Phosphorus NMR and Ab Initio Modelling of P–N Bond Rotamers of a Sterically Crowded Chiral β‐P4S3 Diamide

Reaction of bicyclic β‐P₄S₃I₂ with enantiomerically pure (R)‐Hpthiq (1‐phenyl‐1,2,3,4‐tetrahydroisoquinoline) and Et₃N gave a solution of a single diastereomer of the unusually stable diamide β‐P₄S₃(pthiq)₂, accounting for 83 % of the phosphorus content. Despite the steric bulk of the substituents, each amide group of this could adopt either of two rotameric positions about their P–N bonds, so that, at 183 K, ³¹P NMR multiplets for four rotamers could be observed and the spectra of three of them analysed fully. The large ²J(P–P–P) coupling became greater (253, 292, 304 Hz) with decreasing abundance of the individual rotamers. The rotamers were modelled at the ab initio RHF/3–21G* level, and relative NMR chemical shifts predicted by the GIAO method using a locally dense basis set, allowing the observed spectra to be assigned to structures. Calculations at the same level for the model compound α‐P₄S₃(pthiq)Cl confirmed the assignments of low‐temperature rotamers of α‐P₄S₃(pthiq)I reported previously. Changes in observed P–P coupling constants and ³¹P chemical shifts, on rotating a pthiq substituent, could then be compared between β‐P₄S₃(pthiq)₂ and α‐P₄S₃(pthiq)I, confirming both sets of assignments. The most abundant rotamer of β‐P₄S₃(pthiq)₂ was not the one with the least sterically crowded sides of both pthiq substituents pointing towards the P₄S₃ cage, because of interaction between the two substituents. Only by using a DFT method could relative abundances of rotamers of β‐P₄S₃(pthiq)₂ be predicted to be in the observed order. Use of racemic Hpthiq gave also the two diastereomers of β‐P₄S₃(pthiq)₂ with C_s symmetry, for which the room temperature ³¹P{¹H} NMR spectra were analysed fully.     

Coordination chemistry of the water-soluble ligand TPPTP and formation of a [Mo(CO)5(m-TPPTP)] monolayer on an alumina surface

Phosphonate and phosphonic acid functionalized phosphine complexes of platinum(II) were prepared via direct reaction of the ligands with K2PtCl4 in water. Either cis or trans geometries were found depending on the nature of the ligand. The crystal structure of P(3-C6H4PO3H2)3.2H2O (6b) (triclinic, P1, a = 8.3501(6) A, b = 10.1907(6) A, c = 14.6529(14) A, alpha = 94.177(6) degrees, beta = 105.885(6) degrees, gamma = 108.784(5) degrees, Z = 2) shows a layered arrangement of the phosphonic acid. The phosphonodiamide complex cis-[PtCl2(P[4-C6H4PO[N(CH3]2]]3)2].3H2O (10) was synthesized in 89% yield and hydrolyzed to the phosphonic acid complex using dilute HCl. Aqueous phase and silica gel supported catalytic phosphonylation of phenyl triflate using palladium phosphine complexes was achieved. A molybdenum complex, Mo(CO)5[P3-C6H4PO3H2)3] (11), was synthesized in situ and grafted to an alumina surface. XPS, RBS, and AFM studies confirm the formation of a monolayer of 11 on the alumina surface.     

Diastereoselective synthesis of 3,6-disubstituted 3,6-dihydropyridin-2-ones

In a short sequence, 5-vinyloxazolidin-2-ones were converted into the 3,6-disubstituted 3,6-dihydropyridin-2-ones via Pd-catalysed carbonylation and enolate alkylation with high diastereoselectivity. Alkylation of 6-substituted N-methylpyridin-2-ones gives stereoselectively the 3,6-anti diastereoisomer with MeI, BuI and i-PrI. Alkylation of the corresponding N-BOC pyridinones gives the 3,6-syn diastereoisomer with high selectivity.     

Frequency measurements on far-infrared laser emissions of carbonyl fluoride (COF2)

The frequencies of 9 optically-pumped far-infrared emissions from COF₂ have been measured by harmonic mixing in a Schottky diode with harmonics of 3-and 4-mm band klystron radiation. The measured emissions lie in the wavelength range 1135–358 m. The results are compared with frequencies predicted from mid-infrared spectroscopy.     

Frequency measurements on far-infrared emissions from12C16O2-pumped methyl chloride and from12C18O2-pumped difluoromethane

The frequencies of 42 far-infrared laser lines have been measured by mixing with high-order harmonics of microwave frequencies in a Josephson junction. A total of 5 emissions between 334 and 1887 m have been measured from¹²C¹⁶O₂-pumped methyl chloride (CH₃Cl) and 37 emissions between 116 and 1092 m in¹²C¹⁸O₂-pumped difluoromethane (CH₂F₂). Additional data is given on the laser emission characteristics.Division of Electrical Science, National Physical Laboratory     

Determination of emamectin benzoate in medicated fish feed

A method was developed to quantitate emamectin benzoate in fish feed at levels between 5 and 15 ppm. The active ingredient is extracted from 20 g medicated feed into aqueous-methanolic solvent by overnight shaking. A solid-phase extraction procedure using a 2 g C18 cartridge is then used to concentrate the active residue and remove interfering matrix components. The extracted drug and internal standard are eluted from the cartridge, evaporated to dryness, and reconstituted in methanol. A control feed sample and fortified control working standard are simultaneously prepared. Remaining interferences and sample analysis are further separated on a gradient liquid chromatographic system. Recovery of emamectin benzoate from fortified feeds ranged from 97 to 100%, with a coefficient of variation (CV) of 1.2%. Determination of emamectin benzoate in medicated feeds resulted in CVs ranging from 2.3 to 4.2% and recoveries of 88 to 98% of label claim.     

Optical spectra of sodium microclusters

Photoabsorption spectra have been measured for free neutral sodium clusters containing fromN=3 to 40 atoms. In the size range ofN≈3 to 5, a transition occurs from molecule-like absorption to collective excitations of the valence electrons. ForN≈6 to 12, the data are well described by an ellipsoidal shell model. In open-shell clusters, the multiple surface plasma resonances expected for spheroidal or ellipsoidal shapes are observed. The experimental resonance positions provide a sensitive measurement of the cluster distortions. ForN?13, the per atom strength of these collective resonances is reduced; this may be due to peak fragmentation caused by interaction between the surface plasmon and nearby single-electron resonances. In three distinct wavelength regions, one of which corresponds to the position of the Na atom “D-lines”, additional absorption is seen in the spectra of all investigated clusters.     

A total synthesis of (+/-)-alpha-cyclopiazonic acid using a cationic cascade

The indolic terpene alkaloid alpha-cyclopiazonic acid has been prepared in 11 steps from indole-4-methanol; the key step is a carbocationic cascade, terminated by a 4-nitrosulfonamide group and initiated by benzylic carbocation formation directly from the intermediate , which gives the tetracyclic product in 74% yield.     

A total synthesis of (±)faranal,the true trail pheromone of pharaoh's ant, monomorium pharaonis

A relatively brief total synthesis of (±)-Faranal [3$\text{SR}$,4$\text{RS}$), (6$\text{E}$,1O$\text{Z}$)-3,4,7, 11-tetramethyl-6,10-tridecadien-l-al] (1) is reported.