made according to the nature of the coupling partner and substrate (as depicted Fig. ). All reactions of the same coupling partner category were held-out (e.g. boronic derivatives, see Fig. ). Models were trained on the rest of the dataset, and used to predict the yields of the held-out reactions (Fig. -Coupling Partner Hold-out). Predictive performance reported for these experiments indicates whether the model is able to predict yields on coupling reactions using a different category of partners than the reactions of the training set. Again, the models fail to extrapolate to new coupling partners categories.