Evidence for pentaalkylphosphorane intermediates in the reaction of dienes at the bridging phosphorus in P-methylphosphole dimers

The rate of loss of the phosphorus atom in the 7-phosphanorbornene moiety of P-methyl phosphole dimers is greatly increased when the dimes are heated in the presence of 1,3-dienes. The major products are 3-phospholenes and 3a, 7a-dihydrophosphindoles, formed in retrocycloaddition of the P(V) adduct of the diene and the phosphine.     

On-line preconcentration with different solid adsorbents for lead determination

An on-line column preconcentration method based on the combined use of ammonium O,O-diethyldithiophosphate and activated carbon or polyurethane foam as adsorbents has been developed for the determination of Pb in water samples. The complexed Pb was eluted with ethanol and determined by flame atomic absorption spectrometry. The optimum preconcentration conditions are given for each adsorbent. The enrichment factors were 63 and 294, and the detection limits (3sigma) 3 microg L(-1) and 0.8 microg L(-1), respectively, for the carbon and foam systems. When the optimized procedures were applied to the determination of Pb in water samples the recovery efficiency was > 96%.     

SYNTHESIS AND 31P NMR STUDY OF DIHYDRONAPHTHALENO- AND NAPHTHALENO-DERIVATIVES OF PHOSPHOLENE OXIDES

Abstract

Naphthalenophospholenes (dihydrobenzo[e] and [g]-phosphindoles) represent a new heterocyclic type that forms in 65-80% yield on dehydrogenation with Pd–C of the corresponding dihydronaphthaleno derivatives. The latter are readily accessible from hydrolysis of cycloadducts of certain vinyldihydronaphthalenes with P(III) chlorides. Six members of this family, as well as some derived phosphines and phosphonium salts, have been prepared. A phenanthrenophospholene oxide, also a new system, was synthesized similarly. ³¹P nmr chemical shifts were appreciably (5-10 ppm) upfield in aromatized phosphine oxides relative to the dihydro forms. It is proposed that this shift results more from a change in the steric environment about phosphorus, as the carbon beta- to it in the adjacent ring changes from tetrahedral to planar geometry, rather than from a change in the degree of interaction of a carbon p-orbital with phosphorus. The upfield shift was even more pronounced (13 ppm) for a phosphine. Most of the new compounds were characterized also by ¹³C nmr spectroscopy.     

Chemistry of the 2,3-oxaphosphabicyclo[2.2.2]octene ring system: Extrusion of metaphosphates

The 2,3-oxaphosphabicyclo[2.2.2]octene 3-oxide (or sulfide) ring system is of considerable value because it easily fragments on being heated or irradiated (254 nm) to provide three-coordinate phosphoryl species. The system is synthesized by O-insertion with peracids into a C P bond of 7-phosphanorbornene derivatives with a variety of P-substituents. With rare exception, the insertion has been found to proceed with retention of the configuration at phosphorus, as established by X-ray and NMR techniques. The thermal fragmentation that produces the metaphosphate derivatives EtO PO₂, EtO P(S)O, and Et₂N PO₂ follows first-order kinetics, and is independent of the concentration of a trapping agent for these species. Solvent effects and activation parameters join in defining a retrocycloaddition mechanism that ejects the free metaphosphate. The species Ph PO₂ can also be easily generated either thermally or photochemically. Metaphosphates have been found to attack ethereal oxygen in epoxides and oxetanes, and may undergo anchimeric participation with a properly placed methoxy group on the substituent used in the 2,3-oxaphosphabicyclo[2.2.2]octene precursor.     

Generation of methylenephosphine oxides by thermal fragmentation of derivatives of the 2-phosphabicyclo [2.2.2] octa-5,7-diene oxide ring system

Differential thermal analysis and differential scanning calorimetry showed that the title compounds decomposed at 240–260°C with release of the fragment RP(O) = CH₂. Mass spectral studies also showed this to be a fragmentation pathway. The extruded methylenephosphine oxide could be trapped with ethanol, hydroquinone, or by reaction with the surface OH groups of silica gel.     

33S NMR shieldings and chemical bonding in compounds of sulfur

Sulfur nuclear magnetic resonance (NMR) chemical shieldings have been determined at the correlation-including density functional theory scaled B3LYP/6-311+G(nd,p)//B3LYP/6-311+G(d,p) and modified MP2/6-311+G(nd,p) estimated infinite order Møller-Plesset levels with n = 2 for sulfur. The calculations span the range of sulfur shieldings and show agreement with experiment of about 3% of the shielding range. The atoms-in-molecules delocalization index and a covalent bond order from specific localized orbitals in the DFT approach are used to characterize sulfur's bonding and to relate it, where possible, to the calculated shieldings. © 2004 Wiley Periodicals, Inc. Heteroatom Chem 15:216–224, 2004; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/hc.20000     

Stereostructure of 8-chloro-5,6-di(methoxycarbonyl)-4,7-dimethyl-2-ethoxy-2-phosphabicyclo[2.2.2]octa-5,7-diene 2-oxide

The first X-ray structure of a phosphabicyclooctadiene, together with the NMR and mass spectral characterization of its isomers, is reported. © John Wiley & Sons, Inc.