Reversible Ligand Pairing and Sorting Processes Leading to Heteroligated Palladium(II) Complexes with Hemilabile...

Halide-induced ligand pairing and sorting processes have been observed in the context of Pd(II) complexes with hemilabile P,S and P,O ligands. Mixing of the ligands Ph₂PCH₂CH₂SMe (7) and Ph₂PCH₂CH₂SPh (8) with a Pd(II) precursor in CH₂Cl₂ results in a mixture of [(7)₂ClPd]Cl, [(8)₂Cl₂Pd], and [(7)(8)ClPd]Cl complexes at 20 °C. This equilibrium can be driven toward the heteroligated structure [(7)(8)ClPd]Cl by (1) cooling the mixture or (2) precipitation with hexanes, leading to the exclusive formation of semiopen heteroligated complex cis-[κ ²-(7)-κ ¹-(8)ClPd]Cl (9a), as confirmed by a single-crystal X-ray diffraction study and solid state CPMAS ³¹P{¹H} NMR spectroscopy. Dissolution of 9a in CH₂Cl₂ leads to the original mixture of complexes, which illustrates the reversible nature of this ligand pairing and sorting process. Similar processes occur when a combination of P,S and P,O ligands is used. The semiopen heteroligated complexes can be chemically manipulated in a reversible fashion to form closed complexes, allowing for control of the relative position and flexibility between neighboring substituents in these "tweezer"-like structures. Control experiments suggest these ligand sorting and pairing processes occur via a halide-induced ligand rearrangement (HILR) reaction.