A change in ligand hapticity promotes Lewis base dissociation

We report a phosphine 1-azaallyl ligand L2 [2-(diphenylphosphino)-2'-(3,3-dimethyl-1-azaallyl)-1,1'-biphenyl], which enables reversible coordination of Lewis bases through changes in ligand hapticity. In the palladium methyl complex [Pd(CH₃)(L2)], L2 adopts a κ¹-P;η³-NCC coordination mode. Pyridine binding induces reorganization to a κ²-PN mode, while reversion to the κ¹-P;η³-NCC mode facilitates pyridine dissociation. These interconversions were established by ¹³C{¹H} and ¹H-³¹P HMBC NMR spectroscopy, X-ray absorption spectroscopy, and density-functional theory calculations. The results highlight a ligand-controlled mechanism for reversible substrate coordination based on tunable binding modes.