My PhD dissertation - Institut Fresnel

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suitably substituted dilithiobiphenyls and allowed rotational activation barrier to be
calculated. Correlation of the results obtained with known literature data suggested a
coordinative interaction between the lithium and oxygen atoms, causing a higher
activation energy than envisioned. As a matter of fact, in both cases the free enthalpy
values determined fell in the same range as those of bridged dilithiobiaryls, which
supported the idea of an internal rigidity induced by the lithium-oxygen coordination.
These assumptions should certainly be supported by a comparative study
between the dilithiobiphenyls used and their metal-free congeners (H instead of Li). In
the lithiated species, the two lithium atoms should logically tend to seek the proximity
of the oxygens and coordinate them, causing a certain rigidity of the molecule. In
contrast, it would be highly plausible that, in the metal-free congeners, no coordination,
thus no additional constraints exist in the biphenyl unit. In this eventuality, the
rotational activation barrier should be lower in the case of metal-free species,
corroborating the proposed hypothesis. Other usefull informations could possibly be
obtain by replacing the coordinating oxygens in the biphenyls used, by nitrogen or
carbon atom.
Finally, various phosphonium salts and phosphine oxides were prepared to
address another field of application of organophosphorus compounds. These substrates
served as probes for assessing relative stabilities of several alkyl carbanions. Based on
the use of the alkaline decomposition of phosphonium salts, the method developed was
meant to accurately determine differences in ease of cleavage between several alkyl
substituents and was believed to directly correlate to their corresponding carbanions
basicity. The data collected in this work provided unprecedented informations
concerning secondary and tertiary alkyl carbanions in solution. When available, gas
phase basicities of alkyl anions were compared to the results obtained by alkaline
decomposition of phosphoniums salts. The relative stabilities observed in solution were
coherent with the observed experimental reactivity but did parallel inverse order of the
reported gas phase results, as one could expect.
To provide a better overview on the factors influencing the alkaline
decompositionof phosphonium salts, it would be interesting to perform other
decompositions with phosphonium of the type RnR'pP + , X - where n and p would be
varied. These experiments would hopefully allow an estimation of the effective
importance of internal strains on the cleavage of the P–C bond from phosphonium salts.