Cation Stabilities, Electrophilicities, and “Carbene Analogue” Character of Low Coordinate Phosphorus Cations

✍ Scribed by Dietrich Gudat

• Publisher: John Wiley and Sons
• Year: 1998
• Tongue: English
• Weight: 394 KB
• Volume: 1998
• Category: Article
• ISSN: 1434-1948
• DOI: 10.1002/(sici)1099-0682(199808)1998:8<1087::aid-ejic1087>3.0.co;2-3

✦ Synopsis

The stabilities of low coordinated phosphorus cations can be from a balance between π-donation into the empty p(P) orbital and electrostatic stabilization by polar P-R σ-bonds. expressed in the frame of the HSAB concept by the transferred charge density ∆q(N) which a cation receives A further stabilizing effect, which is of similar magnitude as in isoelectronic carbenes or silylenes, may arise from cyclic upon formation of a donor-acceptor adduct with a Lewis base N. This concept allows to differentiate between relative π-conjugation between a diaminophosphenium fragment and an adjacent double bond. Substituent effects influence stabilities towards different reaction partners, and to compare the electrophilicities of phosphenium ions to those further the nature of the frontier orbitals of phosphenium ions, resulting in orbital sequences which resemble those of of isoelectronic carbenes and silylenes. An analysis of substituent influences on ∆q(H) in cations [P(R) 2 ] + suggests carbenes, allyl anions, or phospholides, respectively. The absence of frontier orbital related changes in reactivity an increasing stabilizing power of substituents in the series R = Cl Ͻ CH 3 Ͻ OH, SH Ͻ NH 2 . The same ordering was patterns suggests that in all reactions, including metal complex formation, phosphenium ions behave as purely derived from isodesmic hydride transfer reactions. Interpretation of population analyses suggests that the electrophilic rather than ambiphilic species. individual substituent contributions to cation stabilities result