Photocatalytic reactivity tuning by heterometal and addenda metal variation in Lindqvist polyoxometalates

A systematic study into the effects of metal substitution on the visible-light photocatalytic activity of prototype metal oxide cluster anions is presented. Four isostructural Lindqvist clusters [VxM6−xO19](2+x)− (M = W, Mo, x = 1, 2) with photooxidative activity in the visible range are reported. It is shown that the photooxidative performance correlates with the number of vanadium atoms in the cluster. Further, two divergent reaction mechanisms are observed depending on the type of addenda metal (i.e. Mo or W) used. When comparing the reactivity under aerated vs. de-aerated conditions, it was found that molybdate-based clusters show significantly increased reaction rates in the absence of oxygen; in contrast, marginally reduced reaction rates were observed for the tungstate-based species under de-aerated conditions. Wavelength-dependent quantum efficiency studies provide insight into the visible-light reactivity of all four species. Radical scavenging experiments suggest that the photocatalysis proceeds via formation of hydroxyl radicals. Cluster recycling studies demonstrate the robust nature of the homogeneous photocatalysts

Visible light photooxidative performance of a high-nuclearity molecular bismuth vanadium oxide cluster

The visible light photooxidative performance of a new high-nuclearity molecular bismuth vanadium oxide cluster, H3[{Bi(dmso)3}4V13O40], is reported. Photocatalytic activity studies show faster reaction kinetics under anaerobic conditions, suggesting an oxygen-dependent quenching of the photoexcited cluster species. Further mechanistic analysis shows that the reaction proceeds via the intermediate formation of hydroxyl radicals which act as oxidant. Trapping experiments using ethanol as a hydroxyl radical scavenger show significantly decreased photocatalytic substrate oxidation in the presence of EtOH. Photocatalytic performance analyses using monochromatic visible light irradiation show that the quantum efficiency Φ for indigo photooxidation is strongly dependent on the irradiation wavelength, with higher quantum efficiencies being observed at shorter wavelengths (Φ395nm ca. 15%). Recycling tests show that the compound can be employed as homogeneous photooxidation catalyst multiple times without loss of catalytic activity. High turnover numbers (TON ca. 1200) and turnover frequencies up to TOF ca. 3.44 min−1 are observed, illustrating the practical applicability of the cluster species

Photocatalytic reactivity tuning by heterometal and addenda metal variation in Lindqvist polyoxometalates

A systematic study into the effects of metal substitution on the visible-light photocatalytic activity of prototype metal oxide cluster anions is presented. Four isostructural Lindqvist clusters [VxM6−xO19](2+x)− (M = W, Mo, x = 1, 2) with photooxidative activity in the visible range are reported. It is shown that the photooxidative performance correlates with the number of vanadium atoms in the cluster. Further, two divergent reaction mechanisms are observed depending on the type of addenda metal (i.e. Mo or W) used. When comparing the reactivity under aerated vs. de-aerated conditions, it was found that molybdate-based clusters show significantly increased reaction rates in the absence of oxygen; in contrast, marginally reduced reaction rates were observed for the tungstate-based species under de-aerated conditions. Wavelength-dependent quantum efficiency studies provide insight into the visible-light reactivity of all four species. Radical scavenging experiments suggest that the photocatalysis proceeds via formation of hydroxyl radicals. Cluster recycling studies demonstrate the robust nature of the homogeneous photocatalysts

Carbon-Rich Ruthenium Allenylidene Complexes Bearing Heteroscorpionate Ligands

A series of ruthenium allenylidene complexes bearing polyaromatic substituents have been prepared starting from [Ru­(bdmpza)­Cl­(PPh₃)₂] (<b>1</b>) (bdmpza = bis­(3,5-dimethyl­pyrazol-1-yl)­acetato). Reacting <b>1</b> with 1,1-bis­(3,5-di-<i>tert</i>-butyl­phenyl)-1-methoxy-2-propyne results in the formation of two structural isomers of an allenylidene complex [Ru­(bdmpza)­Cl­(CCC­(Ph^<i>t</i>Bu₂)₂)­(PPh₃)] (<b>5A</b>/<b>5B</b>), as well as the related carbonyl complex [Ru­(bdmpza)­Cl­(CO)­(PPh₃)] (<b>4A</b>/<b>4B</b>). Conversion of 9-ethynyl-9-fluorenol leads to the corresponding allenylidene complex [Ru­(bdmpza)­Cl­(CC(FN))­(PPh₃)] (<b>7A</b>/<b>7B</b>) (FN = fluorenyl). Based on anthraquinone, a new synthetic route toward 10-ethynyl-10-hydroxy­anthracen-9-one via the trimethylsilyl-protected propargyl alcohol is described, and subsequent conversion of this compound to the allenylidene complex ([Ru­(bdmpza)­Cl­(CC(AO))­(PPh₃)] (<b>12A</b>/<b>12B</b>) (AO = anthrone) is reported. The synthetic route from 7<i>H</i>-benzo­[<i>no</i>]­tetraphen-7-one to the propargyl alcohol 7-ethynyl-7<i>H</i>-benzo­[<i>no</i>]­tetraphen-7-ol is described, which is followed by the transformation into the allenylidene complex [Ru­(bdmpza)­Cl­(CC(BT))­(PPh₃)] (<b>17A</b>/<b>17B</b>) (BT = benzotetraphene). The molecular structures of <b>4B</b>, <b>7A</b>, <b>7B</b>, <b>12A</b>, <b>12B</b>, <b>13A</b>, and <b>17A</b> have been characterized by single-crystal X-ray crystallography, and these analyses suggest that <b>17A</b> might function as a “metal-tuned organic field effect transistor”. The electrochemical properties of the allenylidene complexes have been studied via cyclic voltammetry, and time-dependent DFT calculations have been conducted to assign weak absorptions in the NIR region to forbidden MLCT transitions

Carbon-Rich Ruthenium Allenylidene Complexes Bearing Heteroscorpionate Ligands

A series of ruthenium allenylidene complexes bearing polyaromatic substituents have been prepared starting from [Ru­(bdmpza)­Cl­(PPh₃)₂] (<b>1</b>) (bdmpza = bis­(3,5-dimethyl­pyrazol-1-yl)­acetato). Reacting <b>1</b> with 1,1-bis­(3,5-di-<i>tert</i>-butyl­phenyl)-1-methoxy-2-propyne results in the formation of two structural isomers of an allenylidene complex [Ru­(bdmpza)­Cl­(CCC­(Ph^<i>t</i>Bu₂)₂)­(PPh₃)] (<b>5A</b>/<b>5B</b>), as well as the related carbonyl complex [Ru­(bdmpza)­Cl­(CO)­(PPh₃)] (<b>4A</b>/<b>4B</b>). Conversion of 9-ethynyl-9-fluorenol leads to the corresponding allenylidene complex [Ru­(bdmpza)­Cl­(CC(FN))­(PPh₃)] (<b>7A</b>/<b>7B</b>) (FN = fluorenyl). Based on anthraquinone, a new synthetic route toward 10-ethynyl-10-hydroxy­anthracen-9-one via the trimethylsilyl-protected propargyl alcohol is described, and subsequent conversion of this compound to the allenylidene complex ([Ru­(bdmpza)­Cl­(CC(AO))­(PPh₃)] (<b>12A</b>/<b>12B</b>) (AO = anthrone) is reported. The synthetic route from 7<i>H</i>-benzo­[<i>no</i>]­tetraphen-7-one to the propargyl alcohol 7-ethynyl-7<i>H</i>-benzo­[<i>no</i>]­tetraphen-7-ol is described, which is followed by the transformation into the allenylidene complex [Ru­(bdmpza)­Cl­(CC(BT))­(PPh₃)] (<b>17A</b>/<b>17B</b>) (BT = benzotetraphene). The molecular structures of <b>4B</b>, <b>7A</b>, <b>7B</b>, <b>12A</b>, <b>12B</b>, <b>13A</b>, and <b>17A</b> have been characterized by single-crystal X-ray crystallography, and these analyses suggest that <b>17A</b> might function as a “metal-tuned organic field effect transistor”. The electrochemical properties of the allenylidene complexes have been studied via cyclic voltammetry, and time-dependent DFT calculations have been conducted to assign weak absorptions in the NIR region to forbidden MLCT transitions

Carbon-Rich Ruthenium Allenylidene Complexes Bearing Heteroscorpionate Ligands

A series of ruthenium allenylidene complexes bearing polyaromatic substituents have been prepared starting from [Ru­(bdmpza)­Cl­(PPh₃)₂] (<b>1</b>) (bdmpza = bis­(3,5-dimethyl­pyrazol-1-yl)­acetato). Reacting <b>1</b> with 1,1-bis­(3,5-di-<i>tert</i>-butyl­phenyl)-1-methoxy-2-propyne results in the formation of two structural isomers of an allenylidene complex [Ru­(bdmpza)­Cl­(CCC­(Ph^<i>t</i>Bu₂)₂)­(PPh₃)] (<b>5A</b>/<b>5B</b>), as well as the related carbonyl complex [Ru­(bdmpza)­Cl­(CO)­(PPh₃)] (<b>4A</b>/<b>4B</b>). Conversion of 9-ethynyl-9-fluorenol leads to the corresponding allenylidene complex [Ru­(bdmpza)­Cl­(CC(FN))­(PPh₃)] (<b>7A</b>/<b>7B</b>) (FN = fluorenyl). Based on anthraquinone, a new synthetic route toward 10-ethynyl-10-hydroxy­anthracen-9-one via the trimethylsilyl-protected propargyl alcohol is described, and subsequent conversion of this compound to the allenylidene complex ([Ru­(bdmpza)­Cl­(CC(AO))­(PPh₃)] (<b>12A</b>/<b>12B</b>) (AO = anthrone) is reported. The synthetic route from 7<i>H</i>-benzo­[<i>no</i>]­tetraphen-7-one to the propargyl alcohol 7-ethynyl-7<i>H</i>-benzo­[<i>no</i>]­tetraphen-7-ol is described, which is followed by the transformation into the allenylidene complex [Ru­(bdmpza)­Cl­(CC(BT))­(PPh₃)] (<b>17A</b>/<b>17B</b>) (BT = benzotetraphene). The molecular structures of <b>4B</b>, <b>7A</b>, <b>7B</b>, <b>12A</b>, <b>12B</b>, <b>13A</b>, and <b>17A</b> have been characterized by single-crystal X-ray crystallography, and these analyses suggest that <b>17A</b> might function as a “metal-tuned organic field effect transistor”. The electrochemical properties of the allenylidene complexes have been studied via cyclic voltammetry, and time-dependent DFT calculations have been conducted to assign weak absorptions in the NIR region to forbidden MLCT transitions

Multiply Bonded Metal(II) Acetate (Rhodium, Ruthenium, and Molybdenum) Complexes with the <i>trans</i>-1,2-Bis(<i>N</i>‑methylimidazol-2-yl)ethylene Ligand

The synthesis and structural characterization of new coordination polymers with the <i>N</i>,<i>N</i>-donor ligand <i>trans</i>-1,2-bis­(<i>N</i>-methylimidazol-2-yl)­ethylene (<i>trans</i>-bie) are reported. It was found that the acetate-bridged paddlewheel metal­(II) complexes [M₂(O₂CCH₃)₄(<i>trans</i>-bie)]_<i>n</i> with M = Rh, Ru, Mo, and Cr are linked by the <i>trans</i>-bie ligand to give a one-dimensional alternating chain. The metal–metal multiple bonds were analyzed with density functional theory and CASSCF/CASPT2 calculations (bond orders: Rh, 0.8; Ru, 1.7; Mo, 3.3)