Stephan Schulz
@uni-due.de
University of Duisburg-Essen
Scopus Publications
Scopus Publications
Mahendra K. Sharma, Hanns M. Weinert, Christoph Wölper, and Stephan Schulz
Wiley
AbstractGallaphosphene L(Cl)GaPGaL 1 (L=HC[C(Me)N(Ar)]2; Ar=2,6‐iPr2C6H3) reacts with N‐heterocyclic carbenes RNHC (RNHC=[CMeN(R)]2C; R=Me, iPr) to RNHC‐coordinated phosphinidenes RNHC→PGa(Cl)L (R=Me 2 a, iPr 2 b) and with isonitriles RNC (R=iPr, Cy) to 1,3‐phosphaazaallenes L(Cl)GaP=C=N−R (R=iPr 3 a, Cy 3 b), respectively. Quantum chemical calculations reveal that 2 a/2 b possess two localized lone pair of electrons, whereas 3 a/3 b only show one localized lone pair as was reported for gallaphosphene 1. 2 b reacts with 2.5 equivalents of a borane (THF ⋅ BH3) to the NHC‐stabilized phosphinidene‐borane complex [iPrNHC→P(BH2)]2(BH3)3 4 with concomitant formation of LGa(H)Cl 5. 2–5 are characterized by heteronuclear (1H, 13C{1H}, 31P{1H}) NMR and IR spectroscopy, elemental analysis, and single crystal X‐ray diffraction (sc‐XRD).
Sascha Saddeler, Ulrich Hagemann, Georg Bendt, and Stephan Schulz
Wiley
AbstractCore‐shell Co3O4@CoO nanoparticles were prepared by calcination of rock‐salt CoO and fully characterized by PXRD, TEM and XPS measurements. XPS studies showed that the Co(III) cation concentration steadily increased and the OER activity of the resulting core‐shell Co3O4@CoO nanoparticles decreased with increasing calcination time, which was attributed to the increasing presence of catalytically inactive Co(III) cations. The decrease in OER activity was also observed for untreated CoO nanoparticles (1) after chronopotentiometric (CP) treatment at 10 mA cm−2 for 18 h. The IR and EEL spectra of the resulting nanoparticles are comparable to those of a fully oxidized Co3O4 sample (1–300), that was prepared by calcining of the CoO sample (1) for 1 h at 300 °C.
Bin Li, Christoph Wölper, Hanns Micha Weinert, Hannah Siera, Gebhard Haberhauer, and Stephan Schulz
Wiley
AbstractReactions of LGa(Cl)P(cAAC) (L=HC[C(Me)N(2,6‐iPr2C6H3)]2, MecAAC (MecAAC=1‐(2,6‐di‐iso‐propylphenyl)‐3,3,5,5‐tetramethyl‐pyrrolidin‐2‐ylidene) with NaPCO and NaN3 gave LGa(PCO)P(MecAAC) (1) and LGa(N3)P(MecAAC) (2), respectively. DFT calculations on the nature of compounds 1 and 2 reveal a phosphaalkene rather than a carbene‐phosphinidene structure. The reaction of 1 with MecAAC resulted in a nucleophilic attack of the electron‐rich P atom on the γ‐C backbone of the β‐diketiminate ligand to give compound 3 as the major product and cyclic 1,2‐diphospha‐1,3‐butadiene LGa(P2OC)MecAAC (4) in minor yield.
Christoph Helling, Lotta Döhler, Oleksandr Kysliak, Helmar Görls, Phil Liebing, Christoph Wölper, Robert Kretschmer, and Stephan Schulz
Royal Society of Chemistry (RSC)
The superior basicity and enhanced reducing capability of the bis(gallanediyl) CyL2Ga21 compared to its monometallic counterpart LGa 2 is attributed to a synergistic interaction between the two GaI centres.
Leon Kapp, Christoph Wölper, Hannah Siera, Gebhard Haberhauer, and Stephan Schulz
Royal Society of Chemistry (RSC)
Catalytic hydroboration of aldehydes and ketones is achieved with alkoxysilylene 2. Quantum chemical calculations gave insights into the energetics of its formation and provide possible catalytic reaction mechanism.
Anna Bücker, Alexander Gehlhaar, Christoph Wölper, and Stephan Schulz
Royal Society of Chemistry (RSC)
The electron-rich acyclic germylene LGa(μ–Cl)GeArMes (1) activates unpolar bonds as is shown in oxidative addition reactions with H2 and P4, yielding L(Cl)GaGe(H)2ArMes (2) and L(Cl)Ga(P4)GeArMes (3).
Jannis Fidelius, Kai Schwedtmann, Sebastian Schellhammer, Jan Haberstroh, Stephen Schulz, Rongjuan Huang, Max C. Klotzsche, Antonio Bauzá, Antonio Frontera, Sebastian Reineke,et al.
Elsevier BV
Felix T. Haase, Eduardo Ortega, Sascha Saddeler, Franz-Philipp Schmidt, Daniel Cruz, Fabian Scholten, Martina Rüscher, Andrea Martini, Hyo Sang Jeon, Antonia Herzog,et al.
Royal Society of Chemistry (RSC)
Electrocatalytic OER activity of Co3O4 is enhanced by Fe near-surface decoration with a more pronounced formation of Co–FeOx(OH)y reaction zones comprising distinct redox-active Fe3+ and Co2+ sites as shown by comprehensive operando studies.
Hanns Micha Weinert, Christoph Wölper, Aleksa Radović, George E. Cutsail, Hannah Siera, Gebhard Haberhauer, and Stephan Schulz
Wiley
AbstractDiarsene [L(MeO)GaAs]2 (L=HC[C(Me)N(Ar)]2, Ar=2,6‐iPr2C6H3, 4) reacts with MeOTf and MeNHC (MeNHC=1,3,4,5‐tetra‐methylimidazol‐2‐ylidene) to the diarsene [L(TfO)GaAs]2 (5) and the carbene‐coordinated diarsene [L(MeO)GaAsAs(MeNHC)Ga(OMe)L] (6). The NHC‐coordination results in an inversion of the redox properties of the diarsene 4, which shows only a reversible reduction event at E1/2=−2.06 V vs Fc0/+1, whereas the carbene‐coordinated diarsene 6 shows a reversible oxidation event at E1/2=−1.31 V vs Fc0/+1. Single electron transfer reactions of 4 and 6 yielded [K[2.2.2.]cryp][L(MeO)GaAs]2 (8) and [L(MeO)GaAsAs(MeNHC)‐Ga(OMe)L][B(C6F5)4] (9) containing the radical anion [L(MeO)GaAs]2⋅− (8⋅−) and the NHC‐coordinated radical cation [L(MeO)GaAsAs(MeNHC)Ga(OMe)L]⋅+ (9⋅+), respectively, while the salt‐elimination reaction of the triflate‐coordinated diarsene 5 with Na[B(C6F5)4] gave [LGaAs]2[B(C6F5)4]2 (11) containing the dication [LGaAs]22+ (112+). Compounds 1–11 were characterized by 1H and 13C NMR, EPR (8, 9), IR, and UV‐Vis spectroscopy and by single crystal X‐ray diffraction (sc‐XRD). DFT calculations provided a detailed understanding of the electronic nature of the diarsenes (4, 6) and the radical ions (8⋅−, 9⋅+), respectively.
Carsten Placke-Yan, Georg Bendt, Soma Salamon, Joachim Landers, Heiko Wende, Ulrich Hagemann, and Stephan Schulz
Royal Society of Chemistry (RSC)
A versatile route for the synthesis of 8 to 10 nm sized metal-doped spinel MxCo3−xO4 nanoparticles (M = Al, V, Cr, Mn, Fe, Ni; x = 0.05, 0.1, 0.2) with homogeneous dopant distribution and their electrocatalytic OER performance is reported.
Yannick Schulte, Christoph Wölper, Susanne M. Rupf, Moritz Malischewski, Daniel J. SantaLucia, Frank Neese, Gebhard Haberhauer, and Stephan Schulz
Springer Science and Business Media LLC
Anna Bücker, Christoph Wölper, and Stephan Schulz
Elsevier BV
Anna Bücker, Christoph Wölper, Hannah Siera, Gebhard Haberhauer, and Stephan Schulz
Royal Society of Chemistry (RSC)
L(Cl)Ga-substituted germylenes react with ethylene with insertion into the Ga–Ge bonds to digermenes, which undergo [2 + 2] cycloaddition with ethylene to give 1,2-digermacyclobutanes.
Eduard Glöckler, Leon Kapp, Christoph Wölper, Marcel Schumacher, André H. Gröschel, and Stephan Schulz
Royal Society of Chemistry (RSC)
We report the structures and activity of homo- and heteroleptic ketodiiminate zinc complexes in the ring-opening polymerization of l-lactide. Homobimetallic complex 2 selectively gave cyclic polylactide, while linear polymers were formed with mononuclear complex 3.
Mahendra K. Sharma, Hanns M. Weinert, Bin Li, Christoph Wölper, Justin T. Henthorn, George E. Cutsail, Gebhard Haberhauer, and Stephan Schulz
Wiley
AbstractLGa(P2OC)cAAC 2 features a 1,2‐diphospha‐1,3‐butadiene unit with a delocalized π‐type HOMO and a π*‐type LUMO according to DFT calculations. [LGa(P2OC)cAAC][K(DB‐18‐c‐6)] 3[K(DB‐18‐c‐6] containing the 1,2‐diphospha‐1,3‐butadiene radical anion 3⋅− was isolated from the reaction of 2 with KC8 and dibenzo‐18‐crown‐6. 3 reacted with [Fc][B(C6F5)4] (Fc=ferrocenium) to 2 and with TEMPO to [L−HGa(P2OC)cAAC][K(DB‐18‐c‐6)] 4[K(DB‐18‐c‐6] containing the 1,2‐diphospha‐1,3‐butadiene anion 4−. The solid state structures of 2, 3K(DB‐18‐c‐6], and 4[K(DB‐18‐c‐6] were determined by single crystal X‐ray diffraction (sc‐XRD).
Shiyang He, Amin Bahrami, Xiang Zhang, Magdalena Ola Cichocka, Jun Yang, Jaroslav Charvot, Filip Bureš, Alla Heckel, Stephan Schulz, and Kornelius Nielsch
Elsevier BV
Hanns M. Weinert, Christoph Wölper, and Stephan Schulz
MDPI AG
Monovalent group 13 diyls are versatile reagents in oxidative addition reactions. We report here [1,4]-cycloaddition reactions of β-diketiminate-substituted diyls LM (M = Al, Ga, In, Tl; L = HC[C(Me)NDipp]2, Dipp = 2,6-iPr2C6H3) with various 1,2-diketones to give 5-metalla-spiro[4.5]heterodecenes 1, 4–6, and 8–10, respectively. In contrast, the reaction of LTl with acenaphthenequinone gave the [2,3]-cycloaddition product 7, with Tl remaining in the +1 oxidation state. Compound 1 also reacted with a second equivalent of butanedione as well as with benzaldehyde in aldol-type addition reactions to the corresponding α,β-hydroxyketones 2 and 3, while a reductive activation of a benzene ring was observed in the reaction of benzil with two equivalents of LAl to give the 1,4-aluminacyclohex-2,4-dien 12. In addition, the reaction of L’BCl2 (L = HC[C(Me)NC6F5]2) with one equivalent of benzil in the presence of KC8 gave the corresponding 5-bora-spiro[4.5]heterodecene 13, whereas the hydroboration reaction of butanedione with L’BH2 (14), which was obtained from the reaction of L’BCl2 with L-selectride, failed to give the saturated 5-bora-spiro[4.5]heterodecane.
Hanns M. Weinert, Yannick Schulte, Alexander Gehlhaar, Christoph Wölper, Gebhard Haberhauer, and Stephan Schulz
Royal Society of Chemistry (RSC)
Salt metathesis of L(TfO)Ga-substituted dipnictenes allowed for the synthesis of heavy dipnictene dications, which can be considered as isoelectronic analogues of the butadiene dication.
Stephan Schulz and Christian Müller
Wiley
Xiaofei Sun, Alexander Hinz, Stephan Schulz, Lisa Zimmermann, Manfred Scheer, and Peter W. Roesky
Royal Society of Chemistry (RSC)
Insertion and functionalization of gallasilylenes [LPhSi–Ga(Cl)LBDI] (LPh = PhC(NtBu)2; LBDI = [{2,6-iPr2C6H3NCMe}2CH]) into the cyclo-E5 rings of [Cp*Fe(η5-E5)] (Cp* = η5-C5Me5; E = P, As) are reported.
Bin Li, Hanns Micha Weinert, Christoph Wölper, and Stephan Schulz
American Chemical Society (ACS)
Sepideh Izadi, Ahana Bhattacharya, Sarah Salloum, Jeong Woo Han, Lauritz Schnatmann, Ulrike Wolff, Nicolas Perez, Georg Bendt, Inga Ennen, Andreas Hütten,et al.
Wiley
Three-dimensional topological insulators (3D TI) exhibit conventional parabolic bulk bands and protected Dirac surface states. A thorough investigation of the different transport channels provided by the bulk and surface carriers using macroscopic samples may provide a path toward accessing superior surface transport properties. Bi2 Te3 materials make promising 3D TI models; however, due to their complicated defect chemistry, these materials have a high number of charge carriers in the bulk that dominate the transport, even as nanograined structures. To partially control the bulk charge carrier density, herein the synthesis of Te-enriched Bi2 Te3 nanoparticles is reported. The resulting nanoparticles are compacted into nanograined pellets of varying porosity to tailor the surface-to-volume ratio, thereby emphasizing the surface transport channels. The nanograined pellets are characterized by a combination of resistivity, Hall- and magneto-conductance measurements together with (THz) time-domain reflectivity measurements. Using the Hikami-Larkin-Nagaoka (HLN) model, a characteristic coherence length of ≈200 nm is reported that is considerably larger than the diameter of the nanograins. The different contributions from the bulk and surface carriers are disentangled by THz spectroscopy, thus emphasizing the dominant role of the surface carriers. The results strongly suggest that the surface transport carriers have overcome the hindrance imposed by nanoparticle boundaries.
Swapnil Varhade, Emmanuel Batsa Tetteh, Sascha Saddeler, Simon Schumacher, Harshitha Barike Aiyappa, Georg Bendt, Stephan Schulz, Corina Andronescu, and Wolfgang Schuhmann
Wiley
The electrocatalytic activity for the oxygen evolution reac-tion in alkaline electrolyte of hexagonal spinel Co3O4 nanoparticles derived using scanning electrochemical cell microscopy (SECCM) is correlated with scanning electron microscopy and atomic force microscopy images of the droplet landing sites. A unique way to deconvolute the intrinsic catalytic activity of individual crystal facets of the hexagonal Co3O4 spinel particle is demonstrated in terms of the turnover frequency (TOF) of surface Co atoms. The top surface expo-sing 111 crystal planes displayed a thickness-dependent TOF with a TOF of about 100 s-1 at a potential of 1.8 V vs RHE and a particle thickness of 100 nm. The edge of the particle exposing (110) planes, however, showed an average TOF of 270 ± 68 s-1 at 1.8 V vs RHE and no correlation with particle thickness. However, the higher atomic density of Co atoms on the edge surface (2.5 times of the top) renders the overall catalytic activity of the edge planes significantly higher than that of the top planes. The use of a free-diffusing Os- complex in the alkaline electrolyte revealed the low electrical conductivity through individual particles which explains the thickness-dependent TOF of the top planes and could be a reason for the low activity of the top (111) planes.
Janis Timoshenko, Felix T. Haase, Sascha Saddeler, Martina Rüscher, Hyo Sang Jeon, Antonia Herzog, Uta Hejral, Arno Bergmann, Stephan Schulz, and Beatriz Roldan Cuenya
American Chemical Society (ACS)
Bimetallic transition-metal oxides, such as spinel-like CoxFe3–xO4 materials, are known as attractive catalysts for the oxygen evolution reaction (OER) in alkaline electrolytes. Nonetheless, unveiling the real active species and active states in these catalysts remains a challenge. The coexistence of metal ions in different chemical states and in different chemical environments, including disordered X-ray amorphous phases that all evolve under reaction conditions, hinders the application of common operando techniques. Here, we address this issue by relying on operando quick X-ray absorption fine structure spectroscopy, coupled with unsupervised and supervised machine learning methods. We use principal component analysis to understand the subtle changes in the X-ray absorption near-edge structure spectra and develop an artificial neural network to decipher the extended X-ray absorption fine structure spectra. This allows us to separately track the evolution of tetrahedrally and octahedrally coordinated species and to disentangle the chemical changes and several phase transitions taking place in CoxFe3–xO4 catalysts and on their active surface, related to the conversion of disordered oxides into spinel-like structures, transformation of spinels into active oxyhydroxides, and changes in the degree of spinel inversion in the course of the activation treatment and under OER conditions. By correlating the revealed structural changes with the distinct catalytic activity for a series of CoxFe3–xO4 samples, we elucidate the active species and OER mechanism.
Jian Zhang, Wenhui He, Thomas Quast, João R. C. Junqueira, Sascha Saddeler, Stephan Schulz, and Wolfgang Schuhmann
Wiley
Abstract Electrochemically converting nitrate to ammonia is an essential and sustainable approach to restoring the globally perturbed nitrogen cycle. The rational design of catalysts for the nitrate reduction reaction (NO3RR) based on a detailed understanding of the reaction mechanism is of high significance. We report a Cu2O+Co3O4 tandem catalyst which enhances the NH3 production rate by ≈2.7‐fold compared to Co3O4 and ≈7.5‐fold compared with Cu2O, respectively, however, most importantly, we precisely place single Cu2O and Co3O4 cube‐shaped nanoparticles individually and together on carbon nanoelectrodes provide insight into the mechanism of the tandem catalysis. The structural and phase evolution of the individual Cu2O+Co3O4 nanocubes during NO3RR is unveiled using identical location transmission electron microscopy. Combining single‐entity electrochemistry with precise nano‐placement sheds light on the dynamic transformation of single catalyst particles during tandem catalysis in a direct way.