Isomerization, organophosphorus compounds

Although boron is more accurately described as a metalloid rather than a metal, this section is concluded by two papers that describe the structures and bonding in several organoboron/organophosphorus compounds that display ylidic character. The X-ray structure of 9-borylanthracene (88) shows that only one of the diisopropylphosphine moieties is bonded to the boron in the solid state. However, H NMR evidence shows that an intramolecular bond-switching process takes place very rapidly in solution. The structures of a series of borabenzene adducts of phosphorus ylides, iminophosphoranes and tertiary phosphines have also been determined. Treatment of l-chloro-3,5-dimethyl-2-(trimethylsilyl)-l,2-dihydroborinine (89) with methylenetriphenylphosphorane (90) produces (triphenylphosphonio)methanide-3,5-dimethylborabenzene (91). However, if the reaction sequence is reversed and (90) is treated with (89), then (trimethylsilyl)(triphenylphosphonio)methanide-3,5-dimethylborabenzene (92) is obtained (Scheme 26). Treatment of an isomeric mixture of l-chloro(trimethyl-silyl)dihydroborinines (93) with N-(triphenylphosphoranylidene)aniline (94) produces iV-(triphenylphosphonio)anilide-borabenzene (95) (Scheme 27). Crystal structures of (91), (92) and (95) show that the P-C or P-N bonds are... 

These observations have been rationalized in terms of phosphorane stability and the relative ease of permutational isomerism as the ligands are varied. Phosphine oxides are mentioned in a brief review of stereochemical reaction cycles of organophosphorus compounds. ... 

The addition to the stationary phase of compounds that suppress chemical reactions between the sample components is an original and important development in the analysis of reactive trace components. For example, during the analysis of organophosphorus compounds with a tendency to isomerize, an isomerization inhibitor was added to the liquid stationary phase, which made analysis of these compounds possible [33]. 

The formation of alkynephosphonic diesters through the isomerization of alkynyl phos-phorus(III) esters and subsequent prototropic rearrangement of the propadienylphos-phonic acid derivatives has already been discussed. An early listing of alkynyl-phosphonic and -phosphinic acid derivatives (and also related types of organophosphorus compounds) is available ... 

Capillary electrophoresis-mass spectrometry (GEMS) can detect isomeric degradation products from organophosphorus compounds [56]. Table 20.2 shows the migration order (analogous to the elution order in... 

Although no isomerization of electron-rich organophosphorus compounds are known, [l,2]-migrations of aryl substituents from phosphorus to carbon do take place if... 

Thermal degradation occurs when heat causes compounds to undergo structural changes, leading to the formation of simpler species. For example, many organophosphorus esters isomerize when heated... 

Several further reports have appeared on the interaction of tervalent phosphorus isocyanates and a-ketocarboxylic esters, giving (22) (see Organophosphorus Chemistry Vol. 7, p. 126 Vol. 8, p. 107) in the case of ethyl benzoylformate, the isomeric compounds (23) and (24 R =Ph, R = C02Et) are also formed, and the... 

J. M. Battershill, P. M. Edwards and M. K. Johnson, Toxicological assessment of isomeric pesticides a strategy for testing of chiral organophosphorus (OP) compounds for delayed polyneuropathy in a regulatory setting, Eood Chem. Toxicol, 2004, 42, 1279-1285. 

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