Metallathiacrown Ethers: Synthesis and Characterization of Transition-Metal Complexes Containing α,ω-Bis(phosphite)-Polythioether Ligands and an Evaluation of Their Soft Metal Binding Capabilities
作者:Justin R. Martin、Aaron L. Lucius、Gary M. Gray
DOI:10.1021/acs.organomet.5b00693
日期:2015.9.28
The metallathiacrown ethers cis-Mo(CO)(4)2,2'-(C12H8O2)PO-(CH2CH2S)(n)CH2CH2OP(2,2'-(O2H8C12))} (n = 2, 3) and cis-Mo(CO)(4)2,2'-(C12H8O2) POCH2CH2S-1-(C6H4)-2-SCH2CH2OP (2,2'-(O2H8C12))} have been prepared as soft metal selective molecular receptors. Multinudear NMR spectroscopy and X-ray crystallography have been used to show that byproducts formed during the syntheses of the metallathiacrown ethers cis-Mo(CO)(4)2,2'-(C12H8O2)PO-(CH2CH2S)(n)CH2CH2OP(2,2'-(O2H8C12))} (n = 2, 3) are homobinudear complexes with cis-Mo(CO)(4)(P-donor)(S-donor) centers. The abilities of the metallathiacrown ethers to bind PdC12 and PtC12 have been assessed using P-31H-1} NMR spectroscopy and X-ray crystallography. The complexes showed null results with PtCl2; however, the PtCl2 experiments showed that the complexes cis-Mo(CO)(4)2,2'-(C12H8O2)PO-(CH2CH2S)(n)CH2CH2OP(2,2'-(O2H8C12))} (n = 2, 3) formed heterobinudear cis,cis-Mo(CO)(4)2,2'-(C12H8O2)PO-(CH2CH2S)(n)CH2CH2OP(2,2'-(O2H8C12))} (n = 2, 3) complexes. The P-31H-1} NMR spectra of these complexes suggest a cis-PtS2Cl2 coordination environment in each, which leads to asymmetric binding in the latter complex. Binding of HgCl2 by the complexes cis-Mo(CO)(4)2,2'-(C12H8O2)PO-(CH2CH2S)(n)CH2CH2OP(2,2'-(O2H8C12))} (n = 2, 3) has been studied using (31P)H-1} NMR spectroscopy. Each complex was titrated with HgCl2, and the quantitative shifts in the P-31H-1} NMR spectra were fit to a binding mechanism. The n = 2 metallathiacrown ether binds HgC12 to form a 1:1 complex with Ka = 12.0(0.2) M-1. In contrast, interaction of HgCl2 with the n = 3 metallathiacrown ether results in isomerization to the trans complex, and HgCl2 binds to both isomers. A model has been adapted to fit the titration data of this complex and to extract equilibrium constants for each step in the cycle: the cis-trans equilibrium of the free,K-free (0.570 (0.004)), and bound, K-bond (0.16 (0.03)), metallathiacrown ethers, as well as the association binding constants for the cis, k(cis), ([4.1(0.3)] X 10(2)M(-1)) and trans, 'cans ([1.1( 0.2)] X 10(2) M-1), metallathiacrown ethers. The equilibrium constants demonstrate that the cis metallathiacrown ether binds more strongly to the HgCl2 than does the trans metallathiacrown ether and that the cis-trans equilibrium favors the cis metallathiacrown ether.