Synthesis and Characterization of Sterically Encumbered Derivatives of Aluminum Hydrides and Halides: Assessment of Steric Properties of Bulky Terphenyl Ligands

The synthesis and characterization of several sterically encumbered monoterphenyl derivatives of aluminum halides and aluminum hydrides are described. These compounds are [2,6-Mes(2)C(6)H(3)AlH(3)LiOEt(2)](n)() (1), (Mes = 2,4,6-Me(3)C(6)H(2)-), 2,6-Mes(2)C(6)H(3)AlH(2)OEt(2) (2), [2,6-Mes(2)C(6)H(3)AlH(2)](2) (3), 2,6-Mes(2)C(6)H(3)AlCl(2)OEt(2) (4), [2,6-Mes(2)C(6)H(3)AlCl(3)LiOEt(2)](n)() (5), [2,6-Mes(2)C(6)H(3)AlCl(2)](2) (6), TriphAlBr(2)OEt(2) (7), (Triph = 2,4,6-Ph(3)C(6)H(2)-), [2,6-Trip(2)C(6)H(3)AlH(3)LiOEt(2)](2) (8) (Trip = 2,4,6-i-Pr(3)C(6)H(2)-), 2,6-Trip(2)C(6)H(3)AlH(2)OEt(2) (9), [2,6-Trip(2)C(6)H(3)AlH(2)](2) (10), 2,6-Trip(2)C(6)H(3)AlCl(2)OEt(2) (11), and the partially hydrolyzed derivative [2,6-Trip(2)C(6)H(3)Al(Cl)(0.68)(H)(0.32)(&mgr;-OH)](2).2C(6)H(6) (12). The structures of 2, 3a, 4, 6, 7, 9a, 10a, 10b, 11, and 12 were determined by X-ray crystallography. The structures of 3a, 9a, 10a, and 10b, are related to 3, 9, and 10, respectively, by partial occupation of chloride or hydride by hydroxide. The compounds were also characterized by (1)H, (13)C, (7)Li, and (27)Al NMR and IR spectroscopy. The major conclusions from the experimental data are that a single ortho terphenyl substituent of the kind reported here are not as effective as the ligand Mes (Mes = 2,4,6-t-Bu(3)C(6)H(2)-) in preventing further coordination and/or aggregation involving the aluminum centers. In effect, one terphenyl ligand is not as successful as a Mes substituent in masking the metal through agostic and/or steric effects.     

PERI-INTERACTIONS IN NAPHTHALENES, 21. SUBSTITUENT EFFECTS IN (8-DIMETHYLAMINO-NAPHTH-1-YL)- AND [2-DIMETHYLAMINO-METHYL)PHENYL] - PHOSPHINES ON THE 31P-NMR SIGNAL POSITIONS

Abstract

Contrary to claims in the literature, the ³¹P NMR signal positions of ortho-dimethylaminomethyl-substituted triarylphosphines do not provide evidence for hypercoordination at phosphorus; the observed highfield shifts relative to triphenylphosphine are rather due to the ortho-effect. In (8-dimethylamino-naphth-1-yl)phosphines, the signal positions similar to that of triphenylphosphine are the result of the highfield ortho-effect and a lowfield peri-substituent effect of about the same magnitude whose nature remains to be explored.     

Buchbesprechungen

Ohne Zusammenfassung     

Buchbesprechungen

Ohne Zusammenfassung     

Methane as a Selectivity Booster in the Arc‐Discharge Synthesis of Endohedral Fullerenes: Selective Synthesis of the Single‐Molecule Magnet Dy2TiC@C80 and Its Congener Dy2TiC2@C80

The use of methane as a reactive gas dramatically increases the selectivity of the arc‐discharge synthesis of M‐Ti‐carbide clusterfullerenes (M=Y, Nd, Gd, Dy, Er, Lu). Optimization of the process parameters allows the synthesis of Dy₂TiC@C₈₀‐I and its facile isolation in a single chromatographic step. A new type of cluster with an endohedral acetylide unit, M₂TiC₂@C₈₀, is discovered along with the second isomer of M₂TiC@C₈₀. Dy₂TiC@C₈₀‐(I,II) and Dy₂TiC₂@C₈₀‐I are shown to be single‐molecule magnets (SMM), but the presence of the second carbon atom in the cluster Dy₂TiC₂@C₈₀ leads to substantially poorer SMM properties.     

Optimale adaptive Devisenarbitrage

Zusammenfassung Im vorliegenden Beitrag wird ein auf dem Dynamischen Programmieren aufbauendes Verfahren zur Optimierung der mehrstufigen Devisenarbitrage aufgezeigt, das eine beliebige Begrenzung der Zahl der Stufen erlaubt.Zunächst wird das Entscheidungsproblem kurz umrissen. Nach der anschließenden Erläuterung anhand eines bis dreistufigen Vier-Währungs-Arbitrageprozesses werden der Lösungsansatz verallgemeinert, ein geeigneter Programmablaufplan dargestellt und einige Hinweise zur Adaptivität und zur Möglichkeit, Tauschmengenrestriktionen zu berücksichtigen, angefügt. Darauf werden Ansatz und Rechenaufwand mit denen der Verfahren vonJaeschke [1966] undMüller-Merbach [1970] undTimm [1970] verglichen, die sich an Tauschprozessen ohne Stufenbegrenzung orientieren.

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Summary The following contribution presents a dynamic programming approach to optimize arbitrage of exchange for any sum of stages and currencies desired.At first the decision problem is shortly outlined. After the following exemplification by means of an up-to-three-stage four-currencies arbitrage process the approach is generalized, an appropriate flow-diagram is presented and some additional remarks concerning the adaptivity of the procedure and the possibility to include restrictions in the exchangeable amount are made. After that, approach and computation needs are compared with those of the methods ofJaeschke [1966] andMüller-Merbach [1970] andTimm [1970], which are orientated towards arbitrage processes without stage restrictions.

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Der Verfasser dankt Herrn Professor Dr.Müller-Merbach für wertvolle Vorschläge zur Verbesserung und Ergänzung (insbes. Abschnitt 8.) des ursprünglichen Manuskripts.     

Ionen—VIII : Das tetraphenyloborat-ion als kernresonanzverschiebungsreagens bei quartären ammonium-kationen

B(C₆H₅)₄^? is a useful NMR shift reagent for quaternary ammonium cations. The signals of N^?CH protons are shifted to higher field by up to 4·2 ppm. More distant protons experience a much smaller shielding. Within certain limits, the signal position can be chosen arbitrarily. The utility of salt mixtures for signal assignment is demonstrated.