title: Secondary Sphere Hydrogen Bonding in Monocopper Complexes of Potentially Dinucleating Bis(carboxamide) Ligands.
abstract: Reaction of a macrocyclic ligand precursor comprising two bis(carboxamido)pyridine units (H4L4) connected by ethylene linkers with NMe4OH and CuX2(X = Cl, OAc, or OTf) yielded monocopper complexes [NMe4][(H2L4)Cu(X)] (X = Cl (3), OAc (4), or OH (5)), in contrast to previous work using a related ligand with ortho-phenylene linkers wherein dicopper compounds were isolated. X-ray structures of the complexes revealed hydrogen bonding from the free carboxamide N-H groups in the doubly protonated form of the ligand (H2L4-) to the monodentate fourth ligand coordinated to the Cu(II) ion. Similar secondary sphere hydrogen bonding interactions were identified in multinuclear compounds [NMe4]2[((H2L4)Cu)n(CO3)] (n = 2 or 3) that were isolated from exposure of5to air. Cyclic voltammetry revealed oxidations of3and5at potentials ~300 mV higher than analogous monocopper complexes of bis(arylcarboxamido)pyridine ligands which lack the intramolecular hydrogen bonds, consistent with removal of electron density from the metal center by the hydrogen bonding array. Another ligand variant (H4L5) with ortho-phenylene linkers and only one bis(carboxamido)pyridine moiety yielded monocopper complexes [NMe4][(H2L5)Cu(OAc)] • DMF (8) and [NMe4][(H2L5)CuCl)] • CH3CN (9), but the X-ray structures revealed a different hydrogen bonding arrangement to the solvate molecules. Nonetheless, a high redox potential for9was observed, consistent with intramolecular hydrogen bonding interactions in solution.
authors.affiliation: Department of Chemistry and Center for Metals and Biocatalysis, University of Minnesota, 207 Pleasant St. SE, Minneapolis, Minnesota 55455.
authors.forename: Benjamin D
authors.initials: BD
authors.lastname: Neisen
authors.affiliation: Department of Chemistry and Center for Metals and Biocatalysis, University of Minnesota, 207 Pleasant St. SE, Minneapolis, Minnesota 55455.
authors.forename: Pavlo
authors.initials: P
authors.lastname: Solntsev
authors.affiliation: Department of Chemistry and Center for Metals and Biocatalysis, University of Minnesota, 207 Pleasant St. SE, Minneapolis, Minnesota 55455.
authors.forename: Mohammad R
authors.initials: MR
authors.lastname: Halvagar
authors.affiliation: Department of Chemistry and Center for Metals and Biocatalysis, University of Minnesota, 207 Pleasant St. SE, Minneapolis, Minnesota 55455.
authors.forename: William B
authors.initials: WB
authors.lastname: Tolman
keywords: copper; hydrogen bonding; macrocycles; redox