- Kinetics of nucleophilic attack on coordinated organic moieties. XXVI. An extended nucleophilicity scale for nucleophilic addition to the cation +
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A nucleophilicity scale is established for the addition of ca. 40 different nucleophiles to the cyclohexadienyl ring of the cation + (I).The factors controlling nucleophilicity towards cation I are discussed, and comparisons made with data for reactions of the nucleophiles with other model organic and inorganic substrates such as MeI and trans-.
- Ghazy, Tahany,Kane-Maguire, Leon A. P.
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- Kinetics of Nucleophilic Attack on Co-ordinated Organic Moieties. Part 21. Factors governing the Nucleophilicity of Phosphorus Nucleophiles towards (1+)
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Synthetic and kinetic studies are reported for the addition of a wide range of tertiary phosphines and phosphites to the dienyl ring of (1+) (1).All the reactions obey the expression kobs. = k1, except for the reversible additions of P(CH2CH2CN)3 and P(C6H4Me-2)3 which follow the two-term equation, kobs.=k1 + k-1.A good correlation (r=0.98) is found between log k1 and the Tolman Σ X values of the phosphorus nucleophiles.The Broensted slope of 0.5 derived from a linear plot of log k1 vs. pKa for triarylphosphines demonstrates the importance of basicity in controlling nucleophilicity towards (1).Nucleophile polarisability is shown to play a minor role.Steric factors, quantified by negative deviations from the above plots by P(C6H4Me-2)3 and P(C6H11)3, are shown to be much more important than in related reactions with ethyl iodide.The Hammett slope ρ of -1.32 observed for the additions of triarylphosphines to (1) suggest moderate, but far from complete, phosphorus-carbon bond formation in the transition states.A similar conclusion is drawn from the novel anchimeric assistance observed in the unexpectedly rapid reaction with P(C6H4OMe-2)3 (k2-MeO/kH = 91).Finally, comparison with other results provides an electrophilicity order for an extended series of organometallic cations covering a reactivity range of ca. 1E6 between (1+) and (1+).
- Atton, Jennifer G.,Kane-Maguire, Leon A. P.
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p. 1491 - 1498
(2007/10/02)
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