O=P(i‐PrNCH2CH2)3NCH3+: Novel effect of quaternization on the structural metrics of the bicyclic cage

The title cation features the longest distance between the bridgehead atoms (3.56 Å) so far recorded for phosphatrane cages despite a nontetrahedral CN_brigeheadC angle (∼114°). The 70.8° N_bridgeheadCCN torsion angles in the bridging moieties produce a substantial twist along the C₃ axis of the structure that does not easily allow racemization of the cage. The resulting rigidity of the twisted cage gives rise to AB patterns for the methylene protons of this cation and its analogues. © 1999 John Wiley & Sons, Inc. Heteroatom Chem 10:255–258, 1999     

Separation and characterization of underivatized oligosaccharides using liquid chromatography and liquid chromatography-electrospray ionization mass spectrometry

Native cyclodextrin-based columns are particularly useful for the analysis of oligosaccharides because the retention of these carbohydrates is based mainly on the hydrogen bonding interactions of oligosaccharide hydroxyl groups with the stationary phase. Thus, the retention time predictably increases with the number of analyte hydroxyl groups, which corresponds to the elongation of the oligosaccharide chain. High-performance liquid chromatography (HPLC) coupled to electrospray ionization (ESI) mass spectrometry (MS) was used for the separation and characterization of underivatized oligosaccharide mixtures. With the limits of detection as low as 50 pg, all individual components of oligosaccharide mixtures (up to 11 glucose units long) were baseline resolved on a Cyclobond I 2000 column and detected using ESI-MS. Low flow rates and narrow I.D. columns increase the ESI-MS sensitivity significantly. The method showed potential usefulness for the sensitive and quick analysis of hydrolysis products of polysaccharides, and for trace levels of individual oligosaccharide or oligosaccharide isomers from biological systems.     

Pd2(dba)3/P(i-BuNCH2CH2)3N-catalyzed Stille cross-coupling of aryl chlorides

[reaction: see text] The Pd(2)(dba)(3)/P(i-BuNCH(2)CH(2))(3)N (1d) catalyst system is highly effective for the Stille cross-coupling of aryl chlorides with organotin compounds. This method represents only the second general method for the coupling of aryl chlorides. Other proazaphosphatranes possessing benzyl substituents also generate very active catalysts for Stille reactions. Noteworthy features of the method are: (a) commercial availability of ligand 1d, (b) the wide array of aryl chlorides that can be coupled, and (c) applicability to aryl, vinyl, and allyl tin reagents.     

Shell Structures in Molecular Orbital Energy Diagrams for “Small” Fullerene Cages: Free-Electron Versus Generator Orbital Models

The nearly spherical nature of small fullerene cages C _N (N<70) suggests that their molecular orbital (MO) energy diagrams should show a shell structure. Although group theoretical analysis of the Hückel-type energies for icosahedral and other highly symmetric cages confirms this assumption, this has not been established for fullerene cages in general. This work presents a simple computational algorithm based upon the canonical orthogonalization of generator orbitals (GOs) to analyze the -MO energy diagrams for any fullerene cage C _N , and demonstrates the validity of a shell structure in these diagrams. Results are compared to simple central force (spherical) models for the calculations of -MO energies in fullerene cages. The GO approach provides a ready assignment of the -MOs to individual spherical harmonics and allows valuable interpretations of various physical phenomena.     

(t-Bu)2PN=P(i-BuNCH2CH2)3N: new efficient ligand for palladium-catalyzed C-N couplings of aryl and heteroaryl bromides and chlorides and for vinyl bromides at room temperature

By employing Pd(OAc)2, Cs2CO3, or NaOH, and the new ligand (t-Bu)2PN=P(i-BuNCH2CH2)3N (3a), an electronically diverse array of aryl bromides and chlorides possessing base-sensitive substituents (nitro, ester, and keto) provide coupling products with bulky aryl amines in good to excellent yields. Aryl halides possessing other functional groups including cyano, amino, trifluoromethyl, and phenol, coupled with equal ease, producing highly functionalized amines in good to excellent yields. Moreover, an aryl chloro group can be preserved in the presence of a bromo substituent under our reaction conditions. BOC-protected amines also participated efficiently. Heterocyclic bromides and chlorides underwent clean couplings with amines in excellent yields. An important strength of our protocol is the use of lower palladium loadings than those reported earlier, without compromising yields. The air-stable palladium complex (eta3-cinnamyl)PdCl.(3a) (5) was also employed successfully in C-N coupling reactions while the crotyl analogue was less efficacious. The 3a/Pd(OAc)2 catalyst system promotes, for the first time, efficient coupling of vinyl bromides with a variety of amines to produce imines and enamines at room temperature.     

31P–31P SPIN-SPIN COUPLINGS IN SYMMETRICAL AND UNSYMMETRICAL DERIVATIVES OF P(NMeNMe)3P

Abstract

The syntheses and characterization of seven new unsymmetrical derivatives of the type YP(NMeNMe)₃PZ are reported. Where Y = O or NPh: Z = S, Se, Br⁺ and where Y = a lone pair, Z = Br⁺ Also reported are the new symmetrical derivatives where Y = Z = (OC)₅W or (OC)₃Ni and the new monovalent cage cations YP(NMeCH₂)₃CMe⁺ where Y = Ph₃C and Br. Conductivity and ³¹P nmr evidence for the formulation of the phosphonium cations is presented. ³J³¹P³¹P couplings, obtained directly from the ³¹P nmr spectra of the unsymmetrical derivatives, are found to rise upon successively oxidizing the phosphorus atoms, and a rationale is offered. This coupling is also extracted from the ¹⁸³W and ⁷⁷Se satellite peaks in the ³¹P spectra of the symmetrical derivatives where Y = Z = (OC)₅W and Se, respectively.

A self-consistent set of assignments of the ³¹P chemical shifts is arrived at for YP(NMeNMe)₃PZ compounds and the useful role of LIS reagents in analyzing their proton spectra is delineated. The ¹³C nmr spectral parameters of these derivatives are also presented.     

Facile synthesis of monomeric alumatranes

Alumatranes, tricyclic neutral molecules featuring a transannular N --> Al bond, can act as Lewis acids that activate substrates in the axial coordination site. Treatment of tris(2-hydroxy-3,5-dimethylbenzyl)amine with AlMe(3) afforded dimeric (AlL)(2) 1 [wherein L = tris(2-oxy-3,5-dimethylbenzyl)amine]. X-ray diffraction analysis revealed bridging between AlL monomers by two Al-O bonds. Reactions of 1 with substrates containing O or N donors generated the alumatranes THF-AlL 2, PhCHO-AlL 3, H(2)NCH(2)CH(2)NH(2)-AlL 4, and [PhO-AlL](-) 5, in which the apical added ligand on the five-coordinate aluminum center causes variation in the transannular bond distance. Water coordinates with 1 at -20 degrees C to form the alumatrane H(2)O-AlL 6 that undergoes partial hydrolysis at room temperature to produce 7, which X-ray crystallography showed to be composed of four AlL fragments linked by an (H(2)O)(2)(HO)(2)Al(OH)(2)Al(OH)(2)(H(2)O)(2) framework in which the O(4)AlO(2)AlO(4) moiety is of local D(2)(h)() symmetry. According to X-ray analysis, 7 can crystallize in at least two polymorphic modifications: triclinic 7a and monoclinic 7b. The reaction of 3 with water also generated 6 and 7, depending on the reaction temperature. Dimeric 1 was found to promote the reaction of benzaldehyde with trimethylsilyl cyanide at room temperature to provide 2-trimethylsilyoxyphenylacetonitrile in 95% yield.     

Working group report: Heavy-ion physics and quark-gluon plasma

This is the report of Heavy Ion Physics and Quark-Gluon Plasma at WHEPP-09 which was part of Working Group-4. Discussion and work on some aspects of quark-gluon plasma believed to have created in heavy-ion collisions and in early Universe are reported.