Browsing by Author "Niecke, Edgar"

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Open Access
31P NMR spectroscopic investigations of low-coordinated multiple bonded PN systems
(1994) Niecke, Edgar; Gudat, Dietrich
In 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.
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, Edgar
Novel 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.
Open Access
First examples of η1-ligated halogenophosphaalkenes - crystal structures of trans-[RhCl(PPh3)2{η1-PX=C(SiMe3)2}] (X = F or Cl)
(1989) Hitchcock, Peter B.; Meidine, Mohamed F.; Nixon, John F.; Wang, Hongrui; Gudat, Dietrich; Niecke, Edgar
Syntheses and single crystal X-ray diffraction studies of the η1-halogenophosphaalkene complexes trans-[RhCl(PPh3)2{η1-PX=C(SiMe3)2}] (X = F, Cl) are reported.
Open Access
Iminophosphane - unkonventionelle Hauptgruppenelement-Verbindungen
(1991) Niecke, Edgar; Gudat, Dietrich
Niederkoordinierte Phosphorverbindungen zählen angesichts der großen Zahl stabiler Verbindungen längst nicht mehr zu den „Exoten” unter den Hauptgruppenelement-Verbindungen. Neben P-C-Mehrfachbindungssystemen, deren Chemie durch die enge Verwandtschaft mit organischen Verbindungen geprägt wird, gilt das Interesse vor allem P-N-Mehrfachbindungssystemen (Iminophosphanen). Diese Verbindungsklasse zeichnet sich durch eine ungewöhnliche Strukturvielfalt und ein variationsreiches chemisches Verhalten aus, so daß Iminophosphane zu wertvollen Synthesebausteinen in der Organoelementchemie wurden.
Open Access
Iminophosphanes: unconventional compounds of main group elements
(1991) Niecke, Edgar; Gudat, Dietrich
The large number of known stable compounds in which phosphorus has a low coordination number makes it clear that such compounds can no longer be regarded as "exotic" in main group chemistry. While the rich chemistry of P-C multiply bonded systems makes clear their affinity to their organic congeners, iminophosphanes in particular are also of increasing importance. The linkage of a phosphinidine fragment with an imine fragment via a multiple bond gives rise to a class of compounds with an unusually wide range of structural types. This in turn leads to a broad spectrum of chemical behavior which makes iminophosphanes extremely useful synthetic building blocks in organoelement chemistry.
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, Mechtild
The synthesis and studies on the reactive behaviour of metallophospha-alkenes are reported.
Open Access
Methylenphosphanyl-Komplexe von Chrom, Molybdän, Wolfram, Eisen und Nickel: Synthese und Reaktionen
(1993) Niecke, Edgar; Metternich, Hans-Jürgen; Nieger, Martin; Gudat, Dietrich; Wenderoth, Peter; Malisch, Wolfgang; Hahner, Christoph; Reich, Wolfgang
The reaction of the functionalized P/C double bond systems X-P=C(R)SiMe3 [R = SiMe3 and X = Cl (1a), Cp* (5a) or R = Ph and X = Br (1b), Cp* (5b)] with alkali carbonylmetallates or carbonyl complexes of group 6, 8, and 10 metals leads to the formation of the transition metal-substituted phosphaalkenes [{M}-P=C(R)SiMe3 3a-j and 4a-i], in which the P-C fragment acts as a one-electron donor. Depending on the nucleophilicity of the transition metal anion used, but also on the methylene carbon substituents [1a: (SiMe3)2; 1b: (Ph)-SiMe3], a different stability of the (methylenephosphanyl)1-metal complexes is observed, which results in a broad spectrum of reactivities. As demonstrated by the reactions of the (methylenephosphanyl)metal complexes with sulfonic acid derivatives (10a-c), diverse transition metal complexes (11a-c), as well as chalcogenes (14a-c, 15), a change in the reactivity is observed, indicating a transition from an olefinic to a carbenic character of the methylenephosphane. In comparison to the phenyl-substituted derivatives 4a-i the bis(trimethyl)1-substituted species 3a-j exhibit an increased reactivity. This is reflected in the easy decarbonylation of 3a-d to the phosphavinylidene complexes 12a-d.
Open Access
Olefin-, Carben- und Nitren-Analoge im Phosphorsystem
(1985) Niecke, Edgar; Böske, Jürgen; Gudat, Dietrich; Güth, W.; Lysek, Manfred; Symalla, Erhard
Mit der Entdeckung der resonanzstabilisierten Phosphamethincyanine durch Dimroth und Hoffmann /1/ und Phosohabenzole durch Märkl /2/ Mitte der sechziger Jahre hat eine stürmische Entwicklung auf dem Gebiet der Phosphorverbindungen mit Phosphor-Element-(p-p)-π-Bindungen eingesetzt. Im Verlauf dieser Aktivitäten gelang 1973 in unserem Arbeitskreis /3/ und 1976 Becker /4/ mit der Synthese der ersten Imino- und Methylenphosphane der Zugang zu isolierbaren Systemen mit Phosphor-Stickstoff- und Phosphor-Kohlenstoff-Doppelbindungen. Einen weiteren Höhepunkt dieser Forschungen stellt die Entdeckung des Diphosphensystems durch Yoshifuji und Mltarbeiter 1981 dar /5/, mit der erstmals die Verifizierung einer (3p-3p)-π-Bindung beim Phosphor gelang. Der folgende Bericht gibt eine Zusammenfassung von eigenen Arbeiten über die drei letztgenannten Verbindungssysteme, wobei der Vergleich der Chemie dieser Verbindungen mit bekannten Systemen der organischen Chemie eine zentrale Rolle spielt.
Open Access
Pentamethylcyclopentadienyl[bis(trimethylsilyl)methylen]phosphan - ein Phosphaalken mit einer reaktiven PC-Einfachbindung
(1985) Gudat, Dietrich; Niecke, Edgar; Krebs, Bernt; Dartmann, Mechtild
Synthesis, spectroscopic data and X-ray structure determination of a novel phosphaalkene, Me5C5-P=C(SiMe3)2 1, are reported. It is shown by dynamic 1H-NMR spectroscopy that 1 exhibits thermal E/Z-isomerization of the double bond at ambient temperature. Reactions of 1 involve electrophilic attack of the π-system with hard (H+) and soft (Ag+) Lewis-acids, and an unusual cleavage of a PC-single bond on reaction with metal complexes (MeCN)3M(CO)3, (M = Mo, W).
Open Access
Phosphorus carbene and olefine analogues
(1987) Niecke, Edgar; Gudat, Dietrich; Leuer, Martina; Lysek, Manfred; Symalla, Erhard
A representative of the yet unknown parent iminophosphane is ButP=NBut 1 which has been recognized as an carbenic analogue for some time. The unusual properties of 1 prompted our investigations of the synthesis of further phosphorus(III)-(p-p)π-bonds systems with an orbital sequence (HOMO= n(P), LUMO= T (P=X)) as well as the reaction behaviour of this class of compounds.
Open Access
Phosphorus(III) double bond systems, carbene and alkene analogues : the electronic structure of imino- and methylene-phosphanes
(1985) Niecke, Edgar; Gudat, Dietrich; Schoeller, Wolfgang W.; Rademacher, Paul
Frontier orbital assignment in iminophosphanes in carried out by utilizing a linear relationship between differences in optical transitions and ionisation potentials confirming the ambident reaction behaviour of these compounds.
Open Access
Phosphorus-31 solid-state NMR study of iminophosphines: influence of electronic structure and configuration of the double bond on phosphorus shielding
(1994) Gudat, Dietrich; Hoffbauer, Wilfried; Niecke, Edgar; Schoeller, Wolfgang W.; Fleischer, Ulrich; Kutzelnigg, Werner
The principal elements of the 31P nuclear magnetic shielding tensors of iminophosphines of the type R-P=N-aryl (aryl = C6H2tBu3; R = tBu, Ph3Sn(tBu)N, aryl-N=P-(tBu)N, aryl-NH, aryl-N=P-(adamantyl)N, Ph2N, carbazolyl, tBu2C=N, iminofluorenyl, Cl, Br, I; 5-16) are determined from high-resolution solid-state MAS (magic angle spinning) NMR spectra. Comparison of the data with the results of IGLO calculations on shielding tensors of model compounds is used to assign the orientation of the principal axes system in the molecular frame. The observed shieldings can be correlated with structural features of the compounds. In (E)-configured alkyl- and amino-iminophosphines, the component at high field (δ33) is approximately perpendicular to the RPN plane and the low-field component (δ11) is in this plane and close to the P-R bond. Introduction of π-donor substituents (R'2N) at phosphorus produces large increases in δ11, which can be related to corresponding changes in the n-π* electronic transition energies. A similar effect is found for a change of the double-bond geometry from (E)- to (Z)-configuration. Electronegative halogen substituents (Cl, Br) give rise to a further substantial increase in the tensor component at high field, δ33. Furthermore, a change of the orientation of the principal axes system in the molecular frame occurs, with δ33 being aligned close to the P,N bond axis and the intermediate component, δ22, perpendicular to the RPN plane. A discussion of these effects is given in terms of partial triple-bond character for the P,N bond. The shape of the shielding tensor of the iodo compdound (16) suggests that the electronic environment of the P,N moiety is similar to other systems containing a genuine triple bond. The unique difference between the isotropic chemical shifts in the solid state and in solution (Δδ 118 ppm) in this case indicates that this phenomenon is confined to the solid state and can be attributed to the substantial polarization of the P,I bond, which is a consequence of the observed intermolecular association.
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.
Open Access
Reaction of P-halogeno-phospha-alkenes with alkene complexes of nickel and platinum: η2-co-ordination and unusual oxidative addition behaviour
(1989) Gudat, Dietrich; Meidine, Mohamed F.; Nixon, John F.; Niecke, Edgar
Phospha-alkenes X-P=CTMS2(X = F, Cl, I; TMS = SiMe3) display different reaction behaviour towards metal complexes (Bu3P)2Ni(cod)(cod = cyclo-octa-1,5-diene) or (Ph3P)2Pt(C2H4), respectively, undergoing either co-ordination to give η2-phospha-alkene complexes or alternatively oxidative addition of the P-X bond, forming phospha-alkenyl-metal(II) complexes, [(R3P)2M(X)(σ-P=CTMS2)].
Open Access
Reactions of an iminophosphoranylidene carbenoid
(1994) Schilbach, Wolfgang; Gönna, Volker von der; Gudat, Dietrich; Nieger, Martin; Niecke, Edgar
Interesting trapping products with phosphanes and chlorotrimethylsilane result from reactions with the novel intermediate phosphoranylidene carbenoid 1: These lead to the phosphoniomethanide 2 with PPh3, the dihydrodiphosphete 3 with PMe3, and the imino(methylene)phosphorane 4 with ClSiMe3. R = 2,4,6-tBu3C6H2, R′ = Ph, Me.
Open Access
Reactions of iminophosphanes with chlorotris(triphenylphosphine)rhodium(I): generation and NMR identification of the first iminophosphanerhodium(I) and iminophosphanerhodium(III) complexes
(1993) Romanenko, Vadim D.; Ruban, Alexander V.; Roshenko, Alexander B.; Povolotskii, Mark I.; Sarina, Tatjana V.; Gudat, Dietrich; Niecke, Edgar
Iminophosphanes [RO-P=NAr] (R = Me, 2-MeC6H4; Ar = 2,4,6-Bu'3C6H2) 1a,b react with RhClL3 (L = Ph3P) via ligand exchange to give KP-iminophosphane complexes of rhodium(i) [RhCl(MeOP=NAr)2L] 2 and [PhCl(2-MeC6H4OP=NAr)L2] 3. Under analogous conditions, P-halogenoiminophosphanes [X-P=NAr] (X = Cl, Br, I) 3a–c undergo a facile oxidative addition of the P-X bond, forming five-coordinate iminophosphanerhodium(III) complexes of composition [L2Cl(X)Rh(σ-P=BAr)] 5.
Open Access
Reaktionen eines Iminophosphoranylidencarbenoids
(1994) Schilbach, Wolfgang; Gönna, Volker von der; Gudat, Dietrich; Nieger, Martin; Niecke, Edgar
Interessante Abfangprodukte mit Phosphanen und Chlortrimethylsilan bildet das neuartige intermediär gebildete Phosphoranylidencarbenoid 1: Mit PPh3 entsteht das Phosphoniomethanid 2, mit PMe3 das Dihydrodiphosphet 3 und mit ClSiMe3 bildet sich das Imino(methylen)phosphoran 4. R = 2,4,6-tBu3C6H2, R′ = Ph, Me.
Open Access
Säurekatalysierte Isomerisierung des [2+1]-Cyclodimers eines Iminophosphans zum Diazadiphosphetidin
(1986) Niecke, Edgar; Gudat, Dietrich; Symalla, Erhard
Nicht das Azadiphosphiridin 2, sondern das Diazadiphosphetidin 3 entsteht bei der Reduktion von 1. Das als Intermediat nachzuweisende 2 wird durch Lewis- oder Brønsted-Säuren in 3 umgewandelt. Mit F3CSO3H als Säure konnten die Zwischenstufen der Isomerisierung, 4 und 5, isoliert werden (R=tBu; X=F3CSO3).
Open Access
Synthese und Struktur aminosubstituierter Tetraphosphetane
(1991) Appel, Rolf; Gudat, Dietrich; Niecke, Edgar; Nieger, Martin; Porz, Christoph; Westermann, Hermann
A number of aminotetraphosphetanes could be obtained by reductive dehalogenation of dichlorophosphines with magnesium as well as by elimination of chlorotrimethylsilane from vicinal chlorosily-functionalized biphosphines and from [2+2]-cyclodimerization of aminodiphosphenes, respectively. The molecular structures of several tetraphosphetanes are reported and discussed. The torsion-angle of the four-membered rings varies from 22,5 to 45,7 depending on the size und electronegativity of the exocyclic ligands.
Open Access
Synthesis of a phosphavinyl complex via shift of a pentamethylcyclopentadienyl from phosphorus to iron
(1986) Gudat, Dietrich; Niecke, Edgar; Arif, Atta M.; Cowley, Alan H.; Quashie, Sapé
The reaction of the phosphaalkene (μ1-Me5C5)P=C(SiMe3)2 with Fe2(CO)9 affords the μ1 (P-bonded) complex (μ1-Me5C5)[(CO)4Fe]P=C(SiMe3)2 (4). Photolysis of 4 produces the phosphavinyl complex [Fe-{μ1-P=C(SiMe3)2}(η5-Me5C5)(CO)2] (5). Compound 5 can also be prepared via the metathetical reaction of (Me3Si)2C=PCl with K[Fe(η5-Me5C5)(CO)2]. The structure of 5 has been determined by X-ray crystallography.