Exocyclic Coordination of Thiamacrocycles Leading to cis- and trans-Palladium(II) Complexes and a Tripalladium(II) Complex Incorporating Acetimidic Anhydride.

Preferential formation of cis- or trans-palladium(II) complexes controlled via the exocyclic binding sites embedded in dithiamacrocycles (L1 = -S(CH2)2S-; L2 = -S(CH2)2O(CH2)2S-) is reported. From the reaction with K2PdCl4, the shorter sulfur-to-sulfur separation in L1 preferentially leads to the formation of cis-[Pd(L1)Cl2] (1), while L2, incorporating a larger sulfur-to-sulfur separation, coordinates in a trans fashion to form a cyclic dimer, trans-[Pd2(L2)2Cl4] (2). The observed results illustrate the possibility for the controlled formation of cis/trans square-planar complexes through binding-site design. When palladium(II) acetate was substituted for K2PdCl4 in the above reaction, L1 gave no product, while L2 resulted in the formation of a unique tripalladium(II) complex, [Pd3(L2)(CH3C(═N)OC(═N)CH3)(CH3COO)4] (3), in which three PdII atoms are linked by acetimidic anhydride, CH3C(═N)OC(═N)CH3, derived from the acetonitrile solvent employed. In the 1H NMR spectrum for 3, specific methylene signals for methylene protons adjacent to S donors exhibit large complexation-induced splitting of the geminal proton signals into axial and equatorial proton peaks, thus indicating magnetically nonequivalent geminal protons that reflect the restricted conformation of the metallabicycle.