scholarly journals Control of cerium oxidation state through metal complex secondary structures

2015 ◽  
Vol 6 (12) ◽  
pp. 6925-6934 ◽  
Author(s):  
Jessica R. Levin ◽  
Walter L. Dorfner ◽  
Patrick J. Carroll ◽  
Eric J. Schelter
Keyword(s):  
Alkali Metal ◽  
Metal Complex ◽  
Oxidation State ◽  
Coordination Sphere ◽  
Electronic Structures ◽  
Secondary Structures ◽  
Secondary Coordination Sphere

A series of alkali metal cerium diphenylhydrazido complexes, Mx(py)y[Ce(PhNNPh)4], M = Li, Na, and K, x = 4 (Li and Na) or 5 (K), and y = 4 (Li), 8 (Na), or 7 (K), were synthesized to probe how a secondary coordination sphere would modulate electronic structures at a cerium cation.

scholarly journals Using internal electrostatic fields to manipulate the valence manifolds of copper complexes

2021 ◽  
Author(s):  
Alexander B. Weberg ◽  
Samuel P. McCollom ◽  
Laura M. Thierer ◽  
Michael R. Gau ◽  
Patrick J. Carroll ◽  
...  
Keyword(s):  
Coordination Sphere ◽  
Copper Complexes ◽  
Photophysical Properties ◽  
Redox Potentials ◽  
Electrostatic Effects ◽  
Electrostatic Fields ◽  
Secondary Coordination Sphere

Secondary coordination sphere electrostatic effects tune the valence manifolds of copper centers, impacting molecular geometries, photophysical properties, and redox potentials.

Pyridinediimine Iron Dicarbonyl Complexes with Pendant Lewis Bases and Lewis Acids Located in the Secondary Coordination Sphere

2013 ◽  
Vol 2013 (22-23) ◽  
pp. 4008-4015 ◽  
Author(s):  
Zachary Thammavongsy ◽  
Micah E. LeDoux ◽  
Andrew G. Breuhaus-Alvarez ◽  
Takele Seda ◽  
Lev N. Zakharov ◽  
...  
Keyword(s):  
Coordination Sphere ◽  
Lewis Acids ◽  
Lewis Bases ◽  
Secondary Coordination Sphere

scholarly journals Ligand-Based H2 Transfer with Dihydrazonopyrrole Complexes of Nickel

2020 ◽  
Author(s):  
Andrew McNeece ◽  
Kate Jesse ◽  
Alexander S. Filatov ◽  
Joseph Schneider ◽  
John Anderson
Keyword(s):  
Coordination Sphere ◽  
Computational Analysis ◽  
Metal Center ◽  
Electron Storage ◽  
Precise Control ◽  
Secondary Coordination Sphere ◽  
Proton Donors ◽  
Redox Change

Biology uses precise control over proton, electron, H-atom, or H<sub>2</sub> transfer to mediate challenging reactivity. While synthetic complexes have made incredible strides in replicating secondary coordination electron or proton donors, there are comparatively fewer examples of ligands that can mediate both proton and electron storage. Rarer still are ligands that can store full H<sub>2</sub> equivalents. Here we report a dihydrazonopyrrole Ni complex where an H<sub>2</sub> equivalent can be stored on the ligand periphery without any redox change at the metal center. This ligand-based storage of H<sub>2</sub> can be leveraged for catalytic hydrogenations. Kinetic and computational analysis suggests a rate determining H<sub>2</sub> binding step followed by comparatively facile H–H scission to hydrogenate the ligand. This system is an unusual example where a synthetic system can mimic biology’s ability to mediate H<sub>2</sub> transfer via secondary coordination sphere-based processes.

scholarly journals Synthesis and Characterization of Super Bulky β-Diketiminato Group 1 Metal Complexes

Inorganics ◽  
2021 ◽  
Vol 9 (9) ◽  
pp. 72
Author(s):  
Dafydd D. L. Jones ◽  
Samuel Watts ◽  
Cameron Jones
Keyword(s):  
Nmr Spectroscopy ◽  
Alkali Metal ◽  
Metal Complexes ◽  
Oxidation State ◽  
Synthesis And Characterization ◽  
X Ray Crystallography ◽  
Low Oxidation State ◽  
Bulky Ligand ◽  
Group 1

Sterically bulky β-diketiminate (or Nacnac) ligand systems have recently shown the ability to kinetically stabilize highly reactive low-oxidation state main group complexes. Metal halide precursors to such systems can be formed via salt metathesis reactions involving alkali metal complexes of these large ligand frameworks. Herein, we report the synthesis and characterization of lithium and potassium complexes of the super bulky anionic β-diketiminate ligands, known [TCHPNacnac]− and new [TCHP/DipNacnac]− (ArNacnac = [(ArNCMe)2CH]−) (Ar = 2,4,6-tricyclohexylphenyl (TCHP) or 2,6-diisopropylphenyl (Dip)). The reaction of the proteo-ligands, ArNacnacH, with nBuLi give the lithium etherate compounds, [(TCHPNacnac)Li(OEt2)] and [(TCHP/DipNacnac)Li(OEt2)], which were isolated and characterized by multinuclear NMR spectroscopy and X-ray crystallography. The unsolvated potassium salts, [{K(TCHPNacnac)}2] and [{K(TCHP/DipNacnac)}∞], were also synthesized and characterized in solution by NMR spectroscopy. In the solid state, these highly reactive potassium complexes exhibit differing alkali metal coordination modes, depending on the ligand involved. These group 1 complexes have potential as reagents for the transfer of the bulky ligand fragments to metal halides, and for the subsequent stabilization of low-oxidation state metal complexes.

scholarly journals Beyond the Active Site: Mechanistic Investigations of the Role of the Secondary Coordination Sphere and Beyond on Multi-Electron Electrocatalytic Reactions and Their Relations Between Kinetics and Thermodynamics

2020 ◽  
Author(s):  
Vincent Wang
Keyword(s):  
Thermodynamic Parameters ◽  
Coordination Sphere ◽  
Active Site ◽  
Rate Constants ◽  
Reduction Reaction ◽  
Rate Limiting Step ◽  
Limiting Step ◽  
Secondary Coordination Sphere ◽  
Catalytic Rate ◽  
Rate Limiting

<p>The development of an electrocatalyst with a rapid turnover frequency, low overpotential and long-term stability is highly desired for fuel-forming reactions, such as water splitting and CO<sub>2</sub> reduction. The findings of the scaling relationships between the catalytic rate and thermodynamic parameters over a wide range of electrocatalysts in homogeneous and heterogeneous systems provide useful guidelines and predictions for designing better catalysts for those redox reactions. However, such relationships also suggest that a catalyst with a high catalytic rate is typically associated with a high overpotential for a given reaction. Inspired by enzymes, the introduction of additional interactions through the secondary coordination sphere beyond the active site, such as hydrogen-bonding or electrostatic interactions, have been shown to offer a promising avenue to disrupt these unfavorable relationships. Herein, we further investigate the influence of these cooperative interactions on the faster chemical steps, in addition to the rate-limiting step widely examined before, for molecular electrocatalysts with the structural and electronic modifications designed to facilitate the dioxygen reduction reaction, CO<sub>2</sub> reduction reaction and hydrogen evolving reaction. Based on the electrocatalytic kinetic analysis, the rate constants for faster chemical steps and their correlation with the corresponding thermodynamic parameters are evaluated. The results suggest that the effects of the secondary coordination sphere and beyond on these fuel-forming reactions are not necessarily beneficial for promoting all chemical steps and no apparent relation between rate constants and thermodynamic parameters are found in some cases studied here, which may implicate the design of electrocatalysts in the future. Finally, these analyses demonstrate that the characteristic features for voltammograms and foot-of-the-wave-analysis plots are associated with the specific kinetic phenomenon among these multi-electron electrocatalytic reactions, which provides a useful framework to probe the insights of chemical and electronic modifications on the catalytic steps quantitatively (i.e. kinetic rate constants) and to optimize some of critical steps beyond the rate-limiting step.</p>

Designing the Secondary Coordination Sphere in Small-Molecule Catalysis

Synlett ◽  
2020 ◽  
Author(s):  
Inbal L. Zak ◽  
Santosh C. Gadekar ◽  
Anat Milo
Keyword(s):  
Statistical Analysis ◽  
Coordination Sphere ◽  
Small Molecule ◽  
Active Sites ◽  
Decisive Role ◽  
Hierarchical Arrangement ◽  
Organometallic Catalysis ◽  
Secondary Coordination Sphere

AbstractThe application of secondary-sphere interactions in catalysis was inspired by the hierarchical arrangement of the microenvironment of metalloprotein active sites and has been adopted mainly in organometallic catalysis. The study of such interactions has enabled the deliberate orientation of reaction components, leading to control over reactivity and selectivity by design. Although not as common, such interaction can play a decisive role in organocatalysis. Herein, we present several examples of small-molecule organometallic- and organocatalysis, highlighting the advantages offered by carefully designing the secondary sphere.1 Introduction2 Secondary-Sphere Design in Organometallic Catalysis3 Secondary-Sphere Modification in Organocatalysis4 Using Statistical Analysis to Systematically Tune and Probe Secondary-Sphere Interactions5 Conclusion

scholarly journals Kinetic Study of CO2 Hydration by Small-Molecule Catalysts with A Second Coordination Sphere that Mimic the Effect of the Thr-199 Residue of Carbonic Anhydrase

Biomimetics ◽  
2019 ◽  
Vol 4 (4) ◽  
pp. 66
Author(s):  
Park ◽  
Lee
Keyword(s):  
Hydrogen Bonding ◽  
Carbonic Anhydrase ◽  
Coordination Sphere ◽  
Active Site ◽  
Hydration Reaction ◽  
Ph Titration ◽  
Hydration Rate ◽  
Pka Value ◽  
Secondary Coordination Sphere ◽  
Hydrogen Bonding Network

Zinc complexes were synthesized as catalysts that mimic the ability of carbonic anhydrase (CA) for the CO2 hydration reaction (H2O + CO2 → H+ + HCO3-). For these complexes, a tris(2-pyridylmethyl)amine (TPA) ligand mimicking only the active site, and a 6-((bis(pyridin-2-ylmethyl)amino)methyl)pyridin-2-ol (TPA-OH) ligand mimicking the hydrogen-bonding network of the secondary coordination sphere of CA were used. Potentiometric pH titration was used to determine the deprotonation ability of the Zn complexes, and their pKa values were found to be 8.0 and 6.8, respectively. Stopped-flow spectrophotometry was used to confirm the CO2 hydration rate. The rate constants were measured to be 648.4 and 730.6 M-1s-1, respectively. The low pKa value was attributed to the hydrogen-bonding network of the secondary coordination sphere of the catalyst that mimics the behavior of CA, and this was found to increase the CO2 hydration rate of the catalyst.

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