Differentiation of Oxygen Atom Chirality in Copper(II) Complexes with Dipicolylamine‐Derived Ligands

Abstract

The ether coordination of the oxygen atom to the copper(II) center supported by dipicolylamine (DPA)‐derived ligands,N‐[2‐(2‐pyridylmethyloxy)ethyl]‐N,N‐bis(2‐pyridylmethyl)amine (LPy), N‐[2‐(2‐quinolylmethyloxy)ethyl]‐N,N‐bis(2‐pyridylmethyl)amine (LQ), N‐[3‐(2‐pyridylmethyloxy)‐1‐propyl]‐N,N‐bis(2‐pyridylmethyl)amine (L′Py), N‐{2‐[1‐(2‐pyridyl)ethyloxy]ethyl}‐N,N‐bis(2‐pyridylmethyl)amine (LPy*1), N‐[2‐(2‐pyridylmethyloxy)‐1‐propyl]‐N,N‐bis(2‐pyridylmethyl)amine (LPy*2), and N‐[2‐(carboxymethyloxy)ethyl]‐N,N‐bis(2‐pyridylmethyl)amine (HLCOO), have been examined. The factors that facilitate the coordination of the ether oxygen atom of these ligands to the copper center and the control of chirality around the copper‐coordinated oxygen atom are discussed. The copper center exhibits a pentacoordinate geometry with these ligands, as evidenced by X‐ray crystallography. The steric effect of the quinoline ring in the LQ complex prevents the coordination of a perchlorate anion to the copper center, which affords the pentacoordinate divalent complex with a shorter copper–oxygen bond than that for the corresponding pyridine ligand (LPy). The six‐membered chelate in the L′Py complex also exhibits a shorter Cu–O distance. The conformation of the oxygen atom of the LPy complex is unstable because of fast lone pair inversion, but this inversion is prevented for the complexes with chiral ligands, LPy*1 and LPy*2. Upon chelation to the metal center, the HLCOO ligand forms a pentacoodinate monomer complex that further affords a 1‐D polymer structure. With respect to the oxygen chirality, the water content of the solvent governs the formation of either a homochiral polymer (R‐R‐R‐R‐ or S‐S‐S‐S‐) or an alternative chirality polymer (R‐S‐R‐S‐). In this case, the isomers with respect to the oxygen chirality were separated and characterized.

Synthesis, Reactions, and Structures of Heterocycle-Tethered Boranes and Their Precursors

“…Analysis of the two molecules present in the packing diagram revealed that one has RR and the other has SS configuration, as shown in Figure . Although three-coordinate chiral oxygen molecules have been reported, , as far as we know, four-coordinate oxygen chirality has not been reported. The molecule has one approximate C 2 axis passing through two lithium atoms.…”

“…Analysis of the two molecules present in the packing diagram revealed that one has RR and the other has SS configuration, as shown in Figure 5. Although three-coordinate chiral oxygen molecules have been reported, 31,32 as far as we know, four-coordinate oxygen 6) Å is considerably lower than 2.736(11) Å found in complex 3; however, it remains longer than those in several reported complexes. 23−25 The X-ray structure of complex 6 (see SI, Figure S61) revealed the six-membered chelate ring formed by the pyrazolylmethyl(methoxy)borate anion with the lithium atom containing two DMAP molecules.…”

Evaluation of oxygen-containing pentadentate ligands with pyridine/quinoline/isoquinoline binding sites via the structural and electrochemical properties of mononuclear copper(ii) complexes

“…Tables S1–S2† shows a summary of the crystallographic parameters and diffraction conditions. Interatomic distances and angles around the metal centre are listed in Tables 1 and S3,† respectively, in which two previously reported complexes ( PPP-Cu and PPQ-Cu ) 57 were included.…”

Control of stereogenic oxygen in a helically chiral oxonium ion

“…The only empirical measurement of the inversion barrier for a trivalent oxygen compound is for the epoxide-derived oxonium salt 2 that has a barrier to inversion of 42 kJ mol −1 , which is substantially below that required to maintain configurational stability at ambient temperature 7 . Consequently, there are no examples of the isolation of enantioenriched oxonium ions in which the oxygen atom 17,18 is the sole stereogenic centre (Fig. 1b).…”