Given our initial stereoelectronic rationale as a means of postulated activation, we aimed to discern this on a structural basis investigating single point modifications of the core scaffold (Figure ). Introducing a stronger C-X bond suppressed reactivity, suggesting bond dissociation energy as a pivotal factor. However, formal activation of these substrates could be readily enabled by the simple inclusion of NaI via an in situ Finkelstein exchange. Occupation of the boron p-orbital inhibited activation, further supporting stereoelectronic effects as the origin for bond activation. X-ray crystallography unveiled a dihedral angle of ca. 86°, 28 increasing the stereoelectronic similarities in the ground state to the venerable Ahn-Eisenstein model (Figure ). Having suitably established the requirement of the boron p-orbital, additive and C-I bond as a prerequisite for activation, we investigated the origin of photoactivation via UV/vis spectroscopy (Figure ). The presence of α-iodo precursor 2a at model reaction concentration showed no absorption in the emission region of the Kessil light source suggesting direct irradiation and homolytic cleavage was inefficient (Figure (i), grey). However, after stirring with 2,6-lutidine, a band with a substantial bathochromic shift appeared (λmax ~400 nm) most likely due to the formation of an EDA complex (Figure (i), red). Consciously aware of the stark differences in steric parameters of the 2,6-dtbpy system we also investigated precursor 2b in the presence of 2,6-dtbpy (Figure 1C (i), green). To our surprise, no EDA was detected despite this system showing comparable reactivity under model reaction conditions. Irradiating a reaction mixture at 427 nm containing precursor 2b and 2,6dtbpy revealed a new band with λmax ~ 364 nm (Figure (ii), grey). While this band and coloration may suggest formation of an EDA complex, this was instead attributed to triiodide formation based on commercial reagents and control experiments [λmax ~ 364 nm] (Figure (ii), red and green respectively). The formation of the triiodide species, does however, indicate efficient homolytic cleavage of the C-X bond to generate the respective α-boryl and iodine radical. It is pertinent to note, the inclusion of styrene reagent had no effect on UV/Vis properties of the EDA or triiodide (see SI for full details). With these data describing the origin of photoactivation, we investigated the presence of radicals and possible chain processes. Radical clock experiments provided strong evidence for the generation of both an α-boryl and benzylic radical while quantum yield excluded the possibility of an efficient chain process (see SI for full details). With the absence of a chain process we looked to push the boundaries of this reactivity further in a competition experiment (Figure ). Despite an excess of α-iodo silane 30, reactivity was completely selective for α-halo boron activation underpinning the opportunity for chemoselective activation. Taking all results in to consideration, we tentatively propose the following mechanism as operational (Figure ). While the formation of an EDA complex using 2a and 2,6-lutidine is clear by UV/Vis, the large oxidation potentials of pyridine derivatives renders single electron-transfer (SET) unlikely. We propose in this case, EDA or aggregation aids in homolytic cleavage of the weak C-I bond to form the desired α-boryl radical 32 (supported by radical clock) and an iodine radical stabilised by 2,6-lutidine (34). The electron-deficient αboryl radical can then engage styrene to form a benzylic radical 33 (supported by radical clock). Translation of the benzylic radical to the E-isomer product can proceed via two possible mechanisms. Recombination or radical polar cross-over to the benzylic iodide, can allow closed shell elimination via the pyridine derived base.