Papers by Matthias Schwalbe
Inorganic Chemistry, 2015
A series of heterodinuclear complexes (M-1-Re) based on a phenanthroline (phen) extended tetrames... more A series of heterodinuclear complexes (M-1-Re) based on a phenanthroline (phen) extended tetramesityl porphyrin ligand (H2-1) has been prepared. The phen moiety of this ligand selectively coordinates a Re(I) tricarbonyl chloride unit, whereas the metal in the porphyrin moiety has been varied: namely, Cu, Pd, Zn, Co, or Fe was used. These dinuclear complexes were fully characterized by standard analytical methods. Additionally, a crystal structure of Cu-1-Re·5.5(C7H8)·0.5(C6H6) could be obtained, and extended time-resolved emission lifetime measurements were conducted. Furthermore, their ability to catalyze the photochemical reduction of CO2 to CO was investigated. Light-driven CO2 reduction experiments were performed in dimethylformamide (DMF) using triethylamine (TEA) as the sacrificial electron donor. The TONs (turnover numbers) of CO were determined and revealed a surprising catalytic activity that is obviously independent from the redox activity of the porphyrin metal. We have recently shown that the parent M-1 compounds are active photocatalysts, but the catalytic activity was dependent on the redox activity of the porphyrin metal. In the case of the new heterodinuclear complexes M-1-Re reported in this study, the catalytic active center seems to be the Re(I) moiety and not the porphyrin. Surprisingly, Zn-1-Re proved to be the most active compound in this series showing a TONCO of 13 after 24 h of illumination using a >375 nm cutoff filter while all other compounds showed minimal activity under this condition.
Coordination Chemistry Reviews, 2012
Chemistry (Weinheim an der Bergstrasse, Germany), Jan 20, 2015
Eight [Ir(bpy)Cp*Cl](+) -type complexes (bpy= bipyridine, Cp*=1,2,3,4,5-pentamethylcyclopentadien... more Eight [Ir(bpy)Cp*Cl](+) -type complexes (bpy= bipyridine, Cp*=1,2,3,4,5-pentamethylcyclopentadienyl) containing differently substituted bipyridine ligands were synthesized and characterized. Cyclic voltammetry (CV) of the complexes in Ar-saturated acetonitrile solutions showed that the redox behavior of the complexes could be fine tuned by the electronic properties of the substituted bipyridine ligands. Further CV in CO2 -saturated MeCN/H2 O (9:1, v/v) solutions showed catalytic currents for CO2 reduction. In controlled potential electrolysis experiments (MeCN/MeOH (1:1, v/v), Eapp =-1.80 V vs Ag/AgCl), all of the complexes showed moderate activity in the electrocatalytic reduction of CO2 with good stability over at least 15 hours. This electrocatalytic process was selective toward formic acid, with only traces of dihydrogen or carbon monoxide and occasionally formaldehyde as byproducts. However, the turnover frequencies and current efficiencies were quite low. No direct correlation...
Dalton transactions (Cambridge, England : 2003), Jan 14, 2014
The synthesis and characterisation of an asymmetric potential bridging ligand bmptpphz (bmptpphz ... more The synthesis and characterisation of an asymmetric potential bridging ligand bmptpphz (bmptpphz = 2,17-bis(4-methoxyphenyl)tetrapyrido[3,2-a:2',3'-c:3'',2''-h:2''',3'''-j] phenazine) is presented. This ligand contains a 1,10-phenanthroline (phen) and a 2,9-disubstituted phen sphere and possesses a strong absorbance in the visible. Facile coordination of the phen sphere to a Ru(tbbpy)2 core leads to Ru(bmptpphz) ([(tbbpy)2Ru(bmptpphz)](PF6)2; tbbpy = 4,4'-di-tert-butyl-2,2'-bipyridine). UV-vis, emission, resonance Raman and theoretical investigations show that this complex possesses all properties associated with a Ru(tpphz) ([(tbbpy)2Ru(tpphz)](PF6)2; tpphz = tetrapyrido[3,2-a:2',3'-c:3'',2''-h:2''',3'''-j] phenazine) moiety and that the ligand based absorbances in the vis-part also populate an MLCT like state. The coordination of a Pd-core in the new 2,9-disubstituted phen spher...
Current opinion in chemical biology, Jan 18, 2015
Four-electron reduction of dioxygen to water and splitting of water to dioxygen are extremely imp... more Four-electron reduction of dioxygen to water and splitting of water to dioxygen are extremely important processes in the context of attaining clean renewable energy sources. High-valent metal-oxo cores are proposed as reactive intermediates in these vital processes, although they have only been isolated in extremely rare cases in the biological systems thereby making the mechanism ambiguous. Recent biomimetic studies have, however, aided in our understanding of the fundamental reactivity of the high-valent metal-oxo species in various reactions relevant to energy conversion. All these studies are summarized in the present review.
European Journal of Inorganic Chemistry, 2014
ABSTRACT Through an optimized synthetic procedure, metalloligand 5, which features a hetero-Pacma... more ABSTRACT Through an optimized synthetic procedure, metalloligand 5, which features a hetero-Pacman scaffold comprising a porphyrin and a terpyridine moiety, has been assembled by a double Suzuki reaction. In a subsequent step, a ruthenium-bipyridine fragment was introduced at the terpyridine coordination site of metalloligand 5 to form complex 6, which was fully characterized and its potential application in water oxidation catalysis tested. A number of side-products were isolated and characterized during the two-step synthesis procedure, including a hydroxylated version of the boronic acid substituted precursor molecule derived by a base-assisted rearrangement. The compounds described herein extend the Pacman concept to the assembly of different metal combinations with different coordination spheres and their interactions in the activation of small molecules.
BioInorganic Reaction Mechanisms, 2012
O-O bond formation is one of the key reactions that ensure life on earth. Dioxygen is produced in... more O-O bond formation is one of the key reactions that ensure life on earth. Dioxygen is produced in photosystem II, as well as in chlorite dismutase. The reaction mechanisms occurring in the enzyme active sites are controversially discussed -although their structures have been resolved with less unambiguity. Artificial molecular catalysts have been developed in the last years to obtain vital insights into the O-O bond formation step. This review put together the scarce literature on the topic that helped in understanding the key steps in the O-O bond formation reactions mediated by high-valent oxo complexes of the first-row transition metals.
Nachrichten aus der Chemie, 2010
ABSTRACT Gelänge es, Wasser durch Licht effizient in Wasserstoff und Sauerstoff zu spalten, wäre ... more ABSTRACT Gelänge es, Wasser durch Licht effizient in Wasserstoff und Sauerstoff zu spalten, wäre das die Lösung der Energieprobleme der Menschheit. Ein inspirierendes Vorbild für diese katalytische Umsetzung ist die biologische Photosynthese. Die Herausforderung für die Chemie besteht darin, geeignete Photokatalysatoren zu entwickeln.
Journal of the American Chemical Society, 2011
The construction of a new class of compounds--the hangman corroles--is provided efficiently by th... more The construction of a new class of compounds--the hangman corroles--is provided efficiently by the modification of macrocyclic forming reactions from bilanes. Hangman cobalt corroles are furnished in good yields from a one-pot condensation of dipyrromethane with the aldehyde of a xanthene spacer followed by metal insertion using microwave irradiation. In high oxidation states, X-band EPR spectra and DFT calculations of cobalt corrole axially ligated by chloride are consistent with the description of a Co(III) center residing in the one-electron oxidized corrole macrocycle. These high oxidation states are likely accessed in the activation of O-O bonds. Along these lines, we show that the proton-donating group of the hangman platform works in concert with the redox properties of the corrole to enhance the catalytic activity of O-O bond activation. The hangman corroles show enhanced activity for the selective reduction of oxygen to water as compared to their unmodified counterparts. The oxygen adduct, prior to oxygen reduction, is characterized by EPR and absorption spectroscopy.
Journal of Organometallic Chemistry, 2006
The nickel(0) complex [Ni(bpy)(cod)] (bpy: 2,2 0 -bipyridine, cod: cycloocta-1,5-diene) was used ... more The nickel(0) complex [Ni(bpy)(cod)] (bpy: 2,2 0 -bipyridine, cod: cycloocta-1,5-diene) was used as a mild reducing reagent for the synthesis of the extremely reactive low-valent palladium complexes [Pd 2 X 2 (cod) 2 ] (1: X = Cl, 2: X = Br), Pd(cod) 2 (3) and Pd(norbornene) 3 (4). The X-ray analysis of 1 showed that the two [Pd(cod)(Cl)] moieties are only connected by a short Pd(I)-Pd(I) bond (bond length: 2.5379(4) Å ) with the chloride ions as monodentate ligands. The X-ray structure of 3 which is also known to be an extremely reactive compound could be determined by X-ray diffraction. As expected, the Pd(0) centre is surrounded by the two cod ligands to form a PdC 4 tetrahedron with typical Pd-C bond lengths. The crystal structure of 3 shows it to be very similar to the closely related complexes M(cod) 2 (M: Ni, Pt). The X-ray structure of 4 displays that the Pd(0) centre is in a trigonal planar environment of the three olefin groups. According to 1 H NMR measurements the complexes have the same structure in solution as found in the solid state.
Inorganic Chemistry, 2011
Iron corroles modified with a xanthene scaffold are delivered from easily available starting mate... more Iron corroles modified with a xanthene scaffold are delivered from easily available starting materials in abbreviated reaction times. These new iron corroles have been spectroscopically examined with particular emphasis on defining the oxidation state of the metal center. Investigation of their electronic structure using (57)Fe Mössbauer spectroscopy in conjunction with density functional theory (DFT) calculations reveals the non-innocence of the corrole ligand. Although these iron corroles contain a formal Fe(IV) center, the deprotonated corrole macrocycle ligand is one electron oxidized. The electronic ground state of these complexes is best described as an intermediate spin S = 3/2 Fe(III) site strongly antiferromagnetically coupled to the S = 1/2 of the monoradical dianion corrole [Fe(III)Cl-corrole(+•)]. We show here that iron corroles as well as xanthene-modified and hangman xanthene iron corroles are redox active and catalyze the disproportionation of hydrogen peroxide via the catalase reaction, and that this activity scales with the oxidation potential. The meso position of corrole macrocycle is susceptible toward nucleophilic attack during catalase turnover. The reactivity of peroxide within the hangman cleft reported here adds to the emerging theme that corroles are good at catalyzing two-electron activation of the oxygen-oxygen bond in a variety of substrates.
Organic letters, Jan 5, 2010
A two-step synthetic method has been designed to furnish hangman porphyrins in good yields from e... more A two-step synthetic method has been designed to furnish hangman porphyrins in good yields from easily available starting materials. The use of the microwave irradiation technique has been found to be valuable for delivering the carboxylic acid hanging group in a much simplified and less time-consuming basic ester hydrolysis (4 h vs 7 days under harsh acidic conditions). The new route facilitates the synthesis of various hangman porphyrins that previously had limited or no access.
European Journal of Inorganic Chemistry, 2008
Irradiation of a ruthenium polypyridyl complex in the presence of oxygen leads to the oxidation o... more Irradiation of a ruthenium polypyridyl complex in the presence of oxygen leads to the oxidation of a benzodipyridophenazine ligand to a quinone. The corresponding tetraazatetrapyridopentacene complex is not oxidized under the same conditions.
European Journal of Inorganic Chemistry, 2008
Keywords: Ruthenium / Bipyridine / Microwave-assisted reaction / Raman spectroscopy Poly(bipyridi... more Keywords: Ruthenium / Bipyridine / Microwave-assisted reaction / Raman spectroscopy Poly(bipyridine)ruthenium complexes with carboxylate anchor groups are key components in dye-sensitised solar cells. In this contribution, an improved microwave-assisted synthetic procedure is presented for the important building block [RuCl 2 (dcmb) 2 ] (dcmb = 4,4Ј-dimethoxycarbonyl-2,2Јbipyridine), which results in short reaction times and high purity. The methyl esters are easily deprotected to give free carboxylate functions. In addition, a full structural, spectral and electrochemical characterisation of a series of complexes [a]
European Journal of Inorganic Chemistry, 2007
ABSTRACT The syntheses of the complexes [M(TmMe)(CO)2(NO)] (M = Mo, W) by reaction of NOBF4 with ... more ABSTRACT The syntheses of the complexes [M(TmMe)(CO)2(NO)] (M = Mo, W) by reaction of NOBF4 with [M(TmMe)(CO)3]– are reported and their spectroscopic characterisation and crystal structures are described. The analogous Cr complex could not be prepared by this methodology. The complexes adopt the expected pseudo-octahedral geometry. Complexes [M(L)(CO)2(NO)] (M = Cr, Mo, W; L = Cp, Tp and TmMe) together with the hypothetical [Mo(CO)2(NO)]+ cation were subjected to DFT calculations. Geometry-optimised structures closely parallel the crystallographic determinations and indicate that the complex [Cr(TmMe)(CO)2(NO)] is not inherently unstable. The DFT calculations allow the assignment of the C–O and N–O stretches in the IR spectrum and give insight into both the M–NO bonding and the metal to tripodal ligand bonding. The electron-donor strengths are confirmed to lie in the order TmMe > Tp > Cp. A side reaction of the B–H moiety of the TmMe anion with NO+ results in the isolation of the dimethylformamide adduct of (trismethimazolyl)borane, providing further evidence that the reaction pathways of the TmR ligands are more varied and less passive than in the chemistry of the nitrogen-based scorpionates.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)
Dalton Transactions, 2007
The synthesis and structure of two related sodium complexes are reported which demonstrate that s... more The synthesis and structure of two related sodium complexes are reported which demonstrate that sulfur can preferentially complex to sodium irrespective of the presence of more apposite donor species such as DMF.
Dalton Transactions, 2010
The complex [(dmcb) 2 Ru(dppz)](PF 6 ) 2 shows unexpected luminescence in water implying fundamen... more The complex [(dmcb) 2 Ru(dppz)](PF 6 ) 2 shows unexpected luminescence in water implying fundamentally different excited state relaxation pathways than are typically observed for complexes of this kind.
Dalton Transactions, 2010
A series of novel regioselective substituted tpphz ligands and two novel mononuclear ruthenium co... more A series of novel regioselective substituted tpphz ligands and two novel mononuclear ruthenium complexes of the type [(tbbpy)(2)Ru(tpphzR(n))](PF(6))(2) (where tbbpy = 4,4'-di-tert.-butyl-2,2'-bipyridine, tpphz = tetrapyrido[3,2-a:2',3'-c:3'',2''-h:2''',3'''-j]phenazine, with n = 2 and R represents the bromine substituents at different positions) have been synthesized. All compounds were completely characterized by NMR and MS spectroscopy, absorption and steady-state emission spectroscopy as well as emission lifetime and electrochemical measurements. Additionally the solid-state structures of the two isomers [(tbbpy)(2)Ru(Br(2)tpphz)](PF(6))(2) 6 and [(tbbpy)(2)Ru(tpphzBr(2))](PF(6))(2) 7 are presented and compared with the results of density-functional theory calculations (DFT). Furthermore calculated Raman spectra were obtained by means of DFT calculations and used to assign the vibrational modes of the measured off resonance Raman spectra. A clear influence caused by the electronic effects of the…
Chemistry - A European Journal, 2013
Soft scorpionates have thus far been seen mainly as a family of ligands. Their chemistry is exten... more Soft scorpionates have thus far been seen mainly as a family of ligands. Their chemistry is extended here to the production of novel cationic macrocycles using dihaloalkanes. By replacing the dihaloalkanes with mild oxidising agents (NO(+), I2) we obtain two unique polycyclic heterocycles. The mechanism which leads to the formation of these polycyclic heterocycles is investigated using ab initio DFT calculations.
Chemistry - A European Journal, 2009
Photoinduced electron-transfer processes within a precatalyst for intramolecular hydrogen evoluti... more Photoinduced electron-transfer processes within a precatalyst for intramolecular hydrogen evolution [(tbbpy)(2)Ru(tpphz)PdCl(2)](2+) (RuPd; tbbpy = 4,4'-di-tert-butyl-2,2'-bipyridine, tpphz = tetrapyrido[3,2-a:2',3'c:3'',2'',-h:2''',3'''-j]phenazine) have been studied by resonance Raman and ultrafast time-resolved absorption spectroscopy. By comparing the photophysics of the [(tbbpy)(2)Ru(tpphz)](2+) subunit Ru with that of the supramolecular catalyst RuPd, the individual electron-transfer steps are assigned to kinetic components, and their dependence on solvent is discussed. The resonance Raman data reveal that the initial excitation of the molecular ensemble is spread over the terminal tbbpy and the tpphz ligands. The subsequent excited-state relaxation of both Ru and RuPd on the…
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Papers by Matthias Schwalbe