Rüdiger Beckhaus

Protic ionic liquid and ionic melts prepared from methanesulfonic acid and 1H-1,2,4-triazole as high temperature PEMFC electrolytes

Protic ionic liquid and ionic melts were prepared from the combination of methanesulfonic acid (CH3SO3H) and 1H-1,2,4-triazole (C2H3N3) at various molar ratios. The thermal properties, crystal structure, acid–base interactions, ionic conductivity, proton conduction behavior and electrochemical stability of the system were studied. The equimolar composition, 1,2,4-triazolium methanesulfonate (C2H4N3+·CH3SO3− (1)), was a proton transfer salt with a melting point of around 134 °C. Single crystal and powder XRD data, as well as TGA results, revealed that the base-rich region was a mixture of 1 and 1H-1,2,4-triazole. Infrared analysis and single crystal data suggested that the C2H3N3–CH3SO3H system exists in a strongly hydrogen-bonded network. Systematic investigation of the ionic conductivity showed that the ionic conductivity reached local maxima at the compositions of [C2H3N3]/[CH3SO3H] = 10/90 and 80/20, respectively, while it exhibited a local minimum at the equimolar composition. The temperature dependence of the ionic conductivity was found to obey the Vogel–Fulcher–Tamman (VFT) equation. The fitting of the conductivity data to the VFT equation showed that the carrier ion concentration versus the mole fraction of 1H-1,2,4-triazole exhibited a volcano shape. In addition, the C2H3N3–CH3SO3H system showed adequate electrochemical stability under PEMFC conditions as measured by linear sweep voltammetry. The relatively high ionic conductivity, wide electrochemical window and good thermal stability demonstrated that the C2H3N3–CH3SO3H system is a suitable candidate for high temperature PEMFC electrolytes.

Efficient Access to Titanaaziridines by CH Activation of N‐Methylanilines at Ambient Temperature

Titanaaziridines or η(2)-imine titanium complexes are considered key intermediates of the titanium-catalyzed hydroaminoalkylation of alkenes. Herein, we present an efficient synthetic route to this class of compounds, starting from N-methylanilines and a bis(η(5):η(1)-pentafulvene)titanium complex. Consecutive reactions on the η(2)-methyleneaniline complexes, characterized for the first time, prove a high chemical versatility. In particular, hydroaminoalkylation products were found in reactions of the three-membered titanacycles with alkenes. For the first time, all the intermediates of the hydroaminoalkylation of alkenes were isolated and characterized.

A Novel Route to Fulvene Complexes of Titanium—Diastereoselective Complexation of Pentafulvenes to Cyclopentadienyltitanium Fragments

An alternative to the known thermally induced syntheses of fulvene complexes of early transition metals is now provided by the direct reductive complexation of pentafulvenes to [CpTiCl] fragments. These generally highly diastereoselective reactions enable a broad variation of substitution patterns and establish an extensive subsequent chemistry.

Molekulares Design von übergangsmetallkomplexverbindungen zur aktivierung kleiner moleküle: II. Zur Carbonylierung von Bis(π-pentamethylcyclopentadienyl)metall-1,3-Dien-Komplexen Cp★2M(1,3-Dien) (M Zr, Hf)Bildung einkerniger Metall-Endiolate☆

Abstract Bis(π-pentamethylcyclopentadienyl)metal-(η- s-cis -diene) complexes of zirconium and hafnium react with carbon monoxide under mild conditions to give mononuclear metal-endiolates 18–20 quantitatively. The corresponding isomeric trans -diene complexes react with carbon monoxide to give metallocene-dicarbonyls Cp★ 2 M(CO) 2 (Cp★  C 5 (CH 3 ) 5 ), whereas in the case of M  Hf a monocarbonyl-η 2 -butadiene complex is formed in solution. All compounds were characterized by spectroscopic measurements.

Synthese und charakterisierung eines stabilen heterobimetallischen TitanCobalt komplexes mit unverbrückter TiCo-bindung

Abstract Unusually stable [(tC4H9O)3Ti-Co(CO)4] has been prepared by treating the appropriate carbonylmetallate anion with chloro titanium t-butoxide as well as by protolysis of CH3Ti(OtC4H9)3 with HCo(CO)4. Spectroscopic data indicate that the alkoxide and carbonyl ligands are nonbridging, establishing C3v-symmetry at the cobalt atom.

Reactions of Pentafulvene Complexes of Titanium with Carbonyl Compounds − Diastereoselective Synthesis of σ,π-Chelate Complexes with Cp~O Ligands

The compound Cp*Ti[η6-C5H4C(H)(tBu)]Cl (1) reacts with ketones, aldehydes, and esters to give σ,π-chelate complexes with Cp~O ligands through insertion of the carbonyl group into the Ti−C(H)(tBu) bond. Starting from diastereomerically pure 1, the reaction with symmetric ketones R2CO led to the formation of two diastereomeric products. The diastereomeric ratio could be controlled by steric and electronic properties of the substituent R. Thus, this procedure provides an easy approach to complexes with Cp~O ligands where new chiral centres are formed directly in the coordination sphere of the metal atom through a side-differentiated attack of the carbonyl compound at the titanium atom. All products were thoroughly characterized. Crystal structure determinations were carried out on 2a, 3a, 5, 6b, and 9a. (© Wiley-VCH Verlag GmbH, 69451 Weinheim, Germany, 2002)

SYNTHESIS AND STRUCTURAL CHARACTERIZATION OF AZATITANACYCLOBUTANE DERIVATIVES

The titanocene vinylidene intermediate [Cp*2Ti=C=CH2] (9) reacted with the carbodiimides R−N=C=N−R [R = p-CH3C6H4 (19a), C6H11 (19b)] to give the N=C-cycloaddition products [Cp*2Ti{−NR−C(=NR)−(C=CH2)−}] [(R = p-CH3C6H4 (20a), C6H11 (20b)]. The X-ray structure of 20a in form of a surprisingly stable n-hexane clathrate is presented. The azatitanacyclobutane [Cp*2Ti{−NPh−C(Ph)(H)−(C=CH2)−}] (22) was formed from the reaction between 9 and benzylidene aniline [PhN=C(Ph)H (21)]. Reactivity studies showed that azatitanacyclobutanes are unreactive upon typical ring-enlargement reactions as observed for other four-membered titanacycles.

Structure and reactivity of four-membered titanacycles—theoretical studies

Abstract The equilibrium geometries of a series of four-membered titanacycles with exocyclic methylene group Cl 2 Ti–X–Y–C CH 2 (X: CH 2 , CH, O, S, N, P; Y: CH 2 , CH, CO, CCH 2 , N–CH 3 ) and two derivatives without exocyclic methylene group Cl 2 Ti–X–CH 2 –C H 2 (X: CH 2 , O) have been calculated at the HF level of theory by using an effective core potential basis set. The geometries were compared with data from X-ray structures for the corresponding compound Cp* 2 Ti–X–Y–C CH 2 . The structures of the planar four-membered titanacycles are well represented by the model complexes. The chloride ligands are good theoretical substitutes for the bent metallocene system with cyclic ligand systems in the intersecting plane between the Cp* ligands. The calculated metal–carbon bond distances are found to be shorter than in the X-ray structures of the real molecules. Total energies are calculated at the MP2 level and are used to predict the reactivity of the compounds. Titanacyclobutanes with an exocyclic methylene group are more stable than titanacyclobutanes without this group. Oxatitanacyclobutanes are subject to cycloreversion under formation of Cl 2 TiO and allene. Azatitanacyclobutenes undergo spontaneous ring opening reactions. These statements are further supported by the analysis of the molecular orbitals of some selected derivatives.

Intermolecular coupling reactions of inversely polarized carbene ligands starting from the Cp2*TiCCH2 intermediate and chromium carbene complexes

The titanaallene intermediate [Cp2*TiCCH2] (2), generated thermally from Cp2*Ti(CHCH2)CH3 (1), reacts with methoxyalkylcarbene complexes (CO)5CrC(OCH3)R (3) [R=CH3 (a), CD3 (b), Et (c)] by CC-coupling of the carbene ligands to give the heterodinuclear complexes Figure options Download full-size image Download as PowerPoint slide (4) and Figure options Download full-size image Download as PowerPoint slide (5). An unusual isomerization of the exocyclic double bond, which occurs by thermal conversion 4c→5c, can be explained considering ionic resonance forms. The addition of one CO molecule to 5c leads to a displacement of the methoxy coordination. On the other hand, the aminocarbene complex (CO)5CrC(NHiPr)CH3 (8), which is less electrophilic than alkoxycarbenes, reacts with 2 to give a dinuclear dititanacyclobutene complex (9). Its blue-violet colour is probably caused by a twist around the single bond C(β)–C(β) of the dititanacyclobutene unit.

Crystal structures of titanium–aluminium and –gallium complexes bearing two μ2-CH3 units

The molecular structures of two isotypic titanium(III) complexes bearing an trimethylaluminium or -gallium motif are reported. In both compounds, two methyl groups coordinate to the metal atoms, viz. Ti and Al(Ga), and in a μ 2 manner.