Light-Driven Hydrogen Production from Aqueous Protons using Molybdenum Catalysts

Homogeneous light-driven systems employing molecular molybdenum catalysts for hydrogen production are described. The specific Mo complexes studied are six-coordinate bis­(benzenedithiolate) derivatives having two additional isocyanide or phosphine ligands to complete the coordination sphere. Each of the complexes possesses a trigonal prismatic coordination geometry. The complexes were investigated as proton reduction catalysts in the presence of [Ru­(bpy)₃]²⁺, ascorbic acid, and visible light. Over 500 TON are obtained over 24 h. Electrocatalysis occurs between the Mo^IV/Mo^III and Mo^III/Mo^II redox couples, around 1.0 V vs SCE. Mechanistic studies by ¹H NMR spectroscopy show that upon two-electron reduction the Mo­(CNR)₂(bdt)₂ complex dissociates the isocyanide ligands, followed by addition of acid to result in the formation of molecular hydrogen and the Mo­(bdt)₂ complex

Light-Driven Hydrogen Production from Aqueous Protons using Molybdenum Catalysts

Homogeneous light-driven systems employing molecular molybdenum catalysts for hydrogen production are described. The specific Mo complexes studied are six-coordinate bis­(benzenedithiolate) derivatives having two additional isocyanide or phosphine ligands to complete the coordination sphere. Each of the complexes possesses a trigonal prismatic coordination geometry. The complexes were investigated as proton reduction catalysts in the presence of [Ru­(bpy)₃]²⁺, ascorbic acid, and visible light. Over 500 TON are obtained over 24 h. Electrocatalysis occurs between the Mo^IV/Mo^III and Mo^III/Mo^II redox couples, around 1.0 V vs SCE. Mechanistic studies by ¹H NMR spectroscopy show that upon two-electron reduction the Mo­(CNR)₂(bdt)₂ complex dissociates the isocyanide ligands, followed by addition of acid to result in the formation of molecular hydrogen and the Mo­(bdt)₂ complex

Crystal Structures of Au₂ Complex and Au₂₅ Nanocluster and Mechanistic Insight into the Conversion of Polydisperse Nanoparticles into Monodisperse Au₂₅ Nanoclusters

We previously reported a size-focusing conversion of polydisperse gold nanoparticles capped by phosphine into monodisperse [Au₂₅(PPh₃)₁₀(SC₂H₄Ph)₅Cl₂]²⁺ nanoclusters in the presence of phenylethylthiol. Herein, we have determined the crystal structure of [Au₂₅(PPh₃)₁₀(SC₂H₄Ph)₅Cl₂]²⁺ nanoclusters and also identified an important side-producta Au(I) complex formed in the size focusing process. The [Au₂₅(PPh₃)₁₀(SC₂H₄Ph)₅Cl₂]²⁺ cluster features a vertex-sharing bi-icosahedral core, resembling a rod. The formula of the Au(I) complex is determined to be [Au₂(PPh₃)₂(SC₂H₄Ph)]⁺ by electrospray ionization (ESI) mass spectrometry, and its crystal structure (with SbF₆^– counterion) reveals Au–Au bridged by −SC₂H₄Ph and with terminal bonds to two PPh₃ ligands. Unlike previously reported [Au₂(PR₃)₂(SC₂H₄Ph)]⁺ complexes in the solid state, which exist as tetranuclear complexes (i.e., dimers of [Au₂(PR₃)₂(SC₂H₄Ph)]⁺ units) through a Au···Au aurophilic interaction, in our case we found that the [Au₂(PPh₃)₂(SC₂H₄Ph)]⁺ complex exists as a single entity, rather than being dimerized to form a tetranuclear complex. The observation of this Au(I) complex allows us to gain insight into the intriguing conversion process from polydisperse Au nanoparticles to monodisperse Au₂₅ nanoclusters

Crystal Structures of Au₂ Complex and Au₂₅ Nanocluster and Mechanistic Insight into the Conversion of Polydisperse Nanoparticles into Monodisperse Au₂₅ Nanoclusters

We previously reported a size-focusing conversion of polydisperse gold nanoparticles capped by phosphine into monodisperse [Au₂₅(PPh₃)₁₀(SC₂H₄Ph)₅Cl₂]²⁺ nanoclusters in the presence of phenylethylthiol. Herein, we have determined the crystal structure of [Au₂₅(PPh₃)₁₀(SC₂H₄Ph)₅Cl₂]²⁺ nanoclusters and also identified an important side-producta Au(I) complex formed in the size focusing process. The [Au₂₅(PPh₃)₁₀(SC₂H₄Ph)₅Cl₂]²⁺ cluster features a vertex-sharing bi-icosahedral core, resembling a rod. The formula of the Au(I) complex is determined to be [Au₂(PPh₃)₂(SC₂H₄Ph)]⁺ by electrospray ionization (ESI) mass spectrometry, and its crystal structure (with SbF₆^– counterion) reveals Au–Au bridged by −SC₂H₄Ph and with terminal bonds to two PPh₃ ligands. Unlike previously reported [Au₂(PR₃)₂(SC₂H₄Ph)]⁺ complexes in the solid state, which exist as tetranuclear complexes (i.e., dimers of [Au₂(PR₃)₂(SC₂H₄Ph)]⁺ units) through a Au···Au aurophilic interaction, in our case we found that the [Au₂(PPh₃)₂(SC₂H₄Ph)]⁺ complex exists as a single entity, rather than being dimerized to form a tetranuclear complex. The observation of this Au(I) complex allows us to gain insight into the intriguing conversion process from polydisperse Au nanoparticles to monodisperse Au₂₅ nanoclusters

Synthesis and Characterization of Heterobimetallic Iridium–Aluminum and Rhodium–Aluminum Complexes

We demonstrate the synthesis and characterization of a new class of late-transition-metal–aluminum heterobimetallic complexes via a novel synthetic pathway. Complexes of this type are exceedingly rare. Joint experimental and theoretical data sheds light on the electronic effect of ligands containing aluminum moieties on late-transition-metal complexes

From Seconds to Femtoseconds: Solar Hydrogen Production and Transient Absorption of Chalcogenorhodamine Dyes

A series of chalcogenorhodamine dyes with oxygen, sulfur, and selenium atoms in the xanthylium core was synthesized and used as chromophores for solar hydrogen production with a platinized TiO₂ catalyst. Solutions containing the selenorhodamine dye generate more hydrogen [181 turnover numbers (TONs) with respect to chromophore] than its sulfur (30 TONs) and oxygen (20 TONs) counterparts. This differs from previous work incorporating these dyes into dye-sensitized solar cells (DSSCs), where the oxygen- and selenium-containing species perform similarly. Ultrafast transient absorption spectroscopy revealed an ultrafast electron transfer under conditions for dye-sensitized solar cells and a slower electron transfer under conditions for hydrogen production, making the chromophore’s triplet yield an important parameter. The selenium-containing species is the only dye for which triplet state population is significant, which explains its superior activity in hydrogen evolution. The discrepancy in rates of electron transfer appears to be caused by the presence or absence of aggregation in the system, altering the coupling between the dye and TiO₂. This finding demonstrates the importance of understanding the differences between, as well as the effects of the conditions for DSSCs and solar hydrogen production