Kenneth C. Caster

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

Abstract 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.

Thermal degradation of dimers of phospholes

Abstract The pathway followed by dimers of P-methylphospholes in their thermal degradation in solution is strongly dependent on the concentration. At low concentrations (around 0.04 M) in n-decane or toluene as solvent, decomposition is extensive after 17 h in the range 120–130°C. The major product is the P-methylphosphole from de-dimerization. At concentrations above 1.0 M, decomposition is faster and intermolecular interactions are more important. These interactions dominate over de-dimerization and lead to the loss of the bridging P in the 7-phosphanorbornene moiety to yield the cis-3a,7a-dihydrophosphindole system. From the dimer of 1,3-dimethylphosphole, isomeric dihydrophosphindoles are formed, which differ in location of the methyl group on the 6-membered ring and in configuration at phosphorus. These seem to result from attack by a phosphine group as a nucleophile on the bridging P, followed by bond rearrangements in the resulting phosphoranide ion. Decomposition was faster in the presence of tri-...

PHOSPHINIMINES DERIVED FROM PHOSPHOLE DIMERS BY THE STAUDINGER REACTION

Abstract The Staudinger reaction of phenyl azide with the phosphine groups of phosphole dimers gives bis(phenylimino) derivatives. Hydrolysis or methanolysis leads to diphosphine dioxides with retention of configuration at the bridging phosphorus and inversion at the 2-phospholene phosphorus. This reaction is useful in providing access to a new isomeric form of the phosphole oxide dimer framework. Amines catalyze the rearrangement at the 2-phospholene phosphorus to the isomeric form which is commonly produced on dimerization of phosphole oxides. Amides also catalyze the inversion at the 2-phospholene group in the Staudinger product. Both the original and the rearranged Staudinger product were found to be reduced with trichlorosilane to give the same diphosphine.

Variations in properties of bridged phosphorus heterocycles

Abstract Highly strained cyclic phosphine oxides can give anomalous results (inversion, C-P cleavage) on deoxygenation with HSiCl3 or C6H5SiH3. Use of the pyridine complex of HSiCl3 generally overcomes these difficulties, and a number of strained phosphines were prepared. Definite trends in 31P NMR shifts among saturated and unsaturated structures have been observed. Phosphines in the 7-phosphanorbornene system are particularly prone to form P(V) cycloadducts, which then decompose by a reverse McCormack-type of reaction. The reactivity is so high that even dienes form adducts with these phosphines.

A new synthesis of P-methylphospholes by flash vacuum pyrolysis of the diphosphines derived from phosphole oxide dimers

Under thermal conditions where intermolecular interactions are minimized, as in flash vacuum pyrolysis, the diphosphines derived from deoxygenation of P-methylphosphole oxide dimers are excellent sources of P-methylphospholes.