Bindungssituation in NHC- und Phosphin-Komplexen [(L)m(EmHn)] (m = 1, 2; n = 0 – 4) der Gruppen 13 – 15 und ihre Anwendbarkeit als lösliche Wasserstoffspeicher

In der vorliegenden Arbeit ist die Bindungssituation und die Reaktivität von NHC- und PMe3-Komplexen [(L)m(EmHn)] (m = 1, 2; n = 0 – 4) der Gruppen 13 – 15 analysiert. Die Basis dafür bilden die synthetisch bekannte Hydrierung des Magnesium(I)-Dimers [(L)2(Mg2)] (L = [(MesNCMe)2CH]- mit Mes = Mesityl) unter Dimerisierung zweier [(NHCDipp)(AlH3)] zu [(NHCDipp)2(Al2H4)] und einige weitere synthetisch bekannten Verbindungen [(L)2(E2)]. Darüber hinaus ist auf bisher unbekannte Verbindungen [(L)n(EnHm)] der Gruppen 13 – 15 ausgeweitet. Als Liganden sind die Modellsysteme NHC mit Methylliganden an N und PMe3 verwendet. Neben der Optimierung von Geometrien und der Berechnung von Reaktionsenergien der Komplexierung, Dimerisierung und Wasserstoffabspaltung sind diverse Bindungsanalysen durchgeführt. Dazu zählen die Energiedekompositionsanalyse mit ihrer Erweiterung der Natural Orbitals for Chemical Valence (EDA-NOCV) der Donor-Akzeptor-, sowie der E–E-Bindungen, außerdem die Bindungsindizes nach Wiberg (WBI) der E–H-, E–E- und Donor-Akzeptorbindungen, die NBO-Partialladungen der beteiligen Bindungsatome und die Untersuchung der Lewis-Struktur mittels NBO-Analyse. Die Untersuchung der Hydrierung des Magnesium(I)-Dimers bezüglich der Einsetzbarkeit verschiedener Gruppe 13-Monomere [(L)(EH3)] als Wasserstofflieferanten ergibt energetisch eine Vergünstigung der Reaktion bei der Verwendung schwererer Komplexe und des Phosphinliganden. Beide verwendete Liganden verfügen über ein HOMO eines freien Elektronenpaars, welches zur σ-Donierung fähig ist, die sich in der EDA-NOCV für die NHC-Liganden als stärker ausgeprägt darstellt als in PMe3. Das NHC-LUMO+1 zeigt allgemein bessere π-Rückdonierungseigenschaften als das analoge Orbital in PMe3, bei dem jedoch auch das orthogonale und energetisch entartete zweite LUMO+1 bei entsprechender Komplexsymmetrie zu π-Rückdonierung im Stande ist. Innerhalb der Gruppen weisen die Geometrien der Dimerkomplexe [(L)2(E2Hn)] zum Teil unterschiedliche Strukturmotive auf. Dabei zeigt sich für die Komplexe der leichteren Atome in den Gruppen eine eher planarer Koordination an E und trans-angeordnete Liganden, während für schwerere E die Tendenz zur pyramidalen Koordination an E, sowie in einigen Fällen zur gauche-angeordneten Liganden ansteigt. Letztere Eigenschaften sind in den PMe3-Komplexen stärker ausgeprägt als in denen mit NHC. Mit wenigen Ausnahmen, die bereits durch stark unterschiedliche Bindungsmotive auffallen, ergibt die EDA-NOCV Donor-Akzeptorbindungen in den analysierten Komplexen der Gruppen 13 bis 15, die in den NHC-Verbindungen stärker sind als in denen des Phosphinliganden. Letztere weisen dafür stärkere E–E-Bindungen auf. Auch die Wiberg-Bindungsindizes der entsprechenden Bindungen korrelieren mit diesem Befund. Die NBO-Analyse zeigt weiterhin deutlich höhere negative Partialladungen an den EmHn-Einheiten der Phosphinverbindungen, deren Grund auch in der geringeren π-Rückdonierung zum Phosphinliganden zu finden ist. Des Weiteren zeigt sich in der Form der Molekülorbitale und in der Analyse der Lewis-Struktur der Verbindungen ein Trend zur Stabilisierung von Elektronendichte und damit die Ausbildung freier Elektronenpaare bzw. die stärkere Lokalisierung von E–E-π-Bindungen an E für schwerere Komplexe innerhalb der Gruppen. Dies kann durch den inert pair-Effekt erklärt werden und wird durch den Einsatz von PMe3 verstärkt. Dadurch ergibt sich auch die Tendedenz schwererer Komplexe zur Abweichung von planarer Koordination an E bzw. der trans-Anordnung der Liganden. Insgesamt haben die Komplexe der in der zweiten Periode angesiedelten Heteroatome Bor, Kohlenstoff und Stickstoff in der EDA-NOCV stärkere Donor-Akzeptor- und E–E-Bindungen als in ihren schwereren Homologen. Ebenso sind dort in der NBO-Analyse deutlich höhere Partialladungen am Mittelfragment zu finden, was unter anderem durch die hohen Elektronegativitäten dieser Atome begründet werden kann. In diesem Zusammenhang wird auch für die E–H-Bindungen eine protische Bindungssituation festgestellt im Gegensatz zu den hydridischen Bindungen in den schwereren Homologen

Analysis of the E–E Bond in Group-13 Complexes [(PMe3)2(E2Hn)] (E = B – In, n = 4, 2, 0)

Quantum chemical calculations at the BP86/def2-TZVPP level have been carried out for the donor-acceptor complexes [(PMe3)2(E2Hn)] for n = 4, 2, 0. The focus of this works lies on the E–E bonding situation. The electronic structure of the molecules was analyzed with the EDA-NOCV meth-od and with NBO calculations. The EDA-NOCV analysis of the E–E interactions in [(PMe3)2(E2Hn)] (n = 4, 2, 0) provide deep insights into the nature and the strength of the bonds. The calculated intrinsic interactions ΔEint suggest that the trend for the bond strength of the E–E single bond [(PMe3)(H)2E–E(H)2(PMe3)] has the order B > Ga > Al > In. The orbital interactions ΔEorb which exhibit the same trend as ΔEint have one dominant contribution which comes from the coupling of the singly occupied orbitals in the (PMe3)(H)2E fragments. A slightly different trend B > Ga ~ In > Al is found for the in-teraction energy ΔEint of the E–E bonds in [(PMe3)(H)E–E(H)(PMe3)]. The orbital term ΔEorb which has the order B > Ga > In > Al has one major and one minor component which in case of the boron compound may be identified with a σ and a π bond. The heavier homologues [(PMe3)(H)E–E(H)(PMe3)] (E = Al – In) have pyramidally coordinated atoms E. The dominant orbital interactions in the latter species come from the formation of a “slipped” π bond while the minor component comes from the formation of the σ bond. This can be explained with the change in the hybridization of the orbitals at atom E along the formation of the E–E bond. The compounds [(PMe3)E–E(PMe3)] exhibit three different types of bonding situations depending on atoms E. The boron system [(PMe3)B≡B(PMe3)] has a classical triple bond which consist of a σ bond that provides 56 % to the orbital interactions and two degenerate π bonds which contribute 40 % to the covalent bonding. The aluminium and gallium complexes [(PMe3)E–E(PMe3)] (E = Al, Ga) are also triply bonded species where the covalent bonding has one strong and two weaker components. The strong component comes from the “slipped” π bond while the minor components come from the formation of the σ and π bonds. The indium complex [(PMe3)In–In(PMe3)] has only an In–In single bond and two electron lone pairs at the indium atoms. The charge donation Me3P → E2(Hn) ← PMe3 has for all atoms E the trend for n 4 > 2 > 0

Synthesis, characterization, and computational analysis of the dialanate dianion, [H3Al-AlH3]2− : a valence isoelectronic analogue of ethane

C.J. and A.S. gratefully acknowledge financial support from the Australian Research Council, while C.J. thanks the U.S. Air Force Asian Office of Aerospace Research and Development (FA2386-14-1-4043) for funding. G.F. acknowledges financial support from the Deutsche Forschungsgemeinschaft.The first example of a well-defined binary, low-oxidation-state aluminum hydride species that is stable at ambient temperature, namely the dianion in [{(DepNacnac)Mg}2(μ-H)]2[H3Al-AlH3] (DepNacnac=[(DepNCMe)2CH]−, Dep=2,6-diethylphenyl), has been prepared via a magnesium(I) reduction of the alanate complex, (DepNacnac)Mg(μ-H)3AlH(NEt3). An X-ray crystallographic analysis has shown the compound to be a contact ion complex, which computational studies have revealed to be the source of the stability of the aluminum(II) dianion.PostprintPeer reviewe

Statistical phase estimation and error mitigation on a superconducting quantum processor

Quantum phase estimation (QPE) is a key quantum algorithm, which has been widely studied as a method to perform chemistry and solid-state calculations on future fault-tolerant quantum computers. Recently, several authors have proposed statistical alternatives to QPE that have benefits on early fault-tolerant devices, including shorter circuits and better suitability for error mitigation techniques. However, practical implementations of the algorithm on real quantum processors are lacking. In this paper we practically implement statistical phase estimation on Rigetti's superconducting processors. We specifically use the method of Lin and Tong [PRX Quantum 3, 010318 (2022)] using the improved Fourier approximation of Wan et al. [PRL 129, 030503 (2022)], and applying a variational compilation technique to reduce circuit depth. We then incorporate error mitigation strategies including zero-noise extrapolation and readout error mitigation with bit-flip averaging. We propose a simple method to estimate energies from the statistical phase estimation data, which is found to improve the accuracy in final energy estimates by one to two orders of magnitude with respect to prior theoretical bounds, reducing the cost to perform accurate phase estimation calculations. We apply these methods to chemistry problems for active spaces up to 4 electrons in 4 orbitals, including the application of a quantum embedding method, and use them to correctly estimate energies within chemical precision. Our work demonstrates that statistical phase estimation has a natural resilience to noise, particularly after mitigating coherent errors, and can achieve far higher accuracy than suggested by previous analysis, demonstrating its potential as a valuable quantum algorithm for early fault-tolerant devices.Comment: 24 pages, 13 figure

Measuring Electron Correlation. The Impact of Symmetry and Orbital Transformations

In this perspective, the various measures of electron correlation used in wavefunction theory, density functional theory and quantum information theory are briefly reviewed. We then focus on a more traditional metric based on dominant weights in the full configuration solution and discuss its behaviour with respect to the choice of the $N$-electron and the one-electron basis. The impact of symmetry is discussed and we emphasize that the distinction between determinants, configuration state functions and configurations as reference functions is useful because the latter incorporate spin-coupling into the reference and should thus reduce the complexity of the wavefunction expansion. The corresponding notions of single determinant, single spin-coupling and single configuration wavefunctions are discussed and the effect of orbital rotations on the multireference character is reviewed by analysing a simple model system. In molecular systems, the extent of correlation effects should be limited by finite system size and in most cases the appropriate choices of one-electron and $N$-electron bases should be able to incorporate these into a low-complexity reference function, often a single configurational one

Alternative Splicing of Fibroblast Growth Factor Receptor IgIII Loops in Cancer

Alternative splicing of the IgIII loop of fibroblast growth factor receptors (FGFRs) 1–3 produces b- and c-variants of the receptors with distinctly different biological impact based on their distinct ligand-binding spectrum. Tissue-specific expression of these splice variants regulates interactions in embryonic development, tissue maintenance and repair, and cancer. Alterations in FGFR2 splicing are involved in epithelial mesenchymal transition that produces invasive, metastatic features during tumor progression. Recent research has elucidated regulatory factors that determine the splice choice both on the level of exogenous signaling events and on the RNA-protein interaction level. Moreover, methodology has been developed that will enable the in depth analysis of splicing events during tumorigenesis and provide further insight on the role of FGFR 1–3 IIIb and IIIc in the pathophysiology of various malignancies. This paper aims to summarize expression patterns in various tumor types and outlines possibilities for further analysis and application

d-d Dative Bonding Between Iron and the Alkaline-Earth Metals Calcium, Strontium, and Barium

Double deprotonation of the diamine 1,1 '-(tBuCH(2)NH)-ferrocene (1-H-2) by alkaline-earth (Ae) or Eu(II)metal reagents gave the complexes1-Ae (Ae=Mg, Ca, Sr, Ba) and1-Eu.1-Mg crystallized as a monomer while the heavier complexes crystallized as dimers. The Fe...Mg distance in1-Mg is too long for a bonding interaction, but short Fe...Ae distances in1-Ca,1-Sr, and1-Ba clearly support intramolecular Fe...Ae bonding. Further evidence for interactions is provided by a tilting of the Cp rings and the related(1)H NMR chemical-shift difference between the Cp alpha and beta protons. While electrochemical studies are complicated by complex decomposition, UV/Vis spectral features of the complexes support Fe -> Ae dative bonding. A comprehensive bonding analysis of all1-Ae complexes shows that the heavier species1-Ca,1-Sr, and1-Ba possess genuine Fe -> Ae bonds which involve vacant d-orbitals of the alkaline-earth atoms and partially filled d-orbitals on Fe. In1-Mg, a weak Fe -> Mg donation into vacant p-orbitals of the Mg atom is observed

Steps ahead in understanding the catalytic isomerization mechanism of linear allylic alcohols in water: dynamics, bonding analysis and crystal structure of a 2-allyl-intermediate.

The isomerization of 1-penten-3-ol into 3-pentanone catalyzed by [RuCp(H2O-κO)(PTA)2](CF3SO3) (1CF3SO3) (PTA = 1,3,5-triaza-7-phosphaadamantane) was studied and two water soluble ruthenium catalyst reaction intermediates were characterized. The main intermediate, the complex [RuCp(exo-2-1-penten-3-ol)(PTA)2](CF3SO3)·2H2O (exo- 2CF3SO3·2H2O) was isolated and characterized by NMR in solution and by single-crystal X-ray diffraction in solid state, constituting the first example of a fully characterized complex containing a coordinated 2-allylic alcohol and the first crystal structure for a water-soluble metal complex containing a 2-allyl ligand. NMR and Eyring analysis show the crucial involvement of water molecules both in the transformation of allylic alcohol into a ketone as well as in the concomitant isomerization of the exo-coordinated substrate into the endo conformer. DFT structure and bonding analyses are used to assess the relative stabilities of the isomers and how the metal drives the electronic distribution on the substrate

Neutron Scattering Techniques for Studying Metal Complexes in Aqueous Solution.

Neutron scattering combined with ab initio calculations provides a powerful tool for studying metal complexes in different solvents and, particularly, in water. The majority of traditional characterization techniques in catalysis provide only limited information on homogeneous catalytic processes. Neutron scattering, on the other hand, thanks to its sensitivity to hydrogen atoms, and therefore water molecules, can be used to build detailed models of reaction paths and to observe, at a molecular level, the influence of solvent molecules on a catalytic process. In this Mini- Review we describe several examples on how neutron scattering combined with ab initio calculations can be used to examine the nature of the interaction of water molecules with catalytically active metal complexes in solution