Synthesis and Characterization of a Family of Systematically Varied Tris(2-pyridyl)methoxymethane Ligands:  Copper(I) and Copper(II) Complexes

Abstract

An efficient modular protocol for synthesizing a series of facial-capping tris-pyridyl ligands, based on the tris(2-pyridyl)methoxymethane backbone, has been developed which allows for systematic variations of the steric demands at the periphery of the ligand. The coordination chemistry of one such family of ligands that positions 0-->3 methoxy groups at the periphery with Cu(I) and Cu(II) is presented. The ligands are tris(2-pyridyl)methoxymethane (L(0)()), bis(2-pyridyl)(2-(6-methoxy)pyridyl)methoxymethane (L(1)()), bis(2-(6-methoxy)pyridyl)(2-pyridyl)methoxymethane (L(2)()), and tris(2-(6-methoxy)pyridyl)methoxymethane (L(3)()). The ligand exchange behavior and, to a lesser extent, the structures of the these complexes vary dramatically given the small perturbation of introducing methoxy substituents. Two distinct coordination modes are observed for the Cu(I) complexes, both in solution and the solid state. One is a pseudo-tetrahedral coordination comprised of the facial-capping, tris-pyridyl ligand and a monodentate ligand such as CH(3)CN, CO, or PPh(3). The other structural type is also a pseudo-tetrahedral Cu(I) monomer formed by two tris-pyridyl ligands coordinated in a bidentate manner with preferable binding by the nonmethoxy pyridyl subunits. With the exception of the most sterically hindered ligand, L(3)(), which only displays monoligation to Cu(I), all ligands form both types of Cu(I) complexes, and the formation is controlled by stoichiometry. Both competitive ligand binding experiments and ligand substitution with CO(g) show that the [(L(0)())(2)Cu](+) and [(L(1)())(2)Cu](+) complexes have nearly equivalent stability in aprotic solvent, and greater stability than the [(L(2)())(2)Cu](+) complex due to inclusion of bulky methoxypyridines into the Cu(I) coordination sphere. The Cu(II) complexes of the ligand series generate "bis-tris", [(L(0)()(-->)(3)())(2)Cu](2+), complexes, with the Cu(II) ligated in a tetragonally distorted octahedral coordination environment. The degree of bulk at the ligand periphery dictates the Cu(II)-ligand bond lengths both in solution and the solid state. In these complexes, the bulky pyridyl ring prefers to bind in the axial position. For the most sterically encumbered ligand, L(3)(), the bisligated Cu(II) complex is moisture sensitive, reacting to give a monoligated, tris-aqua species, [L(3)()Cu(H(2)O)(3)](2+).

Biomimetic Copper(I)-CO Complexes: A Structural and Dynamic Study of a Calix[6]arene-Based Supramolecular System

“…Again, n CO increases for a chelating system, such as tris(pyridyl)methoxymethane tripods (2093 ± 2102 cm À1 ). [61] With the calixarene-based ligand, the expected increase of 40 cm À1 relative to 2-picoline, as a result of steric constraint, would give values (> 2125 cm À1 ) that could only account for a very weak CuÀ(CO) bond.…”

Combined Studies on the Surface Coordination Chemistry of Benzotriazole at the Copper Electrode by Direct Electrochemical Synthesis and Surface‐Enhanced Raman Spectroscopy

“…The Cu 5 (BTA) 5 -(PPh 3 ) 4 Cl complex crystallizes as a pentanuclear complex, and its molecular structure is illustrated in Figure 2. Because the benzotriazolate ion has a charge of -1, the pentacopper complex is a mixed-valent material that contains [55] In addition to Cu1 (or Cu2) being coordinated to two nitrogen atoms in two different For the Cu I ion bridged by the axial benzotriazolate anion and the chloride ion, the average distance between the surrounding Cu I ion is 5.315 Å and the distance increases to about 5.886 Å for the Cu I ion bridged by the equatorial benzotriazolate anions, whereas the average distance of about 3.500 Å between the surrounding Cu I and central Cu II ions is much shorter than the above-mentioned value. The structure of the complex bears resemblance to that of Cu 5 (BTA) 6 (t-C 4 H 9 NC) 4 , [44] where the latter contains an extra BTA -group instead of the bridging chloride ion.…”

Toward an Allosteric Metallated Container

“…[8,11] Tris(6-methoxypyrid-2-yl)methanol, a ligand related to 4, was shown to form a distorted octahedral 2:1 complex with Cu 2+ (crystal structure), again with tridentate N,N,N-coordination of both ligands ( Figure 3). [12] Spectrophotometric titration of 4 (50 µ) with ZnSO 4 in water/methanol (1:1) was followed by relatively small absorbance changes in the UV region of the spectrum and confirms smooth formation of a complex [Zn (4) 2 ] 2+ by linear absorbance increase at 280 nm for 0-0.5 equiv. of Zn …”