SOLUTION THERMOCHEMICAL STUDY OF LIGAND SUBSTITUTION-REACTION OF NOVEL PYRROLYL-SUBSTITUTED TERTIARY PHOSPHINE-LIGANDS IN THE L(2)FE(CO)(3)SYSTEM

The enthalpies of reaction of (BDA)Fe(CO)(3) (BDA = (C6H5)CH=CHC(O)CH3 , benzylideneacetone) with a series of novel phosphine ligands, PPh(3- x)(pyrrolyl)(x) (x = 1-3) and P(pyrrolidinyl)(3), leading to the forma tion of (L)(2)Fe(CO)(3) complexes (L = phosphine) have been measured b y solution calorimetry in THF at 50 degrees C. The range of reaction e nthalpies spans some 32 kcal mol(-1). The overall relative order of st ability established is as follows (PR(3); -Delta H, kcal mol(-1):P(NC4 H4)(3) < P(NC4H4)(2)Ph < P(NC4H4)Ph(2) << P(NC4H8)(3). A quantitative analysis of ligand effect of the present and previously obtained data for L(2)Fe(CO)(3) complexes helps clarify the exact steric versus elec tronic ligand contributions to the enthalpy of reaction in this system . Furthermore, the present enthalpy information helps in the estimatio n of useful electronic parameters associated with the novel phosphine series.