Cationic yet Stronger Donor: A Surprising Partner Effect and the Partner Strategy in Accelerating a Pincer-Co Catalyzed Nitrile Hydroboration Reaction

A strategy to tune the catalytic behavior of a organometallic catalysts rather than ligand engineering is suggested in this work, by computationally studying the effect of (18-crown-6)K+, W(CO)3 and W(PMe3)3 on the reactivity of a Pincer-Co catalyzed nitrile hydroboration reaction through π-coordination to the ligand aromatic ring. These extra additives, as called by the partners, binds the central phenyl ring of the ligand by either dispersion or chemical bonding. The electron-richness of the cobalt center is tuned by the partner, and follows the order (18-crown-6)K+ > W(PMe3)3 > no partner > W(CO)3. While the influence of covalent W-containing partners parallels the electron-richness of W, the non-covalent partner, (18-crown-6)K+, surprisingly increases the donor ability of the Pincer ligand, through polarization effect. All the elementary steps involved in the nitrile hydroboration reaction are influenced by the partner, and the overall barrier is lowered by a surprisingly large extent of 4.9 kcal/mol in the presence of (18-crown-6)K+, suggesting a charming partner effect to be explored by experimentalists that the reactivity of a catalyst can be consecutively tuned without ligand modification.

Amalgamation and Scrutinizing of Leucine Derivatives Schiff bases Complexes as Antimicrobial Agent

: The enhanced applications of Schiff bases metal complexes of amino acid derivatives have captured the attention of researchers for the synthesis of leucine derivatives of Schiff bases metal complexes. Amino acids are considered to be essential part of food supplements as well as derivatives of Schiff bases in coordination chemistry due to their donor ability. The leucine derivatives Schiff bases ligand have been synthesized by condensation reaction between amine of leucine with aldehyde or ketone bearing molecules attached with them. These complexes were characterized by different spectroscopic tools in order to confirm their structural geometries. The structural geometries are considered to be very important in order to improve the antimicrobial potential of leucine derivative metal complexes. By taking into account the antimicrobial potential of titled compounds, a comprehensive review of leucine derivatives of Schiff bases metal complexes has been compiled.

Increasing the CO2 Reduction Activity of Cobalt Phthalocyanine by Modulating the σ-donor Strength of Axially Coordinating Ligands

<p>Axial coordination of a pyridyl moieties to CoPc (either exogenous or within poly-4-vinylpyridine polymer) dramatically increases the complex’s activity for CO₂RR. It has been hypothesized that axial coordination to the Co active site leads to an increase in the Co dz² orbital energy, which increases the complex’s nucleophilicity and facilitates CO₂ coordination compared to the parent CoPc complex. The magnitude of the energy increase in the Co dz² orbital should depend on the σ-donor strength of the axial ligand—a stronger σ-donating ligand (L) will increase the overall CO₂RR activity of axially coordinated CoPc(L) and vice versa. To test this, we have studied a series of CoPc(L) complexes where the σ-donor strength of L is varied. We show that CoPc(L) reduces CO₂ with an increased activity as the σ-donor ability of L is increased. These observed electrochemical activity trends are correlated with computationally-derived CO₂ binding energy and charge transfer terms as a function of σ-donor strength. The findings of this study supports our hypothesis that the increased CO₂RR activity observed upon axial coordination to CoPc is due to the increased energy of the dz² orbital, and highlight an important design consideration for macrocyclic MN₄-based electrocatalysts.</p><p> </p><p> </p>

Increasing the CO2 Reduction Activity of Cobalt Phthalocyanine by Modulating the σ-donor Strength of Axially Coordinating Ligands

<p>Axial coordination of a pyridyl moieties to CoPc (either exogenous or within poly-4-vinylpyridine polymer) dramatically increases the complex’s activity for CO₂RR. It has been hypothesized that axial coordination to the Co active site leads to an increase in the Co dz² orbital energy, which increases the complex’s nucleophilicity and facilitates CO₂ coordination compared to the parent CoPc complex. The magnitude of the energy increase in the Co dz² orbital should depend on the σ-donor strength of the axial ligand—a stronger σ-donating ligand (L) will increase the overall CO₂RR activity of axially coordinated CoPc(L) and vice versa. To test this, we have studied a series of CoPc(L) complexes where the σ-donor strength of L is varied. We show that CoPc(L) reduces CO₂ with an increased activity as the σ-donor ability of L is increased. These observed electrochemical activity trends are correlated with computationally-derived CO₂ binding energy and charge transfer terms as a function of σ-donor strength. The findings of this study supports our hypothesis that the increased CO₂RR activity observed upon axial coordination to CoPc is due to the increased energy of the dz² orbital, and highlight an important design consideration for macrocyclic MN₄-based electrocatalysts.</p><p> </p><p> </p>

Increasing the CO2 Reduction Activity of Cobalt Phthalocyanine by Modulating the σ-donor Strength of Axially Coordinating Ligands

<p>Axial coordination of a pyridyl moieties to CoPc (either exogenous or within poly-4-vinylpyridine polymer) dramatically increases the complex’s activity for CO₂RR. It has been hypothesized that axial coordination to the Co active site leads to an increase in the Co dz² orbital energy, which increases the complex’s nucleophilicity and facilitates CO₂ coordination compared to the parent CoPc complex. The magnitude of the energy increase in the Co dz² orbital should depend on the σ-donor strength of the axial ligand—a stronger σ-donating ligand (L) will increase the overall CO₂RR activity of axially coordinated CoPc(L) and vice versa. To test this, we have studied a series of CoPc(L) complexes where the σ-donor strength of L is varied. We show that CoPc(L) reduces CO₂ with an increased activity as the σ-donor ability of L is increased. These observed electrochemical activity trends are correlated with computationally-derived CO₂ binding energy and charge transfer terms as a function of σ-donor strength. The findings of this study supports our hypothesis that the increased CO₂RR activity observed upon axial coordination to CoPc is due to the increased energy of the dz² orbital, and highlight an important design consideration for macrocyclic MN₄-based electrocatalysts.</p><p> </p><p> </p>

New 3-Ethynylaryl Coumarin-Based Dyes for DSSC Applications: Synthesis, Spectroscopic Properties, and Theoretical Calculations

A set of 3-ethynylaryl coumarin dyes with mono, bithiophenes and the fused variant, thieno [3,2-b] thiophene, as well as an alkylated benzotriazole unit were prepared and tested for dye-sensitized solar cells (DSSCs). For comparison purposes, the variation of the substitution pattern at the coumarin unit was analyzed with the natural product 6,7-dihydroxycoumarin (Esculetin) as well as 5,7-dihydroxycomarin in the case of the bithiophene dye. Crucial steps for extension of the conjugated system involved Sonogashira reaction yielding highly fluorescent molecules. Spectroscopic characterization showed that the extension of conjugation via the alkynyl bridge resulted in a strong red-shift of absorption and emission spectra (in solution) of approximately 73–79 nm and 52–89 nm, respectively, relative to 6,7-dimethoxy-4-methylcoumarin (labs = 341 nm and lem = 410 nm). Theoretical density functional theory (DFT) calculations show that the Lowest Unoccupied Molecular Orbital (LUMO) is mostly centered in the cyanoacrylic anchor unit, corroborating the high intramolecular charge transfer (ICT) character of the electronic transition. Photovoltaic performance evaluation reveals that the thieno [3,2-b] thiophene unit present in dye 8 leads to the best sensitizer of the set, with a conversion efficiency (η = 2.00%), best VOC (367 mV) and second best Jsc (9.28 mA·cm−2), surpassed only by dye 9b (Jsc = 10.19 mA·cm−2). This high photocurrent value can be attributed to increased donor ability of the 5,7-dimethoxy unit when compared to the 6,7 equivalent (9b).

The Search for Molecular Corks Beyond Carbon Monoxide: A Quantum Mechanical Study of N-Heterocyclic Carbene Adsorption on Pd/Cu(111) and Pt/Cu(111) Single Atom Alloys

<p>Periodic Density Functional Theory calculations reveal the potential application of 10 imidazole based N-heterocyclic carbenes to behave as “molecular corks” for hydrogen storage on single atom alloys, comprised of Pd/Cu(111) or Pt/Cu(111). Calculations show that functionalizing the NHC with different electron withdrawing/donating functional groups results in different binding energies of the NHC with the alloy surfaces. The results are compared to DFT calculations of carbon monoxide bound to these alloys. The Huynh electronic parameter (is calculated for several simple imidazole NHCs to gauge σ-donor ability, while Se-NMR of and P-NMR calculations of selenourea derivatives and carbene-phosphinidene adducts, respectively, have been utilized to gauge π-acidity of the NHCs. It is demonstrated that consideration of both σ and π donating/accepting ability must be considered when predicting the surface-adsorbate binding energy. It was found that electron withdrawing groups tend to weaken the NHC-surface interaction while electron withdrawing substituents tend to strengthen the interaction.</p>