A Family of Tri- and Dimetallic Pyridine Dicarboxamide Cryptates: Unusual O,N,O-Coordination and Facile Access to Secondary Coordination Sphere Hydrogen Bonding Interactions

Abstract

A series of tri- and dimetallic metal complexes of pyridine dicarboxamide cryptates are reported in which changes to the base and metal source result in diverse structure types. Addition of strong bases, such as KH or KN(SiMe3)2, followed by divalent metal halides allows direct access to trinuclear complexes in which each metal center is coordinated by a dianionic N,N,N-chelate of each arm. These complexes bind a guest K(+) cation within the central cavity in a trigonal planar coordination environment. Minor changes to the solvent and equivalents of base used in the syntheses of the triiron(II) and tricobalt(II) complexes affords two trinuclear clusters with atypical O,N,O-coordination by each pyridine dicarboxamide arm; the amide carbonyl O atoms are oriented toward the interior of the cavity to coordinate to each metal center. Finally, varying the base enables the selective synthesis of dinuclear nickel(II) and copper(II) complexes in which one pyridine dicarboxamide arm remains protonated. These amide protons are at one end of a hydrogen bonding network that extends throughout the internal cavity and terminates at a metal bound hydroxide, carbonate, or bicarbonate donor. In the dinickel complex, the bicarbonate cannot be liberated as CO2 either thermally or upon sparging with N2, which differs from previously reported monometallic complexes. The carbonate or bicarbonate ligands likely arise from sequestration of atmospheric CO2 based on the observed reaction of the di(hydroxonickel) analog.

Aldehyde Deformylation and Catalytic C–H Activation Resulting from a Shared Cobalt(II) Precursor

“…Unlike the hydrocarbon oxidation reactions, the Ph 3 P reactions were followed by 1 H NMR. As has been found for other systems, the catalyst-free reaction between PhIO and Ph 3 P did not yield any Ph 3 PO …”

“…As has been found for other systems, the catalyst-free reaction between PhIO and Ph 3 P did not yield any Ph 3 PO. 64…”

Alkane Oxidation: Methane Monooxygenases, Related Enzymes, and Their Biomimetics

“…This conclusion was supported by EPR analysis of the oxygenated complexes, which showed the signal for a mononuclear Cu­(II) center and the remaining two Cu­(II) centers linked by hydroxo groups. − Magnetic studies revealed a ferromagnetically coupled Cu­(II)­Cu­(II) center along with an isolated Cu­(II) in these complexes . Although these tricopper complexes do not typically support hydrocarbon oxidation, they represent a popular approach to the problem, and ligand-assisted formation of trinuclear complexes has been reported for other metal ions such as manganese, iron, cobalt, and zinc, as well. − …”

Thermally Persistent High-Spin Ground States in Octahedral Iron Clusters

“…Previously, well-defined polynuclear clusters could be obtained from dimensional reduction of 3D-lattices. − Unfortunately, examples of dimensional reduction are limited in number, and to date, most current cluster syntheses rely on self-assembly reactions that lack control of the resulting cluster constitution, geometry, and local metal coordination environments. − Thus, reliable methods to assemble polynuclear clusters are required to rigorously undertake electronic structure evaluation of mixed valent clusters. Our lab and others − have reported the synthesis of clusters with varying nuclearity (three metals and higher) templated within a polynucleating ligand architecture to predispose the metal ions to bind in a specific manner to form the polynuclear aggregate. The resulting clusters have been utilized to explore the nature of the metal–metal interactions by varying auxiliary ligand coordination to the polynuclear system, analyzing the effect of distance between the metals to develop magneto-structural correlations, and assessing electronic structure perturbations as a function of cluster redox level. − …”