Unprecedented Spectroscopic and Computational Evidence for Allenyl and Propargyl Titanocene(IV) Complexes: Electrophilic Quenching of Their Metallotropic Equilibrium

The synthesis and structural characterization of allenyl titanocene(IV) [TiClCp₂(CH=C=CH₂)] 3 and propargyl titanocene(IV) [TiClCp₂(CH₂?C≡C?(CH₂)₄CH₃)] 9 have been described for the first time. Advanced NMR methods including diffusion NMR methods (diffusion pulsed field gradient stimulated spin echo (PFG‐STE) and DOSY) have been applied and established that these organometallics are monomers in THF solution with hydrodynamic radii (from the Stokes–Einstein equation) of 3.5 and 4.1 Å for 3 and 9 , respectively. Full ¹H, ¹³C, Δ¹H, and Δ¹³C NMR data are given, and through the analysis of the Ramsey equation, the first electronic insights into these derivatives are provided. In solution, they are involved in their respective metallotropic allenyl–propargyl equilibria that, after quenching experiments with aromatic and aliphatic aldehydes, ketones, and protonating agents, always give the propargyl products P (when carbonyls are employed), or allenyl products A (when a proton source is added) as the major isomers. In all the cases assayed, the ratio of products suggests that the metallotropic equilibrium should be faster than the reactions of 3 and 9 with electrophiles. Indeed, DFT calculations predict lower Gibbs energy barriers for the metallotropic equilibrium, thus confirming dynamic kinetic resolution.     

Homoleptic Tetrakis(silyl) Complexes of Pd0 and Pt0 Featuring Metal‐Centred Heterocubane Structures: Evidence for the Existence of the Corresponding Mononuclear PdI and PtI Complexes

We report on the first homoleptic tetrakis(silyl) complexes of zerovalent Group 10 metals. The compounds [MLi₄{Si(3,5‐Me₂pz)₃}₄] (M=Pd and Pt; 3,5‐Me₂pz=3,5‐dimethylpyrazolyl) exhibit very appealing metal‐centred heterocubane structures with the central d¹⁰ metal atoms surrounded by four silicon and four lithium atoms. Both compounds were characterised in detail, including X‐ray crystal‐structure analysis and 2D NMR spectroscopic methods such as ⁷Li,²⁹Si and ⁷Li,¹⁹⁵Pt HMQC. Cyclic voltammetry studies, in combination with density functional theory (DFT) calculations, revealed that the corresponding mononuclear cationic d⁹‐M^I and dicationic d⁸‐M^II complexes are accessible by stepwise one‐electron oxidation of the title compounds. Electron paramagnetic resonance (EPR) investigations provided evidence for the existence of the corresponding paramagnetic palladium(I) and platinum(I) complexes.     

On the Solution Behaviour of Benzyllithium⋅(−)‐Sparteine Adducts and Related Lithium Organyls – A Case Study on Applying 7Li,15N{1H} HMQC and Further NMR Methods,Including Some Investigation into Asymmetric Synthesis

2D ⁷Li,¹⁵N heteronuclear shift correlation through scalar coupling has successfully been applied to several lithium organyls consisting of polydentate N ligands such as N,N,N′,N′‐tetramethylethylenediamine (tmeda), N,N,N′,N′,N′′‐pentamethyldiethylentriamine (pmdta) and (?)‐sparteine. Structural insights on the conformation of benzyllithium ? pmdta ( 5 ) in a toluene solution and the strength of ion pairing in combination with PGSE NMR measurements, ¹H,¹H‐NOESY and ¹H,⁷Li‐HOESY experiments are presented. By studying in detail the formation of 5 in solution, a transient species has been observed for the first time and assigned to a pre‐complex of nBuLi and pmdta. In addition, the solution behaviour of the complex formed between benzyllithium and (?)‐sparteine ( 8 ) has been studied by PGSE and multinuclear NMR spectroscopy. The straightforward synthesis and first applications in asymmetric lithiations are also reported, which show that the new system benzyllithium ? (?)‐sparteine ( 8 ) provide poorer enantioselective induction than the classical nBuLi ? (?)‐sparteine ( 6 ). The results were supported by deprotonation experiments confirming that the formation of 8 relies on two relevant factors, namely temperature and lithiating reagent. The existence of 8 may thus interfere with the asymmetric induction when the system nBuLi ? (?)‐sparteine is used in the enantioselective deprotonations of N‐Boc‐N‐(p‐methoxyphenyl)‐benzylamine conducted in toluene.     

Hydrophilic membrane-based humidity control.

A dehumidification system for low gravity plant growth experiments requires the generation of no free-liquid condensate and the recovery of water for reuse. In the systems discussed in this paper, the membrane is a barrier between the humid air phase and a liquid-coolant water phase. The coolant water temperature combined with a transmembrane pressure differential establishes a water flux from the humid air into the coolant water. Building on the work of others, we directly compared different hydrophilic membranes for humidity control. In a direct comparison of the hydrophilic membranes, hollow fiber cellulose ester membranes were superior to metal and ceramic membranes in the categories of condensation flux per surface area, ease of start-up, and stability. However, cellulose ester membranes were inferior to metal membranes in one significant category, durability. Dehumidification systems using mixed cellulose ester membranes failed after operational times of only hours to days. We propose that the ratio of fluid surface area to membrane material area (approximately = membrane porosity) controls the relative performances among membranes. In addition, we clarified design equations for operational parameters such as the transmembrane pressure differential. This technology has several potential benefits related to earth environmental issues including the minimization of airborne pathogen release and higher energy efficiency in air conditioning equipment. Utilizing these study results, we designed, constructed, and flew on the space shuttle missions a membrane-based dehumidification system for a plant growth chamber.     

Integral lattices in TQFT

We find explicit bases for naturally defined lattices over a ring of algebraic integers in the SO(3)-TQFT-modules of surfaces at roots of unity of odd prime order. Some applications relating quantum invariants to classical 3-manifold topology are given.     

Higher Bott-Chern forms and Beilinson's regulator

In this paper, we prove a Gauss-Bonnet theorem for the higher algebraic K-theory of smooth complex algebraic varieties. To each exact n-cube of hermitian vector bundles, we associate a higher Bott-Chen form, generalizing the Bott-Chern forms associated to exact sequences. These forms allow us to define characteristic classes from K-theory to absolute Hodge cohomology. Then we prove that these characteristic classes agree with Beilinson's regulator map. Oblatum 21-III-1997 & 12-VI-1997     

Effect of the medium in hexacyanoferrate (III)-iodide and peroxodisulfate-iodide reaction

The kinetics of the two reactions hexacyanoferrate (III)-iodide and peroxodisulfate-iodide in several isodielectric water-cosolvent mixtures have been studied. The results can be rationalized as a consequence of the cosolventwater interaction.

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(III) -. -.