title: How to insulate a reactive site from a perfluoroalkyl group: photoelectron spectroscopy, calorimetric, and computational studies of long-range electronic effects in fluorous phosphines P((CH(2))(m)(CF(2))(7)CF(3))(3).
abstract: 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).
authors.affiliation: Institut für Organische Chemie, Friedrich-Alexander Universität Erlangen-Nürnberg, Henkestrasse 42, 91054 Erlangen, Germany.
authors.forename: Haijun
authors.initials: H
authors.lastname: Jiao
authors.forename: Sylvie
authors.initials: S
authors.lastname: Le Stang
authors.forename: Tibor
authors.initials: T
authors.lastname: Soós
authors.forename: Ralf
authors.initials: R
authors.lastname: Meier
authors.forename: Klaus
authors.initials: K
authors.lastname: Kowski
authors.forename: Paul
authors.initials: P
authors.lastname: Rademacher
authors.forename: Laleh
authors.initials: L
authors.lastname: Jafarpour
authors.forename: Jean-Benoit
authors.initials: JB
authors.lastname: Hamard
authors.forename: Steven P
authors.initials: SP
authors.lastname: Nolan
authors.forename: J A
authors.initials: JA
authors.lastname: Gladysz