We then decided to evaluate the environmental impact of our procedure via comparison with an analogous iridium-catalysed process. A 30 mmol scale-up of the nickel/iridium catalysed procedure initially reported by MacMillan was reported by chemists from Bayer AG Pharmaceuticals in 2020, using an immersionwell batch-reactor. We calculated the Total Carbon Release (TCR), a metric developed by Novartis to assess the environmental impact of chemical processes, for the two procedures, providing a breakdown of the contribution from solvent, reagents, and photocatalyst (Scheme 4B). Whilst the TCR (kgCO2eq/kg) we calculated from solvent and reagents was approximately equal for both procedures, the contribution from the photocatalyst differs greatly. In the case of iridium, the contribution is 491 kgCO2eq/kg, accounting for over 50% of the TCR of the entire process. In contrast, the contribution from gCN accounts for <1% of the TCR of the synthesis, and results in a value of <50% of that of the iridium-based process.