Synthesis and Structural Characterisation of Palladium(II) Complexes with N,N′,N-Tridentate N′-Substituted N,N-Di(2-picolyl)amines and their Application to Methyl Methacrylate Polymerisation

The reaction of [Pd(CH3CN)2Cl2] with N′-substituted N,N-di(2-picolyl)amine-based ancillary ligands, for example N,N-di(2-picolyl)cyclohexylmethylamine (L1), N,N-di(2-picolyl)benzylamine (L2), N,N-di(2-picolyl)aniline (L3), and 1,4-bis[bis(2-pyridylmethyl)aminomethyl]benzene (L4), in the presence of NaClO4 in ethanol yields a new series of [(NN′N)PdCl]X (X = ClO4, Cl) complexes, i.e. mononuclear [LnPdCl]ClO4 (Ln = L1, L2, L3) and binuclear [L4Pd2Cl2]Cl2. X-Ray crystallographic analysis determined that the Pd atom in complexes [(NN′N)PdCl]X showed a slightly distorted square-planar geometry involving three nitrogen atoms and a chlorido ligand. Moreover, the unit cell included a ClO4– or Cl– anion as the counterion. The complex [L1PdCl]ClO4 showed the highest catalytic activity for the polymerisation of methyl methacrylate in the presence of modified methylaluminoxane at 60°C among the mononuclear PdII complexes. Specifically, the activity of binuclear [L4Pd2Cl2]Cl2 was 2-fold higher than the corresponding mononuclear [L2PdCl]ClO4 per active palladium metal centre.

Theoretical treatment of one electron redox transformation of a small molecule using f-element complexes

DFT calculations can provide useful insights into low-valent f-element single electron transfer reactivity.

Thermodynamics and high-pressure kinetics of a fast carbon dioxide fixation reaction by a (2,6-pyridinedicarboxamidato-hydroxo)nickel(ii) complex

The thermodynamics and high-pressure kinetics of the fastest CO₂ fixation reaction by a metal-bound hydroxide resulted in a clear mechanistic picture and characterization of a very compact five-coordinate transition state.

Designed synthesis of CO2-promoted copper(ii) coordination polymers: synthesis, structural and spectroscopic characterization, and studies of versatile functional properties

A series of CO₂-promoted Cu(ii) coordination polymers in different coordination environments has been synthesized.

Ligand noninnocence of thiolate/disulfide in dinuclear copper complexes: solvent-dependent redox isomerization and proton-coupled electron transfer

Copper thiolate/disulfide interconversions are related to the functions of several important proteins such as human Sco1, Cu-Zn superoxide dismutase (SOD1), and mammalian zinc-bonded metallothionein. The synthesis and characterization of well-defined synthetic analogues for such interconversions are challenging yet provide important insights into the mechanisms of such redox processes. Solvent-dependent redox isomerization and proton-coupled electron transfer mimicking these interconversions are observed in two structurally related dimeric μ,η(2):η(2)-thiolato Cu(II)Cu(II) complexes by various methods, including X-ray diffraction, XAS, NMR, and UV-vis. Spectroscopic evidence shows that a solvent-dependent equilibrium exists between the dimeric μ-thiolato Cu(II)Cu(II) state and its redox isomeric μ-disulfido Cu(I)Cu(I) form. Complete formation of μ-disulfido Cu(I)Cu(I) complexes, however, only occurs after the addition of 2 equiv of protons, which promote electron transfer from thiolate to Cu(II) and formation of disulfide and Cu(I) via protonation of the coordinating ligand. Proton removal reverses this reaction. The reported unusual reductive protonation/oxidative deprotonation of the metal centers may serve as a new chemical precedent for how related proteins manage Cu ions in living organisms.

Visible-light photoredox catalysis: selective reduction of carbon dioxide to carbon monoxide by a nickel N-heterocyclic carbene-isoquinoline complex

The solar-driven reduction of carbon dioxide to value-added chemical fuels is a longstanding challenge in the fields of catalysis, energy science, and green chemistry. In order to develop effective CO2 fixation, several key considerations must be balanced, including (1) catalyst selectivity for promoting CO2 reduction over competing hydrogen generation from proton reduction, (2) visible-light harvesting that matches the solar spectrum, and (3) the use of cheap and earth-abundant catalytic components. In this report, we present the synthesis and characterization of a new family of earth-abundant nickel complexes supported by N-heterocyclic carbene-amine ligands that exhibit high selectivity and activity for the electrocatalytic and photocatalytic conversion of CO2 to CO. Systematic changes in the carbene and amine donors of the ligand have been surveyed, and [Ni((Pr)bimiq1)](2+) (1c, where (Pr)bimiq1 = bis(3-(imidazolyl)isoquinolinyl)propane) emerges as a catalyst for electrochemical reduction of CO2 with the lowest cathodic onset potential (E(cat) = -1.2 V vs SCE). Using this earth-abundant catalyst with Ir(ppy)3 (where ppy = 2-phenylpyridine) and an electron donor, we have developed a visible-light photoredox system for the catalytic conversion of CO2 to CO that proceeds with high selectivity and activity and achieves turnover numbers and turnover frequencies reaching 98,000 and 3.9 s(-1), respectively. Further studies reveal that the overall efficiency of this solar-to-fuel cycle may be limited by the formation of the active Ni catalyst and/or the chemical reduction of CO2 to CO at the reduced nickel center and provide a starting point for improved photoredox systems for sustainable carbon-neutral energy conversion.

Chemical adsorption enhanced CO2 capture and photoreduction over a copper porphyrin based metal organic framework

Effective CO2 capture and activation is a prerequisite step for highly efficient CO2 reduction. In this study, we reported a case of Cu(2+) in a porphyrin based MOF promoted enhanced photocatalytic CO2 conversion to methanol. Compared with the sample without Cu(2+), the methanol evolution rate was improved as high as 7 times. In situ FT-IR results suggested that CO2 chemical adsorption and activation over Cu(2+) played an important role in improving the conversion efficiency.

Computational approaches to the chemical conversion of carbon dioxide

The conversion of CO₂ into fuels and chemicals is viewed as an attractive route for controlling the atmospheric concentration and recycling of this greenhouse gas, but its industrial application is limited by the low selectivity and activity of the current catalysts. Theoretical modeling, in particular density functional theory (DFT) simulations, provides a powerful and effective tool to discover chemical reaction mechanisms and design new catalysts for the chemical conversion of CO₂, overcoming the repetitious and time/labor consuming trial-and-error experimental processes. In this article we give a comprehensive survey of recent advances on mechanism determination by DFT calculations for the catalytic hydrogenation of CO₂ into CO, CH₄, CH₃OH, and HCOOH, and CO₂ methanation, as well as the photo- and electrochemical reduction of CO₂. DFT-guided design procedures of new catalytic systems are also reviewed, and challenges and perspectives in this field are outlined.

Radiolytic formation of non-toxic Cr(III) from toxic Cr(VI) in formate containing aqueous solutions: A system for water treatment

Toxic hexavalent chromium Cr(VI) in the form of potassium dichromate was radiolytically reduced to non-toxic trivalent chromium Cr(III) in N(2)O-saturated aqueous solutions containing formate. This reduction by the electron donor (CO(2)H/CO(2)(-)) produced by continuous radiolysis of water, was a linear function of the absorbed dose. This reaction was pH and dose rate dependent. pH was an important parameter in the reduction, as it affects both chemical speciation of Cr(VI) and formate. Possible mechanisms related to dose rate dependence of removal of Cr(VI) are presented. At pH 3 a decrease in the radiation induced reduction of Cr(VI) was observed with increasing hydrogen peroxide concentration. A mechanism to account for this variation is proposed. These findings suggest that irradiation of Cr(VI) solutions in presence of formate can be effective, economical and simple means for treatment of waste water contaminated with hexavalent Cr(VI).

Solvation and evolution dynamics of an excess electron in supercritical CO2

We present an ab initio molecular dynamics simulation of the dynamics of an excess electron solvated in supercritical CO2. The excess electron can exist in three types of states: CO2-core localized, dual-core localized, and diffuse states. All these states undergo continuous state conversions via a combination of long lasting breathing oscillations and core switching, as also characterized by highly cooperative oscillations of the excess electron volume and vertical detachment energy. All of these oscillations exhibit a strong correlation with the electron-impacted bending vibration of the core CO2, and the core-switching is controlled by thermal fluctuations.