Supramolecular Chemistry of BrettPhos and BrettPhos Oxide: Breakup of Isostructurality via Order-Disorder Phase Transitions

The metal binding phosphine ligand BrettPhos (BP) is widely used in palladium catalyzed C-N coupling reactions. However, molecular conformations and supramolecular chemistry of this well-known molecule and its readily oxidized form - BrettPhos oxide (BPO) - remain unexplored. Here, we discuss the crystal structures and structural interrelationships of BP, BPO, and four solvatomorphs of BPO. Comparison of molecular conformations and crystal packing along with a quantitative analysis of intermolecular interactions bring out the isostructurality of BP and BPO. The electrostatic, spatial, and hydrogen bonding features of this isostructural pair (BP, BPO) are discussed in detail with the quantitative tool of energy framework analysis. While there are no strong hydrogen bonds present in both the structures, the molecular pairs linked by C-H···O hydrogen bonds were noted to exhibit interaction energies as high as ∼ -73 kJ/mol with a significant dispersion contribution. The competitive roles of shape complementarity and electrostatic complementarity in the crystal packing of these molecules have also been discussed. Due to the presence of the P=O group, BPO exhibited formation of hydrogen bond assisted solvatomorphs, which are dominated by electrostatic interactions. Temperature dependent phase transitions observed in these crystals reveal distinct preferences of BP and BPO for their respective low temperature structures, resulting in the breakup of isostructurality observed at room temperature.