Exocyclic Coordination of Thiamacrocycles Leading to cis- and trans-Palladium(II) Complexes and a Tripalladium(II) Complex Incorporating Acetimidic Anhydride
journal contributionposted on 2020-10-13, 17:10 authored by Seulgi Kim, Hyunsoo Ryu, Jack K. Clegg, Leonard F. Lindoy, Shim Sung Lee
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.