Exocyclic Coordination of Thiamacrocycles Leading
to cis- and trans-Palladium(II)
Complexes and a Tripalladium(II) Complex Incorporating Acetimidic
Anhydride
posted on 2020-10-13, 17:10authored bySeulgi 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.