Sn Porphyrin Research Articles

A PEGylated Tin Porphyrin Complex for Electrocatalytic Proton Reduction: Mechanistic Insights into Main-Group-Element Catalysis.

Electrocatalytic proton reduction to form dihydrogen (H2 ) is an effective way to store energy in the form of chemical bonds. In this study, we validate the applicability of a main-group-element-based tin porphyrin complex as an effective molecular electrocatalyst for proton reduction. A PEGylated Sn porphyrin complex (SnPEGP) displayed high activity (-4.6 mA cm-2 at -1.7 V vs. Fc/Fc+ ) and high selectivity (H2 Faradaic efficiency of 94 % at -1.7 V vs. Fc/Fc+ ) in acetonitrile (MeCN) with trifluoroacetic acid (TFA) as the proton source. The maximum turnover frequency (TOFmax ) for H2 production was obtained as 1099 s-1 . Spectroelectrochemical analysis, in conjunction with quantum chemical calculations, suggest that proton reduction occurs via an electron-chemical-electron-chemical (ECEC) pathway. This study reveals that the tin porphyrin catalyst serves as a novel platform for investigating molecular electrocatalytic reactions and provides new mechanistic insights into proton reduction.

A PEGylated Tin Porphyrin Complex for Electrocatalytic Proton Reduction: Mechanistic Insights into Main‐Group‐Element Catalysis

AbstractElectrocatalytic proton reduction to form dihydrogen (H2) is an effective way to store energy in the form of chemical bonds. In this study, we validate the applicability of a main‐group‐element‐based tin porphyrin complex as an effective molecular electrocatalyst for proton reduction. A PEGylated Sn porphyrin complex (SnPEGP) displayed high activity (−4.6 mA cm−2 at −1.7 V vs. Fc/Fc+) and high selectivity (H2 Faradaic efficiency of 94 % at −1.7 V vs. Fc/Fc+) in acetonitrile (MeCN) with trifluoroacetic acid (TFA) as the proton source. The maximum turnover frequency (TOFmax) for H2 production was obtained as 1099 s−1. Spectroelectrochemical analysis, in conjunction with quantum chemical calculations, suggest that proton reduction occurs via an electron‐chemical‐electron‐chemical (ECEC) pathway. This study reveals that the tin porphyrin catalyst serves as a novel platform for investigating molecular electrocatalytic reactions and provides new mechanistic insights into proton reduction.

Photosensitizers for H2 Evolution Based on Charged or Neutral Zn and Sn Porphyrins.

We report a comparison between a series of zinc and tin porphyrins as photosensitizers for photochemical hydrogen evolution using cobaloxime complexes as molecular catalysts. Among all the chromophores tested, only the positively charged zinc porphyrin, [ZnTMePyP4+]Cl4, and the neutral tin porphyrin derivatives, Sn(OH)2TPyP, Sn(Cl2)TPP-[COOMe]4, and Sn(Cl2)TPP-[PO(OEt)2]4, were photocatalytically active. Hydrogen evolution was strongly affected by the pH value as well as the different concentrations of both the sensitizer and the catalyst. A comprehensive photophysical and electrochemical investigation was conducted in order to examine the mechanism of photocatalysis. The results derived from this study establish fundamental criteria with respect to the design and synthesis of porphyrin derivatives for their application as photosensitizers in photoinduced hydrogen evolution.

Carbon Dioxide Dimer Radical Anion as Surface Intermediate of Photoinduced CO2 Reduction at Aqueous Cu and CdSe Nanoparticle Catalysts by Rapid-Scan FT-IR Spectroscopy.

Monitoring of visible light sensitized reduction of CO2 at Cu nanoparticles in aqueous solution by rapid-scan ATR FT-IR spectroscopy on the time scale of seconds allowed structural identification of a one-electron intermediate and demonstrated its kinetic relevancy for the first time. Isotopic labeling (12C: 1632, 1358, 1346 cm-1; 13C: 1588, 1326, 1316 cm-1) revealed a species of carbon dioxide dimer radical anion structure, most likely bound to the catalyst surface through carbon. Intermediacy of Cu-C(═O)OCO2- surface species is in agreement with a recently proposed mechanism for electrocatalytic CO2 reduction at Cu metal nanoparticles based on Tafel slope analysis. Spontaneous decrease of the intermediate after termination of the photosensitization pulse (Sn porphyrin excited at 405 nm) was accompanied by the growth of HCO3-. CO was produced as well, but sensitive detection required photolysis for tens of minutes. A direct kinetic link between a C2O4- surface intermediate and the CO product was also demonstrated for photocatalyzed CO2 reduction at aqueous CdSe nanoparticles, where first order growth of a Cd-C(═O)OCO2- species was accompanied by rise of CO (monitored by a fast Ni complex trap) and HCO3- showing a distinct induction period. The detection of the one-electron surface intermediate and confirmation of its catalytic relevancy was enabled by the delivery of electrons one-by-one by the photosensitization method. The observation of carbon dioxide dimer radical anion points to approaches for rate enhancements of heterogeneous CO2 reduction by creating catalytic environments that favor formation of this intermediate.

Photochemical hydrogen evolution using Sn-porphyrin as photosensitizer and a series of Cobaloximes as catalysts

Herein, we report a photochemical hydrogen evolution system consisting of various cobalt based catalysts, a metallated Sn porphyrin as photosensitizer and a triethanolamine as a sacrificial electron donor in acetonitrile/H2O (1:1) solution. Since a tin metallated porphyrin is used for the first time as photosensitizer in this type of systems, a systematic study was performed in order to elucidate the best conditions for H[Formula: see text]production. Upon visible irradiation hydrogen production was detected with the best result obtained at pH 7 with a TON of 150, after 100 h in the presence of catalyst 1. Moreover, when TiO2 nanoparticles were added at the catalytic system 2 the hydrogen production was increased from 53 TON to 131 TON, under the same experimental conditions.

Insight into the cocatalyst effect of 4A molecular sieve on Sn(II) porphyrin-catalyzed B–V oxidation of cyclohexanone

The cocatalyst effect of 4A molecular sieve (4A-MS) on the catalytic activity of tin(II) meso-tetraphenylporphyrin (SnTPP) was investigated in the aerobic Baeyer–Villiger oxidation of cyclohexanone in the presence of benzaldehyde as reductant, remarkable enhancement on the yield of ɛ-caprolactone was achieved (from 21% to 83%). The in situ Raman spectroscopy confirmed the interaction between 4A-MS and the carbonyl group of benzaldehyde and cyclohexanone molecules. The major role of 4A-MS was to active cyclohexanone and benzaldehyde molecules by the coordination between the oxygen atom of carbonyl group and the Lewis acid site of 4A-MS. The activated benzaldehyde tended to combine dioxygen easily, which resulted in the accelerated generation rate of peroxybenzoic acid and the high-valent Sn porphyrin (PorSnIVO). Accordingly, the slow generation rate of Criegee adduct intermediate by the reaction between cyclohexanone and high-valent Sn porphyrin was accelerated. A cocatalytic mechanism involving the activated cyclohexanone and benzaldehyde was proposed.

Engineering of Sn-porphyrin networks on the silica surface: sensing of nitrophenols in water.

Sn-porphyrin networks were engineered on the surface of a thin layer chromatography (TLC) plate via Sonogashira coupling of the Sn-porphyrin building block and 1,4-diiodobenzene. The Sn-porphyrin film showed a strong Soret band absorption at 422 nm, emission at 600-630 nm, and excellent sensing performance toward nitrophenols in water.

Green Photocatalytic Synthesis of Au Nanoparticles/Multi-walled Carbon Nanotubes Nanocomposites and their Application for Glucose Sensing

In this communication, we report on a novel green photocatalytic route to synthesize Au nanoparticles/multi-walled carbon nanotubes (AuNPs/MWCNTs) nanocomposites with the use of Sn-porphyrin (SnP) as a high-efficiency photocatalyst to reduce Au3+ to form AuNPs onto MWCNTs. Such AuNPs/MWCNTs nanocomposites exhibit good catalytic performance toward both oxidation and reduction of H2O2. An electrochemical glucose biosensor was further constructed by dropping glucose oxidase on the surface of AuNPs/MWCNTs nanocomposites modified glassy carbon electrode. The biosensor shows linear response toward different concentrations of glucose from 1 to 33 mM (r = 0.998) and the detection limit at 0.5 V is estimated to be 240 mu M at a signal-to-noise ratio of 3.

Ternary Nanocomposites of Porphyrin, Angular Au Nanoparticles and Reduced Graphene Oxide: Photocatalytic Synthesis and Enhanced Photocurrent Generation

A noble strategy: A photocatalytic strategy toward organic–inorganic ternary nanocomposites of Sn-porphyrin (SnP), angular Au nanoparticles (AuNPs), and reduced graphene oxide (RGO) using SnP as an effective photocatalyst for the reduction of both GO and AuIII under visible-light irradiation. The synergistic effect of surface plasmon resonance excitation in AuNPs and SnP leads to a 27-fold increase in the photocurrent.

A [2]Catenane and Pretzelane Based on Sn–Porphyrin and Crown Ether

AbstractA [2]catenane and a pretzelane that consist of one aromatic dialkylammonium spacer, one dibenzo‐24‐crown‐8 (DB24C8) unit, and one Sn–porphyrin dihydroxide component were synthesized. In the [2]catenane, dibenzo‐24‐crown‐8 and the Sn–porphyrin dihydroxide are two independent components, whereas in the pretzelane, dibenzo‐24‐crown‐8 and the Sn–porphyrin dihydroxide are linked covalently. The interlocked molecules were obtained by the axial ligation of Sn–porphyrin dihydroxide with the resorcinol moieties of both termini in the aromatic dialkylammonium spacer.

Porphyrin‐Based Switchable Molecular Turnstiles

The design, synthesis and structural characterisation, in solution, of two new molecular turnstiles based on Sn-porphyrin derivatives are described. The system is composed of a stator (5-(4-pyridyl)-10,15,20-triphenylporphyrin), a hinge (Sn(IV)) and a rotor (handle equipped with 2,6-pyridinedicarboxamide as a tridentate coordinating site or its Pd(II) complex). The presence of interaction sites, both on the stator and the rotor, offers the possibility of switching between an open state (free rotation of the handle around the porphyrin) and a closed state (blockage of the rotation) by either establishment of hydrogen bonds between the stator and the rotor or by the simultaneous binding of Pd by both coordinating groups.

Donor−Acceptor Biomorphs from the Ionic Self-Assembly of Porphyrins

Microscale four-leaf clover-shaped structures are formed by self-assembly of anionic and cationic porphyrins. Depending on the metal complexed in the porphyrin macrocycle (Zn or Sn), the porphyrin cores are either electron donors or electron acceptors. All four combinations of these two metals in cationic tetra(N-ethanol-4-pyridinium)porphyrin and anionic tetra(sulfonatophenyl)porphyrin result in related cloverlike structures with similar crystalline packing indicated by X-ray diffraction patterns. The clover morphology transforms as the ionic strength and temperature of the self-assembly reaction are increased, but the structures maintain 4-fold symmetry. The ability to alter the electronic and photophysical properties of these solids (e.g., by altering the metals in the porphyrins) and to vary cooperative interactions between the porphyrin subunits raises the possibility of producing binary solids with tunable functionality. For example, we show that the clovers derived from anionic Zn porphyrins (electron donors) and cationic Sn porphyrins (electron acceptors) are photoconductors, but when the metals are reversed in the two porphyrins, the resulting clovers are insulators.

Unique Solvatochromism of a Membrane Composed of a Cationic Porphyrin−Clay Complex

A novel optically transparent membrane composed of porphyrin-clay mineral complexes was developed. Reversible solvatochromism behavior of the membrane was successfully observed, due to an orientation change of porphyrin in the clay interlayer space. The lambda(max) value of porphyrin was 423 nm in acetone, while it was 464 nm in hexane. The color of the membrane changed from pink to green through to brown, when Sn porphyrin was used. The mechanism for solvatochromism in the present system is very unique compared to those for conventionally reported materials.

Molecular organization in self-assembled binary porphyrin nanotubes revealed by resonance Raman spectroscopy

Porphyrin nanotubes were formed by the ionic self-assembly of tetrakis(4-sulfonatophenyl) porphyrin diacid (H(4)TPPS(4)(2-)) and Sn(IV) tetra(4-pyridyl) porphyrin (Sn(OH(-))(X)TPyP(4+/5+) [X = OH(-) or H(2)O]) at pH 2.0. As reported previously, the tubes are hollow as revealed by transmission electron microscopy, approximately 60 nm in diameter, and can be up to several micrometres long. The absorption spectrum of the porphyrin nanotubes presents monomer-like Soret bands, as well as two additional red-shifted bands characteristic of porphyrin J-aggregates (offset face-to-face stacks). To elucidate the origin of the J-aggregate bands and the internal interactions of the porphyrins, the resonance Raman spectra have been obtained for the porphyrin nanotubes with excitations near resonance with the Soret J-aggregate band and the monomer-like bands. The resonance Raman data reveal that the Sn porphyrins are not electronically coupled to the J-aggregates within the tubes, which are formed exclusively by H(4)TPPS(4)(2-). This suggests that the internal structure of the nanotubes has H(4)TPPS(4)(2-) in aggregates that are similar to the widely studied H(4)TPPS(4)(2-) self-aggregates and that are segregated from the Sn porphyrins. Possible internal structures of the nanotubes and mechanisms for their formation are discussed.

Electron transfer photosensitized by a tin lipoporphyrin in solution, micelles, and at water—organic solvent interfaces

Electron transfer photosensitized by a tin lipoporphyrin [Sn(IV) octakis((methoxycarbonyl-methyl)- meso-tetrakis-(((eicosanyloxy)carbonyl) phenyl)-porphyrin (SnLipoP)] is investigated under various solution conditions using a donor—SnLipoP—methylviologen (MV 2+) ternary system, where the donor is triethanolamine (TEA) or ethylenediaminetetraacetic acid (EDTA). The photoreaction of SnLipoP is compared with the photoreactions sensitized by common Sn porphyrins like tin protoporphyrin IX (SnPP) and octaethylporphyrin (SnOEP). A constant photoreaction rate is observed in a water/organic solvent (hexane, benzene) two-phase system in which the porphyrin (SnLipoP, SnOEP) is in the organic solvent and MV 2+ is in the aqueous phase. The rate is monitored by the change in the UV—visible absorption spectra produced by aqueous methylviologen radical MV ·+. In contrast with the two-phase system, macroscopically homogeneous solutions (aqueous SnPP and micellar solutions of SnLipoP, SnPP and SnOEP) give pseudo-logarithmic rates. These electron-transfer processes are completely consistent with reductive primary electron transfer to the tin porphyrin and optical shielding effects. Differences in the rates for SnLipoP and the other Sn porphyrins are explained by structural differences in the porphyrins. In particular, the structure of the porphyrin influences the phase in which the porphyrin resides, its location relative to interfacial regions, and the way it interacts with itself and other system components.

Metallomacrocycles with metalmetal bonds: synthesis, characterization and electrochemistry of [(P)SnRe(CO) 5]BF 4 and [{(P)Sn} 2Re(CO) 4]BF 4 derivatives, where P = tetra- p-tolyporphyrin or tetra- m-tolylporphyrin

The synthesis and characterization of bimetallic and trimetallic porphyrins of the type [(P)SnRe(CO) 5]BF 4 and [{(P)Sn} 2Re(CO) 4]BF 4 are reported where P is the dianion of tetra- p-tolyporphyrin (TpTP) or tetra- m-tolyporphyrin (TmTP). These metal-metal bonded complexes were synthesized by reaction of Re 2(CO) 10 with the corresponding (P)SnCl 2 derivatives in 1,2-dichlorobenzene followed by a reaction with NaBF 4 or TBABF 4 in toluene to give the BF − 4 salt. Each compound was characterized by a variety of spectroscopic and electrochemical techniques while the structures were assigned on the basis of FAB mass spectral data and by comparison of their physicochemical properties with data for related metalmetal bonded porphyrins previously synthesized in our laboratories. Each [(P)SnRe(CO) 5]BF 4 complex undergoes two reversible one-electron reductions at the porphyrin π-ring system while each [{(P)Sn} 2Re(CO) 4]BF 4 derivatives exhibits four reversible reductions in accordance with the presence of two Sn porphyrin units having interacting redox centers. These reductions also occur at the conjugated macrocycle. The first oxidation of each compound is irreversible and is associated with a cleavage of the tinrhenium bond.