Universität Stuttgart
Permanent URI for this communityhttps://elib.uni-stuttgart.de/handle/11682/1
Browse
45 results
Search Results
Item Open Access Zur Elektronenstruktur von Phosphor(III)-p-π-Bindungssystemen: UV- und PE-spektroskopische Untersuchungen an Methylenphosphanen vom Typ R-P=C(SiMe3)2(1987) Gudat, Dietrich; Niecke, Edgar; Sachs, Werner; Rademacher, PaulDie UV- und die He-I-Photoelektronenspektren der Methylenphosphane R-P=C(SiMe3)2 3 (R = Cl, F, OBut, NHBut, SBut, NHSiMe3, NEt2, NPri2, 2,2,6,6-Me4C5H6N, N(But)SiMe3, N(SiMe3)2, Me, But) werden diskutiert. Die Zuordnung der Ionisationspotentiale zu π(P=C)- bzw. n(P)-Orbitalen ist konsistent mit den UV-Daten sowie semieempirischen MNDO-Rechnungen. Die π-Akzeptorwirkung der Silylsubstituenten bewirkt bei den alkylsubstituierten Verbindungen 31,m eine Umkehr der Abfolge der π(P=C)- und n(P)–I.P.'s im Vergleich zu bisher untersuchten Phosphaalkenen sowie theoretischen Vorhersagen. Einführung von RO- bzw. RS-Substituenten in 3c,d führt zur Ausbildung eines mesomeriestabilisierten 3-Zentren-4-Elektronen-π-Bindungssystems. Bei den Aminomethylenphosphanen 3e-k können in Abhängigkeit von der Raumerfüllung der Substituenten zwei unterschiedliche Konformere unterschieden werden, die sich durch die Stellung des Aminrestes bezüglich der Molekülsymmetrieebene unterscheiden. Die Koexistenz beider Konformere kann am Beispiel von 3h durch temperaturabhängige UV-Untersuchungen belegt werden. Die bemerkenswerten Unterschiede der 31P- und 13C-NMR-Daten von 3e-k können im Zusammenhang mit der beobachteten Konformationsisomerie erklärt werden.Item Open Access Annellated 1,3,4,2-triazaphospholenes-simple modular synthesis and a first exploration of ligand properties(2022) Richter, Ferdinand; Birchall, Nicholas; Feil, Christoph M.; Nieger, Martin; Gudat, DietrichThe successful use of 1,3,4,2-triazaphospholenes (TAPs) as organo-catalysts stresses the need for efficient synthetic routes to these molecules. In this study, we establish the [1 + 4]-cycloaddition of PBr3 to azo-pyridines as a new approach to preparing pyrido-annellated TAPs in a single step from easily available precursors. The modular assembly of the azo-component via condensation of primary amines and nitroso compounds along with the feasibility of post-functionalization at the P-Br bond under conservation of the heterocyclic structure allows, in principle, to address a wide range of target molecules, which is illustrated by prototypical examples. The successful synthesis of a transition metal complex confirms for the first time the ability of a TAP to act as a P-donor ligand. Crystallographic studies suggest that hyperconjugation effects and intermolecular interactions induce a qualitatively similar ionic polarization of the P-Br bonds in TAPs as in better known isoelectronic diazaphospholenes.Item Open Access Metallophospha-alkenes: a simple access and some reactivities involving the phosphorus atom(1985) Gudat, Dietrich; Niecke, Edgar; Malisch, Wolfgang; Hofmockel, Ullrich; Quashie, Sapé; Cowley, Alan H.; Arif, Atta M.; Krebs, Bernt; Dartmann, MechtildThe synthesis and studies on the reactive behaviour of metallophospha-alkenes are reported.Item Open Access Coordination isomerism in pentamethylcyclopentadienyl-substituted iminophosphanes: from classical structures to a π-complexed iminophosphenium ion(1992) Gudat, Dietrich; Schiffner, Hans M.; Nieger, Martin; Stalke, Dietmar; Blake, Alexander J.; Grondey, Hiltrud; Niecke, EdgarNovel iminophosphanes of the type (Me5C5)P=NR [R = C6H2tBu3 (5a), Si-i-Pr3 (5b), SiMe3 (5c)] are prepared via either thermolytic or base-promoted elimination reactions and characterized by analytical and spectroscopic methods. The x-ray crystal structures of 5a,b establish the presence of coordination isomerism of the cyclopentadienyl ring, which at the same time strongly alters the characteristics of the P-N multiple bond. For 5a, η1-attachment of the Me5C5 moiety to the phosphorus and a localized phosphorus-carbon σ-bond are found, and the P-N double bond compares to that of alkylated iminophosphanes (rPN = 155.1 (8) pm). 5b exhibits η2-coordination of the cyclopentadienyl ring leading to increased P-N triple-bond character, as evidenced by shortening of the P-N distance (153.3 (3) pm) and the remarkable opening of the nitrogen valence angle (153.3 (2)°). The structure is discussed as an intramolecular π-complex between a formal cyclopentadienyl anion and an iminophosphenium cation. The 1H and 13C NMR spectra show that rapid elementotropic rearrangements around the five-membered ring take place both in solution and in the solid state. The unique temperature dependence of δ31P in solution together with the considerable differences in δ 31P between the solution and solid states are interpreted in a model assuming a "haptotropic" mechanism for the fluxionality involving dynamic η1/η2-coordination isomerizations in solution. As expected, nucleophilic displacement of the Me5C5 moiety takes place in the reaction of 5b,c with LiC6H2tBu3, yielding the iminophosphanes tBu3H2C6P=NR (R = Si-i-Pr3 (8b), SiMe3 (c)) as products.Item Open Access Synthesis and thermally and light driven cleavage of an N‐heterocyclic diphosphine with inorganic backbone(2020) Blum, Markus; Feil, Christoph M.; Nieger, Martin; Gudat, DietrichA diphosphine with an unsupported PP bond connecting two carbon‐free “inorganic” 1,3,2,4,5‐diazaphosphadisilolidine rings was prepared by reductive coupling of a P‐chloro‐substituted monocyclic precursor molecule. VT‐EPR studies revealed that the diphosphine exists in solution, like other compounds of this kind, in dynamic equilibrium with the corresponding phosphinyl radicals. Determination of the radical concentration from the EPR spectra permitted to calculate thermochemical parameters for the homolytic PP bond fission. The results disclose that both the enthalpy and entropy of dissociation are higher than in topologically related bi(diazaphospholidines). The impact of the entropy term allows explaining that, regardless of the presence of an energetically rather stable PP bond, the onset of dissociation is observable even at ambient temperature. Irradiation experiments showed that radical formation cannot only be induced thermally, but also by photolysis.Item Open Access 31P NMR spectroscopic investigations of low-coordinated multiple bonded PN systems(1994) Niecke, Edgar; Gudat, DietrichIn this chapter, we attempt to give a systematic analysis of the influence on the 31P chemical shift and coupling 1JPN in terms of substituent effects, double-bond stereochemistry, and molecular dynamics for iminaphosphines and related compounds containing partial phosphorus-nitrogen triple-bond character. Although the main focus is on properties in the isotropic phase, reflecting that the majority of measurements were made in solution, the tensorial properties of the chemical shift as obtained from solid-state NMR measurements are also mentioned.Item Open Access Azasilatrane methanolysis pathways: stereoelectronic influences(1990) Gudat, Dietrich; Verkade, John G.Trigonal-bipyramidal azasilatranes of the type ZSi(NHCH2CH2)3N (Z = H, Me, OEt) solvolyze in MeOH to give N(CH2CH2NH2)3 (tren) and ZSi(OMe)3. Whereas intermediates in this reaction are not detected, ZSi[N-(SiR3)CH2CH2]3N species afford detectable intermediates of the type ZSi[N(SiR3)CH2CH2]n(NHCH2CH2)3-nN (n = 1, 2) before complete conversion to tren and ZSi(OMe)3 occurs. In cases where steric encumbrances weaken the Si-Nax bond in these molecules, monocyclic intermediates are detected. In contrast, methanolysis of HSi[N(BMe2)CH2CH2]3N gives N(CH2CH2NHBMe2)3 (and HSi-(OMe)3), which in the presence of CD3OD gives (CD3O)nSi(OMe)4-n and the novel adduct N-[CH2CH2NHD·B(OCD3)Me2]3. The possible steric and electronic influences of the equatorial substituents on the solvolysis pathways are discussed.Item Open Access Silyl‐ and germyl‐substituted diorganophosphonites(2023) Hettich, Thomas D.; Rudolf, Richard; Birchall, Nicholas; Nieger, Martin; Gudat, DietrichReactions of metalated diorganophosphonite boranes with triorganosilyl and ‐germyl halides provided borane adducts of diorgano(tetryl)phosphonites. Further treatment with excess Et3N or DABCO yielded the borane‐free species (RO)2P‐ER′>3 (E=Si, Ge; R, R′=alkyl, aryl). The products of all reactions were characterized by elemental analyses and NMR data, and in selected cases by MS and single‐crystal XRD studies. Reactions of selected ligands with Ni(CO)4 and selenium were shown to produce Ni(CO)‐complexes or diorgano(tetryl) phosphonoselenoates (RO)(R′3E)P=Se, respectively, which were identified spectroscopically but could not be isolated. Evaluation of the TEP and 1JPSe coupling constants were used for a first assessment of the electron donor properties of the new molecules.Item Open Access Transfer of a pentamethylcyclopentadienyl ligand from phosphorus to nickel: generation and spectroscopic characterization of the first examples of metalloiminophosphanes [(η5-Me5C5)(R3P)Ni-P=NBut](R = Et, Bu, or Ph)(1987) Gudat, Dietrich; Niecke, EdgarReaction of (Me5C5)P=NBut with [(R3P)2Ni(cod)](cod = cyclo-octa-1,5-diene)(R = Et, Bu, or Ph) produces complexes [(R3P)2Ni(C5Me5)P=NBut], which rearrange to yield the novel metal-substituted iminophosphanes, [(R3P)(η5-C5Me5)Ni–P=NBut] and free phosphane R3P, the new complexes being identified by means of n.m.r. spectroscopy; similarly, the metallophospha-alkenes, [(R3P)(η5-C5Me5)Ni–P=C(SiMe3)2] are formed via reaction of (Me5C5)P=C(SiMe3)2 and [(R3P)Ni(alkene)2].Item Open Access Reaction of (pentamethylcyclopentadienyl)(tert-butylimino)-phosphane with tris(acetonitrile)tricarbonylmolybdenum(0): evidence for a metalloiminophosphane intermediate(1986) Gudat, Dietrich; Niecke, Edgar; Krebs, Bernt; Dartmann, Mechtild(η1-Me5C5)P=N(t-Bu) (1) was prepared in a two-step synthesis from Me5C5PCl2. Reaction of 1 with (MeCN)3Mo(CO)3 affords the spirocyclic compound (η1-Me5C5PN(t-Bu)PN(T-Bu)C(O)Mo(CO)2(η5-C5Me5) (5), whose structure was determined by x-ray crystallography. A metalloiminophosphine, (η5-Me5C5)(CO)3MoP=N(t-Bu) (7), is proposed to be the key intermediate in the formation of 5.