Influence of ortho Methyl and Isopropyl Substituents on the Reactivity of N-t-Butyl P-Arylphosphonamidic Chlorides with Isopropylamine and t-Butylamine: Steric Acceleration of Metaphosphonimidate Formation by an Elimination-Addition Mechanism; Contrasting Behaviour of N,N-Dimethyl P-A...

DOI: 10.1039/P19870001399

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Journal of the Chemical Society. Perkin transactions I p. 1399 - 1406 (1987)

Update date:2022-08-04

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Authors:

Freeman, Sally

Harger, Martin J.

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Article abstract of DOI:10.1039/P19870001399

The two types of phosphonamidic chloride ArP(O)(Cl)NMe2, (5) and ArP(O)(Cl)NHBu^t (7) have been prepared with Ar=Ph, o-MeC6H4, 2,4,6-Me3C6H2, and 2,4,6-Prⁱ3C6H2.Both types give the expected phosphonic diamide substitution products with PrⁱNH2 and Bu^tNH2 in MeCN, but the two types display contrasting reactivity.With Bu^tNH2 the NMe2 substrates (5) become progressively less reactive as the degree of steric crowding increases, and although the decrease is quite small (70-fold overall) it seems consistent with an associative N2(P)> mechanism.These substrates react >=100 times faster with PrⁱNH2, than with Bu^tNH2 and in PrⁱNH2-Bu^tNH2 competitive experiments they give almost exclusively (>=99percent) the product derived from the less hindered PrⁱNH2.For the NHBu^t substrates (7) with Bu^tNH2, there is little difference in reactivity between the Ph and o-MeC6H4 compounds, and between the 2,4,6-Me3C6H2 and 2,4,6-Prⁱ3C6H2 compounds, but remarkably the more crowded pair of substrates is the more reactive, by a factor of ca. 100.Also, in competitive experiments these substrates display relatively little preference for reaction with PrⁱNH2.Here a dissociative elimination-addition mechanism, with a metaphosphonimidate intermediate, is seen to be important.A possible explanation of the steric acceleration is advanced.The ability of (7; Ar=Ph) to undergo substitution by elimination-addition makes possible the phosphonylation of unreactive nucleophiles such as Bu^tOH and Prⁱ2NH under mild conditions.

Full text of DOI:10.1039/P19870001399

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