Small Substituents Make Large Differences: Aminopyrimidinyl Phosphanes Undergoing C-H Activation

Palladium complexes synthesised from (C6H5CN)2PdCl2 and (2‐aminopyrimidinyl)phosphanes show different coordination modes depending on the nature of the amino substituent attached to the pyrimidine ring. Whereas P,N‐coordination is observed for primary and secondary amino groups, tertiary amino groups lead to C–H activation at the pyrimidine ring. These differences result in strongly different catalytic activities in the Suzuki–Miyaura coupling reaction. The palladium complexes were characterised spectroscopically and bymeans of X‐ray structural analysis. DFT calculations were carried out to differ between the electronic and steric effects that are responsible for their behaviour in catalysis. NH2 versus NR2: Subtle steric requirements determine the reactivity of palladium complexes bearing aminopyrimidinyl phosphane ligands and their performance as catalysts in Suzuki–Miyaura coupling reactions.