To steer the GA towards synthetically accessible ligands, the Gaussian score modifier suggested by Gao and Coley is used together with the synthetic accessibility scoring function developed by Ertl and Schuffenhauer . Each catalyst consists of 3 anionic and either 1 or 2 neutral ligands. Thus, the ligands will have different SA scores. The SA is evaluated in two steps. First as the average of the individual SA score for all ligands. Anionic ligands were neutralized before calculating the SA score. Secondly, an additional Gaussian modifier was applied to the average SA score. This modifier decreases impact of the SA on the final score by squeezing the upper range of SA scores together. The idea was to diminish the impact of the SA score for catalysts that already had average SA scores above 0.5. This was done to prevent ligands with non-ideal SA scores at first, from being quickly neglected without any chance of improving through crossover. See Figure in the SI for further details.