Anion Capture at the Open Core of a Geometrically Flexible Dicopper(II,II) Macrocycle Complex

Abstract

Multicopper active sites for small molecule activation in materials and enzymatic systems rely on controlled but adaptable coordination spheres about copper clusters for enabling challenging chemical transformations. To translate this constrained flexibility into molecular multicopper complexes, developments are needed in both ligand design for clusters and synthetic strategies for modifying the cluster cores. The present study investigates the chemistry of a class of pyridyldiimine-derived macrocycles with geometrically flexible aliphatic linkers of varying lengths (nPDI2, n = 2, 3). A series of dicopper complexes bound by the nPDI2 ligands are described and found to exhibit improved solubility over their parent analogs due to the incorporation of 4-tBu groups on the pyridyl units and the use of triflate counterions. The ensuing synthetic study investigated methods for introducing various bridging ligands (µ-X; X = F, Cl, Br, N3, NO2, OSiMe3, OH, OTf) between the two copper centers within the macrocycle-supported complexes. Traditional anion metathesis routes were unsuccessful, but the abstraction of bridging halides resulted in “open-core” complexes suitable for capturing various anions. The geometric flexibility of the nPDI2 macrocycles was reflected in the various solid-state geometries, Cu–Cu distances, and relative Cu coordination spheres on variation in the identity of the captured anion.

Reactivity Profile of a Formally Dicobalt(0) Complex Bound by a Redox-Active Macrocycle

“…Taken together, we propose the major species at room temperature to represent an average of three hydride complexes ( A1 , A2 , and A3 ; Scheme ) that bind PMe 3 ligands on the same side of the macrocycle as one another ( cis -phosphines). This configuration was observed crystallographically for A1 , and the geometries for A2 and A3 are proposed based on data for related M 2 (μ-E) complexes bound by the 3 PDI 2 macrocycle. ,− While crystalline samples of A1 equilibrate with A2 , A3 , and B at room temperature, the interconversion between “ A ” and B appears to slow dramatically at lower temperatures. This behavior, along with the methylene 1 H NMR spectral pattern for B , is consistent with an unfolded ligand geometry supporting a linear Co–H–Co core and trans- phosphines .…”

“…This behavior, along with the methylene 1 H NMR spectral pattern for B, is consistent with an unfolded ligand geometry supporting a linear Co−H− Co core and trans-phosphines. 22 We have previously observed the capacity of the constrained geometry of the n PDI 2 framework to enforce unusual bridging ligand configurations; however, in this case, where the bridging ligand is small, the flexibility appears to create varied and dynamic behavior.…”

“…This configuration was observed crystallographically for A1 , and the geometries for A2 and A3 are proposed based on data for related M 2 (μ-E) complexes bound by the 3 PDI 2 macrocycle. ,− While crystalline samples of A1 equilibrate with A2 , A3 , and B at room temperature, the interconversion between “ A ” and B appears to slow dramatically at lower temperatures. This behavior, along with the methylene 1 H NMR spectral pattern for B , is consistent with an unfolded ligand geometry supporting a linear Co–H–Co core and trans- phosphines . We have previously observed the capacity of the constrained geometry of the n PDI 2 framework to enforce unusual bridging ligand configurations; however, in this case, where the bridging ligand is small, the flexibility appears to create varied and dynamic behavior.…”