Showing papers by "Martin Lutz published in 2019"
TL;DR: This catalyst outperforms closely related bi- and tridentate phosphine-based Ni catalysts and suggests a reaction pathway involving a hemilabile interaction of the C=O unit with the nickel center.
Abstract: Adaptive ligands, which can adapt their coordination mode to the electronic structure of various catalytic intermediates, offer the potential to develop improved homogeneous catalysts in terms of activity and selectivity. 2,2′-Diphosphinobenzophenones have previously been shown to act as adaptive ligands, the central ketone moiety preferentially coordinating reduced metal centers. Herein, the utility of this scaffold in nickel-catalyzed alkyne cyclotrimerization is investigated. The complex [(p-tolL1)Ni(BPI)] (p-tolL1 = 2,2′-bis(di(para-tolyl)phosphino)-benzophenone; BPI = benzophenone imine) is an active catalyst in the [2 + 2 + 2] cyclotrimerization of terminal alkynes, selectively affording 1,2,4-substituted benzenes from terminal alkynes. In particular, this catalyst outperforms closely related bi- and tridentate phosphine-based Ni catalysts. This suggests a reaction pathway involving a hemilabile interaction of the C═O unit with the nickel center. This is further borne out by a comparative study of t...
31 citations
TL;DR: A naphthyridine‐derived expanded pincer ligand is described that can host two copper(I) centers, which enables cooperative activation of H2 giving an unusual butterfly‐shaped Cu4H2 complex.
Abstract: A naphthyridine-derived expanded pincer ligand is described that can host two copper(I) centers. The proton-responsive ligand can undergo reversible partial and full dearomatization of the naphthyridine core, which enables cooperative activation of H2 giving an unusual butterfly-shaped Cu4 H2 complex.
29 citations
TL;DR: It is demonstrated that a subtle change in molecular structure coupled with the understanding of assembly processes of enantiomers and racemates, in both dilute solution and concentrated gels, acts as a stepping stone to rationally control the organization in the solid-state.
Abstract: Chirality plays a central role in biomolecular recognition and pharmacological activity of drugs and can even lead to new functions such as spin filters. Although there have been significant advances in understanding and controlling the helical organization of enantiopure synthetic molecular systems, rationally dictating the assembly of mixtures of enantiomer (including racemates) is nontrivial. Here we demonstrate that a subtle change in molecular structure coupled with the understanding of assembly processes of enantiomers and racemates, in both dilute solution and concentrated gels, acts as a stepping stone to rationally control the organization in the solid-state. We have studied trans-1,2-disubstituted cyclohexanes as model systems with carboxamide, thioamide, and their combination as functional groups. On comparing the gelation propensity of individual enantiomers and racemates, we find that racemates of carboxamide, thioamide, and their combination adopt self-sorting, coassembly, and mixed organization, respectively. Remarkably, these modes of assembly of racemates were also retained in solid-state. These results point out that studying the solution-phase assembly is a key link for connecting molecular structure with the assembly in the solid-state, even for racemates.
18 citations
TL;DR: This catalytic study contributes to the field of cobalt‐catalyzed hydrosilylation reactions and shows the first example of catalysis employing the dpbp ligand in combination with a base metal.
Abstract: The hydrosilylation of unsaturated compounds homogeneously catalyzed by cobalt complexes has gained considerable attention in the last years, aiming at substituting precious metal-based catalysts. In this study, the catalytic activity of well-characterized CoII and CoI complexes of the pToldpbp ligand is demonstrated in the hydrosilylation of 1-octene with phenylsilane. The CoI complex is the better precatalyst for the mentioned reaction under mild conditions, at 1 mol-% catalyst, 1 h, room temperature, and without solvent, yielding 84 % of octylphenylsilane. Investigation of the substrate scope shows lower performance of the catalyst in styrene hydrosilylation, but excellent results with allylbenzene (84 %) and acetophenone (> 99 %). This catalytic study contributes to the field of cobalt-catalyzed hydrosilylation reactions and shows the first example of catalysis employing the dpbp ligand in combination with a base metal.
16 citations
TL;DR: In this paper, the reaction mechanism of asymmetric hydrogenation of functionalized alkenes catalyzed by a supramolecular rhodium complex has been investigated and it was shown that hydrogen bonds are formed between the catalyst and the substrate in the early stages of the mechanism.
Abstract: The reaction mechanism of the asymmetric hydrogenation of functionalized alkenes catalyzed by a supramolecular rhodium complex has been investigated. In-depth NMR analysis combined with X-ray crystal structure determination show that hydrogen bonds are formed between the catalyst and the substrate in the early stages of the mechanism. Detailed kinetic data obtained from UV–vis stopped-flow experiments and gas-uptake experiments confirm that the hydrogen bonds are playing a crucial role in the mechanism. A complete DFT study of the various competitive paths of the reaction mechanism allowed us to identify how these hydrogen bonds are involved in the determining steps of the reaction.
15 citations
TL;DR: A bidentate ligand with an integrated anion receptor forms dimeric rhodium complexes that become monomeric upon binding acetate guest, which is the basis for effector responsive hydroformylation catalysis.
Abstract: Herein, we report a supramolecular rhodium complex that can form dimeric or monomeric Rh-species catalytically active in hydroformylation, depending on the binding of effectors within the integrated DIM-receptor. X-ray crystal structures, in situ (high-pressure (HP)) spectroscopy studies, and molecular modelling studies show that in the absence of effectors, the preferred Rh-species formed is the dimer, of which two ligands coordinate to two rhodium metals. Importantly, upon binding guest molecules, -effectors-, to the DIM-receptor under hydroformylation conditions, the monomeric Rh-active species is formed, as evidenced by a combination of in situ HP NMR and IR spectroscopy studies and molecular modelling. As the monomeric complex has different catalytic properties from the dimeric complex, we effectively generate a catalytic system of which the properties respond to the presence of effectors, reminiscent of how the properties of proteins are regulated in nature. Indeed, catalytic and kinetic experiments show that both the selectivity and activity of this supramolecular catalytic system can be influenced in the hydroformylation of 1-octene using acetate as an effector that shift the equilibrium from the dimeric to monomeric species.
14 citations
TL;DR: In this paper, the azido-phenylene-isocyanide precursor complex, the protic NHC complex, and the asymmetric bimetallic iridium hydride complex were investigated for ligand-based reactivity.
10 citations
TL;DR: In this paper, the coordination chemistry of 2.2.pyridylphosphinines towards ReI has been investigated and compared to the structurally analogous 2,2.bipyridine derivatives.
Abstract: The coordination chemistry of 2‐(2′‐pyridyl)‐4,6‐diarylphosphinines towards ReI has been investigated and compared to the structurally analogous 2,2′‐bipyridine derivatives. The different steric properties of the chelating pyridylphosphinines with respect to substituted bipyridines lead to considerable differences in the structures of the mononuclear [(P^N)Re(CO)3X] and [(N^N)Re(CO)3X] (X = Cl, Br) complexes, both in the solid state and in solution. The phosphinine‐based coordination compounds are highly sensitive towards nucleophilic attack and react reversibly with water at the P=C double bond.
7 citations
TL;DR: The tris-N-heterocycle germanide (tmim)Ge– (1) was synthesized by nucleophilic substitution for the tmim3– trianion on GeCl2·dioxane, providing a convenient model for investigating the influence of the central atom on the properties of isoelectronic ligands.
6 citations
TL;DR: In this article, the authors show that poly(n)-containing silicates with bidentate triphenylphosphane, biphenyl, and Me ligands are conformationally dynamic with a barrier of ca. 10 kcal mol 1.
Abstract: Silicates with five organic groups are conformationally dynamic even with two bidentate ligands. Symmetry breaking by incorporating a single nitrogen or phosphorus atom provides insight into their dynamic behavior. N‐containing silicates with bidentate 2‐phenylpyridine, biphenyl, and a Me ( 8 ), Et ( 9 ) or Ph ( 10 ) ligand were studied comprehensively by NMR spectroscopy and DFT theory to reveal two isoenergetic conformers with a barrier of ca. 10 kcal mol–1. P‐containing silicate 14 with bidentate triphenylphosphane, biphenyl, and Me ligands is subject to multiple Berry pseudorotations, turnstile rotations, and conformational flexibility of the P‐center. The stability increased by masking the P‐center with a BH3 group ( 16 ). DFT and NMR modeling reveal two isoenergetic conformers for 16 with a barrier of ca. 19 kcal‧mol–1 for a complex interconversion pathway. This barrier bodes well for the design of configurationally stable chiral‐at‐metal transition metal catalysts.
5 citations
TL;DR: In this article, the chiral supramolecular aggregates based on C 3 -symmetric triphenylamine-based dyes are used for photoelectrochemical cells.
Abstract: Recent studies on water-splitting photoelectrochemical cells (PECs) have demonstrated the intriguing possibility of controlling the spin state in this chemical reaction to form H 2 and O 2 by exploiting the chirality of organic π-conjugated supramolecular polymers. Although this fascinating phenomenon has been disclosed, the chiral supramolecular materials reported thus far are not optimized for acting as efficient photosensitizer for dye-sensitized PECs. In this work we report on the design, synthesis, and characterization of chiral supramolecular aggregates based on C 3 -symmetric triphenylamine-based dyes that are able to both absorb visible light and control the spin state of the process. Variable temperature-dependent spectroscopic measurements reveal the assembly process of the dyes and confirm the formation of chiral aggregates, both in solution as well as on solid supports. Photoelectrochemical measurements on TiO 2 -based anodes validate the advantage of using chiral supramolecular aggregates as photosensitizer displaying higher photocurrent compared to achiral analogues. Moreover, fluorimetric tests for the quantification of the hydrogen peroxide produced, confirm the possibility of controlling the spin of the reaction exerting spin-selection with chiral supramolecular polymers. These results represent a further step towards the next-generation of organic-based water-splitting solar cells.
TL;DR: The title high-spin iron(II) complex is six-coordinated with two trifluoromethanesulfonato and four tetrahydrofuran ligands and is isostructural with the corresponding Co, Ni and Zn complexes known from the literature.
Abstract: The title compound, [Fe(CF3SO3)2(C4H8O)4], is octahedral with two trifluoromethanesulfonate ligands in trans positions and four tetrahydrofurane molecules in the equatorial plane. By the conformation of the ligands the complex is chiral in the crystal packing. The compound crystallizes in the Sohncke space group P212121 and is enantiomerically pure. The packing of the molecules is determined by weak C—H...O hydrogen bonds. The crystal studied was refined as a two-component inversion twin.