## Abstract

By application of the QALE model (quantitative analysis of ligand effects) to the standard reduction potentials (E degrees values) and the standard enthalpies of reduction (Delta H degrees) of the eta-Cp(CO)(PZ(3))Fe(COMe)(+/0) couple (PZ(3)= a phosphorus(III) ligand), and nu(CO) for eta-Cp(CO)(PZ(3))Fe(COMe)(0), we have determined that a minimum of four parameters are necessary to describe the stereoelectronic properties of the set of ligands PPhi(Pyr)(3-i) (Pyr = pyrrolyl) and P(NC4H8)(3) (NC4H8=pyrrolidinyl). These parameters are chi(d), theta, E-ar and the pi acidity parameter, pi(p). The values of these parameters were determined by linear regression analysis of a set of QALE equations. The coefficients of these equations were based on the analyses of data for PR3, PPhiR3-i, P(p-XC6H4)(3), P(OR)(3), and P(O-p-XC6H4)(3). The parameters for P(Pyr)(3) are chi(d)=31.9 +/- 0.7, theta=145 +/- 3, E-ar=3.3 +/- 0.2 and pi(p)=1.9 +/- 0.2; and for P(NC4H8)(3) the parameters are chi(d)=-1.2 +/- 1.4, theta=145 +/- 5, E-ar=-0.6 +/- 0.4 and pi(p)=0.9 +/- 0.3. P(Pyr)(3) is a poor sigma donor that possesses an E-ar parameter comparable to P(p-XC6H4)(3) and a pi acidity that is about two thirds that of P(OR)(3) and half that of P(O-p-XC6H4)(3). On the other hand, P(NC4H8)(3), which is one of the strongest sigma donor phosphorus(III) ligands, is a weak pi acid with a value for E-ar that is statistically indistinguishable from zero. PPhi(Pyr)(3-i) and P(NC4H8)(3) appear to be isosteric to P(p-XC6H4)(3).

Original language | English |
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Pages (from-to) | 1349-1357 |

Number of pages | 9 |

Journal | Journal of Chemical Society, Perkin Transactions 2 |

Issue number | 7 |

DOIs | |

Publication status | Published - 2000 |

## Keywords

- ENTHALPY-ENTROPY RELATIONSHIP
- METAL-CARBONYL CLUSTERS
- UNIMOLECULAR REACTION SYSTEMS
- STATISTICAL-MECHANICAL MODEL
- PI-ACCEPTOR CHARACTER
- ISOKINETIC RELATIONSHIP
- SUBSTITUTION-REACTIONS
- EXPLORING STEREOSELECTIVITY
- PHOSPHORUS(III) LIGANDS
- L(2)FE(CO)(3) SYSTEM