Quantitative Evaluation of Lewis Acidity of Metal Ions with Different Ligands and Counterions in Relation to the Promoting Effects of Lewis Acids on Electron Transfer Reduction of Oxygen

2003 ◽  
Vol 68 (12) ◽  
pp. 4720-4726 ◽  
Author(s):  
Kei Ohkubo ◽  
Saija C. Menon ◽  
Akihiro Orita ◽  
Junzo Otera ◽  
Shunichi Fukuzumi
Keyword(s):  
Electron Transfer ◽  
Metal Ions ◽  
Quantitative Evaluation ◽  
Lewis Acids ◽  
Lewis Acidity

scholarly journals Revealing the Influence of Secondary Metals on Redox-Active Palladium Complexes

2022 ◽  
Author(s):  
Riddhi Golwankar ◽  
Amit Kumar ◽  
Victor Day ◽  
James Blakemore
Keyword(s):  
Electron Transfer ◽  
Metal Ions ◽  
Lewis Acids ◽  
Reorganization Energy ◽  
Palladium Complexes ◽  
Lewis Acidity ◽  
X Ray Diffraction ◽  
Isolation And Characterization ◽  
Redox Active ◽  
Energy Penalty

Incorporation of redox-inactive metals into redox-active complexes and catalysts attracts attention for engendering new reactivity modes, but this strategy has not been extensively investigated beyond the first-row of the transition metals. Here, the isolation and characterization of the first series of heterobimetallic complexes of palladium with mono-, di-, and tri-valent redox-inactive metal ions are reported. A Reinhoudt-type heteroditopic ligand with a salen-derived [N2,O2] binding site for Pd and a crown-ether-derived [O6] site has been used to prepare isolable adducts of the Lewis acidic redox-inactive metal ions (Mn+). Comprehensive data from single-crystal X-ray diffraction analysis reveal distinctive trends in the structural properties of the heterobimetallic species, including an uncommon dependence of the Pd•••M distance on Lewis acidity. The reorganization energy associated with reduction of the heterobimetallic species is strongly modulated by Lewis acidity, with the slowest heterogeneous electron transfer kinetics associated with the strongest incorporated Lewis acids. This hitherto unexplored reorganization energy penalty for electron transfer contrasts with prior thermodynamic studies, revealing that kinetic parameters should be considered in studies of reactivity involving heterobimetallic species.

Molecular assemblies based on strong axial coordination in metal complexes of saddle-distorted dodecaphenylporphyrins

2015 ◽  
Vol 19 (01-03) ◽  
pp. 32-44 ◽  
Author(s):  
Tomoya Ishizuka ◽  
Shunichi Fukuzumi ◽  
Takahiko Kojima
Keyword(s):  
Electron Transfer ◽  
Metal Ions ◽  
Metal Complexes ◽  
Photoinduced Electron Transfer ◽  
Oxidation Potential ◽  
Metal Center ◽  
Lewis Acidity ◽  
Central Metal ◽  
Axial Coordination ◽  
Keggin Type

In this mini-review, we have highlighted our works on metal complexes having saddle-distorted dodecaphenylporphyrin (DPP) and its derivative as ligands in the light of enhancement of the Lewis acidity of a metal center coordinated by the porphyrin. The important point through this mini-review is ill-overlap of the out-of-plane lone pairs of pyrrole nitrogen atoms with σ-orbitals of the metal center bound to the saddle-distorted porphyrin core. The enhanced Lewis acidity of the central metal ions enabled us to construct stable molecular complexes through axial coordination using metal–DPP (M(DPP)) moieties ( M = Mo V or Sn IV ) and molecular or ionic entities with Lewis-basic coordination sites, including Keggin-type polyoxometallates (POM), which are known to have weak Lewis basicity and thus hard to coordinate to metal ions. A discrete 1:2 complex with a Ru -substituted POM performs catalytic substrate oxidation reactions in organic solvents. A 1:1 complex between Sn IV ( DPP ) and a Keggin-type POM exhibited photoinduced electron transfer, in which the Sn IV ( DPP ) moiety acts as an electron donor and the POM as an electron acceptor. Besides POM, other electron acceptors, including μ3-oxo trinuclear Ru III clusters and anthraquinone, having carboxyl groups as a linker unit also formed stable complexes with DPP-metal complexes as axial ligands to perform photoinduced electron transfer. Successful photoreactions of the M(DPP)-acceptor complexes are mainly enabled by the enhanced Lewis acidity of the DPP-metal complexes for the stabilization of the assemblies and also by lowering the oxidation potential of the porphyrin ligand to gain larger driving force of electron transfer to form an electron-transfer state with avoiding intersystem crossing. The stability and photochemical behavior are in sharp contrast to those for metal complexes with planar porphyrins as ligands.

Quantitative Evaluation of Lewis Acidity of Organotin Compounds and the Catalytic Reactivity in Electron Transfer

2001 ◽  
Vol 30 (10) ◽  
pp. 978-979 ◽  
Author(s):  
Kei Ohkubo ◽  
Tomoyoshi Suenobu ◽  
Hiroshi Imahori ◽  
Akihiro Orita ◽  
Junzo Otera ◽  
...  
Keyword(s):  
Electron Transfer ◽  
Quantitative Evaluation ◽  
Organotin Compounds ◽  
Lewis Acidity ◽  
Catalytic Reactivity

scholarly journals Promotion and Tuning of the Electrochemical Reduction of Hetero- and Homobimetallic Zinc Complexes

2021 ◽  
Author(s):  
Shaun Kelsey ◽  
Amit Kumar ◽  
Allen G. Oliver ◽  
Victor W. Day ◽  
James Blakemore
Keyword(s):  
Metal Ions ◽  
Lewis Acids ◽  
Xrd Analysis ◽  
Bimetallic Complexes ◽  
Prior Work ◽  
X Ray Diffraction ◽  
Redox Active ◽  
Reorganization Energies ◽  
Potential Shifts ◽  
Cyclic Voltammetry Data

Compounds containing multiple metals attract significant interest due to the useful redox and reactivity properties of such species. Here, the electrochemical properties of a family of macrocyclic complexes that feature a zinc(II) center paired with a second redox-inactive metal cation in heterobimetallic (Na+, Ca2+, Nd3+, Y3+) motifs or a homobimetallic (Zn2+) motif have been investigated. The new complexes were prepared via a divergent strategy, isolated, and structurally characterized by single-crystal X-ray diffraction (XRD) analysis. XRD results show that the structure of the complexes is modulated by the identity of the incorporated secondary metal ions. Cyclic voltammetry data reveal that ligand-centered reduction is promoted in the bimetallic complexes and that the paired metal ions synergistically influence the redox properties of the complexes. Similar to prior work from our group and others, the bimetallic complexes containing stronger Lewis acids undergo more significant reduction potential shifts; contrasting with prior work on complexes containing redox-active metals, however, the zinc(II) complexes studied here display faster electron transfer (as judged by lower reorganization energies, λ) when incorporating di- or tri-valent Lewis acids in contrast to monovalent (and more weakly acidic) sodium. The quantified trends in these data offer insights that help distinguish metal- versus ligand-centered reduction of bimetallic complexes.<br>

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