Jörg Daniels

Efficient Air‐Stable Organometallic Low‐Molecular‐Mass Gelators for Ionic Liquids: Synthesis, Aggregation and Application of Pyridine‐Bridged Bis(benzimidazolylidene)–Palladium Complexes

Novel pincer-type, pyridine-bridged bis(benzimidazolylidene)-palladium complexes 5-7 were synthesised from cheap commercial precursors under microwave assistance. Although simple in structure, carbene complexes 5a,b are efficient low-molecular-mass metallogelators. They gelate not only a broad variety of protic and aprotic organic solvents, but also different types of customary ionic liquids (such as imidazolium, pyridinium, pyrazolidinium, piperidinium and ammonium salts) at concentrations as low as 0.5 mg mL(-1). The morphologies of the resulting 3D gel networks composed from long and thin fibres were studied by TEM and light microscopy for a selection of organic and ionic liquids. The achiral gelators are able to induce the formation of helical fibres. The thermal stability of the gel samples increases with the gelator concentration as demonstrated by thermoreversible DSC studies. Temperature-dependent NMR and X-ray diffraction studies, as well as comparisons with pincer complex analogues bearing shorter alkyl chains, suggest that the 3D networks responsible for gelation are based on non-covalent interactions, such as pi-stacking, van der Waals interactions, and hydrogen and metal-metal bonding. Ionic liquids and gels obtained from them and 5a,b display comparable high conductivities, which characterises pyridine-bridged bis(benzimidazolylidene)-palladium pincer complexes as air-stable metallo gelators that efficiently immobilise ionic liquids in low gelator concentration indicating--beyond catalysis--their potential applications in electrochemical devices.

Novel access to azaphosphiridine complexes and first applications using Brønsted acid-induced ring expansion reactions

Synthesis of azaphosphiridine complexes 3a-e was achieved via thermal group transfer reaction using 2H-azaphosphirene complex 1 and N-methyl C-aryl imines 2a-e (i) or via reaction of transient Li/Cl phosphinidenoid complex 5 (prepared from dichloro(organo)phosphane complex 4) using 2a-c (ii), respectively. Reaction of complexes 3a,d and trifluoromethane sulfonic acid in the presence of dimethyl cyanamide led to a highly bond- and regioselective ring expansion yielding 1,3,4sigma3lambda3-diazaphosphol-2-ene complexes 8a,d after deprotonation with NEt3. 31P NMR reaction monitoring revealed that protonation of complex 3a yields the azaphosphiridinium complex 6a, unambiguously identified by NMR spectroscopy at low temperature. All isolated products were characterized by multinuclear NMR spectroscopy, IR and UV/Vis (for 3a,d, 6a, 8a,d), MS and single-crystal X-ray crystallography in the cases of complexes 3b-d, 8a and 8d. DFT studies on the reaction mechanism and compliance constants of the model complex of 6a are presented.

Synthesis and crystal structure of (NEt3Me)2CsP11·5NH3

Abstract Two caesium cations of Cs 3 P 11 were exchanged for two NEt 3 Me + cations in liquid ammonia, yielding (NEt 3 Me) 2 CsP 11 ·5NH 3 . The crystal structure determination shows linear 1 ∞ [CsP 11 ] − chains along the crystallographic b axis, which are separated by NEt 3 Me + cations. Five ammonia molecules of crystallization complete the coordination sphere of the Cs cations. FT-IR frequencies in the region of the P 3− 11 molecular vibrations are in agreement with the values reported previously for the alkali metal undecaphosphides.

Synthesis, Structure, and Reactions of 1-tert-Butyl-2-diphenylphosphino-imidazole

Metalation reactions were studied of a sterically demanding imidazole derivative, namely, 1-tert-butylimidazole (1), with different metalation reagents and subsequent reaction with diphenylchlorophosphane. The reaction product, 1-tert-butyl-2-diphenylphosphino-imidazole (2), was subjected to oxidation and complexation reactions to yield the corresponding products Ph(2)(Imi)P-E (E = O (3), S (4), Se (5), W(CO)(5) (8)) and in the case of borane-THF the N-BH(3) coordination product 10 was obtained. The analytical data of the new compounds are discussed, including X-ray diffraction studies of 3-5.

A Zwitterionic Phosphonio-1, 2, 4-Diazaphospholide and Neutral 1, 2, 4-Diazaphosphole — A Comparative Study of Molecular Structures and Co-ordination Properties†

The bis-phosphonio-1, 2, 4-diazaphospholide salt (1[Cl]) reacts with complex boron hydrides under selective extrusion of one PPh3 moiety to give borane adducts of a novel zwitterionic phosphonio-1, 2, 4-diazaphospholide. Both the Et3B adduct 2b and the free zwitterionic heterocycle 3, which was liberated by further reaction of 2b with NEt3, were characterized by spectroscopic data and 2b, as well, by a single crystal X-ray diffraction study. The comparison of the structural data with those of a neutral 1, 2, 4-diazaphosphole and a lithium-1, 2, 4-diazaphospholide which was formed by deprotonation of the parent 1, 2, 4-diazaphosphole 4a discloses trends in endocyclic bonding distances which can be rationalized in terms of a charge dependent shift in the π-electron distribution. First studies of the co-ordination properties reveal for both 2b and 4a a marked preference to bind two M(CO)5-fragments (M = Cr, W) via the lone-pairs of the phosphorus and one nitrogen atom; mononuclear complexes with P-co-ordinated heterocycles are formed as intermediates. A single crystal X-ray diffraction study of the dinuclear complex [Cr2(CO)10(μ2-C2H3N2P-κP, κN)] (10a) together with spectroscopic studies (including 183W NMR studies of tungsten complexes) suggests that ML back donation is more efficient for P- than for N-bound metal fragments. No evidence for π-co-ordination of the 1, 2, 4-diazaphosphole ring to a Cr(CO)3 fragment was obtained. Ein Zwitterionisches Phosphonio-1, 2, 4-Diazaphospholid und Neutrales 1, 2, 4-Diazaphosphol — Eine Vergleichende Studie von Molekulstrukturen und Koordinationseigenschaften Das Bis-phosphonio-1, 2, 4-diazaphospholid-Salz (1[Cl]) reagiert mit komplexen Borhydriden unter selektiver Abspaltung einer PPh3-Gruppe zu Boranaddukten eines neuen zwitterionischen Phosphonio-1, 2, 4-diazaphospholids. Sowohl das Et3B-Addukt 2b als auch der freie zwitterionische Heterocyclus 3, der durch weitere Reaktion von 2b mit NEt3 freigesetzt wurde, wurden durch spektroskopische Daten und 2b zusatzlich durch eine Einkristall-Rontgenstrukturanalyse charakterisiert. Der Vergleich der Strukturdaten mit denen eines neutralen 1, 2, 4-Diazaphosphols und eines Lithium-1, 2, 4-diazaphospholids, das durch Deprotonierung der Stammverbindung 1, 2, 4-Diazaphosphol 4a erhalten wurde, zeigen Trends in den endocyclischen Bindungslangen, die im Sinne ladungsabhangiger Variationen der π-Elektronenverteilung rationalisiert werden konnen. Erste Studien der Koordinationseigenschaften zeigen sowohl fur 2b als auch 4a eine deutliche Praferenz zur Bindung von zwei M(CO)5-Fragmenten (M = Cr, W) uber die freien Elektronenpaare des Phosphor- und eines Stickstoffatoms; einkernige Komplexe mit P-koordinierten Heterocyclen entstehen als Zwischenstufen. Eine Einkristall-Rontgenstrukturanalyse des zweikernigen Komplexes [Cr2(CO)10(μ2-C2H3N2P-κP, κN)] (10a) in Verbindung mit spektroskopischen Untersuchungen (einschlieslich 183W NMR Untersuchungen der Wolframkomplexe) geben Hinweise fur eine effizientere M°L Ruckbindung von P- im Vergleich zu N-gebundenen Metallfragmenten. Anzeichen fur eine π-Koordination des 1, 2, 4-Diazaphospholrings an ein Cr(CO)3-Fragment wurden nicht erhalten.

Conformational Flexibility of Tetralactam Macrocycles and Their Intermolecular Hydrogen‐Bonding Patterns in the Solid State

Despite their rigid scaffold, tetralactam macrocycles (TLMs) display a remarkable degree of conformational flexibility, as revealed by analysis of the corresponding X-ray crystal structures. This flexibility is not limited to the rotatability of the TLM amide groups but also applies to the m-xylene rings, and it thus has a great impact on the overall shape of the macrocycle cavity. The conformational properties of the TLMs give rise to a broad variety of intermolecular hydrogen-bonding patterns, including infinite ladders, an interesting catemer motif, and short C-HO=C hydrogen bonds. These results are in accord with previous theoretical calculations, support a structural model proposed earlier for an interpretation of scanning tunneling microscopy images, and substantially contribute to the understanding of the adaptability of macrocyclic scaffolds, which is crucial for guest binding or templated syntheses with TLMs.

Layers built from caesium cations and heptaphosphanortricyclane anions: synthesis and crystal structure of [NEt3Me][Cs2P7]·NH3 and [NEt4][Cs2P7]·4NH3

Exchange of one caesium cation of Cs3P7 for NEt3Me+ or NEt4+ in liquid ammonia gave [NEt3Me][Cs2P7]·NH31 and [NEt4][Cs2P7]·4NH32, respectively. The crystal structure of the compounds have been determined. They show the existence of corrugated ∞2[Cs2P7]– layers stacked along the crystallographic a axis in both compounds. The layers are topologically equivalent in 1 and 2. While the layers are repeated in the same orientation in 1, stacking mode AAA, they have two different orientations in 2, stacking mode ABAB, where B is related to A by a mirror plane. The space between the layers contains ammonia of solvation completing the co-ordination of caesium, and the tetraalkylammonium cations.

Exploring the Palladium and PlatinumBis(pyridine) Complex Motif by NMR Spectroscopy, X‐ray Crystallography, (Tandem) Mass Spectrometry, and Isothermal Titration Calorimetry: Do Substituent Effects Follow Chemical Intuition?

A series of ten palladium-bis(pyridine) complexes, as well as their corresponding platinum complexes, have been synthesized. The pyridine ligands in each series carried different σ-donor and/or π-acceptor/donor substituents at the para-position of their pyridine rings. These complexes were analysed by NMR spectroscopy, X-ray crystallography, (tandem) MS, and isothermal titration calorimetry (ITC) to validate whether these methods allowed us to obtain a concise and systematic picture of the relative and absolute thermodynamic stabilities of the complexes, as determined by the electronic effects of the substituents. Interestingly, the NMR spectroscopic data hardly correlated with the expected substituent effects but the heteronuclear platinum-phosphorus coupling constants did. Crystallographic data were found to be blurred by packing effects. Instead, tandem MS and ITC data were in line with each other and followed the expected trends.

[1,3-Bis(4-nitrophenyl)triazenido](triphenylphosphine)gold(I)

In the title complex, [Au(C(12)H(8)N(5)O(4))(C(18)H(15)P)], the coordination geometry about the Au(I) ion is linear, with one deprotonated 1,3-bis(4-nitrophenyl)triazenide ion, [O(2)NC(6)H(4)N=N-NC(6)H(4)NO(2)](-), acting as a monodentate ligand (two-electron donor), and one neutral triphenylphosphine molecule completing the metal coordination. The triazenide ligand is almost planar (r.m.s. deviation = 0.0767 A), with the largest interplanar angle being 11.6 (7) degrees between the phenyl ring of one of the terminal 4-nitrophenyl substituents and the plane defined by the N=N-N triad. The Au-N and Au-P distances are 2.108 (5) and 2.2524 (13) A, respectively. Pairs of molecules generated by centrosymmetry are associated into a supramolecular array via intermolecular C-H...O interactions, and N...C and N...O pi-pi interactions.

Extended π conjugation in 2H-1,4,2-diazaphosphole complexes

Thienyl substituted 2H-1,4,2-diazaphosphole complexes 3a,b were prepared via highly selective ring-expansion reactions of 2H-azaphosphirene complex 1 and nitriles with our new synthetic protocol using triflic acid and NEt3. The single-crystal X-ray structures of 3a,b show that the 3,5-substituents adopt a coplanar arrangement with the diazaphosphole ring resulting in extended π-conjugation, thus giving rise to absorptions at long wavelengths in their UV/Vis spectra. On the basis of Time-Dependent DFT (TD-DFT) calculations the longest-wavelength absorption could be assigned to a metal–ligand charge transfer (MLCT) process and another low-energy band was interpreted as a superposition of π–π* and n–π* transitions. Protonation of the ring nitrogen yields a pronounced bathochromic shift of all bands along with an increase in their intensity. These effects can be explained by the different extent to which the orbital energies are affected by protonation.