Interconversion between cyclodimer and cyclotrimer: Synthesis and characterization of cyclo-[Pd(II)Cl2(N–N)] complexes

The reaction of (COD)PdCl2 (COD = 1,5-cyclooctadiene) with (3-Py)2SiR1R2 (3-Py = 3-pyridyl; R1 = Ph, R2 = Ph (m-pdps); R1 = Ph, R2 = Me (m-pmps)) in acetone affords single crystals consisting of cyclodimers, [PdCl2((3-Py)2SiR1R2)]2, whereas the same reaction in a mixture of dichloromethane and ethanol yields amorphous spheres consisting of cyclotrimers, [PdCl2((3-Py)2SiR1R2)]3. In a boiling chloroform solution, the cyclodimers are completely converted to cyclotrimers. These cyclotrimers, in the 10−60 °C range, are partly returned to cyclodimers. By contrast, the reaction of (COD)PdCl2 with (3-Py)2SiR1R2 (R1 = Bu, R2 = Me (m-pbms); R1 = dodecyl, R2 = Me (m-pddms)) yields amorphous spheres consisting of cyclotrimers irrespective of solvents. Both [PdCl2(m-pbms)]3 and [PdCl2(m-pddms)]3 are initially cyclotrimers in chloroform, but they exist as a mixture of cyclodimers and cyclotrimers in solution in the 10−60 °C range. The metallacycles tend to form cyclodimers in the order m-pdps > m-pmps > m-pbms > m-pddms. The equilibrium between cyclodimers and the cyclotrimers is sensitive to solvent, temperature, and concentration as well as molecular structure.