Long-lived MLCT states for Ru(ii) complexes of ferrocene-appended 2,2'-bipyridines

Heterobimetallic Gold/Ruthenium Complexes Synthesized via Post-functionalization and Applied in Dual Photoredox Gold Catalysis

The synthesis of heterobimetallic Au^I /Ru^II complexes of the general formula syn- and anti-[{AuCl}(L1∩L2){Ru(bpy)₂ }][PF₆ ]₂ is reported. The ditopic bridging ligand L1∩L2 refers to a P,N hybrid ligand composed of phosphine and bipyridine substructures, which was obtained via a post-functionalization strategy based on Diels-Alder reaction between a phosphole and a maleimide moiety. It was found that the stereochemistry at the phosphorus atom of the resulting 7-phosphanorbornene backbone can be controlled by executing the metal coordination and the cycloaddition reaction in a different order. All precursors, as well as the mono- and multimetallic complexes, were isolated and fully characterized by various spectroscopic methods such as NMR, IR, and UV-vis spectroscopy as well as cyclic voltammetry. Photophysical measurements show efficient phosphorescence for the investigated monometallic complex anti-[(L1∩L2){Ru(bpy)₂ }][PF₆ ]₂ and the bimetallic analogue syn-[{AuCl}(L1∩L2){Ru(bpy)₂ }][PF₆ ]₂ , thus indicating a small influence of the {AuCl} fragment on the photoluminescence properties. The heterobimetallic Au^I /Ru^II complexes syn- and anti-[{AuCl}(L1∩L2){Ru(bpy)₂ }][PF₆ ]₂ are both active catalysts in the P-arylation of aryldiazonium salts promoted by visible light with H-phosphonate affording arylphosphonates in yields of up to 91 %. Both dinuclear complexes outperform their monometallic counterparts.

[(η6-p-Cymene)[3-(pyrid-2-yl)-1,2,4,5-tetrazine]chlororuthenium(II)]+, Redox Noninnocence and Dienophile Addition to Coordinated Tetrazine

The bidentate ligand 3-(pyrid-2-yl)-1,2,4,5-tetrazine (TzPy) coordinated in the complex [CyRuCl(TzPy)]PF₆ ([1]⁺; Cy = η⁶-p-cymene) shows noninnocent behavior and can be modified through the addition of dienophiles, vinylferrocene (ViFc) or ethynylferrocene (EthFc). The kinetics and transition-state thermodynamic analysis of the reaction of [1]⁺ + ViFc found ΔG^⧧(298 K) = 67 kJ mol^-1, while that of [1]⁺ + EthFc was ΔG^⧧(298 K) = 83 kJ mol^-1. The room temperature second-order rate of [1]⁺ + EthFc, k₂ = 1.51(4) × 10^-2 M^-1 s^-1, was 3 orders of magnitude faster than that of EthFc + TzPy, k₂ = 1.05(15) × 10^-4 M^-1 s^-1. The [1H₂Fc]⁺ complex was converted to [1Fc]⁺ by oxidation with oxygen and 3,5-di-tert-butyl-o-quinone, and the molecular structure of [1Fc]⁺ was determined by single-crystal X-ray diffraction. The title complex [1]⁺ showed a quasi-reversible reduction in the cyclic voltammogram, and the electrochemical reduction mechanism was determined by UV-vis spectroelectrochemistry (SEC) experiments, as well as supported by density functional theory (DFT) calculations. The dihydropyridazine [1H₂Fc]⁺ and pyridazine [1Fc]⁺ states of the ligand showed ligand noninnocence similar to that of the parent tetrazine but at a cathodically shifted potential. The dihydropyridazine [1H₂Fc]⁺ showed a mixture of several products; however, upon oxidation, only a single product, [1Fc]⁺, was formed from the endo addition of the dienophile to [1]⁺. The electrochemical mechanism of [1Fc]⁺ was also studied by cyclic voltammetry and UV-vis SEC experiments, as well as supported by DFT calculations.

Exploring Solvent-Related Reactions and Corresponding Band Gap Tuning Strategies for Carbon Nanodots Based on Solvothermal Synthesis

The role of the solvent in the solvothermal synthesis of carbon nanodots (CDs) is a long-standing puzzle for comprehensively understanding the CD formation mechanism and the relevant band gap tuning phenomenon. The controversy regarding solvent effect continues, largely because the importance of solvent-related reactions (SRs) has been ignored. In this Letter, we report that the SRs, i.e., oxidation-assisted solvent-involved dehydration and solvent-promoted oligomerization of phenylene/pyridinediamine (PD/PyD), are observed and dominate the formation of corresponding CDs by producing highly C₂H₄/C₂H₄O-featured species of precursors and PEG-like oligomer chains, which is very different from previously proposed theories. Moreover, our findings reveal that the photoluminescence (PL) of as-synthesized CDs originates from fluorophores formed by SRs and can be tailored by fluorophore engineering. Based on the SRs theory, three strategies for PL band gap tuning have been demonstrated.