and functionality, it is not without its limitations. Namely, there are a limited number of commercial organometallic reagents compared to that of the carboxylic acid. This often requires the practitioner to synthesize bespoke organometallic reagents for more structurally complex crosscoupling partners, which undoubtedly adds additional concession steps to any synthesis. To this end, several reports have emerged that leverage an exogenous reductant (Zn, Hantzsch ester under photochemical activation, , dual photoredox/Ni-catalysis or electrochemical reduction ) and C(sp 2 )-electrophile equivalents to mimic the overall transformations achieved in the organometallic approach but under milder reaction conditions. Further, this approach leverages more commercially available and benchtop stable C(sp 2 )-halides and pseudohalides. Such modifications fall under the second category of reductive activation for decarboxylative cross-coupling. While the mechanism for such reductive cross electrophile couplings is still under investigation, it is generally hypothesized that they adhere to the following catalytic cycle. First, the Ni(II) precursor is reduced by the exogenous reductant to afford a low valent Ni(I) species. This reduced species undergoes oxidative addition to the C(sp 2 )-halide to generate at Ni(III) complex which undergoes comproportionation to generate a Ni(II) intermediate. This intermediate captures a radical generated from decarboxylation of the RAE to give a Ni(III) species. This species undergoes reductive elimination to give the desired coupled product and a Ni(I) species which can trigger decarboxylation of the RAE through SET and re-enter the catalytic cycle as Ni(II). As previously mentioned, the mechanism for these reductive radical cross-couplings is still under heavy investigation. Additional mechanisms proceeding through Ni(0/II/III/I) cycles have also been proposed. Additionally, efforts are further complicated by the mechanistic fluidity of such systems as a function of the starting materials enlisted (ex: alkyl halide vs. alkyl RAEs). On the other side of the reactivity paradigm lies methods that leverage oxidative activation of a free carboxylic acid typically under photoinduced electron transfer (PET) conditions using an excited state iridium(III)-based photocatalyst and C(sp 2 ) electrophiles. Upon excitation, the iridium(III) catalyst enters an excited triplet state after intersystem crossing. This excited species can act as a strong oxidant which oxidizes the carboxylic acid to generate a carbon-centered radical with loss of CO2. The reduced photocatalyst then facilitates the generation of Ni(0) and regenerates the Ir(III) photocatalyst. Ni(0) undergoes oxidative addition with the electrophile to generate a Ni(II) complex which captures a carbon centered radical affording a transient Ni(III) intermediate. This intermediate undergoes reductive elimination to afford the desired cross coupled product and a Ni(I) intermediate that can re-enter the catalytic cycle upon reduction by the reduced Ir(II) photocatalyst. The three possible ways to control and promote the decarboxylative C(sp 3 )-C(sp 2 ) cross-coupling offer unique advantages and disadvantages in terms of functional group tolerance and robustness (Figure ). The nucleophilic crosscoupling approach is limited by the organometallic species, which may compromise the chemoselectivity of the reaction. The electrophilic cross-coupling is generally the most versatile and robust, due to the mild reaction conditions. Recent works from our group showed that the use of silver-nanoparticle functionalized electrodes can expand the scope of the reductive coupling to challenging vinyl iodides and aryl halides, delivering molecules that were otherwise difficult to access (vide infra). However, reactions that involve the use of redox active esters are limited by the presence of unprotected primary and secondary amines, which can react with the activated esters. Finally, the oxidative cross-coupling approach provides an orthogonal process to forge C(sp 3 )-C(sp 2 ) in a decarboxylative fashion. Moreover, the use of carboxylic acid can be advantageous in avoiding the intermediacy of RAEs. One limiting factor of the oxidative strategy is that redox labile functional groups can competitively quench the photocatalyst, affecting the outcome of the reaction. The complementary nature of these different categories is graphically outlined in a "user-guide" format in Figure with references to assist medicinal chemists in need of the best conditions for a particular use-case.