Showing papers by "Martin Lutz published in 2017"
TL;DR: The efficient hydrogenation of esters with manganese catalysts based on simple bidentate aminophosphine ligands at Mn concentrations as low as 0.2 mol % in the presence of sub‐stoichiometric amounts of KOtBu base is reported.
Abstract: Catalytic hydrogenation of carboxylic acid esters is essential for the green production of pharmaceuticals, fragrances, and fine chemicals. Herein, we report the efficient hydrogenation of esters with manganese catalysts based on simple bidentate aminophosphine ligands. Monoligated Mn PN complexes are particularly active for the conversion of esters into the corresponding alcohols at Mn concentrations as low as 0.2 mol % in the presence of sub-stoichiometric amounts of KOtBu base.
149 citations
TL;DR: This investigation unambiguously reveals that thermodynamic immiscibility and crystallization direct the self-assembly of ODMS-based block molecules, and highlights the “ingredient approach” to obtain perfect order in sub-10 nm structured materials with a simple strategy built on a crystalline “hard” moiety and an incompatible “soft” ODMS partner.
Abstract: Block molecules belong to a rapidly growing research field in materials chemistry in which discrete macromolecular architectures bridge the gap between block copolymers (BCP) and liquid crystals (LCs). The merging of characteristics from both BCP and LCs is expected to result in exciting breakthroughs, such as the discovery of unexpected morphologies or significant shrinking of domain spacings in materials that possess the high definition of organic molecules and the processability of polymers. Here we report the bulk self-assembly of two families of monodisperse block molecules comprised of naphthalenediimides (NDIs) and oligodimethylsiloxanes (ODMS). These materials are characterized by waxy texture, strong long-range order, and very low mobility, typical properties of conformationally disordered crystals. Our investigation unambiguously reveals that thermodynamic immiscibility and crystallization direct the self-assembly of ODMS-based block molecules. We show that a synergy of high incompatibility betw...
41 citations
TL;DR: Results show for the first time that phosphinines can be used efficiently as π-accepting ligands in Au(i)-catalyzed cycloisomerization reactions.
Abstract: Gold(i) complexes based on a 2,4,6-triarylphosphinine and a mesoionic carbene derivative have been prepared and characterized crystallographically. Although structurally related, both heterocycles differ significantly in their donor/acceptor properties. These opposed electronic characteristics have been exploited in Au(i)-catalyzed cycloisomerization reactions. For the conversion of the standard substrate dimethyl 2-(3-methylbut-2-enyl)-2-(prop-2-ynyl)malonate the results obtained for both Au-catalysts were found to be very similar and comparable to the ones reported in the literature for other carbene- or phosphorus(iii)-based Au(i)-complexes. In contrast, a clear difference between the catalytic systems was found for the cycloisomerization of the more challenging substrate N-2-propyn-1-ylbenzamide. A combination of the phosphinine-based complex and [AgSbF6] or [Cu(OTf)2] leads to a catalytic species, which is more active than the mesoionic carbene-based coordination compound. We attribute these differences to the stronger π-accepting ability of phosphinines in comparison to mesoionic carbenes. The here presented results show for the first time that phosphinines can be used efficiently as π-accepting ligands in Au(i)-catalyzed cycloisomerization reactions.
32 citations
TL;DR: These unprecedented pathways grant access to both P1 - and P3 -containing organophosphorus compounds in two simple steps from white phosphorus.
Abstract: Two [3+1] fragmentations of the Lewis acid stabilized bicyclo[1.1.0]tetraphosphabutanide Li[Mes*P4⋅ BPh3] (Mes*=2,4,6-tBu3C6H2) are reported. The reactions proceed by extrusion of a P1 fragment, induced by either an imidazolium salt or phenylisocyanate, with release of the transient triphosphirene Mes*P3, which was isolated as a dimer and trapped by 1,3-cyclohexadiene as a Diels–Alder adduct. DFT quantum chemical computations were used to delineate the reaction mechanisms. These unprecedented pathways grant access to both P1- and P3-containing organophosphorus compounds in two simple steps from white phosphorus.
31 citations
TL;DR: To enable synthetic access to compact entangled multimacrocyclic molecules, a new strategy is developed that is covalently connected to the linear precursors, and spatially directs the sterically congested backfolding macrocyclizations that are required to give quasi[1]catenanes.
Abstract: Due to their well-defined three-dimensional geometry, spiro compounds are widely utilized in drug research. From the central tetrahedral carbon atom, besides the regular structure, an inverted spiro connectivity may be envisioned. Here we disclose the synthesis of this molecule class that we have coined quasi[1]catenanes. Next to their fascinating and aesthetic shape, the higher compactness as compared to regular spiro bicycles is noteworthy. To enable synthetic access to compact entangled multimacrocyclic molecules, we have developed a new strategy. The key element is a template, which is covalently connected to the linear precursors, and spatially directs the sterically congested backfolding macrocyclizations that are required to give quasi[1]catenanes. Similarly, quasi[1]rotaxanes are made.
24 citations
TL;DR: In this paper, a bis-isoindoline-bis-pyridine ligand platform based on the BPBP ligand (BPBP = N,N′-bis(2-picolyl)-2,2′-bipyrrolidine) has been synthesized and applied in selective aliphatic C-H oxidation with hydrogen peroxide under mild conditions.
Abstract: Iron complexes derived from a bis-isoindoline-bis-pyridine ligand platform based on the BPBP ligand (BPBP = N,N′-bis(2-picolyl)-2,2′-bis-pyrrolidine) have been synthesized and applied in selective aliphatic C–H oxidation with hydrogen peroxide under mild conditions. The introduction of benzene moieties on the bis-pyrrolidine backbone leads to an increased preference of tertiary over secondary C–H bond oxidation (3°/2° ratio up to 33). On the other hand, substituting the meta-position of the pyridines with bulky silyl groups affords enhanced secondary C–H oxidation selectivity and generally leads to higher product yields and mass balances.
22 citations
TL;DR: The reactivity of the geminal phosphinoborane tBu2PCH2BPh2 towards terminal alkynes, nitriles and nitrilium salts is investigated and insight into the reaction mechanisms was gained by DFT calculations.
Abstract: The reactivity of the geminal phosphinoborane tBu2PCH2BPh2 towards terminal alkynes, nitriles and nitrilium salts is investigated. Terminal alkynes react via C–H bond splitting (deprotonation) resulting in the formation of phosphonium borates. In contrast, both nitriles and nitrilium salts undergo addition reactions resulting in the formation of five-membered heterocycles. All compounds were characterized by multinuclear NMR spectroscopy, and single-crystal X-ray structure determinations. Insight into the reaction mechanisms was gained by DFT calculations.
21 citations
TL;DR: The selective synthesis of purely organic cages offering hetero-sequenced functionalized cavities and the largest described cage has been investigated towards its ability for guest encapsulation and is able to selectively encapsulate functionalized arenes that offer a matching substitution pattern.
16 citations
TL;DR: Structural changes in the ligand framework make BMIMPh2- as a perceptible non-innocent ligand in contrast to NacNac type ligands.
Abstract: A new β-diiminate ligand (the bis(1-methyl-4,5-diphenyl-1H-imidazol-2-yl)methane anion, BMIMPh2- ) is introduced, in which the ligand framework bears an extended imidazole-based π-system in conjugation with a formal β-diketiminates (NacNac) backbone. Bis-ligated transition metal complexes (Co, Zn) featuring this anionic ligand undergo a series of four consecutive single-electron oxidations that are all ligand-based. The singly and doubly oxidized complexes can be synthesized on a preparative scale and have been fully characterized by various spectroscopic techniques. This is in sharp contrast to the corresponding NacNac-based complexes in which only singly oxidized complexes were isolated and characterized. Single crystal X-ray structure determination revealed a correlation between the intra-ligand metrical parameters and the oxidation state of BMIMPh2- . These structural changes in the ligand framework make BMIMPh2- as a perceptible non-innocent ligand in contrast to NacNac type ligands.
13 citations
TL;DR: In this article, the thermally stable adduct Ph3POH+OTf is efficiently converted into triphenylphosphine at 100 °C in the presence of readily available hydrosiloxanes.
Abstract: Recently, Bronsted acids, such as phosphoric acids, carboxylic acids, and triflic acid, were found to catalyze the reduction of phosphine oxides to the corresponding phosphines. In this study, we fully characterize the HCl, HOTf, and Me2SiHOTf adducts of triphenylphosphine oxide and find that the thermally stable adduct Ph3POH+OTf– is efficiently converted into triphenylphosphine at 100 °C in the presence of readily available hydrosiloxanes. Under the same reaction conditions, also Ph3POSiMe2H+OTf– selectively affords triphenylphosphine indicating that silylated phosphine oxides are likely intermediates in this process.
12 citations
TL;DR: Kinetic experiments using the strong organic base 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) show that all three possible isohexide dinitrile isomers exist within a dynamic equilibrium, and an epimerization mechanism based on density functional theory (DFT) calculations is proposed.
Abstract: Building blocks of isohexides extended by one carbon atom at the 2- or 5-positions are now synthetically accessible by a convenient, selective, base-catalyzed epimerization of the corresponding dinitriles. Kinetic experiments using the strong organic base 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) show that all three possible isohexide dinitrile isomers exist within a dynamic equilibrium. An epimerization mechanism based on density functional theory (DFT) calculations is proposed. Structural identification of all three possible isomers is based on NMR analysis and single crystal x-ray crystallography. DFT calculations confirm that the observed crystal structures are indeed the lowest energy conformers of these isohexide derivatives.
TL;DR: Oxidation of complexes using ferrocenium in the presence of Cl- ions regenerated the original [M(BMdiPhIK)Cl2] complexes, showing the reversibility of the coupling process.
Abstract: The ability of the bis(imidazolyl)ketone ligand BMdiPhIK (bis(1-methyl-4,5-diphenylimidazolyl)ketone) to function as a redox active ligand has been investigated. The reduction of [M(BMdiPhIK)Cl2] (M = Fe and Zn) complexes resulted in a pinacol-type coupling to form dinuclear complexes featuring very weak and abnormally elongated C–C bonds (1.729(5) and 1.708(3) A for Fe and Zn, respectively). Oxidation of these complexes using ferrocenium in the presence of Cl− ions regenerated the original [M(BMdiPhIK)Cl2] complexes, showing the reversibility of the coupling process. This makes it a potentially interesting approach for the storage of electrons and application of the BMdiPhIK ligand as a redox active ligand.
TL;DR: Interestingly, complex 5 also acts as a catalyst for electrochemical N3 − oxidation (E p≈−0.23 V vs. Fc+/0) in the presence of excess azide, of potential relevance for the design of azide‐based and direct ammonia fuel cells, expelling only harmless dinitrogen as an exhaust gas.
Abstract: One-electron oxidation of the rhodium(I) azido complex [Rh(N3)(PNP)] (5), bearing the neutral, pyridine-based PNP ligand 2,6-bis(di-tert-butylphosphinomethyl)pyridine, leads to instantaneous and selective formation of the mononuclear rhodium(I) dinitrogen complex [Rh(N2)(PNP)]+ (9+). Interestingly, complex 5 also acts as a catalyst for electrochemical N3− oxidation (Ep≈−0.23 V vs. Fc+/0) in the presence of excess azide. This is of potential relevance for the design of azide-based and direct ammonia fuel cells, expelling only harmless dinitrogen as an exhaust gas.
TL;DR: Select first steps are reported by reacting P4 with a metal anion [Cp*Fe(CO)2]− (Cp-=C5(CH3)5), which, in the presence of bulky Lewis acids, leads to unique TM‐substituted LA‐stabilized bicyclo anions, allowing controllable stepwise metalate‐mediated functionalization of P4.
Abstract: The development of selective functionalization strategies of white phosphorus (P4) is important to avoid the current chlorinated intermediates. The use of transition metals (TMs) could lead to catalytic procedures, but these are severely hampered by the high reactivity and unpredictable nature of the tetrahedron. Herein, we report selective first steps by reacting P4 with a metal anion [Cp*Fe(CO)2]− (Cp*=C5(CH3)5), which, in the presence of bulky Lewis acids (LA; B(C6F5)3 or BPh3), leads to unique TM‐substituted LA‐stabilized bicyclo[1.1.0]tetraphosphabutanide anions [Cp*Fe(CO)2(η1‐P4⋅LA)]−. Their P‐nucleophilic site can be subsequently protonated to afford the transient LA‐free neutral butterflies exo,endo‐ and exo,exo‐Cp*Fe‐ (CO)2(η1‐P4H), allowing controllable stepwise metalate‐mediated functionalization of P4.
TL;DR: In this paper, a series of alkyl-substituted cyclopentadienyl-based trioxo-rhenium complexes (Cp'Re(CO)3) were synthesized.
Abstract: Cyclopentadienyl-based tricarbonyl rhenium complexes (Cp'Re(CO)3) are convenient precursors for the corresponding cyclopentadienyl-based trioxo-rhenium complexes (Cp'ReO3), which are potential catalysts for the deoxydehydration (DODH) of diols to olefins. In order to evaluate the influence of different Cp-substituents, a series of alkyl-substituted Cp'Re(CO)3 complexes (1a-8a) were synthesized. High yields (86-98%) were obtained from the reaction of Re2(CO)10 with the corresponding Cp'H ligands (1-8), in which the electron donating character of Cp increases with the number of substituents. Aryl-substituted analogous complexes 10a-12a were accessed via salt metathesis of ReBr(CO)5 with the lithium salt of the deprotonated ligand (Cp'Li), and aryl groups were found to decrease electron donation. Furthermore, an unusual [6+4] cycloaddition reaction of (CpMe4H)Re(CO)3 8a with excess ligand resulted in the highly asymmetrical Cp'Re(CO)3 complex 9a. Finally, the reaction of the tetraphenylcyclopentadienone ligand with Re2(CO)10 lead to the isolation of two unusual compounds: Re(CO)3 complexes of the Shvo-type hydroxytetraphenylcyclopentadienyl ligand, (Ph4Cp(OH))Re(CO)3 13a, and of a benzofuran-fused cyclopentadienyl ligand, (Ph3Cp(C6H4O))Re(CO)3 14a. X-ray crystal structures were obtained for the new Cp'Re(CO)3 complexes 2a (CptBu2H3)Re(CO)3, 7a (1,2,3-Me3(tetrahydroindenyl))Re(CO)3, 9a, 13a and 14a, which all have the typical three-legged 'piano-stool' configuration.
TL;DR: The title compound of as discussed by the authors contains two copper(II) cations in special positions (one on a twofold rotation axis and one on an inversion centre) and the salicylate ligand in its dianionic form.
Abstract: The title compound, {[Cu2(C7H4O3)2(H2O)2]·2H2O}n, contains two copper(II) cations in special positions (one on a twofold rotation axis and one on an inversion centre) and the the salicylate ligand in its dianionic form. By four- and six-coordinate metal coordination, chains are formed parallel to [001], which are extended by O—H⋯O hydrogen bonding into sheets extending parallel to (100). These sheets are weakly connected by O—H⋯O hydrogen bonding via the non-coordinating lattice water molecules into a three-dimensional network.
14 Dec 2017
TL;DR: In this paper, the first crystal structure of iron(III) salicylate without additional counterions was presented and the structure solution of the twin was shown and an explanation based on the crystal packing was provided.
Abstract: In this contribution, we present the first crystal structure of iron(III) salicylate without additional counterions. The octahedral complex contains two salicylate and two water molecules as ligands. One salicylate is mono-anionic while the other is di-anionic. Because of the centrosymmetry of the complex, the acidic hydrogen atom is disordered on the midpoint between two salicylate oxygens. The structure determination of the tiny crystal indicates the presence of reticular twinning. The structure solution of the twin is shown and an explanation based on the crystal packing is provided.
TL;DR: The methyl-substituent in para-methyl-l-phenylalanine has, in contrast to fluorine, no polar interactions with protons of neighboring molecules, which might allow for the well-defined modulation of the crystal structure at 230 K.
Abstract: The crystal structure of para-methyl-l-phenylalanine at 230 K resembles that of the para-fluorinated analogue from the literature but is commensurately modulated with seven molecules in the asymmetric unit (Z′ = 7). At 100 K, the superstructure loses its modulation, leading to a unit cell with Z′ = 1, with clear disorder in the phenyl ring orientations. The methyl-substituent in para-methyl-l-phenylalanine has, in contrast to fluorine, no polar interactions with protons of neighboring molecules, which might allow for the well-defined modulation of the crystal structure at 230 K.
10 Apr 2017
TL;DR: The synthesis and analysis of [FeI(BMBIK)]+ using scanning tunneling microscopy, scanning Tunneling spectroscopy, and atomic force microscopy are the first steps toward mechanistic studies of homogeneous catalysts with redox noninnocent ligands at the single molecule level.
Abstract: Here, we report the bulk synthesis of [FeII(BMBIK)Cl2] bearing the redox noninnocent bis(methylbenzimidazolyl)ketone (BMBIK) ligand and the synthesis of the similar complex [FeI(BMBIK)]+ on a Au(111) surface using lateral manipulation at the atomic level. Cyclic voltammetry and scanning tunneling spectroscopy are shown to be useful techniques to compare the coordination compound in solution with the one on the surface. The total charge, as well as the oxidation and spin state of [FeI(BMBIK)]+, are investigated by comparison of the shape of the lowest unoccupied molecular orbital (LUMO), visualized by tunneling through the LUMO, with theoretical models. The similar reduction potentials found for the solution and surface compounds indicate that the major effect of lowering the LUMO upon coordination of BMBIK to the iron center is conserved on the surface. The synthesis and analysis of [FeI(BMBIK)]+ using scanning tunneling microscopy, scanning tunneling spectroscopy, and atomic force microscopy are the firs...