The original Pd pincer complex synthesis revisited: low-temperature C-H bond activation masked by oligomerisation

Cyclopalladation to form palladium pincer complexes is typically performed at elevated temperatures. Here we show that diphosphine pincer ligands with aromatic backbones cyclometallate to the corresponding palladium pincer complexes at room temperature as well as at -40 °C. Although the reaction in itself is very fast, the conversion is hampered by the formation of oligomeric coordination compounds, which only slowly transform into pincer complexes and explains the need for using high temperatures. The C-H activation event is almost barrierless and not rate-limiting in the cyclometallation; the results are further supported by DFT studies.