New Tripodal Tridentate Ligands with {NS_2} Donor Set and a Backbone Hydroxo Anchor, and Their Copper(I) and Copper(II) Complexes

摘要

A series of five tripodal tridentate ligands (HO)C[(CH_2)_xNR_2](CH_2SR)_2 (HL~1-HL~5) with {NS_2} donor set has been synthesized via an efficient two-step protocol starting from 1,3-dichloroacetone. All five ligands bear a backbone hydroxo group that is available for further functionalization. The five ligands differ by the type of N-donor (NR_2 = pyridine- 2-yl or imidazol-2-yl), by the spacer between the backbone-C and the N-donor heterocycle (x = 0, 1), and with respect to their topology, viz. whether two thioether-S are part of a cyclic 1,4-dithiacycloheptane fragment or not (R = Et or -CH_2-). Copper(I) and copper(II) complexes have been prepared and studied in solution (ESI-MS, UV/Vis, and NMR spectroscopy in case of the copper(I) complexes) as well as in solid state (single-crystal X-ray diffraction of [(HL~2)Cu(MeCN)]n(OTf)n, [(HL~3)Cu(MeCN)](PF_6) and [(HL~5)Cu(MeCN)]_n(PF_6)_n as well as [(L_4)_2Cu_3(MeCN)_3](PF_6)_2 and [(L_2)_2Cu_2Cl_2], [(L_3)_4Cu_4](OTf)_4, and [(L_4)_2Cu_2(MeCN)_2](OTf)_2; SQUID magnetometry of [(L_2)_2Cu_2Cl_2] and [(L_3)_4Cu_4](OTf)_4,). The ligand scaffolds show ambidentate character depending on the metal ion oxidation state. All copper(I) ions are found in distorted tetrahedral environment comprising an {NS_2} ligation of the tridentate ligand as well as an exogenous MeCN; either mononuclear complex cations or 1D polymeric structures are found. In case of all copper(II) complexes the backbone-alcohol group is deprotonated and bridges two metal ions, giving dinuclear or tetranuclear species with antiferromagnetic coupling. The Cu-S bond lengths are found to vary significantly, which reflects the plasticity of the Cu-thioether bond known from metalloproteins and synthetic analogs.