P-X bonds

It is the only example of a free, persistent phosphirenylium ion, and also, only one stable transition-metal complex of this species was published [78,79]. Quantum chemical calculations [80,81] indicated that in the halogeno-phosphirenes the P-X bonds already possesses a high ionic character and can be described as interactions between phosphirenylium and halide ions. The aromatic character of the phosphirenylium ion was shown to be based on a three-centre two-electron bond of 7i-type and the resonance energy was assessed by calculation to 38 kcal/mol. Before the generation of 32, substituted phosphirenylium ions were... [Pg.89]

Metabolism of most OP pesticides yields alkylphosphates or alkyl-(di)-thiophosphates as a result of the hydrolysis of the P-X bond in the OP... [Pg.5]

During the last few years, both neutral and cationic 1,3,2-diazaphospholes and NHP have been studied extensively by computational methods. The best part of these studies focused on a discussion of n-electron delocalization and their implication on chemical reactivities and stabilities, the explanation of the unique ionic polarization of exocyclic P-X bonds noted for some species, and the evaluation of structural and spectroscopic properties with the aim of helping in the interpretation of experimental data. [Pg.82]

Reports on the sensitivity of many neutral and cationic NHP derivatives towards air and moisture reveal in most cases pronounced reactivity even with traces of H20 causing P-X bond hydrolysis whereas genuine oxidation processes appear to play a role only for P-H and P-alkyl NHPs [71]. Controlled hydrolysis proceeds at low temperature as depicted in Scheme 9 to give secondary phosphine oxides 17 as initial product which may react further with excess NHP to phosphinous acid anhydrides 18.3 Both products may be obtained as isolable products starting from P-chloro NHPs [48], Hydrolysis at ambient temperature may be unselective and... [Pg.87]

The ionic P-P bond polarization renders P-phosphino-NHPs highly active reactants for various metathesis and addition reactions at exceedingly mild conditions. Metathesis is observed in reactions with alcohols, chloroalkanes, and complex transition metal halides (Schemes 11 and 12) [39, 73], Of particular interest are the reactions with chlorotrimethylstannane which yield equilibria that are driven by a subtle balance of P-X bond strengths to yield either diphosphines or P-chloro-NHPs as preferred product (Scheme 11). Chlorotrimethylsilane does not react with... [Pg.89]

P-phosphino-NHPs but the reverse reaction of a P-chloro NHP with diphenyl-trimethylsilylphosphine and subsequent reaction with a chloroalkane can be combined to produce high yields of P-alkyl-diphenylphosphines [74], Since the chloro-NHP is recovered in the second step, the overall reaction can be performed by employing this species merely as catalyst (Scheme 13). NMR investigations confirm that the appropriate P-phosphino-NHPs are in fact key intermediates in the resulting catalytic cycle, and it has been pointed out that P-X bond polarization represents a crucial factor for the overall acceleration of the catalyzed P-C... [Pg.90]

In the tetra-bridged phosphocavitands, the preorganized structure is imposed by the fixed boat-chair conformation of the four fused eight-mem-bered rings. Inwards (i) and outwards (o) configurations are defined relatively to the endo and exo orientations of the P=X bonds (X=0, S, electron pair), and six different stereoisomers arise from the equatorial or axial orientation of the substituents on the phosphorus atoms (Scheme 3). [Pg.59]

We now have to consider the so-called irregular rearrangements . These involve dissociation by breaking a P —X bond to give a P+ X ionic structure, and have been studied by Westheimer (open chain phosphoranes) (76JA179) and Ramirez (cyclic phosphoranes) (71APO(9)25). Polar solvents, acid catalysis and even change of temperature can influence the equilibrium. [Pg.535]

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