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This study advances strategy and design in catalysts and reagents for fluorous and supercritical CO(2) chemistry by defining the structural requirements for insulating a typical active site from a perfluoroalkyl segment. The vertical ionization potentials of the phosphines P((CH(2))(m)R(f8))(3) (m = 2 (2) to 5 (5)) are measured by photoelectron spectroscopy, and the enthalpies of protonation by calorimetry (CF(3)SO(3)H, CF(3)C(6)H(5)). They undergo progressively more facile (energetically) ionization and protonation (P(CH(2)CH(3))(3) > 5 > 4 approximately equal to P(CH(3))(3) > 3 > 2), as expected from inductive effects. Equilibrations of trans-Rh(CO)(Cl)(L)(2) complexes (L = 2, 3) establish analogous Lewis basicities. Density functional theory is used to calculate the structures, energies, ionization potentials, and gas-phase proton affinities (PA) of the model phosphines P((CH(2))(m)()CF(3))(3) (2'-9'). The ionization potentials of 2'-5' are in good agreement with those of 2-5, and together with PA values and analyses of homodesmotic relationships are used to address the title question. Between 8 and 10 methylene groups are needed to effectively insulate a perfluoroalkyl segment from a phosphorus lone pair, depending upon the criterion employed. Computations also show that the first carbon of a perfluoroalkyl segment exhibits a much greater inductive effect than the second, and that ionization potentials of nonfluorinated phosphines P((CH(2))(m)CH(3))(3) reach a limit at approximately nine carbons (m = 8).

Aryl-2-(4-pyridyl)-cyclopropanes 970 3.6.8 Cyclopropylamines 970 3.6.9 Cyclopropenyl−Metal Complexes 971 4. Electronic Structure and Reactivity of Cyclopropane Compounds 971 4.1 Intramolecular Rearrangements Involving Cyclopropane Rings 971 4.2 Anchimeric Assistance of Solvolytic Reactions of 7-Norbornyl Derivatives 971 4.3 Cycloaddition Reactions 971 4.4 Radical Reactions of Bicyclo[1.1.0]butanes 972 4.5 Conclusion 972 5. Conclusions and Outlook 972 6. Acknowledgment 972 7. Note Added after ASAP Posting 972 8. References 972

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