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

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 PhPCHCHSMe () and PhPCHCHSPh () with a Pd(II) precursor in CHCl results in a mixture of [()ClPd]Cl, [()ClPd], and [()()ClPd]Cl complexes at 20 °C. This equilibrium can be driven toward the heteroligated structure [()()ClPd]Cl by (1) cooling the mixture or (2) precipitation with hexanes, leading to the exclusive formation of semiopen heteroligated complex -[ -()- -()ClPd]Cl (), as confirmed by a single-crystal X-ray diffraction study and solid state CPMAS P{H} NMR spectroscopy. Dissolution of in CHCl 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.